Expression of a vomeronasal receptor gene (V1r) and G protein α subunits in goat, Capra hircus, olfactory receptor neurons

Abstract

Most mammals have two distinct olfactory epithelia, the olfactory epithelium (OE) and vomeronasal epithelium (VNE), containing, respectively, olfactory receptor neurons (ORNs) and vomeronasal receptor neurons (VRNs). Olfactory receptors (ORs), which couple to G alpha olf, are generally expressed by ORNs, whereas two vomeronasal receptor families (V1rs and V2rs) coupled respectively to G alpha i2 and G alpha o, are expressed by VRNs. Previously, we reported that one goat V1rs (gV1ra1) is expressed by ORNs and VRNs. To investigate the characteristics of vomeronasal-receptor-expressing ORNs in mammals we performed double-label in situ hybridization for gV1ra1, G alpha i2, G alpha olf, olfactory marker protein (OMP), and growth association protein 43 (GAP43). Goat V1r-expressing ORNs are categorized into two types situated in different areas of the epithelium. The first type of V1r-expressing ORN coexpressed G alpha i2, but not OMP or GAP43. The second type of V1r-expressing ORN expresses G alpha olf and OMP, but not G alpha i2 or GAP43. These findings suggest that the two types of V1r-expressing ORN in goat OE function using different G protein alpha subunits for chemoreception.

Diverse Systems for Pheromone Perception: Multiple Receptor Families in Two Olfactory Systems

“…Preventing the VNO from functioning does not affect the female responses to the male pheromone, thus suggesting that the main olfactory system plays a role in the perception of the pheromone, although the vomeronasal system also seems to function (Gelez and Fabre-Nys, 2004). Interestingly, in contrast to rodents, goat V1R genes are expressed in both the VNO and the OE (Wakabayashi et al, 2002;Wakabayashi et al, 2007). These results may support the notion that V1Rs are good candidates for the goat pheromone receptors.…”

“…It should be noted that some goat V1R-expressing cells in the OE co-express Golf (Wakabayashi et al, 2007), thus implying that a similar signal transduction pathway mediated by V1R-Golf exists in both humans and goats.…”

The Role of the Terminal Nerve and GnRH in Olfactory System Neuromodulation

“…Interestingly, members of these two families have also been found to be expressed in small numbers in the olfactory epithelium of frogs (Xenopus laevis, Date-Ito et al, 2008), goats (Capra hircus, Wakabayashi et al, 2002;Wakabayashi et al, 2007), mice (Mus musculus, Karunadasa et al, 2006), and humans (Rodriguez et al, 2000). The phylogenetic diversity of these animals indicates that olfactory epithelial expression of V1R and V2R genes may be widespread among tetrapods, suggesting the existence of four classes of olfactory receptor neurons: those expressing ORs, TAARs, V1Rs, and V2Rs.…”

Existence of Gα<i>_i2</i>-Expressing Axon Terminals in the Goat Main Olfactory Bulb

“…However, Gα o is not expressed in the goat VNO [8], and functional V2R genes have not been identified in goat genome [10], suggesting that goats have only the V1R-Gα i2 pathway in the vomeronasal SNs. In addition, V1R/Gα i2 -expressing SNs exist not only in the VNO but also in the OE [11]. Thus, it would be interesting to know whether a subset of the Gα i2 -expressing axons projects to the MOB and forms glomeruli in it, even though the goat AOB has been reported to receive the Gα i2 -expressing axon terminals [8].…”

“…In goats, however, no Grueneberg ganglion has been identified, and Gα o was not expressed in the Gα i2 -immunoreactive clusters in the MOB (data not shown). Considering that the V1R/Gα i2 -expressing SNs are found in both VNO and OE [11], some V1R/Gα i2 -expressing mature SNs in the OE and/ or VNO are likely to project their axons to the MOB in goats. Previous reports showed that the OE is required to detect the male effect pheromone in goats and sheep [3].…”