Maturation of guinea pig sperm in the epididymis involves the modification of proacrosin oligosaccharide side chains

Zona Pellucida sperm-binding protein 3 receptor distribution during Gopc-/- globozoospermic spermatogenesis

Globozoospermia is a type of teratozoospermia characterized by round morphology of the sperm head. Gopc^-/- infertile globozoospermic murine model has failures during spermiogenesis, such as the incorrect biogenesis of the acrosome, disorganized acroplaxome and manchette, round nuclei and spiral flagella. In this study, Western blot, RT-PCR, immunohistochemistry and immunogold were done for the localization of the acrosome protein Zona Pellucida sperm-binding protein 3 receptor (ZP3R), also called sp56, in wild type and Gopc^-/- mice testis. The ZP3R protein was located in the acrosome and pseudo-acrosome vesicles of wild type and Gopc^-/- mice, respectively. Also, it is distributed through the cytoplasm of the haploid spermatids only. The incorrect spermiogenesis of Gopc^-/- mice causes a deregulation in the expression of ZP3R in the globozoospermic spermatids. Our results suggest that although the lack of GOPC causes a failure during the transport of the pre-acrosomal vesicles, the acrosome protein ZP3R is localized in the acrosome and is distributed through the cytoplasm only during spermiogenesis. Furthermore, the failure in spermiogenesis does not impair the synthesis of ZP3R and its localization in the pre-acrosomal vesicles.

Junctional adhesion molecule A: expression in the murine epididymal tract and accessory organs and acquisition by maturing sperm

STUDY QUESTION

Is junctional adhesion molecule A (JAM-A), a sperm protein essential for normal motility, expressed in the murine post-testicular pathway and involved in sperm maturation?

SUMMARY ANSWER

JAM-A is present in the prostate and seminal vesicles and in all three regions of the epididymis where it is secreted in epididymosomes in the luminal fluid and can be delivered to sperm in vitro.

WHAT IS KNOWN ALREADY

JAM-A shares with the plasma membrane Ca2+ATPase 4 (PMCA4, the major Ca2+ efflux pump in murine sperm) a common interacting partner, CASK (Ca2+/CaM-dependent serine kinase). JAM-A, like PMCA4, plays a role in Ca2+ regulation, since deletion of Jam-A results in significantly elevated intracellular Ca2+ levels and reduced sperm motility. Recently, PMCA4 was reported to be expressed in the epididymis and along with CASK was shown to be in a complex on epididymosomes where it was transferred to sperm. Because of the association of JAM-A with CASK in sperm and because of the presence of PMCA4 and CASK in the epididymis, the present study was performed to determine whether JAM-A is expressed in the epididymis and delivered to sperm during their maturation.

STUDY DESIGN, SIZE, DURATION

The epididymides, prostate and seminal vesicles were collected from sexually mature C57BL/6J and Institute for Cancer Research mice and antibodies specific for JAM-A and Ser285 -phosphorylated JAM-A (pJAM-A) were used for the analysis. Tissues, sperm and epididymal luminal fluid (ELF) were studied. Epididymosomes were also isolated for study. Caput and caudal sperm were co-incubated with ELF individually to determine their abilities to acquire JAM-A in vitro.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sections of all three regions of the epididymis were subjected to indirect immunofluorescence analysis. Epididymal tissues, fluid, sperm, prostate and seminal vesicle tissues were analyzed for JAM-A and/or pJAM-A via western blotting analysis. The relative amounts of JAM-A and pJAM-A among epididymal tissues, ELF and sperm were detected by western blot via quantification of band intensities. Epididymosomes were isolated by ultracentrifugation of the ELF after it was clarified to remove cells and tissue fragments, and the proteins western blotted for JAM-A and pJAM-A, and exosomal biochemical markers. FACS analysis was used to quantify the amount of JAM-A present on caput and caudal sperm, as well as the amount of JAM-A acquired in vitro after their co-incubation with ELF.

MAIN RESULTS AND THE ROLE OF CHANCE

Western blots revealed that JAM-A is expressed in all three regions of the epididymis, the prostate and seminal vesicles. As confirmed by indirect immunofluorescence, a western blot showed that JAM-A has a higher expression in the corpus and caudal regions, where it is significantly (P < 0.01) more abundant than in the caput. Both JAM-A and Ser285-phosphorylated JAM-A (pJAM-A) are secreted into the ELF where it is highest in the distal regions. In the ELF, both JAM-A and pJAM-A were detected in epididymosomes. Western blotting of sperm proteins showed a significant (P < 0.01) increase of JAM-A and pJAM-A in caudal, compared with caput, sperm. Flow-cytometric analysis confirmed the increase in JAM-A in caudal sperm where it was 1.4-fold higher than in caput ones. Co-incubation of caput and caudal sperm with ELF demonstrated ~2.3- and ~1.3-fold increases, respectively, in JAM-A levels indicating that epididymosomes transfer more JAM-A to caput sperm that are less saturated with the protein than caudal ones.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

First, although the ELF was clarified prior to ultracentrifugation for epididymosome isolation, we cannot rule out contamination of the epididymosomal proteins by those from epididymal epithelial cells. Second, the JAM-A detected in the prostate and seminal vesicles might not necessarily be secreted from those organs and may only be present within the tissues, where it would be unable to impact sperm in the ejaculate.

