tag:theconversation.com,2011:/au/topics/zebrafish-4444/articlesZebrafish – The Conversation2023-08-07T12:43:56Ztag:theconversation.com,2011:article/2051102023-08-07T12:43:56Z2023-08-07T12:43:56ZZebrafish are a scientist’s favorite for early-stage research – especially to study human blood disorders<figure><img src="https://images.theconversation.com/files/540000/original/file-20230728-23-tbljsp.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2048%2C1299&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">As an animal model, the zebrafish offers many advantages that save researchers time and money.</span> <span class="attribution"><a class="source" href="https://flic.kr/p/wBu5Uz">Uri Manor/NICHD via Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Scientists have <a href="https://doi.org/10.7554/eLife.05959">relied on animal models</a> as an alternative to testing on human tissues and cells for decades. But not just any organism can adequately model how human cells behave. Researchers take into account how quickly the organism can mature, how many offspring it can produce and how often it can reproduce. When studying genetics and developmental biology, one of the most important qualities to consider is how similar the model organism’s genes are to human genes.</p>
<p>Although humans and fish certainly look very different, the zebrafish has proved to be an excellent model organism for scientists studying <a href="https://doi.org/10.1242%2Fdev.083147">hematopoiesis</a>, or the development of blood cells.</p>
<p>In the <a href="https://www.espinlab.com">Espín Lab</a> at Iowa State University, <a href="https://scholar.google.com/citations?user=O2ux60wAAAAJ&hl=en">we study</a> the early stages of blood development, particularly the birth of blood stem cells, which happens only once during embryonic development. We focus on a specific set of genes that play a significant but somewhat elusive role in the molecular pathways involved in this process. Although we want to understand how these genes work in the context of human blood development, testing on human embryos is obviously ethically impossible. To circumvent these challenges, we use zebrafish instead.</p>
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<span class="caption">The National Institute of Child Health and Human Development houses the largest zebrafish facility in the U.S. Each tank contains live zebrafish used in research.</span>
<span class="attribution"><a class="source" href="https://flic.kr/p/HJ4qwU">Ernesto del Aguila III/NHGRI via Flickr</a></span>
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<h2>Zebrafish as a model organism</h2>
<p>Zebrafish have several traits that make them excellent model organisms.</p>
<p>For one, one female zebrafish can produce <a href="https://doi.org/10.1046/j.1365-2141.2003.04682.x">hundreds of embryos per week</a>. This is important to scientists because having larger sample numbers strengthens the accuracy of the data they collect in their experiments.</p>
<p>Zebrafish embryos are also able to develop quickly. One day of development in zebrafish is equivalent to approximately 90 days of human development. This means that researchers can save time and observe the different stages of development much sooner than with other organisms.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/BD4gqmGdFyY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This time-lapse video shows the first 22 hours of zebrafish development after fertilization, with blood vessels labeled green. Blood has already formed at this stage of development.</span></figcaption>
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<p>Another useful quality of zebrafish is that they are <a href="https://doi.org/10.1046/j.1365-2141.2003.04682.x">translucent during early development</a>. As soon as their embryos are fertilized, scientists can observe cells and tissues form and clearly see the effects of modifying different genes.</p>
<p>Perhaps the most important feature of zebrafish for scientists is their genetic makeup. Approximately <a href="https://doi.org/10.1038/nature12111">70% of zebrafish genes</a> have similar analogs in people, allowing researchers to study how certain genes work.</p>
<h2>Studying blood disorders with zebrafish</h2>
<p>Beyond sharing a significant percentage of genes with people, zebrafish are especially useful to blood development research because they produce the <a href="https://doi.org/10.1046/j.1365-2141.2003.04682.x">same types of blood cells</a>. Just like people, zebrafish have <a href="https://doi.org/10.1016/j.bcmd.2013.07.006">erythroid</a>, <a href="https://doi.org/10.1038/nri.2017.86">lymphoid</a> and <a href="https://doi.org/10.1016/j.biocel.2004.01.020">myeloid</a> cell types that are responsible for numerous roles in the body, like circulating oxygen and regulating inflammation and immunity. Mature blood cells are derived from blood stem cells. Therefore, studying how these stem cells are made would aid in developing treatment for numerous blood disorders that rely on blood stem cell therapies, such as leukemia, lymphoma and anemia.</p>
<p>Labs like ours use zebrafish to study how specific cell signaling pathways contribute to the birth, development and maturation of these blood stem cells. This knowledge provides context for how healthy cells work and communicate, because cells rely on signals from other cells to know which genes they need to turn on to produce specific proteins and molecules. </p>
<p>For example, we have previously shown how <a href="http://dx.doi.org/10.1016/j.cell.2014.10.031">inflammatory signaling pathways</a> are needed for zebrafish to properly develop the <a href="https://doi.org/10.15283/ijsc19127">hematopoietic stem cells</a> that produce multiple kinds of blood cells. We are currently exploring how these inflammatory pathways produce human blood stem cells. While most cells receive certain signals that trigger them to express certain genes, <a href="https://theconversation.com/triggering-cancer-cells-to-become-normal-cells-how-stem-cell-therapies-can-provide-new-ways-to-stop-tumors-from-spreading-or-growing-back-191559">stem cells</a> are capable of developing into multiple types of cells in an organism. Stem cells are undifferentiated, meaning that they are not yet limited to expressing or following only certain parts of the DNA like more mature, differentiated cells. </p>
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<figcaption>
<span class="caption">This image shows blood cells (magenta) in blood vessels (yellow) on the yolk of a 2-day-old zebrafish embryo, which is roughly the size of a grain of rice.</span>
<span class="attribution"><a class="source" href="https://flic.kr/p/2j6TzAo">Daniel Castranova/National Institute of Child Health and Human Development, NIH via Flickr</a></span>
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<p>For patients with blood-related disorders like leukemia, there are currently limited treatment options. <a href="https://theconversation.com/gut-bacteria-nurture-the-immune-system-for-cancer-patients-a-diverse-microbiome-can-protect-against-dangerous-treatment-complications-184427">Bone marrow transplants</a> are among these options. But there is a shortage of matching donors, and the procedure can be risky because of <a href="https://www.cancerresearchuk.org/about-cancer/coping/physically/gvhd/about">graft-versus-host disease</a>, in which the donor’s healthy immune cells attack the recipient’s body cells. </p>
<p>A possible solution is to use a special kind of stem cell called an <a href="https://doi.org/10.1038/cr.2008.309">induced pluripotent stem cell</a>. To make these cells, scientists use a special set of proteins called Yamanaka factors to turn on specific genes that revert a mature, differentiated cell into an immature, undifferentiated cell. From this point, the cells can be manipulated to express certain genes at specific times, told which part of their DNA to read or which signals to follow. </p>
<p>However, to properly direct these stem cells, researchers need a more complete understanding of the molecular signals involved and how they contribute to early blood development. To bridge these gaps, labs like ours rely on zebrafish to test their theories about the roles that certain genes and proteins play in development.</p>
<p>Model organisms like zebrafish are what allow scientists to get one step closer to solving real-world problems every day.</p><img src="https://counter.theconversation.com/content/205110/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Raquel Espín-Palazón receives funding from NIH, Carver Charitable Trust, Fundacion Seneca, American Heart Association, Iowa State University</span></em></p><p class="fine-print"><em><span>Gabrielle Dubansky does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Of the many qualities that make the zebrafish a model organism, the fact that it shares 70% of the genes humans have makes it an ideal candidate for developmental biology research.Gabrielle Dubansky, Master's Candidate in Molecular, Cellular and Developmental Biology, Iowa State UniversityRaquel Espín-Palazón, Assistant Professor of Genetics, Development and Cell Biology, Iowa State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2053732023-07-10T12:32:06Z2023-07-10T12:32:06ZZebrafish share skin-deep similarities with people, making them helpful models to study skin conditions like vitiligo and melanoma<figure><img src="https://images.theconversation.com/files/536160/original/file-20230706-27-zx3jhz.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2121%2C1412&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The melanocytes in zebrafish stripes share many similarities to those in people.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/zebrafish-isolated-on-black-background-royalty-free-image/1134340984">Dan Olsen/iStock via Getty Images Plus</a></span></figcaption></figure><p>Melanocytes are a small subset of epidermal cells that play an outsize role in protecting your skin from the damaging effects of sun exposure. They do this by synthesizing <a href="https://www.ncbi.nlm.nih.gov/books/NBK459156/">melanins, which are pigments</a> sent to other skin cells to shield them from harmful ultraviolet light. A lack of functioning melanocytes causes a <a href="https://doi.org/10.1101/cshperspect.a017046">wide range of skin conditions</a>, including skin cancer and <a href="https://theconversation.com/explainer-what-is-vitiligo-26647">vitiligo, an autoimmune condition</a> in which the body attacks melanocytes and causes patches of depigmented skin. </p>
<p>For nearly 20 years, <a href="https://profiles.umassmed.edu/display/130115">I have been studying</a> melanocytes and the role they play in disease. Difficulties growing human melanocytes <a href="https://theconversation.com/lab-grown-meat-techniques-arent-new-cell-cultures-are-common-tools-in-science-but-bringing-them-up-to-scale-to-meet-societys-demand-for-meat-will-require-further-development-208343">in cell cultures</a> have led researchers like me to use alternative models to study them. </p>
<p><a href="http://www.ceollab.com">My lab</a> and others have pioneered the use of zebrafish to study melanocytes. Using this small freshwater fish as a model organism, my team and I recently discovered a new way in which <a href="https://doi.org/10.7554/eLife.78942">melanocytes regenerate</a>. This process enables flexibility for these cells to recover from injuries and may be applicable to other types of tissues.</p>
<h2>What zebrafish and people have in common</h2>
<p>New students and nonscientists often ask me, “Why zebrafish?” There are several reasons why zebrafish are good models to study melanocytes.</p>
<p>Melanocytes in zebrafish are <a href="https://doi.org/10.1016/j.jid.2021.10.016">similar in many ways</a> to those in people. These cells develop in embryos in the same way those in humans do, use the same genetic programs and make the same melanins. Melanocyte dysfunction in zebrafish also leads to the same diseases and cancers found in people. </p>
<p>Unlike melanocytes in mouse or human skin, zebrafish melanocytes are externally visible in their dark stripes and spotted scales. Researchers can place the whole fish directly under a microscope and see the cells without the need for a biopsy. </p>
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<a href="https://images.theconversation.com/files/536163/original/file-20230706-21-43u981.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Zebrafish against white background" src="https://images.theconversation.com/files/536163/original/file-20230706-21-43u981.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/536163/original/file-20230706-21-43u981.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/536163/original/file-20230706-21-43u981.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/536163/original/file-20230706-21-43u981.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/536163/original/file-20230706-21-43u981.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/536163/original/file-20230706-21-43u981.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/536163/original/file-20230706-21-43u981.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Zebrafish melanocytes can be found in their dark stripes and spotted scales.</span>
<span class="attribution"><span class="source">Craig Ceol</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>Importantly, researchers can manipulate and perform experiments on zebrafish melanocytes in ways that are unethical or not feasible to do with people. Unlike studies that use isolated melanocytes in a petri dish, these experiments can take place in the context of a whole animal, where we can monitor the surrounding skin and other biological factors for their influence on how melanocytes behave and function.</p>
<h2>Diversity of melanocyte stem cells</h2>
<p>In work spearheaded by <a href="https://www.researchgate.net/scientific-contributions/William-Tyler-Frantz-2121259175">Tyler Frantz</a>, a graduate student in my lab, our team has focused our attention on the process by which new melanocytes <a href="https://doi.org/10.7554/eLife.78942">regenerate after injury</a>.</p>
<p>Melanocyte regeneration is important for recovering from skin disorders such as vitiligo. It’s also relevant to age-related conditions like <a href="https://doi.org/10.1111/brv.12648">hair graying</a>, in which melanocyte stem cells either die or become dormant and no longer produce the mature melanocytes that give hair its color.</p>
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<a href="https://images.theconversation.com/files/536164/original/file-20230706-21-yzkuvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close-up of zebrafish melanocytes -- small dark circles clustered in a band" src="https://images.theconversation.com/files/536164/original/file-20230706-21-yzkuvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/536164/original/file-20230706-21-yzkuvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/536164/original/file-20230706-21-yzkuvw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/536164/original/file-20230706-21-yzkuvw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/536164/original/file-20230706-21-yzkuvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/536164/original/file-20230706-21-yzkuvw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/536164/original/file-20230706-21-yzkuvw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The small dark circles clustered in a band across this photo are zebrafish melanocytes, magnified 100 times.</span>
<span class="attribution"><span class="source">Craig Ceol</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>To study melanocyte regeneration, we removed these cells from zebrafish and followed their process of regrowth. Since melanocyte stem cells in zebrafish are externally visible, we tracked these cells in real time to see how they divided and matured. Additionally, we measured which genes were expressed in individual melanocyte stem cells and their descendants during regeneration. </p>
<p>We found that dying melanocytes trigger this regenerative process by sending the signal for melanocyte stem cells – cells that can give rise to new melanocytes – to activate. Surprisingly, we identified two types of stem cells that each took a different route to make new melanocytes. One type of stem cell directly converted into melanin-producing melanocytes. The other type of stem cell divided to create two types of daughter cells. One type was new melanocytes, and the other was new stem cells ready to respond to future injury.</p>
<p>Researchers have known that a single stem cell is capable of <a href="https://doi.org/10.1038/s41580-022-00568-6">making the multiple types of cells</a> needed to regenerate tissue. Our zebrafish studies indicate that multiple different stem cells in skin, and potentially other tissues, can together reconstruct one particular cell type after injury. The involvement of multiple stem cells likely enables regeneration to nimbly adjust to different types of injuries.</p>
<h2>From fish to people</h2>
<p>Our findings from zebrafish are likely relevant to human skin. When we examined cells taken from the <a href="https://doi.org/10.1126/scitranslmed.abd8995">fluid within a blister</a> in human skin, we found cells that look remarkably similar to zebrafish melanocyte stem cells. We are planning to see whether these human cells are activated in skin regeneration to make new melanocytes, which would confirm their identity as melanocyte stem cells. </p>
<p>Ultimately, we envision using these findings to develop treatments that reinvigorate melanocyte stem cells, which could help reverse skin color loss in vitiligo and other diseases. Such treatments may also help counteract age-related pigment loss in hair and skin.</p>
<p>The unique features of zebrafish have allowed us to uncover a new mode of cellular regeneration. Because of cross-species similarities, we expect that these and many other findings from research using zebrafish may be applied to human biology.</p><img src="https://counter.theconversation.com/content/205373/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Craig Ceol receives funding from the National Institutes of Health, US Department of Defense and JW Holdings Pharmaceuticals.</span></em></p>Zebrafish melanocytes cause diseases similar to those in people when they don’t work properly. Studying how they regenerate after injury could lead to new treatments for hair color loss and vitiligo.Craig Ceol, Assistant Professor of Molecular Medicine, UMass Chan Medical SchoolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1991462023-02-06T20:03:50Z2023-02-06T20:03:50ZRare genetic disease may protect Ashkenazi Jews against tuberculosis – new study<p>Tuberculosis, humanity’s greatest infectious killer, is caused by bacteria that usually affect the lungs but can also affect many other organs in the body. In 2021, around <a href="https://www.who.int/teams/global-tuberculosis-programme/tb-reports/global-tuberculosis-report-2022/tb-disease-burden/2-1-tb-incidence">10.6 million people</a> worldwide fell ill with tuberculosis (TB) and 1.6 million people died from the disease. </p>
<p>However, around 95% of people who are infected with the bacteria that cause TB don’t become ill. Their immune system manages to successfully destroy the bug.</p>
<p>My colleagues and I are interested in what makes some people susceptible to TB, while others appear to be protected. We use zebrafish to study the disease as their immune systems share many similarities with those of humans, and it is possible to manipulate their genes in the lab. In our <a href="https://www.pnas.org/doi/full/10.1073/pnas.2217673120">latest study</a>, published in the online journal PNAS, we have used this kind of manipulation to show the genes carried by many Ashkenazi Jews that put them at a higher risk of a rare disease also help protect them against TB.</p>
