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 rer io, neural crest-derived pigment cells generate different pigment patterns during different phases of the life cycle. Whereas early larvae exhibit sim ple stripes of melanocytes and silver iridophores in a background of yellow xanthophores, this pigment pattern is transformed at metamorphosis into th at of the adult, comprising a series of dark melanocyte and iridophore stri pes, alternating with light stripes of iridophores and xanthophores. Althou gh several genes have been identified in D. rerio that contribute to the de velopment of both early larval and adult pigment patterns, comparatively li ttle is known about genes that are essential for pattern formation during j ust one or the other life cycle phase. In this study, we identify the gene responsible for the rose mutant phenotype in D. rerio. rose mutants have wi ld-type early larval pigment patterns, but fail to develop normal numbers o f melanocytes and iridophores during pigment pattern metamorphosis and exhi bit a disrupted pattern of these cells. We show that rose corresponds to en dothelin receptor hi (ednrb1), an orthologue of amniote Ednrb genes that ha ve long been studied for their roles in neural crest and pigment cell devel opment. Furthermore, we demonstrate that D. rerio ednrb1 is expressed both during pigment pattern metamorphosis and during embryogenesis, and cells of melanocyte, iridophore, and xanthophore lineages all express this gene. Th ese analyses suggest a phylogenetic conservation of roles for Ednrb signali ng in the development of amniote and teleost pigment cell precursors. As mu rine Ednrb is essential for the development of all neural crest derived mel anocytes, and D. rerio ednrb1 is required only by a subset of adult melanoc ytes and iridophores, these analyses also reveal variation among vertebrate s in the cellular requirements for Ednrb signaling, and suggest alternative models for the cellular and genetic bases of pigment pattern metamorphosis in D. rerio. (C) 2000 Academic Press.