The mouse epididymal transcriptome: transcriptional profiling of segmental gene expression in the epididymis

Regulation of gene expression by estrogen and testosterone in the proximal mouse reproductive tract

The role of estrogen and testosterone in the regulation of gene expression in the proximal reproductive tract is not completely understood. To address this question, mice were treated with testosterone or estradiol, and RNA from the efferent ducts and caput epididymides was processed and hybridized to Affymetrix M430 2.0 microarrays. Analysis of array output identified probe sets in each tissue with altered levels in hormone-treated versus control animals. Hormone treatment efficacy was confirmed by determination of serum hormone levels before and after treatment and by observed changes in transcript levels of previously reported hormone-responsive genes. Tissue-specific hormone sensitivity was observed with 2867 and 3197 probe sets changing significantly in the efferent ducts after estrogen and testosterone treatment, respectively. In the caput epididymidis, 117 and 268 probe sets changed after estrogen and testosterone treatment, respectively, demonstrating a greater response to hormone in the efferent ducts than in the caput epididymidis. Transcripts sharing similar profiles in the intact and hormone-treated animals compared with castrated controls were also identified. Ontology analysis of probe sets revealed that a significant number of hormone-regulated transcripts encode proteins associated with lipid metabolism, transcription, and steroid metabolism in both tissues. Real-time RT-PCR was used to confirm array data and to investigate other potential hormone-responsive regulators of proximal reproductive tract function. The results of this work reveal previously unknown responses to estrogen in the caput epididymidis and to testosterone in the efferent ducts, as well as tissue-specific hormone sensitivity in the proximal reproductive tract.

New insights into epididymal biology and function

BACKGROUND

The epididymis performs an important role in the maturation of spermatozoa including their acquisition of progressive motility and fertilizing ability. However, the molecular mechanisms that govern these maturational events are still poorly defined. This review focuses on recent progress in our understanding of epididymal function including its development, role of the luminal microenvironment in sperm maturation, regulation and novel mechanisms the epididymis utilizes to carry out some of its functions.

METHODS

A systematic search of Pubmed was carried out using the search term 'epididymis'. Articles that were published in the English language until the end of August 2008 and that focused on the specific topics described above were included. Additional papers cited in the primary reference were also included.

RESULTS

While the majority of these findings were the result of studies in animal models, recent studies in the human epididymis are also presented including gene profiling studies to examine regionalized expression in normal epididymides as well as in those from vasectomized patients.

CONCLUSIONS

Significant progress has been made in our understanding of epididymal function providing new insights that ultimately could improve human health. The data also indicate that the human epididymis plays an important role in sperm maturation but has unique properties compared with animal models.

Development and morphogenesis of the Wolffian/epididymal duct, more twists and turns

The epididymis serves a critical function of preparing the male germ cells for fertilization. In order for the epididymis to carry out this role it must undergo a highly coordinated succession of molecular and morphogenic events during development. These events begin with the formation of the Wolffian or nephric duct, the embryonic precursor of the male reproductive system, and end with the three-dimensional coiled postnatal epididymis that is comprised of several distinctly functional segments. How the duct changes from a simple straight tube to a highly convoluted structure will be the focus of this article. In reviewing the literature's current understanding of epididymal morphogenesis, we will highlight some of the classic morphological studies and discuss some of the more recent genetic models that have all served to contribute to our understanding of this system. Where published information is scarce we will provide potential hypotheses that warrant further investigation and may open up new directions of exploration using the epididymis as a model for tubular morphogenesis.

Beta-defensin 22 is a major component of the mouse sperm glycocalyx

Surface components of sperm isolated from the cauda epididymides were stabilized by whole sperm fixation for immunization of rabbits. The resulting immunoglobulins (Igs) recognized a single protein of 130 kDa (non-reduced) or 54-57 kDa (reduced) on western blots of cauda sperm. Igs recognized the same 54-57 kDa protein band on whole tissue blots of the corpus and cauda epididymidis and vas deferens. No immunoreactive bands were detected on blots of the prostate, seminal vesicles, testes, caput epididymis, or any of various non-reproductive tissues. Removal of sperm from the vas deferens prior to blotting eliminated the detection of the sperm antigen. Antibodies raised to synthetic peptides, identical in amino acid sequence to two unique spans of DEFB22, recognized the same 130/54-57 kDa antigen on western blots of both caudal sperm and the purified antigen isolated with the anti-sperm Ig. From indirect immunofluorescence, both the anti-sperm and anti-peptide Igs appeared to localize to the entire sperm surface, a pattern confirmed at the ultrastructural level. Real-time PCR identified the corpus epididymides as the major site of expression of DEFB22, with negligible expression in the testes, caput epididymides, and vas deferens. Immunostaining of epididymal sections showed DEFB22 being released into the lumen at the distal caput/proximal corpus, with sperm becoming intensely coated with DEFB22 as they reached the distal corpus. Most uterine sperm recovered from mice 4 h following copulation exhibited DEFB22 coating the entire sperm surface. By contrast, some sperm recovered from the oviduct and cumulus extracellular matrix showed loss of DEFB22 from the sperm head.