<p>Our team had <a href="https://pubmed.ncbi.nlm.nih.gov/27015311/">previously found</a> that zebrafish with genetic mutations in certain enzymes in their cells became more susceptible to TB. These enzymes are found in the cells’ lysosomes, components that break down unwanted material including proteins and fats. When the production of these enzymes is reduced, it can lead to a build-up of toxic material. </p>
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<img alt="Zebrafish" src="https://images.theconversation.com/files/508163/original/file-20230204-12489-ksctj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/508163/original/file-20230204-12489-ksctj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/508163/original/file-20230204-12489-ksctj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/508163/original/file-20230204-12489-ksctj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/508163/original/file-20230204-12489-ksctj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/508163/original/file-20230204-12489-ksctj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/508163/original/file-20230204-12489-ksctj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Zebrafish are used to study TB.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/zebrafish-danio-rerio-aquarium-fish-212364877">Kazakov Maksim/Shutterstock</a></span>
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<p>One type of cell that is vulnerable to this build-up is the macrophage, a cell that “eats” toxic material, including bacteria and waste products. In lysosomal disorders, the macrophages move slowly and become enlarged because they accumulate undigested material in their lysosomes, making them less able to fight infection. </p>
<p>Macrophages need to move quickly to attack invading bacteria and viruses. Their name means “big eater”, and this is exactly what they do. But with lysosomal disorders, they’re unable to break down the food they eat, which makes them bloated and sluggish, unable to perform their duties.</p>
<h2>Resistant to infection</h2>
<p>However, when our group genetically engineered zebrafish to model one of these lysosomal disorders, called Gaucher disease (pronounced go-SHAY), we found something very unexpected: these fish were TB-resistant rather than susceptible.</p>
<p>Gaucher disease is a rare disease that can affect anyone, but rates are significantly high among Ashkenazi Jews – around <a href="https://gaucher-institute.com/burden-of-disease/epidemiology-of-gaucher-disease/gaucher-disease-in-the-ashkenazi-jewish-population">one in 800 births</a>. In most cases, the illness can be relatively mild, with symptoms including enlarged spleen and liver, and anaemia. Around two-thirds of people carrying two copies of the most common genetic variant are unaware they are carriers.</p>
<p>We made zebrafish with genetic variants that cause Gaucher disease in Ashkenazi Jews and, as expected, their macrophages became enlarged and could not break down an unusual type of fat called sphingolipids. Yet when the fish were exposed to TB, we were surprised to discover that they were resistant to infection. </p>
<p>The reason for this resistance to infection was because of the fatty chemical that accumulates in the macrophages in Gaucher disease. This fatty chemical was found to act as a solvent that can kill TB bacteria within minutes by disrupting their cell walls.</p>
<p>These fish unknowingly landed us in a debate that’s been going on in human genetics <a href="https://www.pnas.org/doi/full/10.1073/pnas.2217673120">for decades</a>: are Ashkenazi Jews – who we know are at a much greater risk of Gaucher disease – somehow less likely to get TB infection? The answer appears to be yes.</p>
<p>The Ashkenazi Jewish diaspora has experienced centuries of persecution, often forced to live in ghettos and migrate from country to country. They would have been highly exposed to TB, which spreads more widely among poorer living conditions and densely populated urban areas. </p>
<p>These genetic variants can increase the risk of Gaucher disease, but they also help protect against TB, giving them a selective advantage – that is, making the variants more likely to be passed down from generation to generation and therefore spread within the population. A similar phenomenon is seen in groups where people carry genetic variants that <a href="https://www.nature.com/articles/nature.2011.9342">protect them from malaria</a> but when more than one copy is present, causes harmful anaemia or even sickle cell disease.</p>
<p>Unlike the example of sickle cell anaemia, however, only people who carry two copies of the Gaucher genetic variant – one from each parent – are likely to be protected against TB. That’s because having one “healthy” gene generates enough of the enzyme to clear the bacteria-killing fatty chemical so that it does not accumulate.</p>
<p>This discovery may provide clues to possible new treatments for TB. Drugs that mimic the effects of Gaucher disease – specifically the build-up of the fatty chemical that acts as a solvent – might be useful in the global fight against TB.</p><img src="https://counter.theconversation.com/content/199146/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lalita Ramakrishnan receives funding from the Wellcome Trust, UK and the National Institutes of Health, USA</span></em></p><p class="fine-print"><em><span>Laura Whitworth does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Ashkenazi Jews are significantly more susceptible to a rare genetic disorder known as Gaucher disease.Lalita Ramakrishnan, Professor, Microbiology, University of CambridgeLaura Whitworth, Group Laboratory Manager, Department of Medicine, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1761652022-02-06T08:34:19Z2022-02-06T08:34:19ZZebrafish research reveals green rooibos tea’s anxiety-busting properties<figure><img src="https://images.theconversation.com/files/443686/original/file-20220201-25-7le1xb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Zebrafish are genetically similar to humans. </span> <span class="attribution"><span class="source">Damien Schumann</span></span></figcaption></figure><p>Rooibos tea is a uniquely South African product. The plant, <em>Aspalathus linearis</em>, grows mainly in the Cederberg area of the country’s Western Cape province. And it’s not just a tasty beverage. It is caffeine-free; <a href="https://www.sciencedirect.com/science/article/abs/pii/S1756464616302699?via%3Dihub">research has proved</a> that it has anti-inflammatory properties. It’s also been found to ease pain and <a href="https://pubmed.ncbi.nlm.nih.gov/33982505/">reduce allergies</a>. Rooibos is also good <a href="https://pubmed.ncbi.nlm.nih.gov/30183052/">for heart health</a>.</p>
<p>As our <a href="https://pubs.rsc.org/en/content/articlehtml/2021/fo/d1fo03178c">new study shows</a>, rooibos tea – specifically unfermented or green rooibos – may also help to reduce anxiety. Our research found that this extract of the tea, prepared using ethanol rather than water, has anxiolytic properties. This means it prevents or lessens the degree of anxiety a person experiences.</p>
<p>We didn’t reach this conclusion by testing the tea on human subjects, though. There’s a huge variation in anxiety severity, so a study in humans would require too many participants to give us sufficient statistical power, and thus be too expensive. </p>
<p>Instead, we used zebrafish. The small, striped tropical fish may seem like an odd choice, until you realise that they are genetically quite similar to humans. For more than 80% of the genes known to cause disease in humans, <a href="https://pubmed.ncbi.nlm.nih.gov/30320468/">similar genes are represented</a> in zebrafish. </p>
<p>This fact prompted Stellenbosch University’s Faculty of Medicine and Health Sciences to set up the Zebrafish Research Unit just more than a year ago. Several studies are under way involving advanced analytical pharmacology, toxicology, therapeutic target identification and drug discovery. This study is one of the first to stem from the laboratory.</p>
<h2>A variety of data</h2>
<p>My <a href="http://www.sun.ac.za/english/faculty/healthsciences/Clinical%20Pharmacology/Pages/Staff.aspx">research group</a> studies the connection between psychological stress and chronic inflammatory disease. This is especially important in South Africa: the South African Depression and Anxiety group <a href="https://www.sadag.org/">estimates</a> that many as one in six South Africans suffer from anxiety or depression. Furthermore, the current <a href="https://businesstech.co.za/news/lifestyle/498579/leading-causes-of-death-in-south-africa-2/">top 10 causes of death</a> in South Africa, like TB, diabetes and respiratory disease, all have inflammation as a common characteristic.</p>
<p>Zebrafish are ideal for drug discovery especially in the context of neurological and inflammatory conditions. We are able to do thorough testing including not only behavioural assessment and seeing how specific treatments work, but also assessing the risks of overdosing and long-term use of potential treatments.</p>
<p>So, we set out to employ our zebrafish models to see whether rooibos might have any positive effects on anxiety. Most of our research is done at the early larval stage, when the zebrafish are not yet considered a sentient animal. It’s a more ethical way of using a live organism in research, as they cannot experience pain at that stage.</p>
<p>We immersed the 2mm-long zebrafish larvae in different concentrations of rooibos in a small dish. Essentially, they were swimming in tea; this is absorbed through their skin as well as through their gills, since their mouths are not yet open. </p>
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Read more:
<a href="https://theconversation.com/pasha-127-allergies-vs-rooibos-can-this-south-african-plant-help-sufferers-169753">Pasha 127: Allergies vs rooibos: can this South African plant help sufferers?</a>
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<p>At different points, specialised equipment tracked their movement and this was used to construct behavioural patterns. Using a model of anxiety – which entails exposing the larvae to alternating bright light and darkness for short periods of time – we assessed whether the larvae swimming in rooibos were able to remain calm, by comparing their behaviour to that of unsupplemented larvae. Normally, in this model, the larvae would “freeze” in bright light, followed by hyperactivity during the periods of darkness. In our study, rooibos-treated larvae also froze, but did not exhibit the anxious hyperactivity.</p>
<h2>Oxidative stress</h2>
<p>We also performed a test using the live larvae’s behaviour to probe a specific mechanism: a “feel-good” neurotransmitter, <a href="https://www.webmd.com/vitamins-and-supplements/gaba-uses-and-risks">GABA</a>, whose signalling can be manipulated by either enhancing or blocking its receptor. If the receptor is blocked, the larvae exhibit a hyperactive seizure-like behaviour. In our study, rooibos was able to completely prevent this response – in fact, it showed similar results to an anti-epileptic drug known to work through GABA. </p>
<p>The behavioural tests were complemented by whole body analyses for oxidative stress and anti-oxidant activity, as well as some cell culture work using human cells. In these models, we showed that green rooibos was able to protect human neurons against oxidative stress. </p>
<p><a href="https://pubmed.ncbi.nlm.nih.gov/27034739/">Oxidative stress</a> increases during life and is actually responsible for ageing, so a product that can protect the brain from oxidative stress, can essentially slow our ageing process. In a world where advances in medicine are allowing us to grow older, it is becoming more and more important to be able to prevent the brain from ageing.</p>
<p>Taken together, our data suggest that green rooibos tea could be considered as a functional brain food. The research suggests it may be a good option as a starting ingredient in the development of new <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4336979/">nutraceuticals</a> – pharmaceutical alternatives which claim physiological benefits. </p>
<p>The results of this study mean that we could have uncovered nature’s contribution to treating some of South Africa’s health problems. It shows that drinking green rooibos tea may have a calming effect if you suffer from anxiety.</p>
<h2>Zebrafish in research</h2>
<p>This certainly won’t be the last piece of research from our lab or <a href="https://theconversation.com/fish-on-acid-microdosing-zebrafish-with-lsd-shows-its-potential-benefits-for-humans-172218">others</a> that use zebrafish in drug discovery. The fish, which originate in Malaysia, may be the new rodent in research. Apart from their genetic similarities to humans, when in their larval stage the fish are fairly transparent; that makes them great for microscopy.</p>
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Read more:
<a href="https://theconversation.com/how-the-zebrafish-got-its-stripes-102070">How the zebrafish got its stripes</a>
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<p>We have a couple of tanks where we breed with the adult stock. The fish can live up to three years in a laboratory, compared to about a year in nature (because of excellent care in the lab, but also the absence of natural predators). </p>
<p>In terms of future research, assessing these effects in humans is on the cards. We are also generating very promising results on rooibos in the context of inflammatory bowel syndrome, a chronic condition affecting approximately <a href="https://pubmed.ncbi.nlm.nih.gov/32981524/">10% of the global population</a> and which is the most common co-morbidity to anxiety disorders.</p><img src="https://counter.theconversation.com/content/176165/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Carine Smith receives funding from the South African NRF and the South African Rooibos Council. No funders have any input into study design or reporting of data. </span></em></p>Zebrafish are ideal for drug discovery especially in the context of neurological and inflammatory conditions.Carine Smith, Professor in Pharmacology, Division for Clinical Pharmacology, Stellenbosch UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1722182022-02-02T18:52:15Z2022-02-02T18:52:15ZFish on acid? Microdosing zebrafish with LSD shows its potential benefits for humans<figure><img src="https://images.theconversation.com/files/443433/original/file-20220131-126279-j84hlf.jpg?ixlib=rb-1.1.0&rect=0%2C15%2C2600%2C1650&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Because of their social nature and the fact that they share 70 per cent of their DNA with humans, zebrafish make ideal test subjects.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><iframe style="width: 100%; height: 175px; border: none; position: relative; z-index: 1;" allowtransparency="" src="https://narrations.ad-auris.com/widget/the-conversation-canada/fish-on-acid-microdosing-zebrafish-with-lsd-shows-its-potential-benefits-for-humans" width="100%" height="400"></iframe>
<p>Microdosing — <a href="https://www.theguardian.com/society/2021/dec/02/people-microdosing-on-psychedelics-to-improve-wellbeing-during-pandemic">regularly ingesting small amounts of a psychedelic substance</a> — has gone mainstream.</p>
<p>Believed to increase productivity, spark creativity or improve open-mindedness, the microdosing of psychedelic drugs is gaining popularity with both academic researchers and those interested in experimenting.</p>
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Read more:
<a href="https://theconversation.com/microdosers-of-lsd-and-magic-mushrooms-are-wiser-and-more-creative-101302">'Microdosers' of LSD and magic mushrooms are wiser and more creative</a>
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<p>But microdosing may offer more beyond its mood-boosting abilities.</p>
<p>Using zebrafish and our new method for precise and repeated drug administration, my colleagues and I are studying LSD and terpenes (chemicals in plants responsible for their scent, among other things) in a series of projects exploring potential novel treatments for mental illness and alcohol use disorder.</p>
<p>Zebrafish might seem an odd choice in studying human health, but <a href="https://doi.org/10.1038/nature12111">they share 70 per cent of their genes with us</a> and are a popular nonhuman organism used by scientists to study biological processes. They are also incredibly social, making them <a href="https://dx.doi.org/10.1038/s12276-021-00571-5">well-suited for behavioural studies into psychiatric disorders</a> and <a href="https://doi.org/10.1038/nrd46277">drug discovery</a>.</p>
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Read more:
<a href="https://theconversation.com/animals-in-research-zebrafish-13804">Animals in research: zebrafish</a>
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<p>However, past drug research using zebrafish has studied “chronic” administration — putting fish in a drug solution for weeks. Since humans require (at the very least) some sleep, this administration can’t accurately reflect human consumption patterns.</p>
<h2>Dose control</h2>
<p>To address this limitation, we developed a new method to dose multiple fish accurately and efficiently for exact exposure times. By placing an insert into the housing tank, we can move groups of fish from their housing tank into a dosing tank for a precise dosing period, more closely mimicking the way that a person might consume drugs or alcohol.</p>
<p>To verify that this new dosing procedure could have behavioural and neurochemical effects, we completed a series of projects using our new method to examine the effects of alcohol and nicotine.</p>
<p>First, we tested the zebrafish with a daily moderate dose or a weekly binge-level dose of ethanol for three weeks. We found a significant difference in <a href="https://doi.org/10.1371/journal.pone.0063319">location preference in the daily moderate group</a> compared to controls during a withdrawal period, which implies there were neurological changes. </p>
<p>Then we followed up with a study using <a href="https://doi.org/10.7717/peerj.6551">lower doses for shorter periods of time</a>. Here, we saw decreased boldness and increased anxiety-like behaviour during withdrawal from the highest dose (<a href="http://dx.doi.org/10.7717/peerj.2994">opposite to what is seen after an acute single-dose</a>). </p>
<p>Similarly, testing the model <a href="https://doi.org/10.1038/s41598-020-65382-6">using nicotine</a>, we found again that acute doses decreased anxiety-like behaviour while repeated dosing led to an increase of anxiety-like behaviour during withdrawal.</p>
<p>For humans, having an alcoholic drink or a cigarette <a href="https://doi.org/10.1176/ajp.147.6.685">can decrease anxiety, and the inverse is observed in withdrawal</a>. Our zebrafish model is consistent with this, which has given us confidence that we can test novel compounds with potential therapeutic effects in humans.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/443573/original/file-20220131-142871-nfbzlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a short glass drink with alcohol next to an ashtray with a smoldering cigarette in it. in the background, out of focus, a man wearing a blue shirt and surgical mask" src="https://images.theconversation.com/files/443573/original/file-20220131-142871-nfbzlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/443573/original/file-20220131-142871-nfbzlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/443573/original/file-20220131-142871-nfbzlc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/443573/original/file-20220131-142871-nfbzlc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/443573/original/file-20220131-142871-nfbzlc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/443573/original/file-20220131-142871-nfbzlc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/443573/original/file-20220131-142871-nfbzlc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Researchers have been finding that cigarette and alcohol consumption has increased during the pandemic. These substances can reduce anxiety, but withdrawal from them can increase it.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
