Interactions of labeled epididymal secretory proteins with spermatozoa after injection of 35S-methionine in the mouse

Next-generation sequencing analysis reveals segmental patterns of microRNA expression in yak epididymis

MicroRNAs (miRNAs) have emerged as potent regulators of gene expression and are widely expressed in biological systems. In reproduction, they have been shown to have a significant role in the acquisition and maintenance of male fertility, whereby deletion of Dicer in mouse germ cells leads to infertility. Evidence indicates that this role of miRNAs extends from the testis into the epididymis, controlling gene expression and contributing to regional variations in gene expression. In this study, RNA sequencing technology was used to investigate miRNA expression patterns in the yak epididymis. Region-specific miRNA expression was found in the yak epididymis. In all, 683 differentially expressed known miRNAs were obtained; 190, 186 and 307 differentially expressed miRNAs were identified for caput versus corpus, corpus versus cauda and caput versus cauda region pairs respectively. Kyoto Encyclopedia of Genes and Genomes results showed endocytosis as the most enriched pathway across region pairs, followed by protein processing in the endoplasmic reticulum, phagosome, spliceosome and biosynthesis of amino acids in region pair-specific hierarchical order. Gene ontology results showed varied enrichment in terms including cell, biogenesis, localisation, binding and locomotion across region pairs. In addition, significantly higher miR-34c expression was seen in the yak caput epididymidis relative to the corpus and cauda epididymidis.

Epidermal growth factor regulates connexin 43 in the human epididymis: role of gap junctions in azoospermia

BACKGROUND

Gap junctions (GJs) allow for direct communication between adjacent cells. They are composed of connexons consisting of transmembrane proteins, connexins (Cxs). The objectives of this study were to determine if GJ proteins GJA1 (Cx43), GJB1 (Cx32) and GJB2 (Cx26) are present in the epididymis of men with a normal epididymis, to assess whether or not Cx expression and localization are altered in azoospermic patients, and to determine if epidermal growth factor (EGF) regulates GJA1 expression.

METHODS

Epididymides were obtained from men with localized testis cancer with active spermatogenesis and histologically normal epididymal tubule (group 1), men with non-obstructive azoospermia secondary to Sertoli-cell only syndrome (group 2) and from azoospermic men with normal spermatogenesis and epididymal obstruction (group 3). Epididymides were subdivided into three segments: caput, corpus and cauda. Quantitative real-time RT-PCR was performed to assess GJA1, GJB1, GJB2 and EGF receptor (EGFR) mRNA levels in epididymides from patients from each group (all n=3, except n=1 for caput blockage). A human caput epididymal cell line was then used to determine the role of EGFR signaling on the regulation of human epididymal GJA1.

RESULTS

Real-time RT-PCR analysis revealed that GJA1, GJB1, GJB2 and EGFR were expressed along the human epididymis. In the cauda epididymidis of group 2 and 3 men, we observed a significant decrease in GJA1 (P=0.0456 and P=0.0465, respectively) and GJB1 (P=0.0450 and P=0.0497, respectively) mRNA levels when compared with group 1 men. We also observed a decrease in EGFR mRNA levels (P=0.0358) in the cauda epididymidis of group 3 men when compared with group 1. Immunocytochemistry revealed that in the epididymis, GJA1 and EGFR were localized between basal and principal cells and between adjacent principal cells. In group 2 and 3 patients, however, we noted a dramatic increase in cytosolic immunostaining for both GJA1 and EGFR in both principal and basal cells. Using a human caput epididymal cell line derived from fertile men, we demonstrated that changes in GJA1 phosphorylation could be regulated by EGF (P=0.015) and the extracellular regulated kinase 1/2 signaling pathway (P=0.03). Furthermore, while the phosphoinositide-3-kinase (PI3K)/AKT signaling pathway did not alter GJA1 phosphorylation, treatment with PI3K/AKT inhibitor LY294002 significantly (P=0.024) inhibited the EGF-stimulated increase in GJA1 total protein levels at 24 h. Immunolocalization indicated that loss of PI3K/AKT signaling was associated with increased cytosolic localization of Cx43 in this cell line.

CONCLUSIONS

Together, these data suggest that in azoospermic men decreased expression of EGFR may be responsible for decreasing GJA1 levels and increasing its cytosolic localization via the PI3K/AKT signaling pathway.

Role of microRNAs in controlling gene expression in different segments of the human epididymis

Background

The molecular mechanisms implicated in regionalized gene expression in the human epididymis have not yet been fully elucidated. Interestingly, more than 200 microRNAs (miRNAs) have been identified in the human epididymis and could be involved in the regulation of mRNA stability and post-transcriptional expression in this organ.

