Purification and characterization of two forms of beta-D-galactosidase from rat epididymal luminal fluid: evidence for their role in the modification of sperm plasma membrane glycoprotein(s)

Removal of sialic acid from bull sperm decreases motility and mucus penetration ability but increases zona pellucida binding and polyspermic penetration in vitro

This study tested the hypothesis that sperm sialic acid (Sia) is required to reach the site of fertilization, and that successful fertilization requires recognition of Sia from both the sperm and oocyte to occur. In addition, it has recently been reported that Siglecs (Sia-binding-immunoglobulin-like lectins) are present on the sperm surface. Thus, the possibility that the recognition of oocyte Sia was sperm-Siglec-mediated was also addressed. Sperm exposed to neuraminidase (NMase) exhibited lower overall and progressive motility, which translated to a decreased ability to swim through cervical mucus from cows in oestrus. In addition, when either sperm or cumulus-oocyte complexes (COCs) were treated with NMase, a decrease in cleavage and blastocyst rate was observed. However, incubation of sperm with increasing concentrations of anti-Siglec-2, -5, -6 and -10 antibodies prior to fertilization had no effect on their fertilizing ability. Interestingly, treatment with NMase increased the number of sperm bound to the ZP but also the rate of polyspermic fertilization. Flow cytometry analysis revealed no differences in the percentage of capacitated or acrosome-reacted sperm. These results suggest that Sia are required to reach the site of fertilization but need to be removed for sperm-oocyte interaction. However, fine regulation is needed to avoid abnormal fertilization which can lead to impaired embryo development.

Epididymal α-l-fucosidase and its possible role in remodelling the surface of bull spermatozoa

The mammalian epididymis provides an appropriate environment for sperm maturation. During the epididymal transit, spermatozoa undergo biochemical and morphological changes that lead to the acquisition of the fertilizing capacity. In this study we analysed the fucosylation status of membrane glycoproteins in the spermatozoa obtained from different regions of the bull epididymis. High amounts of fucose were detected on caput spermatozoa (R.F.I. = 1010 ± 20.35), mostly located in the post-acrosome zone. A significant decrease in the fucose levels was detected toward the cauda (R.F.I. = 540.5 ± 49.93) (P < 0.05). This decrease was in line with the increased activity of α-l-fucosidase in the cauda fluid. In sperm from the cauda, the defucosylation occurred in some proteins, whereas others showed higher fucosylation rates. A significant decrease of fucose in the gametes was observed upon incubation of crude cauda fluid with caput spermatozoa (from R.F.I. = 1.45 ± 0.08 to 1.06 ± 0.03) (P < 0.05) indicating that the α-l-fucosidase present in the epididymal fluid is active on spermatozoa. Moreover, this effect was blocked with specific enzyme inhibitors. These results provide direct evidence that the α-l-fucosidase from epididymal fluid participates in the fucose removal from spermatozoa, as a step of sperm maturation in the bull epididymis.

Glycosidases in porcine follicular fluid and their effect on zona pellucida-AWN 1 spermadhesin interaction

Oligosaccharide moieties on the surface of the oocyte belong to the key molecules that direct the course of fertilization and are subjected to changes during oocyte maturation in the follicle. In our study, we focused on the activities of five glycosidases in the fluids from porcine secondary and preovulatory follicles (α-l-fucosidase, α-d-galactosidase, β-d-galactosidase, β-D-N-acetylhexosaminidase, and α-d-mannosidase). All of them were detected active at neutral and acidic pH. However, changes in their activities associated with follicle development were observed only in the case of α-d-mannosidase, which was increased (P < 0.001), and β-d-galactosidase, which was decreased (P < 0.001) at neutral pH, and of α-d-galactosidase and β-N-acetylhexosaminidase, which were decreased (P < 0.0001) at the acidic pH. The comparison of glycosidases from follicular fluid and from blood plasma using red native electrophoresis revealed that most of the glycosidases are present in more than one isoenzyme form; some of them were detected mainly in the follicular fluid. Finally, we tested the effect of glycosidases on the interaction between zona pellucida and AWN 1 spermadhesin (putative sperm receptor of zona pellucida) and demonstrated that the effect of both β-d-galactosidase and to a lesser degree α-d-mannosidase led to a decrease in this interaction. We can hypothesize that these two glycosidases modulate the amount of zona pellucida oligosaccharide moieties and/or their structures for an optimal sperm binding in pigs.

