Characterization of low Mr zona pellucida binding proteins from boar spermatozoa and seminal plasma

Immunocontraceptive target repertoire defined by systematic identification of sperm membrane alloantigens in a single species

Sperm competence in animal fertilization requires the collective activities of numerous sperm-specific proteins that are typically alloimmunogenic in females. Consequently, sperm membrane alloantigens are potential targets for contraceptives that act by blocking the proteins' functions in gamete interactions. Here we used a targeted proteomics approach to identify the major alloantigens in swine sperm membranes and lipid rafts, and thereby systematically defined the repertoire of these sperm-specific proteins in a single species. Gilts with high alloantibody reactivity to proteins in sperm membranes or lipid rafts produced fewer offspring (73% decrease) than adjuvant-only or nonimmune control animals. Alloantisera recognized more than 20 potentially unique sperm membrane proteins and five sperm lipid raft proteins resolved on two-dimensional immunoblots with or without prior enrichment by anion exchange chromatography. Dominant sperm membrane alloantigens identified by mass spectrometry included the ADAMs fertilin α, fertilin ß, and cyritestin. Less abundant alloantigens included ATP synthase F1 β subunit, myo-inositol monophosphatase-1, and zymogen granule membrane glycoprotein-2. Immunodominant sperm lipid raft alloantigens included SAMP14, lymphocyte antigen 6K, and the epididymal sperm protein E12. Of the fifteen unique membrane alloantigens identified, eleven were known sperm-specific proteins with uncertain functions in fertilization, and four were not previously suspected to exist as sperm-specific isoforms. De novo sequences of tryptic peptides from sperm membrane alloantigen "M6" displayed no evident homology to known proteins, so is a newly discovered sperm-specific gene product in swine. We conclude that alloimmunizing gilts with sperm membranes or lipid rafts evokes formation of antibodies to a relatively small number of dominant alloantigens that include known and novel sperm-specific proteins with possible functions in fertilization and potential utility as targets for immunocontraception.

Polyspermic penetration in porcine IVM-IVF systems

Although techniques for in vitro production of porcine embryos have proceeded very rapidly during the past decade, polyspermic penetration still remains a persistent obstacle to porcine in vitro fertilization (IVF) systems. Considerable research on in vitro polyspermic penetration in porcine in vitro-matured (IVM) oocytes has been undertaken to try to solve this problem. In the current paper, recent advancements in overcoming the problems of polyspermy in porcine IVF systems are reviewed. Partial induction of the acrosome reaction of boar spermatozoa in IVF media that contain caffeine is likely to be one of the major causes of polyspermy. A reduction in the number of incompletely acrosome-reacted spermatozoa, which can bind tightly to the zona pellucida and mask free sperm receptors of the zona pellucida, could reduce the incidence of polyspermic penetration; however, morphological differences in the reaction of the zona pellucida have been observed between IVM and ovulated oocytes, which suggests that altered zona morphology may be another cause of polyspermic penetration. It has been shown that the developmental ability of polyspermic porcine embryos to the blastocyst stage is similar to that of normal embryos but that developmental competence to term is much lower. To overcome the current problems of polyspermy, it is suggested that future efforts should be focused on controlling boar sperm function and/or sperm-zona binding to achieve the final maturation associated with normal zona modifications of porcine oocytes at fertilization.

Expression of progesterone receptor(s) during capacitation and incidence of acrosome reaction induced by progesterone and zona proteins in boar spermatozoa

Sperm acrosome reaction (AR) is a prerequisite step for in vivo fertilization. In the vicinity of the oocyte, zona protein(s) (ZP) and progesterone (P4), a component of follicular fluid, are proven to be responsible for physiological AR induction. In the present study, a thorough analysis of the role of the progesterone receptor (PR) in this processing including in vitro physiological studies and biochemical isolation and characterization of the receptor protein was conducted. Following capacitation for 0, 2, 4 and 6h, pooled fertile boar semen samples (n=6) with >70% sperm motility were labeled with P4-BSA-FITC (100 microg/ml) to detect the activation of PR. Parallel sperm samples were treated with P4 (10 microg/ml) for 20 min to test AR inducing efficiency at different time points. To compare the ability of ZP and P4 to induce AR, spermatozoa capacitated in a modified medium supplemented with 1mg/ml heparin for 4h, were then treated with heat solubilized ZP (150 microg/ml), P4 (10 microg/ml) or ZP+P4 for 20 min. FITC-peanut agglutinin staining was applied to observe the disrupt acrosomal morphology. A purification protocol for crude boar sperm membrane proteins was developed based on ligand-receptor affinity chromatography procedures. The PR proteins were then identified by using mAb C262 raised against intracellular PR, combined with second antibody (SDS-PAGE, Western blotting). Their N-terminal amino acid sequence was determined. The amount of PR-activated spermatozoa was enhanced with time (onset: 27+/-5%, 2h: 41+/-4%, 4h: 49+/-3% and 6h: 52+/-4%, mean+/-S.E., n=6) as evidenced by increasing percentage of spermatozoa with completed cap fluorescent staining. In parallel sperm samples, percentages of AR induced by P4 were 9+/-2, 14+/-2, 18+/-2, and 24+/-2%, respectively. In solvent control at all time points, less than 10% spermatozoa had undergone AR. Capacitation for 4h or greater time periods resulted in optimal percentage of PR-activated and acrosome-reacted spermatozoa. After sperm incubation in heparin-medium, ZP+P4 treatment induced greater amounts of AR than either P4 or ZP alone (13+/-1% compared with 8+/-1 and 10+/-1%, P<0.01). Inducing capacity of P4 was comparable to that of ZP. The molecule weights of two apparent PR molecular masses were detected to be at Mr 74 kDa and Mr 63 kDa. N-terminal amino acid sequence of 74 kDa protein was XPXNIVLIFADXLXY, which had 78% homology to arylsulfatase A and 88% homology to 72 kDa protein from boar spermatozoa. The activation of PR is associated with the capacitating process and that appears to be required for P4-induced AR. P4 and ZP appear to be equally capable of independently inducing the AR but lack synergetic or additive effects in this induction process. Both might represent alternative pathways thus resulting in alternative systems for induction of the prerequisite acrosomal exocytosis (supported by NSC 90-2313-B-005-114; 91-2313-B-005-131).

