Molecular cloning, expression patterns and functional characterization of Gpr3 in the orange-spotted grouper (Epinephelus coioides)

G Protein-coupled receptor 3 (Gpr3) plays a critical role in maintaining oocyte meiotic arrest in mammals. To ascertain the function of Gpr3 in oocyte maturation in fish, the Gpr3 cDNA was cloned from orange-spotted grouper (Epinephelus coioides). The open reading frame of cloned sequence was 993 bp in length, encoding 330 amino acids. Gpr3 was primarily expressed in brain regions and ovary. During oocyte maturation induced by human chorionic gonadotropin (hCG), Gpr3 expression levels were dramatically elevated in follicular cell layers. Functional analysis showed that Gpr3 could constitutively active the cAMP/PKA signaling pathway, and hCG treatment activated Gpr3 promoter activities in cultured eukaryotic cells expressing luteinizing hormone receptors (LHRs). Finally, the role of Gpr3 in oocyte maturation was studied. Sphingosine 1-phosphate (S1P), an agonist of Gpr3, had no effect on oocyte maturation in vivo, suggesting that Gpr3 may be not involved in oocyte maturation in orange-spotted grouper.