Regulation of highly homologous major urinary proteins in house mice quantified with label-free proteomic methods

Variation in mouse chemical signals is genetically controlled and environmentally modulated

In most mammals and particularly in mice, chemical communication relies on the detection of ethologically relevant fitness-related cues from other individuals. In mice, urine is the primary source of these signals, so we employed proteomics and metabolomics to identify key components of chemical signalling. We show that there is a correspondence between urinary volatiles and proteins in the representation of genetic background, sex and environment in two house mouse subspecies Mus musculus musculus and M. m. domesticus. We found that environment has a strong influence upon proteomic and metabolomic variation and that volatile mixtures better represent males while females have surprisingly more sex-biased proteins. Using machine learning and combined-omics techniques, we identified mixtures of metabolites and proteins that are associated with biological features.

Nephrotoxicity evaluation and proteomic analysis in kidneys of rats exposed to thioacetamide

Thioacetamide (TAA) was administered orally at 0, 10, and 30 mg/kg body weight (BW) daily to Sprague–Dawley rats aged 6–7 weeks for 28 consecutive days. Nephrotoxicity and proteomics were evaluated in the kidneys of rats exposed to TAA. The BW decreased, however, the relative kidneys weight increased. No significant histopathologic abnormalities were found in the kidneys. The numbers of monocytes and platelets were significantly increased. However, the mean corpuscular volume and hematocrit values were decreased significantly in rats exposed to 30 mg/kg BW TAA. The expression levels of Kim-1 and NGAL were increased 4 to 5-fold in the kidneys, resulting in significant nephrotoxicity. Proteomic analysis was conducted and a total of 5221 proteins spots were resolved. Of these, 3 and 21 protein spots were up- and downregulated, respectively. The validation of seven proteins was performed by Western blot analysis. The expression level of ASAP2 was significantly upregulated, whereas RGS14, MAP7Dl, IL-3Rα, Tmod1, NQO2, and MUP were reduced. Sixteen isoforms of MUP were found by the 2DE immunoblot assay and were significantly downregulated with increasing exposure to TAA. MUP isoforms were compared in the liver, kidneys, and urine of untreated rats and a total of 43 isoforms were found.

Regulation of Sexually Dimorphic Expression of Major Urinary Proteins

Male house mice excrete large amounts of protein in their urinary scent marks, mainly composed of Major Urinary Proteins (MUPs), and these lipocalins function as pheromones and pheromone carriers. Here, we review studies on sexually dimorphic MUP expression in house mice, including the proximate mechanisms controlling MUP gene expression and their adaptive functions. Males excrete 2 to 8 times more urinary protein than females, though there is enormous variation in gene expression across loci in both sexes. MUP expression is dynamically regulated depending upon a variety of factors. Males regulate MUP expression according to social status, whereas females do not, and males regulate expression depending upon health and condition. Male-biased MUP expression is regulated by pituitary secretion of growth hormone (GH), which binds receptors in the liver, activating the JAK2-STAT5 signaling pathway, chromatin accessibility, and MUP gene transcription. Pulsatile male GH secretion is feminized by several factors, including caloric restriction, microbiota depletion, and aging, which helps explain condition-dependent MUP expression. If MUP production has sex-specific fitness optima, then this should generate sexual antagonism over allelic expression (intra-locus sexual conflict) selectively favoring sexually dimorphic expression. MUPs influence the sexual attractiveness of male urinary odor and increased urinary protein excretion is correlated with the reproductive success of males but not females. This finding could explain the selective maintenance of sexually dimorphic MUP expression. Producing MUPs entails energetic costs, but increased excretion may reduce the net energetic costs and predation risks from male scent marking as well as prolong the release of chemical signals. MUPs may also provide physiological benefits, including regulating metabolic rate and toxin removal, which may have sex-specific effects on survival. A phylogenetic analysis on the origins of male-biased MUP gene expression in Mus musculus suggests that this sexual dimorphism evolved by increasing male MUP expression rather than reducing female expression.