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<h2>Potential therapies</h2>
<p>Terpenes are a large and diverse group of aromatic compounds. They are responsible for the smell, taste and pigmentation of plants. Many terpenes — like those found in tea, lemongrass, cannabis and citrus fruits — <a href="https://dx.doi.org/10.1007/978-3-030-31269-5_15">have medical benefits</a>.</p>
<p>We found that zebrafish acutely dosed with the terpene limonene (found in citrus fruit peels and cannabis) and myrcene (found in cannabis and hops), showed a significant reduction in anxiety-like behaviour. One observation that may be clinically significant is that — contrary to nicotine or alcohol — no negative effects were seen after repeated dosing for seven days, <a href="https://doi.org/10.1038/s41598-021-98768-1">suggesting minimal to no addictive potential</a>. </p>
<p><a href="https://doi.org/10.1038/s41598-021-98768-1">This study</a>, alongside <a href="https://doi.org/10.1078/094471102321621304">previous research</a>, suggests that the terpenes limonene and beta-myrcene possess sedative and anti-anxiety effects that have potential as valuable therapeutic compounds for the treatment of a variety of mental health conditions.</p>
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<a href="https://images.theconversation.com/files/443561/original/file-20220131-141004-b3qulk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="close-up of a hand holding tweezers handling small squares of cardboard that are microdose tabs" src="https://images.theconversation.com/files/443561/original/file-20220131-141004-b3qulk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/443561/original/file-20220131-141004-b3qulk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/443561/original/file-20220131-141004-b3qulk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/443561/original/file-20220131-141004-b3qulk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/443561/original/file-20220131-141004-b3qulk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/443561/original/file-20220131-141004-b3qulk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/443561/original/file-20220131-141004-b3qulk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">There is a growing interest in microdosing psychedelics to increase productivity and spark creativity.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
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<h2>Prairie psychedelic research</h2>
<p>Some of the most influential research into psychedelics <a href="https://www.thecanadianencyclopedia.ca/en/article/psychedelic-research-in-1950s-saskatchewan">began in Saskatchewan in the 1950s</a>. British-born psychiatrist Humphry Osmond <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC381240/">used LSD and mescaline to treat alcoholism</a>, with single doses showing a 50 to 90 per cent recovery rate over two years.</p>
<p>However, while Osmond saw success in large single-dose treatments, the acute administrations required continuous monitoring of the patient over the seven- to 15-hour “trip” to prevent any <a href="https://dx.doi.org/10.1124/pr.115.011478">harm arising from impaired judgment</a>. From a therapeutic perspective, this would be very time-intensive for clinicians, and is not feasible. </p>
<p>This is where microdosing comes in. With the potential to be <a href="https://doi.org/10.1007/s00213-019-05417-7">easy and safe</a>, we believe this pattern of exposure to be more therapeutically relevant, as doses are small enough to be safely self-administered with the proper guidance of a clinician.</p>
<h2>Future knowledge</h2>
<p>In our first study, we repeatedly microdosed our zebrafish with LSD. Using behavioural neuroscience tests to quantify locomotion, boldness and anxiety-like behaviour, we observed no impact on behaviour after 10 days of repeated dosing. Like with terpenes, this may suggest a lack of withdrawal symptoms or addictive potential, which is encouraging for clinically viability for use in humans.</p>
<p>Our current study examines the effects of LSD microdosing on the symptoms of alcohol withdrawal, <a href="https://policyoptions.irpp.org/magazines/april-2021/covid-19-shows-us-why-canada-needs-a-federal-alcohol-act/">which is a growing issue in Canadian health care</a>.</p>
<p>In Canada, the negative effects of alcohol are widely felt. Fetal alcohol spectrum disorder remains the leading developmental disability in Canada, and alcohol harm is a top <a href="https://www.cihi.ca/sites/default/files/document/report-alcohol-hospitalizations-en-web.pdf">cause of injury and death</a>. It costs Canadians <a href="https://csuch.ca/publications/CSUCH-Canadian-Substance-Use-Costs-Harms-Infographic-2020-en.pdf">billions of dollars in lost productivity, and is a burden on the health-care and judicial systems</a>. Treatment and rehabilitation can be costly, time consuming and bogged down in lengthy wait times — if accessible at all.</p>
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Read more:
<a href="https://theconversation.com/fetal-alcohol-spectrum-disorder-amid-covid-19-fewer-services-potential-boost-in-rates-145593">Fetal alcohol spectrum disorder amid COVID-19: Fewer services, potential boost in rates</a>
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<p>Further research into other psychedelics, like psilocin (the psychoactive compound in psilocybin, or “magic mushrooms”), are also planned with the goal of providing scientific evidence to help determine whether these substances should be used in larger clinical trials in humans.</p>
<p>Psychedelics may provide assistance, but despite increasing evidence that LSD and psilocin <a href="https://doi.org/10.1016/j.pharmthera.2003.11.002">are non-addictive and low risk</a>, they remain highly restricted. Perhaps with more research and the continuing shift in public perception, we might yet again see LSD being used as a radical treatment for mental health and addiction.</p><img src="https://counter.theconversation.com/content/172218/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Trevor James Hamilton receives funding from the Natural Sciences and Engineering Research Council of Canada (NSERC). </span></em></p>Growing interest in psychedelics has spurred new research decades after hallucinogenics were tested in Saskatchewan in the 1950s. And an unassuming common fish is proving a useful test subject.Trevor James Hamilton, Associate Professor in Neuroscience (Department of Psychology), MacEwan UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1745782022-01-10T20:24:35Z2022-01-10T20:24:35ZWhere are memories stored in the brain? New research suggests they may be in the connections between your brain cells<figure><img src="https://images.theconversation.com/files/439936/original/file-20220110-15-16w9k6u.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2121%2C1412&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Physically removing bad or unwanted memories by altering synapses in the brain may one day be possible.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/3d-digital-neuro-multicolored-colorful-royalty-free-illustration/1266784432"> apagafonova/iStock via Getty Images Plus</a></span></figcaption></figure><p>All memory storage devices, from your brain to the RAM in your computer, store information by changing their physical qualities. Over 130 years ago, pioneering neuroscientist <a href="https://doi.org/10.1016/0166-2236(94)90101-5">Santiago Ramón y Cajal</a> first suggested that the brain stores information by rearranging the connections, or synapses, between neurons.</p>
<p>Since then, neuroscientists have attempted to understand the physical changes associated with memory formation. But visualizing and mapping synapses is challenging to do. For one, synapses are very small and tightly packed together. They’re roughly <a href="https://doi.org/10.1002/cmr.a.21249">10 billion times smaller</a> than the smallest object a standard clinical MRI can visualize. Furthermore, there are approximately <a href="https://doi.org/10.1038/d41586-019-02208-0">1 billion synapses</a> in the mouse brains researchers often use to study brain function, and they’re all the same opaque to translucent color as the tissue surrounding them.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/440080/original/file-20220110-25-pau5jj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram showing structure of a chemical synapse and neurotransmitter release." src="https://images.theconversation.com/files/440080/original/file-20220110-25-pau5jj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/440080/original/file-20220110-25-pau5jj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=462&fit=crop&dpr=1 600w, https://images.theconversation.com/files/440080/original/file-20220110-25-pau5jj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=462&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/440080/original/file-20220110-25-pau5jj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=462&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/440080/original/file-20220110-25-pau5jj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=581&fit=crop&dpr=1 754w, https://images.theconversation.com/files/440080/original/file-20220110-25-pau5jj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=581&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/440080/original/file-20220110-25-pau5jj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=581&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Synapses comprise the very end of the transmitting neuron, the very beginning of the receiving neuron, and the tiny gap between them.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/structure-of-a-typical-chemical-synapse-royalty-free-illustration/499581991">ttsz/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<p>A <a href="https://doi.org/10.1073/pnas.2107661119">new imaging technique</a> my colleagues <a href="https://scholar.google.com/citations?user=z040dHgAAAAJ&hl=en">and I</a> developed, however, has allowed us to map synapses during memory formation. We found that the process of forming new memories changes how brain cells are connected to one another. While some areas of the brain create more connections, others lose them.</p>
<h2>Mapping new memories in fish</h2>
<p>Previously, researchers focused on <a href="https://doi.org/10.1038/37601">recording the electrical signals</a> produced by neurons. While these studies have confirmed that neurons change their response to particular stimuli after a memory is formed, they couldn’t pinpoint what drives those changes. </p>
<p>To study how the brain physically changes when it forms a new memory, we created 3D maps of the synapses of zebrafish before and after memory formation. We chose <a href="https://dx.doi.org/10.1016%2Fj.tips.2013.12.002">zebrafish</a> as our test subjects because they are large enough to have brains that function like those of people, but small and transparent enough to offer a window into the living brain.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/440055/original/file-20220110-13-zgc7bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Black and white image of larval zebrafish." src="https://images.theconversation.com/files/440055/original/file-20220110-13-zgc7bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/440055/original/file-20220110-13-zgc7bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=229&fit=crop&dpr=1 600w, https://images.theconversation.com/files/440055/original/file-20220110-13-zgc7bp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=229&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/440055/original/file-20220110-13-zgc7bp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=229&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/440055/original/file-20220110-13-zgc7bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=288&fit=crop&dpr=1 754w, https://images.theconversation.com/files/440055/original/file-20220110-13-zgc7bp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=288&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/440055/original/file-20220110-13-zgc7bp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=288&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Zebrafish are particularly fitting models for neuroscience research.</span>
<span class="attribution"><span class="source">Zhuowei Du and Don B. Arnold</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>To induce a new memory in the fish, we used a type of learning process called <a href="https://blogs.scientificamerican.com/thoughtful-animal/what-is-classical-conditioning-and-why-does-it-matter/">classical conditioning</a>. This involves exposing an animal to two different types of stimuli simultaneously: a neutral one that doesn’t provoke a reaction and an unpleasant one that the animal tries to avoid. When these two stimuli are paired together enough times, the animal responds to the neutral stimulus as if it were the unpleasant stimulus, indicating that it has made an <a href="https://www.verywellmind.com/what-is-associative-memory-5198601">associative memory</a> tying these stimuli together.</p>
<p>As an unpleasant stimulus, we gently heated the fish’s head with an infrared laser. When the fish flicked its tail, we took that as an indication that it wanted to escape. When the fish is then exposed to a neutral stimulus, a light turning on, tail flicking meant that it’s recalling what happened when it previously encountered the unpleasant stimulus.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/439943/original/file-20220110-23-rn0bk5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram illustrating classical conditioning of a dog to salivate in response to a ringing bell." src="https://images.theconversation.com/files/439943/original/file-20220110-23-rn0bk5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/439943/original/file-20220110-23-rn0bk5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=464&fit=crop&dpr=1 600w, https://images.theconversation.com/files/439943/original/file-20220110-23-rn0bk5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=464&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/439943/original/file-20220110-23-rn0bk5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=464&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/439943/original/file-20220110-23-rn0bk5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=583&fit=crop&dpr=1 754w, https://images.theconversation.com/files/439943/original/file-20220110-23-rn0bk5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=583&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/439943/original/file-20220110-23-rn0bk5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=583&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Pavlov’s dog is the most well-known example of classical conditioning, in which a dog salivates in response to a ringing bell because it has formed an associative memory between the bell and food.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/lilita/8441057768">Lili Chin/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>To create the maps, we genetically engineered zebrafish with neurons that produce fluorescent proteins that bind to synapses and make them visible. We then imaged the synapses with a custom-built microscope that uses a much lower dose of laser light than standard devices that also use fluorescence to generate images. Because our microscope caused less damage to the neurons, we were able to image the synapses without losing their structure and function.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/440053/original/file-20220110-27-14nulz7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Image of magenta-colored neurons in a live fish brain, with the synapses colored in green" src="https://images.theconversation.com/files/440053/original/file-20220110-27-14nulz7.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/440053/original/file-20220110-27-14nulz7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=766&fit=crop&dpr=1 600w, https://images.theconversation.com/files/440053/original/file-20220110-27-14nulz7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=766&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/440053/original/file-20220110-27-14nulz7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=766&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/440053/original/file-20220110-27-14nulz7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=963&fit=crop&dpr=1 754w, https://images.theconversation.com/files/440053/original/file-20220110-27-14nulz7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=963&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/440053/original/file-20220110-27-14nulz7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=963&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This image shows neurons in a live fish brain, with the synapses colored in green.</span>
<span class="attribution"><span class="source">Zhuowei Du and Don B. Arnold</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>When we compared the 3D synapse maps before and after memory formation, we found that neurons in one brain region, the anterolateral dorsal pallium, developed new synapses while neurons predominantly in a second region, the anteromedial dorsal pallium, lost synapses. This meant that new neurons were pairing together, while others destroyed their connections. Previous experiments have suggested that the <a href="https://doi.org/10.1523/JNEUROSCI.4930-03.2004">dorsal pallium</a> of fish may be analogous to the amygdala of mammals, where fear memories are stored.</p>
<p>Surprisingly, changes in the strength of existing connections between neurons that occurred with memory formation were small and indistinguishable from changes in control fish that did not form new memories. This meant that forming an associative memory involves synapse formation and loss, but not necessarily changes in the strength of existing synapses, as previously thought.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/YLVdRPVj-XM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Researchers from Howard Hughes Medical Institute captured video of the firing neurons of a baby zebrafish as it sees things and tries to move.</span></figcaption>
</figure>
<h2>Could removing synapses remove memories?</h2>
<p>Our new method of observing brain cell function could open the door not just to a deeper understanding of how memory actually works, but also to potential avenues for treatment of neuropsychiatric conditions like PTSD and addiction. </p>
<p><a href="https://www.verywellmind.com/what-is-associative-memory-5198601">Associative memories</a> tend to be much stronger than other types of memories, such as conscious memories about what you had for lunch yesterday. Associative memories induced by classical conditioning, moreover, are thought to be analogous to <a href="https://doi.org/10.1038/s41467-020-15121-2">traumatic memories that cause PTSD</a>. Otherwise harmless stimuli similar to what someone experienced at the time of the trauma can trigger recall of painful memories. For instance, a bright light or a loud noise could bring back memories of combat. Our study reveals the role that synaptic connections may play in memory, and could explain why associative memories can last longer and be remembered more vividly than other types of memories. </p>