Adaptive evolution in rodent seminal vesicle secretion proteins

Proteins involved in reproductive fitness have evolved unusually rapidly across diverse groups of organisms. These reproductive proteins show unusually high rates of amino acid substitutions, suggesting that the proteins have been subject to positive selection. We sought to identify seminal fluid proteins experiencing adaptive evolution because such proteins are often involved in sperm competition, host immunity to pathogens, and manipulation of female reproductive physiology and behavior. We performed an evolutionary screen of the mouse prostate transcriptome for genes with elevated evolutionary rates between mouse and rat. We observed that secreted rodent prostate proteins evolve approximately twice as fast as nonsecreted proteins, remarkably similar to findings in the primate prostate and in the Drosophila male accessory gland. Our screen led us to identify and characterize a group of seminal vesicle secretion (Svs) proteins and to show that the gene Svs7 is evolving very rapidly, with many amino acid sites under positive selection. Another gene in this group, Svs5, showed evidence of branch-specific selection in the rat. We also found that Svs7 is under selection in primates and, by using three-dimensional models, demonstrated that the same regions have been under selection in both groups. Svs7 has been identified as mouse caltrin, a protein involved in sperm capacitation, the process responsible for the timing of changes in sperm activity and behavior, following ejaculation. We propose that the most likely explanation of the adaptive evolution of Svs7 that we have observed in rodents and primates stems from an important function in sperm competition.

Transcriptome analysis of a cDNA library from adult human epididymis

Mammalian Gene Collection (MGC) verified over 9000 human full-ORF genes and FLJ Program reported 21 243 cDNAs of which 14 409 were unique ones and 5416 seemed to be protein-coding. The pity is that epididymis cDNA library was missing in their sequencing target list. Epididymis is a very important male accessory sex organ for sperm maturation and storage. Fully differentiated spermatozoa left from testis acquire their motility and capacity for fertilization via interactions with the epididymal epithelium duct lumen during passage through this convoluted duct. Here, we report that 20 000 clones from a healthy male epididymis cDNA library have been sequenced. The sequencing data provided 8234 known sequences and 650 unknown cDNA fragments. Hundred and six of 650 unknown cDNA clone inserts were randomly selected for fully sequencing. There were 25 unknown unique sequences and 19 released but unreported sequences came out. By northern blot analysis, four sequences randomly selected from the 19 released sequences with no known function showed positive mRNA signals in epididymis and testis. The signals for three of six from those unknown group showed as epididymis abundant in a region-specific manner but not in the testis and other tissues tested. All the sequencing data will be available on the website www.sdscli.com.

Cellular signaling by fibroblast growth factors (FGFs) and their receptors (FGFRs) in male reproduction

The major function of the reproductive system is to ensure the survival of the species by passing on hereditary traits from one generation to the next. This is accomplished through the production of gametes and the generation of hormones that function in the maturation and regulation of the reproductive system. It is well established that normal development and function of the male reproductive system is mediated by endocrine and paracrine signaling pathways. Fibroblast growth factors (FGFs), their receptors (FGFRs), and signaling cascades have been implicated in a diverse range of cellular processes including: proliferation, apoptosis, cell survival, chemotaxis, cell adhesion, motility, and differentiation. The maintenance and regulation of correct FGF signaling is evident from human and mouse genetic studies which demonstrate that mutations leading to disruption of FGF signaling cause a variety of developmental disorders including dominant skeletal diseases, infertility, and cancer. Over the course of this review, we will provide evidence for differential expression of FGFs/FGFRs in the testis, male germ cells, the epididymis, the seminal vesicle, and the prostate. We will show that this signaling cascade has an important role in sperm development and maturation. Furthermore, we will demonstrate that FGF/FGFR signaling is essential for normal epididymal function and prostate development. To this end, we will provide evidence for the involvement of the FGF signaling system in the regulation and maintenance of the male reproductive system.

Cloning and identification of a novel sperm binding protein, HEL-75, with antibacterial activity and expressed in the human epididymis

BACKGROUND

The HEL-75 protein is a beta-defensin that was identified by analyzing a human epididymis cDNA library. Studying its function may not only elucidate the mechanisms of host defense, but may also provide new alternatives for novel therapeutic drugs for reproductive tract infections.

METHODS

The HEL-75 gene was amplified by PCR, and its structure and function were predicted and analyzed with bioinformatics tools. Polyclonal serum was raised against recombinant HEL (rHEL)-75 protein. The gene expression pattern was analyzed with RT-PCR and immunofluorescent staining. Finally, the antimicrobial activity and function during fertilization of HEL-75 were analyzed using a colony-forming unit assay and IVF, respectively.

RESULTS

The human HEL-75 gene is located on chromosome 20p13 and encodes a 95 amino acid protein with a predicted N-terminal signal peptide of 22 amino acids. The protein has six conserved cysteine residues, characteristic of members of the beta-defensin superfamily, as well as several potential post-translational modification sites. At the transcriptional level, HEL-75 was expressed in the epididymis and lung, but only in the epididymis at the translational level. Immunofluorescent staining showed that HEL-75 protein bound spermatozoa in the epididymis. RHEL-75 protein could kill Escherichia coli in vitro in a dose- and time-dependent fashion. However, no effect was observed on sperm motility nor fertilization when spermatozoa were blocked with anti-rHEL-75 polyclonal serum.

CONCLUSION

HEL-75 is a new beta-defensin expressed in the epididymis and on sperm; it may play an important role in host defense.

Adaptive evolution of proteins secreted during sperm maturation: an analysis of the mouse epididymal transcriptome

A common pattern observed in molecular evolution is that reproductive genes tend to evolve rapidly. However, most previous studies documenting this rapid evolution are based on genes expressed in just a few male reproductive organs. In mammals, sperm become motile and capable of fertilization only after leaving the testis, during their transit through the epididymis. Thus, genes expressed in the epididymis are expected to play important roles in male fertility. Here, we performed evolutionary genetic analyses on the epididymal transcriptome of mice. Overall, epididymis-expressed genes showed evidence of strong evolutionary constraint, a finding that contrasts with most previous analyses of genes expressed in other male reproductive organs. However, a subset of epididymis-specialized, secreted genes showed several signatures of adaptive evolution, including an increased rate of nonsynonymous evolution. Furthermore, this subset of genes was overrepresented on the X chromosome. Immunity and protein modification functions were significantly overrepresented among epididymis-specialized, secreted genes. These analyses identified a group of genes likely to be important in male reproductive success.

