vomeronasal organ pheromone receptor type-1 family, member of the seven-transmembrane G protein-coupled receptor superfamily
This family represents vomeronasal type-1 receptors (V1Rs) that are specifically expressed in the vomeronasal organ (VNO), which is the sensory organ of the accessory olfactory system present in amphibians, reptiles, and non-primate mammals such as mice and rodents, but it is non-functional or absent in humans, apes and monkeys. The VNO detects pheromones, chemicals released from animals that can influence social and reproductive behaviors, such as male-male aggression or sexual mating, in other members of the same species. On the other hand, the olfactory epithelium, which contains olfactory receptor neurons inside the nasal cavity, is responsible for detecting odor molecules (smells). There are two types of vertebrate pheromones: (1) small volatile molecules such as 2-heptanone, a substance in the urine of both male and female that extends estrous cycle length in female mice; and (2) water-soluble molecules such as the major histocompatibility complex (HMC) class-I peptide, which can induce the pregnancy block effect, the tendency for female rodents to abort their pregnancies upon exposure to the scent of an unknown male. While V1Rs and G-alpha(i2) protein are co-expressed in the apical neurons of the VNO, V2Rs (type-2 vomeronasal receptors) and G-alpha(o) protein are coexpressed in the basal layer of the VNO. Activation of V1R or V2R causes stimulation of phospholipase pathway, generating diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3). V1Rs have a short N-terminal extracellular domain, whereas V2Rs contain a long N-terminal extracellular domain, which is believed to bind pheromones. Although V1Rs share the seven-transmembrane domain structure with V1Rs and olfactory receptors, they share little sequence similarity with each other.