WIDER IMPLICATIONS OF THE FINDINGS

Although performed in the mouse the study has implications for humans, as the highly conserved JAM-A is a signaling protein in human sperm. There is physiological significance to the finding that JAM-A, which regulates sperm motility and intracellular Ca2+, exists in elevated levels in the cauda where sperm gain motility and fertilizing ability. The study suggests that the acquisition of JAM-A in the epididymal tract is involved in the mechanism by which sperm gain their motility during epididymal maturation. This increased understanding of sperm physiology is important for aspects of ART.

STUDY FUNDING AND COMPETING INTEREST(S)

The work was supported by NIH-RO3HD073523 and NIH-5P20RR015588 grants to P.A.M.-D. The authors declare there are no conflicts of interests.

A novel testis-specific protein, PRAMEY, is involved in spermatogenesis in cattle

Preferentially expressed antigen in melanoma (PRAME) is a cancer/testis antigen that is predominantly expressed in normal testicular tissues and a variety of tumors. The function of the PRAME family in spermatogenesis remains unknown. This study was designed to characterize the Y-linked PRAME (PRAMEY) protein during spermatogenesis in cattle. We found that PRAMEY is a novel male germ cell-specific, and a germinal granule-associated protein that is expressed in spermatogenic cells during spermatogenesis. The intact PRAMEY protein (58 kDa) was detected in different ages of testes but not in epididymal spermatozoa. A PRAMEY isoform (30 kDa) was highly expressed only in testes after puberty and in epididymal spermatozoa. This isoform interacts with PP1γ2 and is likely the mature protein present in the testes and sperm. Immunofluorescent staining demonstrated that PRAMEY was located predominantly in the acrosome granule of spermatids, and in acrosome and flagellum of spermatozoa. Immunogold electron microscopy further localized the PRAMEY protein complex to the nucleus and several cytoplasmic organelles, including the rough endoplasmic reticulum, some small vesicles, the intermitochondrial cement, the chromatoid body and the centrioles, in spermatogonia, spermatocytes, spermatids and/or spermatozoa. PRAMEY was highly enriched in and structurally associated with the matrix of the acrosomal granule (AG) in round spermatids, and migrated with the expansion of the AG during acrosomal biogenesis. While the function of PRAMEY remains unclear during spermatogenesis, our results suggest that PRAMEY may play an essential role in acrosome biogenesis and spermatogenesis.Free Chinese abstract: A Chinese translation of this abstract is freely available at http://www.reproduction-online.org/content/153/6/847/suppl/DC1.FreeSpanish abstract: A Spanish translation of this abstract is freely available at http://www.reproduction-online.org/content/153/6/847/suppl/DC2.

The Acrosomal Matrix

The acrosome, a single exocytotic vesicle on the head of sperm, has an essential role in fertilization, but the exact mechanisms by which it facilitates sperm-egg interactions remain unresolved. The acrosome contains dozens of secretory proteins that are packaged into the forming structure during spermatogenesis; many of these proteins are localized into specific topographical areas of the acrosome, while others are more diffusely distributed. Acrosomal proteins can also be biochemically classified as components of the acrosomal matrix, a large, relatively insoluble complex, or as soluble proteins. This review focuses on recent findings using genetically modified mice (gene knockouts and transgenic "green acrosome" mice) to study the effects of eliminating acrosomal matrix-associated proteins on sperm structure and function. Some gene knockouts produce infertile phenotypes with obviously missing, specific activities that affect acrosome biogenesis during spermatogenesis or interfere with acrosome function in mature sperm. Mutations that delete some components produce fertile phenotypes with subtler effects that provide useful insights into acrosomal matrix function in fertilization. In general, these studies enable the reassessment of paradigms to explain acrosome formation and function and provide novel, objective insights into the roles of acrosomal matrix proteins in fertilization. The use of genetically engineered mouse models has yielded new mechanistic information that complements recent, important in vivo imaging studies.

Plasma membrane Ca2+-ATPase 4 in murine epididymis: secretion of splice variants in the luminal fluid and a role in sperm maturation

Plasma membrane Ca(2+)-ATPase isoform 4 (PMCA4) is the primary Ca(2+) efflux pump in murine sperm, where it regulates motility. In Pmca4 null sperm, motility loss results in infertility. We have shown that murine sperm PMCA4b interacts with Ca(2+)/CaM-dependent serine kinase (CASK) in regulating Ca(2+) homeostasis and motility. However, recent work indicated that the bovine PMCA4a splice variant (missing in testis) is epididymally expressed, along with 4b, and may be transferred to sperm. Here we show, via conventional and in situ RT-PCR, that both the splice variants of Pmca4 mRNA are expressed in murine testis and throughout the epididymis. Immunofluorescence localized PMCA4a to the apical membrane of the epididymal epithelium, and Western analysis not only confirmed its presence but showed for the first time that PMCA4a and PMCA4b are secreted in the epididymal luminal fluid (ELF), from which epididymosomes containing PMCA4a were isolated. Flow cytometry indicated the presence of PMCA4a on mature caudal sperm where it was increased ~5-fold compared to caput sperm (detected by Western blotting) and ~2-fold after incubation in ELF, revealing in vitro uptake and implicating PMCA4a in epididymal sperm maturation. Coimmunoprecipitation using pan-PMCA4 antibodies, revealed that both variants associate with CASK, suggesting their presence in a complex. Because they have different kinetic properties for Ca(2+) transport and different abilities to bind to CASK, our study suggests a mechanism for combining the functional attributes of both PMCA4 variants, leading to heightened efficiency of the pump in the maintenance of Ca(2+) homeostasis, which is crucial for normal motility and male fertility.

