Molecular characterization and expression analysis of chitinase from the pearl oyster Pinctada fucata

Chitinase is an enzyme that plays an important role in the chitin metabolism of a wide range of organisms. However, the function of chitinase in the pearl oyster Pinctada fucata is yet to be determined. In this study, a chitinase gene (named PfChi1) was cloned from P. fucata and its expression profiles were investigated. The full-length cDNA of PfChi1 was 2743bp and consisted of a 2187-bp open reading frame encoding 728 amino acid residues, a 47-bp 5'-untranslated region (UTR), and a 509-bp 3'-UTR. Similar to other known chitinases, the PfChi1 protein is composed of an N-terminal leading signal peptide, a catalytic domain, a linker region, and a C-terminal chitin-binding domain. The results of qRT-PCR showed that PfChi1 was expressed in a wide range of tissues with relatively high levels in the mantle, muscle, gill, and gonad, and relatively low levels in hemocytes, the intestine, and the digestive gland (P<0.05). In situ hybridization showed that PfChi1 was mainly expressed in the mantle edge, particularly in the outer epithelial cells of the inner fold, whereas few hybridization signals were detected in the inner epithelial cells of the middle fold. A shell damage experiment indicated that PfChi1 transcript levels were up-regulated significantly (P<0.05) at 24h after shell damage and decreased gradually thereafter, followed by shell regeneration, indicating that PfChi1 is involved in shell formation. In addition, PfChi1 expression was higher in trochophore larvae than in other developmental stages (P<0.05), indicating a possible association with the formation of prodissoconch shells. To the best of our knowledge, this study is the first to report the potential biomineralization function of a chitinase in P. fucata.