Isolation of the zona pellucida and purification of its glycoprotein families from pig oocytes

Ligands and Receptors Involved in the Sperm-Zona Pellucida Interactions in Mammals

Sperm-zona pellucida (ZP) interaction, involving the binding of sperm surface ligands to complementary carbohydrates of ZP, is the first direct gamete contact event crucial for subsequent gamete fusion and successful fertilization in mammals. It is a complex process mediated by the coordinated engagement of multiple ZP receptors forming high-molecular-weight (HMW) protein complexes at the acrosomal region of the sperm surface. The present article aims to review the current understanding of sperm-ZP binding in the four most studied mammalian models, i.e., murine, porcine, bovine, and human, and summarizes the candidate ZP receptors with established ZP affinity, including their origins and the mechanisms of ZP binding. Further, it compares and contrasts the ZP structure and carbohydrate composition in the aforementioned model organisms. The comprehensive understanding of sperm-ZP interaction mechanisms is critical for the diagnosis of infertility and thus becomes an integral part of assisted reproductive therapies/technologies.

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.

Sperm binding to porcine oviductal cells is mediated by SRCR domains contained in DMBT1

The oviduct is an organ in which a subpopulation of sperm is stored in a reservoir, preserving its fertilizing potential. In porcine, two oviductal proteins have been identified in relation to sperm binding, Annexin A2 and Deleted in Malignant Brain Tumor 1 (DMBT1). DMBT1 is a multifunctional, multidomain glycoprotein, and the characteristics of all of its domains, as well as its carbohydrates, make them candidates for sperm binding. In this work, we challenge sperm for binding to pig oviductal cells on primary culture, after treatment with antibodies specific for the different domains present in DMBT1. Only anti-SRCR antibodies produced inhibition of sperm binding to cells. Thus, SRCR is the main domain in DMBT1 promoted sperm binding to form the reservoir in the oviduct, and this function is probably elicited through the polypeptide itself.

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.

Heparin binding analysis of boar sperm and its relation with farrowing capacity

New methods for the evaluation of semen quality according to in vivo reproductive data are useful tools for identifying boars of lower fertility among individuals with standard semen parameters. In this study, indirect fluorescence microscopy was used to evaluate the heparin binding site distribution upon capacitation of sperm from eight boars arbitrarily distributed into Groups I and II according to differential farrowing rates (Group I: ≥ 70%, Group II: < 70%). Additionally, the ability of sperm to bind to solubilised zona pellucida (ZP) was assayed in the presence or absence of heparin. Samples of two individuals of Group II showed lower percentage of B pattern in relation to other individuals (P < 0.001). The number of spermatozoa attached to ZP after 2 h of incubation in capacitating conditions with heparin was significantly lower than in its absence (P < 0.0001). These results suggest that heparin binding site distribution concerning capacitation may be indicative of the availability of proteins involved in the fertilisation process, specifically at the initial sperm-oocyte recognition. Differences in heparin binding site dynamics during capacitation may help identify a subpopulation of individuals with lower fertilising capacity and normal spermiogram, which is particularly useful at high-production establishments.

Characterization of sperm surface protein patterns of ejaculated and capacitated boar sperm, with the detection of ZP binding candidates

Complementary molecules on the surface of both gametes are responsible for the interaction of sperm protein receptors with zona pellucida (ZP) saccharide structures, and many primary sperm receptors for ZP glycoproteins have been disclosed in various mammals. For our study, proteins were obtained from the surface of ejaculated and in vitro capacitated boar sperm. The isolated proteins were characterized by 1D- and 2D-electrophoretic protein profiles, and by glycoprotein staining. Our results show quantitative and qualitative differences in protein and glycoprotein patterns between ejaculated and capacitated sperm. Far-western blotting with ZP glycoproteins identified 17 interactions in the subproteome of the ejaculated sperm and 14 interactions in the subproteome of the capacitated sperm. High-molecular-mass proteins, coincident with binding to ZP, were sequence-identified. Angiotensin-converting enzyme (ACE), polycystic kidney disease receptor and egg jelly receptor (PKDREJ), and acrosin precursor were successfully identified. This is the first time PKDREJ has been identified on the surface of boar spermatozoa.

Involvement of N-glycosylation of zona glycoproteins during meiotic maturation in sperm-zona pellucida interactions of porcine denuded oocytes

The present study was conducted to delineate whether N-glycosylation of zona pellucida (ZP) glycoproteins occurred during meiotic maturation and whether this N-glycosylation played a role in sperm-ZP interactions of porcine cumulus denuded oocytes (DOs). After mechanical removal of cumulus cells from cumulus oocyte complexes (COCs), DOs were cultured for 44 h in in vitro maturation (IVM) culture. The experiments were carried out to determine the effects of tunicamycin, a specific N-glycosylation inhibitor, for various intervals during IVM on sperm-ZP interactions in porcine DOs. The results determined that DOs could induce meiotic maturation, although the maturation rate of DOs was earlier than that of COCs. In addition, N-glycosylation of ZP glycoproteins occurred during meiotic maturation and was crucial in sperm-ZP interactions, was responsible for sperm penetration, sperm binding to ZP and induction of acrosome reaction in ZP-bound sperm. However, the inhibition of N-glycosylation by tunicamycin during IVM did not influence ZP hardness and male pronuclear formation, indicating that this N-glycosylation was involved in the initial stage of fertilization. We conclude that 24-44 h of N-glycosylation of ZP glycoproteins during meiotic maturation was crucial in sperm penetration and sperm binding to ZP and the induction of acrosome reaction in sperm bound to ZP of porcine DOs.

