Cres2 and Cres3: new members of the cystatin-related epididymal spermatogenic subgroup of family 2 cystatins

Distinct actions of testicular endocrine and lumicrine signaling on the proximal epididymal transcriptome

The epididymal function and gene expression in mammals are under the control of the testis. Sex steroids are secreted from the testis and act on the epididymis in an endocrine manner. There is another, non-sex steroidal secreted signaling, named lumicrine signaling, in which testis-derived secreted proteins go through the male reproductive tract and act on the epididymis. The effects of such multiple regulations on the epididymis by the testis have been investigated for many genes. The recent development of high-throughput next-generation sequencing now enables us a further comparative survey of endocrine and lumicrine action-dependent gene expression. In the present study, testis-derived endocrine and lumicrine actions on epididymal gene expression were comparatively investigated by RNA-seq transcriptomic analyses. This investigation utilized experimental animal models in which testis-derived endocrine and/or lumicrine actions were interfered with, such as unilateral or bilateral orchidectomy. By bilateral orchidectomy, which interferes with both endocrine and lumicrine actions, 431 genes were downregulated. By unilateral orchidectomy, which also interferes with endocrine and lumicrine actions by the unilateral testis, but the endocrine action was compensated by the contralateral testis, 283 genes were downregulated. The content of such genes downregulated by unilateral orchidectomy was like those of lumicrine action-interfered efferent duct-ligation, W/Wv, and Nell2-/- mice. When genes affected by unilateral and bilateral orchidectomy were compared, 154 genes were commonly downregulated, whereas 217 genes were specifically downregulated only by bilateral orchidectomy, indicating the distinction between endocrine and lumicrine actions on the proximal epididymal transcriptome. Comparative transcriptome analyses also showed that the expressions of genes emerging since Amniota were notably impacted by bilateral orchidectomy, unilateral orchidectomy, and lumicrine action-interfering treatments; the degree of influence from these treatments varied based on the evolutionary stage beyond Amniota. These findings unveil an evolutional transition of regulated gene expression in the proximal epididymis by two different testis-derived signaling mechanisms.

Busulfan administration replicated the characteristics of the epididymal initial segment observed in mice lacking testis-epididymis lumicrine signaling

The physiological functions of the mammalian epididymis are typically regulated by the testes. In addition to sex steroids secreted by testicular Leydig cells, which act on the epididymis in an endocrine manner, there is a non-sex-steroidal signaling pathway known as the lumicrine pathway. This lumicrine signaling pathway involves ligand proteins secreted from germ cells within the testicular seminiferous tubules traversing the male reproductive tract, which induce epithelial differentiation in the epididymis. These findings prompted an inquiry into whether treatments influencing testis physiology can disrupt epididymal function by interfering with testis-epididymis communication. Busulfan, an alkylating agent commonly used to deplete testicular germ cells in reproductive biology, has not been sufficiently explored because of its effects on the epididymis. This study investigated the effects of busulfan administration on the proximal epididymis using histological and transcriptomic analyses. Notably, busulfan, as opposed to the vehicle dimethyl sulfoxide (DMSO), altered the morphology of the initial segment of the epididymis, leading to a reduction in the cell height of the luminal epithelium. RNA sequencing identified 185 significantly downregulated genes in the proximal epididymis of busulfan-administered mice compared to DMSO-administered mice. Comparative transcriptome analyses revealed similarities between the epididymal transcriptome of busulfan-administered mice and lumicrine-deficient mice, such as efferent-duct-ligated W/Wv and Nell2-/- mice. However, this differed from that of bilaterally orchidectomized mice, in which both the endocrine and lumicrine signaling pathways were simultaneously ablated. Collectively, these results suggested that the harmful effects of busulfan on the proximal epididymis are secondary consequences of the ablation of testis-epididymis lumicrine signaling.

Characteristics and function of a novel cystatin gene in the pine wood nematode Bursaphelenchus xylophilus

Bursaphelenchus xylophilus is the pathogen that causes pine wilt disease (PWD). The disease has caused significant economic losses and damage to forests. However, the pathogenic mechanism of B. xylophilus remains unclear. Cystatins are involved in various biological processes where they regulate normal proteolysis and also play a role in pathogenicity, but their functions in B. xylophilus are unknown. Therefore, we cloned the full-length cDNA of a cystatin gene of B. xylophilus (Bx-cpi-1) by rapid-amplification of cDNA ends and analyzed its characteristics with bioinformatic methods. In situ mRNA hybridization analyses showed that transcripts of Bx-cpi-1 were abundantly expressed in the reproductive organs of B. xylophilus. The expression of Bx-cpi-1 was investigated using qPCR. Bx-cpi-1 was expressed during each of the different developmental stages of B. xylophilus. The highest gene expression was at the egg stage. After infection of Pinus massoniana, the expression of Bx-cpi-1 increased. The functions of Bx-cpi-1 were verified by RNA interference. The feeding rate, reproduction and pathogenicity of B. xylophilus all decreased as a result of silencing of the Bx-cpi-1 gene. These results revealed that Bx-cpi-1 may be a variant of a type II cystatin gene which is involved in the development and pathogenic process of B. xylophilus.

Summary:Bx-cpi-1, a variant of a type II cystatin gene, was abundantly expressed in the reproductive organs of Bursaphelenchusxylophilus, and involved in the development and pathogenicity of B. xylophilus.