Methods

Using a miRNA microarray approach, we investigated the correlation between miRNA signatures and gene expression profiles found in three distinct regions (caput, corpus and cauda) of human epididymides from 3 donors. In silico prediction of transcript miRNA targets was performed using TargetScan and Miranda software's. FHCE1 immortalized epididymal cell lines were cotransfected with mimic microRNAs and plasmid constructs containing the 3′UTR of predicted target genes downstream of the luciferase gene.

Results

We identified 35 miRNAs differentially expressed in the distinct segments of the epididymis (fold change ≥2, P-value≤0.01). Among these miRNAs, miR-890, miR-892a, miR-892b, miR-891a, miR-891b belonging to the same epididymis-enriched cluster located on the X chromosome, are significantly more expressed in the corpus and cauda regions than in the caput. Interestingly, a strong negative correlation (r = −0,89, P-value≤0.001) was found between the pattern of expression of miR-892b and its potential mRNA target Esrrg (Estrogen Related Receptor Gamma) and with miR-145 and Cldn10 mRNA (r = −0,92, P-value≤0.001). We confirmed that miR-145 and miR-892b inhibit the expression of the luciferase reporter via Cldn10 and Esrrg 3′ UTRs, respectively.

Conclusion

Our study shows that the expression of miRNAs is segmented along the human epididymis and correlates with the pattern of target gene expression in different regions. Therefore, epididymal miRNAs may be in control of the maintenance of gene expression profile in the epididymis, which dictates segment-specific secretion of proteins and establishes physiological compartments that directly or indirectly affect sperm maturation and fertility.

The N-linked carbohydrate moiety of male reproductive tract CD52 (mrt-CD52) interferes with the complement system via binding to C1q

Antisperm antibody detected in infertile female patients' sera has been shown to correlate with reduced fertility. The antibody showed strong complement-dependent cytotoxicity as determined by the sperm immobilization test (SIT). CD52 is a human glycosylphosphatidylinositol (GPI)-anchored antigen present in lymphocytes and male reproductive tracts (mrt), including mature sperm and seminal plasma. Recently, purified mrt-CD52 from human seminal plasma has been reported to interfere with the classical complement pathway, but not lectin binding or alternative pathways of the complement system. The purpose of this study is to determine which stage of the classical pathway mrt-CD52 regulates. mrt-CD52 was purified from human seminal plasma or intact sperm membrane. Immunoprecipitation assay was performed with the reaction of mrt-CD52, human complement and mAb H6-3C4. Immunoprecipitate was formed by the carbohydrate moiety of mrt-CD52, but not by the GPI-anchor peptide. The C1q molecule (29 kDa) was detected in the immunoprecipitates by Western blotting analysis probed with anti C1q antibody, indicating that the carbohydrate moiety of mrt-CD52 binds to C1q. Also, the complement-dependent SIT revealed that purified CD52 inhibited sperm immobilization activity by antisperm antibody. These results suggest that mrt-CD52 protects sperm function from complement attack if antisperm antibody is generated in the female reproductive tracts.

Characterization of the proteomes associating with three distinct membrane raft sub-types in murine sperm

Mammalian sperm are transcriptionally and translationally inactive. To meet changing needs in the epididymis and female tract, they rely heavily on post-translational modifications and protein acquisition/degradation. Membrane rafts are sterol and sphingolipid-enriched micro-domains that organize and regulate various pathways. Rafts have significance in sperm by transducing the stimulus of sterol efflux into changes in intracellular signaling that confer fertilization competence. We recently characterized three biochemically distinct sub-types of sperm rafts, and now present profiles for proteins targeting to and associating with these sub-types, along with a fraction largely comprised of "non-raft" domains. Proteomics analysis using a gel-based LC-MS/MS approach identified 190 strictly validated proteins in the raft sub-types. Interestingly, many of these are known to be expressed in the epididymis, where sperm membrane composition matures. To investigate potential roles for rafts in epididymal protein acquisition, we compared the expression and localization of two different sterol-interacting proteins, apolipoprotein-A1 (apoA1) and prominin-1 (prom1) in sperm from different zones. We found that apoA1 was gradually added to the plasma membrane overlying the acrosome, whereas prom1 was not, suggesting different mechanisms for raft protein acquisition. Our results define raft-associating proteins, demonstrate functional similarities and differences among raft sub-types, and provide insights into raft-mediated epididymal protein acquisition.

