Biochemical characterization of two ram cauda epididymal maturation-dependent sperm glycoproteins

New insights into epididymal function in relation to sperm maturation

Testicular spermatozoa acquire fertility only after 1 or 2 weeks of transit through the epididymis. At the end of this several meters long epididymal tubule, the male gamete is able to move, capacitate, migrate through the female tract, bind to the egg membrane and fuse to the oocyte to result in a viable embryo. All these sperm properties are acquired after sequential modifications occurring either at the level of the spermatozoon or in the epididymal surroundings. Over the last few decades, significant increases in the understanding of the composition of the male gamete and its surroundings have resulted from the use of new techniques such as genome sequencing, proteomics combined with high-sensitivity mass spectrometry, and gene-knockout approaches. This review reports and discusses the most relevant new results obtained in different species regarding the various cellular processes occurring at the sperm level, in particular, those related to the development of motility and egg binding during epididymal transit.

Preservation of sperm within the mouse cauda epididymidis in salt or sugars at room temperature

The development of preservation techniques for male gametes at room temperature might allow us to store them in a simple and cost-effective manner. In this study, we studied the use of pure salt or sugar to preserve the whole cauda epididymidis, because it is known that food can be preserved in this way at room temperature for long periods. Mouse epididymides were placed directly in powdered salt (NaCl) or sugars (glucose or raffinose) for 1 day to 1 year at room temperature. Spermatozoa were recovered from the preserved organs after being rehydrated with medium and then isolated sperm heads were microinjected into fresh oocytes. Importantly, the oocyte activation capacity of spermatozoa was maintained after epididymal storage in NaCl for 1 year, whereas most untreated spermatozoa failed to activate oocytes within 1 month of storage. Pronuclear morphology, the rate of extrusion of a second polar body and the methylation status of histone H3 lysine 9 (H3K9me3) in those zygotes were similar to those of zygotes fertilized with fresh spermatozoa. However, the developmental ability of the zygotes decreased within 1 day of sperm storage. This effect led to nuclear fragmentation at the 2-cell embryo stage, irrespective of the storage method used. Thus, although the preserved sperm failed to allow embryo development, their oocyte activation factors were maintained by salt storage of the epididymis for up to 1 year at room temperature.

The adult boar testicular and epididymal transcriptomes

Background

Mammalians gamete production takes place in the testis but when they exit this organ, although spermatozoa have acquired a specialized and distinct morphology, they are immotile and infertile. It is only after their travel in the epididymis that sperm gain their motility and fertility. Epididymis is a crescent shaped organ adjacent to the testis that can be divided in three gross morphological regions, head (caput), body (corpus) and tail (cauda). It contains a long and unique convoluted tubule connected to the testis via the efferent ducts and finished by joining the vas deferens in its caudal part.

Results

In this study, the testis, the efferent ducts (vas efferens, VE), nine distinct successive epididymal segments and the deferent duct (vas deferens, VD) of four adult boars of known fertility were isolated and their mRNA extracted. The gene expression of each of these samples was analyzed using a pig generic 9 K nylon microarray (AGENAE program; GEO accession number: GPL3729) spotted with 8931 clones derived from normalized cDNA banks from different pig tissues including testis and epididymis. Differentially expressed transcripts were obtained with moderated t-tests and F-tests and two data clustering algorithms based either on partitioning around medoid (top down PAM) or hierarchical clustering (bottom up HCL) were combined for class discovery and gene expression analysis. Tissue clustering defined seven transcriptomic units: testis, vas efferens and five epididymal transcriptomic units. Meanwhile transcripts formed only four clusters related to the tissues. We have then used a specific statistical method to sort out genes specifically over-expressed (markers) in testis, VE or in each of the five transcriptomic units of the epididymis (including VD). The specific regional expression of some of these genes was further validated by PCR and Q-PCR. We also searched for specific pathways and functions using available gene ontology information.

