Cloning, characterization and expression prolife analysis of ldlr: Insight into purple shell formation in Cyclina sinensis

The clam Cyclina sinensis is an economically important marine bivalve, and the diversity of its shell colour has potential applications in breeding. In this study, the distribution of purple pigments in the clam shell was examined, and Raman spectroscopy was conducted. The levels of total carotenoids and four common carotenoids in various tissues were also determined and analysed. Furthermore, the full‐length cDNA of a low‐density lipoprotein receptor gene (ldlr) was cloned and characterized, and the tissue distribution of ldlr gene expression was analysed. The results showed that purple pigments existed mainly in the nacre layer of the shell from the purple‐shell clam, in which strong Raman peaks for carotenoids were observed, suggesting that carotenoids might be the main components of purple pigments in the purple shell. The TCC and the levels of four common carotenoids were higher in the outer margin of the mantle and shell of purple‐shell clams than in those of white‐shell clams, and the ldlr mRNA was highly expressed in the outer margin of the mantle in purple‐shell clams. Taken together, our results suggest a possible molecular mechanism governing the selective transport of carotenoids in the mantle of purple‐shell clams and shell colour formation. The results of this study will help to elucidate the colour formation mechanism in clam shells.