Identification and validation of mouse sperm proteins correlated with epididymal maturation

Sperm need to mature in the epididymis to become capable of fertilization. To understand the molecular mechanisms of mouse sperm maturation, we conducted a proteomic analysis using saturation dye labeling to identify proteins of caput and cauda epididymal sperm that exhibited differences in amounts or positions on two-dimensional gels. Of eight caput epididymal sperm-differential proteins, three were molecular chaperones and three were structural proteins. Of nine cauda epididymal sperm-differential proteins, six were enzymes of energy metabolism. To validate these proteins as markers of epididymal maturation, immunoblotting and immunofluorescence analyses were performed. During epididymal transit, heat shock protein 2 was eliminated with the cytoplasmic droplet and smooth muscle γ-actin exhibited reduced fluorescence from the anterior acrosome while the signal intensity of aldolase A increased, especially in the principal piece. Besides these changes, we observed protein spots, such as glutathione S-transferase mu 5 and the E2 component of pyruvate dehydrogenase complex, shifting to more basic isoelectric points, suggesting post-translational changes such dephosphorylation occur during epididymal maturation. We conclude that most caput epididymal sperm-differential proteins contribute to the functional modification of sperm structures and that many cauda epididymal sperm-differential proteins are involved in ATP production that promotes sperm functions such as motility.

The epididymal influence on sperm maturation

Consideration of the function of the epididymis has undergone profound changes over the last century during which it has moved from a largely neglected male reproductive organ to one that is an increasingly exploited source of sperm for assisted reproduction strategies. From histological studies in the lizard1 it was considered that, ‘…the cells lining the epididymal canal produce a material necessary for the spermatozoa during their passage through the organ …’ whereas a fertility study with guinea-pigs stated boldly that, ‘… changes undergone [by spermatozoa in the epididymis] are not conditioned by some specific action of epididymal secretion …’. The former view found favour in a review of the literature which concluded that, ‘… there are specific epididymal secretions necessary for sperm maturation and survival …’, although the nature of the secretions were not then known. However, this concept, currently held by most of those studying the epididymis of animals, was again contradicted on the basis of clinical work: ‘… it certainly is possible for sperm that have never passed through any length of the epididymis at all to mature on their own …’.

Predicted seminal astacin-like protease is required for processing of reproductive proteins in Drosophila melanogaster

During mating, males provide females with seminal fluids that include proteins affecting female physiology and, in some cases, reproductive behavior. In several species these male-derived modulators of reproduction are processed upon transfer to the female, suggesting molecular interaction between the sexes. Males could increase their reproductive success by contributing to regulation of this processing; consistent with this hypothesis, seminal fluids are rich in proteolysis regulators. However, whether these molecules carry out processing of male-derived reproductive modulators is unknown. We tested for this role using RNAi to knock down individually 11 Drosophila seminal fluid proteases and protease inhibitors. We found that CG11864, a predicted astacin-type metalloprotease in seminal fluid, is necessary to process two other seminal proteins: the ovulation hormone ovulin (Acp26Aa) and the sperm storage protein Acp36DE. This processing occurs only after all three proteins have entered the female. Moreover, CG11864 itself is processed inside males while en route to the female and before its action in processing ovulin and Acp36DE. Thus, processing of seminal proteins is stepwise in Drosophila, beginning in the male after the proteins leave their site of synthesis and continuing within another organism, the mated female, and the male-donated protease CG11864 is an agent of this latter processing.

Expression and secretion of rat SPAM1(2B1 or PH-20) in the epididymis: role of testicular lumicrine factors

Rat sperm surface antigen Sperm Adhesion Molecule1, SPAM1 (a.k.a. 2B1 or PH-20) is a plasma membrane-bound glycoprotein with hyaluronidase activity and putative roles during fertilization. Previously the antigen was thought to be testis-specific but recently it has been shown to be synthesized in the epididymis (mouse, macaque and human). Using the efferent ductule ligated (EDL) rat as a model to produce a sperm-free androgen-maintained epididymis, we have examined the factors regulating the expression of epididymal 2B1. RT-PCR and in situ transcript hybridization (ISH) studies showed that 2B1 mRNA is transcribed in the principal cells in all three regions of the epididymis. Its cognate protein was also detected by Western blot analysis in sperm-free cytosols from normal epididymis and found to undergo endoproteolytic cleavage into 2 subunits of similar size to the sperm-bound form. Immunohistochemistry with a monoclonal antibody to 2B1 confirmed that the protein is present in the epididymal epithelium and luminal secretions. The intensity of staining was much stronger in the sperm-free EDL epididymis than that in the normal (sperm-present) epididymis. The protein was shown to have hyaluronidase activity at neutral pH and both its quantity and activity appeared to be greater in the EDL epididymis. It is suggested that a soluble form of SPAM1 glycoprotein is synthesized and released in the epididymis and that in addition to androgens, its regulation may involve a cross-talk between the tubule epithelium and lumicrine factors, the latter possibly of testicular origin.

