Cloning, characterization and expression analysis of calcium channel β subunit from pearl oyster (Pinctada fucata)

The absorption, transport and localization of calcium underlie the basis of biomineralization, and Ca2+ entry into epithelial cell is the primary step in shell formation. However, the related mechanism of Ca2+ transport is poorly documented at the gene or protein level. L-type voltage-dependent calcium channels may be involved in calcium transport for biomineralization in some marine invertebrates. In this study, a full-length cDNA of a voltage-dependent calcium channel β subunit from Pinctada fucata (PCaβ) was cloned, and its amino acid sequence was deduced. PCaβ shared 51%–67% apparently sequence identity with voltage-dependent calcium channel β subunits from other species. However, PCaβ was much shorter than other voltage-dependent calcium channel β subunits particularly at the carboxyl terminus, indicating that it is likely a truncated β subunit isoform. Semi-quantitative RT-PCR analysis showed that PCaβ was expressed in all the tested tissues and that it had a higher expression level in the gill tissue and hemolymph than in other tissues, suggesting that L-type voltage-dependent calcium channels are responsible for Ca2+ absorption in the gill and Ca2+ entry into hemocytes. In the mantle, PCaβ mRNA was predominantly expressed in the inner and middle folds of the mantle epithelium, suggesting that L-type voltage-dependent calcium channels are involved in Ca2+ absorption from the ambient medium in the mantle. All these results suggest that voltage-dependent calcium channels are involved in Ca2+ uptake and transport during oyster biomineralization.