Organization of the human gene encoding the epididymis-specific EP2 protein variants and its relationship to defensin genes

The EP2 gene codes for at least nine message variants that are all specifically expressed in the epididymis. These variants putatively encode small secretory proteins that differ in their N- and C-termini, resulting in proteins that can have little or no sequence similarity to each other. We have isolated and sequenced the human EP2 gene to determine the molecular origin of these variants. The EP2 gene has two promoters, eight exons, and seven introns. Exons 3 and 6 encode protein sequences homologous to beta-defensins, a family of antimicrobial peptides. This sequence homology and the arrangement of promoters and defensin-encoding exons suggest that the EP2 gene originated from two ancestral beta-defensin genes arranged in tandem, each contributing a promoter and two exons encoding a leader sequence and a defensin peptide. The proposed evolutionary relationship between the EP2 gene and defensin genes is supported by the observation that the EP2 gene is located on chromosome 8p23 near the defensin gene cluster and is separated by 100 kilobases or less from DEFB2, the gene for beta-defensin-2. While the EP2 gene transcribes beta-defensin-like message variants, most of the known message variants code for nondefensin proteins or proteins containing only a partial defensin peptide sequence. We suggest that, during its evolution, the EP2 gene has acquired new functions that may be important for sperm maturation and/or storage in the epididymis.

Seminal vesicle production and secretion of growth hormone into seminal fluid

Production of foreign proteins in the tissues of transgenic animals represents an efficient and economical method of producing therapeutic and pharmaceutical proteins. In this study, we demonstrate that the mouse P12 gene promoter specific to the male accessory sex gland can be used to generate transgenic mice that express human growth hormone (hGH) in their seminal vesicle epithelium. The hGH is secreted into the ejaculated seminal fluids with the seminal vesicle lumen contents containing concentrations of up to 0.5 mg/ml. As semen is a body fluid that can be collected easily on a continuous basis, the production of transgenic animals expressing pharmaceutical proteins into their seminal fluid could prove to be a viable alternative to use of the mammary gland as a bioreactor.

Isolation and biological characterization of boar sperm capacitation-related antigen

PROBLEM

Monoclonal anti-capacitated sperm antibody has been used as a probe to identify, isolate, and characterize specific, fertilization-related antigen with some characteristic features that point to its possible significance in immunocontraception.

METHOD OF STUDY

Fast protein liquid chromatography (FPLC), enzyme-linked immunosorbent assay (ELISA), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and isoelectrofocusing were used for isolation, immunochemical and physicochemical characterization of a monoclonal antibody (mAb) 1F10 cognate antigen. Sperm-zona pellucida binding and hemizona assay were used for testing the biological roles of mAb 1F10 and Ag 1F10 in boar and human fertilization processes.

RESULTS

The Ag 1F10 was found to be eluted in the eighth protein peak of FPLC-fractionated Nonidet P40 (NP40) extracts of capacitated boar spermatozoa. The SDS-PAGE and immunoelectrofocusing experiments showed that Ag 1F10 is a protein composed of a single peptide chain with a relative molecular mass of 68/70 kDa and an isoelectric point of 3.5. It was demonstrated that the zona binding activity of spermatozoa preincubated in the presence of mAb 1F10 was significantly inhibited both in porcine and human in vitro fertilization (IVF) systems. A dose-dependent manner of inhibition of the sperm/ligand activities of porcine and human zona pellucida was observed when the effect of purified Ag 1F10 was investigated by its preincubation with zona pellucida.

CONCLUSIONS

It is assumed that the protein bearing the epitope recognized by mAb 1F10 may be accepted as one of the molecules with receptor function in sperm-zona pellucida interaction during fertilization.

