Mutational Analysis of Endothelin Receptor b1(rose) during Neural Crest and Pigment Pattern Development in the Zebrafish Danio rerio

Pigment patterns of fishes are a tractable system for studying the genetic and cellular bases for postembryonic phenotypes. In the zebrafish Danio rerio,neural crest-derived pigment cells generate different pigment patterns during different phases of the life cycle. Whereas early larvae exhibit simple stripes of melanocytes and silver iridophores in a background of yellow xanthophores, this pigment pattern is transformed at metamorphosis into that of the adult, comprising a series of dark melanocyte and iridophore stripes, alternating with light stripes of iridophores and xanthophores. Although several genes have been identified in D. reriothat contribute to the development of both early larval and adult pigment patterns, comparatively little is known about genes that are essential for pattern formation during just one or the other life cycle phase. In this study, we identify the gene responsible for the rosemutant phenotype in D. rerio. rosemutants have wild-type early larval pigment patterns, but fail to develop normal numbers of melanocytes and iridophores during pigment pattern metamorphosis and exhibit a disrupted pattern of these cells. We show that rosecorresponds to endothelin receptor b1(ednrb1), an orthologue of amniote Ednrbgenes that have long been studied for their roles in neural crest and pigment cell development. Furthermore, we demonstrate that D. rerio ednrb1is expressed both during pigment pattern metamorphosis and during embryogenesis, and cells of melanocyte, iridophore, and xanthophore lineages all express this gene. These analyses suggest a phylogenetic conservation of roles for Ednrb signaling in the development of amniote and teleost pigment cell precursors. As murine Ednrbis essential for the development of all neural crest derived melanocytes, and D. rerio ednrb1is required only by a subset of adult melanocytes and iridophores, these analyses also reveal variation among vertebrates in the cellular requirements for Ednrb signaling, and suggest alternative models for the cellular and genetic bases of pigment pattern metamorphosis in D. rerio.