<p>Currently the most common treatment for PTSD, <a href="https://doi.org/10.1176/appi.psychotherapy.2002.56.1.59">exposure therapy</a>, involves repeatedly exposing the patient to a harmless but triggering stimulus in order to suppress recall of the traumatic event. In theory, this indirectly remodels the synapses of the brain to make the memory less painful. Although there has been some success with exposure therapy, patients are <a href="https://doi.org/10.1093/ilar/ilu008">prone to relapse</a>. This suggests that the underlying memory causing the traumatic response has not been eliminated.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/rHg_SlEqJGc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Conceptually tied to classical conditioning, prolonged exposure therapy is one way to treat PTSD.</span></figcaption>
</figure>
<p>It’s still unknown whether synapse generation and loss actually drive memory formation. <a href="https://dornsife.usc.edu/arnold">My laboratory</a> has developed technology that can quickly and precisely <a href="https://doi.org/10.1038/nmeth.3894">remove synapses</a> without damaging neurons. We plan to use similar methods to remove synapses in zebrafish or mice to see whether this alters associative memories.</p>
<p>[<em>Over 140,000 readers rely on The Conversation’s newsletters to understand the world.</em> <a href="https://memberservices.theconversation.com/newsletters/?source=inline-140ksignup">Sign up today</a>.]</p>
<p>It might be possible to physically erase the associative memories that underlie devastating conditions like PTSD and addiction with these methods. Before such a treatment can even be contemplated, however, the synaptic changes encoding associative memories need to be more precisely defined. And there are obviously serious ethical and technical hurdles that would need to be addressed. Nevertheless, it’s tempting to imagine a distant future in which synaptic surgery could remove bad memories.</p><img src="https://counter.theconversation.com/content/174578/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Don Arnold receives funding from the National Institutes of Health, the National Institute on Neurological Disorders and Stroke, and the McKnight Foundation.</span></em></p>Understanding where and how memories are formed could lead to more ways to treat conditions like PTSD and addiction.Don Arnold, Professor of Biological Sciences and Biomedical Engineering, USC Dornsife College of Letters, Arts and SciencesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1579292021-03-31T13:46:44Z2021-03-31T13:46:44ZFive ways fish are more like humans than you realise<figure><img src="https://images.theconversation.com/files/392799/original/file-20210331-21-4uvtu.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2835%2C1871&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/zebrafish-marine-fish-school-ink-painting-1909273081">Xu Wei Chao/Shutterstock</a></span></figcaption></figure><p>You’ve probably heard that <a href="http://www.bbc.com/earth/story/20170426-why-fish-do-not-deserve-their-reputation-for-forgetfulness">fish have a three-second memory</a>, or that they’re <a href="https://www.sciencedaily.com/releases/2013/08/130808123719.htm">incapable of feeling pain</a>. Neither of these statements is true, but it’s telling that these misconceptions don’t crop up for other vertebrates. </p>
<p>Perhaps it’s because fish appear so different from us. They don’t seem to have any capacity for facial expression, or vocal communication – and we don’t even breathe the same air. Collectively, these differences put fish so <a href="https://www.jstor.org/stable/j.ctt14bssx9">far away from humans</a> that we struggle to relate to them.</p>
<p>But when scientists have conducted experiments to discover more about fish – including their neurobiology, their social lives and mental faculties – they’ve found time and time again that fish are more complex than they’re often given credit for. Above all, fish seem to have more in common with us than we might like to admit.</p>
<p>In my research I often work with zebrafish – <a href="https://theconversation.com/uk/topics/zebrafish-4444">the aquatic lab rat</a>. Here are five fascinating things that I, and other researchers, have discovered about them and their kind.</p>
<h2>1. Fish lose their memory as they age</h2>
<p>As humans age, <a href="https://www.mayoclinic.org/diseases-conditions/mild-cognitive-impairment/symptoms-causes/syc-20354578">our memories decline</a>. Scientists work to understand the biology of cognitive decline in order to predict how we can help people age better and develop treatments for conditions such as Alzheimer’s disease and dementia.</p>
<p>In humans, <a href="http://www.scholarpedia.org/article/Working_memory">working memory</a> – the mental process that we use to carry out everyday tasks – declines as we get older. My colleagues and I found something similar when we <a href="https://brainandbehaviourlab.jimdofree.com/">observed zebrafish</a> at six and 24 months of age swimming around in a Y-shaped <a href="https://link.springer.com/article/10.3758/s13428-020-01452-x?mc_cid=547790ee2b&mc_eid=%5bUNIQID%5d&error=cookies_not_supported&code=4d6ad3aa-c687-42cd-8806-000ff03c9448">maze</a>.</p>
<p><a href="https://www.biorxiv.org/content/biorxiv/early/2021/02/05/2020.06.05.136077.full.pdf">We found</a> that the older fish struggled to navigate the maze compared to younger ones. What’s more, when we designed a virtual version of the task for humans, we found that people in their 70s showed exactly the same deficits as fish.</p>
<figure class="align-center ">
<img alt="A school of fish surrounds a tropical coral reef." src="https://images.theconversation.com/files/392806/original/file-20210331-15-13idrfh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/392806/original/file-20210331-15-13idrfh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/392806/original/file-20210331-15-13idrfh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/392806/original/file-20210331-15-13idrfh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/392806/original/file-20210331-15-13idrfh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/392806/original/file-20210331-15-13idrfh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/392806/original/file-20210331-15-13idrfh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The navigating abilities of fish can deteriorate after a certain age.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/off-north-sulawesi-indonesia-plethora-small-126712838">Ethan Daniels/Shutterstock</a></span>
</figcaption>
</figure>
<h2>2. Fish like the same drugs as humans</h2>
<p>I mean, they <em>really</em> like them. Biologists Tristan Darland and John Dowling at Harvard University in the US found that zebrafish <a href="https://www.pnas.org/content/pnas/98/20/11691.full.pdf">particularly like cocaine</a>, which they tested by dangling the drug in their tank when the fish hung around a certain visual pattern. This preference for cocaine was heritable too. Offspring of fish with a penchant for the drug passed it on to their children – <a href="https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1360-0443.2008.02213.x">a pattern reported in humans</a>.</p>
<p>Zebrafish also show patterns of compulsive drug-seeking seen in people suffering with addiction. <a href="http://brennanlab.sbcs.qmul.ac.uk/">Caroline Brennan’s research group</a> at Queen Mary University of London found that fish would put up with being chased with a net if it meant <a href="https://jeb.biologists.org/content/211/10/1623">gaining access to cocaine</a>. </p>
<p>Working with Brennan’s group and Pfizer, we tested a range of other drugs – opiates, stimulants, alcohol and nicotine – to see what zebrafish can tell us about the abuse potential of new drugs (something that has to happen before they’re licensed). It turned out <a href="https://jpet.aspetjournals.org/content/363/1/66?casa_token=zE3v2ifhYIwAAAAA:WTwBF3qb9zcIphk1Blkm20fNvWDDUl8SpnKgLV_c8oIR7mIwV9ysi8IviXB3xTnk8EpoZqDJY5vm">they loved them all</a>. </p>
<p>Except, that is, THC – the main psychoactive ingredient in cannabis. It seems zebrafish wouldn’t make great hippies.</p>
<h2>3. Fish remember their friends</h2>
<p>You probably already know that fish are social animals. They can synchronise their behaviour in schools so that each individual mirrors the movements of their neighbour and the group appears to move as one.</p>
<p>What you probably didn’t know is that individual fish can also <a href="https://www.sciencedirect.com/science/article/pii/S0003347206001096?casa_token=XF66hW1vyBEAAAAA:qZzK8T1VopPiTmtecMSYJ7IQUxxJMptyxkC9KeOojQEuz93jAxOMBjqfiGDNILzyWtnKbH-3fBA">recognise</a> another fish from their own group (by smell, typically). Young fish prefer their own relatives, but as they get older, adult females prefer familiar females but unfamiliar males. This ultimately helps to prevent inbreeding.</p>
<p>Fish <a href="https://oliveiralab.files.wordpress.com/2017/05/madeira_olvieira_2017.pdf">retain this memory for 24 hours</a>, preferring to approach a new fish rather than the last one they spent time with. This shows that their social memories are strong, blowing the whole “three-second memory” rumour out of the water.</p>
<figure class="align-center ">
<img alt="Two Japanese Koi swim together in a pond." src="https://images.theconversation.com/files/392804/original/file-20210331-15-8uo2to.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/392804/original/file-20210331-15-8uo2to.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/392804/original/file-20210331-15-8uo2to.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/392804/original/file-20210331-15-8uo2to.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/392804/original/file-20210331-15-8uo2to.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/392804/original/file-20210331-15-8uo2to.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/392804/original/file-20210331-15-8uo2to.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Fish can recognise friends and family.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/japanese-koi-fish-swim-pond-isolate-1558675907">Bignai/Shutterstock</a></span>
</figcaption>
</figure>
<h2>4. Fish feel pain</h2>
<p>They really do. In 2003, biologists <a href="https://www.wellbeingintlstudiesrepository.org/cgi/viewcontent.cgi?article=1043&context=acwp_vsm">Victoria Braithwaite and Lynne Sneddon</a>, then at the University of Edinburgh and the Roslin institute, put acid in the lips of trout. The fish showed classic pain responses – moving away, rubbing their lips on the bottom of the tank, increasing their respiration – which disappeared completely once the fish were given a painkiller.</p>
<p>The question remains though, <em>how</em> do fish experience pain? What does pain <em>mean</em> to the animal? Pain is not just the perception of a physical event, such as stubbing your toe. It is <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3152687/">often an emotional experience</a> too. Some researchers think fish <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4356734/">don’t</a> experience pain in this way, essentially arguing that although they <em>feel</em> pain, they aren’t mentally capable of having an emotional response to that pain, and so their suffering should concern us less. This is because, they argue, fish lack parts of the brain that, in humans and other higher vertebrates, are associated with the mental experience of pain.</p>
<p>But this argument is no longer so convincing. Decades of work show that all manner of shapes, sizes and organisations of brain exist in nature, and that many complex behaviours arise in animals lacking the apparent brain structures that have been linked, in humans and other primates, to these higher processes. </p>
<p>In fact, it seems that brain structures themselves may be <a href="https://www.gatsby.ucl.ac.uk/workshop-2004/references/brownandbowman.pdf">less important than we thought</a>, so fish could have a more sophisticated experience of the world than we imagine, albeit using a brain that’s quite different to ours. </p>
<h2>5. Fish can be impatient</h2>
<p>In my lab, we’re interested in something called <a href="https://d1wqtxts1xzle7.cloudfront.net/49297826/Bari_2013_Inhibition_and_Impulsivity-_behavioral_and_neural_basis_of_response_control..pdf?1475439143=&response-content-disposition=inline%3B+filename%3DInhibition_and_impulsivity_Behavioral_an.pdf&Expires=1617039989&Signature=avou16IY%7ENO9rto8SpC1-dsl57Hj4sjpX4xkyGFC260vEykJedqzsMjhYDuK13iP07CjCfJ8TgXBhf44fslcGxeqB-1UqU0plQ3E%7EkjbHLf1hbXWrprKoRrfJ7Ealer4SmfFv%7E97I%7EKBOdLRcFgliZ4p1jzkts2htiAxt2umxVrd8Z5vIrJ4Xjnk0LUOxwzmBRSC5cDLNwKvdgD46%7EK%7ECuNOQjxoUeRlygp7r3bK9g00aIXwunQRAhSbFFu%7E3-snBrIh8zaIOZ2uOWlPq-uQ27mqqNtyp0vOlNAfhcL2dH3oWFKbKzonZrtsMYvVZiaWmQoLTDquY9E%7EfJ3HQHakNg__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA">impulse control</a>. This is someone’s ability to plan their behaviour and wait for the best time to perform it. Poor impulse control is a trait seen in people with a range of psychiatric conditions, including attention deficit hyperactivity disorder, addiction, or obsessive compulsive disorder.</p>
<p><a href="https://www.frontiersin.org/articles/10.3389/fnsys.2013.00065/full">We trained zebrafish</a> over several weeks in a series of trials using a purpose-built tank. In each trial, fish had to wait for a light to come on at the opposite end of the tank before they could swim into a chamber to get food. If they swam in early, they were disappointed with no food, and had to start all over again. We saw huge variation in their ability or desire to wait. Some fish were very impatient, while others didn’t mind waiting. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4167589/">We even found</a> that a drug used to treat ADHD also makes fish less impatient.</p>
<p>So, perhaps next time you see a fish you’ll think twice before dismissing it as a waterborne automaton, fit only for tartare sauce and mushy peas.</p><img src="https://counter.theconversation.com/content/157929/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matt Parker and/or members of his research group currently receive(s) research funding from European Regional Development Fund (INTERREG France-Channel-England), PTDF – Petroleum Technology Development Fund (Nigeria), Alzheimer’s Research UK, Foundation for Liver Research, CAPES foundation, Brazil, Economic and Social Research Council (UK).</span></em></p>You share the same drug habits, the same age-related memory problems and are similarly impatient when forced to wait for food.Matt Parker, Senior Lecturer in Neuroscience and Psychopharmacology, University of PortsmouthLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1519482020-12-15T14:21:16Z2020-12-15T14:21:16ZA tropical fish evolved to endure rising temperatures – but it may not be fast enough to survive climate change<figure><img src="https://images.theconversation.com/files/374934/original/file-20201214-21-6k6xmj.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2000%2C1125&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Zebrafish are small, freshwater fish native to South Asia.</span> <span class="attribution"><span class="source">Per Harald Olsen/NTNU</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The climate is changing, and heatwaves are becoming more common and intense as a result. For the Great Barrier Reef, the <a href="https://oceanservice.noaa.gov/facts/gbrlargeststructure.html#:%7E:text=The%20Great%20Barrier%20Reef%20is,reef%20system%20in%20the%20world.">world’s largest structure</a> of living tissue, the consequences are clear. The reef suffered its <a href="https://www.theguardian.com/environment/2020/mar/26/great-barrier-reefs-latest-bleaching-confirmed-by-marine-park-authority#:%7E:text=Guardian%20Australia%20revealed%20on%20Wednesday,nine%2Dday%20aerial%20survey%20trip.">third mass coral bleaching</a> event in five years in 2020, caused by prolonged periods with high water temperatures. Conservation scientists recently downgraded the ecosystem’s condition to “<a href="https://www.theguardian.com/environment/2020/dec/03/great-barrier-reef-outlook-critical-as-climate-change-called-number-one-threat-to-world-heritage">critical</a>”.</p>
<p>You might expect mobile animals like fish to fare better, but their body temperatures closely match that of the surrounding water. Fish can of course swim and escape high temperatures to an extent – and many species have <a href="https://www.nature.com/articles/nclimate1539">shifted their ranges poleward</a> or into deeper, cooler waters. But migration isn’t always possible. Freshwater fish, for instance, are restricted to their native rivers or lakes. Their ability to adapt to high temperatures may decide whether or not they endure.</p>
<p>Whether an organism does survive a heatwave may depend on its <a href="https://www.nature.com/articles/s41598-018-25593-4">upper thermal tolerance</a> – the temperature at which the organism can no longer function. Some fish populations are already living in water close to their temperature limits and so only have a small margin of additional warming they can safely tolerate. As heatwaves become more extreme and <a href="https://science.sciencemag.org/content/305/5686/994">maximum temperatures increase</a>, those species that cannot evolve fast enough to tolerate them may go extinct.</p>
<p>In <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.2011419117">a recent study</a>, colleagues at the Norwegian University of Science and Technology and I measured the evolution of thermal tolerance using a wild population of zebrafish. Working in a lab, we selectively bred fish which excelled at resisting high temperatures. Over six generations we selected more than 20,000 of these zebrafish in an experiment lasting three years.</p>
<h2>Climate change is outpacing evolution</h2>
<p>Zebrafish are the lab rats of the aquatic world, but <a href="https://www.liebertpub.com/doi/full/10.1089/zeb.2019.1778">in the wild</a>, they can be found in shallow ponds and streams in South Asia, at temperatures very <a href="https://academic.oup.com/conphys/article/7/1/coz036/5521853">close to their thermal limits</a>. Shallow water can heat up rapidly during heatwaves, so zebrafish are an ideal species to help us understand whether evolution will keep up with rising temperatures.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/375102/original/file-20201215-18-5w5bfn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Panorama of a shallow mountain stream in the Indian jungle." src="https://images.theconversation.com/files/375102/original/file-20201215-18-5w5bfn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/375102/original/file-20201215-18-5w5bfn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=255&fit=crop&dpr=1 600w, https://images.theconversation.com/files/375102/original/file-20201215-18-5w5bfn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=255&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/375102/original/file-20201215-18-5w5bfn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=255&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/375102/original/file-20201215-18-5w5bfn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=320&fit=crop&dpr=1 754w, https://images.theconversation.com/files/375102/original/file-20201215-18-5w5bfn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=320&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/375102/original/file-20201215-18-5w5bfn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=320&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Zebrafish live in shallow freshwater habitats which can overheat quickly.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/panorama-mountain-river-jungle-india-goa-511938031">Mr. Tempter/Shutterstock</a></span>