Male reproductive tract antimicrobial expression in the extremes of ages of rats

Alterations in the global gene expression profile are considered to contribute to the various physiological and pathological changes during the course of ageing. Genes that code for the molecular components of the innate system are alter markedly as ageing occurs; and this may define the susceptibility of very young and very old individuals to reproductive tract infections. The expression pattern of genes that code for beta-defensins (effectors of innate immune response) in male reproductive tract tissues of different stages of ageing is not yet reported. Further, the induction of beta-defensins during endotoxin challenge and whether epigenetic modulators can influence the expression of these genes in different stages of ageing are not reported. We analyzed the basal mRNA levels of beta-defensins and defensin-like proteins (Sperm Associated Antigen 11 (SPAG11) family members), their induction during endotoxin challenge and modulation by epigenetic modifiers (Trichostatin A and Azacytidine) in the caput, cauda, testis, prostate and seminal vesicle of rats that represent early stage to late stages of life (20 day to 730 day old). We observed differential basal gene expression pattern in the male reproductive tract tissues and the induction by LPS was not consistent neither among the age groups not the tissues analyzed. Trichostatin A and Azacytidine also influenced antimicrobial gene expression and the pattern was not consistent in different tissues obtained from different age groups. Results of this study demonstrate that antimicrobial gene expression varies to a great extent during ageing and is strongly influenced by endotoxins and epigenetic modulators.

Selection signatures in candidate genes and QTL for reproductive traits in Nellore heifers

The identification of selection signature genes may help to detect genomic regions that underwent artificial selection and contributed to phenotypic diversity. The aim of this study, therefore, was to detect selection signatures in candidate genes and quantitative trait locus (QTL) for reproductive traits in a Nellore population being selected for sexual precocity. A total of 2035 Nellore heifers, sourced from breeding programs focused on sexual precocity, were used. Candidate genes and some specific QTL related to reproductive traits were chosen based on published literature and Animal QTL databases, respectively, for investigation whether these regions were affected by selection. Selection signature DNA sequences were detected in the selected regions using the extended haplotype homozygosity (EHH) and relative extended haplotype homozygosity (REHH) methods. From 22,241 single nucleotide polymorphisms (SNPs) located in the candidate genes and QTL, 17,312 SNPs generated 2756 haplotype blocks. A total of 7518 EHH tests were analyzed using haplotypes with a frequency of more than 25%, for which there were 39 tests that were significant for REHH (P<0.01). Selection signature DNA sequences were detected that contained several QTLs for important reproductive traits in cattle, suggesting that reproductive traits may have been affected by selection for sexual precocity in this population. Forty-six genes were located in the selection signature regions, whereas 24 genes participated in important biological processes or pathways that may underlie sexual precocity. These results indicate there are possible molecular mechanisms related to sexual precocity in the Nellore breed.

The epididymal amyloid matrix: structure and putative functions

BACKGROUND

We previously demonstrated the normal mouse epididymal lumen contains a non-pathological amyloid matrix that surrounds spermatozoa and plays important roles in sperm maturation and protection.

OBJECTIVE

The objective herein was to present a review of this work, including studies showing the amyloid structures of four members of the CRES (cystatin-related epididymal spermatogenic) subgroup are integral and essential components of the amyloid matrix.

METHODS

We used conformation-dependent reagents that recognize the cross-β-sheet structure characteristic of amyloid, including thioflavin S (ThS), thioflavin T (ThT), anti-amyloid antibodies, and X-ray diffraction, as well as negative-stain transmission electron microscopy (TEM) to visualize amyloid structures in the epididymal lumen. Antibodies that specifically detect each CRES subgroup family member were also used in indirect immunofluorescence analysis.

RESULTS AND DISCUSSION

The epididymal lumen contains an amyloid matrix that surrounds maturing spermatozoa and represents a functional amyloid. Alterations in the structure of the amyloid matrix by the loss of the CRES subgroup members or the overexpression of cystatin C result in epididymal pathologies, including infertility. Preliminary data suggest the epididymal amyloid matrix is structurally and functionally similar to bacterial biofilms.

CONCLUSION

Together, these results suggest the amyloid matrix serves important roles in epididymal function including sperm maturation and protection.

Cystatin-related epididymal spermatogenic subgroup members are part of an amyloid matrix and associated with extracellular vesicles in the mouse epididymal lumen

STUDY QUESTION

Do the CRES (cystatin-related epididymal spermatogenic) subgroup members, including CRES2, CRES3 and cystatin E2, contribute to the formation of a nonpathological, functional amyloid matrix in the mouse epididymal lumen?

SUMMARY ANSWER

CRES2, CRES3 and cystatin E2 self-assemble with different aggregation properties into amyloids in vitro, are part of a common amyloid matrix in the mouse epididymal lumen and are present in extracellular vesicles.

WHAT IS KNOWN ALREADY

Although previously thought only to be pathological, accumulating evidence has established that amyloids, which are highly ordered protein aggregates, can also carry out functional roles in the absence of pathology. We previously demonstrated that nonpathological amyloids are present in the epididymis; specifically, that the reproductive cystatin CRES forms amyloid and is present in the mouse epididymal lumen in a film-like amyloid matrix that is intimately associated with spermatozoa. Because the related proteins CRES2, CRES3 and cystatin E2 are also expressed in the epididymis, the present studies were carried out to determine if these proteins are also amyloidogenic in vitro and in vivo and thus may coordinately function with CRES as an amyloid structure.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

The epididymides from CD1 and Cst8 (CRES)129SvEv/B6 gene knockout (KO) and wild-type mice and antibodies that specifically recognize each CRES subgroup member were used for immunohistochemical and biochemical analyzes of CRES subgroup proteins. Methods classically used to identify amyloid, including the conformation-dependent dyes thioflavin S (ThS) and thioflavin T (ThT), conformation-dependent antibodies, protein aggregation disease ligand (which binds any amyloid independent of sequence) and negative stain electron microscopy (EM) were carried out to examine the amyloidogenic properties of CRES subgroup members. Immunofluorescence analysis and confocal microscopy were used for colocalization studies.

