Quantitative expression of shell matrix protein genes and their correlations with shell traits in the pearl oyster Pinctada fucata

Abstract

Shell matrix proteins play an important role in the regulation of shell growth and formation in the pearl oyster, Pinctada fucata. This study compared the expression levels of seven shell matrix protein genes ( aspein, prismalin-14, n16, n19, nacrein, msi7, and efcbp) in pearl oysters of various sizes [large (L), medium (M), and small (S)] and analyzed the correlations between expression level and shell size. Except for efcbp and msi7, significant correlations were detected between the expression levels of matrix protein genes and shell size: n19 expression displayed a negative correlation ( P < 0.01) with increasing shell size, whereas expression levels of aspein, prismalin-14, n16, and nacrein were greater in oysters with larger shell sizes. Furthermore, stronger correlations were found with shell height for genes related to prismatic layer of shell than shell weight; and with shell weight for genes related to nacreous layer of shell, which makes sense because prismatic proteins are considered to contribute to the extension of the shell length; and nacreous proteins are responsible for the shell thickness. These results contribute to a better understanding of the shell growth mechanisms of the pearl oyster.