Role of posttranslational protein modifications in epididymal sperm maturation and extracellular quality control

The epididymal lumen is a complex microenvironment in which spermatozoa acquire motility and fertility. Spermatozoa are synthetically inactive and therefore the maturation process requires their interaction with proteins that are synthesized and secreted in a highly regionalized manner by the epididymal epithelium. In addition to the integration of epididymal secretory proteins, posttranslational modifications of existing sperm proteins are important for sperm maturation and acquisition of fertilizing potential. Phosphorylation, glycosylation, and processing are several of the posttranslational modifications that sperm proteins undergo during epididymal transit resulting in changes in protein function and localization ultimately leading to mature spermatozoa. In addition to these well-characterized modifications, protein aggregation and cross-linking also occur within the epididymal lumen and may represent unique mechanisms for controlling protein function including that for maturation as well as for extracellular quality control.

Biological Processes that Prepare Mammalian Spermatozoa to Interact with an Egg and Fertilize It

In the mouse and other mammals studied, including man, ejaculated spermatozoa cannot immediately fertilize an egg. They require a certain period of residence in the female genital tract to become functionally competent cells. As spermatozoa traverse through the female genital tract, they undergo multiple biochemical and physiological changes collectively referred to as capacitation. Only capacitated spermatozoa interact with the extracellular egg coat, the zona pellucida. The tight irreversible binding of the opposite gametes triggers a Ca(2+)-dependent signal transduction cascade. The net result is the fusion of the sperm plasma membrane and the underlying outer acrosomal membrane at multiple sites that causes the release of acrosomal contents at the site of sperm-egg adhesion. The hydrolytic action of the acrosomal enzymes released, along with the hyperactivated beat pattern of the bound spermatozoon, is important factor that directs the sperm to penetrate the egg coat and fertilize the egg. The sperm capacitation and the induction of the acrosomal reaction are Ca(2+)-dependent signaling events that have been of wide interest to reproductive biologists for over half a century. In this paper, we intend to discuss data from this and other laboratories that highlight the biological processes which prepare spermatozoa to interact with an egg and fertilize it.

Molecular biology of sperm maturation in the human epididymis

Male infertility is a frequent cause of childlessness, and, indeed, a comparison of the contributions to conception failure made by male and female factors shows them to be equally frequent. In practice, male infertility appears to be resistant to most treatments. However, the major reason for this may be that often attempts are carried out without knowing the cause of the problem. Unlike in women, obstructions and hormonal disorders are rare in male infertility. Rather, it would appear that sperm disorders are the most common cause, reflecting a variety of pathogenetic mechanisms. Defects in sperm morphology, defective sperm movement, deficient development or functional failure of the acrosome, and the excessive generation of reactive oxygen species are changes that are often seen in infertile semen, but little is known about their aetiology. In 5–10% of men being treated for infertilty, an autoimmune reaction against spermatozoa is observed. Although the correlation between the presence of systemic antisperm antibodies and fertility potential is poor, the appearance of sperm-bound antibodies of immunoglobulin class IgA in semen seems to be closely associated with infertility. Studies in laboratory animals and humans have shown that complementary adhesion molecules are located on the surface of oocytes and spermatozoa. These molecules interact and lead to gamete fusion. Abnormalities in these molecules on the sperm surface might be expected to contribute to male infertility. However, their clinical significance has not yet been documented, and the molecular basis of human gamete interaction is far from being understood. Therefore, the key to understanding male infertility may lie in basic research which directly targets the fundamental cellular and molecular biology of the human spermatozoon.

The novel epididymis-specific beta-galactosidase-like gene Glb1l4 is essential in epididymal development and sperm maturation in rats

We describe a novel epididymis-specific cDNA named Glb1l4, which was isolated from rat epididymis by differential display of mRNAs. Glb1l4 cDNA contains 2607 nucleotides and encodes a 637-amino acid protein with 50% similarity to mouse beta-galactosidase. The gene is located on chromosome 8q13, spanning 21 exons. Northern blot analysis reveals that Glb1l4 is specifically expressed in the caput region of epididymis and upregulated by androgen. A specific polyclonal antiserum against the N-terminal peptide of GLB1L4 has been produced. Western blot analysis and immunohistochemistry assay reveal that GLB1L4 is specifically expressed in the principal cells of the caput epididymis. Interestingly, its expression peaks at Postnatal Day 45 in mRNA level and at Postnatal Day 60 in protein level while the epididymis column cells undergo differentiation. Moreover, within this very period this secretory protein is confined inside the cell with a change of subcellular distribution pattern, which implies its important roles in the cell differentiation process. Only after the epididymal epithelium differentiation is completed and the spermatozoa enter the epididymal lumen is the GLB1L4 secreted into the luminal fluid and bound on the sperm head. Our results suggest that GLB1L4 may play various roles in principal cell differentiation and sperm maturation.