MAIN RESULTS AND THE ROLE OF CHANCE

Immunoblot and immunofluorescence analyzes showed that CRES2, CRES3 and cystatin E2 were primarily found in the initial segment and intermediate zone of the epididymis and were profoundly downregulated in epididymides from CRES KO mice, suggesting integrated functions. Except for CRES3, which was only detected in a particulate form, proteins were present in the epididymal lumen in both soluble and particulate forms including in a film-like matrix and in extracellular vesicles. The use of amyloid-specific reagents determined that all CRES subgroup members were present as amyloids and colocalized to a common amyloid matrix present in the epididymal lumen. Negative stain EM, dot blot analysis and ThT plate assays showed that recombinant CRES2, CRES3 and cystatin E2 formed amyloid in vitro, albeit with different aggregation properties. Together, our studies demonstrate that a unique amyloid matrix composed of the CRES family of reproductive-specific cystatins and cystatin C is a normal component of the mouse epididymal lumen and may play a functional role in sperm maturation by coordinating interactions between the luminal fluid and spermatozoa.

LIMITATIONS, REASONS FOR CAUTION

The structures examined in our studies were isolated from luminal fluid obtained by puncture of the epididymis and therefore we cannot rule out some contamination by epithelial cells. Although our studies show CRES family members are associated with extracellular vesicles, we have yet to determine if proteins are present on the surface or are within the vesicles. We also have not established if narrow/apical cells are the source of the CRES family extracellular vesicles. CRES and CRES2 have been previously found in the human epididymis and associated with spermatozoa; however, we have yet to determine if the human CRES subgroup proteins are amyloidogenic and if an amyloid matrix is present in the human epididymal lumen.

WIDER IMPLICATIONS OF THE FINDINGS

Understanding the regulation and biological roles of amyloids, such as the CRES subgroup amyloid matrix that functions without causing pathology, could have broad implications for understanding pathological amyloids including those associated with neurodegenerative diseases and prionopathies.

LARGE SCALE DATA

None.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by NIH grants RO1HD033903 and RO1HD056182 to G.A.C. The authors declare there are no conflicts of interest.

Molecular modeling of the human sperm associated antigen 11 B (SPAG11B) proteins

Antimicrobial proteins and peptides are ubiquitous in nature with diverse structural and biological properties. Among them, the human beta-defensins are known to contribute to the innate immune response. Besides the defensins, a number of defensin-like proteins and peptides are expressed in many organ systems including the male reproductive system. Some of the protein isoforms encoded by the sperm associated antigen 11B (SPAG11) gene in humans are beta-defensin-like and exhibit structure dependent and salt tolerant antimicrobial activity, besides contributing to sperm maturation. Though some of the functional roles of these proteins are reported, the structural and molecular features that contribute to their antimicrobial activity is not yet reported. In this study, using in silico tools, we report the three dimensional structure of the human SPAG11B proteins and their C-terminal peptides. web-based hydropathy, amphipathicity, and topology (WHAT) analyses and grand average of hydropathy (GRAVY) indices show that these proteins and peptides are amphipathic and highly hydrophilic. Self-optimized prediction method with alignment (SOPMA) analyses and circular dichroism data suggest that the secondary structure of these proteins and peptides primarily contain beta-sheet and random coil structure and alpha-helix to a lesser extent. Ramachandran plots show that majority of the amino acids in these proteins and peptides fall in the permissible regions, thus indicating stable structures. The secondary structure of SPAG11B isoforms and their peptides were not perturbed with increasing NaCl concentration (0-300 mM) and at different pH (3, 7, and 10), thus reinforcing our previously reported observation that their antimicrobial activity is salt tolerant. To the best of our knowledge, for the first time, results of our study provide vital information on the structural features of SPAG11B protein isoforms and their contribution to antimicrobial activity.

Antimicrobial activity and molecular mechanism of the CRES protein

Cystatin-related epididymal spermatogenic (CRES) protein, a member of the cystatin superfamily of cysteine protease inhibitors (also known as CST8), exhibits highly specific, age-dependent expression in mouse testis and epididymis. The CRES protein possesses four highly conserved cysteine residues which govern the overall conformation of the cystatins through the formation of two disulfide bonds. Previous studies have revealed that other cystatin family members, such as cystatin 3 and cystatin 11, show antibacterial activity in vitro. This prompted us to investigate the potential antimicrobial activity of the CRES protein. Colony forming assays and spectrophotometry were used to investigate the effects of recombinant CRES protein on Escherichia coli (E. coli) and Ureaplasma urealyticum (Uu), respectively, in vitro. After incubation of E. coli with CRES recombinant protein fused with glutathione-S-transferase (GST), a substantial decrease in colony forming units was observed, and the effect was dose and time dependent. Furthermore, it took longer for Uu to grow to plateau stage when incubated with GST-CRES recombinant protein compared with the control GST. The antibacterial and Anti-Uu activities were not impaired when the cysteine residues of CRES protein were mutated, indicating that the antimicrobial effect was not dependent on its disulfide bonds. Functional analysis of three CRES polypeptides showed that the N-terminal 30 residues (N30) had no antimicrobial activity while N60 showed similar activity as full-length CRES protein. These results suggest that the active center of CRES protein resides between amino acid residues 31 and 60 of its N-terminus. Mechanistically, E. coli membrane permeabilization was increased in a dose-dependent manner, and macromolecular synthesis was inhibited on treatment with GST-CRES. Together, our data on the antimicrobial activities of CRES protein suggest that it is a novel and innate antimicrobial protein which protecting the male reproductive tract against invading pathogens.

