Analysis of mouse major urinary protein genes: variation between the exonic sequences of group 1 genes and a comparison with an active gene out with group 1 both suggest that gene conversion has occurred between MUP genes

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.

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.

Observation of heterogeneous gene products by FT-ICR MS

The ability of FT-ICR MS to resolve isotopic variants of intact proteins for each of the charge states formed by electrospray ionization offers a sensitive, rapid method for detecting "low mass" heterogeneity, where this is defined as the presence of structural variants differing in mass by 2 Da or less. Such heterogeneity may reflect biological or chemical modifications of structure or may result from the coexpression of related proteins from a multi-gene family. In the analytical approach described here, comparisons are made between observed isotopic distributions and those expected for predicted protein sequences. Close agreement is demonstrated for a homogeneous model protein, and the utility of the method has been evaluated in the study of mouse major urinary proteins (MUPs), a group of closely related sequences. Divergence of the experimental isotopic distribution from distributions predicted for known MUP sequences can be explained, in quantitative terms, by the coexpression of closely related sequences. This approach provides a facile method for the assessment of protein homogeneity and for the detection of structural variants, without recourse to proteolytic digestion and analysis of the resulting products.

Sex-Dependent Liver Gene Expression Is Extensive and Largely Dependent upon Signal Transducer and Activator of Transcription 5b (STAT5b): STAT5b-Dependent Activation of Male Genes and Repression of Female Genes Revealed by Microarray Analysis

Sexual dimorphism in mammalian liver contributes to sex differences in physiology, homeostasis, and steroid and foreign compound metabolism. Many sex-dependent liver genes are regulated by sex differences in pituitary GH secretion, with the transcription factor, signal transducer and activator of transcription (STAT5b), proposed to mediate signaling by the pulsatile, male plasma GH profile. Presently, a large-scale gene expression study was conducted using male and female mice, wild type and Stat5b inactivated, to characterize sex differences in liver gene expression and their dependence on STAT5b. The relative abundance of individual liver RNAs was determined for each sex-genotype combination by competitive hybridization to 23,574-feature oligonucleotide microarrays. Significant sex differences in hepatic expression were seen for 1603 mouse genes. Of 850 genes showing higher expression in males, 767 (90%) were down-regulated in STAT5b-deficient males. Moreover, of 753 genes showing female-predominant expression, 461 (61%) were up-regulated in STAT5b-deficient males. In contrast, approximately 90% of the sex-dependent genes were unaffected by STAT5b deficiency in females. Thus: 1) STAT5b is essential for sex-dependent liver gene expression, a characteristic of approximately 1600 mouse genes (4% of the genome); 2) male-predominant liver gene expression requires STAT5b, or STAT5b-dependent factors, which act in a positive manner; and 3) many female-predominant liver genes are repressed in males in a STAT5b-dependent manner. Several of the STAT5b-dependent male genes encode transcriptional repressors; these may include direct STAT5b targets that repress female-predominant genes in male liver. Several female-predominant repressors are elevated in STAT5b-deficient males; these may contribute to the major loss of male gene expression seen in the absence of STAT5b.

Codependence of growth hormone-responsive, sexually dimorphic hepatic gene expression on signal transducer and activator of transcription 5b and hepatic nuclear factor 4alpha

Targeted disruption of the signal transducer and activator of transcription 5b gene (STAT5b) leads to decreased expression in male mouse liver of a male-predominant cytochrome (Cyp) 2d protein, whereas female-predominant Cyp2b proteins are increased. Presently, we characterize the effects of STAT5b deficiency on 15 specific, individual Cyp RNAs and other sexually dimorphic liver gene products. All seven male-specific RNAs investigated were decreased to normal female levels in STAT5b-deficient male liver, whereas five of eight female-specific RNAs, designated class I female genes, were increased in expression up to 200-fold or more. STAT5b deficiency had a much more modest effect on the expression of these genes in females. Hypophysectomy and GH replacement studies demonstrated positive GH pulse regulation of all seven male RNAs and negative GH pulse regulation of class I, but not class II, female RNAs in wild-type, but not in STAT5b-deficient, male mice. A majority of the sex-specific genes responded in parallel to the loss of STAT5b and the loss of hepatocyte nuclear factor 4alpha, indicating that both transcription factors are essential and suggesting they may coregulate sexually dimorphic liver gene expression. Continuous GH treatment of intact male mice, which overrides the endogenous male, pulsatile plasma GH pattern, down-regulated all seven male RNAs and induced expression of the five class I female RNAs within 4-7 d; however, induction of class II female RNAs was delayed until d 7-14. Given the slow responses of all 15 genes to changes in plasma GH status, GH regulation of sex-specific Cyp expression is proposed to be indirect and mediated by STAT5b- and hepatocyte nuclear factor 4alpha-dependent factors that may include repressors of female-specific Cyps and other targets of GH action.