Glycosidase determination in bovine oviducal fluid at the follicular and luteal phases of the oestrous cycle

Gamete recognition and binding of spermatozoa to the oviduct are carbohydrate-mediated processes in which several glycosidases are thought to have a role, although this has not been demonstrated unequivocally. Oviducal fluid is the biological milieu in which fertilisation and early embryo development take place, but the enzyme composition of oviducal fluid is largely unknown. The aim of the present study was to determine glycosidase activity and protein content in bovine oviducal fluid (bOF) and the volume of fluid collected per oviduct. Oviducts obtained from a slaughterhouse were classified as either in the follicular or luteal phase on the basis of ovarian luteal morphology. Oviducal fluid was aspirated, centrifuged and the volume determined. Samples were then frozen until assay. Substrates conjugated to 4-methylumbelliferyl were used to screen for the activity of seven glycosidases at pH 7.2. The results indicate that bOF has alpha-l-fucosidase, beta-N-acetyl-glucosaminidase, beta-d-galactosidase, alpha-D-mannosidase and beta-N-acetyl-galactosaminidase activity during both phases of the cycle, with the specific activity of the latter two enzymes being higher during the follicular phase. There was no N-acetyl-neuraminidase or alpha-d-galactosidase activity detected in bOF at either phase of the oestrous cycle at pH 7.2, but activity for both glycosidases was detected at pH 4.4. There were no differences in protein concentration or the volume of bOF collected between the two phases of the cycle. These findings indicate that oviducal fluid exhibits glycosidase activity, with specific variations throughout the oestrous cycle, suggesting that these enzymes play a role in carbohydrate-mediated events.

Determination of glycosidase activity in porcine oviductal fluid at the different phases of the estrous cycle

Sperm-oocyte binding and gamete-oviductal epithelium interactions are carbohydrate-mediated events occurring in the oviductal fluid (OF). Thus, knowledge about the activities of glycosidases (enzymes catalyzing hydrolytic cleavage of terminal sugar residues) in this milieu would help us understand the molecular mechanisms involved in these events. This work was carried out to investigate the glycosidase activity, protein content, and volume of OF collected from gilts and sows. Oviducts were classified into four phases of the estrous cycle (early follicular, late follicular, early luteal, and late luteal) based on the appearance of the ovaries. OF was aspirated, centrifuged, measured for volume, and frozen until assay. Substrates conjugated to 4-methylumbelliferyl were used to screen the activities of seven different glycosidases at physiological pH (7.2). alpha-L-Fucosidase and beta-N-acetyl-glucosaminidase activities increased at the late follicular phase to decrease after ovulation. beta-D-Galactosidase, alpha-D-mannosidase, and beta-N-acetyl-galactosaminidase showed higher activities at the early follicular phase, which decreased after ovulation. N-Acetyl-neuraminidase and alpha-D-galactosidase did not show activity at any phase of estrous cycle neither in sows nor in gilts at pH 7.2, although it did at acidic pH (4.4) in the follicular and luteal phase samples. Total protein also changed during the cycle showing the maximum secretion at the late follicular phase (2118.6+/-200.7 microg/oviduct). The highest volumes of OF were collected from the oviducts at the late follicular phase (50.7+/-1.3 microl/oviduct). These results indicate that OF from sows and gilts shows glycosidase activity varying throughout the estrous cycle suggesting a role of these enzymes in carbohydrate-mediated events.

Whole Mount Enzyme Histochemistry as a Rapid Screen at Necropsy for Expression of β-Galactosidase (LacZ)–Bearing Transgenes: Considerations for Separating Specific LacZ Activity from Nonspecific (Endogenous) Galactosidase Activity

Whole mount enzyme histochemistry to localize lacZ-bearing transgenes (lacZ-WMH) also detects endogenous β-galactosidases. The experiments reported here evaluated lacZ-WMH as a potential tool for transgene expression analysis during high-throughput rodent necropsies. A lacZ-WMH survey of organs from adult, wild-type, male and female mice (C57BL/6, FVB/N) and female rats (Sprague-Dawley) performed at the optimal pH (≥ 7.0) for bacterial lacZ yielded intense endogenous staining in the gonads, kidney, male accessory sex organs, salivary glands, submucosal glands in the duodenum, and thyroid. Substantial staining occurred in the adrenal cortex, lymph nodes, and linings of the gastrointestinal tract, the urinary bladder and uterus, and (for rat only) in the adenohypophysis, bone marrow, thymus, and trigeminal ganglia. Endogenous galactosidases were distributed similarly in sections of flash-frozen organs used for slide-based lacZ histochemistry (lacZ-SBH) at pH ≤ 5.0 (optimal for eukaryotic enzymes). Cerebral neurons were labeled only by lacZ-SBH. At pH 7.4, endogenous but not specific lacZ activity was abolished for lacZ-SBH, while endogenous activity was not halted without reducing specific activity for lacZ-WMH. These data demonstrate that lacZ-WMH is feasible during rodent necropsies for many but not all organs if species-, strain-, and sex-specific divergence in endogenous galactosidase activity is considered and special fixation (3% paraformaldehyde for 3 hours at 4°C) is used.

