Binding of both acrosome-intact and acrosome-reacted guinea pig sperm to the zona pellucida during in vitro fertilization

Microfluidics facilitating the use of small extracellular vesicles in innovative approaches to male infertility

Sperm are transcriptionally and translationally quiescent and, therefore, rely on the seminal plasma microenvironment for function, survival and fertilization of the oocyte in the oviduct. The male reproductive system influences sperm function via the binding and fusion of secreted epididymal (epididymosomes) and prostatic (prostasomes) small extracellular vesicles (S-EVs) that facilitate the transfer of proteins, lipids and nucleic acids to sperm. Seminal plasma S-EVs have important roles in sperm maturation, immune and oxidative stress protection, capacitation, fertilization and endometrial implantation and receptivity. Supplementing asthenozoospermic samples with normospermic-derived S-EVs can improve sperm motility and S-EV microRNAs can be used to predict non-obstructive azoospermia. Thus, S-EV influence on sperm physiology might have both therapeutic and diagnostic potential; however, the isolation of pure populations of S-EVs from bodily fluids with current conventional methods presents a substantial hurdle. Many conventional techniques lack accuracy, effectiveness, and practicality; yet microfluidic technology has the potential to simplify and improve S-EV isolation and detection.

The stallion sperm acrosome: Considerations from a research and clinical perspective

During the fertilization process, the interaction between the sperm and the oocyte is mediated by a process known as acrosomal exocytosis (AE). Although the role of the sperm acrosome on fertilization has been studied extensively over the last 70 years, little is known about the molecular mechanisms that govern acrosomal function, particularly in species other than mice or humans. Even though subfertility due to acrosomal dysfunction is less common in large animals than in humans, the evaluation of sperm acrosomal function should be considered not only as a complementary but a routine test when individuals are selected for breeding potential. This certainly holds true for stallions, which might display lower levels of fertility in the face of "acceptable" sperm quality parameters determined by conventional sperm assays. Nowadays, the use of high throughput technologies such as flow cytometry or mass spectrometry-based proteomic analysis is commonplace in the research arena. Such techniques can also be implemented in clinical scenarios of males with "idiopathic" subfertility. The current review focuses on the sperm acrosome, with particular emphasis on the stallion. We aim to describe the physiological events that lead to the acrosome formation within the testis, the role of very specific acrosomal proteins during AE, the methods to study the occurrence of AE under in vitro conditions, and the potential use of molecular biology techniques to discover new markers of acrosomal function and subfertility associated with acrosomal dysfunction in stallions.

Porcine model for the study of sperm capacitation, fertilization and male fertility

Mammalian fertilization remains a poorly understood event with the vast majority of studies done in the mouse model. The purpose of this review is to revise the current knowledge about semen deposition, sperm transport, sperm capacitation, gamete interactions and early embryonic development with a focus on the porcine model as a relevant, alternative model organism to humans. The review provides a thorough overview of post-ejaculation events inside the sow's reproductive tract including comparisons with humans and implications for human fertilization and assisted reproductive therapy (ART). Porcine methodology for sperm handling, preservation, in vitro capacitation, oocyte in vitro maturation, in vitro fertilization and intra-cytoplasmic sperm injection that are routinely used in pig research laboratories can be successfully translated into ART to treat human infertility. Last, but not least, new knowledge about mitochondrial inheritance in the pig can provide an insight into human mitochondrial diseases and new knowledge on polyspermy defense mechanisms could contribute to the development of new male contraceptives.

Impact of glycosylation on the unimpaired functions of the sperm

One of the key factors of early development is the specification of competence between the oocyte and the sperm, which occurs during gametogenesis. However, the starting point, growth, and maturation for acquiring competence during spermatogenesis and oogenesis in mammals are very different. Spermatogenesis includes spermiogenesis, but such a metamorphosis is not observed during oogenesis. Glycosylation, a ubiquitous modification, is a preliminary requisite for distribution of the structural and functional components of spermatids for metamorphosis. In addition, glycosylation using epididymal or female genital secretory glycans is an important process for the sperm maturation, the acquisition of the potential for fertilization, and the acceleration of early embryo development. However, nonemzymatic unexpected covalent bonding of a carbohydrate and malglycosylation can result in falling fertility rates as shown in the diabetic male. So far, glycosylation during spermatogenesis and the dynamics of the plasma membrane in the process of capacitation and fertilization have been evaluated, and a powerful role of glycosylation in spermatogenesis and early development is also suggested by structural bioinformatics, functional genomics, and functional proteomics. Further understanding of glycosylation is needed to provide a better understanding of fertilization and embryo development and for the development of new diagnostic and therapeutic tools for infertility.

The molecular basis of gamete recognition in mice and humans

Successful fertilization heralds the onset of development and requires both gamete recognition and a definitive block to polyspermy. Sperm initially bind and penetrate the extracellular zona pellucida (ZP) that surrounds ovulated eggs, but are unable to bind the zona surrounding preimplantation embryos. The ZP of humans is composed of four (ZP1-4) and that of mouse three (ZP1-3) glycoproteins. Models for gamete recognition developed in mice had proposed that sperm bind to ZP3 glycans. However, phenotypes observed in genetically engineered mice are not consistent with this widely accepted model. More recently, taking advantage of the observation that human sperm do not bind to mouse eggs, human ZP2 was defined as the zona ligand in transgenic mouse models using gain-of-function assays. The sperm-binding site is an N-terminal domain of ZP2 that is cleaved by ovastacin, a metalloendoprotease released from egg cortical granules following fertilization. Proteolysis of this docking site provides a definitive block to polyspermy as sperm bind to uncleaved, but not cleaved ZP2 even after fertilization and cortical granule exocytosis. While progress has been made in defining the ZP ligand, less headway has been made in identifying the cognate sperm receptor. Although a number of sperm receptor candidates have been documented to interact with specific proteins in the ZP in vitro, continued fertility after genetic ablation of the cognate gene indicates that none are essential for gamete recognition. These on-going investigations inform reproductive medicine and suggest new therapies to improve fertility and/or provide contraception, thus expanding reproductive choices for human couples.