Whole-body heat exposure induces membrane changes in spermatozoa from the cauda epididymidis of laboratory mice

This study was carried out to determine if exposure to hot environmental temperatures had a direct, detrimental effect on sperm quality. For this the effect of whole-body heat exposure on epididymal spermatozoa of laboratory mice was investigated. C57BL/6 mice (n = 7) were housed in a microclimate chamber at 37 degrees C-38 degrees C for 8 h per day for three consecutive days, while control mice (n = 7) were kept at 23 degrees C-24 degrees C. Cauda epididymal spermatozoa were obtained 16 h after the last heat treatment. The results showed that sperm numbers were similar in the two groups (P = 0.23), but after heat treatment, a significant reduction in the percentage of motile sperm was present (P < 0.0001). Membrane changes of the spermatozoa were investigated by staining with phycoerythrin (PE)-conjugated Annexin V, which detects exteriorization of phosphotidylserine from the inner to the outer leaflet of the sperm plasma membrane, and 7-aminoactinomycin D (7-AAD), which binds to the sperm nucleus when the plasma membrane is damaged. The percentage of spermatozoa showing positive staining with Annexin V-PE or 7-AAD or both, was significantly higher (P < 0.05) in heat-exposed mice compared with controls. These results show that whole-body heat exposure to 37 degrees C-38 degrees C induces membrane changes in the epididymal spermatozoa of mice, which may lead to apoptosis.

Functional characterization of a conditionally immortalized mouse epididymis caput epithelial cell line MEPC5 using temperature-sensitive simian virus 40 large T-antigen

A conditionally immortalized epididymis caput cell line, MEPC5, was established by infecting primary cultured mouse epididymis caput cells with a temperature-sensitive simian virus 40 large T-antigen. At a permissive temperature of 33 degrees C, the large T-antigen was expressed and the cells grew continuously. However, the downregulation of T-antigen at a nonpermissive temperature of 39 degrees C and the upregulation of cell density at 33 degrees C were associated with growth arrest and the increased protein expression of p21(waf1), a cell cycle inhibitor. The cells expressed epididymal caput-expressed genes such as phosphatidylethanolamine binding protein, polyoma enhancer activator 3, ME1, sulfated glycoprotein-2 (SGP-2), androgen receptor, and retinoic acid receptor alpha. Interestingly, the expression levels of ME1 and SGP-2 were significantly elevated under the cell growth-restricted conditions. The established mouse epididymis caput epithelial cell line MEPC5 retains some characteristics of differentiated epididymis epithelial cells, and should prove an excellent model for studies of gene expression and the physiological functions of epididymis caput epithelial cells.

Impact of a mild scrotal heat stress on DNA integrity in murine spermatozoa

An increase in scrotal temperature can lead to the production of poor quality spermatozoa and infertility. In the present study we have used mice to examine the impact of mild, scrotal heat stress (42 °C for 30 min) on numbers of spermatozoa as well as on the integrity of their DNA. Spermatozoa recovered from the epididymides hours (1 to 24) or days (7 to 32) after treatment were analysed using COMET and sperm chromatin structure (SCSA) assays. The treatment induced a stress response in both the testis and the epididymis that was associated with reduced expression of the cold inducible RNA binding protein (Cirp) and an increase in germ cell apoptosis (Apotag positive cells). Although spermatozoa present in the epididymis at the time of heating contained correctly packaged DNA, its integrity was compromised by heat stress. In addition, although some germ cells, which were present within the testis at the time of heat stress, were removed by apoptosis, many germ cells completed their development and were recovered as motile spermatozoa with damaged DNA. In conclusion, these data demonstrate that scrotal heat stress can compromise the DNA integrity of spermatozoa and this may have clinical implications for patients undergoing IVF and intra-cytoplasmic sperm injection (ICSI).

Immortalization by large T-antigen of the adult epididymal duct epithelium

The SV40 large T-antigen has been widely used to convert various cell types to a transformed phenotype, and also to induce progressive tumours in transgenic animals. The objectives of this review are to compare and discuss three different approaches to generate epididymal epithelial cell lines using the large T-antigen. In the first approach, retroviral transfection of primary cultures was used to immortalize canine epididymal cells in vitro; the other two approaches used transgenic mice expressing the large T-antigen. In one of these in vivo approaches, a construct consisting of the coding sequence of a temperature sensitive (ts) SV40 large T-antigen was inserted in a mouse genome. When the cells are exposed to the permissive temperature of 33 degrees C, functional expression of the large T-antigen occurs and cells start to proliferate. In the second in vivo approach a tissue-specific promoter, the 5kb GPX5 promoter, was used to direct expression of the large T-antigen to the epididymal duct epithelium.