Glycan-modifying enzymes in luminal fluid of the mammalian epididymis: an overview of their potential role in sperm maturation

Testicular spermatozoa and those present within the proximal regions of the epididymis are unable to bind to the zona pellucida, the extracellular coat that surrounds the oocyte, and fertilize the egg. They acquire progressive motility and fertilizing ability during passage through the epididymis. Mammalian spermatozoa undergo biochemical and physiological changes during epididymal transit that are collectively termed epididymal maturation. The process involves several intracellular and extracellular changes in the spermatozoon, including remodeling of the sperm plasma membrane and modifications of glycan moieties of the sperm surface glycoconjugates. Two sets of glycan-modifying enzymes, namely glycohydrolases that cleave sugar residues and glycosyltransferases that add sugar residues to the existing glycoconjugates, are present in the epididymal luminal fluid that surrounds spermatozoa. Thus, it is reasonable to expect that glycan chains present on the sperm surface will interact with these glycan-modifying enzymes in the epididymal fluid. In this article, I have attempted to summarize and present an overview on the potential role of these glycan-modifying enzymes in sperm maturation.

A Lichen Lectin Specifically Binds to the alpha-1,4-Polygalactoside Moiety of Urease Located in the Cell Wall of Homologous Algae

A lectin from the lichen Evernia prunastri developing arginase activity (EC. 3.5.3.1) binds to the homologous algae that contain polygalactosilated urease (EC. 3.5.1.5) in their cell walls acting as a lectin ligand. The enzyme bound to its ligand shows to be inactive to hydrolyze of arginine. Hydrolysis of the galactoside moiety of urease in intact algae with alpha-1,4-galactosidase (EC. 3.2.1.22) releases high amount of D-galactose and impedes the binding of the lectin to the algal cell wall. However, the use of beta-,4-galactosidase (EC.3.2.1.23) releases low amounts of D-galactose from the algal cell wall and does not change the pattern of binding of the lectin to its ligand. The production of glycosilated urease is restricted to the season in which algal cells divide and this assures the recognition of new phycobiont produced after cell division by its fungal partner.

Glycosylation of the male genital ducts and spermatozeugmata formation in the clearnose skate Raja eglanteria

Genital ducts of three male Raja eglanteria were fixed and embedded in epoxy and methacrylate resin. Epoxy resin sections from the Leydig gland, upper and lower epididymis, ductus deferens and seminal vesicle were stained with 20 labelled lectins to examine their glycosylation. The Leydig gland consisted of columnar epithelial cells expressing N-linked glycans, N-acetyl galactosamine, glucosamine and lactosamine residues and sialic acid. Interspersed were ciliated cells of a different glycotype. The upper epididymis of cuboidal epithelium had a strongly glycosylated, ciliated apical surface and cytoplasmic granules that stained heavily with many lectins, with increased glycosylation compared to the Leydig gland. In the lower epididymis, tall, vacuolated cells showed some differences and a slight reduction in lectin staining. The ductus deferens contained two cell types and showed increased terminal N-acetyl galactosamine. The ciliated cuboidal epithelium of the seminal vesicle had marked differences from the ductus epithelium, with decreased N-acetyl galactosamine and lactosamine expression but increased subterminal N-acetyl lactosamine and galactosamine expression and sialylation. Spermatozoa were suspended in a glycosylated matrix and, in the seminal vesicle, were embedded in solid masses of matrix forming spermatozeugmata. These data show changes in glycan expression along the male genital tract, probably related to the nurture and maturation of the spermatozoa as they travel towards the seminal vesicle.

Identification and partial characterization of α-1,4-glucosidase activity in equine epididymal fluid

The expression of alpha-1,4-glucosidase activity was fluorometrically and electrophoretically assessed in the epididymal fluid and seminal plasma of stallions. alpha-Glucosidase specific activity in the epididymis increased significantly from the proximal caput to the cauda. Stallion epididymal glucosidase maintained activity in a wide range of pH, with two distinct peaks (around pH 4.0 and 6.0, respectively). Enzyme activities at different pH, inhibition assays with sodium dodecyl sulfate (SDS) and maltotriose (MTT, selective inhibitors of alpha-glucosidases "acidic" and "neutral" isoforms, described in other tissues) and the electrophoretic analysis in native and native/SDS-PAGE conditions, indicated that stallion epididymal glucosidase was due to two catalytically active forms. These forms, analyzed by non-denaturing electrophoresis, exhibited different electrophoretic mobility and molecular weight. Samples from the proximal caput of the epididymis were rich in Form II or "neutral" form, whereas the "acid" or Form I seemed to be predominate in the cauda epididymal region. At physiological pH, Form II was predominant in the seminal plasma. The physiological role(s) of these forms is uncertain, but based on their ability to hydrolyze glucosidic linkage, they probably are involved in degradation/modifications of epididymal fluid and/or spermatozoa glycoconjugates, thereby participating in plasma membrane remodeling associated with sperm maturation.