Pheromones that correlate with reproductive success in competitive conditions

The major urinary proteins (MUPs) of house mice (Mus musculus) bind and stabilize the release of pheromones and other volatile organic compounds (VOCs) from urinary scent marks, which mediate chemical communication. Social status influences MUP and VOC excretion, and the urinary scent of dominant males is attractive to females. Urinary pheromones influence the sexual behavior and physiology of conspecifics, and yet it is not known whether they also affect reproductive success. We monitored the excretion of urinary protein and VOCs of wild-derived house mice living in large seminatural enclosures to compare the sexes and to test how these compounds correlate with reproductive success. Among males, urinary protein concentration and VOC expression correlated with reproductive success and social status. Territorial dominance also correlated with reproductive success in both sexes; but among females, no urinary compounds were found to correlate with social status or reproductive success. We found several differences in the urinary protein and volatile pheromones of mice in standard cages versus seminatural enclosures, which raises caveats for conventional laboratory studies. These findings provide novel evidence for chemical signals that correlate with male reproductive success of house mice living in competitive conditions.

Biological Roles of Lipocalins in Chemical Communication, Reproduction, and Regulation of Microbiota

Major evolutionary transitions were always accompanied by genetic remodelling of phenotypic traits. For example, the vertebrate transition from water to land was accompanied by rapid evolution of olfactory receptors and by the expansion of genes encoding lipocalins, which - due to their transporting functions - represent an important interface between the external and internal organic world of an individual and also within an individual. Similarly, some lipocalin genes were lost along other genes when this transition went in the opposite direction leading, for example, to cetaceans. In terrestrial vertebrates, lipocalins are involved in the transport of lipophilic substances, chemical signalling, odour reception, antimicrobial defence and background odour clearance during ventilation. Many ancestral lipocalins have clear physiological functions across the vertebrate taxa while many other have - due to pleiotropic effects of their genes - multiple or complementary functions within the body homeostasis and development. The aim of this review is to deconstruct the physiological functions of lipocalins in light of current OMICs techniques. We concentrated on major findings in the house mouse in comparison to other model taxa (e.g., voles, humans, and birds) in which all or most coding genes within their genomes were repeatedly sequenced and their annotations are sufficiently informative.

Label-free proteomics study on Shewanella putrefaciens regulated by ε-poly-lysine treatment

AIMS

The purpose of this study was to investigate the regulatory mechanism of ε-PL on Shewanella putrefaciens.

METHODS AND RESULTS

Proteomics analysis of inhibitory effect of ε-PL against S. putrefaciens was performed by label-free quantitative assay based on high-resolution mass spectrometry (MS). Quantification of 2206 proteins was obtained with high confidence, and a total of 36 differentially expressed proteins (DEPs), with 10 and 26 proteins showing upregulation and downregulation, respectively, were identified. Upon Go functional enrichment, 11, 5 and 8 specific Go terms in biological processes, molecular functions and cellular components were identified, respectively. Six KEGG pathways, including 'ribosome', were significantly enriched. Among the ribosome pathway, there were seven DEPs and all of them were distributed on large and small subunits of ribosome.

CONCLUSIONS

The significant downregulation of proteins, large subunits of ribosomal proteins RP-L18, L30 and L27, small subunits ribosomal proteins S16 and S20, and RNA polymerase β' subunit protein rpoC were the critical action sites of ε-PL to inhibit S. putrefaciens growth.

SIGNIFICANCE AND IMPACT OF THE STUDY

Shewanella putrefaciens is one of the representative fish-spoilage bacteria regardless of fish type, and poses significant problems for the fish brewery. A better understanding of the antibacterial mechanism of ε-PL on S. putrefaciens could make important contributions to development of biological control strategies of these economically important pathogens.