Defective protein kinase A and C pathways are common causes of disordered zona pellucida (ZP)--induced acrosome reaction in normozoospermic infertile men with normal sperm-ZP binding

OBJECTIVE

To determine association between defective protein kinases C (PKC) and A (PKA) and disordered zona pellucida (ZP)-induced acrosome reaction (DZPIAR) in normozoospermic infertile men with normal sperm-ZP binding.

DESIGN

Sperm from DZPIAR infertile men were treated without (control) or with (test) phorbol myristate acetate (PMA, PKC activator) or dibutyryl cyclic AMP (dbcAMP, PKA activator) under in vitro standard culture condition. The ZP-induced AR was assessed and compared between control and test.

SETTING

Public and private hospital-based clinical assisted reproduction technology (ART) centers.

PATIENT(S)

A total of 51 DZPIAR infertile men were involved in this study.

INTERVENTION(S)

None.

MAIN OUTCOMES MEASURE(S)

Sperm-ZP binding and the ZP-induced IAR.

RESULT(S)

Both PMA and dbcAMP enhanced ZP-induced AR up to a normal level (≥25%) in some subjects with DZPIAR: 29 (57%) with PMA and 27 (53%) with dbcAMP. Overall 35 (69%) had the ZP-induced AR enhanced to normal by PMA or dbcAMP but 16 (31%) had little or no response to either agent. Fourteen men responded to the two activators differently: 8 effective only with PMA and 6 effective only with dbcAMP.

CONCLUSION(S)

Defective upstream of PKC and PKA pathways are highly associated with disordered ZPIAR in normozoospermic infertile men with normal sperm-ZP binding.

Transitional states of acrosomal exocytosis and proteolytic processing of the acrosomal matrix in guinea pig sperm

In this study, we adapted a FluoSphere bead-binding assay to study the exposure and release of guinea pig sperm acrosomal components during the course of capacitation and acrosomal exocytosis. Prior to capacitation or the initiation of exocytosis, acrosomal proteins were not accessible to FluoSpheres coated with antibodies against two acrosomal matrix (AM) proteins, AM67 and AM50; during the course of capacitation and ionophore-induced acrosomal exocytosis, however, we detected the transient exposure of the solid-phase AM proteins on the surface of guinea pig sperm using the antibody-coated fluorescent beads. Several different transitional stages leading to complete acrosomal exocytosis were classified, and we propose these represent true, functional intermediates since some of the AM proteins are orthologues of mouse proteins that bind the zona pellucida (ZP) of unfertilized eggs. In addition, we present evidence that implicates acrosin in the proteolytic processing of AM50 during AM disassembly. Thus, we propose that the transitional states of acrosomal exocytosis involve early binding of AM proteins to the ZP (by what visually appear to be "acrosome-intact" sperm), maintenance of ZP binding that coincides with the progressive exposure of AM proteins, and gradual proteolytic disassembly of the AM to allow sperm movement through the ZP. We feel this "transitional states" model provides a more refined view of acrosomal function that supports a move away from the widely held, overly simplistic, and binary "acrosome-reaction" model, and embraces a more dynamic view of acrosomal exocytosis that involves intermediate stages of the secretory process in ZP binding and penetration.

Post-translational modifications in glycosylation status during epididymal passage and significance in fertility of a 33 kDa glycoprotein (MEF3) of rhesus monkey (Macaca mulatta)

The present study reports data on post-translational modifications in the glycosylation status during epididymal passage and significance in fertility of a 33 kDa glycoprotein of rhesus monkey (Macaca mulatta), designated as MEF3 (monkey epididymal fluid protein 3). MEF3 exhibited strong affinity for N-linked alpha-D-mannose groups and O-linked N-Ac-galactosamine linkages in epididymal fluids and exhibited moderate affinity for N-Ac-glucosaminylated (wheat germ agglutinin), fucosylated (Tetragonolotus purpurea), and N-Ac-galactosamine (peanut agglutinin) residues on more mature corpus and caudal spermatozoa in a maturation-dependent manner on Western blots probed with specific biotinylated lectins. Polyclonal antiserum raised against affinity-purified MEF3 from caudal epididymal fluid (CEF) cross-reacted specifically with CEF and caudal sperm membrane of macaque and with Triton X-100 extract of ejaculated human spermatozoa, suggesting the existence of antigenically related components in both species. The tangled agglutination caused by anti-33 kDa serum of human spermatozoa, along with localization of MEF3 on entire sperm surface of epididymal and testicular sperm of monkey and human spermatozoa, suggest the significance of MEF3 in sperm function. The 100% inhibition of fertility of immunized female rabbits with this protein in vivo and inhibition of human sperm penetration in zona-free hamster eggs in vitro suggests the functional significance of MEF3 in fertility. Together, these results clearly indicate that MEF3 has potential significance as a target for antibodies that inhibit sperm function and fertility.

Rapid sperm acrosome reaction in the absence of acrosomal CD46 expression in promiscuous field mice (Apodemus)

There is pronounced promiscuity and sperm competition in long-tailed field mice (Apodemus sylvaticus). These mice have evolved unusual sperm behaviour favouring rapid fertilisation, including dynamic formation of sperm trains and their subsequent dissociation. The cell surface complement regulatory (CReg) protein CD46 is broadly expressed in eutherian mammals other than rodents, in which it is expressed solely on the spermatozoal acrosomal membrane. Ablation of the CD46 gene has been associated with a faster acrosome reaction (AR) rate in inbred laboratory mice. Here, we demonstrate that wild-caught field mice of three species, A. sylvaticus, A. flavicollis and A. microps, exhibit a more rapid AR than wild-caught house mice Mus musculus or inbred laboratory BALB/c mice. We also demonstrate that wild-caught field mice of these three species, unlike house mice, produce alternatively spliced transcripts of testicular CD46 mRNA lacking exons 5-7 or 6-7, together with an extended 3' - and often truncated 5'-utr, leading to failure to express any sperm CD46 protein in both the testis and epididymis. Male field mice may therefore have traded expression of this CReg protein for acrosomal instability, providing a novel genus-specific strategy to favour rapid fertilisation and competitive advantage in the promiscuous reproductive behaviour of wild field mice.