Major urinary proteins, alpha(2U)-globulins and aphrodisin

The major urinary proteins (MUPs) are proteins secreted by the liver and filtered by the kidneys into the urine of adult male mice and rats, the MUPs of rats being also referred to as alpha(2U)-globulins. The MUP family also comprises closely related proteins excreted by exocrine glands of rodents, independently of their sex. The MUP family is an expression of a multi-gene family. There is complex hormonal and tissue-specific regulation of MUP gene expression. The multi-gene family and its outflow are characterized by a polymorphism which extends over species, strains, sexes, and individuals. There is evidence of evolutionary conservation of the genes and their outflow within the species and evidence of change between species. MUPs share the eight-stranded beta-barrel structure lining a hydrophobic pocket, common to lipocalins. There is also a high degree of structural conservation between mouse and rat MUPs. MUPs bind small natural odorant molecules in the hydrophobic pocket with medium affinity in the 10(4)-10(5) M(-1) range, and are excreted in the field, with bound odorants. The odorants are then released slowly in air giving a long lasting olfactory trace to the spot. MUPs seem to play complex roles in chemosensory signalling among rodents, functioning as odorant carriers as well as proteins that prime endocrine reactions in female conspecifics. Aphrodisin is a lipocalin, found in hamster vaginal discharge, which stimulates male copulatory behaviour. Aphrodisin does not seem to bind odorants and no polymorphism has been shown. Both MUPs and aphrodisin stimulate the vomeronasal organ of conspecifics.

Glycosylated major urinary protein of the house mouse: characterization of its N-linked oligosaccharides

A minor component of the major urinary protein complex of the house mouse was chromatographically isolated and ascertained to be a previously suspected glycoprotein. Using highly sensitive mass-spectrometric techniques for sequencing and linkage analysis, the N-linked oligosaccharides of this glycoprotein were characterized. They were determined to be of the complex type with a wide heterogeneity. The heterogeneity was due to both the degree of sialylation and the presence of galactose residues in either beta(1-3) or beta(1-4) linkages. The biantennary structures were the most pronounced glycans, while tri- and tetraantennary entities were minor.

Screening for genes up-regulated in 5/6 nephrectomized mouse kidney

BACKGROUND

In diabetic and nondiabetic renal diseases, glomerular hyperfiltration is believed to play a central role in the subsequent progression of glomerulosclerosis and interstitial renal scarring. To identify genes involved in the process of hyperfiltration and hypertrophy, a polymerase chain reaction (PCR)-based subtraction method, that is, representational difference analysis of cDNA (cDNA-RDA), was employed.

METHODS

Ten-week-old ICR mice were 5/6 nephrectomized and sham operated. After two weeks, mRNAs were isolated from control and remnant kidneys and were subjected to the cDNA-RDA procedure.

RESULTS

We identified 10 known and 9 novel genes. Among 19 clones, 12 clones (8 known and 4 novel) showed 1.5- to 6-fold up-regulation by Northern blot analyses. The remaining seven clones were rarely expressed genes and were barely detected by Northern blot analyses, and their up-regulated expression was confirmed by Southern blot analysis using the PCR-amplified representative amplicons. The known genes included kidney androgen-regulated protein, major urinary protein, lysozyme M, metalloproteinase-3 tissue inhibitor, chaperonin 10, cytochrome oxidase I, epsilon-sarcoglycan, ribosomal protein S3a, G-proteingamma10 subunit, and splicing factor 9G8. All of the isolated known genes have not been reported to be up-regulated in the nephrectomized mouse kidney and suggest the possible role of androgen action, mitochondrial functions, matrix metabolism, cell-matrix interactions, and intracellular signaling events in the initiation of the progressive renal injury of the remnant kidney. Furthermore, cDNA-RDA facilitates the discovery of novel genes, including two kidney-specific genes.

CONCLUSIONS

The isolated known and novel genes may be involved in the pathobiological process of initial hyperfiltration and hypertrophy of remnant kidney.

Gene conversion of major histocompatibility complex genes in the mouse spermatogenesis is a premeiotic event

The molecular genetic mechanism of gene conversion in higher eukaryotes remains unknown. We find it of considerable interest to determine when during spermatogenesis gene conversion occurs. We have therefore purified pachytene spermatocytes and haploid spermatocytes from adult mice and analyzed these fractions for the presence of gene conversion products resulting from the transfer between the major histocompatibility complex class II genes Ebd and Abk in a polymerase chain reaction assay. We have further isolated spermatogenic cells from prepubescent mice and analyzed them for the presence of the same gene conversion products. We can detect gene conversion products in testis cells as early as in 8-d-old mice where the only existing spermatogenic cells are spermatogonia. The frequency of gene conversion products remains the same as the cells reach meiosis in 18-d-old mice, and is unchanged after meiosis is completed in haploid spermatocytes. Gene conversion of this specific fragment therefore appears to be a premeiotic event and, consequently, relies on genetic mechanisms other than normal meiotic recombination.