Conclusion

This study described for the first time the complete transcriptomes of the testis, the epididymis, the vas efferens and the vas deferens on the same species. It described new genes or genes not yet reported over-expressed in these boar tissues, as well as new control mechanisms. It emphasizes and fulfilled the gap between studies done in rodents and human, and provides tools that will be useful for further studies on the biochemical processes responsible for the formation and maintain of the epididymal regionalization and the development of a fertile spermatozoa.

Piezo-assisted in vitro fertilization of mouse oocytes with spermatozoa retrieved from epididymides stored at 4 degree C

This study was performed to investigate the effect of partial zona pellucida incision by piezo micromanipulation (ZIP) on the in vitro fertilizing ability of stored mouse spermatozoa. The storage conditions were optimized by storing the mouse epididymides at 4 C in mineral oil or in the mouse body for up to 4 days after death, and the retrieved spermatozoa were used to fertilize fresh oocytes. No significant difference was observed in fertilization rates between the treatments when epididymides were stored for up to 2 days, but the fertilization rates in mineral oil were higher (P<0.05) than those in the mouse body at 3 (41.4 vs. 16.2%) and 4 days (26.0 vs. 15.8%). Spermatozoa retrieved from epididymides stored in mineral oil were then used to fertilize fresh and vitrified oocytes with or without ZIP treatment. The fertilization rates of the ZIP fresh oocytes were higher than those of the zona-intact oocytes at each time point (1 to 4 days). After ZIP, the fertilization rates of spermatozoa stored for 1 and 2 days (91.2 and 86.6%, respectively) were similar (P>0.05) to that of fresh spermatozoa (91.9%). In regard to vitrified oocytes, the fertilization rates of zona-intact and ZIP oocytes using fresh spermatozoa were 46.7 and 84.7%, while the fertilization rates of vitrified ZIP oocytes using spermatozoa stored for 1 to 4 days ranged from 49.3 to 79.6%. When 2-cell embryos derived from ZIP fresh and vitrified oocytes inseminated with 2 day-stored spermatozoa were transferred into recipient females, 47.9 and 15.0% of the embryos developed to term, respectively. These results indicate that storing mouse epididymides at 4 C in mineral oil is more suitable than storage in the mouse body and that the ZIP technique improves the in vitro fertilizing ability of stored mouse spermatozoa in fresh oocytes and significantly increases the fertilization rate of vitrified oocytes with fresh spermatozoa.

Epididymal P34H protein deficiency in men evaluated for infertility

Our study aimed to compare the frequency of epididymal protein P34H deficiency in a population of men undergoing routine infertility evaluation with that in men with proven fertility. Our results suggest that a significant proportion of men investigated for male infertility may be epididymal protein P34H deficient.

Isolation and biochemical characteristics of a molecular form of epididymal acid phosphatase of boar seminal plasma

The fluid of boar epididymis is characterized by a high activity of acid phosphatase (AcP), which occurs in three molecular forms. An efficient procedure was developed for the purification of a molecular form of epididymal acid phosphatase from boar seminal plasma. We focused on the epididymal molecular form, which displayed the highest electrophoretic mobility. The purification procedure (dialysis, ion exchange chromatography, affinity chromatography and hydroxyapatite chromatography) used in this study gave more than 7000-fold purification of the enzyme with a yield of 50%. The purified enzyme was homogeneous by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The purified molecular form of the enzyme is a thermostable 50kDa glycoprotein, with a pI value of 7.1 and was highly resistant to inhibitors of acid phosphatase when p-nitrophenyl phosphate was used as the substrate. Hydrolysis of p-nitrophenyl phosphate by the purified enzyme was maximally active at pH of 4.3; however, high catalytic activity of the enzyme was within the pH range of 3.5-7.0. Kinetic analysis revealed that the purified enzyme exhibited affinity for phosphotyrosine (K(m)=2.1x10(-3)M) and was inhibited, to some extent, by sodium orthovanadate, a phosphotyrosine phosphatase inhibitor. The N-terminal amino acid sequence of boar epididymal acid phosphatase is ELRFVTLVFR, which showed 90% homology with the sequence of human, mouse or rat prostatic acid phosphatase. The purification procedure described allows the identification of the specific biochemical properties of a molecular form of epididymal acid phosphatase, which plays an important role in the boar epididymis.

