Selective G protein βγ-subunit compositions mediate phospholipase C activation in the vomeronasal organ

Abstract

Chemosensory neurons of the vomeronasal organ (VNO) are supposed to detect pheromones controlling social and reproductive behavior in most terrestrial vertebrates. Recent studies indicate that pheromone signaling in VNO neurons is mediated via phospholipase C (PLC) activation generating the two second messengers inositol-1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). Since Gαi and Gαo predominantly expressed in VNO neurons are usually not involved in activating PLC, it was explored if PLC activation may be mediated by Gβγ subunits. It was found that a scavenger for βγ dimers reduced the urine-induced IP3 formation in VNO preparations in a dose-dependent manner indicating a role for Gβγ complexes. Towards an identification of the relevant Gβ and Gγ subunit(s), PCR approaches as well as immunohistochemical experiments were performed. It was found that out of the five known Gβ subtypes, only Gβ2 was expressed in both Gαi as well as Gαo neurons. Experimental approaches focusing on the spatial expression profile of identified Gγ subtypes revealed that Gγ8-positive neurons are preferentially localized to the basal region of the vomeronasal epithelium, whereas Gγ2-reactive cells are restricted to the apical Gαi-positive layer of the sensory epithelium. As IP3 formation induced upon stimulation with volatile urinary compounds was selectively blocked by Gγ2-specific antibodies whereas second messenger formation elicited upon stimulation with α2u globulin was inhibited by antibodies recognizing Gγ8, it is conceivable that PLC activation in the two populations of chemosensory VNO neurons is mediated by different Gβγ complexes.