Epididymal protease inhibitor (EPPIN) is differentially expressed in the male rat reproductive tract and immunolocalized in maturing spermatozoa

EPPIN (epididymal protease inhibitor; SPINLW1), an antimicrobial cysteine-rich protein containing both Kunitz and whey acidic protein (WAP)-type four disulfide core protease inhibitor consensus sequences, is a target for male contraception because of its critical role in sperm motility. Here, we characterized EPPIN's expression and cellular distribution in rat tissues and its in vivo regulation by androgens in the epididymis. EPPIN (mRNA and protein) was abundantly expressed in the rat testis and epididymis; we also found that the vas deferens, seminal vesicles, and brain were novel sites of EPPIN expression. PCR studies demonstrated that in addition to Sertoli cells, spermatogenic cells expressed Eppin mRNA. EPPIN was immunolocalized in Sertoli cells and spermatogenic cells (pachytene spermatocytes and round and elongated spermatids) and in epithelial cells and spermatozoa from efferent ductules and epididymis. EPPIN staining was observed on the middle and principal pieces of the flagellum of testicular spermatozoa. Epididymal spermatozoa had more intense EPPIN staining on the flagellum, and the EPPIN staining became apparent on the head and neck regions. This suggested that the EPPIN found on maturing spermatozoa was secreted primarily by the epithelial cells of the epididymis. Surgical castration down-regulated EPPIN expression levels (mRNA and protein) in the caput and cauda epididymis, an effect reversed by testosterone replacement. Altogether, our data suggested that EPPIN expression in rats is more widespread than in humans and mice, and is androgen-dependent in the epididymis. This species could be used as an experimental model to further study EPPIN's role in male fertility.

Isolation and proteomic characterization of the mouse sperm acrosomal matrix

A critical step during fertilization is the sperm acrosome reaction in which the acrosome releases its contents allowing the spermatozoa to penetrate the egg investments. The sperm acrosomal contents are composed of both soluble material and an insoluble material called the acrosomal matrix (AM). The AM is thought to provide a stable structure from which associated proteins are differentially released during fertilization. Because of its important role during fertilization, efforts have been put toward isolating the AM for biochemical study and to date AM have been isolated from hamster, guinea pig, and bull spermatozoa. However, attempts to isolate AM from mouse spermatozoa, the species in which fertilization is well-studied, have been unsuccessful possibly because of the small size of the mouse sperm acrosome and/or its fusiform shape. Herein we describe a procedure for the isolation of the AM from caput and cauda mouse epididymal spermatozoa. We further carried out a proteomic analysis of the isolated AM from both sperm populations and identified 501 new proteins previously not detected by proteomics in mouse spermatozoa. A comparison of the AM proteome from caput and cauda spermatozoa showed that the AM undergoes maturational changes during epididymal transit similar to other sperm domains. Together, our studies suggest the AM to be a dynamic and functional structure carrying out a variety of biological processes as implied by the presence of a diverse group of proteins including proteases, chaperones, hydrolases, transporters, enzyme modulators, transferases, cytoskeletal proteins, and others.

Dynamic expression pattern and subcellular localization of the Rhox10 homeobox transcription factor during early germ cell development

Homeobox genes encode transcription factors that regulate diverse developmental events. The largest known homeobox gene cluster - the X-linked mouse reproductive homeobox (Rhox) cluster - harbors genes whose expression patterns and functions are largely unknown. Here, we report that a member of this cluster, Rhox10, is expressed in male germ cells. Rhox10 is highly transcribed in spermatogonia in vivo and is upregulated in response to the differentiation-inducing agent retinoic acid in vitro. Using a specific RHOX10 antiserum that we generated, we found that RHOX10 protein is selectively expressed in fetal gonocytes, germline stem cells, spermatogonia, and early spermatocytes. RHOX10 protein undergoes a dramatic shift in subcellular localization as germ cells progress from mitotically arrested gonocytes to mitotic spermatogonia and from mitotic spermatogonia to early meiotic spermatocytes, consistent with RHOX10 performing different functions in these stages.

Antimicrobial responses in the male reproductive tract of lipopolysaccharide challenged rats

PROBLEM

Innate immune machinery including the Toll-like receptors (TLRs) confers the first line of defense mechanisms to counter pathogenic microorganisms that enter the body. The male reproductive tract is vulnerable to infection and the role of TLRs and the antimicrobial responses that operate to counter infections in this organ system are poorly understood.

METHOD OF STUDY

Caput and cauda epididymides, testes and seminal vesicles were collected at 0, 3, 6, 9, 12, 15 and 24 h from rats injected intraperitoneally with a single dose of LPS. Plasma testosterone was measured using ELISA. Expression pattern of defensins and Spag11 isoforms were analysed using RT-PCR. Immunohistochemical analyses was performed to determine SPAG11E protein expression following LPS treatment.

RESULTS

We provide the first line of evidence that the male reproductive tract induces the expression of Sperm Associated Antigen 11 (Spag11) mRNA variants and defensins when challenged with lipopolysaccharide (LPS) with a concomitant increase in protein expression. However, there was an inverse relationship between induction of antimicrobial gene expression and plasma testosterone. An increase in the mRNA levels of proinflammatory cytokines was observed parallel to the induction of Spag11 variants and majority of defensin expression in the male reproductive tract.

CONCLUSION

The increase in Spag11 and defensin mRNA in response to LPS administration demonstrates their importance in protecting the male reproductive tract during infection. Results of this study help to understand male reproductive tract innate immune defense mechanisms and to design novel peptide antibiotics to prevent sexually transmitted diseases.

