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Paramyosin is a key component of thick filaments in invertebrate muscles. In this study, we isolated the full length cDNA of paramyosin from Pacific oyster (Crassostrea gigas) , and determined its pattern of expression during myogenesis. The full length paramyosin (CgPM) cDNA contains an open reading frame (ORF) of 2586 bp encoding a 861-amino acid protein. Sequence analysis revealed an assembly competence domain (ACD) and a heptad repeat (d-e-f-g-a-b-c) with 28-residue repeat zones in the CgPM primary structure, a characteristic of coiled-coil protein. Quantitative analysis of CgPM expression revealed a sharp increase in trochophore stage, and peaked at the D-shaped stage. Strong CgPM expression was found in smooth adductor muscle, followed by striated adductor muscle and mantle tissue. Whole-mount in situ hybridization (WISH) showed a restricted pattern of CgPM expression in adductor muscle, larval velum retractor and foot muscles at the umbo and eyed larval stages. These data indicate that CgPM is strongly expressed during larval myogenesis in C. gigas , which provides the basis for further functional studies of paramyosin in oyster to better understand the molecular and cellular mechanisms of muscle formation in mollusks. [Display omitted] • Here, the sequence characteristics and expression profiles of paramyosin in Crassostrea gigas (CgPM) were investigated. The main results are as follows: • Sequence analysis of CgPM revealed an assembly competence domain (ACD) and a heptad repeat (d-e-f-g-a-b-c) with 28-residue repeat zones in the CgPM primary structure, a characteristic of coiled-coil protein. • Quantitative analysis of CgPM expression revealed a sharp increase in trochophore stage, and peaked at the D-shaped stage. • Strong CgPM expression was found in smooth adductor muscle, followed by striated adductor muscle and mantle tissue. • Whole-mount in situ hybridization (WISH) showed a restricted pattern of CgPM expression in adductor muscle, larval velum retractor and foot muscles at the umbo and eyed larval stages. [ABSTRACT FROM AUTHOR]