Allergy to Mus m 1: Allergy to Mus m 1: A review of structural, and immunological features

The prevalence of allergies to pets has been increasing over the past decades. Some of the most important animal-derived allergens are members of the lipocalin protein family, which are found in dander, saliva, and urine. These allergens disperse effectively and are widely present in indoor environments. Exposure to high levels of mouse urinary protein (Mus m 1, hereinafter called 'mouse allergen') has been previously linked to sensitization to mouse, and indicators of asthma severity or control in some studies. To date, this is the only known mouse allergen registered in the IUIS database. This allergen is responsible for 27% of the total T cell response, confirming the dominant role it plays in mouse allergy. Mice have a worldwide distribution affecting both rural and urban areas; hence humans are frequently exposed to mouse-derived proteins. Additionally, exposure to mouse allergens has increased since they are more frequently being made pets, and in addition, exposure of laboratory animal care personnel to mice has been associated with a high risk of developing occupational allergies. Mus m 1 has been recognized as the main mouse allergen, and several studies suggest its clinical relevance. What makes Mus m 1 such an important allergen? In this review, we explored its structural, immunological, and clinical features.

Update on the human and mouse lipocalin (LCN) gene family, including evidence the mouse Mup cluster is result of an "evolutionary bloom"

Lipocalins (LCNs) are members of a family of evolutionarily conserved genes present in all kingdoms of life. There are 19 LCN-like genes in the human genome, and 45 Lcn-like genes in the mouse genome, which include 22 major urinary protein (Mup) genes. The Mup genes, plus 29 of 30 Mup-ps pseudogenes, are all located together on chromosome (Chr) 4; evidence points to an “evolutionary bloom” that resulted in this Mup cluster in mouse, syntenic to the human Chr 9q32 locus at which a single MUPP pseudogene is located. LCNs play important roles in physiological processes by binding and transporting small hydrophobic molecules —such as steroid hormones, odorants, retinoids, and lipids—in plasma and other body fluids. LCNs are extensively used in clinical practice as biochemical markers. LCN-like proteins (18–40 kDa) have the characteristic eight β-strands creating a barrel structure that houses the binding-site; LCNs are synthesized in the liver as well as various secretory tissues. In rodents, MUPs are involved in communication of information in urine-derived scent marks, serving as signatures of individual identity, or as kairomones (to elicit fear behavior). MUPs also participate in regulation of glucose and lipid metabolism via a mechanism not well understood. Although much has been learned about LCNs and MUPs in recent years, more research is necessary to allow better understanding of their physiological functions, as well as their involvement in clinical disorders.

Regulation of volatile and non-volatile pheromone attractants depends upon male social status

We investigated the regulation of chemical signals of house mice living in seminatural social conditions. We found that male mice more than doubled the excretion of major urinary proteins (MUPs) after they acquired a territory and become socially dominant. MUPs bind and stabilize the release of volatile pheromone ligands, and some MUPs exhibit pheromonal properties themselves. We conducted olfactory assays and found that female mice were more attracted to the scent of dominant than subordinate males when they were in estrus. Yet, when male status was controlled, females were not attracted to urine with high MUP concentration, despite being comparable to levels of dominant males. To determine which compounds influence female attraction, we conducted additional analyses and found that dominant males differentially upregulated the excretion of particular MUPs, including the pheromone MUP20 (darcin), and a volatile pheromone that influences female reproductive physiology and behavior. Our findings show that once male house mice become territorial and socially dominant, they upregulate the amount and types of excreted MUPs, which increases the intensities of volatiles and the attractiveness of their urinary scent to sexually receptive females.

Transcriptome signatures of p,p´-DDE-induced liver damage in Mus spretus mice

The use of DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane) in some countries, although regulated, is contributing to an increased worldwide risk of exposure to this organochlorine pesticide or its derivative p,p'-DDE [1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene]. Many studies have associated p,p'-DDE exposure to type 2 diabetes, obesity and alterations of the reproductive system, but their molecular mechanisms of toxicity remain poorly understood. We have addressed this issue by using commercial microarrays based on probes for the entire Mus musculus genome to determine the hepatic transcriptional signatures of p,p'-DDE in the phylogenetically close mouse species Mus spretus. High-stringency hybridization conditions and analysis assured reliable results, which were also verified, in part, by qRT-PCR, immunoblotting and/or enzymatic activity. Our data linked 198 deregulated genes to mitochondrial dysfunction and perturbations of central signaling pathways (kinases, lipids, and retinoic acid) leading to enhanced lipogenesis and aerobic glycolysis, inflammation, cell proliferation and testosterone catabolism and excretion. Alterations of transcript levels of genes encoding enzymes involved in testosterone catabolism and excretion would explain the relationships established between p,p´-DDE exposure and reproductive disorders, obesity and diabetes. Further studies will help to fully understand the molecular basis of p,p´-DDE molecular toxicity in liver and reproductive organs, to identify effective exposure biomarkers and perhaps to design efficient p,p'-DDE exposure counteractive strategies.

