Diverse spatial, temporal, and sexual expression of recently duplicated androgen-binding protein genes in Mus musculus

Androgen-Binding Protein (Abp) Evolutionary History: Has Positive Selection Caused Fixation of Different Paralogs in Different Taxa of the Genus Mus?

Comparison of the androgen-binding protein (Abp) gene regions of six Mus genomes provides insights into the evolutionary history of this large murid rodent gene family. We identified 206 unique Abp sequences and mapped their physical relationships. At least 48 are duplicated and thus present in more than two identical copies. All six taxa have substantially elevated LINE1 densities in Abp regions compared with flanking regions, similar to levels in mouse and rat genomes, although nonallelic homologous recombination seems to have only occurred in Mus musculus domesticus. Phylogenetic and structural relationships support the hypothesis that the extensive Abp expansion began in an ancestor of the genus Mus. We also found duplicated Abpa27's in two taxa, suggesting that previously reported selection on a27 alleles may have actually detected selection on haplotypes wherein different paralogs were lost in each. Other studies reported that a27 gene and species trees were incongruent, likely because of homoplasy. However, L1MC3 phylogenies, supposed to be homoplasy-free compared with coding regions, support our paralog hypothesis because the L1MC3 phylogeny was congruent with the a27 topology. This paralog hypothesis provides an alternative explanation for the origin of the a27 gene that is suggested to be fixed in the three different subspecies of Mus musculus and to mediate sexual selection and incipient reinforcement between at least two of them. Finally, we ask why there are so many Abp genes, especially given the high frequency of pseudogenes and suggest that relaxed selection operates over a large part of the gene clusters.

Effects of spaceflight on the mouse submandibular gland

OBJECTIVE

This study was conducted to determine if the morphology and biochemistry of the mouse submandibular gland is affected by microgravity and the spaceflight environment.

DESIGN

Tissues from female mice flown on the US space shuttle missions Space Transportation System (STS)-131 and STS-135 for 15 and 13 d, respectively, and from male mice flown on the 30 d Russian Bion-M1 biosatellite, were examined using transmission electron microscopy and light and electron microscopic immunohistochemistry.

RESULTS

In contrast to the parotid gland, morphologic changes were not apparent in the submandibular gland. No significant changes in protein expression, as assessed by quantitative immunogold labeling, occurred in female mice flown for 13-15 d. In male mice, however, increased labeling for salivary androgen binding protein alpha (in acinar cell secretory granules), and epidermal growth factor and nerve growth factor (in granular convoluted duct cell granules) was seen after 30 d in space.

CONCLUSION

These results indicate that spaceflight alters secretory protein expression in the submandibular gland and suggest that the sex of the animals and the length of the flight may affect the response. These findings also show that individual salivary glands respond differently to spaceflight. Saliva contains proteins secreted from salivary glands and is easily collected, therefore is a useful biofluid for general medical analyses and in particular for monitoring the physiology and health of astronauts.

Another cat and mouse game: Deciphering the evolution of the SCGB superfamily and exploring the molecular similarity of major cat allergen Fel d 1 and mouse ABP using computational approaches

The mammalian secretoglobin (SCGB) superfamily contains functionally diverse members, among which the major cat allergen Fel d 1 and mouse salivary androgen-binding protein (ABP) display similar subunits. We searched for molecular similarities between Fel d 1 and ABP to examine the possibility that they play similar roles. We aimed to i) cluster the evolutionary relationships of the SCGB superfamily; ii) identify divergence patterns, structural overlap, and protein-protein docking between Fel d 1 and ABP dimers; and iii) explore the residual interaction between ABP dimers and steroid binding in chemical communication using computational approaches. We also report that the evolutionary tree of the SCGB superfamily comprises seven unique palm-like clusters, showing the evolutionary pattern and divergence time tree of Fel d 1 with 28 ABP paralogs. Three ABP subunits (A27, BG27, and BG26) share phylogenetic relationships with Fel d 1 chains. The Fel d 1 and ABP subunits show similarities in terms of sequence conservation, identical motifs and binding site clefts. Topologically equivalent positions were visualized through superimposition of ABP A27:BG27 (AB) and ABP A27:BG26 (AG) dimers on a heterodimeric Fel d 1 model. In docking, Fel d 1-ABP dimers exhibit the maximum surface binding ability of AG compared with that of AB dimers and the several polar interactions between ABP dimers with steroids. Hence, cat Fel d 1 is an ABP-like molecule in which monomeric chains 1 and 2 are the equivalent of the ABPA and ABPBG monomers, respectively. These findings suggest that the biological and molecular function of Fel d 1 is similar to that of ABP in chemical communication, possibly via pheromone and/or steroid binding.

