Laboratoire de Neurobiologie, Communication Chimique, CNRS-UPR 9024, 31 chemin Joseph-Aiguier, 13402, Marseille Cedex 20, France.
In mammals, the vomeronasal organ (VNO) is an anatomically distinct part of the olfactory system. The VNO detects chemical signals (pheromones) produced and received across both sexes. Recent molecular biological investigations have characterized two large multigene families of putative G-protein linked receptors (V1Rs and V2Rs), probably involved in the pheromone detection. The purpose of this study carried out using the VNO of Rattus norvegicus (Wistar) was to obtain a sufficient number of pheromone receptor sequences to allow a meaningful comparison with previously determined homologous sequences from vertebrates. We foccused this study on the V1R family. By RT-PCR, using mRNA from male and female VNOs and primers constructed with consensus sequences, we amplify and clone 33 different putative pheromone receptors -twenty-four from the female, ten from the male. Only one sequence presents 100% identity in the both sexes. These 33 sequences exhibit a high similarity with previously reported mammal pheromone receptors, and classify them unambiguously as members of the same superfamily of seven transmembrane domain receptors. Transmembrane helical regions IV, V, VI and VII as well the extra and intracellular loop regions were delineated using anhydropathy plot. Variabilities are found located within the second and third predicted extracellular loops, and within the fifth and sixth predicted transmembrane domains. We propose that these positions may be part of the specific binding site for pheromones. Comparisons with pheromone receptor sequences from other species suggest that the sequences described in this study belong to three different subfamilies of the V1R class.