Characterization of organic matrix components of pearl oyster, and their implications in shell formation

Abstract

Mollusks make their shells by biomineralization using Ca²⁺ and CO₃^2- from natural environment. In molluscan shells, two types of CaCO₃ crystal which are aragonite and calcite form the species-dependent microstructures. It is believed that shell organic matrices act for control of the crystal types and microstructures. Shell of Pinctada fucata is divided into aragonitic nacreous layer and calcitic prismtic layer. In the recent years, several novel matrix components have been identified in pearl oyster shells by subsequent solubilization of the insoluble matrix, even in the nacreous layer which abounds in the data. In them, we focused our attention on a component, of which the N-terminal amino acid sequence was determined, and attempted cloning genes encoding it. As a result, several clones with typical sequence for the ORF (open reading frame) region were identified and the amino acid sequences were deduced. Further analysis of northern hybridization clarified the tissue specific expressions of the transcripts of the identified genes.

Keywords

pearl oyster / shell microstructure / CaCO₃ crystal polymorphism / organic matrix / repeat sequences