Another cat and mouse game: Deciphering the evolution of the SCGB superfamily and exploring the molecular similarity of major cat allergen Fel d 1 and mouse ABP using computational approaches

The mammalian secretoglobin (SCGB) superfamily contains functionally diverse members, among which the major cat allergen Fel d 1 and mouse salivary androgen-binding protein (ABP) display similar subunits. We searched for molecular similarities between Fel d 1 and ABP to examine the possibility that they play similar roles. We aimed to i) cluster the evolutionary relationships of the SCGB superfamily; ii) identify divergence patterns, structural overlap, and protein-protein docking between Fel d 1 and ABP dimers; and iii) explore the residual interaction between ABP dimers and steroid binding in chemical communication using computational approaches. We also report that the evolutionary tree of the SCGB superfamily comprises seven unique palm-like clusters, showing the evolutionary pattern and divergence time tree of Fel d 1 with 28 ABP paralogs. Three ABP subunits (A27, BG27, and BG26) share phylogenetic relationships with Fel d 1 chains. The Fel d 1 and ABP subunits show similarities in terms of sequence conservation, identical motifs and binding site clefts. Topologically equivalent positions were visualized through superimposition of ABP A27:BG27 (AB) and ABP A27:BG26 (AG) dimers on a heterodimeric Fel d 1 model. In docking, Fel d 1-ABP dimers exhibit the maximum surface binding ability of AG compared with that of AB dimers and the several polar interactions between ABP dimers with steroids. Hence, cat Fel d 1 is an ABP-like molecule in which monomeric chains 1 and 2 are the equivalent of the ABPA and ABPBG monomers, respectively. These findings suggest that the biological and molecular function of Fel d 1 is similar to that of ABP in chemical communication, possibly via pheromone and/or steroid binding.

Analysis of Copy Number Variation in the Abp Gene Regions of Two House Mouse Subspecies Suggests Divergence during the Gene Family Expansions

The Androgen-binding protein (Abp) gene region of the mouse genome contains 64 genes, some encoding pheromones that influence assortative mating between mice from different subspecies. Using CNVnator and quantitative PCR, we explored copy number variation in this gene family in natural populations of Mus musculus domesticus (Mmd) and Mus musculus musculus (Mmm), two subspecies of house mice that form a narrow hybrid zone in Central Europe. We found that copy number variation in the center of the Abp gene region is very common in wild Mmd, primarily representing the presence/absence of the final duplications described for the mouse genome. Clustering of Mmd individuals based on this variation did not reflect their geographical origin, suggesting no population divergence in the Abp gene cluster. However, copy number variation patterns differ substantially between Mmd and other mouse taxa. Large blocks of Abp genes are absent in Mmm, Mus musculus castaneus and an outgroup, Mus spretus, although with differences in variation and breakpoint locations. Our analysis calls into question the reliance on a reference genome for interpreting the detailed organization of genes in taxa more distant from the Mmd reference genome. The polymorphic nature of the gene family expansion in all four taxa suggests that the number of Abp genes, especially in the central gene region, is not critical to the survival and reproduction of the mouse. However, Abp haplotypes of variable length may serve as a source of raw genetic material for new signals influencing reproductive communication and thus speciation of mice.