Biological Effects of Recombinant Human Zona Pellucida Proteins on Sperm Function1

The initial interaction between gametes takes place at the level of the sperm surface and the zona pellucida (ZP), the extracellular matrix of the egg in mammals. Successful fertilization requires the proper molecular recognition of the ZP by the sperm. Recently, human ZP was demonstrated to be composed of four proteins: ZP1, ZP2, ZP3, and ZP4. The goals of this study were to determine the effects of recombinant human ZP2, ZP3, and ZP4 on human sperm acrosomal exocytosis and sperm motility. Exposure of sperm to ZP proteins, alone or in combination, promoted acrosomal exocytosis in a time-dependent manner. This effect occurred in parallel with a considerable decrease in progressive motility, coincident with an increase in nonprogressive sperm motility. An analysis of kinetic parameters of ZP-treated sperm demonstrated that a characteristic motility pattern could be defined by values of curvilinear velocity > 63.9 mum/s and linearity <or= 15.5%. A strong correlation between curvilinear velocity and the amplitude of lateral head displacement was also observed. The incidence of sperm having these particular kinetic parameters increased after exposure to ZP proteins. These studies of two processes involved in sperm penetration through the ZP confirm that zona glycoproteins promote acrosomal exocytosis and now establish an additional role for these components as modifiers of sperm motility.

Anti-Hyaluronidase Oligosaccharide Derived from Chondroitin Sulfate A Effectively Reduces Polyspermy During In Vitro Fertilization of Porcine Oocytes1

The present study was conducted to examine the effects of chondroitin sulfate A-derived oligosaccharide (ChSAO) on hyaluronidase activity and in vitro fertilization (IVF) parameters. The activity of hyaluronidase extracted from preincubated boar sperm was completely blocked by ChSAO at concentrations of 10 microg/ml or higher. After in vitro maturation of porcine cumulus-oocyte complexes, some oocytes were freed from their cumulus cells, and cumulus-intact or cumulus-free oocytes were inseminated with sperm in IVF medium containing various concentrations of ChSAO (0.1-100 microg/ml). In cumulus-intact oocytes, the penetration and the polyspermy rates (39% and 28%, respectively) were significantly decreased by treatment with 100 microg/ml ChSAO compared with those of oocytes treated without ChSAO (63% and 52%, respectively). On the contrary, in cumulus-free oocytes, the addition of 10-100 microg/ml ChSAO significantly reduced the polyspermy rate compared with the control (25-30% versus 53%, respectively), whereas ChSAO had no effect on sperm penetration. Interestingly, ChSAO added to IVF medium significantly decreased the number of sperm bound to the zona pellucida (ZP) of cumulus-free oocytes in a concentration-dependent manner between 0.1 and 100 microg/ml. However, ChSAO had no effect on the time course change in ZP modification after oocyte activation by electrostimulation and the incidence of the acrosome-reacted sperm. Treatment with 100 microg/ml ChSAO during IVF of cumulus-free oocytes significantly increased the proportion of development to the blastocyst stage after in vitro insemination. Therefore, the present findings indicate that hyaluronidase-inhibitory ChSAO is an efficient probe for promoting normal fertilization process in terms of an effective decrease in the incidence of polyspermy during IVF of porcine oocytes.

Effects of scrotal heating on sperm surface protein PH-20 expression in sheep

Sperm surface protein PH-20 expression was studied during spermatogenesis in pubertal and adult sheep, using molecular and histological methods. The effects of 24 hr of insulation raising scrotal temperatures to 39 degrees C on PH-20 expression in ejaculated sheep sperm were also determined. A 282 nt cDNA fragment of ovine PH-20 was identified in total RNA extracts of sheep testes, which exhibited 76% identity at the nucleotide level with the equivalent region of the human sequence. Ovine PH-20 mRNA and immunoreactivity were identified only in adult ram testis and not in peri-pubertal ram testis tubules lacking round spermatids, nor in adult sheep brain, pituitary, heart, spleen, lung, liver, kidney, epididymis, or ovary. Ovine PH-20 protein was distributed predominantly on the postacrosomal membrane and was also present on the anterior membrane of the sperm head in fresh, unheated sheep semen. Scrotal heating caused a significant, transient decrease in the percentage of PH-20 immunoreactive sperm, but did not change the pattern of PH-20 staining on the sperm head. The results strongly suggest that ovine PH-20 is postmeiotically expressed in haploid germ cells in sheep testis and is arrayed on the membrane of the mature ovine spermatozoon. Scrotal heating appears to have few effects on PH-20 expression and distribution on ejaculated sperm.

SAMP32, a testis-specific, isoantigenic sperm acrosomal membrane-associated protein

To identify novel human sperm membrane antigens, we analyzed two-dimensional gels of sperm extracts containing hydrophobic proteins that partitioned into Triton X-114. Four protein spots with isoelectric points (pIs) ranging from 4.5 to 5.5 and apparent molecular weights from 32 to 34 kDa were sequenced by mass spectrometry and found to contain common peptide sequences. Cloning the corresponding cDNA revealed that these protein spots were products of a single gene (SAMP32), encoding a protein of 32 kDa with a predicted pI of 4.57. SAMP32 has a potential transmembrane domain in the carboxyl terminus and is phosphorylated in vivo on serine 256. Northern blotting of eight human tissues and RNA dot blotting of 76 human tissues showed that SAMP32 expression was testis specific. SAMP32 contained an amino terminal domain homologous to the major malarial circumsporozoite surface protein and a domain similar to that of Krp1 from Schizosaccharomyces pombe in its carboxyl terminus. The SAMP32 locus consists of seven exons on chromosome 6q15-16.2. Antiserum against recombinant SAMP32 recognized protein spots originally cored from a two-dimensional gel. This antiserum strongly stained the equatorial segment and faintly stained the acrosome cap of ejaculated human spermatozoa by immunofluorescence. Immunoelectron microscopy showed that SAMP32 was associated with the inner acrosomal membrane in the principal and the equatorial segments of the sperm acrosome. By immunostaining enzyme-dissociated testicular cells, SAMP32 was localized to Golgi phase round spermatids and subsequent stages of acrosome biogenesis. Recombinant SAMP32 reacted with serum from an infertile man, suggesting that it is isoantigenic. Antibodies against recombinant SAMP32 inhibited both the binding and the fusion of human sperm to zona-free hamster eggs.