CCAAT/enhancer binding protein beta regulates expression of the cystatin-related epididymal spermatogenic (Cres) gene

The CRES protein is a member of the cystatin superfamily of cysteine protease inhibitors with restricted expression in stage-specific germ cells, proximal caput epididymidis, and anterior pituitary gonadotroph cells. To elucidate the molecular mechanisms regulating the highly restricted expression of the cres gene, we have sequenced 1.6 kilobases of mouse cres 5' flanking sequence and performed studies to examine the cres gene promoter. Two putative CCAAT/enhancer binding protein (C/EBP) transcription factor binding motifs exist within the first 135 base pairs of cres promoter. Furthermore, our studies demonstrate that cres mRNA levels are dramatically reduced in the epididymides of C/EBP beta-deficient mice. These data suggest that the C/EBP family of transcription factors, in particular C/EBP beta, plays a role in the regulation of cres gene expression. In support of this finding, Northern blot analysis showed that C/EBP beta is the predominant C/EBP family member expressed in the L beta T2 gonadotroph cell line and the proximal caput epididymidis. Also, gel shift and supershift assays demonstrated that C/EBP beta protein in nuclear extracts from L beta T2 gonadotroph cells and epididymal cells bound to the two C/EBP sites in the cres promoter. Finally, to test the in vivo function of the C/EBP sites in cres gene expression, transfection studies were performed in L beta T2 gonadotroph cells and two heterologous cell systems. These experiments showed a significant reduction of cres transactivation when either C/EBP sites were mutated, and no transC/EBP activation of the cres promoter when both C/EBP sites were mutated. Taken together, these studies demonstrate that the C/EBP beta transcription factor is necessary for high levels of cres gene expression in the proximal caput epididymidis and anterior pituitary gonadotroph cells.

Translation of a unique transcript for protein isoaspartyl methyltransferase in haploid spermatids: implications for protein storage and repair

The mammalian testis contains high levels of a protein, L-isoaspartyl (D-aspartyl) O-methyltransferase (PIMT), postulated to play a role in the repair of age-damaged proteins. To examine the regulation of PIMT concentrations during the development of spermatozoa, poly(A)+ RNA was isolated from purified populations of pachytene spermatocytes and round spermatids. Northern blot analysis revealed that a unique 1.1-1.3 kb PIMT transcript is present in preparations of round spermatid and pachytene spermatocyte poly (A)+ RNA. The concentration of this small PIMT transcript is at least four times higher in mRNA isolated from round spermatids than in mRNA isolated from pachytene spermatocytes, indicating that the PIMT gene is actively transcribed during the haploid phase of spermatogenesis. The germ cell-specific PIMT transcripts are distributed between the polysomal fraction and the nonpolysomal fractions of testis RNA, suggesting that translational controls also contribute to the high concentrations of PIMT in mammalian sperm. PIMT function is not essential for spermatogenesis because the testes from transgenic mice lacking PIMT activity have normal levels of protamine transcripts, and because functional sperm can be recovered from the cauda epididymis. The protein repair function of the PIMT may be more important in maintaining the fertilization competence of translationally-inactive mature sperm during the prolonged period of epididymal transit and storage in the male reproductive tract.

Characterization and localization of the rat, mouse and human testicular phosphatidylethanolamine binding protein

A cytosolic 23kDa protein was initially purified from bovine brain and shown to bind phosphatidylethanolamine. Later, it was also characterized in rat and human brain, and it is now known to be widespread, having been found in numerous tissues in several species. Here, we report the high level of mRNA and phosphatidyl ethanolamine binding protein expression in rat testis and to a lesser extent in mouse testis. In human testis, although it was not detectable by Northern blot analysis, the mRNA was shown to be present when PCR amplification was performed. Immunohistochemical experiments revealed that the testicular phosphatidylethanolamine binding protein (tPBP) is principally expressed in the elongated spermatids of both rat and mouse testis. This finding, and the association of tPBP with cellular membranes, suggest its possible implication in membrane remodelling during spermatid maturation.