Individual odour signatures that mice learn are shaped by involatile major urinary proteins (MUPs)

Background

Reliable recognition of individuals requires phenotypic identity signatures that are both individually distinctive and appropriately stable over time. Individual-specific vocalisations or visual patterning are well documented among birds and some mammals, whilst odours play a key role in social recognition across many vertebrates and invertebrates. Less well understood, though, is whether individuals are recognised through variation in cues that arise incidentally from a wide variety of genetic and non-genetic differences between individuals, or whether animals evolve distinctive polymorphic signals to advertise identity reliably. As a bioassay to understand the derivation of individual-specific odour signatures, we use female attraction to the individual odours of male house mice (Mus musculus domesticus), learned on contact with a male’s scent marks.

Results

Learned volatile odour signatures are determined predominantly by individual differences in involatile major urinary protein (MUP) signatures, a specialised set of communication proteins that mice secrete in their urine. Recognition of odour signatures in genetically distinct mice depended on differences in individual MUP genotype. Direct manipulation using recombinant MUPs confirmed predictable changes in volatile signature recognition according to the degree of matching between MUP profiles and the learned urine template. Both the relative amount of the male-specific MUP pheromone darcin, which induces odour learning, and other MUP isoforms influenced learned odour signatures. By contrast, odour recognition was not significantly influenced by individual major histocompatibility complex genotype. MUP profiles shape volatile odour signatures through isoform-specific differences in binding and release of urinary volatiles from scent deposits, such that volatile signatures were recognised from the urinary protein fraction alone. Manipulation using recombinant MUPs led to quantitative changes in the release of known MUP ligands from scent deposits, with MUP-specific and volatile-specific effects.

Conclusions

Despite assumptions that many genes contribute to odours that can be used to recognise individuals, mice have evolved a polymorphic combinatorial MUP signature that shapes distinctive volatile signatures in their scent. Such specific signals may be more prevalent within complex body odours than previously realised, contributing to the evolution of phenotypic diversity within species. However, differences in selection may also result in species-specific constraints on the ability to recognise individuals through complex body scents.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0512-9) contains supplementary material, which is available to authorized users.

Two predominant MUPs, OBP3 and MUP13, are male pheromones in rats

BACKGROUND

In rats, urine-borne male pheromones comprise organic volatile compounds and major urinary proteins (MUPs). A number of volatile pheromones have been reported, but no MUP pheromones have been identified in rat urine.

RESULTS

We used sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing electrophoresis (IEF), nano-liquid chromatography-tandem mass spectrometry (nLC-MS/MS) after in gel digestion of the proteins and quantitative real-time PCR (qRT-PCR) and showed that the levels of two MUPs, odorant-binding protein 3 (OBP3) (i.e. PGCL4) and MUP13 (i.e. PGCL1), in urine and their mRNAs in liver were higher in males than in females and were suppressed by orchidectomy and restored by testosterone treatment (T treatment). We then generated recombinant MUPs (rMUPs) and found that the sexual attractiveness of urine from castrated males to females significantly increased after the addition of either recombinant OBP3 (rOBP3) or recombinant MUP13 (rMUP13). Using c-Fos immunohistochemistry, we further examined neuronal activation in the brains of female rats after they sniffed rOBP3 or rMUP13. Both rOBP3 and rMUP13 activated the accessory olfactory bulb (AOB), medial preoptic area (MPA), bed nucleus of the stria terminalis (BST), medial amygdala (MeA), posteromedial cortical amygdala (PMCo) and ventromedial nucleus of the hypothalamus (VMH), which participate in the neural circuits responsible for pheromone-induced sexual behaviours. In particular, more c-Fos-immunopositive (c-Fos-ir) cells were observed in the posterior AOB than in the anterior AOB.