The epididymal soluble prion protein forms a high-molecular-mass complex in association with hydrophobic proteins

We have shown previously that a 'soluble' form of PrP (prion protein), not associated with membranous vesicles, exists in the male reproductive fluid [Ecroyd, Sarradin, Dacheux and Gatti (2004) Biol. Reprod. 71, 993-1001]. Attempts to purify this 'soluble' PrP indicated that it behaves like a high-molecular-mass complex of more than 350 kDa and always co-purified with the same set of proteins. The main associated proteins were sequenced by MS and were found to match to clusterin (apolipoprotein J), BPI (bacterial permeability-increasing protein), carboxylesterase-like urinary excreted protein (cauxin), beta-mannosidase and beta-galactosidase. Immunoblotting and enzymatic assay confirmed the presence of clusterin and a cauxin-like protein and showed that a 17 kDa hydrophobic epididymal protein was also associated with this complex. These associated proteins were not separated by a high ionic strength treatment but were by 2-mercaptoethanol, probably due to its action on reducing disulphide bonds that maintain the interaction of components of the complex. Our results suggest that the associated PrP retains its GPI (glycosylphosphatidylinositol) anchor, in contrast with brain-derived PrP, and that it is resistant to cleavage by phosphatidylinositol-specific phospholipase C. Based on these results, the identity of the associated proteins and the overall biochemical properties of this protein ensemble, we suggest that 'soluble' PrP can form protein complexes that are maintained by hydrophobic interactions, in a similar manner to lipoprotein vesicles or micellar complexes.

Identification, proteomic profiling, and origin of ram epididymal fluid exosome-like vesicles

Small membranous vesicles, between 25- and 75-nm diameter, were collected by high-speed centrifugation from the ram cauda epididymal fluid and were found to be normal constituents of this fluid and of the seminal plasma. The SDS-PAGE protein pattern of these vesicles was specific and very different from that of the caudal fluid, seminal plasma, sperm extract, and cytoplasmic droplets. After two-dimensional electrophoresis separation and mass spectrometry analysis, several proteins were identified and grouped into i) membrane-linked enzymes, such as dipeptidyl peptidase IV (DPP-IV), neprilysin (NEP), phosphodiesterase-I (E-NPP3), and protein G-beta; ii) vesicle-associated proteins, such as lactadherin (MFEG8-PAS6/7) and vacuolar ATPase; iii) several cytoskeleton-associated proteins, such as actin, ezrin and annexin; and iv) metabolic enzymes. The presence of some of these proteins as well as several different hydrophobic proteins secreted by the epididymis was further confirmed by immunoblotting. These markers showed that the majority of the vesicles originated from the cauda epididymal region. The physical and biochemical characteristics of these vesicles suggest they are the equivalent of the exosomes secreted by several cell types and epithelium. The main membrane-linked proteins of the vesicles were not retrieved in the extract from cauda or ejaculated sperm, suggesting that these vesicles did not fuse with sperm in vivo.

In vitro culture of epithelial cells from the caput, corpus, and cauda epididymis of Sus domesticus

This work describes a protocol to culture epididymal epithelial cells from the caput, corpus, and cauda regions of Sus domesticus. Epididymal epithelial fragments were obtained by dissection and enzymatic digestion with collagenase. About 30 epididymal fragments from each epididymal region were cultured in 24-well culture plates with supplemented RPMI-1640 medium at 37 degrees C, 5% CO2 in air, and 100% humidity. A confluent monolayer of polygonal and tightly packed epithelioid cells from the three epididymal regions was obtained after 12-16 days in culture and maintained in vitro for more than 60 days. The proportion of epididymal epithelial cells in these cultures was assessed by immunofluorescent staining for cytokeratins. Throughout the 2 months of culture, about 80% of the cells were cytokeratin-positive. Electron microscopy observations indicated that cultured cells from caput, corpus, and cauda epididymal regions were tightly adhered to each other by junctional complexes and that stereocilia were present in their apical membranes. Moreover, the presence of an extensive rough endoplasmic reticulum, Golgi apparatus and numerous vesicles in the cytoplasm suggested that cultured cells maintained secretory and absorptive activities. These results show that the epididymal epithelial cells in culture from S. domesticus retain some fundamental features that characterize the epididymal epithelium in the intact organ. This system might be a valuable tool for studying the mechanism of sperm maturation in vitro, including epididymal cell secretions and the analysis of regional differences.

