The repertoire of G-protein-coupled receptors in Xenopus tropicalis

Background: The G-protein-coupled receptor (GPCR) superfamily represents the largest protein family in the human genome. These proteins have a variety of physiological functions that give them well recognized roles in clinical medicine. In Xenopus tropicalis, a widely used animal model for physiology research, the repertoire of GPCRs may help link the GPCR evolutionary history in vertebrates from teleost fish to mammals. Results: We have identified 1452 GPCRs in the X. tropicalis genome. Phylogenetic analyses classified these receptors into the following seven families: Glutamate, Rhodopsin, Adhesion, Frizzled, Secretin, Taste 2 and Vomeronasal 1. Nearly 70% of X. tropicalis GPCRs are represented by the following three types of receptors thought to receive chemosensory information from the outside world: olfactory, vomeronasal 1 and vomeronasal 2 receptors. Conclusion: X. tropicalis shares a more similar repertoire of GPCRs with mammals than it does with fish. An examination of the three major groups of receptors related to olfactory/pheromone detection shows that in X. tropicalis, these groups have undergone lineage specific expansion. A comparison of GPCRs in X. tropicalis, teleost fish and mammals reveals the GPCR evolutionary history in vertebrates.