Epididymosomes are involved in the acquisition of new sperm proteins during epididymal transit

During epididymal transit, spermatozoa acquire new proteins. Some of these newly acquired proteins behave as integral membrane proteins, including glycosylphosphatidylinositol (GPI)-anchored proteins. This suggests that the secreted epididymal proteins are transferred to spermatozoa by an unusual mechanism. Within the epididymal lumen, spermatozoa interact with small membranous vesicles named epididymosomes. Many proteins are associated with epididymosomes and the protein composition of these vesicles varies along the excurrent duct and differs from soluble intraluminal proteins. Some epididymosome-associated proteins have been identified and their functions in sperm maturation hypothesized. These include P25b, a zona pellucida binding protein, macrophage migration inhibitory factor, enzymes of the polyol pathway, HE5/CD52, type 5 glutathione peroxidase, and SPAM1 or PH-20. The electrophoretic patterns of proteins associated to epididymosomes are complex and some of these proteins are transferred to defined surface domains of epididymal spermatozoa. Epididymosomes collected from different epididymal segments interact differently with spermatozoa. This protein transfer from epididymosomes to spermatozoa is time-dependent, temperature-dependent and pH-dependent, and is more efficient in the presence of zinc. Some proteins are segregated to lipid raft domains of epididymosomes and are selectively transferred to raft domains of the sperm plasma membrane. Some evidence is presented showing that epididymosomes are secreted in an apocrine manner by the epididymal epithelial cells. In conclusion, epididymosomes are small membranous vesicles secreted in an apocrine manner in the intraluminal compartment of the epididymis and play a major role in the acquisition of new proteins by the maturing spermatozoa.

Vezatin, a ubiquitous protein of adherens cell-cell junctions, is exclusively expressed in germ cells in mouse testis

In the male reproductive organs of mammals, the formation of spermatozoa takes place during two successive phases: differentiation (in the testis) and maturation (in the epididymis). The first phase, spermiogenesis, relies on a unique adherens junction, the apical ectoplasmic specialization linking the epithelial Sertoli cells to immature differentiating spermatids. Vezatin is a transmembrane protein associated with adherens junctions and the actin cytoskeleton in most epithelial cells. We report here the expression profile of vezatin during spermatogenesis. Vezatin is exclusively expressed in haploid germ cells. Immunocytochemical and ultrastructural analyses showed that vezatin intimately coincides, temporally and spatially, with acrosome formation. While vezatin is a transmembrane protein associated with adherens junctions in many epithelial cells, it is not seen at the ectoplasmic specializations, neither at the basal nor at the apical sites, in the seminiferous epithelium. In particular, vezatin does not colocalize with espin and myosin VIIa, two molecular markers of the ectoplasmic specialization. In differentiating spermatids, ultrastructural data indicate that vezatin localizes in the acrosome. In epididymal sperm, vezatin localizes also to the outer acrosomal membrane. Considering its developmental and molecular characteristics, vezatin may be involved in the assembly/stability of this spermatic membrane.

Segment boundaries of the adult rat epididymis limit interstitial signaling by potential paracrine factors and segments lose differential gene expression after efferent duct ligation

The epididymis is divided into caput, corpus and cauda regions, organized into intraregional segments separated by connective tissue septa (CTS). In the adult rat and mouse these segments are highly differentiated. Regulation of these segments is by endocrine, lumicrine and paracrine factors, the relative importance of which remains under investigation. Here, the ability of the CTS to limit signaling in the interstitial compartment is reviewed as is the effect of 15 days of unilateral efferent duct ligation (EDL) on ipsilateral segmental transcriptional profiles. Inter-segmental microperifusions of epidermal growth factor (EGF), vascular endothelial growth factor (VEGFA) and fibroblast growth factor 2 (FGF2) increased phosphorylation of mitogen activated protein kinase (MAPK) in segments 1 and 2 of the rat epididymis and the effects of all factors were limited by the CTS separating the segments. Microarray analysis of segmental gene expression determined the effect of 15 days of unilateral EDL on the transcriptome-wide gene expression of rat segments 1-4. Over 11,000 genes were expressed in each of the four segments and over 2000 transcripts in segment 1 responded to deprivation of testicular lumicrine factors. Segments 1 and 2 of control tissues were the most transcriptionally different and EDL had its greatest effects there. In the absence of lumicrine factors, all four segments regressed to a transcriptionally undifferentiated state, consistent with the less differentiated histology. Deprivation of lumicrine factors could stimulate an individual gene's expression in some segments yet suppress it in others. Such results reveal a higher complexity of the regulation of rat epididymal segments than that is generally appreciated.