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.

Partial characterization, sperm association and significance of N- and O-linked glycoproteins in epididymal fluid of rhesus monkeys (Macaca mulatta)

The present study investigated regional modifications of glycosylation status, sperm association and functional significance of N- and O-linked glycoproteins in epididymal luminal fluid of the rhesus monkey (Macaca mulatta). The predominant glycoproteins of the epididymal luminal fluid that increase in the extent of glycosylation or unmasking of exposed epitopes in a region-specific, maturation-dependent manner, included those of 150, 116, 68, 64, 58 (N- and O-linked) and 170 kDa (O-linked). The higher expression of 40 (N-linked), 38 (N- and O-linked) and 60, 56 and 33 kDa (O-linked) glycoproteins in the proximal caput epididymal fluid was followed by alteration or reorganization of 60, 38 and 33 kDa (O-linked) glycoproteins in the distal segments of the epididymis. The association of epididymal fluid glycoproteins with maturing spermatozoa was identified by generating polyclonal antiserum against monkey caudal sperm membrane in female albino rabbits. The antiserum crossreacted strongly with 58 and 33 kDa epididymal fluid glycoproteins of monkeys and also reacted with 116, 68, 58, 56 and 33 kDa glycoproteins from Triton X-100 extracts of human spermatozoa, indicating the presence of antigenically related components in both species. The functional significance of epididymal fluid glycoproteins in sperm functions was investigated by raising antiserum against a heavily glycosylated 58 kDa glycoprotein (MEF1) of caudal epididymal fluid, which crossreacted with the Triton X-100 extracts of epididymal spermatozoa of monkey and ejaculated human spermatozoa on immunoblots. In an in vitro micro-sperm agglutination assay, anti-MEF1 serum agglutinated both rat caudal epididymal spermatozoa and human spermatozoa. MEF1 seemed to be involved in fertilization as demonstrated by inhibition of fertility (100%) in female albino rabbits and rats immunized with this protein. A sperm-agglutinating 58 kDa glycoprotein of rhesus monkey epididymis with functional significance in fertility was identified, thus indicating that it is a potential candidate for contraceptive vaccine development.

ESP13.2, a member of the beta-defensin family, is a macaque sperm surface-coating protein involved in the capacitation process

Female macaques produced isoantibodies to a limited number of sperm surface proteins following immunization with sperm components released by phosphatidylinositol-specific phospholipase C (PI-PLC). Washed, acrosome-intact, fixed sperm injected into rabbits elicited a major immune response to one of the same PI-PLC-released proteins, which was shown to be a sperm surface-coating protein. After purification and digestion of the glycoprotein, four peptides were analyzed for amino acid sequence, and all had 100% homology with an epididymal secretory protein, ESP13.2, reported previously to be a small, cationic-rich peptide and a member of the beta-defensin family. Antibodies to purified ESP13.2 recognized a number of protein bands on Western blots of nonreduced PI-PLC-released sperm components and nonreduced whole-sperm extracts. After chemical disulfide reduction, only a single, broad band from 31 to 35 kDa was recognized by anti-ESP13.2 antibodies. Indirect immunofluorescence showed ESP13.2 over the entire surface of ejaculated macaque sperm. Fluorescence was only slightly reduced after sperm were washed through 80% Percoll. A 24-h incubation in capacitating medium significantly reduced the amount of ESP13.2 over the head and midpiece, whereas exposure of the incubated sperm to dbcAMP and caffeine (capacitation activators) resulted in almost complete loss of ESP13.2 from the sperm surface. After activation, ESP13.2 was the primary component released into the medium as judged electrophoretically. Lignosulfonic acid, a potent inhibitor of macaque fertilization in vitro, completely blocked release of ESP13.2 from the sperm surface, even following treatment with activators. These findings suggest that the beta-defensin, ESP13.2, has a function in the capacitation of macaque spermatozoa and may modulate sperm surface-receptor presentation at the time of fertilization.

