A cellular game of run-and-chase could help form the iconic stripes on zebrafish skin. Contact between two types of skin cells, the black “melanophores” and the yellow “xanthophores,” prompts the melanophores to move away and the xanthophores to follow  in hot pursuit, developmental biologists report online this week in the Proceedings of the National Academy of Sciences. The researchers’ models suggest that such interactions lead to the pigment cells separating into the distinct bands of zebrafish stripes. To understand how interactions between cells might lead to striped or spotted skin, the scientists found a way to grow pigment cells from zebrafish tail fins in lab dishes. Pigment cells of the same type didn’t seem to interact. But when xanthophores and melanophores were near each other, the yellow cells (apparently attracted) reached out to touch the black ones. The black ones, in turn, were repulsed by the overture and moved away. Undeterred, the xanthophores followed. (In the video, a yellow xanthophore chases a gray melanophore across the screen.) Cells from a zebrafish mutant called jaguar, which has broader, fuzzier stripes, behaved differently. Their black melanophores do not run from the yellow xanthophores, and the xanthophores do not chase them as ardently. This, the researchers say, could explain the mixed populations of yellow and black cells in the stripes’ fuzzy borders. The team hasn’t yet observed the cell movements in developing fish, but the work may help explain why mutations in genes that make proteins that are part of cell membranes can lead to different skin patterns in fish. It may also help explain how other animals—zebras, jaguars, leopards, or Dalmatians—get their patterned skin.
(Video credit: Hiroaki Yamanaka and Shigeru Kondo)