On the saliva proteome of the Eastern European house mouse (Mus musculus musculus) focusing on sexual signalling and immunity

Abstract

Chemical communication is mediated by sex-biased signals abundantly present in the urine, saliva and tears. Because most studies concentrated on the urinary signals, we aimed to determine the saliva proteome in wild Mus musculus musculus, to extend the knowledge on potential roles of saliva in chemical communication. We performed the gel-free quantitative LC-MS/MS analyses of saliva and identified 633 proteins with 134 (21%) of them being sexually dimorphic. They include proteins that protect and transport volatile organic compounds in their beta barrel including LCN lipocalins, major urinary proteins (MUPs), and odorant binding proteins (OBPs). To our surprise, the saliva proteome contains one MUP that is female biased (MUP8) and the two protein pheromones MUP20 (or ‘Darcin’) and ESP1 in individuals of both sex. Thus, contrary to previous assumptions, our findings reveal that these proteins cannot function as male-unique signals. Our study also demonstrates that many olfactory proteins (e.g. LCNs, and OBPs) are not expressed by submandibular glands but are produced elsewhere–in nasal and lacrimal tissues, and potentially also in other oro-facial glands. We have also detected abundant proteins that are involved in wound healing, immune and non-immune responses to pathogens, thus corroborating that saliva has important protective roles.

On the tear proteome of the house mouse (Mus musculus musculus) in relation to chemical signalling

“…Interestingly, those lipocalins that are produced by lacrimal and nasal tissues, are finally transported to the oral cavity where they are detectable in saliva (Stopka et al, 2016). These proteins are also spread onto the fur with saliva during selfgrooming where they may function as chemical signals.…”

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“…Lacrimal expression of Mup4 and the presence of MUP4 with its ligands in the mouse tears (i.e. along with other signals) and saliva (Stopka et al 2016) may explain the observation of Luo et al (Luo et al 2003;Luo & Katz 2004), who reported that mouth and facial areas are the first and the most frequently investigated areas during mouse social contacts. Moreover, these areas are investigated longer and more frequently in comparison with investigation of the anogenital region.…”

“…The signals that are transported by MUPs or MUPs themselves have been shown to regulate reproductive behaviour of the receiver (Janotova & Stopka 2011;Ma et al 1999;Novotny et al 1986;Roberts et al 2010;Stopka et al 2007), MUPs have a predictive value for the onset of aggressive behaviour and dispersal tendency in male wild house mice (Rusu et al 2008), and one particular MUP -MUP20 or 'Darcin', which in M. m. domesticus is prevailingly expressed by males, has been reported to predict the outcome of malemale territorial competition (Nelson et al 2015), stimulates inherent female attraction for particular males (Roberts et al 2010), and its level decreases in immune-challenged male mice (Lopes & Konig 2016) which presumably shows that the production of MUP20 / MUPs is costly. In M. m. musculus, however, MUP20 was also detected in the saliva of males and females (Stopka et al 2016). Moreover, MUPs and other lipocalins (e.g.…”

“…For example, in our recent study, we have determined the mRNA expression sites for a newly described family of odorant binding proteins (OBP) and provided evidence that the extraorbital lacrimal glands produce high quantities of mRNAs coding OBP5, OBP6, OBP7 and also MUP4, MUP5, and LCN11 (Stopkova et al 2016). Interestingly, most of those lipocalins that are produced by olfactory, vomeronasal, and nasal-associated lymphoid tissues, are finally transported to the oral cavity where digestion starts (Stopka et al 2016). Furthermore, lacrimal glands contain large quantities of transporters of chemical signals essential for sexual signalling during lacrimation, and then during selfgrooming the signals are spread onto the fur with saliva (i.e.…”

“…Therefore, bacteria acquire iron by secretion of high-affinity iron sequestrating siderophores. The mammalian host, however, limits this process by the production of LCN2 (Goetz et al 2002) which efficiently scavenges for catecholate-type siderophores (Flo et al 2004), and is equally expressed by individuals of both sex in mouse saliva (Stopka et al 2016). Other mechanisms of defence involve bactericidal proteins from the PLUNC (palate, lung, and nasal epithelium clone) protein family, defending the mucosal layers of the body against pathogenic microbiota.…”