Quantitative expression analysis of nacreous shell matrix protein genes in the process of pearl biogenesis

A cultured pearl is produced in a pearl sac which forms layers of cells differentiated from an allograft mantle. Previous investigations claimed that genomic DNAs from grafting tissues were persistent during pearl aquaculture. However, the specific living status of the genes regulating pearl formation has remained unknown. This study examined the expression profiles of six genes encoding nacreous shell matrix proteins (NSMPs) in the pearl sac of aquaculture pearl oyster Pinctada fucata by real-time PCR. The comparative analysis of NSMP gene expression in the pearl sac and reference mantle tissues revealed that only a few NSMP genes maintained high transcription levels in the pearl sac. The impaired transcription levels of the nacrein gene refreshed the previous hypothesis, suggesting that CaCO3 required for pearl secretion was not from pearl sac cells. Among the examined genes, only the N19 gene attained high expression levels in the pearl sac. These results provide new insights into the molecular mechanisms involved in pearl biogenesis.