How the zebrafish got its stripes

Animal patterns – the stripes, spots, and rosettes seen in nature – are a source of endless fascination, and now Bath University researchers have developed a robust mathematical model to explain how an important species, the zebrafish, develops its stripes.

In the animal kingdom, the arrangement of skin pigment cells begins during the embryonic stage of development, making pattern formation an area of ​​great interest not only to a lay audience but also to scientists, in particular , developmental biologists and mathematicians.

The zebrafish is invaluable for studying human disease. These humble small freshwater fish may appear to have little in common with mammals, but they actually show many genetic similarities to our species and have a similar list of physical characteristics (including most major organs).

The zebrafish also provides fundamental information about the complexes and often wonderful processes that underlie biology. Studying its striking appearance may, over time, be relevant to medicine, since pattern formation is an important general feature of organ development. therefore, a better understanding of the formation of the pigment pattern could give us an idea of ​​the diseases caused by the disruption of cellular arrangements within the organs.

The new mathematical model devised in Bath paves the way for further explorations in pigment design systems and their similarity between different species. Pigmentation in zebrafish is an example of an emerging phenomenon, one in which individuals (cells in this case), all acting according to their own local rules, can self-organize to form an ordered pattern on a much larger scale than what one might expect. Other examples of emerging phenomena in biology include starling accumulation and synchronized swimming observed in schools of fish.

Dr. Kit Yates, the Bath mathematician who led the study, said: “It is fascinating to think that these different pigment cells, all acting without coordinated centralized control, can reliably produce the streak patterns we see in zebrafish. Our modeling highlights the local rules these cells use to interact with each other to robustly generate these patterns. “

“Why is it important for us to find a correct mathematical model to explain the stripes on the zebrafish?” asks Professor Robert Kelsh, co-author of the study. “In part, because the pigment patterns are interesting and beautiful in their own right. But also because these streaks are an example of a key development process. If we can understand what is happening in the development of a fish embryo pattern, we may be able to gain a deeper insight into the complex choreography of cells within embryos in general. “

The stripes on an adult ‘wild type’ zebrafish are formed from pigment-containing cells called chromatophores. There are three different types of chromatophores in fish, and as the animal develops, these pigment cells move around the surface of the animal, interacting with each other and organizing themselves in the striped pattern for which the fish is named. Occasionally, mutations appear that change the way cells interact with each other during pattern development, resulting in labyrinth-like labyrinth spots or leopard skin.

Scientists know a great deal about the biological interactions necessary for the self-organization of pigment cells in a zebrafish, but there has been some uncertainty as to whether these interactions offer a comprehensive explanation of how these patterns are formed. To test biological theories, Bath’s team developed a mathematical model that incorporated all three cell types and all of their known interactions. The model has proven to be successful, predicting the development of both wild and mutant fish patterns.

Mathematicians have been trying to explain how zebrafish stripes form for many years, however many previous modeling attempts have failed to explain the wide range of mutant patterns observed in fish. Jennifer Owen, the scientist responsible for building and running the model, said: “One of the benefits of our model is that, due to its complexity, it can help predict the developmental defects of some less understood mutants. For example, our model it can help predict cell-cell interactions that are defective in mutants like the leopard, which shows spots. “

The study is published in elife.