Striped fish story reported in ScienceDaily 17 November 2015. Zebrafish are small freshwater fish commonly used in the study of vertebrate embryonic development. As their name suggests, one of their distinctive features is that they have highly contrasting stripes running along each side of the body, although they are blue and yellow, rather than black and white.

The striped pattern is the result of interactions of three different types of pigment cells – melanophores containing black pigment, xanthophores containing yellow, and iridophores, silvery reflective cells. In a developing fish, stem cells have the potential to become any one of these cells. The cells can also move short distances. Previous experiments have also shown the cells get cues from surrounding cells through chemical signalling that determines what type of cell they become and where they move to. Embryonic development also involves cell death, as well as the addition of new cells, in order to achieve the final pattern.

These processes have been closely studied individually, so mathematicians from Brown University have developed a mathematical model to simulate the way they all work together to form and maintain the stripes as the fish grows. Alexandria Volkening of Brown’s Division of Applied Mathematics explained: “The stripe pattern forms dynamically as the fish develops. It’s not like these pigment cells are filling out some kind of prepattern that’s already there. It’s the interactions of the cells over time that causes the patterns to form. We wanted to build a model that simulates this based as much as possible on what’s known about the biology”.

The mathematicians suggest models like this will help scientists understand how complex patterns and structures are formed in living things. Bjorn Sandstede, chair of Brown’s Division of Applied Mathematics, who was also involved in the model development, commented: “If you look at any kind of organism, they start with oocytes, which are roundish structures with little spatial differentiation at all, and you end up with organisms like us that have a complex spatial structure. I think it’s important to try to understand how spatial differentiation occurs. Zebrafish and their stripes are a good model to do that because you can identify the different cells and what they’re doing in the process”.


Editorial Comment: A mathematical model may help scientists understand how complex structures and patterns are formed in living things, but they should remember that mathematical models are the result of intelligent, creative mathematicians applying their knowledge and understanding to a problem, which these days usually involves some complex computer programming – also the result of creative intelligence. We can confidently predict that a better understanding of embryonic development will require more intelligent scientists and more complex computer programs and that further research will reveal that enormous amounts of information are involved in turning a single, simple round cell into a complex structure such as a functioning fish, complete with stripes.

In case anyone is confused about cell death being involved in embryonic development, the type of cell death they are talking about is not what happens when living tissue is damaged or diseased. There is a type of cell death, named apoptosis, which involves the deliberate dismantling of a cell and removal of the fragments, without causing damage or disease to the living organism. This may seem wasteful, but a useful analogy would be the building and later removal of temporary structures during a building project. As such, apoptosis is part of the planned and purposeful design we see in growth and development of living things. (Ref. ichthyology, information technology, embryology)

Evidence News vol. 15, No. 23
2 December 2015
Creation Research Australia