How the Zebrafish Develops its Stripes: How Color Patterns are Created in Animals

The zebrafish owes its name to its bold, blue stripes that alternate with gold ones across its slim body. Now, scientists have taken a closer look at how cells arise to form the "zebra" pattern in this fish, which may shed more light on the development and evolution of patterns seen in the animal world.

Three major pigment cell types-black cells, reflective silvery cells, and yellow cells-emerge during growth in the skin of tiny juvenile zebrafish. These cells arrange as a multilayered mosaic to create the characteristic color pattern. While scientists have known that all three cell types have to interact to form proper stripes, the embryonic origin of the pigment cells that develop the strips has remained a mystery until now.

This study built upon a previous study, when the researchers examined cellular events during stripe pattern formation. Individual juvenile fish carrying fluorescently labeled pigment cell precursors were imaged every day for up to three weeks to chart out the cellular behaviors.

The analysis revealed that the three cell types reach the skin by completely different routes. For example, a pluripotent cell population situated at the dorsal side of the embryo gives rise to larval yellow cells, which cover the skin of the embryo. The black and silvery cells, though, come from a small set of stem cells associated with nerve nodes located close to the spinal cord in each segment. The black cells reach the skin by migrating along the segmental nerves to appear in the stripe region, and the silvery cells pass through the longitudinal cleft that separates the musculature and then multiply and spread in the skin.

What was more interesting is that the researchers found that both the silvery and yellow cells could switch both cell shape and color, depending on their location. It's very possible that variation in these cell behaviors could be to blame for the diversity of color patterns in fish.

"These findings inform our way of thinking about color pattern formation in other fish, but also in animals which are not accessible to direct observation during development such as peacocks, tigers and zebras," said Christiane Nusslein-Volhard, one of the researchers, in a news release.

The findings are published in the journal Science.