Identification of V1R-like Putative Pheromone Receptor Sequences in Non-human Primates. Characterization of V1R Pseudogenes in Marmoset, a Primate Species that Possesses an Intact Vomeronasal Organ

The vomeronasal organ (VNO) is responsible in terrestrial vertebrates for the sensory perception of some pheromones, chemicals that elicit characteristic behaviors among individuals of the same species. Two multigene families (V1R, V2R) that encode proteins with seven putative transmembrane domains that are expressed selectively in different neuron subsets of the VNO have been described in rodents. Pheromone-induced behaviors and a functional VNO have been described in a number of mammals, but this sensory organ seems absent in adult catarrhines and apes, including humans. Until now, only pseudogenes have been isolated in humans, except one putative V1R (hV1RL1) sequence expressed in the main olfactory epithelium. We sought to isolate V1R-like genes in a New World monkey species, the marmoset Callithrix jacchus, that possesses an intact VNO and for which pheromone-induced behavior has been well documented. Using library screening approaches, we have identified five different sequences that exhibit characteristic features of V1R sequences, but that are non-functional pseudogenes. In an attempt to sort out functional V1R genes, we next cloned by polymerase chain reaction (PCR) the primate orthologues of hV1RL1. This approach was successful for gorilla, chimpanzee and orangutan, but not for the other species, including marmoset, probably because these species are too divergent from humans. Chimpanzee and orangutan V1RL1 genes are pseudogenes, whereas the gorilla counterpart is potentially functional. These observations raise the possibility that the V1R family has evolved in such a manner in mammals that every species that relies on a VNO-mediated sensory function possesses its own set of functional vomeronasal genes.