UTTAR PRADESH JOURNAL OF ZOOLOGY

Among the vertebrate model organisms, zebrafish (Danio rerio) is one of the key models for studying pigmentation, pattern formation and their underlying genetic mechanisms. Their genetic materials show high similarity to humans, with the availability of well-characterised pigment and optical transparency during development. Zebrafish exhibit distinct horizontal stripes at the adult stage as a result of the interaction between three forms of chromatophores: iridophores, xanthophores, and melanophores. This review aims to elucidate the genetic and cellular mechanisms of pigmentation in zebrafish, emphasizing the translational relevance of SLC45A2 to human pigment biology. The dynamic cell-cell communication and self-organisation principles responsible for the formation of pigment patterns have been revealed through studies on chromatophore lineage tracing, mutant analysis and mathematical models. The comparative studies reveal the diversified evolution of chromatophore types among the close relatives of Danio species, highlighting the conserved and divergent mechanisms of pigment differentiation. Zebrafish pigment pattern also influenced the behaviour, neurobiology and environmental adaptation as they affect mate selection, social interactions, camouflage and response to stress. The pigment-assorted traits strengthened by advances in transgenic zebrafish models and behavioural assays are used as readouts for neurological toxicity, social behaviour and colour vision. At the molecular level, slc24a5 and slc45a2 are the conserved pigmentation genes regulating melanosome biogenesis, ion homeostasis and synthesis of melanin. Any alteration in these genes results in pigment disorders like oculocutaneous albinism in both humans and zebrafish. However, natural allelic variation in alc45a2 leads to adaptive changes in human skin colour. Research demonstrates that loss of function of slc45a2 due to mutation highlights its role in regulating the melanosome pH, a requirement for maintaining proper tyrosine function and eumelanin formation. Previous studies revealed valuable understanding of the cellular, genetic and evolutionary basis of pigmentation, providing it as a model for understanding pigment biology, human disorders and adaptive colouration mechanisms.