Secreted epididymal glycoprotein 2D6 that binds to the sperm's plasma membrane is a member of the beta-defensin superfamily of pore-forming glycopeptides

The plasma membrane of spermatozoa undergoes substantial remodeling during passage through the epididymal duct, principally because of changes in phospholipid composition, exchange of glycoproteins with epididymal fluid, and processing of existing membrane proteins. Here, we describe the interaction of an epididymal glycoprotein recognized by monoclonal antibody 2D6 with the plasma membrane of rat spermatozoa. Our goals have been to understand more about the mechanism of secretion of epididymal glycoproteins, how they interact with the sperm's plasma membrane, and their disposition within it. Reactivity to 2D6 monoclonal antibody was first detectable in principal cells in the distal caput epididymidis and as a soluble high-molecular-weight complex in the secreted fluid. It was not associated with membranous vesicles in the duct lumen. On cauda spermatozoa 2D6 monoclonal antibody recognized a 24-kDa glycoprotein (the subunit of a disulfide cross-linked homodimer of 48 kDa) that was present on the plasma membrane overlying the sperm tail. Binding of 2D6 to immature spermatozoa in vitro was cell-type specific but not species specific, and the antigen could only be extracted from cauda spermatozoa with detergents. Sequencing studies revealed that the 24-kDa glycoprotein was a member of the beta-defensin superfamily of small pore-forming glycopeptides of which several others (ESP13.2, Bin1b, E-2, EP2, HE2) are found in the epididymis. This evidence suggests that some epididymal glycoproteins are secreted into the luminal fluid in a soluble form and bind to specific regions of the sperm's surface via hydrophobic interactions. Given the antimicrobial function of beta-defensins, they have a putative role in protecting spermatozoa and the epididymis from bacterial infections.

Nature's ingenuity: bypassing the classical secretory route via apocrine secretion

Although it has been suggested that epithelial cells of the male reproductive system are involved in apocrine secretion, this method of secretion is not fully understood. In the present study, apocrine secretion was investigated in epithelial principal cells lining the epididymis and vas deferens (VD) of adult mice. The tissues were fixed by cardiac vascular perfusion with glutaraldehyde for routine electron microscope (EM) analysis and Bouin's fixative for light microscope (LM) immunocytochemistry to access functional roles. In the epididymis and VD, the apex of principal cells revealed protrusions of cytoplasm referred to as apical blebs (ABs). The latter contained solely numerous free ribosomes, 20 nm vesicles and few ER cisternae, suggesting segregation of their contents. While some ABs displayed wide areas of contact with the apical principal cell cytoplasm, others showed thin stalk-like attachment points as well as fissures at the junction of the two areas. Together with images of ABs and their contents deep in the lumen, it is suggested that ABs detach from principal cells whereupon they breakdown to release their contents therein. As ABs of the epididymis were immunoreactive for glutathione-S-transferases (GSTs) and ubiquitin, it is proposed that these proteins are synthesized on free ribosomes in ABs and that apocrine secretion represents the manner whereby they enter the lumen to effectively protect sperm from free radical injury and ubiquitinate proteins for degradation, respectively. ABs of the VD were immunoreactive for 3beta-HSD, suggesting that they are also capable of synthesis of steroids with their release via apocrine secretion. Taken together the data provide evidence for apocrine secretion in the adult mouse epididymis and VD that could play important roles in relation to sperm maturation, protection and viability.

Purification and characterization of the plasma membrane glycosidases of Drosophila melanogaster spermatozoa

Previous studies from our laboratory have demonstrated the presence of two integral proteins with glycosidase activity in the plasma membrane of Drosophila melanogaster spermatozoa and we have suggested that these enzymes might have a role in sperm-egg binding. In this study the glycosidases have been purified and characterized. We have evidenced the presence of three distinct enzymes, two beta-N-acetylhexosaminidase isoforms, named HEX 1 and HEX 2, and an alpha-mannosidase. The molecular size of the native enzymes estimated by gel filtration was 158 kDa for beta-hexosaminidases and 317 kDa for alpha-mannosidase. SDS-PAGE showed that HEX 1 and HEX 2 are dimers formed by subunits with different molecular sizes, whereas alpha-mannosidase consists of three subunits with different molecular weights. All the enzymes are terminally glycosylated. Characterization of the purified enzymes included their 4-methylumbelliferyl-substrate preferences, kinetic properties, inhibitor constants and thermal stability. On the basis of substrate specificity, kinetics and the results of inhibition studies, beta-hexosaminidases appear to differ from each other. HEX 1 and HEX 2 are similar to mammalian isoenzyme A and isoenzyme B, respectively. These findings represent the first report on the characterization of sperm proteins that are potentially involved in interactions with the egg in Insects.