SPAM1 (PH-20) protein and mRNA expression in the epididymides of humans and macaques: utilizing laser microdissection/RT-PCR

BACKGROUND

The Sperm Adhesion Molecule 1 (SPAM1) is an important sperm surface hyaluronidase with at least three functions in mammalian fertilization. Previously our laboratory reported that in the mouse, in addition to its expression in the testis, Spam1 is synthesized in the epididymis where it is found in membranous vesicles in the principal cells of the epithelium in all three regions. Since SPAM1 is widely conserved among mammals the aim of the study was to determine if its expression pattern in the epididymis is conserved in rodents and primates.

METHODS

We used laser microdissection (LM)/RT-PCR on frozen and paraffin-embedded epididymal sections of humans (n = 3) and macaques (n = 2) as well as in situ transcript hybridization to determine if transcripts are present in the epididymal epithelium. Western analysis and immunohistochemistry were used to detect and confirm the protein expression, and hyaluronic acid substrate gel electrophoresis analyzed its hyaluronidase activity. An in silico analysis of the proximal promoter of SPAM1 was also performed to identify relevant putative transcription binding sites for the androgen receptor.

RESULTS

We demonstrate that mRNA unique to SPAM1 is present in the principal cells of the epididymal epithelium in all individuals of both species studied. SPAM1 protein is present in all three regions of the epididymis, as well as the vas deferens, and is localized similarly to the transcripts. SPAM1 was shown to have hyaluronidase activity at pH 7.0. In the proximal promoter of SPAM1 were uncovered putative epididymal transcription factor binding sites including androgen receptor elements (AREs), consistent with epididymal expression.

CONCLUSIONS

These findings allow us to conclude that epididymal SPAM1 is conserved in at least two mammalian classes, rodents and primates. This conservation of expression suggests that the protein is likely to play an important function, possibly in sperm maturation.

Control of membrane fusion during spermiogenesis and the acrosome reaction

Membrane fusion is important to reproduction because it occurs in several steps during the process of fertilization. Many events of intracellular trafficking occur during both spermiogenesis and oogenesis. The acrosome reaction, a key feature during mammalian fertilization, is a secretory event involving the specific fusion of the outer acrosomal membrane and the sperm plasma membrane overlaying the principal piece of the acrosome. Once the sperm has crossed the zona pellucida, the gametes fuse, but in the case of the sperm this process takes place through a specific membrane domain in the head, the equatorial segment. The cortical reaction, a process that prevents polyspermy, involves the exocytosis of the cortical granules to the extracellular milieu. In lower vertebrates, the formation of the zygotic nucleus involves the fusion (syngamia) of the male pronucleus with the female pronucleus. Other undiscovered membrane trafficking processes may also be relevant for the formation of the zygotic centrosome or other zygotic structures. In this review, we focus on the recent discovery of molecular machinery components involved in intracellular trafficking during mammalian spermiogenesis, notably related to acrosome biogenesis. We also extend our discussion to the molecular mechanism of membrane fusion during the acrosome reaction. The data available so far suggest that proteins participating in the intracellular trafficking events leading to the formation of the acrosome during mammalian spermiogenesis are also involved in controlling the acrosome reaction during fertilization.

Characterization of human membrane cofactor protein (MCP; CD46) on spermatozoa

Membrane cofactor protein (MCP; CD46) is a complement regulator widely expressed as four isoforms that arise via alternative splicing. On human spermatozoa, MCP is expressed on the inner acrosomal membrane and alterations of spermatozoa MCP may be associated with infertility. In rodents, expression of MCP is largely restricted to the testes. MCP on human spermatozoa has a unique M(r) pattern that we have investigated. We also characterized MCP expression in mice transgenic (tg) for human MCP. Human MCP expression in the tg mice mimics the human pattern in that it is located on the inner acrosomal membrane and has a faster M(r) than MCP expressed elsewhere. Sequencing of RT-PCR products from the testis indicates that there is not a unique male reproductive tissue specific cytoplasmic tail. Instead, human spermatozoa express MCP bearing cytoplasmic tail two, which is also utilized in most other tissues and contains several signaling motifs. Further, using N-glycosidases, we demonstrate that the unique lower molecular weight of MCP on spermatozoa is secondary to a modification in the N-linked sugars. Specifically, as the spermatozoa mature, but before they reach the epididymis, the three N-linked sugars of MCP are trimmed to less complex structures. While the purpose of this deglycosylation is unknown, we propose that it is a common feature of proteins expressed on the plasma and inner acrosomal membranes of spermatozoa and hypothesize that it is a spermatozoa specific event critical for facilitating sperm-egg interactions.