CONCLUSIONS

The expression of OBP3 and MUP13 was male-biased and androgen-dependent. They attracted females and activated brain areas related to sexual behaviours in female rats, suggesting that both OBP3 and MUP13 are male pheromones in rats. Particularly, an OBP excreted into urine was exemplified to be a chemical signal.

Transcriptomic and Proteomic Profiling Revealed High Proportions of Odorant Binding and Antimicrobial Defense Proteins in Olfactory Tissues of the House Mouse

Mammalian olfaction depends on chemosensory neurons of the main olfactory epithelia (MOE), and/or of the accessory olfactory epithelia in the vomeronasal organ (VNO). Thus, we have generated the VNO and MOE transcriptomes and the nasal cavity proteome of the house mouse, Mus musculus musculus. Both transcriptomes had low levels of sexual dimorphisms, while the soluble proteome of the nasal cavity revealed high levels of sexual dimorphism similar to that previously reported in tears and saliva. Due to low levels of sexual dimorphism in the olfactory receptors in MOE and VNO, the sex-specific sensing seems less likely to be dependent on receptor repertoires. However, olfaction may also depend on a continuous removal of background compounds from the sites of detection. Odorant binding proteins (OBPs) are thought to be involved in this process and in our study Obp transcripts were most expressed along other lipocalins (e.g., Lcn13, Lcn14) and antimicrobial proteins. At the level of proteome, OBPs were highly abundant with only few being sexually dimorphic. We have, however, detected the major urinary proteins MUP4 and MUP5 in males and females and the male-biased central/group-B MUPs that were thought to be abundant mainly in the urine. The exocrine gland-secreted peptides ESP1 and ESP22 were male-biased but not male-specific in the nose. For the first time, we demonstrate that the expression of nasal lipocalins correlates with antimicrobial proteins thus suggesting that their individual variation may be linked to evolvable mechanisms that regulate natural microbiota and pathogens that regularly enter the body along the ‘eyes-nose-oral cavity’ axis.

Differential regulation of vaginal lipocalins (OBP, MUP) during the estrous cycle of the house mouse

Female house mice produce pheromone-carrying major urinary proteins (MUPs) in a cycling manner, thus reaching the maximum urinary production just before ovulation. This is thought to occur to advertise the time of ovulation via deposited urine marks. This study aimed to characterize the protein content from the house mouse vaginal flushes to detect putative vaginal-advertising molecules for a direct identification of reproductive states. Here we show that the mouse vaginal discharge contains lipocalins including those from the odorant binding (OBP) and major urinary (MUP) protein families. OBPs were highly expressed but only slightly varied throughout the cycle, whilst several MUPs were differentially abundant. MUP20 or 'darcin', was thought to be expressed only by males. However, in females it was significantly up-regulated during estrus similarly as the recently duplicated central/group-B MUPs (sMUP17 and highly expressed sMUP9), which in the mouse urine are male biased. MUPs rise between proestrus and estrus, remain steady throughout metestrus, and are co-expressed with antimicrobial proteins. Thus, we suggest that MUPs and potentially also OBPs are important components of female vaginal advertising of the house mouse.

Pru p 3, a marker allergen for lipid transfer protein sensitization also in Central Europe

In the Mediterranean area, lipid transfer proteins (LTPs) are important causes of plant‐food allergies often associated with severe allergic reactions. There, peach LTP (Pru p 3) seems to be the primary sensitizer, whereas in Central Europe, little is known about the importance of LTP sensitization. In this region, allergen extract‐based diagnosis is often complicated by co‐sensitization to Bet v 1, the major birch pollen allergen, its cross‐reactive food allergens, and profilins. We investigated the role of LTP sensitization in Central European patients displaying strong allergic reactions to plant‐derived food. Analysis of IgE reactivity revealed that ten of thirteen patients were sensitized to Pru p 3, nine to Bet v 1, and two to profilin. Our results showed that LTP sensitization represents a risk factor for severe allergic symptoms in Central Europe. Furthermore, the strong IgE reactivity detected in immunoblots of plant‐food extracts indicated that Pru p 3 can be used as a marker allergen for LTP sensitization also in Central European patients.