In vivo regulation of rat epididymal proteins by retinoids: analysis by two-dimensional electrophoresis

The role of retinoids in the regulation of epididymal fluid protein expression was investigated. We compared the patterns of two-dimensional electrophoretic gels of proteins from luminal fluids, cytosols and spermatozoa (from control rats only) of control, retinoid-depleted, retinoid-depleted retinoic acid-complemented and retinoid-depleted testosterone-supplemented rats. This study compared the luminal fluid patterns from the 4 diets and observed 13 proteins whose expression was dependent on nutritional status. Eight were either absent or very weakly expressed in retinoid-depleted animals only, while their presence was obvious in control rats and in the retinoid-deficient retinoic acid- and testosterone-complemented groups. The expression of 8 proteins was greatly enhanced in retinoid-depleted testosterone-supplemented fluids as compared to control fluids. Five of the regulated proteins seemed to be captured by spermatozoa as they were observed in sperm protein patterns of control rats. These results clearly show that the synthesis of several epididymal proteins is influenced by retinoids. Since testosterone-supplemented animals on retinoid-free diet elicited the same response as retinol and retinoic acid ones, testosterone is likely to be the mediator of retinoid action on epididymal protein synthesis. Nevertheless, the observation of one protein whose expression is stimulated by retinoic acid only and is totally independent of testosterone also favors the direct influence of this retinoid.

From structure to function: possible biological roles of a new widespread protein family binding hydrophobic ligands and displaying a nucleotide binding site

A cytosolic 21-23 kDa protein isolated from bovine brain was demonstrated to bind hydrophobic ligands, particularly phosphatidylethanolamine. The protein was encountered in numerous tissues of several species. High expression of the mRNA encoding the 21-23 kDa protein was found in rat testes. Immunohistochemical studies showed the presence of the 21-23 kDa protein in the elongated spermatids and epididymal fluid of rat testis and in brain oligodendrocytes of developing rats. As the bovine, human and rat brain 21-23 kDa proteins had only few sequence homologies with already know proteins, ti was concluded that they belong to a new protein family. In order to get additional information on the structural features of the 21-23 kDa protein, we built a molecular model which displayed a nucleotide binding site. The affinity of the bovine brain 21-23 kDa protein towards nucleotides as well as its association with cytosolic proteins and small GTP-binding proteins were demonstrated. Recently, significant sequence homologies were found with an antigen from Onchocerca volvulus, a fruit fly odorant-binding protein and the yeast protein TFS1 which is a dosage-dependent suppressor of CDC25 mutations. A positive regulation of RAS is carried out by CDC25 product which facilitates the GDP/GTP exchange on RAS proteins. These results imply that 21-23 kDa proteins function in oxidoreduction reactions and signal mechanisms during cell growth and maturation.

Transient appearance of CRES protein during spermatogenesis and caput epididymal sperm maturation

In previous studies we identified an epididymal gene that exhibits homology to the cystatin family of cysteine protease inhibitors. The expression of this gene, termed CRES (cystatin-related epididymal and spermatogenic), was shown to be highly restricted to the proximal caput epididymal epithelium with less expression in the testis and no expression in the 24 other tissues examined. In this report, studies were carried out to examine CRES gene expression in the testis as well as to characterize the CRES protein in the testis and epididymis. In situ hybridization experiments revealed that within the testis CRES gene expression is stage-specific during spermatogenesis and is exclusively expressed by the round spermatids of Stages VII-VIII and the early elongating spermatids of Stages IX and X. Immunohistochemical studies demonstrated that CRES protein was transiently expressed in both the testis and epididymis. Within the testis the protein was localized to the elongating spermatids, whereas within the epididymis CRES protein was exclusively synthesized by the proximal caput epithelium and then secreted into the lumen. Surprisingly, the secreted CRES protein had completely disappeared from the epididymal lumen by the distal caput epididymidis. Western blot analysis of testicular and epididymal proteins showed that the CRES antibody specifically recognized a predominant 19 kDa CRES protein and a less abundant 14 kDa form. These observations suggest that the CRES protein performs a specialized role during sperm development and maturation.

Electron microscopic immunolocalization of the 18 and 29 kilodalton secretory proteins in the mouse epididymis: evidence for differential uptake by clear cells