</figcaption>
</figure>
<p>After breeding zebrafish with the highest levels of thermal tolerance for six generations, we found that this upper limit increased by 0.04°C with each new generation. It’s encouraging that species can evolve this ability, but the rate of change is likely to be too slow for most fishes. And while evolution helped make this species more tolerant of higher temperatures over time, it hindered how well the fish could acclimate. </p>
<p>Acclimation is how animals exposed to environmental change adjust their physiology to cope better in the new conditions. In our experiment, one group of fish acclimated to raised temperatures over two weeks, allowing their thermal tolerance to increase. Acclimation occurs within individuals, while evolution occurs across generations. </p>
<p>But zebrafish cannot keep raising their thermal tolerance infinitely. We found that fish which had evolved to raise their upper thermal tolerance could only acclimate to a smaller amount of further warming. Eventually, their physiology will probably reach a temperature ceiling which they’re unable to overcome, either by evolving or acclimating, making death likely. Zebrafish in their native habitats in India will struggle to keep increasing their tolerance to match the <a href="https://link.springer.com/article/10.1007/s10113-014-0660-6?shared-article-renderer">projected rate of warming</a>.</p>
<p>It’s possible that other tropical species living close to their thermal limits will face a similar situation, and be especially vulnerable to climate change. Temperatures are already exceeding these limits for certain species. Mass deaths following heatwaves have been reported not only for <a href="https://www.pnas.org/content/117/41/25378">fish</a>, but also in warm-blooded animals such as tropical <a href="https://royalsocietypublishing.org/doi/10.1098/rsbl.2009.0702">birds</a> and <a href="https://royalsocietypublishing.org/doi/abs/10.1098/rspb.2007.1385">bats</a>.</p>
<p>Climate change is likely outpacing evolution for many tropical species. Unless we dramatically reduce greenhouse gas emissions, it’s possible that many populations will become extinct over the coming decades.</p><img src="https://counter.theconversation.com/content/151948/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>This work was funded by the Research Council of Norway and the Norwegian University of Science and Technology (NTNU).</span></em></p>Species can evolve to tolerate higher temperatures – but there’s a ceiling beyond which adaptation isn’t possible.Rachael Morgan, Postdoctoral Research Associate in Ecophysiology, University of GlasgowLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1468242020-11-10T13:22:30Z2020-11-10T13:22:30ZFlaws emerge in modeling human genetic diseases in animals<figure><img src="https://images.theconversation.com/files/367575/original/file-20201104-17-pvbobd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This confocal microscope image shows the face of a week-old zebrafish.</span> <span class="attribution"><a class="source" href="https://sites.usc.edu/crumplab/files/2020/10/endoderm_facial_view.jpg">Peter Fabian and Gage Crump</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p><a href="https://crumplab.usc.edu/">My lab</a>, based at the University of Southern California Keck School of Medicine, uses zebrafish to model human birth defects affecting the face. When I tell people this, they are often skeptical that fish biology has any relevance to human health. </p>
<p>But zebrafish have backbones like us, contain by and large the same types of organs, and, critically for genetic research, share many genes in common. <a href="https://crumplab.usc.edu/">My group</a> has exploited these genetic similarities to create zebrafish models for several human birth defects, including <a href="https://doi.org/10.7554/eLife.37024">Saethre-Chotzen Syndrome</a>, in which the bones of the skull abnormally fuse together, and <a href="https://doi.org/10.7554/eLife.16415">early-onset arthritis</a>.</p>
<p>Similar to fish, our bodies develop under the control of about 25,000 genes. The trick is finding out what each gene does. Stunning advances such as CRISPR-based molecular scissors, for which the Nobel Prize in chemistry was just awarded, allow us to precisely change genes, and designer chemicals can silence particular genes. In a recent <a href="https://doi.org/10.1038/s41586-020-2674-1">study from our group published in Nature</a>, however, we find that these tools are still far from perfect. Although CRISPR now allows us to efficiently generate lab animals that can pass human disease mutations onto the next generation, claims that simply injecting CRISPR into embryos or silencing genes with designer chemicals can accurately model human genetic disease are being questioned. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/367316/original/file-20201103-21-jx48ma.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/367316/original/file-20201103-21-jx48ma.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/367316/original/file-20201103-21-jx48ma.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=431&fit=crop&dpr=1 600w, https://images.theconversation.com/files/367316/original/file-20201103-21-jx48ma.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=431&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/367316/original/file-20201103-21-jx48ma.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=431&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/367316/original/file-20201103-21-jx48ma.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=542&fit=crop&dpr=1 754w, https://images.theconversation.com/files/367316/original/file-20201103-21-jx48ma.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=542&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/367316/original/file-20201103-21-jx48ma.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=542&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The humble zebrafish, <em>Danio rerio</em>, is used as a model organism to study human genetics.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/8659392@N07/13896905021/in/photolist-nb2gGH-G2ScJv-2jjF4ny-fKsrZj-Gh96nd-27zGH-bAQzDd-7hHx8W-4JwFeR-wjvq8x-28vbY3h-29SNmC8-29SNmEc-29SNmyk-2bgeoH6-63teZG-7A8YxQ-63oZAZ-7A8YHf-uZWQwM-jLsrGe-5JMzv7-5JMzrE-69ouFc-7A8YC9-HJ4qwU-M6kcwF-ManLk3-ManLr5-ManLqJ-MdvuxM-GiJrnF-vDZ63w-2ABVas-29SNmGM-cv2sYC-FZzffQ-RNFgU4-2joUawt-CUP2xW-cv2sSG-HZxm4U-2bbQFJS-GyaCKH-nZXkb6-Mdvqdp-2eoJxrZ-Sau7dT-Sau73x-s4ukxf">Tohru Murakami</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>Emergence of zebrafish as a model for human genetic disease</h2>
<p>Finding the precise mutation that causes a particular birth defect or a late-onset disease can be tedious work. The human genome is made up of 3 billion building blocks called DNA nucleotides, and changing just one of these can cause devastating birth defects. </p>
<p>To figure out if we have identified the right disease-causing mutation in humans, we typically engineer the same change into the genome of a lab animal. We then breed these animals to generate babies with the disease mutation and look for the appearance of defects similar to those in human patients. </p>
<p>We study zebrafish because they are small, which means we can grow thousands of different genetically modified animals. We routinely use CRISPR to engineer fish that pass on a gene-breaking mutation to the next generation.</p>
<p>We then study the appearance of defects similar to those in humans lacking these genes – in essence creating personalized zebrafish avatars of genetic disease. As zebrafish embryos are transparent and develop rapidly outside the mother, they are particularly useful for understanding how human disease mutations disrupt normal development. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/367311/original/file-20201103-19-1lf2dwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/367311/original/file-20201103-19-1lf2dwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/367311/original/file-20201103-19-1lf2dwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/367311/original/file-20201103-19-1lf2dwk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/367311/original/file-20201103-19-1lf2dwk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/367311/original/file-20201103-19-1lf2dwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/367311/original/file-20201103-19-1lf2dwk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/367311/original/file-20201103-19-1lf2dwk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">At the NHGRI Zebrafish Core, the largest zebrafish facility in the country, researcher Kevin Bishop holds up a tank of zebrafish to observe their behavior and physiology.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/genomegov/27386588184/in/photolist-HJ4qwU-M6kcwF-ManLk3-ManLr5-ManLqJ-MdvuxM-GiJrnF-vDZ63w-2ABVas-29SNmGM-cv2sYC-FZzffQ-RNFgU4-2joUawt-CUP2xW-cv2sSG-HZxm4U-2bbQFJS-GyaCKH-nZXkb6-Mdvqdp-2eoJxrZ-Sau7dT-Sau73x-s4ukxf-BDzA8L-wBu5Uz-2H2dKd-BDzxHq-2izBEnk-2joUoQs-CrwK1d-2iXYiw3-2iXWyFK-GTgkWF-9s8y9c-2jvFNid-BDGZ3t-rrTDWn-2joQbmP-cv2sU5-2joTaEq-dV3KHa-CB6kCz-f3rtso-29SNmPF-2jvELJc-2jvFU8E-2jvFU1R-2bgeoMz/">Ernesto del Aguila III, NHGRI</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>In the race for speed, problems emerge</h2>
<p>Even in zebrafish, engineering animals to lack particular genes can be a time-consuming process. In my lab, we first create gene mutations in embryos, grow these fish to adulthood and then breed fish together to look at defects in the next generation. </p>
<p>This whole process can take a year or longer. Unsurprisingly, many labs are attempting shortcuts. Some are injecting large quantities of CRISPR molecular scissors into animals and then looking for defects in these same animals. Others are using chemicals to turn off, or silence, genes in the embryo rather than permanently changing the genes. </p>
<p>More and more frequently <a href="https://doi.org/10.1016/j.devcel.2014.11.018">studies</a> like this are calling into question the accuracy of these shortcuts. In animals that have been injected with CRISPR molecular scissors, not every cell is changed in the same way. And the chemicals used to silence genes appear to have unintended consequences, poisoning the embryo in a generic way.</p>
<p>For example, <a href="https://doi.org/10.1038/nature23454">researchers in Spain</a> recently reported that a gene called prrx1a was critical for the proper development of the heart. To figure this out, they silenced prrx1a in zebrafish with chemicals. Then, in a second experiment, they injected CRISPR molecular scissors into zebrafish embryos and examined them just one day later for heart defects. </p>
<p>In contrast, <a href="https://doi.org/10.1038/s41586-020-2674-1">we completely removed the prrx1a gene</a> and looked at generations of fish lacking this gene. Hearts in these mutant fish developed perfectly normally, showing that prrx1a was not critical for heart development. Instead, we showed that the heart defects seen upon chemical treatment in the Spanish study were due to a general poisoning of the embryos unrelated to the prrx1a gene. Animals simply injected with CRISPR also showed defects not seen upon complete removal of the prrx1a gene, <a href="https://doi.org/10.1038/s41586-020-2675-0">although the exact reasons for these differences remain a source of active debate</a>.</p>
<p>And not just our group has noticed these flaws. Using similar gene removal as we reported, <a href="https://doi.org/10.1242/dev.193029">the group led by Didier Stainier</a> refuted a study that had used CRISPR injection and gene silencing to link the tek gene to blood vessel development. Given the number of studies relying on gene silencing in lab animals, as opposed to engineering the DNA mutations, the causative genes for many human diseases may need to be reevaluated. </p>
<h2>A path forward with improved genome engineering</h2>
<p>The desire for speed in research must not come at a cost of accuracy and reproducibility. </p>
<p>The good news is that, with the ease of CRISPR, we now know how to engineer the right types of mutations in lab animals to validate human disease mutations. By creating lab animals such as zebrafish that have the mutations engineered into their genomes and then observing whether their offspring develop the same diseases as patients with the mutations, we can be confident in having identified the right human disease gene. </p>
<p>[<em>Deep knowledge, daily.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>.]</p>
<p>Getting it right is important for accurately counseling prospective parents of their genetic risks for certain birth defects, as well as identifying the relevant genes that can be targeted to prevent or even reverse disease. </p>
<p>Science is constantly evolving. While the ability to engineer the genome with CRISPR is opening up endless possibilities for human genetics, researchers must also recognize the limitations of new technologies. Although rapid, directly injecting CRISPR or silencing genes with chemicals gives misleading results too often. In order to confidently identify causative mutations linked to human disease, we will need to continue to study lab animals engineered to carry and pass on the same DNA changes as found in human patients.</p><img src="https://counter.theconversation.com/content/146824/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gage Crump receives funding from the National Institute of Health and has previously received funding from the California Institute of Regenerative Medicine and March of Dimes. </span></em></p>Recent studies using CRISPR to fast-track genetic studies into human disease genes appear flawed.Gage Crump, Professor of Stem Cell Biology and Regenerative Medicine, University of Southern CaliforniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1414602020-07-28T09:22:56Z2020-07-28T09:22:56ZHow mutant zebrafish helped unlock the secret to their stripes – new research<figure><img src="https://images.theconversation.com/files/348379/original/file-20200720-64504-1tn17pj.jpg?ixlib=rb-1.1.0&rect=114%2C572%2C4048%2C2236&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/danio-rerio-236082157">Shutterstock/GrigorevMikhail</a></span></figcaption></figure><p>Zebrafish are one of the most well studied animals on the planet. But how they came by their beautiful black and gold stripes is more of a mystery. Our <a href="https://elifesciences.org/articles/52998">new research</a> used mathematical modelling – and detailed observations of mutant zebrafish patterns – to get to the bottom of one of nature’s oldest secrets. </p>
<p>Estimates suggest that zebrafish are used in over <a href="https://theconversation.com/animals-in-research-zebrafish-13804">600 labs around the world</a> to study diseases that range from <a href="https://academic.oup.com/hmg/article/12/suppl_2/R265/620445">muscular dystrophy</a> to <a href="https://core.ac.uk/download/pdf/2777109.pdf">cancer</a>. It may seem hard to imagine that a tiny tropical fish can tell us anything useful about distinctive human physiology but they are more similar to us than they appear at first glance. They have spines, hearts, livers, bones, eyes and kidneys.</p>
<p>Of equal importance is the opportunity that this hardy fish presents to investigate and understand the fundamental, and beautiful, biological processes that generate the spectacular pattern diversity seen in nature. These patterns are formed by the arrangement of pigments, usually packaged in specialised cells. </p>
<figure class="align-center ">
<img alt="Close up of zebrafish scales" src="https://images.theconversation.com/files/348122/original/file-20200717-21-khndmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/348122/original/file-20200717-21-khndmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/348122/original/file-20200717-21-khndmh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/348122/original/file-20200717-21-khndmh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/348122/original/file-20200717-21-khndmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=419&fit=crop&dpr=1 754w, https://images.theconversation.com/files/348122/original/file-20200717-21-khndmh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=419&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/348122/original/file-20200717-21-khndmh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=419&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Zoom into the zebrafish’s alternating pattern and the stripes of colour resolve into individual pigment cells.</span>
<span class="attribution"><span class="source">Wikimedia/JenniferOwen (adapted by Kit Yates)</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>From a distance zebrafish stripes look like long thin blocks of black or gold pigment. But on closer inspection it can be seen that these stripes are made up of thousands of small and distinct dots of colour. Each dot is a single pigment cell. The three cell types that produce the pattern are black melanophores, yellow xanthophores and silver and blue iridophores. Our research focused on understanding how enough of these cells interacting in the right way can result in the alternating striped patterns on a zebrafish.</p>
<figure class="align-center ">
<img alt="A mutant leopardfish" src="https://images.theconversation.com/files/347779/original/file-20200715-27-67r5db.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/347779/original/file-20200715-27-67r5db.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=474&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347779/original/file-20200715-27-67r5db.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=474&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347779/original/file-20200715-27-67r5db.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=474&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347779/original/file-20200715-27-67r5db.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=596&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347779/original/file-20200715-27-67r5db.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=596&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347779/original/file-20200715-27-67r5db.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=596&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The patterns of the leopard mutant are spots rather than stripes.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/carolineccb/4050116019/">Flickr/carolineCCB</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The mathematical theory that has predominated explanations of how zebrafish’s stripes emerged is <a href="https://theconversation.com/how-animals-got-their-spots-and-stripes-according-to-maths-85053">Turing patterning</a>. The mechanism is named after the visionary war hero, computer pioneer and mathematician <a href="https://theconversation.com/alan-turing-visionary-war-hero-and-the-only-choice-for-the-50-note-106470">Alan Turing</a> who first suggested it. In Turing patterns two different types of “agent” (melanophores and xanthophores in most zebrafish models) move around randomly and interact with each other in a special way, giving rise to a range of possible patterns. Although the patterns look convincing, scientists have not been able to prove this theory of <a href="https://www.crg.eu/en/news/new-theory-deepens-understanding-turing-patterns-biology">animal coat patterning</a>.</p>
<p>But <a href="https://elifesciences.org/articles/52998">our study</a> has demonstrated that the pattern formation mechanism is more complicated than a simple Turing model might suggest. As well as melanophores and xanthophores, we know iridophores also play an important role. These reflective cells give zebrafish their characteristic silvery appearance. Experiments have shown that without iridophores (or either of the other two cell types) the zebrafish’s characteristic striped pattern doesn’t form properly.</p>