Biochemical and binding characteristics of boar epididymal fluid proteins

During the passage through the epididymis, testicular spermatozoa are directly exposed to epididymal fluid and undergo maturation. Proteins and glycoproteins of epididymal fluid may be adsorbed on the sperm surface and participate in the sperm maturation process, potentially in sperm capacitation, gamete recognition, binding and fusion. In present study, we separated proteins from boar epididymal fluid and tested their binding abilities. Boar epididymal fluid proteins were separated by size exclusion chromatography and by high-performance liquid chromatography with reverse phase (RP HPLC). The protein fractions were characterized by SDS-electrophoresis and the electrophoretic separated proteins after transfer to nitrocellulose membranes were tested for the interaction with biotin-labeled ligands: glycoproteins of zona pellucida (ZP), hyaluronic acid and heparin. Simultaneously, changes in the interaction of epididymal spermatozoa with biotin-labeled ligands after pre-incubation with epididymal fluid fractions were studied on microtiter plates by the ELBA (enzyme-linked binding assay) test. The affinity of some low-molecular-mass epididymal proteins (12-17 kDa and 23 kDa) to heparin and hyaluronic acid suggests their binding ability to oviductal proteoglycans of the porcine oviduct and a possible role during sperm capacitation. Epididymal proteins of 12-18 kDa interacted with ZP glycoproteins. One of them was identified as Crisp3-like protein. The method using microtiter plates showed the ability of epididymal fluid fractions to change the interaction of the epididymal sperm surface with biotin-labeled ligands (ZP glycoproteins, hyaluronic acid and heparin). These findings indicate that some epididymal fluid proteins are bound to the sperm surface during epididymal maturation and might play a role in the sperm capacitation or the sperm-zona pellucida binding.

Pig zona pellucida 2 (pZP2) protein does not participate in zona pellucida formation in transgenic mice

The zona pellucida, an extracellular matrix surrounding mammalian oocytes, is composed of three or four glycoproteins. It is well known that the zona pellucida plays several critical roles during fertilization, but there is little knowledge about its formation. The purpose of this study is to examine whether a pig zona pellucida glycoprotein 2 (pZP2) would assemble with mouse zona pellucida. A transgene construct was prepared by placing a minigene encoding pZP2 downstream from the promoter of mouse ZP2. The result showed that the transgenic protein was synthesized in growing oocytes but not incorporated into the zona pellucida. Furthermore, the pZP2 transgene did not rescue the phenotype in ZP2-knockout zona-deficient mice. These results indicate that pZP2 does not participate in mouse zona pellucida formation and the zona pellucida is constituted from its component proteins in a molecular species-specific manner between mice and pigs.

Affinity chromatography of bull seminal proteins on mannan-Sepharose

The interaction of bull seminal plasma proteins and sperm with mannan was investigated using an enzyme-linked binding assay (ELBA). A high mannan-binding activity was found in the protein fraction interacting with heparin. Mannan binding to seminal plasma proteins was inhibited by D-mannose and D-fructose, but not by D-mannose-6-phosphate, D-glucose-6-phosphate, ovalbumin and ovomucoid. Mannan inhibited the binding of bovine zona pellucida glycoproteins both to bull sperm and seminal plasma proteins. Yeast mannan immobilized to divinyl sulfone-activated Sepharose was used for the isolation of mannan-binding proteins. The protein components of this fraction were identified on the basis of relative molecular mass determination and N-terminal amino acid sequencing: RNAase dimer, PDC-109 and a protein homologous to BSP-30K (relative molecular mass 14,500). The isolated proteins were characterized by a high zona pellucida binding activity.

Arylsulfatase a is present on the pig sperm surface and is involved in sperm-zona pellucida binding

We have previously described the affinity of a pig sperm surface protein, P68, to mammalian zonae pellucidae (ZP). In this report, we identified P68 as arylsulfatase A (AS-A) based on the presence of P68 tryptic peptide sequences in the pig testis AS-A cDNA sequence. Our objective was to demonstrate the presence of AS-A on the sperm surface and to elucidate its role in ZP binding. Immunogold electron microscopy revealed the presence of AS-A on the sperm surface. Furthermore, live pig sperm and the extract of peripheral sperm plasma membrane proteins exhibited AS-A's desulfation activity. Significantly, the role of pig sperm surface AS-A in ZP binding was demonstrated by dose-dependent decreases of sperm-ZP binding upon sperm pretreatment with anti-AS-A IgG/Fab, and by the binding of Alexa-430-conjugated sperm surface AS-A to homologous ZP. ZP pretreatment with anti-pig-ZP3 antibody abolished AS-A binding, suggesting that ZP3, recognized as the pig sperm receptor, was AS-A's binding ligand. This was further confirmed by the ability of exogenous ZP3 to competitively inhibit AS-A-ZP binding. Similarly, purified ZP3alpha, a major sperm receptor component of ZP3, exhibited great inhibitory effect on AS-A-ZP binding. All of these results designated a new function of AS-A in gamete interaction.

Prospect for immunocontraception using the NH2-terminal recombinant peptide of human zona pellucida protein (hZPA)

PROBLEM

The zona pellucida is a feasible candidate for contraceptive vaccine. Our previous study showed that a human zona pellucida (ZPA) recombinant protein produced antiserum that inhibited human in vitro fertilization in rabbits. The objective of this study is to examine whether the human recombinant protein produce fertilization-blocking antiserum in a non-human primate.