In previous studies we reported the synthesis, secretion, and immunolocalization at the light microscopic level of two mouse epididymal proteins, MEP 7 and MEP 10 [Rankin et al. (1992b), Biol. Reprod., 46:747-766]. MEP 7 is the mouse homologue of the rat metalloproteins, AEG/D and E, and MEP 10 is the mouse homologue of the rat retinoic acid binding proteins, B and C. We now describe the immunolocalization of MEP 7 and MEP 10 in the mouse epididymis at the electron microscopic level. MEP 7 was localized in the Golgi apparatus, in small electron-lucent secretory vesicles, and on microvilli of the principal cells from the distal caput epididymidis to the cauda. The luminal contents were also immunoreactive in these regions of the epididymis. Although some gold particles were associated with the sperm surface, there was no selective concentration of these particles. In addition, MEP 7 was localized in large (600 nm) supranuclear endocytic vesicles and in infranuclear lysosomes. MEP 10 immunoreactivity was also seen on the microvilli of the principal cells of the distal caput and corpus and the luminal contents from the distal caput to the cauda epididymidis. There was no association of gold particles with the sperm surface. In contrast to MEP 7, there was no detectable MEP 10 immunoreactivity on the organelles of the principal cells involved in protein secretion or endocytosis. Clear cells also demonstrated immunoreactivity to MEP 7 and MEP 10. However, the intensity of immunolabeling, and the number of clear cells labeled, was greater with MEP 10 than MEP 7. In the case of MEP 7, the gold particles were located on the large supranuclear endocytic vesicles and on some infranuclear lysosomes, from the proximal corpus to the middle cauda, while in the case of MEP 10, gold particles were predominantly present in infranuclear lysosomes from the distal caput to the middle cauda. These results suggest that the principal cells are involved in both the secretion and endocytosis of MEP 7. The MEP 10 and MEP 7 proteins present in the lumen of the mouse epididymis are endocytosed from the lumen and degraded in the clear cells. However, the process of endocytosis by the clear cells of these two proteins appears to be different.

Two Golgi integral membrane proteins (GIMPS) exhibit region- and cell type-specific distribution in the epididymis of the adult rat

The epididymis participates in the post-testicular maturation and storage of spermatozoa by secreting proteins into the tubule lumen in a region-specific fashion. The underlying molecular mechanisms leading to biogenesis of these region-specific differences, however, are not known, although components of the Golgi complex membrane container must undoubtedly be intimately involved. Two monoclonal antibodies raised against Golgi integral membrane proteins, recognizing either the cis (GIMPc) or trans Golgi (GIMPt) cisternae, were used as molecular probes of these regions to begin the characterization of the Golgi complex of in vivo and in vitro epididymal cells. Immunolocalization of GIMPs was performed on frozen sections and in cultured cells using biotin-streptavidin-peroxidase immunocytochemistry. In tissue sections, immunostaining of GIMPt was extremely robust in the supranuclear cytoplasm throughout the epididymis. In contrast, no GIMPc immunostaining was detected in the initial segment or in clear cells of the distal caput, corpus, and cauda. Immunodetection of GIMPc and GIMPt in epididymal cells in vitro revealed a reticular, perinuclear pattern, and NH4Cl treatment preferentially disrupted the GIMPt immunolocalization. These results characterizing the molecular components of the Golgi complex will form the basis of additional studies to gain further insight into mechanisms leading to generation of regional differences in epididymal function.

Relationships between molecular interactions (nucleotides, lipids and proteins) and structural features of the bovine brain 21-kDa protein

A cytosolic 21-kDa protein isolated from bovine brain was demonstrated to bind hydrophobic ligands, particularly phosphatidylethanolamine. It was encountered in several tissues and species; however, its accurate function remained partially unknown. In order to obtain information from its structural features, we built a molecular model which revealed it to possess a nucleotide-binding site. In the present research, we describe the affinity of the bovine brain 21-kDa protein for nucleotides, and its association with cytosolic proteins, small GTP-binding proteins and lipid droplets. Our results suggest that, through its association with small GTP-binding proteins, the 21-kDa protein is implicated in signal mechanisms during cell growth and maturation.

Assessment of protein synthesis and secretion by rat seminiferous and epididymal tubules in vivo

In vivo microperifusion and micropuncture were used to study tubule protein synthesis and proluminal secretion by the male reproductive tract in vivo. Seminiferous and caput and cauda epididymal tubules were perifused for 3 h. with [35S]-methionine. Perifused interstitial fluid (IF), lumen fluid (LF), and tubule extract (TE) were collected. Proteins were separated by SDS-PAGE, and autoradiograms were developed. Trichloroacetic acid precipitable proteins in each fluid were determined and a protein synthesis index (PSI) was calculated. PSI values demonstrated that the cauda epididymis synthesized less protein in vivo than did either seminiferous or caput tubules. Seminiferous tubules synthesized and secreted into the tubule lumen a relatively constant panel of proteins. Epididymal tubules synthesized and secreted proteins in a region-specific manner. In the caput epididymis the most prominent secreted bands were consistent with the heavy and light chains of epididymal clusterin. In the cauda epididymis, the most prominent synthesized and secreted protein was a 25 kDa protein consistent with the protein D. The above approach to studying protein synthesis and secretion will allow direct study of the physiological and pathophysiological effects on this important epithelial function in vivo.

