A novel silk-like shell matrix gene is expressed in the mantle edge of the Pacific oyster prior to shell regeneration

During shell formation, little is known about the functions of organic matrices, especially about the biomineralization of shell prismatic layer. We identified a novel gene, shelk2, from the Pacific oyster presumed to be involved in the shell biosynthesis. The Pacific oyster has multiple copies of shelk2. Shelk2 mRNA is specifically expressed on the mantle edge and is induced during shell regeneration, thereby suggesting that Shelk2 is involved in shell biosynthesis. To our surprise, the database search revealed that it encodes a spider silk-like alanine-rich protein. Interestingly, most of the Shelk2 primary structure is composed of two kinds of poly-alanine motifs-GXNAn(S) and GSAn(S)-where X denotes Gln, Arg or no amino acid. Occurrence of common motifs of Shelk2 and spider silk led us to the assumption that shell and silk are constructed under similar strategies despite of their living environments.

► We identified a novel gene, shelk2, in the Pacific oyster. ► Database search revealed that Shelk2 carries a spider silk-like protein. ► Shelk2 is expressed specifically in the mantle edge prior to shell biosynthesis. ► Shelk2 is assumed to be involved in the biosynthesis of shell prismatic layer. ► Our findings suggest oyster shell is constructed by similar strategy to spider silk.