Alterations in the testis and epididymis associated with loss of function of the cystatin-related epididymal spermatogenic (CRES) protein

Cystatin-related epididymal spermatogenic protein (CRES) or cystatin 8 (Cst8 gene) is a member of the cystatin superfamily of cysteine protease inhibitors. It differs from typical cystatins because it lacks consensus sites for cysteine protease inhibition and exhibits reproductive-specific expression. In the present study, we examined CRES expression within the testes, efferent ducts, and epididymides of normal mice by light microscope immunolocalization. Alterations to these tissues in male mice lacking the Cst8 gene (Cst8(-/-2)) were also characterized by histomorphometry and electron microscopy. In the normal testis, CRES was localized exclusively in mid and late elongating spermatids. In the efferent ducts, CRES was localized to the apical region of the epithelial cells suggestive of localization in the endosomes. In the initial segment of the epididymis, principal cells showed supranuclear and luminal reactions. In the cauda region, CRES was present exclusively as aggregates in the lumen and was detected in clear cells. Compared with wild-type mice (Cst8(+/+)), older (10-12 months) Cst8(-/-) mice had modest but statistically significant reductions in tubular, epithelial, and/or luminal profile areas in the testis and epididymis. By electron microscopy, some Cst8(-/-) tubules in the testis were normal in appearance, but others showed a vacuolated seminiferous epithelium, degenerating germ cells, and alterations to ectoplasmic specializations. In the epididymal lumen, abnormally shaped sperm heads and tails were noted along with immature germ cells. In addition, principal cells contained numerous large irregularly shaped lysosomes suggestive of disrupted lysosomal functions. In both the testis and epididymis, however, these abnormalities were not apparent in younger mice (4 months), only in the older (10-12 months) Cst8(-/-) mice. These findings suggest that the altered testicular and epididymal histology reflects a cumulative effect of the loss of CRES and support a role for CRES in maintaining the normal integrity and function of the testis and epididymis.

A novel terminal ampullae peptide is involved in the proteolytic activity of sperm in the prawn, Macrobrachium rosenbergii

As the distal part of the crustacean male reproductive tract, terminal ampullae play important roles in sperm development and storage of mature spermatophores. In the present study, the novel gene terminal ampullae peptide (TAP) was cloned from terminal ampullae of the prawn, Macrobrachium rosenbergii. The cDNA sequence consists of 768 nucleotides, with an open-reading frame of 264 nucleotides which encodes a putative 88-amino acid precursor protein with a 17-amino acid residue signal peptide. Western blotting and immunohistochemical analysis revealed that TAP was distributed on terminal ampullae and sperm, and its expression was related to gonad development. To elucidate the functional role of TAP in vivo, we disrupted the TAP gene by RNA interference (RNAi) and evaluated the effect on fertility and several sperm parameters. Although there was no difference in fertility between RNAi-induced prawns and controls, RNAi treatment decreased the sperm gelatinolytic activity and blocked proteolytic activity on the vitelline coat. These data provide evidence that TAP participates in regulating sperm proteolytic activity, and performs a crucial role in sperm maturation and degradation of the vitelline coat during fertilization.

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.

The reproductive tissue specific cystatin subgroup of genes: expression during gonadal development in wildtype and testatin knockout animals

Testatin has been implicated in fetal testis development due to its restricted expression in pre-Sertoli cells immediately after the onset of Sry gene expression. However, testatin knockout mice showed normal testis development and fertility. We investigated the spatial and temporal expression pattern of the Cres/testatin subgroup of genes, including the novel gene Cstl1/Cres4, in fetal mouse gonads and in adult testis, epididymis and ovary. The genes are related to the family 2 cystatins of protease inhibitors. Using real-time PCR and in situ hybridization we could show that 4 subgroup genes, testatin, CstSC, CstTE-1/Cres3 and Cres are expressed in fetal testis. We also confirmed the expression of testatin, CstE2, CstSC, CstTE-1/Cres3, Cres, CstT and Cstl1/Cres4 in adult testis and CstE2, CstTE-1/Cres3, Cres and CstE1/Cres2 in adult epididymis. In testatin knockout animals, the expression of CstE2 was heavily downregulated in adult testis, but not in adult epididymis, compared to wildtype controls. In conclusion, an explanation for the lack of phenotype in testatin knockout mice could be functional redundancy with another member of the Cres/testatin subgroup. The most likely candidate/s would be CstSC, CstTE-1/Cres3 or Cres as they are expressed in the fetal testicular tubules in early testis differentiation together with testatin.

Age-dependent expression of the cystatin-related epididymal spermatogenic (Cres) gene in mouse testis and epididymis

AIM

To investigate the spatial and temporal expression of the cystatin-related epididymal spermatogenic (Cres) gene in mouse testis and epididymis during postnatal development.

METHODS

The QuantiGene assay and indirect immunofluorescence technique were used to examine the Cres mRNA and Cres protein level in mouse testis and epididymis on postnatal days 14, 20, 22, 28, 35, 49, 70 and 420.

RESULTS

(1) In both the testis and epididymis, Cres mRNA was first detected on day 20, then it increased gradually from day 20 to day 70, and the high expression level maintained till day 420. (2) In the testis, the Cres protein was exclusively localized to the elongating spermatids and was first detected on day 22. The number of Cres-positive spermatids increased progressively till day 49. From day 49 to day 420, the number of Cres-positive cells was almost stable. (3) The Cres protein was first detected on day 20 in the proximal caput epididymal epithelium. By day 35, the expression level of the Cres protein increased dramatically and the high level was maintained till day 420. Moreover, the luminal fluid of the midcaput epididymis was also stained Cres-positive from day 35 on. No Cres-positive staining was observed in distal caput, corpus and cauda epididymis throughout.

CONCLUSION

The Cres gene displays a specific age-dependent expression pattern in mouse testis and epididymis on both the mRNA and protein level.

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.