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

Mammalian tears are produced by lacrimal glands to protect eyes and may function in chemical communication and immunity. Recent studies on the house mouse chemical signalling revealed that major urinary proteins (MUPs) are not individually unique in Mus musculus musculus. This fact stimulated us to look for other sexually dimorphic proteins that may—in combination with MUPs—contribute to a pool of chemical signals in tears. MUPs and other lipocalins including odorant binding proteins (OBPs) have the capacity to selectively transport volatile organic compounds (VOCs) in their eight-stranded beta barrel, thus we have generated the tear proteome of the house mouse to detect a wider pool of proteins that may be involved in chemical signalling. We have detected significant male-biased (7.8%) and female-biased (7%) proteins in tears. Those proteins that showed the most elevated sexual dimorphisms were highly expressed and belong to MUP, OBP, ESP (i.e., exocrine gland-secreted peptides), and SCGB/ABP (i.e., secretoglobin) families. Thus, tears may have the potential to elicit sex-specific signals in combination by different proteins. Some tear lipocalins are not sexually dimorphic—with MUP20/darcin and OBP6 being good examples—and because all proteins may flow with tears through nasolacrimal ducts to nasal and oral cavities we suggest that their roles are wider than originally thought. Also, we have also detected several sexually dimorphic bactericidal proteins, thus further supporting an idea that males and females may have adopted alternative strategies in controlling microbiota thus yielding different VOC profiles.

Molecular heterogeneity in major urinary proteins of Mus musculus subspecies: potential candidates involved in speciation

When hybridisation carries a cost, natural selection is predicted to favour evolution of traits that allow assortative mating (reinforcement). Incipient speciation between the two European house mouse subspecies, Mus musculus domesticus and M.m.musculus, sharing a hybrid zone, provides an opportunity to understand evolution of assortative mating at a molecular level. Mouse urine odours allow subspecific mate discrimination, with assortative preferences evident in the hybrid zone but not in allopatry. Here we assess the potential of MUPs (major urinary proteins) as candidates for signal divergence by comparing MUP expression in urine samples from the Danish hybrid zone border (contact) and from allopatric populations. Mass spectrometric characterisation identified novel MUPs in both subspecies involving mostly new combinations of amino acid changes previously observed in M.m.domesticus. The subspecies expressed distinct MUP signatures, with most MUPs expressed by only one subspecies. Expression of at least eight MUPs showed significant subspecies divergence both in allopatry and contact zone. Another seven MUPs showed divergence in expression between the subspecies only in the contact zone, consistent with divergence by reinforcement. These proteins are candidates for the semiochemical barrier to hybridisation, providing an opportunity to characterise the nature and evolution of a putative species recognition signal.

Diversity of major urinary proteins (MUPs) in wild house mice

Major urinary proteins (MUPs) are often suggested to be highly polymorphic, and thereby provide unique chemical signatures used for individual and genetic kin recognition; however, studies on MUP variability have been lacking. We surveyed populations of wild house mice (Mus musculus musculus), and examined variation of MUP genes and proteins. We sequenced several Mup genes (9 to 11 loci) and unexpectedly found no inter-individual variation. We also found that microsatellite markers inside the MUP cluster show remarkably low levels of allelic diversity, and significantly lower than the diversity of markers flanking the cluster or other markers in the genome. We found low individual variation in the number and types of MUP proteins using a shotgun proteomic approach, even among mice with variable MUP electrophoretic profiles. We identified gel bands and spots using high-resolution mass spectrometry and discovered that gel-based methods do not separate MUP proteins, and therefore do not provide measures of MUP diversity, as generally assumed. The low diversity and high homology of Mup genes are likely maintained by purifying selection and gene conversion, and our results indicate that the type of selection on MUPs and their adaptive functions need to be re-evaluated.