Researchers from the University of Washington found that the re-development of orange-producing xanthophores requires thyroid hormone, the same hormone that turns tadpoles into frogs, suggesting that xanthophores undergo their own metamorphosis.
At the same time thyroid hormone blocks development of the black cells, setting the proper shade overall.
"In the last 10 to 15 years people trying to understand these patterns have concentrated on how the three pigment cell types interact with each other. We showed the tremendous dependence on thyroid hormone for the pattern that develops," Parichy said.
Lead author is Sarah McMenamin, a postdoctoral fellow in Parichy's lab. Funding for the work was provided by the National Institutes of Health, which just awarded Parichy a new $1.25 million grant to study thyroid hormone signaling in pigmentation and melanoma.
Next in the Nature Communications
paper, Parichy's group reports on a gene that drives the unusually early appearance of xanthophores - independent of thyroid hormone - in another species, the pearl danio. Unlike zebrafish this species lacks stripes: its pigment cells are intermingled and arranged uniformly on the body, giving it a pearly orange color.
By expressing this gene the same way in zebrafish, the researchers caused the fish to make extra-early xanthophores and the fish produced a uniform pattern like the pearl danio instead of their usual stripes.