Xenopus V1R vomeronasal receptor family is expressed in the main olfactory system

To date, over 100 vomeronasal receptor type 1 (V1R) genes have been identified in rodents. V1R is specifically expressed in the rodent vomeronasal organ (VNO) and is thought to be responsible for pheromone reception. Recently, 21 putatively functional V1R genes were identified in the genome database of the amphibian Xenopus tropicalis. Amphibians are the first vertebrates to possess a VNO. In order to determine at which point during evolution the vertebrate V1R genes began to function in the vomeronasal system, we analyzed the expression of all putatively functional V1R genes in Xenopus olfactory organs. We found that V1R expression was not detected in the VNO but was specifically detected in the main olfactory epithelium (MOE). We also observed that V1R-expressing cells in the MOE coexpressed Gi2, thus suggesting that the V1R-Gi2-mediated signal transduction pathway, which is considered to play an important role in pheromone reception in the rodent VNO, exists in the amphibian MOE. These results suggest that V1R-mediated signal transduction pathway functions in Xenopus main olfactory system.