MUTATIONS AFFECTING XANTHOPHORE PIGMENTATION IN THE ZEBRAFISH, DANIO-RERIO

In a large-scale screen for mutants with defects in embryonic developm ent we identified 17 genes (65 mutants) specifically required for the development of xanthophores, We provide evidence that these genes are required for three different aspects of xanthophore development, (1) P igment cell formation and migration (pfeffer and salt); (2) pigment sy nthesis (edison, yobo, yocca and brie) and (3) pigment translocation ( esrom, tilsit and tofu). The number of xanthophore cells that appear i n the body is reduced in embryos with mutations in the two genes, salt and pfeffer. In heterozygous and homozygous salt and pfeffer adults, the melanophore stripes are interrupted, indicating that xanthophore c ells have an important function in adult melanophore pattern formation , Most other genes affect only larval pigmentation, In embryos mutant for edison, yobo, yocca and brie, differences in pteridine synthesis c an be observed under UV light and by thin-layer chromatography. Homozy gous mutant females of yobo show a recessive maternal effect, Embryoni c development is slowed down and embryos display head and tail truncat ions, Xanthophores in larvae mutant in the three genes esrom, tilsit a nd tofu appear less spread out, In addition, these mutants display a d efect in retinotectal axon pathfinding, These mutations may affect xan thophore pigment distribution within the cells or xanthophore cell sha pe, Mutations in seven genes affecting xanthophore pigmentation remain unclassified.