The role in spawning of a putative serotonin receptor isolated from the germ and ciliary cells of the gonoduct in the gonad of the Japanese scallop, Patinopecten yessoensis

Serotonin (5-hydroxytriptamin, 5-HT) triggers germinal vesicle breakdown (GVBD) of oocytes and the transporting of the mature oocyte through the gonoduct via cilia motility in bivalves. The 5-HT receptor in the oocyte membrane of the Japanese scallop, Patinopecten yessoensis, has been pharmacologically characterized as a mixed profile of 5-HT1/5-HT2 and is induced by estradiol-17β (E2). Here we report the isolation, cloning, and tissue expression of the 5-HT receptor from the gonad of the Japanese scallop. A full-length cDNA (1818 bp) encoding a putative 5-HT receptor (5-HTpy) of 454 amino acid residues was isolated from the ovary and shared 53.3% and 40.2% homology with the Aplysia 5-HT1ap and mouse 5-HT1A, respectively. The 5-HTpy sequence possessed typical characteristics of 5-HT1, including seven transmembrane domains, a long third inner loop, and a short fourth inner terminal. Phylogenetic analysis suggested that 5-HTpy was classified into the 5-HT1 subtype as well as other invertebrate 5-HT1 receptors. Semi-quantitative RT-PCR showed the expression of the 5-HTpy gene in both the nervous system and peripheral tissues and the induction of expression by E2 in the ovarian tissue. In situ hybridization revealed a strong 5-HTpy signal in the oocytes, spermatids, and ciliary epithelium of the gonoducts in the ovary and testis. These results suggest that the effects of 5-HT on the induction of oocyte maturation, sperm motility, and transport of mature oocytes and sperm through the ciliated epithelium of the gonoducts are mediated by 5-HTpy.