Direct control of shell regeneration by the mantle tissue in the pearl oyster Pinctada fucata

Molluscs rapidly repair the damaged shells to prevent further injury, which is vital for their survival after physical or biological aggression. However, it remains unclear how this process is precisely controlled. In this study, we applied scanning electronic microscope and histochemical analysis to examine the detailed shell regeneration process in the pearl oyster Pinctada fucata. It was found that the shell damage caused the mantle tissue to retract, which resulted in relocation of the partitioned mantle zones with respect to their correspondingly secreting shell layers. As a result, the relocated mantle tissue dramatically altered the shell morphology by initiating de novo precipitation of prismatic layers on the former nacreous layers, leading to the formation of sandwich-like prism-nacre-prism-nacre structure. Real-time PCR revealed the up-regulation of the shell matrix protein genes, which was confirmed by the thermal gravimetric analysis of the newly formed shell. The increased matrix secretion might have led to the change of CaCO3 precipitation dynamics which altered the mineral morphology and promoted shell formation. Taken together, our study revealed the close relationship between the physiological activities of the mantle tissue and the morphological change of the regenerated shells.

Automated summary

Molluscs rapidly repair damaged shells to ensure survival, but the control mechanism of this process is unclear. Using scanning electron microscope and histochemical analysis, this study examined shell regeneration in Pinctada fucata. Damage to the shell caused the mantle tissue to retract, resulting in the rearrangement of mantle zones and the alteration of shell morphology. The up-regulation of shell matrix protein genes and the change in CaCO3 dynamics promoted shell formation. This study reveals the relationship between mantle tissue activities and regenerated shell morphology.