Whether it’s the stripes of a zebra, the spots of a leopard, or the dazzling diversity of colors and patterns displayed by tropical fish, pigment patterns are some of the most striking and memorable traits of an animal. A long-standing question for developmental biologists centers on how such remarkable diversity in color patterns is achieved. Fish, amphibians, and reptiles have many different pigment cell types found just under the skin, each producing a specific color. Different arrangements of these cells produce the remarkable diversity of patterns we see in nature.
Zebrafish, found in most pet stores across the country, are known for their distinct pattern of alternating light and dark stripes. Recently, these horizontal stripes have attracted the attention of scientists seeking to understand how pigment cells are organized to produce complex patterns. Three different pigment cell types contribute to stripe formation. Black melanophores are found in dark stripes, yellow xanthophores are found in light interstripes and iridescent iridophores are found in both stripes and interstripes.
We know that interactions between black melanophores and yellow xanthophores are required for proper stripe development. Zebrafish mutants lacking yellow xanthophores develop disorganized stripes, but the normal striped pattern can be recovered by adding back xanthophores. Because we only see the melanophores and xanthophores in the dark or light stripes, most work to date has focused on the interactions between these two cell types. But are melanophores and xanthophores all there is to zebrafish stripe development?
In our paper we investigated a role for the third pigment cell type, iridescent iridophores, in stripe development. We found that iridophores are the first adult pigment cell type to appear during development and that they do so precisely at the location of the first interstripe. By ablating (aka killing) the iridophores, we show that they are required for the development of xanthophores in the interstripe and also play roles in organizing melanophores into dark stripes on either side. Additionally, we propose that signals from the environment are important for determining where iridophores first appear. Check out the article at PLOS Genetics.
— Larissa Patterson