Studies of an Androgen-Binding Protein Knockout Corroborate a Role for Salivary ABP in Mouse Communication

The house mouse Androgen-binding protein (Abp) gene family is comprised of 64 paralogs, 30 Abpa and 34 Abpbg, encoding the alpha (ABPA) and beta-gamma (ABPBG) protein subunits that are disulfide-bridged to form dimers in secretions. Only 14 Abp genes are expressed in distinct patterns in the lacrimal (11) and submandibular glands (3). We created a knockout mouse line lacking two of the three genes expressed in submandibular glands, Abpa27 and Abpbg27, by replacing them with the neomycin resistance gene. The knockout genotype (-/-) showed no Abpa27 or Abpbg27 transcripts in submandibular gland complementary DNA (cDNA) libraries and there was a concomitant lack of protein expression of ABPA27 and ABPBG27 in the -/- genotype saliva, shown by elimination of these two proteins from the saliva proteome and the loss of cross-reactive material in the acinar cells of the submandibular glands. We also observed a decrease in BG26 protein in the -/- animals, suggesting monomer instability. Overall, we observed no major phenotypic changes in the -/- genotype, compared with their +/+ and +/- siblings raised in a laboratory setting, including normal growth curves, tissue histology, fecundity, and longevity. The only difference is that male and female C57BL/6 mice preferred saliva of the opposite sex containing ABP statistically significantly more than saliva of the opposite sex without ABP in a Y-maze test. These results show for the first time that mice can sense the presence of ABP between saliva targets with and without ABPs, and that they spend more time investigating the target containing ABP.

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

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.

Selection shaped the evolution of mouse androgen-binding protein (ABP) function and promoted the duplication of Abp genes

In the present article, we summarize two aspects of our work on mouse ABP (androgen-binding protein): (i) the sexual selection function producing incipient reinforcement on the European house mouse hybrid zone, and (ii) the mechanism behind the dramatic expansion of the Abp gene region in the mouse genome. Selection unifies these two components, although the ways in which selection has acted differ. At the functional level, strong positive selection has acted on key sites on the surface of one face of the ABP dimer, possibly to influence binding to a receptor. A different kind of selection has apparently driven the recent and rapid expansion of the gene region, probably by increasing the amount of Abp transcript, in one or both of two ways. We have shown previously that groups of Abp genes behave as LCRs (low-copy repeats), duplicating as relatively large blocks of genes by NAHR (non-allelic homologous recombination). The second type of selection involves the close link between the accumulation of L1 elements and the expansion of the Abp gene family by NAHR. It is probably predicated on an initial selection for increased transcription of existing Abp genes and/or an increase in Abp gene number providing more transcriptional sites. Either or both could increase initial transcript production, a quantitative change similar to increasing the volume of a radio transmission. In closing, we also provide a note on Abp gene nomenclature.

Did androgen-binding protein paralogs undergo neo- and/or Subfunctionalization as the Abp gene region expanded in the mouse genome?

The Androgen-binding protein (Abp) region of the mouse genome contains 30 Abpa genes encoding alpha subunits and 34 Abpbg genes encoding betagamma subunits, their products forming dimers composed of an alpha and a betagamma subunit. We endeavored to determine how many Abp genes are expressed as proteins in tears and saliva, and as transcripts in the exocrine glands producing them. Using standard PCR, we amplified Abp transcripts from cDNA libraries of C57BL/6 mice and found fifteen Abp gene transcripts in the lacrimal gland and five in the submandibular gland. Proteomic analyses identified proteins corresponding to eleven of the lacrimal gland transcripts, all of them different from the three salivary ABPs reported previously. Our qPCR results showed that five of the six transcripts that lacked corresponding proteins are expressed at very low levels compared to those transcripts with proteins. We found 1) no overlap in the repertoires of expressed Abp paralogs in lacrimal gland/tears and salivary glands/saliva; 2) substantial sex-limited expression of lacrimal gland/tear expressed-paralogs in males but no sex-limited expression in females; and 3) that the lacrimal gland/tear expressed-paralogs are found exclusively in ancestral clades 1, 2 and 3 of the five clades described previously while the salivary glands/saliva expressed-paralogs are found only in clade 5. The number of instances of extremely low levels of transcription without corresponding protein production in paralogs specific to tears and saliva suggested the role of subfunctionalization, a derived condition wherein genes that may have been expressed highly in both glands ancestrally were down-regulated subsequent to duplication. Thus, evidence for subfunctionalization can be seen in our data and we argue that the partitioning of paralog expression between lacrimal and salivary glands that we report here occurred as the result of adaptive evolution.