Dexamethasone reduces acrosin activity of ram spermatozoa

The aim of this study was to investigate the effect of dexamethasone on acrosin activity of spermatozoa in Chios rams during autumn (breeding season for sheep in Greece), in correlation with possible changes in blood testosterone. Dexamethasone was administered in four equal consecutive intramuscular injections, one every four hours (total dose: 3 mg kg(-1)). Total acrosin activity was determined in semen samples collected 48 h before and on the 4th and 7th day and thereafter once every week until the 77th day after dexamethasone administration. Blood samples for testosterone radioimmunoassays were collected 24 h before, during dexamethasone administration and on the 4th, 7th, 14th and 21st day after administration. Total acrosin activity in spermatozoa was reduced between days 7-28 after dexamethasone administration. Dexamethasone also induced a reduction in mean value and basal level of blood testosterone and inhibited its episodic secretion between 1 and 4 days after administration. As the reduction of acrosin activity appeared relatively soon after dexamethasone administration (7th day), it is likely that the increased amount of dexamethasone did not influence the synthesis of proacrosin in the late spermatids. As glucocorticoid receptors exist in the epididymis and accessory glands in various species, dexamethasone may have a direct influence on the synthesis and/or release of acrosin inhibitors in epididymal fluid or seminal plasma. These changes in acrosin activity in ovine spermatozoa mediated by dexamethasone may be of importance regarding the role of stress in the reduction of sperm fertilizing ability.

Equine sperm-oocyte interaction: the role of sperm surface hyaluronidase

The plasma membrane over the sperm head of several mammalian species has been shown to express a glycerolphosphatidylinositol-linked hyaluronidase known as PH-20. This protein has been associated with the sperm's interaction with the oocyte cumulus matrix and zona pellucida. The characteristics of PH-20 in equine sperm have not been clearly defined. In this study, ejaculated gel-free semen from five stallions and epididymal sperm from isolated epididymis from 10 stallions was used to characterize the PH-20 activity in equine sperm. Affinity purified anti-equine PH-20 polyclonal antibody was used to immunodetect sperm surface-associated PH-20 and immunolabel whole sperm. The intracellular calcium indicator, Fluo-3, was used to assess sperm intracellular calcium. Stallion sperm express a surface-associated hyaluronidase localized to the posterior sperm head region in ejaculated sperm. Following in vitro capacitation and acrosomal exocytosis, the inner acrosomal membrane (IAM) displays intense hyaluronidase fluorescence suggesting that the IAM and hyaluronidase plays a significant role in zona penetration by sperm. Sperm incubated in hyaluronan (HA)-containing capacitation medium display an elevated intracellular calcium concentration (P<0.01) that is associated with translocation of PH-20 antigenic sites on the sperm surface in addition to increases in protein tyrosine phosphorylation. Caput- and cauda-derived sperm display developmentally unique PH-20 immunofluorescence expression patterns. These data suggest that the differential expression of PH-20 in ejaculated and epididymal sperm could be involved in cumulus penetration, sperm-egg recognition, and oolemmal fusion in this species.

Mouse epididymal Spam1 (PH-20) is released in vivo and in vitro, and Spam1 is differentially regulated in testis and epididymis

The sperm adhesion molecule 1 (SPAM1 or PH-20) is an important sperm surface protein with a hyaluronidase activity and bifunctional roles in mammalian fertilization. Recently we reported that in the mouse, Spam1 is synthesized independently in the testis and the epididymis, where it is found in membranous vesicles in the principal cells of the epithelium in all three regions. Here we used mouse epididymal luminal fluid and cultured epididymal epithelial cells to demonstrate that epididymal Spam1 may be a secretory protein. Using a dual environment culture chamber system in which corpus or cauda epithelial cells are cocultured with their corresponding epididymal fibroblasts in medium supplemented with androgens and epidermal growth factor, we show that in 2- to 6-day cultures Spam1 can be detected immunocytochemically in the epithelial cells. The protein was also detected by Western blot analysis in extracts of the cultured cells and in their serum-free conditioned medium, as well as in luminal fluid from fresh caput, corpus, and caudal epididymis. Importantly, it was shown to have hyaluronidase activity, using hyaluronic acid substrate gel electrophoresis, and to be expressed in greater quantities in the corpus compared with the cauda and caput. The results not only confirm our previous finding that Spam1 is synthesized in the epididymis, but extend them by showing that it is released in the luminal fluid where it may effect posttesticular maturation and function of sperm. Results from transcript analysis indicate that epididymal and testicular Spam1 are under different transcriptional regulation.

Regulation of foreign DNA uptake by mouse spermatozoa

We have studied some features of DNA uptake in both mature and immature mammalian spermatozoa. Mature sperm collected from the cauda epididymis are able to incorporate foreign DNA in a buffer containing only salts and calcium. Immature spermatozoa, however, are unable to bind DNA. This seems to be caused by the lack of a functional receptor in the sperm membrane since once this membrane is disrupted by sonication, DNA can be detected in the postacrosome region of the sperm nucleus, matching the distribution of the mature spermatozoa. Comparison between the DNA binding proteins of mature and immature spermatozoa allowed us to identify two bands that could be part of the putative membrane receptor for the DNA. On the other hand, DNA uptake in mature sperm is prevented by the seminal plasma. We have identified two components of the seminal plasma, a calcium-dependent DNase present in the seminal vesicle fluid and several DNA binding proteins secreted by the ventral prostate, that could account for the inhibitory activity. Taken as a whole, our results indicate that DNA uptake by the mammalian spermatozoa is a very specific and highly regulated phenomenon.