LGR4 regulates the postnatal development and integrity of male reproductive tracts in mice

The roles of the leucine-rich repeat domain containing G protein-coupled receptor (GPCR) 4 (Lgr4), which is one of the orphan GPCRs, were analyzed with the Lgr4 hypomorphic mutant mouse line (Lgr4(Gt)). This homozygous mutant had only one-tenth the normal transcription level; furthermore, 60% of them survived to adulthood. The homozygous male was infertile, showing morphologic abnormalities in both the testes and the epididymides. In the testes, luminal swelling, loss of germinal epithelium in the seminiferous tubules, and rete testis dilation were observed. Cauda epididymidis sperm were immotile. Rete testis dilation was due to a water reabsorption failure caused by a decreased expression of an estrogen receptor (ESR1) and SLC9A3 in the efferent ducts. Although we found differential regulation of ESR1 expression in the efferent ducts and the epididymis, the role of ESR1 in the epididymis remains unclear. The epididymis contained short and dilated tubules and completely lacked its initial segment. In the caput region, we observed multilamination and distortion of the basement membranes (BMs) with an accumulation of laminin. Rupture of swollen epididymal ducts was observed, leading to an invasion of macrophages into the lumen. Male infertility was probably due to the combination of a developmental defect of the epididymis and the rupture of the epithelium resulting in the immotile spermatozoa. These results indicate that Lgr4 has pivotal roles to play in the regulation of ESR1 expression, the control of duct elongation through BM remodeling, and the regional differentiation of the caput epididymidis.

Testatin transgenic and knockout mice exhibit normal sex-differentiation

Testatin is identified as a member of the Cystatin family and expressed in germ cells and somatic cells in reproductive tissues. Testatin transcription detectable in males and females at 9.5 days post coitum, before sex-differentiation, is up-regulated just after the onset of sry expression in the male gonads, while is down-regulated to undetectable levels in the female gonads. These expression patterns suggest that Testatin might have some roles in sex-differentiation. To address Testatin function in sex-differentiation, we analyzed the effects of ectopic-expression in females and null-expression in males with testatin transgenic and knockout mice. In the transgenic females, testatin expression was constitutively elevated from embryonic gonad to adult ovary, and its expression was as high as the wild-type male gonads. However, both types of mice were fertile and did not exhibit detectable abnormalities. This suggests that the decrease of endogenous testatin in female gonad is not critical, and the increase of testatin in male gonad is dispensable for sex-differentiation.

Immunolocalization and Regulation of Cystatin 12 in Mouse Testis and Epididymis1

In previous studies, we identified a new member of the male reproductive tract subgroup within family 2 cystatins, termed cystatin 12 (Cst12, previously known as Cst TE-1 or Cres3). The mouse Cst12 mRNA was primarily localized to the Sertoli cells in the testis and to the epithelial cells of the proximal caput region of the epididymis. In this report, studies were carried out to characterize the cystatin 12 (CST12) protein in mouse testis and epididymis. A recombinant His-CST12 fusion protein was expressed in E. coli and purified to generate an anti-CST12 polyclonal antibody. Western blot analysis showed little or no cross-reaction between the anti-CST12 antibody and several other known male reproductive tract cystatins. Immunohistochemistry revealed that CST12 protein was predominantly localized to the cytoplasm of Sertoli cells in the seminiferous epithelium in a stage-dependent manner. All stages showed high levels of expression except stages VII and VIII, in which very limited expression of CST12 was observed. In the epididymis, CST12 was highly expressed in the cytoplasm of the epithelial cells in the proximal caput and secreted into the lumen. The mouse CST12 protein was also detected in other regions of the epididymis; however, the localization varied greatly along the epididymal tubules. Indirect immunofluorescence showed that CST12 protein was localized to the cytoplasmic droplets in both testicular and epididymal spermatozoa. These observations suggest that CST12 protein may play a specialized role during spermatogenesis and sperm maturation. Northern blot analyses demonstrated that Cst12 transcript levels in the epididymis decreased after castration, and testosterone propionate (T) treatment further repressed the expression of this gene. However, 17-beta estradiol (E) administration maintained the expression of Cst12 mRNA after castration, whereas treatment with both T and E failed to maintain Cst12 mRNA levels in epididymis. These results suggest that androgen and estrogen, probably with other testicular factors, are involved in the regulation of this gene.

Normal sexual development and fertility in testatin knockout mice

The testatin gene was previously isolated in a screen focused on finding novel signaling molecules involved in sex determination and differentiation. testatin is specifically upregulated in pre-Sertoli cells in early fetal development, immediately after the onset of Sry expression, and was therefore considered a strong candidate for involvement in early testis development. testatin expression is maintained in the adult Sertoli cell, and it can also be found in a small population of germ cells. Testatin shows homology to family 2 cystatins, a group of broadly expressed small secretory proteins that are inhibitors of cysteine proteases in vitro but whose in vivo functions are unclear. testatin belongs to a novel subfamily among the cystatins, comprising genes that all show expression patterns that are strikingly restricted to reproductive tissue. To investigate a possible role of testatin in testis development and male reproduction, we have generated a mouse with targeted disruption of the testatin gene. We found no abnormalities in the testatin knockout mice with regard to fetal and adult testis morphology, cellular ultrastructure, body and testis weight, number of offspring, spermatogenesis, or hormonal parameters (testosterone, luteinizing hormone, and follicle-stimulating hormone).