A mouse acrosomal cortical matrix protein, MC41, has ZP2-binding activity and forms a complex with a 75-kDa serine protease

Sperm with a large acrosome such as that of guinea pigs and hamsters have a subdomain structure in the anterior acrosome, but the mouse acrosome looks homogeneous and its matrix has not been precisely analyzed. The intra-acrosomal protein MC41 is localized in the cortical region of the mouse anterior acrosome, suggesting a subdomain structure in the mouse acrosome. Thus, the present study was undertaken to analyze the mouse acrosomal matrix using an anti-MC41 antibody. When mouse sperm were treated with 2% Triton X-100, Triton-insoluble matrix components remained in the acrosomal cortical region. Immunogold for MC41 labeled the Triton X-100 and high-salt-insoluble matrix components, demonstrating that MC41 is a subdomain-specific acrosomal matrix protein. We further examined interactions of MC41 with acrosomal proteases and zona proteins. A serine protease of 75 kDa was associated with MC41 under low-salt conditions, presumably forming a complex. Far Western blotting technique indicated that MC41 bound to both ZP2 and ZP2(f) in the presence of high-salt-soluble sperm proteins. In acrosome-reacting sperm, MC41 was present on the hybrid vesicles formed by the fusion of the plasma and outer acrosomal membranes. Presumably, MC41 has a significant role in secondary sperm-zona binding during the acrosomal reaction.

Differential production of reactive oxygen species by subsets of human spermatozoa at different stages of maturation

BACKGROUND

Reactive oxygen species (ROS)-mediated damage to human spermatozoa has been implicated in the pathogenesis of male infertility. Although ROS production by human spermatozoa has been extensively studied, the cell-to-cell variation in ROS production by spermatozoa at different stages of maturation has never been investigated.

METHODS

In this study, we determined ROS production by subsets of human spermatozoa at different stages of maturation isolated by density gradient centrifugation of ejaculated spermatozoa obtained from healthy donors and from patients attending a clinic for infertility screening.

RESULTS

Four different fractions were obtained. ROS production was highest in immature spermatozoa with abnormal head morphology and cytoplasmic retention and lowest in mature spermatozoa and immature germ cells (P < 0.01). ROS production was highest in immature spermatozoa from males with abnormal semen parameters compared with donors (P < 0.0001) or patients with normal semen parameters (P = 0.015). ROS production by immature spermatozoa was inversely correlated with the recovery of motile, mature spermatozoa in the high density fraction 4 (P = 0.01).

CONCLUSIONS

The results of this study indicate that there is significant cell-to-cell variation in ROS production in subsets of spermatozoa at different stages of maturation and that oxidative damage of mature spermatozoa by ROS-producing immature spermatozoa during sperm migration from the seminiferous tubules to the epididymis may be an important cause of male infertility.

Variation of docosahexaenoic acid content in subsets of human spermatozoa at different stages of maturation: implications for sperm lipoperoxidative damage

The oxidation of phospholipid-bound docosahexaenoic acid (DHA) has been shown to be one of the major factors that limit the motile life span of sperm in vitro. Sperm samples show high cell-to-cell variability in life span and, consequently, in susceptibility toward lipid peroxidation. Therefore, we postulated that there is also cell-to-cell variability in DHA concentration in human spermatozoa. In this study, the concentration of DHA in subsets of human spermatozoa isolated by a discontinuous Percoll density gradient was determined by gas chromatography. Four subsets of human spermatozoa were isolated using a discontinuous Percoll gradient: fraction 1 was enriched in immature germ cells and immature sperm, fractions 2 and 3 contained, mostly, immature sperm with cytoplasmic droplets, and fraction 4 contained, for the most part, morphologically normal sperm, as determined by histochemical analysis. The results indicated that there were significant differences in DHA content in sperm from all 4 fractions. DHA content in sperm from fraction 1 was 2.5-fold higher than that found in fraction 4. DHA content in mouse sperm obtained from the seminiferous tubules was 3-fold higher than that found in mouse sperm obtained from the epididymis, consistent with the findings observed in ejaculated human sperm. The results of this study indicate (i) there is cell-to-cell variability in the concentration of DHA in human sperm and (ii) that there is a net decrease in DHA content in sperm during the process of sperm maturation.

PH-20 but not acrosin is involved in sperm penetration of the macaque zona pellucida

In this study, we investigated the functions of PH-20 and acrosin during the interaction of macaque sperm with the zona pellucida. Both of these sperm enzymes have been reported to be present on the inner acrosomal membrane of acrosome reacted sperm, and have been suggested to play a role during secondary sperm-zona binding in other species. Anti-macaque PH-20 IgG, anti-pig acrosin IgG and soybean trypsin inhibitor (SBTI) were used as probes for immunolocalization of the two proteins at the ultrastructural level, and as reagents for blocking sperm penetration of the macaque zona pellucida in vitro. As a control, we performed similar studies with antibodies to CD-46, which is also located on the inner acrosomal membrane, but has no known function in sperm-zona pellucida interaction. After labeling with anti-acrosin IgG, gold label was not present on the sperm surface before the acrosome reaction, but was detected over the entire head of sperm that were induced to acrosome react with calcium ionophore A23187. In contrast, when sperm were induced to acrosome react by binding to intact zona pellucida, acrosin was present in the acrosomal shroud but not on the inner acrosomal membrane. Similar results were obtained when SBTI was used as a probe for enzyme localization. PH-20 and CD-46 were demonstrated on the inner acrosomal membrane of sperm induced to acrosome react by ionophore treatment and by zona binding. Neither anti-acrosin IgG nor anti-CD-46 IgG affected sperm penetration of the zona at concentrations up to 300 microg/ml, but zona penetration was blocked completely when anti-PH-20 IgG (100 microg/ml) was present during sperm-oocyte interaction. Ultrastructural observations of oocytes incubated with anti-PH-20 IgG showed that acrosomal shrouds were present on the zona surface but no sperm had begun to penetrate into the zona substance. We conclude that anti-PH-20 IgG prevented sperm penetration of the macaque zona pellucida by interference with secondary sperm-zona binding, rather than primary sperm-zona binding or the zona-induced acrosome reaction. Acrosin was not detected on the inner acrosomal membrane of sperm that are induced to acrosome react after zona binding, and acrosin does not appear to be critical for sperm penetration of the macaque zona pellucida.

Identification of linear surface epitopes on the guinea pig sperm membrane protein PH-20

The sperm plasma membrane protein PH-20 has previously been shown to be an effective immunogen for protection against fertilization in guinea pigs. To identify immunodominant regions on gpPH-20 that may be related to this contraceptive effect, we used several high-titer immune sera obtained from animals rendered infertile by gpPH-20 injections to screen a set of overlapping peptides that cover the entire 494-residue sequence. Multiple clusters of peptide sequences exhibited specific reactivity. Some of these sequences were then constructed as octameric synthetic peptides and tested for immunogenicity in female guinea pigs. Our results indicated two regions (res. 94-119 and res. 424-444) to be highly immunogenic and both are surface accessible when native gpPH-20 is in solution or anchored on sperm surface. Both anti-peptide antibodies are specific for gpPH-20 and one of them inhibited hyaluronidase activity partially. These monospecific antibodies should be useful probes for further molecular definition of gpPH-20 structure-function relationships.

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.

Biochemical characterization of the PH-20 protein on the plasma membrane and inner acrosomal membrane of cynomolgus macaque spermatozoa

Preparations of sperm membranes (plasma membranes and outer acrosomal membranes) and denuded sperm heads were isolated from macaque sperm, and the PH-20 proteins present were characterized by Western blotting, hyaluronic acid substrate gel analysis, and a microplate assay for hyaluronidase activity. Because we have shown previously that PH-20 is located on the plasma membrane and not on the outer acrosomal membrane, the PH-20 in the membrane preparations was presumed to be plasma membrane PH-20 (PM-PH-20). PM-PH-20 had an apparent molecular weight of 64 kDa and the optimum pH for its hyaluronidase activity was 6.5. The PH-20 associated with denuded sperm heads was localized by immunogold label to the persistent inner acrosomal membrane (IAM) and was presumed to be IAM-PH-20, which included a major 64 kDa form and a minor 53 kDa form. The 53 kDa form was not detected in extracts of denuded sperm heads from acrosome intact sperm that were boiled in nonreducing sample buffer, but was present in extracts of sperm heads from acrosome reacted sperm and in the soluble material released during the acrosome reaction, whether or not the samples were boiled. Substrate gel analysis showed that the hyaluronidase activity of the 53 kDa form of PH-20 was greatest at acid pH, and this activity was probably responsible for the broader and lower optimum pH of IAM hyaluronidase activity. When hypotonic treatment was used to disrupt the sperm acrosome and release the acrosomal contents, less than 0.05% of the total hyaluronidase activity was released. The PH-20 protein released by hypotonic treatment was the 64 kDa form and not the 53 kDa form, suggesting that its source might be the disrupted plasma membranes. Our experiments suggest that the soluble form of hyaluronidase, which is released at the time of the acrosome reaction, is derived from the IAM. This soluble hyaluronidase is composed of both the 64 kDa form and 53 kDa form of PH-20. The 53 kDa form appears to be processed from the 64 kDa form at the time of the acrosome reaction.

Molecules involved in mammalian sperm-egg interaction

To achieve fertilization, sperm and egg are equipped with specific molecules which mediate the steps of gamete interaction. In mammals, the first interaction between sperm and egg occurs at an egg-specific extracellular matrix, the zona pellucida (zp). The three glycoproteins, ZP1, ZP2, and ZP3, that comprise the zp have been characterized from many species and assigned different roles in gamete interaction. A large number of candidate-binding partners for the zp proteins have been described; a subset of these have been characterized structurally and functionally. Galactosyltransferase, sp56, zona receptor kinase, and spermadhesins are thought to participate in the primary binding between sperm and zp and may initiate the exocytotic release of hydrolytic enzymes in the sperm head, the acrosome reaction. Digestion of the zp by these enzymes enables sperm to traverse the zp, at which time the proteins PH20, proacrosin, sp38, and Sp17 are thought to participate in secondary binding between the acrosome-reacted sperm and zp. Once through the zp, sperm and egg plasma membranes meet and fuse in a process reported to involve the egg integrin alpha 6 beta 1 and the sperm proteins DE and fertilin. These molecules and the processes involved in gamete interaction are reviewed in this chapter within a physiological context.

The murine Spam1 gene: RNA expression pattern and lower steady-state levels associated with the Rb(6.16) translocation

Recently we mapped the murine Spam1 gene to the proximal region of chromosome 6 (MMU 6). Based on the map location and physiological characteristics of its encoded sperm antigen, the gene is an attractive candidate for the sperm dysfunction seen in Rb(6.16) translocation heterozygotes and the reduced fertility of homozygotes. We have analyzed the expression of Spam1 mRNA in normal and Rb(6.16) mice. The expression of Spam1 mRNA was found to be: 1) tissue specific; it is expressed exclusively in testis; and 2) developmentally regulated, with a haploid expression. Notably, the steady-state mRNA level of Spam1 in Rb(6.16) homozygotes was 25-30% of that in chromosomally normal consomic mice and those homozygous for Rb(2.8) (7.18). In Rb(6.16) and Rb(6.15) heterozygotes the levels were 61% and 66% of the normal. Studies are currently under way to determine the protein levels and gene structure of Spam1, to detect the underlying cause of the mRNA reduction associated with these translocations.

Comparative study of functional and biochemical parameters in frozen bovine sperm

In order to correlate functional and biochemical parameters, frozen bovine sperm samples presenting diverse motility were studied. Specimens collected from four bulls (A, B, C and D) were graded according to motile spermatozoa percentage and vigour, regarding the sample from bull A as highest motility, those from bulls B and C of intermediate motility and that from bull D of low motility. In order to evaluate lipid peroxidation enhanced by the addition of sodium ascorbate and ferrous sulphate, thiobarbituric acid reactive substances (TBARS) were measured. Values were 0.34 +/- 0.18 and 4.95 +/- 0.31 nmol TBARS/10(8) spermatozoa for samples A and D, respectively. Superoxide dismutase (SOD) activity was 144 +/- 16.48 and 44 +/- 4.0 IU/10(10) spermatozoa for A and D, respectively, while intermediate values were recorded for samples B and C. The capability to undergo acrosome reaction induced by calcium ionophore A23187 was significantly lower for sample D, but differences were negligible for the remaining three samples inter se. Motile spermatozoa percentage correlated closely both with SOD activity (r = 0.92) and with TBARS production (r = -0.80), but not with acrosome reacted percentage (r = 0.65). From correlation data, it would be inferred that motility is not entirely indicative of sperm quality.

Biochemical characterization of a glycosylphosphatidylinositol-linked hyaluronidase on mouse sperm

On the basis of DNA homology to bee venom hyaluronidase, it was recently suggested that the GPI-linked mammalian sperm antigen, PH-20, may function as a cell surface hyaluronidase [Gmachl, M., & Kreil, G. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 3569-3573]. We have quantified the activity of the soluble acrosomal hyaluronidase of mouse sperm and further demonstrate the existence of a membrane-bound hyaluronidase, detected on both acrosome-intact and acrosome-reacted mouse sperm, distinct from the soluble form of the enzyme. The membrane-bound hyaluronidase was specifically released by PI-PLC, indicating that it is GPI linked. Acrosome-intact and acrosome-reacted sperm released several polypeptides (68, 44, 39, 34, 17, and 15 kDa) when treated with PI-PLC. In addition, GPI-linked polypeptides unique to acrosome-intact or to acrosome-reacted sperm were identified. Fractionation of the PI-PLC-released components from acrosome-reacted sperm using size exclusion chromatography revealed a single peak of hyaluronidase activity which comigrates with a 68 kDa GPI-linked protein present in these fractions. Taken together, these data demonstrate the existence of at least two isoforms of hyaluronidase: a soluble form within the acrosomal vesicle which is released during acrosomal exocytosis and a GPI-linked form which is present on the surface of both acrosome-intact and acrosome-reacted sperm. Both forms may be necessary for successful penetration of the extracellular vestments that surround the egg prior to fertilization.

Sperm-binding proteins

Gamete recognition and binding are mediated by specific proteins on the surface of the sperm and egg. Identification and characterization of some of these proteins from several model systems, particularly mouse and sea urchin, have focused interest on the general properties and functions of gamete recognition proteins. Sperm-binding proteins located in egg extracellular coats as well as sperm-binding proteins that are localized to the egg plasma membrane are presented in the context of their structure and function in gamete binding. Unifying and disparate characteristics are discussed in light of the diverse biology of fertilization among species. Outstanding questions, alternative mechanisms and models, and strategies for future work are presented.

A hyaluronidase activity of the sperm plasma membrane protein PH-20 enables sperm to penetrate the cumulus cell layer surrounding the egg

A typical mammalian egg is surrounded by an outer layer of about 3,000 cumulus cells embedded in an extracellular matrix rich in hyaluronic acid. A current, widely proposed model is that the fertilizing sperm, while it is acrosome intact, passes through the cumulus cell layer and binds to the egg zona pellucida. This current model lacks a well-supported explanation for how sperm penetrate the cumulus layer. We report that the sperm protein PH-20 has a hyaluronidase activity and is present on the plasma membrane of mouse and human sperm. Brief treatment with purified, recombinant PH-20 can release all the cumulus cells surrounding mouse eggs. Acrosome intact mouse sperm incubated with anti-PH-20 antibodies can not pass through the cumulus layer and thus can not reach the zona pellucida. These results, indicating that PH-20 enables acrosome intact sperm to penetrate the cumulus barrier, reveal a mechanism for cumulus penetration, and thus provide the missing element in the current model.

Molecular cloning of the human and monkey sperm surface protein PH-20

The guinea pig sperm surface protein PH-20 has an essential function in sperm adhesion to the zona pellucida of guinea pig eggs. Fully effective contraception has been achieved by immunizing either male or female guinea pigs with purified guinea pig PH-20. Here we report the isolation of human and cynomolgus monkey PH-20 cDNAs as a key step toward testing the function of primate PH-20 and the contraceptive efficacy of PH-20 immunization in primates. The deduced amino acid sequence of human PH-20 has 509 residues and is 59% identical with guinea pig PH-20, suggesting they may have a conserved function and immunogenicity. Southern blots show that there is a single PH-20 gene in the human genome and Northern blots of human testis poly(A)+ RNA show a 2.4-kb message. Northern blots of tissues other than testis are negative for PH-20, indicating that human PH-20 is testis-specific.