Synthesis, characterization and hormonal regulation of epididymal proteins during postnatal development of the mouse

Maturation of mammalian spermatozoa depends on their interactions with epididymal proteins. The incorporation of 35S-methionine into these proteins was investigated by in vitro incubation of tissue minces from the mouse epididymis at different ages of postnatal development. The greatest amount of incorporation per wet weight of tissue was seen in 7 to 21-day-old mice. It decreased progressively during development while the rate of proteins released into the medium remained almost constant until the adult state. Separation of labeled proteins on sodium dodecyl sulphate polyacrylamide gels followed by fluorography showed that the great majority of secretory proteins synthesized in adult mouse epididymis could be recovered already from 7-day-old animals. Regional differences appeared at 21 days of age. These were marked by the secretion of proteins characteristic of the proximal (26, 25, 20, 19 kDa) and distal (44, 29 kDa) epididymis. Analysis of cytosol and luminal fluid proteins from prepubertal and adult epididymis revealed a number of proteins of the same mobility as those synthesized and secreted in vitro. Among the luminal proteins which showed variations during development and regional differences, four (29, 26, 20, 19 kDa) were characteristics of the epididymis and three (88, 34, 13 kDa) comigrated with testicular components. Castration or estrogen treatment of prepubertal mice for 4, 3 and 2 weeks inhibited or reduced the synthesis of the luminal proteins which appeared during postnatal development and/or presented regional differences. Testosterone replacement of castrated mice reversed this effect and induced the secretion of new proteins (37, 24 kDa).(ABSTRACT TRUNCATED AT 250 WORDS)

Human sperm proteins from testicular and epididymal origin that participate in fertilization: modulation of sperm binding to zona-free hamster oocytes, using monoclonal antibodies

In order to identify human sperm surface proteins involved in the gamete recognition process, mouse monoclonal antibodies were directed against human spermatozoa and screened with live spermatozoa by enzyme-linked immunosorbent assay (ELISA). Immunoperoxidase staining of human testis showed the early presence of four corresponding proteins on germinal cells, while six were detected primarily in testis fluid. The presence of 17 proteins was evidenced in the epididymis. Eight were detected with a decreasing gradient from the beginning to the end of the organ, including vasa efferentia for three of them. The other nine were observed in only one defined segment, usually the caput epididymis, which was found to be the most active region. Comparison of spermatozoa patterns from testis, vasa efferentia, and the three regions of epididymis pointed out a progressive coating. By contrast, three antibodies displayed a migration of spermatozoa surface domains in the course of epididymal transit. Six antibodies were found to inhibit human spermatozoa adherence to zona-free hamster oocytes, while nine promoted it. Molecular weights of antigens corresponding to nine of the antibodies ranged from 11 to 215 kDa. No correlation could be established with previously described human proteins. These observations emphasize the role of epididymis in human sperm maturation.

Regulation of the epididymal glutathione peroxidase-like protein in the mouse: dependence upon androgens and testicular factors

The protein MEP24 was previously described as a glutathione peroxidase-like molecule specifically secreted by the mouse caput epididymidis. Recently, its binding to the head of spermatozoa was demonstrated. Here, the regulation of MEP24 expression was studied by analyzing transcriptional and translational activities in the epididymis (1) of adult mice castrated on day 60 and given various substitutive testosterone (T) treatments from day 90 and (2) of hemicastrated adult animals. In castrated mice, T treatment induced a significant rise in plasma T and 5 alpha-dihydrotestosterone (DHT) concentrations that greatly exceeded the control values. Owing to efficient regulation, however, the epididymal T and DHT levels were never higher than those of the controls. The restoration of MEP24 mRNA accumulation was complete when the epididymal DHT content returned to its normal value. However, when estimated in a cell-free system, the in vitro translatable MEP24 mRNA level never exceeded 70% of control values, even though the DHT and accumulated mRNAs were restored by 100% or more. In hemicastrates, the T content was normal on the castrated side, while the DHT content exhibited a significant decrease (47%). In this case, the MEP24 mRNA accumulation reached 88% of the normal value, but the translation rate, both in vitro and in vivo, was only about 50%. Ultrastructural studies showed that the normal rough endoplasmic reticulum organization in segment I cells is dependent upon the presence of testicular fluid in the epididymal duct lumen. Thus, this report shows that the MEP24 mRNA steady-state level is completely recovered in the presence of a normal epididymal DHT content, while restoration of the regulation of translation is just partial. This could be related to the cell organization but seems mainly dependent upon the presence of specific mRNA-associated factors which are probably under the control of androgens and/or molecules carried by the testicular fluid.