Function of human epididymal proteins in sperm maturation

Human post-testicular proteins were cloned by subtractive screening of epididymal cDNA libraries, employing testis as the primary negative control. This method identified six human epididymal cDNAs, named HE1-HE6, which are derived from abundant epididymal mRNAs. With the exception of HE5, which turned out to be identical to the lymphocyte surface antigen CD52, they represented completely novel human gene products. To date, there is little information on their function and the mechanism of their deposition on the sperm surface. Unlike the sperm coating antigens, CD52 binds firmly to the sperm membrane via its GPI anchor during epididymal passage. Its synthesis is carefully regulated by the epididymal epithelium. From the results of both in vivo and in vitro studies it was concluded that androgen and temperature are principal factors synergistically modulating epididymal CD52 expression. The human counterparts of two well-known major rodent epididymal proteins, secretory epididymal glutathione peroxidase (sGPX) and acidic epididymal glycoprotein (AEG = Protein DE), were not cloned by the subtractive screening approach, but by RT-PCR amplification.

Isolation of antiSLIP1-reactive boar sperm P68/62 and its binding to mammalian zona pellucida

Single-step purification of boar sperm P68/62 that is cross-reactive with a polyclonal antibody against sulfolipidimmobilizing protein 1 (SLIP1) was achieved by chromatofocusing. This method is useful for obtaining P68/62 in quantity. The two proteins, P68 and P62, were antigenically related, since the antibody generated specifically against the 68-kDa band reacted with both the 68- and 62-kDa bands. Like rat testis SLIP1, purified boar sperm P68/62 bound to sulfogalactosylglycerolipid (SGG) and inhibited sperm-egg binding in a dose-dependent manner when added exogenously to sperm-egg coincubates. This inhibitory effect occurred at the level of the zona pellucida (ZP), and further studies showed that biotinylated boar sperm P68/62 bound to the ZP of unfertilized mouse eggs. Furthermore, biotinylated boar sperm P68/62 bound to isolated ZP of unfertilized eggs from other species, including pig, rat, cat, dog, and human, as well as to ZP of intact fertilized mouse eggs and preimplantation embryos of various developmental stages, although the degree of its binding to the ZP of intact eight-cell embryos, morulae, and blastocysts was much lower than that of fertilized eggs and two-cell embryos. These results suggest that P68/62 of capacitated sperm must act together with other sperm surface proteins/molecules that regulate zona binding specificity within homologous species and in unfertilized eggs. Together with our previous findings, we suggest that rather than being a true ZP receptor, sperm P68/62 may be involved in the initial step of sperm-ZP binding that is adhesive in nature.

Binding of boar spermatozoa to porcine oocytes: effect of low molecular weight 17-kDa protein

The effect of seminal plasma and low molecular weight ACR.3 (17 kDa) protein on boar spermatozoa-porcine oocyte binding was examined. Boar seminal plasma that contains the sperm-adhesive ACR.3 protein was added to spermatozoa prior to their coincubation with oocytes, and the binding capacity of the spermatozoa so treated was compared to that of untreated cells. Similarly, purified ACR.3 protein, that binds to the egg zona pellucida, was added to noncapacitated spermatozoa, and the binding capacity of treated and untreated cells was again evaluated. In the two cases, the treatment of spermatozoa reduced their capacity to bind to the zona pellucida. We propose that the reduction in binding is due to competition for the ACR.3 binding sites on the zona pellucida between the soluble ACR.3 protein and the ACR.3 protein attached to the sperm surface. Furthermore, sperm-ZP binding was examined in the presence of ACR.3 monoclonal antibody, which specifically reacts with ACR.3 protein. Preliminary results show that addition of ACR.3 monoclonal antibody to a suspension of boar spermatozoa prior to their coincubation with oocytes did not markedly change sperm-zona binding in comparison with the control untreated spermatozoa. Our results suggest that ACR.3 protein may mediate the primary sperm-egg zona pellucida binding, and that it is one of the likely candidates for the primary sperm-ZP binding protein.

Human sperm coating antigen from seminal plasma origin

Sperm surface glycoproteins may be involved in sperm-zona pellucida recognition. Some of these coating proteins are of seminal plasma origin and their expression may change in the process of capacitation and acrosome reaction. Sperm specific monoclonal antibodies (mAb) define the presence and role of sperm membrane associated proteins. We have isolated a monoclonal antibody (SEM-12) specific for human sperm that shows, by indirect immunofluorescence, a discontinuous distribution of the antigen on the head and tail surfaces of non capacitated sperm. This antigen is also present in human seminal plasma as detected by ELISA. The antigen is detectable in sperm of goat, ram, and mouse. Two proteins in the range of 80-84 kDa have been isolated by affinity chromatography with SEM-12 mAb. The same result is obtained by immunoprecipitation. This antibody inhibits sperm motility and acrosome reaction (spontaneous and A23187 ionophore induced.

Cloning of boar SPMI gene which is expressed specifically in seminal vesicle and codes for a sperm motility inhibitor protein

Boar semen contains a seminal plasma motility inhibitor (SPMI) that blocks the motility of demembranated-reactivated spermatozoa as well as of intact spermatozoa. In this paper, we describe the primary structure of SPMI, the coding of boar SPMI cDNA gene and its expression in various porcine tissues. