Gene expression patterns and pearl formation in the Japanese pearl oyster (Pinctada fucata): A comparison of gene expression patterns between the pearl sac and mantle tissues

Shell matrix proteins play an important role in the regulation of shell and pearl formation in the Japanese pearl oyster (Pinctada fucata). There is a paucity of information on the function of these proteins and their gene expression patterns. The purpose of this study was to compare the gene expression patterns of six shell matrix proteins (nacrein, msi60, msi31, n16, prismalin-14 and aspein) in the mantle center (MC) (which forms the nacreous layer) and mantle edge (ME) (which forms the prismatic layer), with those in the pearl sac (PS) (which forms the nacreous layer on the pearl surface). There was a significant correlation between the PS and MC (P < 0.05) for the six gene expression patterns. In addition, cluster analysis showed that the expression patterns of the six genes were grouped into three clusters (nacreous cluster: msi60 and n16, prismatic cluster: msi31, prismalin-14 and aspein, and nacrein). These results indicate that formation of the nacreous and prismatic layers of the shell and pearl is affected by the gene expression patterns of the shell matrix proteins, and that the two genes of the nacreous cluster (msi60 and n16) and the three genes of the prismatic cluster (msi31, prismalin-14 and aspein) are regulated by unknown factors.