Differential Gene Expression among the Proximal Segments of the Rat Epididymis Is Lost after Efferent Duct Ligation1

The epididymis has traditionally been divided into the caput, corpus, and cauda regions, which are further organized into intraregional segments. In the rat and mouse, these segments have high degrees of transcriptional differentiation, and what has traditionally been called the initial segment of the rat epididymis actually consists of three transcriptionally different intraregional segments. These segments are regulated by endocrine, lumicrine, and paracrine factors, whose relative importance remains a topic of investigation. In the present study, 15-day unilateral efferent duct ligation (EDL) was used to deprive ipsilateral rat epididymides of lumicrine regulation. Segments 1-4 of EDL epididymides and contralateral, sham-operated tissues were collected individually. Microarray analysis of gene expression was used to determine the effect of lumicrine factor deprivation on the transcriptome-wide gene expression of each segment studied. More than 11 000 genes were detected as being expressed in each of the four segments examined. More than 2000 genes responded significantly to EDL in segment 1, although this number of genes declined in each succeeding segment. Segments 1 and 2 of control tissues were the most different transcriptionally and the most affected by EDL. In the absence of lumicrine factors, the four segments regressed to a transcriptionally undifferentiated state, which was consistent with the less-differentiated histology seen after EDL. Interestingly, for an individual gene, lumicrine factor deprivation could stimulate expression in some segments and suppress expression in other segments. These results reveal a higher complexity to the regulation of rat epididymal segments than heretofore appreciated.

Relocalization of the V-ATPase B2 subunit to the apical membrane of epididymal clear cells of mice deficient in the B1 subunit

An acidic luminal pH in the epididymis contributes to maintaining sperm quiescent during their maturation and storage. The vacuolar H+ATPase (V-ATPase), located in narrow and clear cells, is a major contributor to luminal acidification. Mutations in one of the V-ATPase subunits, ATP6v1B1 (B1), cause distal renal tubular acidosis in humans but surprisingly, B1−/− mice do not develop metabolic acidosis and are fertile. While B1 is located in the apical membrane of narrow and clear cells, the B2 subunit localizes to subapical vesicles in wild-type mouse, rat and human epididymis. However, a marked increase (84%) in the mean pixel intensity of B2 staining was observed in the apical pole of clear cells by conventional immunofluorescence, and relocalization into their apical membrane was detected by confocal microscopy in B1−/− mice compared with B1+/+. Immunogold electron microscopy showed abundant B2 in the apical microvilli of clear cells in B1−/− mice. B2 mRNA expression, determined by real time RT-PCR using laser-microdissected epithelial cells, was identical in both groups. Semiquantitative Western blots from whole epididymis and cauda epididymidis showed no variation of B2 expression. Finally, the luminal pH of the cauda epididymidis was the same in B1−/− mice as in B1+/+ (pH 6.7). These data indicate that whereas overall expression of B2 is not affected in B1−/− mice, significant redistribution of B2-containing complexes occurs from intracellular compartments into the apical membrane of clear cells in B1−/− mice. This relocation compensates for the absence of functional B1 and maintains the luminal pH in an acidic range that is compatible with fertility.

Identification of epididymis-specific transcripts in the mouse and rat by transcriptional profiling

As part of our efforts to identify novel contraceptive targets in the epididymis we performed transcriptional profiling on each of the 10 and 19 segments of the mouse and rat epididymidis, respectively, using Affymetrix whole genome microarrays. A total of 17 096 and 16 360 probe sets representing transcripts were identified as being expressed in the segmented mouse and rat epididymal transcriptomes, respectively. Comparison of the expressed murine transcripts against a mouse transcriptional profiling database derived from 22 other mouse tissues identified 77 transcripts that were expressed uniquely in the epididymis. The expression of these genes was further evaluated by reverse transcription polymerase chain reaction (RT-PCR) analysis of RNA from 21 mouse tissues. RT-PCR analysis confirmed epididymis-specific expression of Defensin Beta 13 and identified two additional genes with expression restricted only to the epididymis and testis. Comparison of the 16 360 expressed transcripts in the rat epididymis with data of 21 other tissues from a rat transcriptional profiling database identified 110 transcripts specific for the epididymis. Sixty-two of these transcripts were further investigated by qPCR analysis. Only Defensin 22 (E3 epididymal protein) was shown to be completely specific for the epididymis. In addition, 14 transcripts showed more than 100-fold selective expression in the epididymis. The products of these genes might play important roles in epididymal and/or sperm function and further investigation and validation as contraceptive targets are warranted. The results of the studies described in this report are available at the Mammalian Reproductive Genetics (MRG) Database (http://mrg.genetics.washington.edu/).

Gene Expression Profiling and Its Relevance to the Blood-Epididymal Barrier in the Human Epididymis1

The luminal environment along the epididymal duct is important for spermatozoal maturation. This environment is unique and created by the blood-epididymal barrier, which is formed by tight and adhering junctions. For the human epididymis, little information exists on the proteins that comprise these junctions. Our objectives were to assess the gene expression profiles in the different segments of the human epididymis and to identify the proteins that make up the blood-epididymal barrier. Using microarrays, we identified 2980 genes that were differentially expressed by at least 2-fold between the various segments. Of the many genes involved in diverse functions, were those that encoded adhesion proteins (cadherins and catenins) and tight junctional proteins (claudins [CLDN] and others). PCR analyses confirmed the microarray data. Immunolocalization of CLDNs 1, 3, 4, 8, and 10 revealed that the localization of CLDNs differed along the epididymis. In all three segments, CLDNs 1, 3, and 4 were localized to tight junctions, along the lateral margins of adjacent principal cells, and at the interface between basal and principal cells. CLDN8 was localized to tight junctions in all three segments, in addition to being localized in the caput along the lateral margins of principal cells, and in the corpus, at the interface between principal and basal cells. CLDN10, tight junction protein 1, and occludin were localized exclusively to tight junctions in all three epididymal segments. These data indicate that the epididymis displays a complex pattern of gene expression, which includes genes that are implicated in the formation of the blood-epididymal barrier, which suggests complex regulation of this barrier.

The Rat Epididymal Transcriptome: Comparison of Segmental Gene Expression in the Rat and Mouse Epididymides1

Regional differences along the epididymis are essential for the establishment of the luminal environment required for sperm maturation. In the current study, 19 morphologically distinct segments of the rat epididymis were identified by microdissection. Total RNA was isolated from each segment and subjected to microarray analysis. Segmental analysis of epididymal gene expression identified more than 16,000 expressed qualifiers, whereas profiling of RNA from whole rat epididymis identified approximately 12,000 expressed qualifiers. Screening a panel of normal rat tissues identified both epididymal-selective and epididymal-specific transcripts. In addition, more than 3500 qualifiers were shown to be present and differentially upregulated or downregulated by more than fourfold between any two segments. The present study complements our previous segment-dependent analysis of gene expression in the mouse epididymis and allows for comparative analyses between datasets. A total of 492 genes was shown to be present on both the MOE430 (mouse) and RAE230_2 (rat) microarrays, expressed in the epididymis of both species, and differentially expressed by more than fourfold in between segments in each species. Moreover, in-depth quantitative RT-PCR analysis of 36 members of the beta defensin gene family showed highly conserved patterns of expression along the lengths of the mouse and rat epididymides. These analyses elucidate global gene expression patterns along the length of the rat epididymis and provide a novel evaluation of conserved and nonconserved gene expression patterns in the epididymides of the two species. Furthermore, these data provide a powerful resource for the research community for future studies of biological factors that mediate sperm maturation and storage.

Novel epididymis-specific mRNAs downregulated by HE6/Gpr64 receptor gene disruption

Targeted disruption of the epididymis-specific HE6/Gpr64 receptor gene in mice led to male infertility. In order to characterize the phenotype at a molecular level, we compared the gene expression patterns of wild type (wt) versus knockout (KO) caput epididymides. The caput region of KO males, although morphologically normal, nevertheless showed an aberrant expression pattern. Combining micro array analysis, differential library screening, Northern blot analysis and quantitative RT-PCR, we found that the knockout of the HE6/Gpr64 receptor was mainly associated with the downregulation of genes specific to the initial segment. The list of KO downregulated transcripts comprised Enpp2/autotaxin, the lipocalins 8 and 9, the beta-defensin Defb42, cystatins 8 and 12, as well as the membrane proteins Adam (A Disintegrin And Metalloprotease) 28, claudin-10, EAAC1, and the novel Me9. Clusterin/ApoJ and osteopontin/Spp1 mRNAs, on the other hand, were upregulated in the KO tissues. The Me9 transcript was studied in further detail, and we report here a cluster of related epididymis-specific genes. Me9 is specifically expressed in the initial segment and is representative of a novel and highly conserved mammalian gene family. The family consists of single-exon genes only; intron-containing paralogs have not yet been ascertained. The cloned cDNA sequences predicted hydrophobic polytopic membrane proteins containing the DUF716 motif. Protein expression was shown in the rodent caput epididymidis but remained uncertain in primates.

Systematic identification and integrative analysis of novel genes expressed specifically or predominantly in mouse epididymis

Background

Maturation of spermatozoa, including development of motility and the ability to fertilize the oocyte, occurs during transit through the microenvironment of the epididymis. Comprehensive understanding of sperm maturation requires identification and characterization of unique genes expressed in the epididymis.

Results

We systematically identified 32 novel genes with epididymis-specific or -predominant expression in the mouse epididymis UniGene library, containing 1505 gene-oriented transcript clusters, by in silico and in vitro analyses. The Northern blot analysis revealed various characteristics of the genes at the transcript level, such as expression level, size and the presence of isoform. We found that expression of the half of the genes is regulated by androgens. Further expression analyses demonstrated that the novel genes are region-specific and developmentally regulated. Computational analysis showed that 15 of the genes lack human orthologues, suggesting their implication in male reproduction unique to the mouse. A number of the novel genes are putative epididymal protease inhibitors or β-defensins. We also found that six of the genes have secretory activity, indicating that they may interact with sperm and have functional roles in sperm maturation.

Conclusion

We identified and characterized 32 novel epididymis-specific or -predominant genes by an integrative approach. Our study is unique in the aspect of systematic identification of novel epididymal genes and should be a firm basis for future investigation into molecular mechanisms underlying sperm maturation in the epididymis.

HOXBES2: a novel epididymal HOXB2 homeoprotein and its domain-specific association with spermatozoa

The sperm from the testis acquires complete fertilizing ability and forward progressive motility following its transit through the epididymis. Acquisition of these characteristics results from the modification of the sperm proteome following interactions with epididymal secretions. In our attempts to identify epididymis-specific sperm plasma membrane proteins, a partial 2.83-kb clone was identified by immunoscreening a monkey epididymal cDNA library with an agglutinating monoclonal antibody raised against washed human spermatozoa. The sequence of the 2.83-kb clone exhibited homology to the region between 1 and 1097 bp of the homeobox gene, Hoxb2. This sequence was found to be species conserved, as revealed by RT-PCR analysis. To obtain a full-length clone of the sequence, 5' RACE-PCR (rapid amplification of cDNA ends PCR) was carried out using rat epididymal RNA as the template. It resulted in a full-length 1.657-kb cDNA encoding a 32.9-kDa putative protein. The protein designated HOXBES2 exhibited homology to the conserved 61-amino acid homeodomain region of the HOXB2 homeoprotein. However, characteristic differences were noted in its amino and carboxyl termini compared with HOXB2. A putative 30-kDa protein was detected in the tissue extracts from adult rat epididymis and caudal spermatozoa, and a 37-kDa protein was detected in the rat embryo when probed with a polyclonal antibody against HOXB2 protein. Multiple tissue Western blot and immunohistochemical analysis further indicated its expression in the cytoplasm of the principal and basal epithelial cells, with maximal expression in the distal epididymal segments. Northern blot analysis detected a single approximately 2.5-kb transcript from the adult epididymis. Indirect immunofluorescence localized the protein to the acrosome, midpiece, and equatorial segments of rat caudal and ejaculated human and monkey spermatozoa, respectively. In conclusion, we have identified and characterized a novel epididymal homeoprotein different from HOXB2 protein and hereafter referred to as HOXBES2, (HOXB2 homeodomain containing epididymis-specific sperm protein) with a probable role in fertilization.