Acid Glycohydrolases in Rat Spermatocytes, Spermatids and Spermatozoa: Enzyme Activities, Biosynthesis and Immunolocalization

Mammalian sperm acrosome contains several glycohydrolases thought to aid in the dispersion and digestion of vestments surrounding the egg. In this study, we have used multiple approaches to examine the origin of acrosome-associated glycohdyrdolases. Mixed spermatogenic cells, prepared from rat testis, were separated by unit gravity sedimentation. The purified germ cells (spermatocytes [SP], round spermatids [RS], and elongated/condensed spermatids [E/CS]) contained several glycohydrolase activities. Metabolic labeling in the cell culture, immunoprecipitation, and autoradiographic approaches revealed that beta-D-galactosidase was synthesized in SP and RS in 88/90 kDa forms which undergo processing in a cell-specific manner. Immunohistochemical approaches demonstrated that the enzyme was localized in Golgi membranes/vesicles, and lysosome-like structures in SP and RS, and forming/formed acrosome of E/CS.

Rat spermatogenic cell beta-D-galactosidase: characterization, biosynthesis, and immunolocalization

In this study we have demonstrated that the rat sperm acrosomal beta-d-galactosidase is expressed in late spermatocytes and spermatids (round, elongated/condensed) during spermatogenesis. The enzyme is an exoglycohydrolase which, along with other exoglycohydrolases and proteases, is thought to aid in penetration of the zona pellucida, the extracellular glycocalyx that surrounds the mammalian egg. The presence of the enzyme in spermatocytes was confirmed by multiple approaches using biochemical, biosynthetic, and immunohistochemical protocols. The germ cells (spermatocytes, round spermatids, and elongated/condensed spermatids), purified from rat testis, were found to contain beta-galactosidase and four other glycohydrolases (beta-d-glucuronidase, alpha-d-mannosidase, alpha-l-fucosidase, and beta-N-acetylglucosaminidase). With the exception of alpha-l-fucosidase, the other enzymes assayed demonstrated a two- to threefold higher activity per cell in spermatocytes than in round spermatids. Immunoblotting approaches of affinity-purified germ cell extracts demonstrated several molecular forms of beta-galactosidase in spermatocytes and round spermatids; one of these forms (62 kDa) was seen only in round spermatids. The biosynthetic approach demonstrated that the enzyme is synthesized in spermatocytes and round spermatids in culture in high-molecular-weight precursor forms (90/88 kDa) which undergo processing to lower molecular weight mature forms in a cell-specific manner. The net result is the formation of predominantly 64- and 62-kDa forms in spermatocytes and round spermatids, respectively. The conversion of precursor forms to mature forms in the diploid and haploid cells in culture is rapid with t(1/2) of 6.5 and 9.0 h, respectively. Immunohistochemical approaches revealed an immunopositive reaction in the Golgi membranes, Golgi-associated vesicles, and lysosome-like structures in the late spermatocytes and early round spermatids. The forming/formed acrosome in round and elongated spermatids was also immunoreactive.

Biosynthesis, processing, and subcellular localization of rat spermbeta-D-galactosidase

During spermatogenesis, spermatids synthesize constituent proteins present in mature spermatozoa; however, little information exists on the molecular processes involved. In previous studies, this laboratory reported the characterization of rat sperm beta-D-galactosidase. In this paper, we report the localization of this enzyme along with its biosynthesis and processing. An antibody against rat luminal fluid beta-D-galactosidase was used to immunolocalize the enzyme in the testis and in epididymal spermatozoa. We found that beta-D-galactosidase is localized within the acrosomal cap of spermatids and in the acrosome and cytoplasmic droplet of epididymal spermatozoa. A combination of germ cell radiolabeling, immunoprecipitation, SDS-PAGE, and autoradiography revealed that spermatids produce two forms of beta-D-galactosidase, 90 and 88 kDa. During pulse-chase analysis, a 56-kDa form appeared. Treatment of beta-D-galactosidase immunoprecipitates from testicular spermatozoa with N-glycanase or Endo H revealed that both the 90- and 88-kDa forms become a 70-kDa polypeptide on SDS-PAGE. Since Endo H or N-glycanase treatment provided similar results, the presence of extensive N-linked high mannose/hybrid-type glycans on these proteins is indicated. Treatment of the 56-kDa form of beta-D-galactosidase with Endo H or N-glycanase resulted in the appearance of 52- and 50-kDa forms, respectively. This result suggests that the 56-kDa form contains N-linked high mannose/hybrid as well as complex oligosaccharides. During epididymal maturation, the 90-kDa form of beta-D-galactosidase persists in caput epididymal spermatozoa and is gradually converted to a major 74-kDa form in cauda spermatozoa. In addition to the 90- to 74-kDa forms, cauda spermatozoa show a 56- to 52-kDa form on Western immunoblots. Since only the high-molecular weight forms of beta-D-galactosidase are present on immunoblots of isolated sperm heads, we suggest that they are acrosomal in origin and that the 56-kDa form, which is processed to 52 kDa in cauda spermatozoa, is associated with the cytoplasmic droplet.

