Characterization of vomeronasal receptor families in the deer mouse Peromyscus maniculatus

Chemical communication by means of pheromones is central to the mating systems of a wide range of organisms. Since mate choice and subsequently, reproductive isolation, are often based on pheromone differences, understanding how pheromone systems diverge is necessary for a complete understanding of the evolutionary process. Because chemoreceptors are the first elements in a cascade of events ultimately modulating behaviors, changes that affect their biochemical properties or expression pattern have the potential to modulate specific behavioral responses. In particular, the activation of sensory neurons in the vomeronasal organ (VNO) is directly associated with behavioral changes, such as aggression, avoidance or mating. The aim of this study is take advantage of recent advances made in our understanding of the molecular bases pheromone and semiochemical detection in the laboratory mouse Mus musculus and apply that knowledge to understand the evolution of pheromone systems in wild populations. To achieve this goal, we are studying deer mice (genus Peromyscus), which diverged from Mus approximately 25 MYA. Here we report on the characterization of vomeronasal receptors (VRs) from one species, P. maniculatus.
We find striking differences in VR repertoire between these two rodent species. First we queried protein sequences of all predicted M. musculus V1Rs and V2Rs against the P. maniculatus genome . In total, we identified 150 and 90 putative V1R and V2R genes, respectively, in the Peromyscus genome, fewer than in M. musculus (239 and 120, respectively). While clades previously identified in the Mus have representatives in Peromyscus, our phylogenetic reconstructions indicate that most gene duplications took place after the split between the two lineages, with few orthologs between species. In V1Rs, several clades show sign of expansion (i.e. V1Re, V1Rl) or contraction (i.e. V1Ra, V1Rc, V1Rd). In V2Rs, many expansions are lineage-specific with several clades identified in Mus having few or no representative in Peromyscus and vice versa. The differences in the chemosensory receptor repertoires likely reflect difference in habitat as well as social and mating behavior of deer mice. Ongoing RNA-Seq experiments will determine which of these receptors are expressed in male and female adults and which will be targets for functional characterization.