Recapitulation of germ cell- and pituitary-specific expression with 1.6 kb of the cystatin-related epididymal spermatogenic (Cres) gene promoter in transgenic mice

The Cres (cystatin-related epididymal spermatogenic) gene encodes the defining member of a new subgroup within the family 2 cystatins of cysteine protease inhibitors. Cres expression is highly tissue- and cell-specific, with messenger RNA (mRNA) present in the testicular round/elongating spermatids, proximal caput epididymal epithelium, gonadotroph cells in the anterior pituitary gland, and corpus luteum of the ovary. To begin to elucidate the molecular mechanisms controlling the tissue- and cell-specific expression of the Cres gene, transgenic mice were generated containing 1.6 kilobases (kb) of the mouse Cres promoter linked to the bacterial chloramphenicol acetyltransferase (CAT) reporter gene. A CAT enzyme-linked immunosorbent assay detected CAT protein in the testis, epididymis, isolated cauda epididymal spermatozoa, and anterior pituitary gland from mice heterozygous and homozygous for the transgene. However, reverse transcription (RT)-PCR did not detect CAT mRNA in any regions of the epididymis, suggesting that the CAT protein detected in the epididymis was from spermatozoa. RT-PCR also did not detect CAT mRNA in the ovary. RT-PCR analysis of the testes from mice of different postnatal ages showed CAT mRNA first detected at day 22, which correlated with the first appearance of Cres mRNA and with the presence of round spermatids. These studies demonstrate that 1.6 kb of Cres promoter contains the DNA elements necessary for germ cell and pituitary gland-specific expression but lacks critical sequences necessary for expression in the epididymis and ovary.

The Blood‐Testis Barrier: Its Biology, Regulation, and Physiological Role in Spermatogenesis

The blood-testis barrier (BTB) in mammals, such as rats, is composed of the tight junction (TJ), the basal ectoplasmic specialization (basal ES), the basal tubulobulbar complex (basal TBC) (both are testis-specific actin-based adherens junction [AJ] types), and the desmosome-like junction that are present side-by-side in the seminiferous epithelium. The BTB physically divides the seminiferous epithelium into basal and apical (or adluminal) compartments, and is pivotal to spermatogenesis. Besides its function as an immunological barrier to segregate the postmeiotic germ-cell antigens from the systemic circulation, it creates a unique microenvironment for germ-cell development and confers cell polarity. During spermatogenesis, the BTB in rodents must physically disassemble to permit the passage of preleptotene and leptotene spermatocytes. This occurs at late stage VII through early stage VIII of the epithelial cycle. Studies have shown that this dynamic BTB restructuring to facilitate germ-cell migration is regulated by two cytokines, namely transforming growth factor-beta3 (TGF-beta3) and tumor necrosis factor-alpha (TNFalpha), via downstream mitogen-activated protein kinases. These cytokines determine the homeostasis of TJ- and basal ES-structural proteins, proteases, protease inhibitors, and other extracellular matrix (ECM) proteins (e.g., collagen) in the seminiferous epithelium. Some of these molecules are known regulators of focal contacts between the ECM and other actively migrating cells, such as macrophages, fibroblasts, or malignant cells. These findings also illustrate that cell-cell junction restructuring at the BTB is regulated by mechanisms involved in the junction turnover at the cell-matrix interface. This review critically discusses these latest findings in the field in light of their significance in the biology and regulation of the BTB pertinent to spermatogenesis.

Molecular evolution of epididymal lipocalin genes localized on mouse chromosome 2

We previously identified two murine secretory proteins, mE-RABP(Lcn5) and mEP17(Lcn8), belonging to the lipocalin family and specifically expressed in the epididymis. The genes are contiguous and localized on mouse chromosome 2. We now show that five other related lipocalin genes, Lcn9, Lcn10, Lcn11, Lcn12, and Lcn13, that evolved by in situ tandem duplication are present on the same locus. Lcn9, Lcn10, Lcn12, and Lcn13 genes, like Lcn5 and Lcn8 genes, are specifically expressed in the mouse epididymis. However, each gene has a distinct spatial expression within the epididymis and different regulation. Analysis of the human genome sequence shows the presence of genes encoding lipocalins with genomic organization, chromosomal arrangement, and orientation similar to that of the corresponding murine genes, indicating that the epididymal cluster is evolutionary conserved. A phylogenetic analysis of the new epididymal proteins reveals their spread position in the lipocalin protein family tree. This suggests the preservation of the regulatory sequences, while protein sequences have greatly diverged, reflecting functional diversity and possibly multifunctionality. In terms of the cluster ancestry, epididymal expression possibly appeared in a PGDS-like lipocalin in amniotes, and the duplications generating the cluster occurred at least in the common ancestor of rodents and primates. The presence and conservation of a cluster of five genes encoding epididymal lipocalins, differently regulated and regionalized in the epididymis, strongly suggests that these proteins may play an important role for male fertility.

Post-testicular sperm environment and fertility

When mammalian spermatozoa exit the testis, they show a highly specialized morphology; however, they are not yet able to carry out their task: to fertilize an oocyte. This property, that includes the acquisition of motility and the ability to recognize and to fuse with the oocyte investments, is gained only after a transit through the epididymis during which the spermatozoa from the testis travel to the vas deferens. The exact molecular mechanisms that turn these cells into fertile gametes still remain mysterious, but surface-modifying events occurring in response to the external media are key steps in this process. Our laboratory has established cartographies of secreted (secretomes) and present proteins (proteomes) in the epididymal fluid of different mammals and have shown the regionalized variations in these fluid proteins along the epididymis. We have found that the main secreted proteins are common in different species and that enzymatic activities, capable of controlling the sperm surface changes, are present in the fluid. Our studies also indicate that the epididymal fluid is more complex than previously thought; it contains both soluble and particulate compartments such as exosome-like vesicles (epididymosomes) and certainly specific glycolipid-protein micelles. Understanding how these different compartments interplay to modify sperm components during their transit will be a necessary step if one wants to control and to ameliorate sperm quality and to obtain valuable fertility markers helpful to establish a male fertility based genetic selection.

