Abstract
BackgroundIn mammals, pheromones play an important role in social and innate reproductive behavior within species. In rodents, vomeronasal receptor type 1 (V1R), which is specifically expressed in the vomeronasal organ, is thought to detect pheromones. The V1R gene repertoire differs dramatically between mammalian species, and the presence of species-specific V1R subfamilies in mouse and rat suggests that V1R plays a profound role in species-specific recognition of pheromones. In ruminants, however, the molecular mechanism(s) for pheromone perception is not well understood. Interestingly, goat male pheromone, which can induce out-of-season ovulation in anestrous females, causes the same pheromone response in sheep, and vice versa, suggesting that there may be mechanisms for detecting "inter-species" pheromones among ruminant species.ResultsWe isolated 23 goat and 21 sheep intact V1R genes based on sequence similarity with 32 cow V1R genes in the cow genome database. We found that all of the goat and sheep V1R genes have orthologs in their cross-species counterparts among these three ruminant species and that the sequence identity of V1R orthologous pairs among these ruminants is much higher than that of mouse-rat V1R orthologous pairs. Furthermore, all goat V1Rs examined thus far are expressed not only in the vomeronasal organ but also in the main olfactory epithelium.ConclusionOur results suggest that, compared with rodents, the repertoire of orthologous V1R genes is remarkably conserved among the ruminants cow, sheep and goat. We predict that these orthologous V1Rs can detect the same or closely related chemical compound(s) within each orthologous set/pair. Furthermore, all identified goat V1Rs are expressed in the vomeronasal organ and the main olfactory epithelium, suggesting that V1R-mediated ligand information can be detected and processed by both the main and accessory olfactory systems. The fact that ruminant and rodent V1Rs have distinct features suggests that ruminant and rodent V1Rs have evolved distinct functions.
Highlights
In mammals, pheromones play an important role in social and innate reproductive behavior within species
Isolation of the goat and sheep V1R genes Based on sequence similarity with 32 previously reported cow V1R genes [21], we identified 23 goat and 21 sheep V1R genes
We isolated these V1R genes using degenerate primers, which were designed based on conserved sequences present in each V1R subfamily among the various vertebrate species
Summary
Pheromones play an important role in social and innate reproductive behavior within species. The vomeronasal receptor type 1 (V1R) [9,10] and V2R [1113] families are expressed in sensory neurons of the rodent VNO Both receptor types belong to the seven-transmembrane domain G protein-coupled receptor family, but they share no sequence similarity. The deletion of 16 mouse V1R genes results in altered social behavior and loss of vomeronasal neuron responsiveness to specific pheromones [14], and V1R (V1Rb2) responds to the mouse pheromone, 2-heptanone [15] These results indicate that V1R functions as a pheromone receptor. Mouse V2R-expressing vomeronasal neurons recognize exocrine gland-secreting peptide 1 [16] They respond to certain pheromone candidates, such as major histocompatibility complex ligand peptide [17] and mouse urinary protein [18]. These results suggest that V2R functions as a pheromone receptor
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