Divergent V1R repertoires in five species: Amplification in rodents, decimation in primates, and a surprisingly small repertoire in dogs

The VIR gene family comprises one of two types Of Putative pheromone receptors expressed in the mammalian vomeronasal organ (VNO). We searched the most recent Mouse, rat, dog, chimpanzee, and human genome Sequence assemblies to compile a near-complete repertoire of VIR genes for each species. Dog, human, and chimpanzee have very few intact VIRs (8, 2, and 0, respectively) compared to more than a hundred intact VIRs ill each of the rat (106) and Mouse (165) genomes. We also provide the first description of the diversity of VIP pseudogenes in these species. We identify at least 165 pseudogenes in mouse, II0 in rat, 102 in chimpanzee, II5 in human, and 54 in dog. Primate and dog pseudogenes are distributed among almost all VIR Subfamilies seen in rodents, indicating that the common ancestor of these species had a diverse VIP repertoire. We find that VIR genes were Subject to strikingly different fates in different species and in different Subfamilies. In rodents, some Subfamilies remained relatively stable or underwent roughly equivalent expansion in mouse and rat; other subfamilies expanded in one species but not the other. The small number of intact VIRs ill the clog genome is unexpected given the presumption that dogs, like rodents, have a functional VNO, and a complex system of pheromone-based behaviors. We identify an intact transient receptor potential channel 2beta in the dog genome, consistent with a functional VNO in dogs. The diminished VIR repertoire in dogs raises questions about the relative contributions of VIRs versus other candidate pheromone receptor genes in the establishment of complex pheromone systems in mammals.