Prostatic acid phosphatase is the main acid phosphatase with 5'-ectonucleotidase activity in the male mouse saliva and regulates salivation

We have previously shown that in addition to the well-known secreted isoform of prostatic acid phosphatase (sPAP), a transmembrane isoform exists (TMPAP) that interacts with snapin (a SNARE-associated protein) and regulates the endo-/exocytic pathways. We have also shown that PAP has 5'-ectonucleotidase and thiamine monophosphatase activity and elicits antinociceptive effects in mouse models of chronic inflammatory and neuropathic pain. Therefore, to determine the physiological role of PAP in a typical exocrine organ, we studied the submandibular salivary gland (SMG) of PAP(-/-) and wild-type C57BL/6J mice by microarray analyses, microRNA sequencing, activity tests, immunohistochemistry, and biochemical and physiological analyses of saliva. We show that PAP is the main acid phosphatase in the wild-type male mouse saliva, accounting for 50% of the total acid phosphatase activity, and that it is expressed only in the granular convoluted tubules of the SMGs, where it is the only 5'-ectonucleotidase. The lack of PAP in male PAP(-/-) mice was associated with a significant increase in the salivation volume under secretagogue stimulation, overexpression of genes related to cell proliferation (Mki67, Aurkb, Birc5) and immune response (Irf7, Cxcl9, Ccl3, Fpr2), and upregulation of miR-146a in SMGs. An increased and sustained acinar cell proliferation was detected without signs of glandular hyperplasia. Our results indicate that in PAP(-/-) mice, SMG homeostasis is maintained by an innate immune response. Additionally, we suggest that in male mice, PAP via its 5'-ectonucleotidase activity and production of adenosine can elicit analgesic effects when animals lick their wounds.

Mammalian pheromones

Mammalian pheromones control a myriad of innate social behaviors and acutely regulate hormone levels. Responses to pheromones are highly robust, reproducible, and stereotyped and likely involve developmentally predetermined neural circuits. Here, I review several facets of pheromone transduction in mammals, including (a) chemosensory receptors and signaling components of the main olfactory epithelium and vomeronasal organ involved in pheromone detection; (b) pheromone-activated neural circuits subject to sex-specific and state-dependent modulation; and (c) the striking chemical diversity of mammalian pheromones, which range from small, volatile molecules and sulfated steroids to large families of proteins. Finally, I review (d) molecular mechanisms underlying various behavioral and endocrine responses, including modulation of puberty and estrous; control of reproduction, aggression, suckling, and parental behaviors; individual recognition; and distinguishing of own species from predators, competitors, and prey. Deconstruction of pheromone transduction mechanisms provides a critical foundation for understanding how odor response pathways generate instinctive behaviors.

Evolution of the ABPA subunit of androgen-binding protein expressed in the submaxillary glands in New and Old World rodent taxa

The salivary androgen-binding proteins (ABPs) are members of the secretoglobin gene family present in mammals. Each ABP is a heterodimer assembled as an ABPA subunit encoded by an Abpa gene and linked by disulfide bridges to an ABPBG subunit encoded by an Abpbg gene. The ABP dimers are secreted into the saliva of mice and then transferred to the pelage after grooming and subsequently to the environment allowing an animal to mark territory with a biochemical signal. The putative role of the mouse salivary ABPs is that of pheromones mediating mate selection resulting in assortative mating in the Mus musculus species complex. We focused on comparing patterns of molecular evolution between the Abpa genes expressed in the submaxillary glands of species of New World and Old World muroids. We found that in both sets of rodents the Abpa genes expressed in the submaxillary glands appear to be evolving under a similar evolutionary regime, with relatively high nonsynonymous substitution rates, suggesting that ABP might play a similar biological role in both systems. Thus, ABP could be involved with mate recognition and species isolation in New World as well as Old World muroids.