DNA microarray analysis of region-specific gene expression in the mouse epididymis

Microarray analysis was carried out to identify genes with enriched expression in the initial segment region of the mouse epididymis. A set of approximately 15 000 clones developed at the National Institutes for Aging and consisting of expressed sequence tags (ESTs) derived from pre- and peri-implantation embryos, Embryonic Day 12.5 female gonad/mesonephros, and newborn ovary were hybridized with probes generated against the initial segment (epididymal region 1) and the remainder of the epididymis (epididymal regions 2-5). The median values for the normalized ratios of region 1 to regions 2-5 from three independent experiments were averaged for each gene/EST using Genespring 5.0 software. The majority of clones showed a ratio of 1.0, suggesting they were expressed at similar levels in all epididymal regions. In addition, 123 clones exhibited 2-fold or higher expression in the initial segment, including Cres3, prostein, lipocalin 2, ALEX3, synaptotagmin-like 4, erm, and milk fat globule factor, whereas 216 clones, including elafin-like 1, lactotransferrin, Sin3B, zinc-finger protein 91, and membrane-type frizzled-related protein, showed 2-fold or higher expression in epididymal regions 2-5. Northern blot analyses of 12 clones predicted by microarray analysis to be either enriched in the initial segment (n = 8), enriched in epididymal regions 2-5 (n = 2), or similar in all regions (n = 2) were carried out. All clones exhibited the expected region-specific expression, thus confirming the microarray results. The studies presented here show a global survey of region-specific gene expression in the epididymis, identifying 15287 sequences, the majority of which have not previously been shown to be expressed in this organ.

Cystatin E1 and E2, new members of male reproductive tract subgroup within cystatin type 2 family

The family of type 2 cystatin proteins is a class of cysteine proteinase inhibitors that function as potent inhibitors of papain-like cysteine proteinases. Recent studies have suggested that cystatins in the male reproductive tract subgroup may perform functions distinct from those of typical cystatins. The objective of the present study was to identify and characterize the expression of new gene members of the cystatin family 2 in mouse male reproductive tissues. Two new members of cystatin family 2, named mouse Cystatin E1 and mouse Cystatin E2 (mCST E1 and mCST E2, respectively), were identified in mice by searching the National Center for Biotechnology Information database for proteins containing homology to known type 2 cystatins. Human CST E1 has recently been reported independently under the name CST 11. The deduced amino acid sequences of these genes have significant homology with the family 2 cystatins, including four conserved cysteine residues at the C-terminus. Similar to other male reproductive subgroup cystatins, the inhibitory motifs are not well conserved in these genes. Northern blot analyses showed that both genes were highly expressed only in the epididymis. In situ hybridization demonstrated that both genes were restricted in their expression to the epithelial cells of the caput and that the highest expression was localized to the initial segment of caput epididymis. Northern blot analyses and in situ hybridization showed that both mCST E1 and E2 mRNA decreased after castration, and treatment with testosterone propionate (T) did not maintain expression of these genes. In fact, T treatment further repressed the expression of these genes in the epididymis following castration. Efferent ductule ligation resulted in a dramatic decrease of epididymal expression of mCST E1 and E2. The expression of mCST E1 mRNA was up-regulated by 17 beta-estradiol (E) administration for 7 days postcastration, whereas no recovery of mCST E1 mRNA level was detected after 14 days of E treatment. Combined E and T (E+T) treatment for 1 and 2 wk reduced the mCST E1 transcripts. The expression of mCST E2 mRNA was maintained by E administration for both 7 and 14 days after castration, whereas treatment of both T and E repressed the expression of mCST E2. Although both mCST E1 and E2 share significant homology with family 2 cystatins, including similar distribution in tissues and localization in epididymis, these genes may have different functions, because their regulation involves different hormones and, probably, other testicular factors.

The cystatin-related epididymal spermatogenic protein inhibits the serine protease prohormone convertase 2

The cystatin-related epididymal spermatogenic (CRES) protein is related to the family 2 cystatins of the cystatin superfamily of cysteine protease inhibitors. However, CRES lacks sequences important for cysteine protease inhibitory activity and is specifically expressed in reproductive and neuroendocrine tissues. Thus, CRES is distinct from cystatins and may perform unique tissue-specific functions. The purpose of the present study was to determine whether CRES functions as a protease inhibitor in in vitro assays. In contrast to mouse recombinant cystatin C, recombinant CRES did not inhibit the cysteine proteases papain and cathepsin B, suggesting that it probably does not function as a typical cystatin. CRES, however, inhibited the serine protease prohormone convertase 2 (PC2), a protease involved in prohormone processing in the neuroendocrine system, whereas cystatin C showed no inhibition. CRES did not inhibit subtilisin, trypsin, or the convertase family members, PC1 and furin, indicating that it selectively inhibits PC2. Kinetic analysis showed that CRES is a competitive inhibitor of PC2 with a K(i) of 25 nM. The removal of N-terminal sequences from CRES decreased its affinity for PC2, suggesting that the N terminus may be important for CRES to function as an inhibitor. These studies suggest that CRES is a cross-class inhibitor that may regulate proprotein processing within the reproductive and neuroendocrine systems.

A new subgroup of the family 2 cystatins

The cystatins are a superfamily of cysteine protease inhibitors. Several genes including Cres (cystatin-related epididymal spermatogenic), testatin, and cystatin T, have been identified that are related to the family 2 cystatins but lack critical consensus sites important for cysteine protease inhibition. In addition, these genes are primarily expressed in the reproductive tract suggesting they may have evolved to perform tissue-specific functions distinct from that of the typical cystatins. This review describes the CRES subgroup within the family 2 cystatins including potential new members and their putative functions in the reproductive tract.