METHOD OF STUDY

The amino terminal regions consisting of pig (198 amino acids) and human (206 amino acids) zona pellucida proteins were prepared by Escherichia coli to produce antisera in bonnet monkeys (Macaca radiata). Antibody production was assessed by immunofluorescent staining and enzyme-linked immunosorbent assay (ELISA). Fertilization-blocking test was carried out using human oocytes that had failed in intracytoplasmic sperm injection (ICSI) treatment under patient's informed consent.

RESULTS

Both antisera against pig and human recombinant proteins recognized native human zona pellucida by immunofluorescent staining. However, anti-recombinant human ZPA reacted to native pig zona protein more strongly than pig zona pellucida by ELISA. When human oocytes were treated with antisera before insemination, anti-human ZPA antiserum inhibited human sperm binding to human zona pellucida, but anti-pig ZPA antiserum did not.

CONCLUSIONS

Bonnet monkey produced fertilization-blocking antibody by immunization with human recombinant ZPA. The homologous or highly similar sequence is effective for developing a contraceptive vaccine when using recombinant peptides.

Functional morphology of the zona pellucida

The zona pellucida (ZP) is an extracellular matrix surrounding the oocyte and the early embryo that exerts several important functions during fertilization and early embryonic development. The ZP of most mammalian species is composed of three major glycoproteins that show considerable heterogeneity due to extensive post-translational modifications. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of the ZP reveals three to four glycoproteins which have been nominated ZPI. ZP2, ZP3 and ZP4. As cloning and characterization of the ZP genes of a variety of mammalian species including domestic animals show a high homology, three classes of ZP genes, ZPA, ZPB and ZPC can be discerned. The corresponding proteins were named ZPA, ZPB and ZPC. Whereas in the mouse ZPB is the primary sperm receptor. the situation is more complicated in other species. For instance, in the pig ZPA has been shown to possess receptor activity. Interaction between gametes during fertilization is at least in part regulated by carbohydrate moieties of the ZP and carbohydrate-binding proteins of the sperm surface. In domestic animals zona proteins are expressed in both the oocyte and granulosa cells in a stage-specific pattern and may play a role in granulosa cell differentiation. The role of ZP glycoproteins in immunocontraception is briefly discussed.

Molecular analysis of a carbohydrate antigen involved in the structure and function of zona pellucida glycoproteins

A lactosaminoglycan-associated antigen is associated with a carbohydrate moiety of all three zona pellucida (ZP) glycoproteins of pig and rabbit but is absent in the mouse and rat. A monoclonal antibody (PS1) recognizing this determinant was obtained by immunizing mice with a porcine ZP glycoprotein isoform purified by two-dimensional polyacrylamide gel electrophoresis. Conditions known to remove O-linked or sialic acid carbohydrate moieties (alkaline reduction; O-glycanase or neuraminidase enzymatic cleavage) did not remove the carbohydrate epitope. However, treatment with endo-beta-glycosidase, endoglycosidase F, or combinations of neuraminidase plus beta-galactosidase, totally removed the determinant, indicating that it is associated with a poly-N-acetyllactosaminoglycan structure present on an N-linked oligosaccharide. Molecular morphology studies using immunofluorescence and confocal microscopy techniques demonstrate that the PS1 antigen is localized at the surface of the ZP. Confirmation of this localization was obtained through studies that show that this antibody will inhibit homologous sperm binding to the pig ZP. Additional analyses using modular contrast microscopy and immunocytochemistry demonstrate that this carbohydrate-associated antigen is localized in discrete layers throughout the ZP matrix. These studies are the first to demonstrate the presence of a lactosaminoglycan type carbohydrate moiety in all three ZP proteins using a monoclonal antibody that appears to be involved in sperm recognition and structural organization.

Pig sperm membrane integrity evaluated by lectin labeling

Sperm integrity is one of the most carefully examined characteristics for artificial insemination in humans and mammals. Techniques have been developed to assess the sperm plasma membrane integrity. Some of them need a well-trained evaluation for correctness, as is the case of the triple stain technique; others are time-consuming and need special equipment, varying from specially adapted microscopes to computer-based analyzers. The authors report the use of fluorescein-labeled peanut agglutinin plus a fluorescein extender that permits an easy evaluation for pig spermatozoa membrane integrity. Sperm integrity in pigs was evaluated before and after zona pellucida-induced acrosome reaction in capacitated sperm. The sperm acrosome reaction was affected when the zona pellucida was reduced.

Caprine sperm acrosome reaction: promotion by progesterone and homologous zona pellucida

Experiments were designed to characterize the effect of progesterone and the zona pellucida (ZP) on the goat sperm acrosome reaction (AR) through a comparative study. Goat spermatozoa were incubated for 4h in Krebs-Ringer bicarbonate media (KRB) for capacitation. Progesterone and ZP stimulated exocytosis of capacitated spermatozoa in a dose-dependent manner. EGTA and La(3+), added 10min before the addition of the agonists, completely abolished the stimulatory effects. Ca(2+) influx was observed to occur through a calcium phosphate transporter. Picrotoxin and bicuculline, two GABA(A)/Cl(-) channel antagonists, also inhibited progesterone-induced AR when added 10min before steroid addition. ZP-induced AR was unaffected by these antagonists. Studies using pertussis toxin (PTX) showed that, unlike ZP, progesterone acts without the involvement of a G-protein. Progesterone-3-(O-carboxymethyl) oxime: BSA conjugate (P-BSA) also induced AR in capacitated sperm suspension. Results suggest that progesterone and ZP induce AR via specific membrane receptors through different mechanisms, both requiring an influx of Ca(2+). It is assumed that both the mechanisms reconcile at some stages of the cascade and elicits a similar physiological response.