Update of the human secretoglobin (SCGB) gene superfamily and an example of 'evolutionary bloom' of androgen-binding protein genes within the mouse Scgb gene superfamily

The secretoglobins (SCGBs) comprise a family of small, secreted proteins found in animals exclusively of mammalian lineage. There are 11 human SCGB genes and five pseudogenes. Interestingly, mice have 68 Scgb genes, four of which are highly orthologous to human SCGB genes; the remainder represent an 'evolutionary bloom' and make up a large gene family represented by only six counterparts in humans. SCGBs are found in high concentrations in many mammalian secretions, including fluids of the lung, lacrimal gland, salivary gland, prostate and uterus. Whereas the biological activities of most individual SCGBs have not been fully characterised, what already has been discovered suggests that this family has an important role in the modulation of inflammation, tissue repair and tumorigenesis. In mice, the large Scgb1b and Scgb2b gene families encode the androgen-binding proteins, which have been shown to play a role in mate selection. Although much has been learned about SCGBs in recent years, clearly more research remains to be done to allow a better understanding of the roles of these proteins in human health and disease. Such information is predicted to reveal valuable novel drug targets for the treatment of inflammation, as well as designing biomarkers that might identify tissue damage or cancer.

Congenic strain analysis reveals genes that are rapidly evolving components of a prezygotic isolation mechanism mediating incipient reinforcement

Two decades ago, we developed a congenic strain of Mus musculus, called b-congenic, by replacing the androgen-binding protein Abpa27(a) allele in the C3H/HeJ genome with the Abpa27(b) allele from DBA/2J. We and other researchers used this b-congenic strain and its C3H counterpart, the a-congenic strain, to test the hypothesis that, given the choice between signals from two strains with different a27 alleles on the same genetic background, test subjects would prefer the homosubspecific one. It was our purpose in undertaking this study to characterize the segment transferred from DBA to the C3H background in producing the b-congenic strain on which a role for ABPA27 in behavior has been predicated. We determined the size of the chromosome 7 segment transferred from DBA and the genes it contains that might influence preference. We found that the "functional" DBA segment is about 1% the size of the mouse haploid genome and contains at least 29 genes expressed in salivary glands, however, only three of these encode proteins identified in the mouse salivary proteome. At least two of the three genes Abpa27, Abpbg26 and Abpbg27 encoding the subunits of androgen-binding protein ABP dimers evolved under positive selection and the third one may have also. In the sense that they are subunits of the same two functional entities, the ABP dimers, we propose that their evolutionary histories might not be independent of each other.

Ascl3 marks adult progenitor cells of the mouse salivary gland

The Ascl3 transcription factor marks a subset of salivary gland duct cells present in the three major salivary glands of the mouse. In vivo, these cells generate both duct and secretory acinar cell descendants. Here, we have analyzed whether Ascl3-expressing cells retain this multipotent lineage potential in adult glands. Cells isolated from mouse salivary glands were cultured in vitro as non-adherent spheres. Lineage tracing of the Ascl3-expressing cells within the spheres demonstrates that Ascl3+ cells isolated from adult glands remain multipotent, generating both duct and acinar cell types in vitro. Furthermore, we demonstrate that the progenitor cells characterized by Keratin 5 expression are an independent population from Ascl3+ progenitor cells. We conclude that the Ascl3+ cells are intermediate lineage-restricted progenitor cells of the adult salivary glands.

Positive selection shaped the convergent evolution of independently expanded kallikrein subfamilies expressed in mouse and rat saliva proteomes

We performed proteomics studies of salivas from the genome mouse (C57BL/6 strain) and the genome rat (BN/SsNHsd/Mcwi strain). Our goal was to identify salivary proteins with one or more of three characteristics that may indicate that they have been involved in adaptation: 1) rapid expansion of their gene families; 2) footprints of positive selection; and/or 3) sex-limited expression. The results of our proteomics studies allow direct comparison of the proteins expressed and their levels between the sexes of the two rodent species. Twelve members of the Mus musculus species-specific kallikrein subfamily Klk1b showed sex-limited expression in the mouse saliva proteomes. By contrast, we did not find any of the Rattus norvegicus species-specific kallikrein subfamily Klk1c proteins in male or female genome rat, nor transcripts in their submandibular glands. On the other hand, we detected expression of this family as transcripts in the submandibular glands of both sexes of Sprague-Dawley rats. Using the CODEML program in the PAML package, we demonstrate that the two rodent kallikrein subfamilies have apparently evolved rapidly under the influence of positive selection that continually remodeled the amino acid sites on the same face in the members of the subfamilies. Thus, although their kallikrein subfamily expansions were independent, this evolutionary pattern has occurred in parallel in the two rodent species, suggesting a form of convergent evolution at the molecular level. On the basis of this new data, we suggest that the previous speculative function of the species-specific rodent kallikreins as important solely in wound healing in males be investigated further. In addition to or instead of that function, we propose that their sex-limited expression, coupled with their rapid evolution may be clues to an as-yet-undetermined interaction between the sexes.