Secretion of glycosidases in human epididymal cell cultures

The dynamics of glycosidase secretion was evaluated in human epididymal cell culture. Epithelial cells from caput, corpus, and cauda epididymis were isolated from tissue obtained from patients undergoing therapeutic orchidectomy due to prostatic carcinoma. The activities of alpha-glucosidase, N-acetylglucosaminidase, beta-glucuronidase, and alpha-mannosidase were analyzed in conditioned culture media. Glycosidase activity was significantly higher in corpus and/or cauda than in caput epididymis. There was a time-dependent increase in enzyme activities that was maximal between 10 and 14 days of culture in all epididymal regions. Epididymal glycosidases are secreted by cultured epithelial cell from human epididymis with an increase toward the distal regions of this organ, which may be related to the dynamics of sperm maturation. Cultures from different epididymal regions may represent a valuable tool to study of human epididymal function.

Androgen regulation of glycosidase secretion in epithelial cell cultures from human epididymis

The human epididymis and its secretions actively promote sperm fertilizing capacity and provide protection for spermatozoa against harmful influences. Among epididymal secretions, glycosidases have been recently studied and associated with molecular changes on the sperm surface. In the present work, we studied the influence of different concentrations of testosterone, dihydrotestosterone and cyproterone acetate on the secretion of alpha-glucosidase, N-acetyl-glucosaminidase, beta-glucuronidase and alpha-mannosidase by isolated and cultured epithelial cells from human caput, corpus and cauda epididymides. Cell cultures were obtained from aggregates of isolated tubule fragments plated on extracellular matrix-covered multi-well plates. Activities of the glycosidases were measured in conditioned culture media and were higher in the distal regions of the epididymis. Testosterone and dihydrotestosterone significantly increase the enzyme secretion in a concentration-dependent manner. This increase was higher in corpus and/or cauda than in caput epididymis. Cyproterone acetate caused a dose-dependent decrease in glycosidase secretion in cultures from all epididymal regions. It is concluded that the secretion of epididymal glycosidases is regulated by androgen, being stimulated by dihydrotestosterone and testosterone and inhibited by the androgen antagonist cyproterone acetate.

Concepts and principles of O-linked glycosylation

The biosynthesis, structures, and functions of O-glycosylation, as a complex posttranslational event, is reviewed and compared for the various types of O-glycans. Mucin-type O-glycosylation is initiated by tissue-specific addition of a GalNAc-residue to a serine or a threonine of the fully folded protein. This event is dependent on the primary, secondary, and tertiary structure of the glycoprotein. Further elongation and termination by specific transferases is highly regulated. We also describe some of the physical and biological properties that O-glycosylation confers on the protein to which the sugars are attached. These include providing the basis for rigid conformations and for protein stability. Clustering of O-glycans in Ser/Thr(/Pro)-rich domains allows glycan determinants such as sialyl Lewis X to be presented as multivalent ligands, essential for functional recognition. An additional level of regulation, imposed by exon shuffling and alternative splicing of mRNA, results in the expression of proteins that differ only by the presence or absence of Ser/Thr(/Pro)-rich domains. These domains may serve as protease-resistant spacers in cell surface glycoproteins. Further biological roles for O-glycosylation discussed include the role of isolated mucin-type O-glycans in recognition events (e.g., during fertilization and in the immune response) and in the modulation of the activity of enzymes and signaling molecules. In some cases, the O-linked oligosaccharides are necessary for glycoprotein expression and processing. In contrast to the more common mucin-type O-glycosylation, some specific types of O-glycosylation, such as the O-linked attachment of fucose and glucose, are sequon dependent. The reversible attachment of O-linked GlcNAc to cytoplasmic and nuclear proteins is thought to play a regulatory role in protein function. The recent development of novel technologies for glycan analysis promises to yield new insights in the factors that determine site occupancy, structure-function relationship, and the contribution of O-linked sugars to physiological and pathological processes. These include diseases where one or more of the O-glycan processing enzymes are aberrantly regulated or deficient, such as HEMPAS and cancer.

