The key role of tyrosinase in color variation of the autotetraploid Carassius auratus

Abstract

The autotetraploid Carassius auratus (4nRR, 4n = 200, RRRR, brownish-yellow coloration), derived from the whole-genome duplication of Carassius auratus red var. (RCC, 2n = 100, RR, red), is a model for understanding the genetics and evolution of polyploid animals. In this study, changes in melanophore and melanin contents indicated differences in melanin metabolism among these two fish species. Tyrosinase (tyr), a key enzyme in melanin biosynthesis, exhibited significant up-regulation in 4nRR, but its role in pigmentation and coloration variation in 4nRR is unknown. Here, color-variant RCC, 4nRR, and their gynogenetic offspring were established and investigated, revealing that 4nRR tyr differentiated from RCC tyr to achieve the effective regulation of 4nRR pigmentation. In RCC, two tyr homeologs have sub-functionalized to synergistically regulate melanogenesis. Furthermore, color variation was tracked at different developmental stages in mutants. Subsequently, four divergent tyr homeologs in 4nRR were localized to four homeologous chromosomes and exhibited predominantly biased expression. Remarkably, yellowish coloration was determined by deficiency of four tyr homeologs rather than single or multiple mutated (<4) homeologs. Further, efficient compensatory regulation was confirmed in mutants, suggesting that all tyr have evolved to cooperatively regulate 4nRR melanogenesis following autopolyploidization. Notably, numerous homozygous gynogenetic offspring were rapidly constructed with stable coloration traits, further demonstrating the regulatory role of tyr homeologs in 4nRR coloration variation, which will enable better generation of novel or tailored strains. These observations reveal a key mechanism underlying coloration formation and variation in 4nRR, while informing skin color–based genetic breeding of polyploid fishes.