G protein Gαo is essential for vomeronasal function and aggressive behavior in mice

Abstract

The rodent vomeronasal organ (VNO) mediates the regulation of species-specific and interspecies social behaviors. We have used gene targeting to examine the role of the G protein Gαo, encoded by the gene Gnao1, in vomeronasal function. We used the Cre-loxP system to delete Gαo in those cells that express olfactory marker protein, which includes all vomeronasal sensory neurons of the basal layer of the VNO sensory epithelium. Using electrophysiology and calcium imaging, we show that the conditional null mice exhibit strikingly reduced sensory responses in V2R receptor-expressing vomeronasal sensory neurons to specific molecular cues, including MHC1 antigens, major urinary proteins, and exocrine gland-secreting peptide. Gαo is also vital for vomeronasal sensing of two Nformylated mitochondrially encoded peptides derived from NADH dehydrogenase 1. Furthermore, we show that Gαo is an essential requirement for the display of male-male territorial aggression as well as maternal aggression in mice. Finally, we show that Gαo-dependent maternal aggression can be induced by major urinary proteins. These cellular and behavioral phenotypes identify Gαo as the primary G-protein α-subunit mediating the detection of peptide and protein pheromones by sensory neurons of the VNO.formyl peptide receptor | olfaction | peptide detection | Trpc2 | social recognition T he mammalian olfactory system comprises a complex array of subsystems, but the functional significance of this organization remains unclear (1). The mouse vomeronasal organ (VNO)-which has attracted specific attention because of its vital role in social communication (2, 3)-consists of at least two distinct layers containing apical (superficial) and basal (deep) populations of vomeronasal sensory neurons (VSNs), which project their axons to discrete regions of the accessory olfactory bulb (AOB) (4-6). These VSN populations are characterized by differential expression of heterotrimeric G proteins and G proteincoupled receptors (GPCRs): apical VSNs express Gαi2 and members of the V1R family of vomeronasal GPCRs (7), whereas basal VSNs express Gαo and members of the V2R receptor family (8-10). VSNs of both layers express the transient receptor potential channel Trpc2 (11-13). Whether these two VNO subsystems function in relative isolation, each specialized to control a distinct subset of social behaviors, or whether they work in a cooperative and integrative manner remains unclear.A series of gene deletion studies has revealed an obligate requirement of Trpc2 (12-14) and at least some V1Rs (15, 16) and V2Rs (17, 18) for the generation of sensory responses in VSN populations. Together, these studies support a model of VSN signaling in which receptor occupancy, through G-protein coupling, causes activation of phospholipase C (PLC) that, in turn, leads to the activation of a Ca 2+ -permeable, Trpc2-dependent cation channel (19). Ca 2+ entry through this channel mediates both negative and positive VSN feedback regulation through calmodulin-dependent sensory adaptation and down...

Mouse urinary peptides provide a molecular basis for genotype discrimination by nasal sensory neurons

“…We used acute VNO tissue slices of B6 mice and high-resolution confocal microscopy to image cellular Ca 2 þ responses to peptide or urine stimulation 21,23,48 . Our previous findings have already established that synthetic MHC peptides are powerful ligands for V2R-expressing VSNs located in the Gao-expressing layer of the VNO 21,23,24 , that a given peptide is detected by more than one V2R receptor 23 and that single amino-acid exchanges within peptides can be distinguished by VSNs 23 . Here, we asked whether individual VSNs are capable of detecting SIINFEKL at relevant concentrations.…”

“…This immunological signature must be interpreted by the olfactory system. It is now well established that, in freely behaving mice, nonvolatile peptides gain access to sensory neurons of both the main olfactory system and the VNO during behavioural situations involving direct physical contact 21,22 , that such peptides are powerful ligands for subsets of vomeronasal and olfactory sensory neurons [21][22][23][24][25] (VSNs and OSNs, respectively), that they induce brain activity downstream from the sensory neurons in vivo 26 , and that synthetic MHC peptide ligands can be discriminated in social preference tests 22 and influence social learning and reproductive function in the context of the Bruce effect test 21 . However, it is important to note that there is also considerable evidence for the use of MHC-independent, individual identity signatures in mice in specific behavioural contexts 27,28 (but see the discussion in Ruff et al 29 ).…”

From sexual attraction to maternal aggression: When pheromones change their behavioural significance

“…This is further supported by behavioural analysis of specific mutants for the G proteins associated to these receptors, namely Gi2 for V1R and Go for V2R (see Fortes-Marco et al, 2013), which differ in their  subunit. In relation to V2R-mediated chemoreception, Go mutants (Chamero et al, 2011) show reduced intermale and maternal aggression. In addition, Loconto et al (2003) analysed a mouse mutant line knockout for β2-microglobulin (generated by Zijlstra et al, 1990), a protein expressed in vomeronasal neurons where it contributes to escort V2R to the cell surface.…”

“…This suggests that, simultaneous signalling through both V1R and V2R receptors is required for the expression of aggression. When one or the other vomeronasal subsystems fails, no aggression is expressed (Chamero et al, 2011). Importantly, AC3 -/-dams do not show maternal aggression (Wang and Storm, 2011).…”

“…17 approaching the nest (see below and Chamero et al, 2011), there is no direct evidence that brevicomin and/or thiazoline are involved in maternal aggression.…”