Genetics and evolution of pigment patterns in fish.

Vertebrate pigment patterns are both beautiful and fascinating. In mammals and birds, pigment patterns are likely to reflect the spatial regulation of melanocyte physiology, via alteration of the colour-type of the melanin synthesized. In fish, however, pigment patterns predominantly result from positioning of differently coloured chromatophores. Theoretically, pigment cell patterning might result from long-range patterning mechanisms, from local environmental cues, or from interactions between neighbouring chromatophores. Recent studies in two fish genetic model systems have made progress in understanding pigment pattern formation. In embryos, the limited evidence to date implicates local cues and chromatophore interactions in pigment patterning. In adults, de novo generation of chromatophores and cell-cell interactions between chromatophore types play critical roles in generating striped patterns; orientation of the stripes may well depend upon environmental cues mediated by underlying tissues. Further genetic screens, coupled with the routine characterization of critical gene products, promises a quantitative understanding of how striped patterns are generated in the zebrafish system. Initial 'evo-devo' studies indicate how fish pigment patterns may evolve and will become more complete as the developmental genetics is integrated with theoretical modelling.