Reinforcement selection acting on the European house mouse hybrid zone

Behavioural isolation may lead to complete speciation when partial postzygotic isolation acts in the presence of divergent-specific mate-recognition systems. These conditions exist where Mus musculus musculus and M. m. domesticus come into contact and hybridize. We studied two mate-recognition signal systems, based on urinary and salivary proteins, across a Central European portion of the mouse hybrid zone. Introgression of the genomic regions responsible for these signals: the major urinary proteins (MUPs) and androgen binding proteins (ABPs), respectively, was compared to introgression at loci assumed to be nearly neutral and those under selection against hybridization. The preference of individuals taken from across the zone regarding these signals was measured in Y mazes, and we develop a model for the analysis of the transition of such traits under reinforcement selection. The strongest assortative preferences were found in males for urine and females for ABP. Clinal analyses confirm nearly neutral introgression of an Abp locus and two loci closely linked to the Abp gene cluster, whereas two markers flanking the Mup gene region reveal unexpected introgression. Geographic change in the preference traits matches our reinforcement selection model significantly better than standard cline models. Our study confirms that behavioural barriers are important components of reproductive isolation between the house mouse subspecies.

A candidate subspecies discrimination system involving a vomeronasal receptor gene with different alleles fixed in M. m. domesticus and M. m. musculus

Assortative mating, a potentially efficient prezygotic reproductive barrier, may prevent loss of genetic potential by avoiding the production of unfit hybrids (i.e., because of hybrid infertility or hybrid breakdown) that occur at regions of secondary contact between incipient species. In the case of the mouse hybrid zone, where two subspecies of Mus musculus (M. m. domesticus and M. m. musculus) meet and exchange genes to a limited extent, assortative mating requires a means of subspecies recognition. We based the work reported here on the hypothesis that, if there is a pheromone sufficiently diverged between M. m. domesticus and M. m. musculus to mediate subspecies recognition, then that process must also require a specific receptor(s), also sufficiently diverged between the subspecies, to receive the signal and elicit an assortative mating response. We studied the mouse V1R genes, which encode a large family of receptors in the vomeronasal organ (VNO), by screening Perlegen SNP data and identified one, Vmn1r67, with 24 fixed SNP differences most of which (15/24) are nonsynonymous nucleotide substitutions between M. m. domesticus and M. m. musculus. We observed substantial linkage disequilibrium (LD) between Vmn1r67 and Abpa27, a mouse salivary androgen-binding protein gene that encodes a proteinaceous pheromone (ABP) capable of mediating assortative mating, perhaps in conjunction with its bound small lipophilic ligand. The LD we observed is likely a case of association rather than residual physical linkage from a very recent selective sweep, because an intervening gene, Vmn1r71, shows significant intra(sub)specific polymorphism but no inter(sub)specific divergence in its nucleotide sequence. We discuss alternative explanations of these observations, for example that Abpa27 and Vmn1r67 are coevolving as signal and receptor to reinforce subspecies hybridization barriers or that the unusually divergent Vmn1r67 allele was not a product of fast positive selection, but was derived from an introgressed allele, possibly from Mus spretus.

High abundance of testosterone and salivary androgen-binding protein in the lateral nasal gland of male mice

To better understand androgen function in the mammalian nose, we have determined the levels of testosterone (T) in the olfactory mucosa (OM, which harbors the olfactory receptor neurons) and the lateral nasal gland (LNG, which is the largest anterior nasal gland) of C57BL/6 mice. The results indicated that, in adult male mice, T levels in the LNG were substantially higher than those in the OM and other non-reproductive or non-endocrine tissues examined, including liver, kidney, and brain. Furthermore, in the LNG, the high T levels were accompanied by high levels of salivary androgen-binding protein (sABP) and low microsomal T-hydroxylase activities. The high abundance of T and sABP in the LNG suggests not only that the LNG is a storage site for androgen, but also the possibility that unusually high T levels may occur in other organs that have abundant expression of sABP but low expression of steroid-metabolizing enzymes. Our findings suggest a critical need to determine androgen levels in various organs, as well as to establish the functional significance of an unusually high T level in the LNG, a gland known for its secretion of biologically active molecules, such as odorant binding proteins and immunoglobulin A, to the nasal cavity.