<h2>Mutant zebrafish</h2>
<p>We wanted to find out which biological phenomena are crucial for pattern formation and which are just incidental. These sorts of questions can be answered with mathematical modelling.</p>
<p>We built an “agent-based” model (a computer code in which each cell is represented as an individual that can move and interact with others) which includes as much of the known biology of zebrafish patterning as possible. Once we had adapted the model to show it could reproduce the patterns seen in normal zebrafish we turned to the patterns formed by mutant zebrafish (fish with a genetic defect which changes their patterning) and tweaked the model rules to make sure it could replicate those too.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Yqcd-GEKm9k?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The model replicates the <em>pfeffer</em> zebrafish mutant’s broken black melanophore stripes on an iridescent iridophore background. <em>Pfeffer</em> mutants are deficient in yellow xanthophores.</span></figcaption>
</figure>
<p>Other mutant zebrafish, whose patterns were not used to build the model in the first place, acted as independent tests of the model’s pattern-replicating ability. Being able to mimic these other patterns gave us confidence in the model rules we had inferred. </p>
<p>As an example, the “choker” mutant has a defect which means silvery iridophores do not migrate to the skin in the normal manner. When we implemented this aberrant delivery of iridohphores in the model (but with essentially all the same rules) it neatly recreated the striking labyrinthine pattern seen in these fish.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/-_D4sO4mMbU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The model replicates the labyrinthine pattern exhibited by <em>choker mutants</em>. These mutant fish lack an initial horizontal stripe of iridophores in the middle of the embryo.</span></figcaption>
</figure>
<p>And then comes the really exciting part. The beauty of mathematical modelling is that once you’re confident your model captures the biology you can start to play around with it and ask biological questions that are difficult to answer through experiments alone.</p>
<p>For example, we were able to show that part of the reason zebrafish stripes are horizontal (as opposed to its mammalian namesake’s vertical stripes) is due to the way in which the body grows as the pattern forms. Faster growth along the head-tail axis (rather than the back-belly axis) of the fish tends to elongate groups of pigment cells into horizontal stripes rather than vertical bars.</p>
<p>Since pattern formation is an important general feature of organ development, there may be medical relevance to our research. A better understanding of pigment pattern formation might give us insights into the diseases caused by defects in cell arrangements.</p>
<p>With a working mathematical model there is no end to the questions we can ask about pigment pattern formation in zebrafish and other species. In particular, our next aim is to investigate the evolutionary origins of stripe formation in the broad family of Danio fish, of which the zebrafish (or Danio rerio) is a member. And that will help us gain an even deeper insight into how the zebrafish really got its stripes.</p><img src="https://counter.theconversation.com/content/141460/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christian Yates does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>We wanted to find out which biological phenomena are crucial for pattern formation and which are just incidental. These sorts of questions can be answered with mathematical modelling.Christian Yates, Senior Lecturer in Mathematical Biology, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1036112018-09-21T14:19:31Z2018-09-21T14:19:31ZWhat zebrafish reveal about importance of looks vs personality in choosing a mate<figure><img src="https://images.theconversation.com/files/237463/original/file-20180921-129856-w91i43.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">'D'you come here often?'</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/zebrafish-zebra-barb-danio-rerio-freshwater-252495334?src=USdpNLGlw6SrttsUzJmcIg-1-22">Mirko Rosenau</a></span></figcaption></figure><p>When it comes to finding a suitable partner to raise a family, we know that our looks and the way we behave are both crucial to how well we succeed. If there is such a thing as love at first sight, it probably involves a combination of the two. But the relative importance of these factors, and how they interact with one another, provokes endless debate in our society. </p>
<p>We can often learn by looking at other species, since it is well established that looks and personality are just as important in helping other animals to choose partners. There have been <a href="http://rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2016.2446">many studies</a> addressing ways in which various animals’ external appearance and colouration patterns <a href="http://www.liebertpub.com/doi/10.1089/zeb.2008.0551">affect</a> sexual selection – not to mention everything from dominance to individual health. </p>
<p>As for personality, many species besides humans show differences in behaviour that are consistent over time and across different situations. Animal personality studies have thrived during the past two decades: from <a href="https://www.ncbi.nlm.nih.gov/pubmed/21236920">initial studies</a> in the 1990s describing a shy-bold continuum that applied to humans and animals alike, to hundreds of <a href="https://www.researchgate.net/publication/292758818_Quick_guide_animal_personality">more recent studies</a> spanning behavioural ecology and neurobiology in many different animal species. This includes some evidence about personality and selection – animals <a href="https://doi.org/10.1111/j.1469-185X.2009.00101.x">tend to</a> choose mates with similar personalities to their own, for example – <a href="https://doi.org/10.1177/0956797616678187">as do humans</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/237464/original/file-20180921-129850-vor625.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/237464/original/file-20180921-129850-vor625.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/237464/original/file-20180921-129850-vor625.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/237464/original/file-20180921-129850-vor625.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/237464/original/file-20180921-129850-vor625.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/237464/original/file-20180921-129850-vor625.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/237464/original/file-20180921-129850-vor625.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/237464/original/file-20180921-129850-vor625.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Typical Pisces.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/chimp-chimpanzee-monkey-ape-sad-pan-553094830?src=hSoHNH_RRKolfG3CKR2zKQ-1-82">Lorna Roberts</a></span>
</figcaption>
</figure>
<p>But how do these choices affect the evolutionary prospects of a species over time? We certainly know that there are <a href="http://rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2016.2446">correlations</a> between “better” colouration patterns and an animal’s health. We also know that certain behaviour traits affect the fitness of a species – more aggressive animals <a href="https://academic.oup.com/beheco/article-lookup/doi/10.1093/beheco/arm144">are more</a> successful at reproduction, for instance. </p>
<p>Curiously, however, researchers have traditionally kept their studies into animal behaviour and external appearance separate from one another. So in <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0203320">our new study</a> we posed the question, what happens when both traits are studied together? Do they interact, and if so, which has more impact on the fitness of the offspring?</p>
<h2>Fishing for answers</h2>
<p>We approached this question using the zebrafish, a small beautifully coloured fish which lives in the tropical streams of the Indian subcontinent. Zebrafish have blue and golden lateral stripes running across their bodies, which bear a resemblance to the vertical stripes on African zebras.</p>
<p>We selected individual fish, screening them for colour phenotypes and at the same time for personality using an established <a href="http://doi.wiley.com/10.1111/mec.12556">risk-taking test</a>. Unlike humans and primates, researchers view fish personalities simply in terms of how “proactive” or “reactive” they are. Proactive animals tend to be bolder and more aggressive, whereas reactive animals are more shy and submissive, among other traits. We therefore split the fish into four different combinations: proactive fish with clear defined colouration; proactive fish with undefined and dulled colouration; reactive fish with clear defined colouration; and reactive fish with undefined and dulled colouration. </p>
<p>To understand the interactions between colouration and personality, we used these four groups to breed specific fish. From the successful crossings we looked at various reproductive parameters, including the number of eggs, survival of the eggs and embryos, and the growth and survival of the larvae up to juvenile stages. For all these parameters, the proactive fish performed best, regardless of their external colouration. Yet the best performers of all were always the proactive fish with defined colouration patterns – both males and females were in this category</p>
<p>This begged the question, why are the proactive fish more fertile? We came up with one possible reason by monitoring the behaviour of males during mating. This showed that the bolder males were more aggressive and protective of the females. As for why the bolder more colour-defined fish were most fertile of all, this might be explained by the <a href="http://www.liebertpub.com/doi/10.1089/zeb.2008.0551">correlations</a> between “better” appearance and healthier animals. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/237465/original/file-20180921-129874-1wrkvid.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/237465/original/file-20180921-129874-1wrkvid.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/237465/original/file-20180921-129874-1wrkvid.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/237465/original/file-20180921-129874-1wrkvid.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/237465/original/file-20180921-129874-1wrkvid.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/237465/original/file-20180921-129874-1wrkvid.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/237465/original/file-20180921-129874-1wrkvid.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/237465/original/file-20180921-129874-1wrkvid.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Nightclubbing.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/chimp-chimpanzee-monkey-ape-sad-pan-553094830?src=hSoHNH_RRKolfG3CKR2zKQ-1-82">Kazakov Maksim</a></span>
</figcaption>
</figure>
<p>Our conclusion was that an animal’s personality surpasses the effect of external appearance in the reproductive success – and therefore the fitness – of a species. We have to add the caveat that outcomes may be affected in the natural world by predator pressure – there is some <a href="https://doi.org/10.1093/beheco/3.2.124,%20http://dx.plos.org/10.1371/journal.pone.0028084">evidence</a> they do less well against predators <a href="http://dx.plos.org/10.1371/journal.pone.0028084">because</a> they tend to take more risks. Having said that, other studies with guppies have <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC38372/pdf/pnas01523-0280.pdf">showed that</a> bolder, more conspicuous fish, tend to be more successful in the competition to find a mate. </p>
<p>At any rate, the study has given us an important insight into the underlying evolutionary drivers for the success of a particular species. In addition, it raises the possibility of using this approach to enable fish farmers to select specific fish that will be more successful at reproducing. </p>
<p>As for what it tells us about humans and the relative importance of looks and personality to the fitness of our offspring, researchers would have to perform more studies to investigate the link between both parents’ personality traits, external characteristics and fitness. For the moment human studies investigating this interactions are very rare.</p><img src="https://counter.theconversation.com/content/103611/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Are pretty blue and gold stripes more important than being a bold little swimmer?Sonia Rey Planellas, Senior research fellow, University of StirlingSimon MacKenzie, Professor of Aquaculture, University of StirlingLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1020702018-09-17T10:50:55Z2018-09-17T10:50:55ZHow the zebrafish got its stripes<figure><img src="https://images.theconversation.com/files/234456/original/file-20180831-195298-yicqm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Zebrafish are known for their black and gold stripes.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/nichd/20092260041">NICHD/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Stripes are common in our lives. It’s a pretty basic pattern, and easy to take for granted. </p>
<p>As an applied mathematician who studies how patterns form in nature, though, I am wowed by the <a href="https://doi.org/10.1016/bs.ctdb.2015.12.012">striped patterns the zebrafish wears</a> across its body and fins. </p>
<p>Take a closer look at zebrafish’s black and gold stripes, and you’ll see <a href="https://doi.org/10.1111/pcmr.12328">different-colored pigment cells</a>, tens of thousands of them. I like to envision these cells as people walking around in a crowded room: Just like us, the cells <a href="https://doi.org/10.1111/j.1755-148X.2008.00504.x">move</a> and <a href="https://doi.org/10.1073/pnas.0808622106">interact</a> with their neighbors. Stripes appear because the cells very carefully <a href="https://doi.org/10.1016/j.cub.2014.11.013">instruct and signal each other on how to behave</a>. They even “shake hands” in some sense <a href="https://doi.org/10.1242/dev.099804">by reaching</a> toward distant cells.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/235432/original/file-20180907-90571-4u471q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/235432/original/file-20180907-90571-4u471q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/235432/original/file-20180907-90571-4u471q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=249&fit=crop&dpr=1 600w, https://images.theconversation.com/files/235432/original/file-20180907-90571-4u471q.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=249&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/235432/original/file-20180907-90571-4u471q.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=249&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/235432/original/file-20180907-90571-4u471q.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=313&fit=crop&dpr=1 754w, https://images.theconversation.com/files/235432/original/file-20180907-90571-4u471q.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=313&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/235432/original/file-20180907-90571-4u471q.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=313&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Look closer at zebrafish’s striped bodysuit and you’ll find the tiny pigment cells that make up its patterns.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Zebrafish_(26436913602).jpg">Images adapted by Alexandria Volkening from Oregon State University/Wikimedia and from Development 2013 (doi:10.1242/dev.096719)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>From a mathematical perspective, zebrafish stripes fall into the field of self-organization, a phenomenon in which individuals interact to produce some pattern much bigger than any individual, without external direction. <a href="https://doi.org/10.1098/rsfs.2012.0025">Bird flocks and schooling fish</a> are also examples of self-organization in nature. No one is on a megaphone calling out directions so that birds flock or pigment cells produce fish stripes, yet remarkably, they both <a href="https://en.wikipedia.org/wiki/Self-organization">organize themselves</a> to create patterns.</p>
<p>Until recently, the research community thought only <a href="https://doi.org/10.1073/pnas.0607790104">two types of cells</a> were involved in zebrafish stripes: black and gold stripes, so black and gold cells. However, <a href="http://eb.mpg.de/emeriti/research-group-colour-pattern-formation/">experiments showed</a> that a third type of pigment cell – <a href="https://doi.org/10.1038/ncb2955">blue and silver iridophores</a> – is <a href="https://doi.org/10.1371/journal.pgen.1003561">critical to pattern formation</a>. Remove it from the skin, and zebrafish have <a href="https://doi.org/10.1242/dev.096719">spots</a>! </p>
<p>So how do thousands of different-colored cells on a growing zebrafish work together to consistently form stripes? To help answer this question, I developed a <a href="https://doi.org/10.1038/s41467-018-05629-z">mathematical model</a> in collaboration with applied mathematics professor <a href="http://www.dam.brown.edu/people/sandsted/">Bjorn Sandstede</a>. In our model, pigment cells are colored dots following prescribed rules and equations for how they move around, <a href="https://doi.org/10.1073/pnas.0808622106">interact</a> and change their color. Cells with different colors behave in different ways. There are lots of <a href="https://doi.org/10.1016/j.tig.2014.11.005">questions about zebrafish</a>, so we decided to focus on the newcomers to the scene: those pesky blue and silver cells.</p>
<p>Math offers a different perspective from typical biological experiments on fish. Biologists can watch how cells behave, but it’s trickier to deduce the signals behind their behavior. Using mathematical models, we can test lots of different possible cell interactions and suggest which ones are actually able to explain the behaviors biologists observe. Biologists can then test our predictions on real fish.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/235305/original/file-20180906-190659-1g1euj.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/235305/original/file-20180906-190659-1g1euj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/235305/original/file-20180906-190659-1g1euj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=215&fit=crop&dpr=1 600w, https://images.theconversation.com/files/235305/original/file-20180906-190659-1g1euj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=215&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/235305/original/file-20180906-190659-1g1euj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=215&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/235305/original/file-20180906-190659-1g1euj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=270&fit=crop&dpr=1 754w, https://images.theconversation.com/files/235305/original/file-20180906-190659-1g1euj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=270&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/235305/original/file-20180906-190659-1g1euj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=270&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">It takes more than black and gold cells to create black and gold stripes. When a mutation causes zebrafish to lose their blue and silver pigment cells, spots form across the body.</span>