Identification of a novel GPI-anchored CRISP glycoprotein, MAK248, located on the posterior head and equatorial segment of cynomolgus macaque sperm

To identify a sperm-surface component that is highly antigenic, we immunized female cynomolgus macaques with glycosylphosphatidylinositol (GPI)-anchored sperm surface proteins that were released following treatment with phosphatidylinositol-specific phospholipase C (PI-PLC). Five different adjuvants were used in combination with the PI-PLC-released proteins, and three of these proteins (24, 48, and 53 kDa) were shown to be potent antigens for immunization of female monkeys. The 53 kDa protein was found to be a surface coating protein and not a GPI-anchored protein. Polyclonal antibodies to the 24 kDa protein and the 48 kDa protein were produced in rabbits. The two antibodies recognized both proteins on Western blots. The same rabbit antibodies recognized 28, 18, and 10 kDa bands on a Western blot of chemically reduced PI-PLC-released proteins, suggesting that the 48 kDa protein is a dimer of the 24 kDa protein, which we refer to as MAK248. Rabbit polyclonal antibodies developed to reduced fragments of the 24 kDa protein showed that the 18 and 10 kDa bands are proteolytic peptide fragments of the 24 kDa protein. Screening of tissues from male macaques showed that MAK248 is expressed only in the epididymis. Microsequencing of two proteolytic fragments of the 18 kDa component showed 100% amino acid homology to a 233 deduced amino acid sequence previously identified in human testes genome. Antibodies to MAK248 recognized a 24 kDa protein released from human sperm exposed to PI-PLC. Antibodies to MAK248 recognized the equatorial segment and posterior head regions of capacitated cynomolgus macaque sperm. Structural analysis suggests that MAK248 is a novel CRISP protein and a member of the CAP (CRISP, Ag 5, PR-1) family of proteins. Based on amino acid sequence homology, it is possible that MAK248 functions as a protease inhibitor.

Prion protein is secreted in soluble forms in the epididymal fluid and proteolytically processed and transported in seminal plasma

The presence of prion protein in sperm and fluids collected from different parts of the ram genital tract was investigated by immunoblotting with monoclonal antibodies. A slightly immunoreactive 25- to 30-kDa protein was recognized on Western blots of testicular and epididymal sperm extracts. Immunoreactivity increased on ejaculated sperm extracts and 2 other bands at 35 and 43 kDa also reacted. Seminal plasma showed several immunoreactive bands, the main bands being detected at 43 and 35 kDa, whereas less reactive bands were observed at 30, 25, 20, and <14 kDa. All these bands strongly decreased in the seminal plasma after vasectomy, indicating a testicular or an epididymal origin. Testicular fluid showed almost no reactivity, whereas caudal epididymal fluid contained the 2 strong immunoreactive bands at 43 and 35 kDa and in some cases a faint 30-kDa band. The 43-kDa band was also found in the fluid from the proximal caput, whereas the 35-kDa band appeared in the distal caput. Immunoprecipitation of (35)S-labeled proteins secreted in the epididymal fluid indicated that the 43-kDa form was synthesized in caput and caudal regions and the 35-kDa form in the distal caput to the distal corpus. Treatment of caudal fluid and seminal plasma by N-glycosidase resulted in the formation of 3 bands: 1 highly reactive at about 25 kDa, a second less reactive at about 28 kDa, and a third at approximately 20 kDa. The pattern of prion protein distribution in epididymal fluids was found to be similar in scrapie-infected rams to that of healthy rams. Cauda epididymal fluid and seminal plasma from infected animals could not be treated directly with proteinase K, because of the presence of protease inhibitors. However, the prion protein immunoprecipitated from these fluids was completely cleaved by proteinase K, whereas in the same conditions this from an infected sheep brain gave the usual resistant band pattern.