Transcriptome-wide analysis reveals candidate genes responsible for the asymmetric pigment pattern in scallop Patinopecten yessoensis

Yesso scallop Patinopecten yessoensis is an economically important marine bivalve species in aquaculture and fishery in Asian countries. The colors of the left and right shells are obviously distinct, typically having reddish-brown for the left and white for the right. This left-right asymmetric pigment pattern is a very unique phenomenon among invertebrates, whereas the molecular mechanisms that control regional differences in pigmentation are not clear. To better understand the left-right asymmetric pigment pattern, we apply Illumina digital gene expression (DGE) to characterize the gene expression profiles in left and right mantle tissues, and identify five differentially expressed genes, including Cytochrome P450 and other four unknown genes. Among the five genes, one gene shows significantly higher expression in the right mantle, while other four exhibit significantly higher expression in the left mantle. We further validate the DGE results by using quantitative real-time PCR for P450, resulting in approximately 32-fold higher expression in the left mantle than that in the right mantle. These findings will not only help assist our understanding of the sophisticated processes of shell pigmentation in scallops, but also provide new insights into the adaptive evolution of phenotypes to maximize survival that underlie the left-right asymmetric pigment pattern in molluscs.