<span class="attribution"><a class="source" href="http://doi.org/10.1242/dev.096719">Development (2013)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Our model suggests there are multiple signals at work that instruct silver and blue cells on the fish skin. All these signals are redundant. A few cues are all the instruction a cell may need in a perfect world, but the world isn’t perfect. For example, we think that nearby black cells signal iridophores to change their density and color. But if there are not any black cells around to transmit that signal, distant gold cells can fill in and provide the same instructions.</p>
<p>You can think of these redundant signals like a bunch of different alarm clocks. If you have an important meeting in the morning, you may set an alarm clock, put a notification on your phone and ask for a wake-up call. All that redundancy means that you will probably get a bunch of cues to wake up. But on the off chance that your phone dies or the front desk forgets to call, it also means you’ll still get to your meeting on time. The redundancy ensures the desired result, even if one signal fails.</p>
<p>The same idea may be at work in zebrafish. <a href="https://doi.org/10.1038/s41467-018-05629-z">Our model</a> suggests that different-colored cells are constantly instructing each other. This ensures that blue and silver iridophores are pummeled with directions from all sides on how to behave. Because there are multiple signals, occasional failures don’t disrupt patterns too much. The result: reliable stripes.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/TpKmqUkdVYI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Our mathematical model simulates how different-colored cells interact to produce zebrafish stripes.</span></figcaption>
</figure>
<p>Why is this important? Zebrafish genes are surprisingly <a href="https://doi.org/10.1038/nature12111">similar to human genes</a>. By understanding how pigment cells interact in normal and mutated zebrafish, researchers may be able to start to link genes to their function.</p>
<p>The story of how zebrafish patterns form isn’t finished yet. For now, though, the next time you see a striped fish, consider pausing a moment to recognize all the work pigment cells put into creating that pattern. Those dependable stripes are pretty darn amazing.</p><img src="https://counter.theconversation.com/content/102070/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alexandria Volkening was funded by the Mathematical Biosciences Institute and the National Science Foundation for this study under grants DMS-1148284, DGE-0228243, and DMS-1440386.</span></em></p>Zebrafish are known for their black and gold stripes, but researchers are still figuring out how pigment cells interact to form these patterns.Alexandria Volkening, Postdoctoral Fellow in Applied Mathematics, The Ohio State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/850532017-10-04T11:42:02Z2017-10-04T11:42:02ZHow animals got their spots and stripes – according to maths<figure><img src="https://images.theconversation.com/files/188730/original/file-20171004-6697-ze4s92.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/macro-shot-zebra-danio-tropical-fish-680522524?src=I3gqRJ4T4k5pIb2RBhE8TQ-2-47">Ian Grainger/Shutterstock</a></span></figcaption></figure><p>The natural world presents a palette of beautiful complexity. From the peacock tail and the <a href="https://www.livescience.com/2820-butterflies-eye-spots.html">eyespots of a butterfly</a>, to the evolving camouflage of the chameleon, nature loves patterns.</p>
<p>Biologists may be able to tell you why an animal has a certain pattern. For example, it may have evolved its skin pattern for <a href="https://static.pexels.com/photos/33118/peacock-animal-iridescent.jpg">mating purposes</a>, as a <a href="https://upload.wikimedia.org/wikipedia/commons/c/cb/Micrurus_tener.jpg">warning sign</a>, or for <a href="https://en.wikipedia.org/wiki/Deception_in_animals#/media/File:Peacock_Flounder_Bothus_mancus_in_Kona.jpg">defence purposes</a>. However, we are still in the dark when it comes to how the patterns are produced.</p>
<p>Although we currently lack the experimental insight, mathematicians have been playing around with pattern formation equations since 1952, when <a href="https://theconversation.com/alan-turings-legacy-is-even-bigger-than-we-realise-34735">the great Alan Turing</a> published the seminal paper, <a href="http://cba.mit.edu/events/03.11.ASE/docs/Turing.pdf">The Chemical Basis of Morphogenesis</a>. In this paper, he presented a theory that said patterns could spontaneously appear using nothing more than a protein’s natural tendency to move randomly through tissue and interact with other cells and proteins.</p>
<p>The theory is incredibly counter-intuitive, and we can only wonder how Turing discovered it. Patterns, as Turing saw them, depend on two components: interacting agents and agent diffusion. Each component on its own does not create a pattern. In fact, diffusion is a well-known pattern destroyer: if you put milk in water (and don’t stir), the milk will diffuse – or spread – out across the cup. You don’t end up with spots, or stripes of milk. You just have a cup of uniform milky water. </p>
<p>Turing’s genius saw through this and he demonstrated that if you combine these two components in just the right way, diffusion could actually drive the system to form spots and stripes. This idea was so far ahead of its time that we are still working on unravelling its complexity 65 years later.</p>
<h2>Light and dark</h2>
<p>Unfortunately, biology refuses to be so simple. Diffusion assumes that the agents which create a pattern – for example, chemicals, proteins or cells – are dumb, in that they move around space randomly. However, in 2014, the experimental lab of Shigeru Kondo demonstrated that cells in particular are <a href="http://www.sciencemag.org/news/2014/01/video-zebrafish-stripes-caused-cells-chase-each-other">more cunning than we thought</a>.</p>
<p>Kondo’s lab works on understanding the black and white stripes presented on zebrafish, a tropical freshwater fish, which is native to the Himalayan region. They discovered that zebrafish skin patterns are made up of a light type of cell (xanthophore) and a dark type of cell (melanophore) that interact with each other. Specifically, the light cells spread out tendrils to investigate their environment. </p>
<p>Unexpectedly, Kondo’s team found that when the light cell touches a dark cell a chasing mechanism is instigated. The light cell slowly moves towards the dark cell while the dark cell quickly “runs away”. Complicating matters further is the fact that the chasing doesn’t occur along a straight line. The cells move at an angle to one another, resulting in a spiralling chase.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/0wECUnwgN8A?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>My work extended Turing’s theory to accommodate this new knowledge of “chasing” cells. First, I modelled the system as a set of discrete, individual cells. This mathematical model is highly accurate, but difficult to work with. I then simplified the model by assuming that there are a large number of cells. </p>
<p>Having more cells may seem to complicate the system, but by increasing the number of cells you can stop worrying about each individual component and simply consider the properties of the whole population. To put this in real world terms, it means that when you consider the Great Wall of China, you do not have to worry about a single brick, but rather see it as the whole structure.</p>
<p>Although I lost accuracy on individual cell locations, the simplification allowed me to use a whole toolbox of other techniques that mathematicians have been constructing over the past 60 years. So I am able to exactly specify the conditions under which cellular populations will produce patterns and conditions under which patterns will not exist.</p>
<p>Incredibly, with the additional complexity of chasing cells we were able to greatly expand the catalogue of available patterns. No longer does a system have to evolve to a stationary pattern of spots or stripes. These chasing cells can produce patterns of rotating hexagons, spots that shuttle past each other and, perhaps most complex of all, constantly evolving stripes that oscillate to and fro.</p>
<p>All of this complexity is wrapped up in the description of how the cells chase one another: if you change the description, you change the pattern. Critically, this confirms one of Kondo’s experimental hypotheses, as not only did he experiment on normal, or wild-type, zebrafish he also experimented on mutant fish that presented broken stripes, spots, or no pattern at all. </p>
<p>Specifically, he discovered that the mutant fish which presented different patterns also presented a different chasing strategy between the dark and light cells. He concluded that the tissue-scale pattern of the skin, could be dictated by the micro-scale pattern of the cells. Incredibly, the mathematics appears to confirm this idea, although more work needs to be done to ensure a complete comparison between theory and experiment.</p>
<p>There is little doubt in my mind that the cellular interactions will still be more complicated than we currently know. Indeed, it maybe another 65 years before we are able to truly pin down the causes of zebrafish pattern formation. In the meantime, you can be sure that mathematics will be providing biologists with a new microscope with which to examine biological problems beyond their current experimental expertise.</p><img src="https://counter.theconversation.com/content/85053/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Woolley would like to thank Cardiff University, St John's College, Oxford and the Mathematical Biosciences Institute (MBI) at Ohio State University, for financially supporting this research through the National Science Foundation grant DMS 1440386. Thomas would also like to recognise the support of BBSRC grant BKNXBKOO BK00.16.</span></em></p>A mathematician has joined the dots between Alan Turing and chasing cells to find out how skin patterns are formed.Thomas Woolley, Lecturer in Applied Mathematics, Cardiff UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/138042013-05-09T03:03:29Z2013-05-09T03:03:29ZAnimals in research: zebrafish<figure><img src="https://images.theconversation.com/files/23016/original/ph2954mg-1367275261.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Zebrafish at the Walter and Eliza Hall Institute.</span> <span class="attribution"><span class="source">Joan Heath</span></span></figcaption></figure><p><strong>Our series, Animals in Research, profiles the top organisms used for science experimentation. Here, we look at <em>Danio rerio</em> - the zebrafish.</strong></p>
<p>Zebrafish are probably not the first creatures that come to mind when it comes to animals that are valuable for medical research.</p>
<p>You might struggle to imagine you have much in common with this small tropical freshwater fish, though you may be inclined to keep a few “zebra danios” in your home aquarium, given they are hardy, undemanding animals that cost only a few dollars each.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/23401/original/94ffft5g-1368067846.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/23401/original/94ffft5g-1368067846.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/23401/original/94ffft5g-1368067846.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=440&fit=crop&dpr=1 600w, https://images.theconversation.com/files/23401/original/94ffft5g-1368067846.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=440&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/23401/original/94ffft5g-1368067846.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=440&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/23401/original/94ffft5g-1368067846.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=553&fit=crop&dpr=1 754w, https://images.theconversation.com/files/23401/original/94ffft5g-1368067846.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=553&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/23401/original/94ffft5g-1368067846.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=553&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Zebrafish embryo.</span>
<span class="attribution"><span class="source">Wellcome images</span></span>
</figcaption>
</figure>
<p>Yet each year more and more scientists are turning to zebrafish to unravel the mechanisms underlying their favourite genetic or infectious disease, be it muscular dystrophy, schizophrenia, tuberculosis or cancer.</p>
<p>My (conservative) estimate is that zebrafish research is now carried out in at least 600 labs worldwide, including 20 in Australia.</p>
<p>So what is it about zebrafish that has taken them from the freshwater rivers and streams of Southeast Asia, beyond the pet shops and into universities and research institutes the world over?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/23124/original/j2d37jyj-1367449393.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/23124/original/j2d37jyj-1367449393.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/23124/original/j2d37jyj-1367449393.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=186&fit=crop&dpr=1 600w, https://images.theconversation.com/files/23124/original/j2d37jyj-1367449393.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=186&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/23124/original/j2d37jyj-1367449393.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=186&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/23124/original/j2d37jyj-1367449393.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=234&fit=crop&dpr=1 754w, https://images.theconversation.com/files/23124/original/j2d37jyj-1367449393.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=234&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/23124/original/j2d37jyj-1367449393.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=234&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">4.5-day-old zebrafish larva.</span>
<span class="attribution"><span class="source">Adam Parslow, Heath Lab</span></span>
</figcaption>
</figure>
<h2>A short history of zebrafish</h2>
<p>A scientist called <a href="http://www.neuro.uoregon.edu/k12/george_streisinger.html">George Streisinger</a>, working at the University of Oregon in Eugene, USA in the 1970s and 80s, recognised the vast potential of this organism for developmental biology and genetics research.</p>
<p>In contrast to <a href="https://theconversation.com/animals-in-research-drosophila-the-fruit-fly-13571">fruit flies</a> and worms, the other simple model organisms established at the time, zebrafish are vertebrates.</p>
<p>They have a backbone, brain and spinal cord as well as several other organs, including a heart, liver and pancreas, kidneys, bones and cartilage, which makes them much more similar to humans than you may have otherwise thought.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/9KG2rrE6ykU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">In just 24 hours, the zebrafish heart is beating and blood is circulating around the body.</span></figcaption>
</figure>
<p>But as a vertebrate model, could they be as useful as mice?</p>
<p>Several things captured Streisinger’s imagination.</p>
<p>Most famously, zebrafish embryos, unlike mouse embryos, develop outside the mother’s body and are transparent throughout the first few days of life. </p>
<p>This provides unparallelled opportunities for researchers to scrutinise the fine details of embryonic vertebrate development without first having to resort to invasive procedures or killing the mother.</p>
<p>But this advantage is enhanced by the fact zebrafish reproduce profusely (each pair can produce <a href="http://toxsci.oxfordjournals.org/content/86/1/6.full">200-300 fertilised eggs</a> every week); an ideal attribute for genetic studies. Again, the large, external embryos are a critical part of this success.</p>
<p>When just one or two cells old, zebrafish embryos can be easily microinjected with mRNA or DNA corresponding to genes of interest; undeterred, they then they go on to grow and reproduce, handing down the injected gene to the next generation.</p>
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<a href="https://images.theconversation.com/files/23056/original/6wkss98j-1367303730.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/23056/original/6wkss98j-1367303730.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/23056/original/6wkss98j-1367303730.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/23056/original/6wkss98j-1367303730.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/23056/original/6wkss98j-1367303730.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/23056/original/6wkss98j-1367303730.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/23056/original/6wkss98j-1367303730.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/23056/original/6wkss98j-1367303730.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A one-cell zebrafish embryo being micro-injected into the yolk with RNA (mixed with a red dye).</span>
<span class="attribution"><span class="source">David Mawdsley, Heath Lab</span></span>
</figcaption>
</figure>
<h2>From zebrafish to humans</h2>
<p>A paper published last month in <a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12111.html">Nature</a> unveiled the long-awaited sequence of the zebrafish genome, revealing that zebrafish, mice and human have 12,719 genes in common.</p>
<p>Put another way, 70% of human genes are found in zebrafish.</p>
<p>But even more notable is the finding that 84% of human disease-causing genes are found in zebrafish.</p>
<p>Perhaps not surprisingly then, when these genes are injected into zebrafish embryos, the growing animals are doomed to acquire the same diseases.</p>
<p>And while zebrafish are still used widely to answer fundamental questions of developmental biology, much current research is directed towards combining their many attributes in studies that are designed to improve human health.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/23009/original/5yhnx7pq-1367218925.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/23009/original/5yhnx7pq-1367218925.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/23009/original/5yhnx7pq-1367218925.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=439&fit=crop&dpr=1 600w, https://images.theconversation.com/files/23009/original/5yhnx7pq-1367218925.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=439&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/23009/original/5yhnx7pq-1367218925.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=439&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/23009/original/5yhnx7pq-1367218925.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=552&fit=crop&dpr=1 754w, https://images.theconversation.com/files/23009/original/5yhnx7pq-1367218925.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=552&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/23009/original/5yhnx7pq-1367218925.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=552&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Confocal micrograph showing the connections of the visual system in a four-day-old zebrafish embryo.</span>
<span class="attribution"><span class="source">wellcome images</span></span>
</figcaption>
</figure>
<p>This is especially true for cancer research where the expression of cancer-causing genes (<a href="http://www.ndsu.edu/pubweb/%7Emcclean/plsc431/cellcycle/cellcycl5.htm">oncogenes</a>) can be directed to specific organs, virtually at will.</p>
<p>This process, known as <a href="http://www.ncbi.nlm.nih.gov/pubmed/17937395">transgenesis</a>, is very straightforward in zebrafish and has allowed researchers to produce zebrafish models of liver, pancreatic, skeletal muscle, blood and skin cancers, <a href="http://www.annualreviews.org/doi/abs/10.1146/annurev-pathol-011110-130330?journalCode=pathmechdis">to name but a few</a>.</p>
