Analysis of shell formation from calcium carbonate crystals in species specific manner

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In molluscs, biominerals of CaCO_3 are formed as shells with extremely divergent morphologies among species, enabling classification and identification of species. Shells are genetically regulated biominerals which consist of an external periostracal layer and an inner calcareous layer which is composed of several layers, such as a foliate, crossed lamellar, prismatic and nacreous layer. These layers are composed of CaCO_3, but their crystal types vary according to species ; in most pearl oysters, calcite in the prismatic layer and aragonite in the nacreous layer. The aragonitic nacreous layer is known as mother-of-pearl and consists of compact tablets of several hundreds nm in diameter. It is reported that its toughness is 1000 times greater than simple aragonite crystals produced by a chemical procedure. In addition to CaCO_3, mollusc shells contain as minor components organic matrix proteins, which are thought to be responsible for the toughness on the nacreous layer and to have some critical roles in calcification. In this research, I carried out analysis of genes expressed in the mantle. The results are as follows :1.Several housekeeping genes that are expressed in the oyster mantle were isolated and their primary structure were determined.2.Novel genes encoding glycine-rich proteins were isolated from the oyster mantle and their primary structure were determined. Recombinant proteins produced using the cDNAs inhibited the calcium carboane crystallization.3.The nacrein protein, which is found in the nacreous layer of the pearl oyster, has inhibitory activity in the calcium carbonate crystallization4.Novel genes encoding glycine-rich proteins in the pearl oyster were discovered and their entire nucleotide sequence were determined.