Molecular characterization and expression profiles of myosin essential light chain gene in the Pacific oyster Crassostrea gigas.

In molluscs, muscle contraction is triggered by a direct binding of Ca to myosin. The myosin essential light chain (MELC) provides the Ca binding site and is of importance for motor function and regulation. In this study, the complete cDNA sequence of MELC gene of the Pacific oyster, Crassostrea gigas, was obtained, and the expression profiles were performed in different tissues and different embryo-larval development stages. The results showed that the full length of C. gigas MELC (CgMELC) cDNA was 659bp, containing a 5'-untranslated region of 73 bp, a 3'-untranslated region of 112bp. The open reading frame encoded a 157 amino acid peptide. The protein sequence of CgMELC contained a conserved EF-hand calcium binding motif, and showed a high sequence identity (68.4-100%) with other bivalves. Quantitative analysis of CgMELC mRNA in tissues indicated that CgMELC was expressed at the highest level in the striated adductor muscle, followed by the smooth adductor muscle and mantle. During the development of embryos and larvae, quantitative analysis and whole-mount in situ hybridization revealed that CgMELC was expressed starting from the blastula stage and abundantly expressed in trochophore and D-shaped larvae, indicating that CgMELC might also be involved in regulation of larval muscle system development. Our data provided valuable information for further researches on the function of MELC and regulation of muscle contraction in oysters.