Mouse sperm protein sp56 is a component of the acrosomal matrix

Previously, we identified the guinea pig sperm acrosomal matrix glycoprotein AM67 and demonstrated that it is most closely related to mouse sperm sp56, initially reported to be a cell-surface protein. On the contrary, our studies demonstrated that sp56 is an intra-acrosomal component. Based upon the homology between guinea pig AM67 and mouse sp56, we hypothesized that sp56 was part of the acrosomal matrix, a structure that had yet to be demonstrated to exist in mouse sperm. In this paper, we show that sp56 first appeared in late meiotic cells and accumulated during spermiogenesis, the haploid stage of spermatogenic cell development. Using affinity-purified anti-peptide antisera, we determined that the molecular weight of sp56 in cauda epididymal sperm approximated that of guinea pig AM67 ( approximately 67 000 M:(r)) and that sp56 was present in a high molecular weight, disulfide-linked complex. The forms of sp56 in pachytene spermatocytes and spermatids had higher molecular weights than was found for the sperm form; the size differences were apparently due to alterations in carbohydrate side chains. The sp56 complex could not be solubilized by the nonionic detergent Triton X-100 but remained associated with the dorsal surface of the mouse sperm head, demonstrating that sp56 is a component of the mouse sperm acrosomal matrix.

Differential release of guinea pig sperm acrosomal components during exocytosis

The contents of the sperm acrosome are compartmentalized at the biochemical and morphological levels. Biochemically, the acrosome can be considered to be comprised of two compartments: one consisting of readily soluble proteins and one containing a particulate acrosomal matrix. To test the hypothesis that compartmentalization affects the release of acrosomal components during the course of secretion in guinea pig sperm, we examined the relationship between the presence of specific proteins and acrosomal status and monitored the recovery of acrosomal constituents in the medium surrounding sperm induced to undergo exocytosis with the ionophore A23187. Cysteine-rich secretory protein 2 (CRISP-2), a soluble component of the acrosome, was rapidly lost from the acrosome soon after ionophore treatment. However, acrosomal matrix components remained associated with the sperm for longer periods. AM67, a matrix component and the guinea pig orthologue of the mouse sperm zona pellucida-binding protein sp56, was released at a slower rate than was CRISP-2 but at a faster rate than were two other matrix proteins, AM50 and proacrosin. Coincident with their release from the sperm, AM50 and proacrosin were posttranslationally modified, probably by proteolysis. The release of proacrosin from the matrix appears associated with the conversion of this protein to the enzymatically active acrosin protease. These results provide strong support for the hypothesis that compartmentalization plays a significant role in regulating the release of proteins during the course of acrosomal exocytosis. Acrosomal matrix proteins remain associated with the sperm for prolonged periods of time following the induction of acrosomal exocytosis, suggesting that transitional acrosomal intermediates may have significant functions in the fertilization process.

Relationship between sperm motility and the processing and tyrosine phosphorylation of two human sperm fibrous sheath proteins, pro-hAKAP82 and hAKAP82

Sperm motility is regulated by the cAMP-dependent protein kinase (protein kinase-A)-mediated phosphorylation of a group of largely unidentified flagellar proteins. Human AKAP82 (hAKAP82) and its precursor protein, pro-hAKAP82, are members of the A-kinase anchor protein (AKAP) family. These proteins tether protein kinase-A to the fibrous sheath of human spermatozoa and presumably localize the activity of the kinase near specific targets in the sperm flagellum. In this way, pro-hAKAP82 and hAKAP82 may be involved in regulating sperm motility. Similar to its homologues in other species, pro-hAKAP82 is proteolytically processed to hAKAP82. However, the amount of processing of pro-hAKAP82 in human spermatozoa is less than the amount of processing of the precursor in other species. We postulated that this lower extent of processing may be related to lower percentages of human sperm motility. In addition, both pro-hAKAP82 and hAKAP82 are tyrosine phosphorylated in a capacitation-dependent manner. Since capacitation is associated with hyperactivated motility, we postulated that tyrosine phosphorylation of pro-hAKAP82/hAKAP82 is associated with changes in motility. However, using a combination of immunofluorescence and immunoblotting approaches, we found no evidence for an association between either processing or tyrosine phosphorylation of pro-hAKAP82/hAKAP82 and significant differences in motility in spermatozoa from normal men.