Evaluation of mouse sperm acrosomal status and viability by flow cytometry

A procedure was developed to evaluate mouse sperm acrosomal status and viability simultaneously utilizing flow cytometry. Four fluorescein isothiocyanate (FITC)-conjugated lectins, peanut agglutinin (PNA), concanavalin agglutinin (ConA), Pisum sativum agglutinin (PSA), and soybean agglutinin (SBA), were investigated, with PNA providing the greatest sensitivity and specificity in distinguishing acrosome-present and acrosome-absent mouse spermatozoa. To expose lectin binding sites, digitonin (20 microM at room temperature for 10 min) was used to permeabilize sperm plasma membranes. Sperm cell viability was determined by Hoechst 33258-(H258) exclusion. To prevent permeabilized cells from staining with H258, salmon sperm DNA (SS-DNA) was applied to bind excess dye in the solutions after supravital staining. Calcium ionophore (A23187; 5 or 20 microM) was used to induce acrosome reactions. The results of flow cytometric analyses were compared with epifluorescence microscopic observation and were highly correlated (r = 0.999; P < 0.001). The method developed provides an objective and efficient procedure to estimate simultaneously both acrosomal status and viability of mouse spermatozoa.

Artificial induction of exocytosis in bull sperm

We have investigated an exocytotic event, the acrosome reaction (AR), induced by treatment of bovine sperm with vesicles composed of dilauroyl phosphatidylcholine (PC12). Cell membrane permeability barriers (dye exclusion), acrosomal status (pisum sativum (PSA) lectin binding), and intracellular Ca2+ (Fluo3 fluorescence) were evaluated utilizing flow cytometry and fluorescence microscopy. By these methods the AR is resolved into four kinetically distinct steps: (a) PC12 transfer to the sperm plasma membrane (PM); (b) increased permeability of the PM to extracellular Ca2+; (c) localized leakage of acrosomal contents at the anterior tip of the sperm; and (d) vesiculation of sperm membranes and complete exposure of acrosomal contents. Evidence for PC12 transfer to sperm includes transfer of a fluorescent PC12 analogue from vesicles to cells and the absence of detectable vesicle--cell fusion. The fusion inducing properties of PC12 appear to reside in the lipid head group as neither dilauroylphosphatidylethanolamine nor dilauroylphosphatidylglycerol stimulated the AR. The effect of PC chain length on AR induction closely parallels the aqueous phase solubility of the lipid tested. The rate and extent of the AR depend on the extracellular calcium concentration. Cells treated in the absence of calcium do not undergo the AR, but do so rapidly (less than 1 min) upon subsequent addition of calcium. This role of Ca2+ is partially filled by Sr2+, but not by Ba2+ or Mg2+. The rate of the AR decreases with decreasing temperature and the AR occurs very slowly below 27 degrees C. Simultaneous evaluation of intracellular calcium and acrosomal status reveals the kinetic relationship between Ca2+ influx and the exposure of acrosomal contents. N-Ethylmaleimide preincubation arrests PC12-treated sperm at an intermediate stage in the AR, characterized by punctate PSA binding over the tip of the sperm head. The AR, a developmentally regulated, receptor-mediated fusion event, synchronously induced here in vitro, provides a useful model for mechanistic studies of exocytosis.

Sperm proteins that serve as receptors for the zona pellucida and their post-testicular modification

The search for molecules on the surface of mammalian sperm that are responsible for the binding of sperm to the zona pellucida has led to the identification of a number of different surface proteins. Different experimental approaches have been used to identify these proteins and the strength of the evidence for their putative role in zona binding is therefore quite variable. In this paper we have discussed some of the approaches that are used to identify cell adhesion molecules and criteria that might be applied in future research. Further research will be required to answer questions as to whether multiple surface antigens are involved in zona binding and if the sperm receptors for the zona are conserved among species. Both of these results would be expected based on what is known about cell adhesion in other systems. We have also discussed the modifications that occur to surface proteins after the sperm leave the testis and how these modifications can potentially activate or increase the efficiency of the function of a protein in zona binding.

Fertilization failure and dysfunctions as possible causes for human idiopathic infertility

Consideration of the most common currently practiced laboratory assays for human spermatozoal fertility are discussed, with reference to the relevance of such assays to success or failure in human in vitro fertilization (IVF). Such IVF therapy should be the definitive challenge for human spermatozoal fertilization ability. However, when fertilization fails, is polyspermic, or is suboptimal, then questions concerning the step or steps in the process of fertilization which are dysfunctional remain unanswered. Quite possibly new assays need to be devised to address these problems, while in the meantime our present laboratory assay systems need to be improved to discern those defects in fertilization which operate in many cases of human idiopathic infertility.

Migration of the guinea pig sperm membrane protein PH-20 from one localized surface domain to another does not occur by a simple diffusion-trapping mechanism

The redistribution of membrane proteins on the surface of cells is a prevalent feature of differentiation in a variety of cells. In most cases the mechanism responsible for such redistribution is poorly understood. Two potential mechanisms for the redistribution of surface proteins are: (1) passive diffusion coupled with trapping, and (2) active translocation. We have studied the process of membrane protein redistribution for the PH-20 protein of guinea pig sperm, a surface protein required for sperm binding to the egg zona pellucida (P. Primakoff, H. Hyatt, and D. G. Myles (1985). J. Cell Biol. 101, 2239-2244). PH-20 protein is localized to the posterior head plasma menbrane of the mature sperm cell. Following the exocytotic acrosome reaction, PH-20 protein moves into the newly incorporated inner acrosomal membrane (IAM), placing it in a position favorable for a role in binding sperm to the egg zona pellucida (D. G. Myles, and P. Primakoff (1984), J. Cell Biol. 99, 1634-1641). To analyze the mechanistic basis for this protein migration, we have used fluorescence microscopy and digital image processing to characterize PH-20 protein migration in individual cells. PH-20 protein was observed to move against a concentration gradient in the posterior head plasma membrane. This result argues strongly against a model of passive diffusion followed by trapping in the IAM, and instead suggests that an active process serves to concentrate PH-20 protein toward the boundary separating the posterior head and IAM regions. A transient gradient of PH-20 concentration observed in the IAM suggests that once PH-20 protein reaches the IAM, it is freely diffusing. Additionally, we observed that migration of PH-20 protein was calcium dependent.

