Melanin metabolism mediated via tyrosinase protein involved in red shell coloration of hard clam, Meretrix meretrix

Molluscan shell color polymorphism is influenced by a variety of factors, and endocrine pigments secreted by mollusks play a crucial role in determining shell coloration. The hard clam (Meretrix meretrix) exhibits one of the most extensive variations in shell color among molluscan species, and the mechanism underlying its shell pigmentation remains largely unexplored. The stable inheritance of red shell color in a newly identified variant of M. meretrix, offers a valuable model for investigating the genetic basis of this phenotype. In this study, we conducted transcriptomic and proteomic analyses of the mantle tissues from both red and white shell clams to elucidate the molecular mechanisms responsible for the observed differences in shell color. Our results revealed that genes and proteins with significant differential expressions were primarily associated with carotenoid metabolism, melanin synthesis, biomineralization, and substance transport. Notably, tyrosinase like protein (encoded by Tyrl), a key enzyme involved in melanin synthesis, exhibited significantly higher transcript and protein levels in red shell clams compared to white shell clams. Consequently, we measured the melanin content and analyzed the expression profile of Mm-Tyrl using qPCR, Western blotting, and immunofluorescence techniques. These findings suggest that melanin and its related metabolic enzyme Mm-Tyrl may serve as novel regulators of red shell pigmentation in M. meretrix. The data presented herein provides new insights into the molecular mechanisms governing red shell coloration in clams and enhance our understanding of shell color polymorphisms in mollusks.