Identification of homologous binding proteins in porcine and bovine gametes

The purpose of this study was to determine if sperm and oocyte proteins that mediate plasma membrane interaction during mammalian fertilization are conserved among porcine and bovine gametes. We examined homologous and heterologous sperm and zona-free oocyte interactions to determine the extent of cross-reactivity between the gametes of these two ungulate species. First, the numbers of ejaculated porcine and bovine sperm bound to the oocyte plasma membrane of intact porcine and bovine oocytes were determined in vitro. There was no significant difference between the number of porcine or bovine sperm that bound to porcine or bovine oocytes (P > 0.25). Second, individual porcine and bovine sperm plasma membrane proteins were identified by binding of homologous or heterologous oocyte plasma membrane to whole sperm plasma membrane on Western ligand blots. The relative amount of labeled oocyte plasma membrane bound to individual sperm plasma membrane proteins was analyzed by laser densitometry. Eight porcine sperm plasma membrane proteins and seven bovine sperm plasma membrane proteins were bound by both porcine and bovine oocyte plasma membrane. A significantly greater relative amount of porcine oocyte plasma membrane than bovine oocyte plasma membrane was bound to the 14- and 10-kD porcine sperm plasma membrane proteins (P < 0.001 and P < 0.01, respectively). A 27-kD bovine sperm plasma membrane protein bound proportionally more bovine oocyte plasma membrane probe than porcine oocyte plasma membrane probe (P < 0.04). These results are consistent with conservation of similar receptor ligand interactions at the gamete plasma membrane among porcine and bovine gametes.

Effect of recombinant boar beta-acrosin on sperm binding to intact zona pellucida during in vitro fertilization

In a previous paper we demonstrated that boar beta-acrosin recombinant proteins were able to bind non-enzymatically to solubilized pig zona pellucida (ZP) glycoproteins. Here we report the participation of boar beta-acrosin in the secondary binding of sperm to intact pig ZP. This was achieved by using two boar recombinant proteins: beta-acrosin and a mutant of the catalytic site, beta-acrosin Ser/Ala(222). Assays of binding between the iodinated recombinant beta-acrosin and whole ZP showed that this binding could be saturated, was specific, and was stable over time. Using autoradiography, we determined that recombinant beta-acrosin bound on the entire surface of the ZP but initially was distributed heterogeneously. This suggests that the ligands for beta-acrosin may not be homogeneously distributed on the ZP. To study the contribution of acrosin in sperm secondary binding to the ZP, we preincubated in vitro-matured oocytes with these recombinant proteins and then performed in vitro fertilization assays. Under the experimental conditions used, binding of beta-acrosin recombinant proteins did not block sperm penetration. These results suggest that there may be other proteins that participate in the secondary binding, and that these proteins may recognize ligands that are different from those blocked by beta-acrosin recombinant proteins.

Analysis of zona pellucida modifications due to cortical granule exocytosis in single porcine oocytes, using enhanced chemiluminescence

The present study was carried out to determine whether modification of zona pellucida (ZP) of a single oocyte following the cortical granule (CG) exocytosis induced by electrical stimulation could be analyzed using enhanced chemiluminescent (ECL) detection of the biotinylated ZP in a porcine oocyte. When a biotinylated ZP derived from a single oocyte matured in vitro was subjected to SDS-PAGE, 3 major bands (ZP1, ZP2 and ZP3) were observed following ECL detection. In these oocytes, CGs staining with fluorescein isothiocyanate (FITC)-labeled peanut agglutinin (FITC-PNA) had formed a monolayer underlying the plasma membrane. Electrical stimulation to induce artificial activation caused a decline in the fluorescent intensity of the CGs with a concomitant decrease in the amounts of ZP1 and ZP2 bands. However, the mobility changes of ZP1 and ZP2 on SDS-PAGE were not found under the inhibitory condition of the CG exocytosis in which oocytes were treated with ethylene glycol-bis(beta-aminoethyl ether) N, N, N',N'-tetraacetic acid (EGTA) or 1, 2-bis(2-aminophenoxy)ethane-N, N, N', N'-tetraacetic acid tetrakis(acetoxymethyl) ester (BAPTA/AM). In addition, when a time-dependent decrease in amounts of ZP1 and ZP2 bands on SDS-PAGE was observed in a single oocyte during activation, a maximum decrease in these bands was detected in oocytes incubated for at least 3.5 h after electrical stimulation. These results show that the method employed, ECL detection of the biotinylated ZP of a single oocyte, is a valuable tool for the analysis of ZP modification resulting from a decrease in amounts of ZP1 and ZP2 glycoproteins in combination with exocytosis of CGs, and that the prolonged period after activation is required for complete ZP modification in porcine oocytes.

Occurrence of reducing terminal N-acetylglucosamine 3-sulfate and fucosylated outer chains in acidic N-glycans of porcine zona pellucida glycoproteins

Structures of acidic N-glycans released from porcine zona pellucida glycoproteins by hydrazinolysis were studied. The results indicated that the acidic glycans are of mono- to tetraantennary complex-type with and without N-acetyllactosamine repeating units. Sulfated residues are not only located at the C-6 position of GlcNAc included in the N-acetyllactosamine repeating units, but also at the C-6 position of GlcNAc in the non-repeated antennae and at the C-3 position of reducing terminal GlcNAc residue. Analysis of the oligosaccharide fragments released by endo-beta-galactosidase digestion and by hydrazine/nitrous acid treatment also revealed that various sulfated and non-sulfated forms of fucosylated structures such as Fucalpha1 --> 2Galbeta1 --> 4(+/-SO3- --> 6)GlcNAc (type 2H), Galbeta1 --> 4(Fucalpha1 --> 3)(+/-SO3- --> 6)GlcNAc(Lex) and Fucalpha1 --> 3 or 4(+/-SO3- --> 6)GlcNAc, are expressed in the repeated outer chain moieties.

Characterization of the functional domains of boar acrosin involved in nonenzymatic binding to homologous zona pellucida glycoproteins

During the first steps of the gamete interaction, the proacrosin/acrosin system seems to play a crucial role in the secondary binding, holding acrosome-reacted spermatozoa during their passage through the zona pellucida. To analyze the functional domains of acrosin, we decided to express recombinant boar acrosin proteins in bacteria and to study their binding capacities to zona pellucida glycoproteins (ZPGPs). The expressed proteins were immunodetected by Western blot with a polyclonal antiacrosin antibody. The recombinant truncated beta-acrosin has a typical hyperbolic curve of a zymogen enzymatic activation. Three of the five recombinant forms (truncated beta-acrosin, Ser/Ala222-truncated beta-acrosin, and truncated beta-acrosin "heavy chain") had the ability to bind ZPGPs. The two shorter forms (the amino and carboxy termini of truncated beta-acrosin) failed to bind. The catalytic site mutant (Ser/Ala222) of truncated beta-acrosin does not differ from the recombinant truncated beta-acrosin in its mechanism of interaction to ZPGPs, indicating that this secondary binding is done by a nonenzymatic process. Our results show that binding between acrosin and ZPGPs depends on the secondary and tertiary structures of acrosin and does not depend on an active catalytic site.

Differential expression of ZPC in the bovine ovary, oocyte, and embryo

Using nonradioactive in situ hybridization (ISH), the mRNA encoding the zona glycoprotein bZPC was localized in bovine ovaries, oocytes, and embryos. In the ovary, the distribution of the mRNA was correlated with the developmental stage of the follicle. Whereas in primordial and primary follicles the mRNA was predominantly seen in the oocyte, it was found in both the oocyte and the follicle cells of secondary and tertiary follicles. In 2-day-old embryos produced by in vitro fertilization (IVF), no mRNA encoding ZPC could be demonstrated. Immunoblotting using monospecific polyclonal antibodies against porcine ZPC revealed a distinct band at a molecular weight of 47 kD in the ovarian cortex of cows, calves, and fetuses as well as in bovine follicle cells. Immunohistochemistry using the ZPC antibody displayed a strong signal in the zona pellucida of bovine oocytes and 2- to 6-day-old embryos as well as in the follicle cells. Our results show that during follicular development bovine ZPC is synthesized by the oocyte of the primary follicle and by both the oocyte and the follicle cells of the secondary and tertiary follicle. After fertilization, the synthesis of the zona protein is finished.

Hetero-oligomerization-dependent binding of pig oocyte zona pellucida glycoproteins ZPB and ZPC to boar sperm membrane vesicles

The zona pellucida surrounding the pig oocyte contains two Mr 55,000 glycoproteins, pZPB and pZPC, which are orthologues of mouse zona proteins ZP1 and ZP3, respectively. We previously reported that isolated boar sperm membrane vesicles possess high affinity binding sites for partially purified pZPB, but not pZPC. Interestingly, co-incubation experiments also implicated pZPB-pZPC complexes as potential ligands. We now report that when depleted of a minor pZPC contaminant by size exclusion chromatography, pZPB lacks independent binding activity. In solid phase binding assays employing immobilized boar sperm membranes, pZPB failed to compete with biotin-(pZPB+pZPC) probe, and biotin-labeled pZPB yielded negligible binding. However, when co-incubated with pZPC prior to the binding assays, pZPB acted as a potent competitor, and biotin-labeled pZPB exhibited high affinity, saturable binding. Binding activity was attributed to pZPB-pZPC heterocomplexes, which were detected in co-incubation mixtures by size exclusion chromatography and Western blot analysis. In the pig, therefore, sperm membranes possess a zona-binding protein with high affinity sites for pZPB-pZPC heterocomplexes, but not free glycoprotein subunits. Consequently, associative interactions between zona molecules can contribute toward both the assembly of the zona matrix and generation of ligands important for sperm-zona interactions.

cDNA cloning and sequence analysis of the Xenopus laevis egg envelope glycoprotein gp43

The glycoproteins of the Xenopus laevis egg envelope function in fertilization and development. As the unfertilizable coelomic egg transits the pars recta region of the oviduct, it is converted to a fertilizable egg by limited proteolysis of the envelope glycoprotein gp43 to gp41. This conversion is caused by an oviductally secreted serine active site protease, oviductin. We cloned a cDNA for gp43 from an oocyte cDNA library. The cDNA encoded a 454 amino acid protein homologous to the ZPC family of glycoproteins previously shown to be present in mammalian and fish egg envelopes. Conserved ZPC domains and motifs present in the Xenopus sequence included a signal peptide sequence, an N-linked glycosylation site, and 12 aligned Cys residues. In mammalian and Xenopus sequences, a furin-like (convertase) site and a C-terminal transmembrane domain were present reflecting the biosynthesis of ZPC in these species via the secretory glycoprotein pathway. However, fish envelope glycoproteins lack these sequences since they are synthesized via a different route (in the liver, transported to the ovary, and assembled into the egg envelope surrounding the oocyte). Consensus amino acid residues were identified by sequence comparisons of seven ZPC family members; 19% of the amino acid residues were invariant and 48% of the residues were identical in at least four of the seven sequences. The consensus sequence was used to make structure-fertilization function predictions for this phylogenetically conserved family of glycoproteins.

In vitro fertilizing capacity of frozen-thawed boar semen

We describe a porcine semen cryopreservation technique and assess the in vitro fertilizing capacity of the frozen-thawed spermatozoa. The thawed spermatozoa did not lose the physiological properties of motility, viability, and acrosome reaction or capacity to fertilize in vitro. Immediately after thawing, the spermatozoa showed 51% mean motility, 60% viability, and 5% induced acrosome reaction. After 2.5 h of incubation in TALP medium, the spermatozoa exhibited 61% motility, 63% viability and 40% induced acrosome reaction. The average in vitro fertilization capacity of thawed spermatozoa was 68% compared with that of spermatozoa from fresh semen (85%). The percentage of polyspermy was highly variable, with frozen-thawed samples ranging from 0 to 28% and fresh samples from 0 to 30%. The results obtained with frozen semen from 5 boars of different breeds did not show considerable variation. This suggests that the freezing-thawing technique is reproducible and adequate for in vitro fertilization.

Localization of the mRNA encoding the zona protein ZP3 alpha in the porcine ovary, oocyte and embryo by non-radioactive in situ hybridization

The mRNA of the zona pellucida glycoprotein ZP3 alpha was localized in frozen sections of pig ovaries, isolated oocytes and early embryos by in situ hybridization using biotinylated oligonucleotide probes. In follicles, the distribution of mRNA for ZP3 alpha was correlated with the developmental stage: in primordial and primary follicles, the mRNA was shown to be predominantly localized in the oocyte. In secondary follicles, mRNA was found in both the oocyte and follicle cells. In tertiary and preovulatory follicles, the follicle cells showed distinct staining, whereas the oocyte was labelled weakly. In the early embryo, i.e. 2 days after fertilization, mRNA for ZP3 alpha could not be demonstrated. Our results suggest that, in the pig, the zona pellucida protein ZP3 alpha is synthesized by the oocyte and the follicle cells in sequence. After fertilization, synthesis of ZP3 alpha is terminated.

Localization of epitopes for monoclonal antibodies at the N-terminus of the porcine zona pellucida glycoprotein pZPC

Zona pellucida glycoproteins play an important role in fertilization. In this study, attempts have been made to identify and define epitopes of monoclonal antibodies (mAbs) possessing contraceptive efficacy in vitro. The porcine zona glycoprotein pZPC, a homologue of mouse/human ZP3, was reduced and alkylated and subsequently digested with trypsin. Reverse-phase HPLC of the tryptic digest yielded twenty two peaks (T1-T22). When tested against mAbs reactive against sequential determinants on pZPC, T11 was immunoreactive with two mAbs, mAb-455 and mAb-467, as shown by antigen inhibition ELISA. IC50 values of 3.1 nM and 8.6 nM were recorded versus mAb-455 and mAb-467 respectively, and approximated the IC50 values obtained with intact pZPC. Amino acid analysis, Edman degradation, and FAB-MS identified T11 as the N-blocked decapeptide pyro-Gln-Pro-Val-Trp-Gln-Asp-Glu-Gly-Gln-Arg derived from the N-terminus of pZPC. Synthesis of overlapping octapeptides further identified VWQDE and WQDE as the minimum motifs with antigenic activity for mAb-455 and mAb-467, respectively. Glycine replacement peptides confirmed residues W,Q,E as critical for binding mAb-455 and W,Q,D,E as critical for binding mAb-467. Both mAbs inhibited binding of boar sperm to zona-encased porcine oocytes. These results, the first to define peptide epitopes of porcine zona glycoprotein, will assist in the design of an immunocontraceptive vaccine based on synthetic peptides corresponding to pZPC or its homologues in other species.

Composition of human zona pellucida as revealed by SDS-PAGE after silver staining

The macromolecular composition of zona pellucida (ZP) isolated from human oocytes and embryos was characterized by one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (1-D- and 2-D-SDS-PAGE) under reducing conditions after silver staining. ZP specimens obtained after in vitro fertilization were removed from pools of heavily fragmented embryos and inseminated oocytes that failed to fertilize. For unfertilized oocytes, two major bands with an apparent molecular weight of, respectively, 96 and 76-54 kDa were observed after 1-D-SDS-PAGE and silver staining. When ZP were isolated from fragmented embryos, the electrophoretic pattern showed a marked attenuation of the 96-kDa band. Silver-stained 2-D-SDS-PAGE analysis of ZP components from unfertilized oocytes revealed the presence of four protein trains: ZP1 (Mr = 92-80 kDa, pl = 4.9-5.9), ZP2 (Mr = 66-58 kDa, pl = 5.0-6.0), ZP3H (high) (Mr = 72-58 kDa, pl = 3.5-5.1), and ZP3L (low) (Mr = 62-54 kDa, pl = 3.5-5.1). The human ZP3 family (ZP3H and ZP3L) showed marked heterogeneity. Fertilization-associated changes were apparent in the electrophoretic pattern. ZP1 (Mr = 92-86 kDa, pl = 5.0-5.8) displayed a dramatic decrease in intensity, and a new component had migrated to a position similar to that of ZP2. This modification may have been responsible for one aspect of the zona reaction, and could have contributed to a zona block to polysperma.

Comparison of the ability of progesterone and heat solubilized porcine zona pellucida to initiate the porcine sperm acrosome reaction in vitro

It has been previously shown that progesterone can initiate the acrosome reaction (AR) of capacitated human and hamster sperm in vivo. We report here that progesterone can initiate a morphologically normal AR in porcine sperm that have undergone capacitation in a Hepes-buffered medium in vitro. In addition, we have compared the abilities of progesterone and heat-solubilized porcine zona pellucida (zona) to initiate the porcine sperm AR. Capacitated porcine sperm were treated with 1 micrograms/ml progesterone, 150 micrograms/ml porcine zona, or solvent control for 10 min. After treatment, sperm were incubated with the supravital dye Hoechst 33258, fixed and the acrosomal status determined in the previously viable sperm by fluorescence microscopy with fluorescein isothiocyanate-labeled Pisum sativum agglutinin (FITC-PSA). There was no significant difference between the percentage of AR initiated by zona compared to that initiated by progesterone. In order to determine whether there was a synergistic interaction between the two AR initiators, both were added simultaneously to capacitated porcine sperm at optimal (1 microgram/ml progesterone, 150 micrograms/ml zona) and suboptimal (75 ng/ml progesterone and 75 micrograms/ml zona) concentrations. Simultaneous addition of the two AR-initiators at the two concentrations stimulated an additive AR-initiating response, rather than a synergistic one. Several possible explanations for the additive results are discussed.

Inhibition of pig oocyte in vitro fertilization by the action of components of the zona pellucida

The aim of the present study was to determine whether the previous addition of porcine zona pellucida (ZP) components to spermatozoa of the same species has an inhibitory effect on in vitro fertilization (IVF). Boar spermatozoa were exposed to whole porcine solubilized zona pellucida (SZP), ZP glycoproteins (55 kDa and 90 kDa) and peptides (37 kDa, 40 kDa and 68kDa). Doses tested were 40, 70 and 100 mug/ml. In vitro fertilization was clearly inhibited by each component when the oocytes were compared with those fertilized with untreated spermatozoa. All the components had an effect in a dose dependent manner.

Isolation and partial purification of plasma membrane from porcine oocytes

Egg plasma membrane (EPM) was isolated in comparatively large amounts from porcine slaughterhouse ovaries. Ovaries were minced, and the oocyte containing fluid was filtered to retrieve zona pellucidae-intact oocytes. The oocytes were homogenized and filtered again to remove zona pellucidae. The egg filtrate was subjected to differential centrifugation to remove membrane bound organelles and the remaining plasma membrane containing material was pelleted by ultracentrifugation. Plasma membranes were further separated from cellular material by sucrose density gradient centrifugation and were collected from portions of the gradient that correspond to the densities of plasma membrane. The purity of isolated plasma membranes was assessed by membrane marker enzyme analysis and transmission electron microscopy. Activities of the plasma membrane marker enzymes 5' nucleotidase and alkaline phosphatase increased from nondetectable levels in the egg filtrate to relatively high levels in the plasma membrane preparation. Marker enzymes for mitochondrial and lysosomal membranes fell from detectable levels in the egg filtrate to levels that were at the lower limits of the assays to detect in the final preparation. Evidence provided by binding of biotin-labeled EPM to capacitated sperm suggests that the isolated EPM retains its biological activity. The procedure presented here represents a novel method of isolating porcine egg plasma membranes for further study involving sperm-egg interaction.

Large-scale isolation of equine zonae pellucidae

A simple and rapid method is described for the large-scale isolation of cumulus cell-free, zona pellucida-intact equine oocytes. Aspiration of palpable antral follicles present on frozen-thawed equine ovaries was accomplished using a constant vacuum source. The resultant follicular fluid, oocytes, and particulate matter were then filtered through a series of nylon screens of alternating mesh openings in combination with sodium citrate-containing buffer to a final volume of approximately 20 ml. This fluid was transferred to scored Petri dishes and a stereomicroscope was used to locate the oocytes for futher processing or storage. The methodology described is inexpensive, time-efficient, and the recovery rate is similar to or better than other methods previously described for equine oocyte recovery. Collected oocytes are adequate for biochemical evaluation of the equine zona pellucida (EZP) as well as sperm-egg binding assays.

Identification of porcine oocyte 55 kDa alpha and beta proteins within the zona pellucida glycoprotein families indicates that oocyte sperm receptor activity is associated with different zone pellucida proteins in different mammalian species

Porcine zona pellucida (pZP) glycoprotein 55 kDa is composed of two core polypeptides, denominated alpha and beta. Sperm receptor activity has been shown to be associated with the oligosaccharide structures attached to the pZP55 alpha component. Here, we report a simple one-step HPLC procedure for the isolation of the alpha- and beta-components of the 55 kDa pZP proteins after enzymatic partial deglycosylation. N-Terminal sequence and protein chemical analysis of native proteins and of internal peptides from the alpha and the beta forms has established their homology with the rabbit 55 kDa zona pellucida glycoprotein and mouse ZP3, respectively. This, in turn, is relevant for a standardization of the ZP nomenclature in mammalian species. Moreover, our results imply that the sperm receptor activity in diverse mammalian species reside on oligosaccharide chains attached to nonhomologous zona pellucida glycoproteins. We hypothesize that acquisition of species-specific activity on the oocyte zona pellucida may thus be related to a species-specific glycosylation process.