cDNA cloning reveals the molecular structure of a sperm surface protein, PH-20, involved in sperm-egg adhesion and the wide distribution of its gene among mammals

Sperm binding to the egg zona pellucida in mammals is a cell-cell adhesion process that is generally species specific. The guinea pig sperm protein PH-20 has a required function in sperm adhesion to the zona pellucida of guinea pig eggs. PH-20 is located on both the sperm plasma membrane and acrosomal membrane. We report here the isolation and sequence of a full-length cDNA for PH-20 (available from EMBL/GenBank/DDBJ under accession number X56332). The derived amino acid sequence shows a mature protein of 468 amino acids containing six N-linked glycosylation sites and twelve cysteines, eight of which are tightly clustered near the COOH terminus. The sequence indicates PH-20 is a novel protein with no relationship to the mouse sperm adhesion protein galactosyl transferase and no significant homology with other known proteins. The two PH-20 populations, plasma membrane and acrosomal membrane, could arise because one form of PH-20 is encoded and differentially targeted at different spermatogenic stages. Alternatively, two different forms of PH-20 could be encoded. Our evidence thus far reveals only one sequence coding for PH-20: Southern blots of guinea pig genomic DNA indicated there is a single PH-20 gene, Northern blots showed a single size PH-20 message (approximately 2.2 kb), and no sequence variants were found among the sequenced cDNA clones. Cross-species Southern blots reveal the presence of a homologue of the PH-20 gene in mouse, rat, hamster, rabbit, bovine, monkey, and human genomic DNA, showing the PH-20 gene is conserved among mammals. Since genes for zona glycoproteins are also conserved among mammals, the general features of sperm and zona proteins involved in mammalian sperm-egg adhesion may have been evolutionarily maintained. Species specificity may result from limited changes in these molecules, either in their binding domains or in other regions that affect the ability of the binding domains to interact.

Carbohydrates and fertilization in animals

A frequently used mechanism for sperm-egg recognition in many species involves complementary protein-carbohydrate interaction. The usual paradigm includes complex glycoconjugates in reproductive tract fluids or on the eggs which are recognized by carbohydrate-binding proteins on the sperm surface. Various glycoconjugates are utilized in the steps of sperm capacitation, sperm binding to the egg extracellular matrix and vitelline membrane and induction of the acrosome reaction. Several types of complex glycoconjugates are involved in these processes, including proteoglycans, lactosaminoglycans, sulfated fucose-containing glycoconjugates, and glycoproteins. There appear to be some structural similarities between active glycoconjugates; they are large in molecular weight and complex, and they are often sulfated, fucosylated, and attached to a protein through serine or threonine residues. In some species, the protein core of the glycoconjugates also participates in the interaction by limiting the binding of carbohydrates to sperm only of the relevant species, likely by providing the proper steric arrangement for the interaction. In other cases the protein core seems to serve more as a crosslinker of the carbohydrate moieties. This review discusses the types of glycoconjugates implicated in fertilization and the complementary lectin-like proteins found on sperm.

Acrosome intact and acrosome-reacted human sperm can initiate binding to the zona pellucida

Mammalian sperm must be acrosome reacted before penetrating the zona pellucida. In some species the sperm undergo the acrosome reaction before binding to the zona pellucida and in other species only acrosome intact sperm can initiate binding to the zona. In this study we addressed the question of acrosomal status and sperm-zona binding with human gametes. Sperm acrosome reactions were induced by treatment with human follicular fluid or N-(6-amino-hexyl)-5-chloro-naphthalene sulfonamide (W-7). The sperm suspensions, containing various percentages of acrosome-reacted sperm, were then incubated with human oocytes for 1 min. The acrosomal status of the sperm population bound to the zona was similar to the acrosomal status of the population of sperm in suspension (R2 = 0.77), regardless of the treatment to induce acrosome reactions. Our interpretation of these results is that both acrosome intact and acrosome-reacted human sperm can initiate binding to the zona pellucida. However, we reported earlier (N. L. Cross, P. Morales, J. W. Overstreet, and F. W. Hanson, 1988, Biol. Reprod. 38, 235-244) that the human zona pellucida is able to induce acrosome reactions. Thus, to exclude the possibility that sperm had undergone the acrosome reaction on the zona within 1 min of binding, sperm were suspended in a nominally calcium-free Tyrode's medium (0 Ca-mTyr) before incubation with oocytes (this medium was supplemented with SrCl2 and spermine to support sperm motility and zona binding). In 0 Ca-mTyr, the proportion of acrosome-reacted sperm on the zona was still highly correlated with the proportion of reacted sperm in suspension, indicating that the sperm were reacted before binding. Evidence that 0 Ca-mTyr effectively inhibited acrosome reactions induced by the zona pellucida was derived from experiments in which sperm were treated with human follicular fluid or control medium and the suspensions were diluted with either 0 Ca-mTyr or control medium.4+ Human oocytes were added for 1 min (pulse) at which time some oocytes were fixed and other oocytes were transferred to sperm-free medium and incubated for 35 min (chase) before fixation. Sperm diluted in control medium, pretreated with either human follicular fluid or control medium, showed a similar increase (40%) in the percentage of acrosome reactions among the zona-bound sperm after the chase. Sperm diluted in 0 Ca-mTyr did not show an increase in the percentage of acrosome-reacted sperm on the zona pellucida after the chase.(ABSTRACT TRUNCATED AT 400 WORDS)

Steroid induced exocytosis: the human sperm acrosome reaction

By a combination of organic precipitation and high pressure liquid chromatography, human sperm acrosome reaction inducing activity has been purified from the fluid aspirated from preovulatory human ovarian follicles and identified as 4-pregnen-3,20-dione (progesterone) and 4-pregnen-17 alpha-ol-3,20-dione (17 alpha-hydroxyprogesterone). It is argued that progesterone is present at the site of fertilization of placental mammals in concentrations sufficient for activity, and hence provides a mechanism of inducing the acrosome reaction, an exocytotic event, in vivo.