Postnatal development and testosterone-dependence of GP-83 and GP-49, two sperm maturation-related glycoproteins in BALB/c mouse epididymis

The secretion of sperm maturation-related molecules by the epididymis is subjected to developmental and hormonal regulation. In the BALB/c mouse, we found that GP-83 and GP-49, two sperm maturation-related glycoproteins, were secreted by the epididymis. The present study investigated the postnatal development and testosterone-dependence of these two molecules. Histochemical localization in paraffin sections revealed that wheat-germ agglutinin (WGA)-binding sites were first present in the epididymis of 4-week-old mice. The distribution of WGA-binding sites was the same as that of more mature mice, i.e., it was first found in the principal cells of the corpus epididymidis, and gradually appeared in the contents of epididymal tubules. On WGA blots, GP-83 and GP-49 were identified in the corpus, and GP-83 was identified in the cauda of the epididymis. In mice that had received unilateral orchiectomy at 4 weeks of age, GP-83 and GP-49 were present in both intact and orchiectomized epididymides 4 weeks after the operation. In the epididymides of mice that had received bilateral orchiectomy, GP-83 and GP-49 were barely identifiable. However, the presence of these two molecules was restored if testosterone was supplemented immediately after orchiectomy. These results indicate that GP-83 and GP-49 are secreted de novo in the epididymis, and that the secretion of these two molecules is developmentally regulated and androgen-dependent.

Lysosomal integral membrane proteins exhibit region and cell type specific distribution in the epididymis of the adult rat

The epididymis, a post-testicular site required for maturation and storage of spermatozoa, is actively involved in exocytic and endocytic events, two phenomena likely to depend on the integrity of the lysosomal system. To study the lysosomal system of the epididymis, five monoclonal antibodies, previously characterized as recognizing five distinct lysosomal integral membrane proteins (LIMPs 1-5), were used as molecular probes of lysosome distribution in cells lining the epithelium. Immunocytochemical localization of LIMPs, using biotin-streptavidin immunoperoxidase methodology, was performed on frozen sections of adult rat epididymides and in cell cultures prepared from either the caput or cauda epididymis. In frozen sections, a heterogeneous distribution of the different LIMPs along the length of the epididymis was observed. For example, the distribution of LIMP 1 (35-50 K) was detected in all cells of the caput and quite dramatically in clear cells of the distal caput, corpus, and cauda epididymis, but specifically not in the principal cells of the distal caput, corpus, and cauda. In contrast, LIMP 2 (64-71 K) was present in all cells of the epididymis, except clear cells. LIMPs 4 and 5 (93 K and 93 K) were detected in all epididymal cells, including the clear cells. Finally, whereas the regional and cell type distribution of LIMP 3 (74 K) in the epididymis was identical to that of LIMPs 4 and 5, the nature of the vesicles immunostained was distinct. In cultured cells, the general immunostaining patterns observed in vivo were maintained during the duration of the primary cultures for all five LIMPs. Our results begin to address the molecular heterogeneity of the lysosomal system along the length of the epididymis, and may suggest in part a basis for underlying structural and functional characteristics of the epididymis leading to the sequential maturation of sperm.

Selective action of androgens on the molecular forms of esterases characterized by two-dimensional gel electrophoresis in the epididymis and vas deferens of the mouse

Molecular forms of esterases were resolved in non-denaturing conditions by using two-dimensional gel electrophoresis with isoelectric focusing in the first dimension and a time-dependent polyacrylamide gradient gel electrophoresis (PAGGE) in the second dimension. This procedure was used to analyse sequential changes in esterase composition along the excurrent genital duct of the mouse and to initiate a specific identification of the androgen-regulated molecular forms. Almost all the 68 variants (pH 3.9-6.4 and 50-300 kDa) revealed by alpha-naphtyl acetate from the fluids of the three parts of the epididymis (caput, corpus, cauda) and vas deferens, could be assigned to the carboxylesterase group as shown by their action on various substrates and sensitivity to inhibitors. Some of these variants co-migrated with those in the serum and testis, whereas other enzyme forms made their first appearance in the caput (13), in the corpus (26) and in the vas deferens (3). The major changes occurred between the caput and the corpus of the epididymis. Only a few acidic spots were not revealed after neuraminidase digestion. Castration of mice (4 weeks) resulted in inhibition of the activity of 34 esterase forms, and thus abolished most of the regional differences in the excurrent duct system. By re-initiating or repressing the synthesis of regional esterase variants, testosterone supplementation (2 and/or 4 weeks) of castrated animals restored the normal esterase pattern in the three epididymal parts, but not in the vas deferens. The major effect of efferent duct ligation (4 weeks) was the emergence in the corpus and cauda of the epididymis of two variants found in the caput of uncastrated mice.