Biochemical maturation of Spam1 (PH-20) during epididymal transit of mouse sperm involves modifications of N-linked oligosaccharides

Indirect immunofluorescence of mouse caput and caudal sperm shows distinctly different distributions of Spaml protein, which is associated with structural and functional differences of the molecule. Spam1 is uniformly distributed over the surface of the head of caput sperm while in caudal sperm, light and confocal microscopy demonstrate that it is localized to the anterior and posterior regions. The hyaluronidase activity of Spaml in acrosome-intact caput sperm was significantly lower (4.3-fold; P < 0.0001) than that of caudal sperm. The increase in enzymatic activity in caudal sperm is accompanied by a reduction in the molecular weight (MW): in extracts from caput sperm there was a major band at approximately 74 kDa and a minor band at approximately 67 kDa; while for the cauda there was a major band at approximately 67 kDa and minor bands at approximately 70 and -56 kDa. Additionally, the bands from caput sperm were 4.9 to 7.7-fold less intense than those from caudal sperm. This decreased affinity for the polyclonal anti-Spaml suggests the presence of different surface characteristics of the molecule from the two epididymal regions. Computer analysis of the protein structure from Spam1 cDNA sequence reveals four putative N-linked glycosylation sites, and enzymatic deglycosylation suggests that all sites are functional. After endoglycosidase activity of extracts from caput and caudal sperm, both show a major band with a MW of approximately 56 kDa, the size of the membrane-anchored polypeptide backbone. Based on the difference in size and intensity of the Spaml bands and hyaluronidase activities from caput and caudal sperm, the data suggest that the activation of Spaml during epididymal maturation is regulated by deglycosylation.

Characterization of mouse epididymal acrosin: comparative studies with acrosin from boar and human ejaculated spermatozoa

Acrosin is an acrosomal protease believed to play a major role in fertilization. It is synthesized as an inactive precursor, proacrosin, which is processed via (auto)proteolysis into active form(s). In this paper, comparative studies on the characteristics of acrosin from mouse, boar and human are reported. The mouse proacrosin/acrosin was especially investigated to clarify whether or not the enzyme undergoes modifications during epididymal maturation. Acrosomal extracts from mature and immature mouse spermatozoa, as well as from ejaculated boar and human spermatozoa, were analysed by means of SDS-electrophoresis, Western blot and activity measurements. The studies showed that epididymal maturation produced a shift in the molecular weight of proacrosin. It was also observed that the activation kinetics differ strongly between the three species studied. Human proacrosin showed a constant substrate turnover, acrosin from boar showed sigmoidal activation kinetics and mouse acrosin, either from the caput or the cauda epididymides, showed a rapid decay in activity, suggesting the presence of an endogenous specific inhibitor.

SOB3, a human sperm protein involved in zona pellucida binding: physiological and biochemical analysis, purification

LB5 antibody was selected from a monoclonal antibody (mAb) library directed against human sperm proteins. LB5 mAb detected the corresponding protein SOB3 in the neck region and the flagellum of most live ejaculated sperm while it labelled, in addition, the acrosome of about 10-20% of spermatozoa. The percentage of LB5 acrosome-stained sperm was significantly correlated with the percentages of either spontaneous or A23187-induced acrosome-reacted sperm. While SOB3 could not be detected in the testis, it appeared in spermatozoa from the corpus epididymis segment. LB5 mAb impaired neither sperm motion parameters, acrosomal reaction triggering, nor sperm binding to zona-free hamster oocytes. By contrast, LB5 Fab fragments (200 micrograms/ml) inhibited sperm binding to human zonae pellicidae by 35.7%. If sperm were induced to acrosome react with A23187 prior to LB5 treatment, the inhibitory effect shifted to 59.9%, while no significant effect was observed following A23187 incubation alone. Western blotting of human sperm and cauda epididymis extracts revealed two bands of 18 and 19 kDa. While no cross-reaction was observed with other tested organs, a similar 18-kDa band was revealed in erythocytes and one of 19 kDa in B-lymphocytes. No cross-reactivity could be evidenced in any animal sperm analyzed. SOB3 was first separated in a 17- to 20-kDa preparative electrophoresis fraction and finally purified by isoelectrofocusing according to its pl of 9.8. These results suggest that SOB3 is localized under the outer acrosomal membrane, that it participates in secondary sperm binding to the zona pellucida, and that it shares homologies with the immune system.

Intra-acrosomal 155,000 dalton protein increases the antigenicity during mouse sperm maturation in the epididymis: a study using a monoclonal antibody MC101

We found an intra-acrosomal antigen of about 155,000 daltons (155 kDa) in a survey using the monoclonal antibody MC101 raised against mouse cauda epididymal spermatozoa. Morphological studies by means of indirect immunofluorescence and immunogold electron microscopy localized the antigen to the cortex region of the anterior acrosome. Avidin biotin complex immunocytochemistry initially demonstrated a faint signal at the anterior acrosome in the testis spermatozoa that increased in intensity as the sperm moved toward the distal epididymis. This incremental immunoreactivity was also confirmed by immunoblotting following one-dimensional SDS-PAGE. The 155 kDa protein band was immunostained, and it was much more intense in the cauda epididymal than in the caput and corpus epididymal spermatozoa. Only a trace or no immunostain was evident in the caput or testis spermatozoa. The antigen localization did not change during passage through the epididymis, being confined at the cortex region of the anterior acrosome. The epididymal epithelial cells were not immunostained. These findings suggested that the 155 kDa protein is biochemically modified, further implying that the biochemical alteration of intra-acrosomal material is involved in sperm maturation in the epididymis.