<p>And when the genomic make-up of these zebrafish tumours is deciphered using the latest DNA sequencing technology, the patterns of mutations, or “gene signatures”, are found to overlap substantially with those in the corresponding human tumours.</p>
<h2>Trialling cancer drugs</h2>
<p>These parallels have encouraged researchers to exploit zebrafish in drug development - in particular for high throughput approaches such as chemical/small molecule screens.</p>
<p>Here, the ability to generate tens of thousands of zebrafish embryos harbouring the same disease-causing mutations is crucial.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/moL5C8SjeJU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Zebrafish development flipbook. Source: RO Karlstrom and DA Kane</span></figcaption>
</figure>
<p>Then, as the tumours grow in the synchronously developing larvae, the fish are transferred to small volumes of water containing chemicals that may stop the growth, or better still, kill the cancer cells. </p>
<p>Large collections of drugs can be screened relatively quickly for anti-cancer efficacy in this way.</p>
<p>One drug, <a href="http://www.ncbi.nlm.nih.gov/pubmed/21430780">Leflunomide</a>, identified in such a screen is now in early phase clinical trials to kill melanoma cells.</p>
<p>The only other drug from a zebrafish chemical screen currently in clinical trials is dimethyl-prostaglandin E2 (<a href="http://www.ncbi.nlm.nih.gov/pubmed/21474107">dmPGE2</a>).</p>
<p>There, the intent is not to kill cancer cells but rather to make mainstream leukaemia treatment more effective.</p>
<p>Studies of dmPGE2 <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2775137/">increased the number</a> of blood stem cells in zebrafish embryos and it is being trialled now as a way to expand the number of stem cells in human cord blood samples.</p>
<p>Human <a href="http://en.wikipedia.org/wiki/Cord_blood?bloodsPage=15">cord blood samples</a> are a valuable commodity to restore bone marrow in leukaemia patients after high dose chemotherapy when a matched bone marrow transplant is unavailable.</p>
<p>But the success of this approach is currently limited by the scant number of stem cells in individual cord blood samples, requiring the use of two precious samples for each patient.</p>
<h2>Tumour growth</h2>
<p>As well as the transgenic zebrafish models of cancer described above, researchers are also <a href="http://www.ncbi.nlm.nih.gov/pubmed/21951540">transplanting cells</a> derived from human tumours into zebrafish embryos and watching them grow and spread.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/23130/original/9k42v79w-1367455929.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/23130/original/9k42v79w-1367455929.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/23130/original/9k42v79w-1367455929.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/23130/original/9k42v79w-1367455929.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/23130/original/9k42v79w-1367455929.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/23130/original/9k42v79w-1367455929.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/23130/original/9k42v79w-1367455929.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/23130/original/9k42v79w-1367455929.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A casper zebrafish.</span>
<span class="attribution"><span class="source">Carolina Biological Supply Company</span></span>
</figcaption>
</figure>
<p>The creation of a <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2292119/">transparent</a> (non-striped) version of adult zebrafish (called casper, after the <a href="http://casper.wikia.com/wiki/Casper_the_Friendly_Ghost">cartoon ghost</a>) means the behaviour of tumour cells inside these living organisms can be followed for days at a time.</p>
<p>Coupled with the advent of high resolution live-imaging techniques, the birth, growth and spread of tumours can be scrutinised in movies that can be played over and over again.</p>
<p>These experiments are usually conducted in zebrafish that have been genetically modified to express genes that glow in specific body compartments, giving researchers the ability to pinpoint potentially critical connections between “host” cells and tumour cells that may determine whether the latter survive or die.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/23123/original/qzrywjcq-1367449385.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/23123/original/qzrywjcq-1367449385.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/23123/original/qzrywjcq-1367449385.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=195&fit=crop&dpr=1 600w, https://images.theconversation.com/files/23123/original/qzrywjcq-1367449385.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=195&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/23123/original/qzrywjcq-1367449385.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=195&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/23123/original/qzrywjcq-1367449385.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=245&fit=crop&dpr=1 754w, https://images.theconversation.com/files/23123/original/qzrywjcq-1367449385.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=245&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/23123/original/qzrywjcq-1367449385.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=245&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Green fluorescent protein expressed in the liver and intestine of a 5-day-old zebrafish.</span>
<span class="attribution"><span class="source">Joan Heath</span></span>
</figcaption>
</figure>
<p>This type of experiment is revealing a complex interplay of potentially beneficial and detrimental components.</p>
<p>While the proximity of immune cells may instigate mechanisms capable of destroying the tumour, the stimulation of new blood and lymphatic vessel growth towards the tumour is more insidious, since it delivers the tumour with both the nutrients it needs to survive and a network to spread throughout the body.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/23122/original/x9m23sn9-1367449245.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/23122/original/x9m23sn9-1367449245.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/23122/original/x9m23sn9-1367449245.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=130&fit=crop&dpr=1 600w, https://images.theconversation.com/files/23122/original/x9m23sn9-1367449245.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=130&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/23122/original/x9m23sn9-1367449245.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=130&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/23122/original/x9m23sn9-1367449245.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=163&fit=crop&dpr=1 754w, https://images.theconversation.com/files/23122/original/x9m23sn9-1367449245.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=163&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/23122/original/x9m23sn9-1367449245.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=163&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Blood vessels and lymphatic system in a 9-day-old zebrafish larva.</span>
<span class="attribution"><span class="source">Ben Hogan/Ludo Le Guen, Institute for Molecular Bioscience, University of Queensland</span></span>
</figcaption>
</figure>
<p>These processes, once properly understood, are likely to provide opportunities for therapeutic intervention in the future.</p>
<h2>The future of zebrafish</h2>
<p>Cancer research is just one part of the zebrafish story. In Australia alone, investigators are also using zebrafish to study metabolic disorders such as: </p>
<ul>
<li><a href="http://www.ncbi.nlm.nih.gov/pubmed/23485929">diabetes</a> </li>
<li>muscle diseases, including <a href="http://hmg.oxfordjournals.org/content/12/suppl_2/R265.full">muscular dystrophy</a></li>
<li><a href="https://theconversation.com/drafts/13571/edit">neurodegenerative disease</a></li>
<li>the response of the host innate immune system to <a href="http://www.sciencedirect.com/science/article/pii/S1532045604001413">bacterial</a> and <a href="http://iai.asm.org/content/78/6/2512.short">fungal</a> infections</li>
</ul>
<p>Excitingly, research is also <a href="http://www.armi.org.au/Facilities/FishCore.aspx">underway</a> in this country to unravel the genetic mechanisms controlling heart, skeletal muscle and nervous tissue regeneration in zebrafish, in the hope that these processes can be one day recapitulated in humans to address the burgeoning socioeconomic problem of tissue degeneration in our ageing population.</p>
<p>So next time you peer into someone’s home aquarium, imagine the biomedical possibilities inherent in this lively and amiable little fish!</p>
<p><strong>To read more in the Animals in Research series, follow the links below:</strong></p>
<p><strong><a href="https://theconversation.com/animals-in-research-drosophila-the-fruit-fly-13571"><em>Drosophila melanogaster</em> (the fruit fly)</a></strong><br>
<strong><a href="https://theconversation.com/animals-in-research-c-elegans-roundworm-14163"><em>C. elegans</em> (roundworm)</a></strong></p><img src="https://counter.theconversation.com/content/13804/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joan Heath receives funding from the National Health and Medical Research Council of Australia and the Ludwig Institute for Cancer Research</span></em></p>Our series, Animals in Research, profiles the top organisms used for science experimentation. Here, we look at Danio rerio - the zebrafish. Zebrafish are probably not the first creatures that come to mind…Joan Heath, Laboratory Head, Walter and Eliza Hall Institute, and Associate Professor of Medical Biology, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/113012012-12-12T19:39:20Z2012-12-12T19:39:20ZThey came from the sea: the gene behind limb evolution<figure><img src="https://images.theconversation.com/files/18607/original/mmx3sktw-1355288430.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">In order to drag themselves onto land, fish-like creatures needed limbs.</span> <span class="attribution"><span class="source">Thierrry</span></span></figcaption></figure><p>In the late <a href="http://science.nationalgeographic.com.au/science/prehistoric-world/devonian/">Devonian period</a>, roughly 365 million years ago, fish-like creatures started venturing from shallow waters onto land.</p>
<p>Among the various adaptations associated with the switch to land life was the conversion of fins into limbs. This transition allowed animals to both navigate aquatic habitats and walk on land.</p>
<p><a href="http://www.ncbi.nlm.nih.gov/pubmed/9262397">We already know</a> that fins and limbs share the same genetic program for their induction and early development. But due to their divergent <a href="http://en.wikipedia.org/wiki/Morphology_%28biology%29">morphological traits</a> (form and structure), it was unknown how a fin could evolve into a limb.</p>
<p>But now, <a href="http://www.cell.com/developmental-cell/abstract/S1534-5807%2812%2900478-9?script=true">a paper</a> published in the journal Developmental Cell by Renata Freitas and colleagues from the University of Andalusia (Seville, Spain), suggests the key to fin-to-limb transition lies in the <a href="http://www.wisegeek.org/what-is-gene-regulation.htm">regulation</a> of the <a href="http://en.wikipedia.org/wiki/Homeotic_gene">homeotic</a> (responsible for the formation of body parts) gene <a href="http://ghr.nlm.nih.gov/gene/HOXD13"><em>hoxd13</em></a>.</p>
<h2>Fingers, toes, fins and more</h2>
<p>Fossil and anatomical data show that the main innovation of land vertebrate (tetrapod) appendages is the <a href="http://www.ncbi.nlm.nih.gov/pubmed/18459983">autopod</a>: the <a href="http://en.wikipedia.org/wiki/Anatomical_terms_of_location#Proximal_and_distal">distal</a> – or furthest from the body – part of the limb where digits develop.</p>
<p>Fish obviously lack fingers and toes but they also lack the <a href="http://en.wikipedia.org/wiki/Gene_signature">expression signature</a> – the repertoire of expressed genes necessary to identify a cellular structure – of an autopod.</p>
<p>Therefore, finding a genetically altered fish with the characteristics of autopod development will explain how the fin-to-limb transition occurred.</p>
<p>So-called <a href="http://www.ncbi.nlm.nih.gov/pubmed/8620844">5’Hoxd genes</a> – genes which can lead to limb and other body-part transformation when mis-expressed – seemed to be ideal candidates to investigate. Especially since it has <a href="http://www.ncbi.nlm.nih.gov/pubmed/17644373">been reported</a> that these genes are involved in autopod development.</p>
<p>In particular, <em>hoxd13</em> has been identified as a key player in autopod development. Why? Because mutations of <em>hoxd13</em> in humans are known to result in <a href="http://en.wikipedia.org/wiki/Syndactyly">syndactyly</a> (the fusion of multiple digits, such as fingers) and <a href="http://en.wikipedia.org/wiki/Polydactyly">polydactyly</a> (the formation of extra digits).</p>
<p>Therefore, Freitas and collaborators speculated, the modification of <em>hoxd13a</em> expression in fish might lead to a limb type of fin.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/18606/original/x5dm3gcf-1355288166.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/18606/original/x5dm3gcf-1355288166.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/18606/original/x5dm3gcf-1355288166.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/18606/original/x5dm3gcf-1355288166.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/18606/original/x5dm3gcf-1355288166.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/18606/original/x5dm3gcf-1355288166.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/18606/original/x5dm3gcf-1355288166.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The researchers used zebrafish to test their ocean-to-land hypothesis.</span>
<span class="attribution"><span class="source">Novartis AG/Flickr</span></span>
</figcaption>
</figure>
<h2>Testing the waters</h2>
<p>To confirm their hypothesis, the authors induced <em>hoxd13a</em> expression during late fin formation in zebrafish. They found that this single gene mis-expression was sufficient to distally expand the endoskeleton territory. In other words, the outer region of the fin started to show signs of becoming a limb.</p>
<p>This was confirmed by cartilage staining and cartilage specific gene expression (<a href="http://en.wikipedia.org/wiki/SOX9"><em>sox9</em></a> and <a href="http://www.ncbi.nlm.nih.gov/pubmed/21723274"><em>col2a1a</em></a>) in the fin fold (the distal-most part of the fin) where cartilage is normally not observed.</p>
<p>This initial result was promising, as conversion of the fin fold into cartilage would be the first step leading to the formation of an autopod. But can <em>hoxd13a</em> over-expression induce fin tissue with an autopodial signature? </p>
<p>The researchers found that <em>hoxd13a</em> over-expression induces the expression domain of genes of distal limb markers (such as <em>hoxd13b</em>, <em>cyp26b1</em> or <em>pea3</em>) into the domain of the truncated fin fold, where they are normally excluded. In other words over-expression of <em>hoxd13a</em> in the fin led to a specific gene signature in the distal part of the fin that is specific to a land vertebrate autopod.</p>
<p>Moreover, the researchers found that a fin-fold-specific gene, such as <em>fgf8a</em>, had its expression dramatically down-regulated, meaning that the fin fold itself was dramatically reduced.</p>
<h2>Primitive limb</h2>
<p>Overall, the cartilage expansion and altered distal limb gene-specific expression observed in <em>hoxd13a</em> over-expression are consistent with the conversion of the distal most part of the fin (the fin fold) into a distal limb-like structure.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/18599/original/yzvdmqpc-1355287622.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/18599/original/yzvdmqpc-1355287622.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=803&fit=crop&dpr=1 600w, https://images.theconversation.com/files/18599/original/yzvdmqpc-1355287622.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=803&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/18599/original/yzvdmqpc-1355287622.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=803&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/18599/original/yzvdmqpc-1355287622.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1009&fit=crop&dpr=1 754w, https://images.theconversation.com/files/18599/original/yzvdmqpc-1355287622.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1009&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/18599/original/yzvdmqpc-1355287622.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1009&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This zebrafish embryo developed a limb that looks more like a leg than a fin, after being engineered to produce the HoxD13 protein.</span>
<span class="attribution"><span class="source">Developmental Cell/Freitas et al.</span></span>
</figcaption>
</figure>
<p>Increased cell proliferation is another feature of distal limb development. Consistent with the previous observation, over-expression of <em>hoxd13a</em> in the fin led to an increase in cell proliferation in the most distal part of the fin. This most distal part is not considered a fin fold anymore, but now an autopod-like structure.</p>
<p>These data mean that modulation of the expression of a single gene – in our case <em>hoxd13a</em> – in the fin lead to a reduction of the fin fold (not present in the limb), development of distal cartilage (essential for digits formation) and specific genes expression that are found in the autopod in tetrapods but not in fish fins. </p>
<p>The final step in this study was to confirm that <em>hoxd13</em> expression is a key feature of autopod formation. That is, the authors needed evidence that <em>hoxd13</em> is regulated differently between fish and tetrapods.</p>
<p><em>Hoxd13</em> is differentially regulated in the zebrafish fin and in the mouse limb. But using the mouse <em>hoxd13</em> regulatory sequence fused to a <a href="http://en.wikipedia.org/wiki/Reporter_gene">reported gene</a> – the <a href="http://en.wikipedia.org/wiki/Green_fluorescent_protein">green fluorescent protein (GFP)</a> – they authors demonstrated that the mammalian regulatory sequence for <em>hoxd13</em> is recognised by the zebrafish.</p>
<p>The authors observed strong GFP expression in the fin <a href="http://en.wikipedia.org/wiki/Mesenchyme">mesenchyme</a> (a type of connective tissue). As the fin matured, the GFP expression was expanded distally.</p>
<p>The paper published by Freitas supports the hypothesis that the modulation of <a href="http://en.wikipedia.org/wiki/Hox_gene">hox genes</a> – such as <em>hoxd13d</em> – expression during late fin development allows for the evolution of fins into the cellular material required for digit formation.</p>
<p>In this way, the paper has much to teach us us about the evolutionary processes that led to a transition from sea- to land-based organisms and the formation of limb formation in land vertebrates.</p><img src="https://counter.theconversation.com/content/11301/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Yann Gibert does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>In the late Devonian period, roughly 365 million years ago, fish-like creatures started venturing from shallow waters onto land. Among the various adaptations associated with the switch to land life was…Yann Gibert, Head, Metabolic Genetic Diseases Research Laboratory, Deakin UniversityLicensed as Creative Commons – attribution, no derivatives.