Extracts from salivary glands stimulate aggression and inositol-1, 4, 5-triphosphate (IP3) production in the vomeronasal organ of mice

Mammals use chemical cues to coordinate social and reproductive behaviors. Chemical cues are detected by the VNO organ (VNO), which is a cartilage-encased elongated organ associated with the vomer bone in the rostral nasal cavity. The resident intruder paradigm was utilized to examine the ability of saliva and its feeder exocrine glands, the submaxillary, parotid, and sublingual glands to mediate aggression in mice. Saliva and extracts from submaxillary and parotid glands, but not extracts from sublingual glands of male CD-1 mice, induced a greater number of attacks and lower latencies to sniff and attack (p<0.05) and significantly increased IP(3) production (p<0.05) versus vehicle (PBS) in CD-1 male mice VNO. We further show that CD-1 male mouse saliva and submaxillary gland extract induced significantly more attacks and a lower latency to attack in lactating female CD-1 mice and produced significantly more inositol triphosphate (IP(3)), indicative of phospholipase C(beta) signaling which mediates pheromonal activity, in CD-1 female VNO compared to PBS. Castrated CD-1 male mouse saliva, and exocrine gland extracts induced significantly less IP(3) production in male VNO and less aggression by CD-1 males and lactating females compared to responses to normal CD-1 male mouse saliva and gland extracts. Thus, chemical cues present in saliva, submaxillary and parotid glands of CD-1 male mice are capable of stimulating aggression in male and female congenic mice which are correlated with significant production of IP(3) in the VNO. Additionally, these stimulations of aggression and IP(3) production are shown to be androgen-dependent.

Proteomics and comparative genomic investigations reveal heterogeneity in evolutionary rate of male reproductive proteins in mice (Mus domesticus)

Male reproductive fitness is strongly affected by seminal fluid. In addition to interacting with the female environment, seminal fluid mediates important physiological characteristics of sperm, including capacitation and motility. In mammals, the male reproductive tract shows a striking degree of compartmentalization, with at least six distinct tissue types contributing material that is combined with sperm in an ejaculate. Although studies of whole ejaculates have been undertaken in some species, we lack a comprehensive picture of the specific proteins produced by different accessory tissues. Here, we perform proteomic investigations of six regions of the male reproductive tract in mice -- seminal vesicles, anterior prostate, dorsolateral prostate, ventral prostate, bulbourethral gland, and bulbourethral diverticulum. We identify 766 proteins that could be mapped to 506 unique genes and compare them with a high-quality human seminal fluid data set. We find that Gene Ontology functions of seminal proteins are largely conserved between mice and humans. By placing these data in an evolutionary framework, we show that seminal vesicle proteins have experienced a significantly higher rate of nonsynonymous substitution compared with the genome, which could be the result of adaptive evolution. In contrast, proteins from the other five tissues showed significantly lower nonsynonymous substitution, revealing a previously unappreciated level of evolutionary constraint acting on the majority of male reproductive proteins.

Species specificity in major urinary proteins by parallel evolution

Species-specific chemosignals, pheromones, regulate social behaviors such as aggression, mating, pup-suckling, territory establishment, and dominance. The identity of these cues remains mostly undetermined and few mammalian pheromones have been identified. Genetically-encoded pheromones are expected to exhibit several different mechanisms for coding 1) diversity, to enable the signaling of multiple behaviors, 2) dynamic regulation, to indicate age and dominance, and 3) species-specificity. Recently, the major urinary proteins (Mups) have been shown to function themselves as genetically-encoded pheromones to regulate species-specific behavior. Mups are multiple highly related proteins expressed in combinatorial patterns that differ between individuals, gender, and age; which are sufficient to fulfill the first two criteria. We have now characterized and fully annotated the mouse Mup gene content in detail. This has enabled us to further analyze the extent of Mup coding diversity and determine their potential to encode species-specific cues.

