title: Endothelin signalling in iridophore development and stripe pattern formation of zebrafish.
abstract: Colour patterns of adult fish are composed of several different types of pigment cells distributing in the skin during juvenile development. The zebrafish, Danio rerio, displays a striking pattern of dark stripes of melanophores interspersed with light stripes of xanthophores. A third cell type, silvery iridophores, contributes to both stripes and plays a crucial role in adult pigment pattern formation. Several mutants deficient in iridophore development display similar adult phenotypes with reduced numbers of melanophores and defects in stripe formation. This indicates a supporting role of iridophores for melanophore development and maintenance. One of these mutants, rose (rse), encodes the Endothelin receptor b1a. Here we describe a new mutant in zebrafish, karneol (kar), which has a phenotype similar to weak alleles of rse with a reduction in iridophore numbers and defects of adult pigment patterning. We show that, unlike rse, kar is not required in iridophores. The gene defective in the kar mutant codes for an endothelin-converting enzyme, Ece2, which activates endothelin ligands by proteolytic cleavage. By morpholino-mediated knockdown, we identify Endothelin 3b (Edn3b) as the ligand for endothelin receptor signalling in larval iridophores. Thus, Endothelin signalling is involved in iridophore development, proliferation and stripe morphogenesis in larvae as well as adult zebrafish. In mammals the pathway is required for melanocyte development; therefore, our results indicate a previously unrecognized close evolutionary relationship between iridophores in zebrafish and melanocytes in mammals.
authors.affiliation: Max-Planck-Institut für Entwicklungsbiologie, 72076 Tübingen, Germany.
authors.forename: Jana
authors.initials: J
authors.lastname: Krauss
authors.affiliation: Max-Planck-Institut für Entwicklungsbiologie, 72076 Tübingen, Germany.
authors.forename: Hans Georg
authors.initials: HG
authors.lastname: Frohnhöfer
authors.affiliation: Max-Planck-Institut für Entwicklungsbiologie, 72076 Tübingen, Germany.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Walderich
authors.affiliation: Max-Planck-Institut für Entwicklungsbiologie, 72076 Tübingen, Germany.
authors.forename: Hans-Martin
authors.initials: HM
authors.lastname: Maischein
authors.affiliation: Max-Planck-Institut für Entwicklungsbiologie, 72076 Tübingen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Weiler
authors.affiliation: Max-Planck-Institut für Entwicklungsbiologie, 72076 Tübingen, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Irion
authors.affiliation: Max-Planck-Institut für Entwicklungsbiologie, 72076 Tübingen, Germany christiane.nuesslein-volhard@tuebingen.mpg.de.
authors.forename: Christiane
authors.initials: C
authors.lastname: Nüsslein-Volhard
keywords: Endothelin signalling; Endothelin-converting enzyme; Iridophores; Pigment pattern formation; karneol