Alternative splicing of a single precursor mRNA generates two subtypes of Gonadotropin-Releasing Hormone receptor orthologues and their variants in the bivalve mollusc Crassostrea gigas.

Despite their economic importance, only very little information is available regarding (neuro)endocrine regulation of reproduction in bivalve molluscs. To gain insights into the molecular control of gonadic development of these animals, G protein-coupled receptors (GPCR) specifically expressed in the gonad of the pacific oyster Crassostrea gigas were investigated. One such receptor, Cg-GnRH-R, an oyster GPCR orthologue of vertebrate GnRH receptors clearly involved in the control of oyster gametogenesis was first identified [Rodet, F., Lelong, C., Dubos, M.P., Costil, K. and Favrel, P., 2005. Molecular cloning of a molluscan Gonadotropin-Releasing Hormone receptor orthologue specifically expressed in the gonad. Biochim Biophys Acta 1730 187-95.]. We report here the characterization of multiple transcripts encoding GnRH-R orthologues (Cg-GnRH-RII-L/Cg-GnRH-RII-S) including a truncated receptor (Cg-GnRH-R-TF) and demonstrate they are generated by the alternative splicing of a single mRNA precursor. The differential structure of these receptors suggests that Cg-GnRH-R on one hand and Cg-GnRH-RII-L/Cg-GnRH-RII-S on the other hand constitute two receptor subtypes with regard to ligand specificity. Pattern of expression of these transcripts suggests that Cg-GnRH-R cognate ligand is specifically involved in the control of gametogenesis while Cg-GnRH-RII-L and Cg-GnRH-RII-S ones likely do not control reproductive functions specifically. Hypothesis on the involvement of this family of receptors in signalling both GnRH and APGWamide in molluscs is discussed.