O-linked neutral sugar chains of porcine zona pellucida glycoproteins

The O-linked sugar chains were liberated from porcine zona pellucida glycoproteins by alkaline-borohydride treatment and the structures of neutral oligosaccharides were determined. The major oligosaccharides had the following structures with type-1 cores, (Gal beta 1-->4GlcNAc beta 1-->3)1 3-Gal bdta 1-->3N-acetylgalactosaminitol (54%) and GlcNAc beta 1-->3(Gal beta 1-->4GlcNAc beta 1-->3)0-1Gal beta 1-->3N- acetylgalactosaminitol (16%). Approximately 6% of the oligosaccharides had the structure with a type-3 core, Gal beta 1-->4GlcNAc beta 1-->3N-acetylgalactosaminitol. Oligosaccharides having alpha-galactose (2%) and beta-GalNAc (4%) at their non-reducing termini were also found as minor components.

Antifertility effect of active immunization with ZP4 glycoprotein family of porcine zona pellucida in hamsters

Female golden hamsters were immunized with solubilized porcine zona pellucida (s-PZP) or ZP4 glycoprotein family isolated from s-PZP by preparative SDS-PAGE. Both antigen preparations induced production of antibodies which reacted not only with porcine zona pellucida but also with the hamster zona pellucida. The hamsters immunized with solubilized porcine zona pellucida mainly produced antibodies reactive to ZP3, while the hamsters immunized with ZP4 mainly produced antibodies reactive to ZP4. The former animals became permanently infertile but the infertility in the latter animals was temporary and they became pregnant later. Histological studies revealed that the ovarian follicles in hamsters immunized with s-PZP were completely destroyed leaving only atrophic follicle-like cell clusters, while in the ovaries of hamsters immunized with ZP4 a number of small follicles with oocytes remained intact. These observations are encouraging for the further characterization of the ZP4 antigens as candidates for the development of a contraceptive vaccine.

Isolation, composition, and biological activity of sugar chains of porcine oocyte zona pellucida 55K glycoproteins

ZP3, a preparation of the 55K families of porcine oocyte zona pellucida, possesses carbohydrate-dependent ligand activity for boar sperm. The aim of the present study was to analyze ZP3 N- and O-linked oligosaccharides with respect to size distribution, composition, and role in sperm-zona recognition events. Digestion of denatured ZP3 with peptide N-glycosidase F (PNGaseF) released the majority of N-glycans which fractionated on Sephadex G-75 resin as a polydisperse population with apparent molecular masses ranging from 1,900-8,200 Da. The higher molecular weight N-glycans were characterized by the presence of strongly anionic sulfated/sialylated polylactosamine structures. Alkaline-borohydride treatment of the PNGaseF-digested core proteins liberated O-glycans as a heterogeneous population of oligosaccharide alcohols, which were fractionated on a Sephadex G-50 column. Compositional analyses indicated sulfated polylactosamine units associated with the higher molecular weight O-glycans. Preincubation of boar sperm with ZP3 or purified O-glycans, but not N-glycans, inhibited subsequent attachment to zona-encased oocytes. Purified O-glycans were, however, 2 to 3 orders of magnitude less effective than ZP3 as competitive ligands. The results document the extreme heterogeneity of the ZP3 carbohydrate moiety, in large part attributable to a broad spectrum of variably sized N- and O-linked sulfated polylactosamines. Ligand competition bioassays suggest that O-glycans mediate, at least in part, the sperm adhesive properties of ZP3 and strongly imply that high-affinity interaction of ZP3 sugar chains with complementary sperm receptors is dependent upon their covalent association with core proteins.

Changes of glycoconjugate contents of the zona pellucida during oocyte growth and development in the golden hamster: a quantitative cytochemical study

We demonstrated here with the high resolution lectin-gold approach and quantitative analysis, changes of glycoconjugates in the hamster zona pellucida (ZP) during oocyte growth and development in the ovary and the oviduct. Glycoconjugates which contain N-acetyl-D-galactosamine as terminal sugar residues are absent in the ovary but are secreted by secretory cells in the oviduct and are added to the ZP of superovulated oocytes during oviductal transit. Glycoconjugates which carry sialic acid as terminal sugar residues appear to be acquired mainly from the ovary. The oviduct contributes little of this particular component to the ZP during the transit of oocytes in the oviduct. On the contrary D-galactose and N-acetylglucosamine associated glycoconjugates, added to the ZP in ovarian follicles, are also secreted by non-ciliated oviductal epithelial cells and these secretory products are transferred to the ZP in significant amount during passage of the oocyte through the oviduct. Lectin-gold labeling of the ZP of superovulated oocytes reveals homogeneous distribution of gold particles throughout the zona matrix. Thus, we conclude that the ZP of hamster superovulated oocytes consists of glycoconjugates that may derive from different origins. Deposition of ZP glycocomponents begins in the ovary. Similar and new glycoconjugates, secreted by oviductal non-ciliated secretory cells, are added to the ZP of oocytes during oviductal transit. At this stage the ZP is made up of a homogeneous matrix of glycoconjugates.

Isolation, characterization, and localization of the zona pellucida binding proteins of boar sperm

In order to isolate the putative zona pellucida-binding proteins (ZPBPs) from boar spermatozoa, a new, simple method has been developed. The new isolation strategy made the most of the highly specific interactions between the components of the gametes. Detergent-extracted boar sperm proteins were submitted to affinity chromatography on a ZP-Sepharose column. SDS-PAGE analyses of the retained fraction under reducing conditions revealed that in addition to a component of Mr 38,000, the predominant ZPBPs contained at least three low molecular weight proteins (Mr less than 20 kDa). The isolated ZPBPs were effective in blocking sperm-oocyte binding in vitro. Using immunofluorescence microscopy, the ZPBPs were shown to be localized primarily in the sperm head, especially in the acrosomal cap region.