Our results show that the mouse Mup gene cluster is composed of two subgroups: an older, more divergent class of genes and pseudogenes, and a second class with high sequence identity formed by recent sequential duplications of a single gene/pseudogene pair. Previous work suggests that truncated Mup pseudogenes may encode a family of functional hexapeptides with the potential for pheromone activity. Sequence comparison, however, reveals that they have limited coding potential. Similar analyses of nine other completed genomes find Mup gene expansions in divergent lineages, including those of rat, horse and grey mouse lemur, occurring independently from a single ancestral Mup present in other placental mammals. Our findings illustrate that increasing genomic complexity of the Mup gene family is not evolutionarily isolated, but is instead a recurring mechanism of generating coding diversity consistent with a species-specific function in mammals.

Sex differences in expression and differential regulation by androgen and estrogen of two odorant-binding tear lipocalins in lacrimal glands of immature hamsters

In adults of several mammalian species, lacrimal glands (LG) have sex differences but there is no report of any sexual dimorphism in LG of immatures. In LG and tears of adult hamsters, we found female-specific expression of two closely related odorant-/pheromone-binding lipocalins, FLP (female lacrimal protein) and MSP (male-specific protein; initially identified in salivary glands of males). Although, both androgens and estrogens markedly repress FLP and MSP in LG of adults, the expression of these lipocalins in females is due to their incomplete repression by endogenous estrogens. Here we report a marked sexual dimorphism in the expression of FLP and MSP in LG and tears of 20-day-old immature hamsters. The age-dependant expression of these lipocalins and effect of neonatal-gonadectomy and sex hormone treatments on their expression in immatures was investigated. FLP and MSP are detectable in LG at 10-day age in both sexes of hamster but by 20-day age levels of both lipocalins show sex differences wherein FLP is several fold higher in males and MSP is obliterated in males. Thereafter, FLP declines in male LG and is obliterated by 36-day age, resulting in female-specific expression of both LG lipocalins as seen in adults. In LG of 20-day-old immatures, FLP and MSP are insensitive to repression by androgen and estrogen, respectively, which was unlike the androgen/estrogen-repressed regulation of both lipocalins in adult LG. The estrogenic repression of FLP and androgenic repression of MSP in LG of immature hamsters could be prevented by treatment with tamoxifen and flutamide, respectively. Our studies indicate that (i) presence of gonads in immatures can have significant effects on LG lipocalins resulting in their sexually dimorphic expression, (ii) in immatures, unlike adults, the repressive effects of estrogen and androgen on LG lipocalins are selective for FLP and MSP, respectively, and (iii) these repressions are likely to be mediated by sex hormone receptors.

Rapid bursts of androgen-binding protein (Abp) gene duplication occurred independently in diverse mammals

BACKGROUND

The draft mouse (Mus musculus) genome sequence revealed an unexpected proliferation of gene duplicates encoding a family of secretoglobin proteins including the androgen-binding protein (ABP) alpha, beta and gamma subunits. Further investigation of 14 alpha-like (Abpa) and 13 beta- or gamma-like (Abpbg) undisrupted gene sequences revealed a rich diversity of developmental stage-, sex- and tissue-specific expression. Despite these studies, our understanding of the evolution of this gene family remains incomplete. Questions arise from imperfections in the initial mouse genome assembly and a dearth of information about the gene family structure in other rodents and mammals.

RESULTS

Here, we interrogate the latest 'finished' mouse (Mus musculus) genome sequence assembly to show that the Abp gene repertoire is, in fact, twice as large as reported previously, with 30 Abpa and 34 Abpbg genes and pseudogenes. All of these have arisen since the last common ancestor with rat (Rattus norvegicus). We then demonstrate, by sequencing homologs from species within the Mus genus, that this burst of gene duplication occurred very recently, within the past seven million years. Finally, we survey Abp orthologs in genomes from across the mammalian clade and show that bursts of Abp gene duplications are not specific to the murid rodents; they also occurred recently in the lagomorph (rabbit, Oryctolagus cuniculus) and ruminant (cattle, Bos taurus) lineages, although not in other mammalian taxa.

CONCLUSION

We conclude that Abp genes have undergone repeated bursts of gene duplication and adaptive sequence diversification driven by these genes' participation in chemosensation and/or sexual identification.