Developmental series of body pigment pattern metamorphosis of wild-type (A–D), kar (E–H) and rse^tLF802 mutant fish (I–L). Posterior trunk regions at the level of dorsal and anal fins are shown. The series of wild type and strong rse were published by Frohnhöfer et al. (Frohnhöfer et al., 2013). At stages PB and PR, kar mutants show only slight reductions in iridophore numbers (compare panels A,B to panels E,F), they still form a continuous sheet just ventral to the horizontal myoseptum. From PR to SP however, this reduction of iridophores becomes more apparent. They do not extend properly into dorsal and ventral interstripe regions (compare panel C and panel G), occasionally, remnants or patches develop (interstripe X1V in panel H). From stage SP onwards the number of melanophores is reduced compared to wild type (compare panels C,D to panels G,H). The early phase of pigment pattern development of strong rse mutants is similar to kar, with slightly stronger reductions in iridophores (I,J). In contrast to kar, however, iridophores do not form dense ridges in interstripe regions and rather are dispersed (K,L). ao: aorta. Scale bars: 250 µm.

kar maps to a region at the beginning of chromosome 15 (A). One marker, G40280, is 100% linked to the mutation and lies in the gene coding for endothelin-converting enzyme 2 (A,C). Chromatograms of ece2 sequences from wild-type and kar mutant fish (B) showing the mutation (the premature Stop codon is underlined). Ece2 is a type II transmembrane protein of 765 aa (D), the C-terminal peptidase domain is lost in the mutants, TM: transmembrane domain. Phylogenetic analysis of the amino acid sequences of Eces from different vertebrate species shows three branches with Ece1, Ecel1 and Ece2 (E).

Wild-type (A) and nac;pfe mutant (B) adult fish for comparison. Transplantations of kar mutant cells into strong rse (C) or nac;pfe (D) mutant recipients result in fish with recovered stripe patterns. In chimeric fish generated by transplantation of nac;pfe donor cells into kar mutant recipient embryos (E,E′) occasionally, very small patches of dense iridophores develop (magnification in E′, white arrows). In the vicinity of these patches melanophores increase in number (black arrow). Labelling of the donors with Tg(β-actin:GFP) (F,F′) shows transplanted donor cells of various cell types next to the patches of dense iridophores.

RNA in situ hybridizations for edn3a and edn3b at 24 hpf and 48 hpf in albino (alb) embryos. The expression of edn3a is not detectable above background (A,B). edn3b expression is detected in the epidermis during these stages (C,D).