Analysis of a putative VPAC2 receptor from sturgeon shed light on molecular and functional evolution of VPAC2R in vertebrates

Abstract

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) are structurally related neuropeptides that exert multiple physiological effects in our body. Their actions are mediated through the activation of three receptors: PAC1R, VPAC1R, and VPAC2R. Despite the importance of these intercellular communicators, there is little information available for PACAP, VIP, and their receptors in extant early vertebrate species. In this study, a full-length VPAC2R cDNA was identified from a sturgeon species, Acipenser schrenskii. This cDNA is 1,498 bp in length encoding for a protein with 427 amino acids. Phylogenetic analysis showed that the sturgeon VPAC2R is structurally more similar to tetrapod VPAC2Rs than teleost VPAC2Rs or PHIRs. By real-time PCR, it was found that the sturgeon VPAC2R was widely distributed in various tissues, with the highest expression in gut and with moderate expression in liver and gonad. In functional cAMP assays, the sturgeon VPAC2R could be stimulated by mammalian and fish VIPs but not human and fish PHIs and PACAPs. These data suggested that the ability of VPAC2R to interact with PACAP evolved after the teleost/ tetrapod split in the tetrapod lineage. Moreover, the previously isolated fish PHIRs which are structurally related to VPAC2Rs in vertebrates may exist only in teleosts via the teleost-specific 3R genome duplication.