Differential expression and antibacterial activity of WFDC10A in the monkey epididymis

The ability of the epididymis to perform its diverse functions stems from its regionalized gene and protein expression patterns. The differences in the gene expression patterns of the caput and cauda regions of the bonnet monkey epididymis were compared using the technique of differential display reverse transcriptase polymerase chain reaction. A transcript showing homology to human whey acidic protein 10 (hWFDC10A) was highly expressed in the monkey caput region. A peptide P2 was designed spanning a region of the monkey WFDC10A (mWFDC10A), which could inhibit the growth of gram-negative bacterial strains of Escherichia coli. P2 could permeabilize the bacterial cell membrane but was unable to permeabilize mammalian cells as evidenced by the lack of hemolysis upon incubation with the peptide. Expression of genes such as mWFDC10A may be essential in providing the first line of defense against microbial infections to the epididymal tract and thus rendering protection to the male gametes sheltered within the epididymis.

Growth Factor-Stimulated Mitogen-Activated Kinase (MAPK) Phosphorylation in the Rat Epididymis Is Limited by Segmental Boundaries1

Previous evidence has shown that sperm maturation is the result of successive events that influence sperm cells as they move through different microenvironments from the caput to the cauda epididymis. The physiological basis for the creation and maintenance of specific microenvironments along the epididymis are poorly understood. Anatomically, the epididymis consists of segments or lobules of epididymal tubule separated by connective tissue septa (CTS). The fact that CTS restrict the diffusion of tracer substances between segments and that certain gene expression patterns are segment-specific suggest that segments may represent functional epididymal units. In this report, we have further investigated epididymal segmentation by focusing on the ability of CTS to limit the effect of biologically relevant molecules, in particular epidermal growth factor (EGF), basic fibroblast growth factor (FGF2), and vascular endothelial growth factor A (VEGFA), in Segments 1 and 2 of the rat epididymis. We have demonstrated that these growth factors activate mitogen-activated kinase (MAPK) in both segments studied and that growth factors injected into the interstitial space of these segments in vivo exhibited a stimulatory effect only in the segment into which they were injected, i.e., MAPK activation was not observed in the adjacent segment. This restricting influence of CTS was abrogated by treatment with collagenase. In addition, we demonstrate the expression of selected forms of these growth factors and their receptors in Segments 1 and 2, and identify potential downstream targets. These results suggest that CTS regulate the trophic influences of growth factors and potentially other paracrine molecules, thus creating functionally separate units within the epididymis.

Epididymal expression of the forkhead transcription factor Foxi1 is required for male fertility

An essential aspect of male reproductive capacity is the immediate availability of fertilization-ready spermatozoa. To ensure this, most mammals rely on post-testicular sperm maturation. In epididymis, germ cells are matured and stored in a quiescent state that readily can be altered to produce active spermatozoa. This depends on active proton secretion into the epididymal lumen. We have identified Foxi1 as an important regulator of gene expression in narrow and clear cells-the major proton secretory cells of epididymal epithelia. Foxi1 appears to be required for the expression of the B1-subunit of the vacuolar H+ -ATPase proton pump and for carbonic anhydrase II as well as the chloride/bicarbonate transporter pendrin. Using transfection experiments, we have identified a Foxi1 binding cis-element in the ATP6V1B1 (encoding the B1-subunit) promoter that is critical for reporter gene activation. When this site is mutated to eliminate Foxi1 binding, activation is also abolished. As a consequence of defect Foxi1-dependent epididymal sperm maturation, we demonstrate that spermatozoa from Foxi1 null males fail to reach the female genital tract in sufficient number to allow fertilization.

Segmental and cellular expression of aquaporins in the male excurrent duct

The male reproductive tract and accessory glands comprise a complex but interrelated system of tissues that are composed of many distinct cell types, all of which contribute to the ability of spermatozoa to carry out their ultimate function of fertilizing an oocyte. Spermatozoa undergo their final steps of maturation as they pass through the male excurrent duct, which includes efferent ducts, the epididymis and the vas deferens. The composition of the luminal environment in these organs is tightly regulated. Major fluid reabsorption occurs in efferent ducts and in the epididymis, and leads to a significant increase in sperm concentration. In the distal epididymis and vas deferens, fluid secretion controls the final fluidity of the luminal content. Therefore, the process of water movement in the excurrent duct is a crucial step for the establishment of male fertility. Aquaporins contribute to transepithelial water transport in many tissues, including the kidney, the brain, the eye and the respiratory tract. The present article reviews our current knowledge regarding the distribution and function of aquaporins in the male excurrent duct.

