Abstract
BACKGROUND: G protein-coupled receptors (GPCRs) are one of the largest families of genes in mammals. Branchiostoma floridae (amphioxus) is one of the species most closely related species to vertebrates. RESULTS: Mining and phylogenetic analysis of the amphioxus genome showed the presence of at least 664 distinct GPCRs distributed among all the main families of GPCRs; Glutamate (18), Rhodopsin (570), Adhesion (37), Frizzled (6) and Secretin (16). Surprisingly, the Adhesion GPCR repertoire in amphioxus includes receptors with many new domains not previously observed in this family. We found many Rhodopsin GPCRs from all main groups including many amine and peptide binding receptors and several previously uncharacterized expansions were also identified. This genome has however no genes coding for bitter taste receptors (TAS2), the sweet and umami (TAS1), pheromone (VR1 or VR2) or mammalian olfactory receptors. CONCLUSION: The amphioxus genome is remarkably rich in various GPCR subtypes while the main GPCR groups known to sense exogenous substances (such as Taste 2, mammalian olfactory, nematode chemosensory, gustatory, vomeronasal and odorant receptors) in other bilateral species are absent.