Identification of protein pheromones that promote aggressive behaviour

Abstract

Mice use pheromones, compounds emitted and detected by members of the same species, as cues to regulate social behaviours such as pup suckling, aggression and mating. Neurons that detect pheromones are thought to reside in at least two separate organs within the nasal cavity: the vomeronasal organ (VNO) and the main olfactory epithelium (MOE). Each pheromone ligand is thought to activate a dedicated subset of these sensory neurons. However, the nature of the pheromone cues and the identity of the responding neurons that regulate specific social behaviours are largely unknown. Here we show, by direct activation of sensory neurons and analysis of behaviour, that at least two chemically distinct ligands are sufficient to promote male-male aggression and stimulate VNO neurons. We have purified and analysed one of these classes of ligand and found its specific aggression-promoting activity to be dependent on the presence of the protein component of the major urinary protein (MUP) complex, which is known to comprise specialized lipocalin proteins bound to small organic molecules. Using calcium imaging of dissociated vomeronasal neurons (VNs), we have determined that the MUP protein activates a sensory neuron subfamily characterized by the expression of the G-protein Galpha(o) subunit (also known as Gnao) and Vmn2r putative pheromone receptors (V2Rs). Genomic analysis indicates species-specific co-expansions of MUPs and V2Rs, as would be expected among pheromone-signalling components. Finally, we show that the aggressive behaviour induced by the MUPs occurs exclusively through VNO neuronal circuits. Our results substantiate the idea of MUP proteins as pheromone ligands that mediate male-male aggression through the accessory olfactory neural pathway.

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

“…The available data indicate that intermale aggression is mediated by the non-volatile, V2R detected major urinary proteins Mup3 and Mup20 (Kaur et al, 2014), but the volatile cues that promote aggression (detected through V1R) have not been identified yet. Surprisingly, whereas in wild-type mice one of these chemosignals alone (the LMW urine fraction, or recombinant MUPs) is able to elicit aggression against castrated males (Chamero et al, 2007), lack of function in one of the subsystems of the VNO (e.g. Gi2 -/-mutants, Norlin et al, 2003; cGo -/-mutants, Chamero et al, 2011) virtually abolishes intermale and maternal aggression.…”

“…When detected by vomeronasal organ, ESP1 stimulates lordosis in females (Haga et al, 2010), whereas some MUPs have been shown to elicit aggression and countermarking in males (Chamero et al, 2007;Kaur et al, 2014) and attraction in females (Roberts et al, 2010). In addition, type I MHC peptides, showing low volatility, may also act as chemosignals that allow mate recognition in the context of the induction of pregnancy failure (Bruce effect; Leinders-Zufall et al, 2004).…”

“…More recently, Chamero et al (2007) analysed the presence of intermale aggressionpromoting compounds in the urine of male mice. To do so, they first fractioned urine into a low molecular weight fraction (LMW) containing most free volatiles, and a high molecular weight fraction (HMW) composed mainly of MUPs and their accompanying volatile ligands.…”

“…MUPs activate basal (Kaur et al, 2014), Go-expressing cells (Chamero et al, 2007), very likely through V2R receptors. For this activation to occur, 2-microglobulin is needed, thus fully…”

Extraordinary Diversity of Chemosensory Receptor Gene Repertoires Among Vertebrates

“…Interestingly, these two gene families share with the V2R family the rapid birth-and-death evolutionary pattern. Very recently, major urinary proteins were identified as V2R-recognizing pheromones in mice and the major urinary protein family size was found to covary with the V2R family size across vertebrates (Chamero et al 2007) . A similar story can be told for the transient receptor potential channel C2 (TRPC2) gene, which encodes an ion channel indispensable for vomeronasal signal transduction.…”