Differential Endocrine Regulation of Genes Enriched in Initial Segment and Distal Caput of the Mouse Epididymis as Revealed by Genome-Wide Expression Profiling1

We have performed genome-wide expression profiling of endocrine regulation of genes expressed in the mouse initial segment (IS) and distal caput of the epididymis by using Affymetrix microarrays. The data revealed that of the 15 020 genes expressed in the epididymis, 35% were enriched in one of the two regions studied, indicating that differential functions can be attributed to the IS and the more distal caput regions. The data, furthermore, showed that 27% of the genes expressed in the IS and/or distal caput epididymidis are under the regulation of testicular factors present in the duct fluid, while bloodborne androgens can regulate for 14% of them. This is in line with the high testis dependency of epididymal physiology. We then focused on genes with moderate or strong expression, showing strict segment enrichment and strong dependency on testicular factors. Analyses of the 59 genes, including upregulated and downregulated genes, fulfilling the criteria indicated that the expression of 18 (17 downregulated genes; 1 upregulated gene) of 19 gonadectomy-responsive genes enriched in the IS was not maintained by the androgen treatment, whereas the expression of all six downregulated genes enriched in the distal caput and the majority of those with no strict segment enrichment of expression (28 of 34; consisting of 23 downregulated and 5 upregulated genes) were maintained by androgens. Hence, it is evident that testicular factors other than androgens are important for the expression of IS-enriched genes, whereas the expression of distal caput-enriched genes is typically regulated by androgens. Identical data were obtained by independent clustering analyses performed for the expression data of 3626 epididymal genes. Several novel genes with putative involvement in epididymal sperm maturation, such as a disintegrin and metallopeptidase domain 28 (Adam28) and a solute carrier organic anion transporter family, member 4C1 (Slco4c1), were identified, indicating that this approach is successful for identifying novel epididymal genes.

Foxa1 and Foxa2 interact with the androgen receptor to regulate prostate and epididymal genes differentially

Previous studies from our group have shown that Foxa1 is expressed in the prostate and interacts with the androgen receptor (AR) to regulate prostate-specific genes such as prostate-specific antigen (PSA) and probasin (PB). We report here that Foxa2 but not Foxa1 is expressed in the epididymis. Further, Foxa2 interacts with the AR to regulate the mouse epididymal retinoic acid binding protein (mE-RABP) gene, an epididymis-specific gene. Binding of Foxa2 to the mE-RABP promoter was confirmed by gel-shift and chromatin immunoprecipitation (ChIP) assays. Overexpression of Foxa2 suppresses androgen activation of the mE-RABP promoter while overexpression of Foxa2 with prostate-specific promoters activates gene expression in an androgen-independent manner. GST pull-down assays determined that both Foxa1 and Foxa2 physically interact with the DNA binding domain of the AR. The interaction between Foxa proteins and AR was further confirmed by gel-shift assays where Foxa protein was recruited to AR binding oligomers even when Foxa binding sites were not present, and AR was recruited to Foxa binding oligomers even in the absence of an AR binding site. Given that Foxa1 and Foxa2 proteins are expressed differentially in the prostate and epididymis, these data suggest that the Foxa proteins have distinct effects on AR-regulated genes in different male reproductive accessory organs.

Identification of novel epididymal genes by expression profiling and in silico gene discovery

We have used both the UniGene RIKEN epididymal EST library and the Affymetrix microarray profiling for identifying novel epididymal genes in mouse. The use of ESTs is a complementary approach to Affymetrix arrays for identifying novel epididymal genes, while only 32% and 28% of ESTs of unknown genes were present in the U74v.2Set and MG 430 2.0 version Affymetrix arrays, respectively. As expected, the probe set for a notably larger proportion of known genes was present in the Affymetrix arrays, and the coverage was greatly improved by the newer array version. Furthermore, many genes with more than five ESTs in the UniGene library showed variable levels of expression in both versions of the Affymetrix arrays. However, both the Affymetrix and EST data correlated well with that obtained by quantitative RT-PCR, and thus, we conclude that the findings of high EST number but only limited expression in the arrays could be considered as false negatives in the Affymetrix arrays.

New approaches for male fertility control: HE6 as an example of a putative target

Reversible contraceptive methods for males are still not available. During the last few years several marketing studies have clearly shown that men and women would welcome a situation where men could assume responsibility for family planning. Schering AG and Organon are currently collaborating to develop a hormonal method for male fertility control based on the combination of etonogestrel as gestagenic component and testosterone undecanoate. To further optimize male contraceptives in terms of improved efficiency, rapid onset, reversibility, fewer side effects and a convenient method of application, a search for innovative non-hormonal approaches was started. During the last few years, numerous proteins were identified which play a specific role in male fertility. These proteins have first to fulfil a set of indication-specific criteria before a drug discovery process can be initiated. The most important criteria for a putative target protein are tissue-selective expression, crucial biological function in fertility, drugable properties and feasibility of assay development for high-throughput-screening and lead optimization. The G-protein-coupled receptor HE6 was selected as target and the above selection criteria were applied. HE6 displays a preferred epididymis-specific expression pattern and belongs to the superfamily of GPCRs, which are well known to be drugable with small molecules. A knockout mouse was generated which revealed an infertility phenotype with the onset occurring 6 weeks after initiation of spermatogenesis at the latest. Surprisingly, no epididymis-specific phenotype was observed. Instead, the reabsorption of testicular fluid along the efferent ducts was strongly affected. No further obvious side effects were observed in male or female mice. This study with HE6 exemplifies how targets for male contraception have to be validated before drug development can start.