The biological and functional significance of the sperm acrosome and acrosomal enzymes in mammalian fertilization

The mammalian spermatozoon undergoes continuous modifications during spermatogenesis, maturation in the epididymis, and capacitation in the female reproductive tract. Only the capacitated spermatozoa are capable of binding the zona-intact egg and undergoing the acrosome reaction. The fertilization process is a net result of multiple molecular events which enable ejaculated spermatozoa to recognize and bind to the egg's extracellular coat, the zona pellucida (ZP). Sperm-egg interaction is a species-specific event which is initiated by the recognition and binding of complementary molecule(s) present on sperm plasma membrane (receptor) and the surface of the ZP (ligand). This is a carbohydrate-mediated event which initiates a signal transduction cascade resulting in the exocytosis of acrosomal contents. This step is believed to be a prerequisite which enables the acrosome reacted spermatozoa to penetrate the ZP and fertilize the egg. This review focuses on the formation and contents of the sperm acrosome as well as the mechanisms underlying the induction of the acrosome reaction. Special emphasis has been laid on the synthesis, processing, substrate specificity, and mechanism of action of the acid glycohydrolases present within the acrosome. The hydrolytic action of glycohydrolases and proteases released at the site of sperm-zona binding, along with the enhanced thrust generated by the hyperactivated beat pattern of the bound spermatozoon, are important factors regulating the penetration of ZP. We have discussed the most recent studies which have attempted to explain signal transduction pathways leading to the acrosomal exocytosis.

Glycosidases are present on the surface of Drosophila melanogaster spermatozoa

We investigated the presence of enzymes on the surface of Drosophila melanogaster spermatozoa that might bind the carbohydrate residues of the egg shell. Spectrophotometric and fluorimetric studies were used on whole spermatozoa to assay galactosyltransferase and glycosidase activities. No galactosyltransferase is present on the sperm surface, whereas two glycosidases, beta-N-acetylglucosaminidase (GlcNAc'ase) and alpha-mannosidase (Man'ase), have been evidenced. They have an optimal pH of 6-6.5 and 4, respectively. The same glycosidases were detected as soluble forms probably secreted by the seminal vesicle epithelium. We suggest that these enzymes might be involved in the recognition of alpha-mannose and beta-N-acetylglucosamine residues present on the egg shell at the site of sperm entry.

Direct evidence for the secretion of lactoferrin and its binding to sperm in the porcine epididymis

Lactoferrin has been for the first time purified from the porcine cauda epididymal fluid as a 70 kDa protein. Both Western and Northern blot analyses show that lactoferrin is synthesized in the regions from the distal caput to the cauda epididymis and secreted into the luminal fluid. Lactoferrin is first secreted as a 75 kDa glycoprotein and its carbohydrate moieties are gradually digested to form 70 kDa protein in the cauda epididymis. Lactoferrin has already bound to the surface of the epididymal sperm because the anti-lactoferrin antiserum induces the mature sperm tail-to-tail agglutination. These results strongly suggest new physiological functions of lactoferrin on the sperm maturation in the epididymis.

Cloning of a human epididymis-specific mRNA, HE6, encoding a novel member of the seven transmembrane-domain receptor superfamily

A novel gene product, HE6, showing homology to the seven transmembrane-domain (Tm7) receptor superfamily, has been cloned by differential screening from a human epididymal cDNA library. The cDNA clone represented an abundant approximately 5-kb mRNA, comprising 0.01% of the cDNA library. Northern blot analysis including various human tissues revealed an epididymis-specific expression. In situ transcript hybridization localized the mRNA within the epithelial cells lining the epididymal duct. Southern blot analysis, employing a fragment encoding part of the amino-terminal extracellular domain as a probe, identified an autosomal single-copy gene in the human genome. Homologous cDNA products showing 90% sequence identity were observed in the epididymides of all mammalian species investigated. A cloning and sequencing strategy, combining approximately 3.7-kb cDNA fragments obtained by conventional cDNA library construction with overlapping 5' rapid amplification of cDNA ends (RACE) fragments, yielded total sequence information of 4.7 kb for the human mRNA. This sequence comprises a long open reading frame of 3.1 kb. A homology search for related sequences revealed highest similarity (25% amino acid identity) with the secretin/vasoactive intestinal peptide (VIP) superfamily of G-protein-coupled receptors. The predicted extracellular amino-terminal extension, however, was much longer than in the other members, and showed similarity to highly glycosylated mucin-like cell-surface molecules.