Role of the epididymis in mediating changes in the male gamete during maturation

This article reviews recent knowledge about events occurring in the epididymis that are important for sperm to fertilise eggs. Well established concepts are stated without references (see Cooper, 1986 for older literature) but recent references are included where they throw light on mechanisms of epididymal function. During their sojourn in the epididymis spermatozoa acquire the capacity to move and to fertilise eggs; they are then stored in a quiescent state prior to ejaculation. The ability of sperm to undergo the events of fertilisation are developed as a result of interactions with certain epididymal secretions. Increases in our knowledge about the genes coding for epididymal secretions has not yet been matched by similar insight into the role that these secretions play in the maturation process. However, information about the changes that occur to the sperm cells during maturation permit certain scenarios to be sketched that may reflect reality. This review is one such attempt to bring the epididymal sperm-epithelial secretion into focus.

Quantitative changes of Ricinus communis agglutinin I and Helix pomatia lectin binding sites in the acrosome of rat spermatozoa during epididymal transit

During passage through the epididymis, spermatozoa undergo a number of changes which result in their acquisition of fertility and motility. Some of the changes that occur include loss of the cytoplasmic droplet and changes in sperm morphology, metabolism and properties of the nucleus and plasma membrane. Changes have also been reported in the acrosomic system of mammalian spermatozoa during their transit through the epididymis. In the present study, the quantitative changes of the glycoconjugate content in the acrosome of rat spermatozoa were examined during their passage through the epididymis using lectin-colloidal gold cytochemistry. Various regions of the epididymis (initial segment, caput, corpus and cauda epididymidis) were fixed by perfusion with 1% or 2% glutaraldehyde buffered in sodium cacodylate (0.1 M), dehydrated in ethanol and embedded without osmication in Lowicryl K4M. Lectin-colloidal gold labeling was performed on thin sections using Ricinus communis agglutinin I (RCA I) or Helix pomatia lectin (HPL) to detect D-galactose- and N-acetyl-D-galactosamine-containing glycoconjugates, respectively. The labeling density over the acrosome of the acrosomic system was evaluated as the number of gold particles per microns 2 of profile area using a Zeiss MOP-3 image analyzer. The overall mean labeling densities over the acrosome of spermatozoa for each lectin was estimated from 4 rats and over the four distinct epididymal regions. The mean labeling density of the acrosome with RCA I and HPL showed a similar pattern along the epididymis, although RCA I revealed approximately twice as many gold particles per epididymal region. In either case, there was a significant decrease in the labeling density of the acrosome of spermatozoa between the initial segment or caput epididymidis and cauda epididymidis (p less than 0.01). A similar decrease was also noted between the initial segment and corpus epididymidis (p less than 0.01). No change was found between the initial segment and caput epididymidis. Controls showed a virtual absence of labeling. These results suggest that in addition to a multitude of changes occurring to spermatozoa during epididymal transit, there are also significant quantitative changes in the glycoconjugate content within the acrosome.

Bovine epididymal sperm proacrosin-acrosin system: quantification and partial characterization

Several studies suggest that acrosin, an acrosomal trypsin-like serine proteinase, plays a role in fertilization. The enzyme is present in an enzymatically inactive precursor form, called proacrosin and is believed to be converted to the enzymatically active form(s) through one/multiple physiological event(s) prior to the sperm penetration of the zona pellucida. Although, the proacrosin-acrosin system of several species has been well documented, the study of the enzyme system in bovine caput and cauda epididymis (where the maturation of spermatozoa occurs) has not been characterized. The present study demonstrates the quantification and partial characterization of the proacrosin-acrosin proteinase system in unpurified acrosomal extracts of bovine caput and cauda epididymal sperm. Proacrosin activation followed the sigmoidal type of activation curve. Activation experiments demonstrate that almost 80-90% of this protein exists in zymogen (proacrosin) form either in ejaculated or caput and cauda epididymal spermatozoa. Time-course activation studies showed that the zymogen in isolated spermatozoa was completely converted to active non-zymogen form in 3 and 5 h after removal from the cauda and caput regions, respectively, at pH 8.0 at 25 degrees C. This conversion was markedly inhibited by calcium in a dose dependent manner and the inhibition was reversible. On the other hand, calcium has a stimulatory effect on the hydrolytic activity of acrosin. These studies reveal that the proacrosin-acrosin system can be identified in crude extracts of bull epididymal and ejaculated sperm.

Protein transport and organization of the developing mammalian sperm acrosome

Experiments indicate that the mammalian acrosome develops as a result of a time-dependent sequence of events which involves protein incorporation into distinct regions or acrosomal domains. These domains can be characterized by electron microscopy and their isolation and partial purification are being accomplished. Recent success in isolating and characterizing major proteins that compromise the Golgi apparatus should accelerate knowledge of the interaction of the Golgi with the developing acrosome. Progress in this area is reviewed with the view that understanding the events involved in the transport of proteins from the Golgi apparatus to the acrosome and the mechanisms involved in positioning and modifying these proteins during spermiogenesis should provide a clearer understanding of how the acrosome develops in preparation for its role in fertilization.