Genome-wide profiling of segmental-regulated transcriptomes in human epididymis using oligo microarray

Sperm maturation during passage through the epididymis depends on regionalized gene expression which maintains the progressively changing environment within the epididymal tubule. Towards defining the genes that drive the sequential maturation of spermatozoa, we profiled regionally regulated gene expression pattern in the epididymis of a fertile young male donor using Affymetrix human genome U133 plus 2.0 microarray representing approximately the whole human genome. Over 15000 transcripts, almost one-third of the total on the array were identified in whole epididymis. Among them, 65% were detected in all three regions of the epididymis, 410 or 2.6% were present only in one region and the remaining 32.4% were distributed in two regions. Region-specific transcripts observed in caput (264), corpus (61) and cauda (81) epididymides were further classified as empirically determined reported genes or ESTs. This study revealed for the first time, the expression in human epididymis of a number of region-specific genes. The original data will be made publicly available on the Shanghai Science and Technology Database (http://www.scbit.org/human_epididymis_transcriptomes).

Expression of functional aromatase in the epididymis: role of androgens and LH in modulation of expression and activity

The primary source of 17beta-estradiol (E2) in the male is the testis, which expresses the enzyme complex aromatase that is involved in E2 biosynthesis. However, recent evidences suggest that the epididymis is also capable of E2 biosynthesis. Our results demonstrate the presence of cytochrome P450 aromatase (P450(AROM)) and 17beta-hydroxysteroid dehydrogenase I messenger ribonucleic acid (mRNA) in the caput and cauda regions of rat epididymis. The androgenic substrates testosterone and androstenedione could be utilized by the rat epididymal aromatase for E2 biosynthesis as assessed by radioimmunoassay. P450(AROM) expression is transcriptionally regulated in a tissue-specific manner by various factors including androgens and luteinizing hormone (LH). Androgens could positively modulate epididymal P450(AROM) mRNA levels as assessed by castration studies, treatment with flutamide or in vitro incubation of tissue minces with 5 alpha-dihydrotestosterone (DHT). Several extra-gonadal tissues including the epididymis are known to express LH receptors (LHR). Our study revealed a higher level of LHR mRNA expression in the cauda region compared to the caput. Caudal membrane extracts could bind human chorionic gonadotropin (hCG), which resulted in the production of cAMP. Interestingly, hCG could also regulate P450(AROM) mRNA expression in vitro and enhance E2 biosynthesis. Together our results highlight the presence of a functional aromatase in the epididymis that is subject to regulation by LH and androgens.

Targeted disruption of tyrosylprotein sulfotransferase-2, an enzyme that catalyzes post-translational protein tyrosine O-sulfation, causes male infertility

Tyrosine O-sulfation is a post-translational modification mediated by one of two Golgi tyrosylprotein sulfotransferases (TPST-1 and -2) expressed in all mammalian cells. Tyrosine sulfation plays an important role in the function of some known TPST substrates by enhancing protein-protein interactions. To explore the role of these enzymes in vivo and gain insight into other potential TPST substrates, TPST-2-deficient mice were generated by targeted disruption of the Tpst2 gene. Tpst2(+/-) mice appear normal and, when interbred, yield litters of normal size with a Mendelian distribution of the targeted mutation. Tpst2(-/-) mice have moderately delayed growth but appear healthy and attain normal body weight by 10 weeks of age. In contrast to Tpst1(-/-) males that have normal fertility, Tpst2(-/-) males are infertile. Tpst2(-/-) sperm are normal in number, morphology, and motility in normal media and appear to capacitate and undergo acrosomal exocytosis normally. However, they are severely defective in their motility in viscous media and in their ability to fertilize zona pellucida-intact eggs. Adhesion of Tpst2(-/-) sperm to the egg plasma membrane is reduced compared with wild type sperm, but sperm-egg fusion is similar or even increased. These data strongly suggest that tyrosine sulfation of unidentified substrate(s) play a crucial role in these processes and document for the first time the critical importance of post-translational tyrosine sulfation in male fertility.

Identification of rat cysteine-rich secretory protein 4 (Crisp4) as the ortholog to human CRISP1 and mouse Crisp4

Cysteine-rich secretory proteins (CRISPs) are present in a diverse population of organisms and are defined by 16 conserved cysteine residues spanning a plant pathogenesis related-1 and a C-terminal cysteine-rich domain. To date, the diversification of mammalian CRISPs is evidenced by the existence of two, three, and four paralogous genes in the rat, human, and mouse, respectively. The current study identifies a third rat Crisp paralog we term Crisp4. The gene for Crisp4 is on rat chromosome 9 within 1 Mb of both the Crisp1 and Crisp2 genes. The full-length transcript for this gene was cloned from rat epididymal RNA and encodes a protein that shares 69% and 91% similarity with human CRISP1 and mouse CRISP4, respectively. Expression of rat Crisp4 is most abundant in the epididymis, with the highest levels of transcription observed in the caput and corpus epididymis. In contrast, rat CRISP4 protein is most abundant in the corpus and cauda regions of the epididymis. Rat CRISP4 protein is also present in caudal sperm extracts, appearing as a detergent-soluble form at the predicted MWR (26 kDa). Our data identify rat Crisp4 as the true ortholog to human CRISP1 and mouse Crisp4, and demonstrate its interaction with spermatozoa in the epididymis.

Analysis of the Human Sperm Proteome

As part of our effort to identify putative protein targets for the development of male contraceptives, we performed an in-depth proteomic analysis of human sperm by liquid chromatography and tandem mass spectrometry. Motile sperm were collected from a single fertile individual and fractionated into detergent-soluble and detergent-insoluble fractions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis separation of these fractions, followed by manual cutting of the gel, yielded 35 gel sections for each fraction to include proteins across the full range of electrophoretic mobility. Proteomic analysis of these gel sections identified more than 1,760 proteins with high confidence, with 1,350 proteins identified in the soluble fraction, 719 identified in the insoluble fraction, and 309 identified in both fractions. This characterization of the human sperm proteome provides a high-resolution, physiologically relevant index of the proteins that comprise human sperm.