Adult phenotype in the mouse can be affected by epigenetic events in the early embryo

Major epigenetic modifications apparently occur during early development in the mouse. The factors that induce such modifications are complex and may involve the various components of a zygote. We have started to explore whether changes in the nucleocytoplasmic composition brought about by micromanipulation can induce phenotypic effects through epigenetic modifications. Nucleocytoplasmic hybrids were therefore prepared by transplanting a female pronucleus into a recipient egg from a different genotype. As a result, the maternal genome was of a different genetic background as compared with the egg cytoplasm. Specifically, experimental zygotes had cytoplasm from the inbred strain C57BL/6, a maternal genome from DBA/2, and a paternal genome from C57BL/6 (termed BDB hybrids). The mirror-image combination, termed DBD, was also made. The reconstituted zygotes were transferred to recipients and allowed to develop to term. Mice born from manipulated zygotes showed transcriptional repression and DNA methylation of major urinary protein genes in their liver, as well as growth deficiency resulting in reduced adult body weight. No altered phenotype was observed in controls in which the maternal pronucleus was simply transplanted back into another zygote of the same genetic background. These results clearly demonstrate phenotypic as well as molecular effects on DNA methylation and expression of at least one gene. Phenotype was therefore no longer predicted by genotype as a result of epigenetic modifications in experimental embryos. What precisely triggers the phenotypic and epigenetic changes is unknown, but presumably, nucleocytoplasmic interactions in hybrid zygotes may be partly responsible.

Application of electrospray ionization mass spectrometry with maximum-entropy analysis to allelic 'fingerprinting' of major urinary proteins

Mixtures of a specific group of proteins, the major urinary proteins (MUPs), believed to have a role in odorant binding, have been analysed by electrospray ionization mass spectrometry. The data obtained from conventional transformed electrospray data confirm that the molecular weights of the protein mixtures, deduced from published sequences, lie in the molecular weight range 18,600 to 19,000 Da. Application of maximum-entropy analysis to the raw electrospray data has confirmed a heterogeneity in MUP composition, consistent with allelic similarities (and differences) between the different mouse strains. This work demonstrates the use of maximum entropy in the assessment of protein content and in the subsequent resolution enhancement of naturally occurring protein mixtures containing components of closely similar molecular mass.

The murine Spi-2 proteinase inhibitor locus: a multigene family with a hypervariable reactive site domain

We have isolated 10 closely linked members of a proteinase inhibitor multigene family from the inbred mouse strain 129. These sequences, termed the Serine Proteinase Inhibitor 2 (Spi-2) genes, appear to have been derived from a common ancestor represented in man by the single copy alpha 1-antichymotrypsin gene. The genes are clustered on two cloned genomic DNA segments spanning 220 kb, and have at least partially retained the intragenic structure of the ancestral Spi-2 gene. Sequence analysis from the final coding exon indicates that most of the mouse genes may be competent to encode functional proteins, some with a predictable inhibitory spectrum, and several representing novel inhibitor types. An oligonucleotide probe designed to one reactive centre sequence enabled the isolation of the cognate expressed transcript from a liver cDNA library. However, whether expressed or not, the reactive centre regions of all the sequences have diverged at a rapid rate relative to structurally defined flanking sequences. The divergence is also appreciably greater than that occurring in an adjacent non-coding sequence. This phenomenon has established novel potential inhibitory specificities, while maintaining a functional inhibitor structure.

Ligand binding characteristics of homologous rat and mouse urinary proteins and pyrazine-binding protein of calf

1. The binding affinities of three classes of homologous proteins, alpha 2u protein from rat urine, major urinary protein of mouse and pyrazine-binding protein of calf nasal mucosa have been determined for a panel of ligands. 2. Best ligands were low threshold odorants for man, but chemically unrelated. 3. The binding spectra of the homologous proteins were different.

Intraspecific evolution of a gene family coding for urinary proteins

The genome of the laboratory mouse contains about 35 major urinary protein (MUP) genes, many of which are clustered on chromosome 4. We have used distance and parsimony methods to estimate phylogenetic relationships between MUP genes from nucleotide sequence and restriction maps. By analyzing coding sequences we show that the genes fall into four main groups of related sequences (groups 1-4). Comparisons of restriction maps and the nucleotide sequences of hypervariable regions that lie 50 nucleotides 5' to the cap sites show that the group 1 genes and probably also the group 2 pseudogenes fall into subgroups. The most parsimonious trees are consistent with the evolution of the array of group 1 and 2 genes by mutation accompanied by a process tending toward homogenization such as unequal crossing-over or gene conversion. The phylogenetic grouping correlates with grouping according to aspects of function. The genomes of the inbred strains BALB/c and C57BL contain different MUP gene arrays that we take to be samples from the wild population of arrays.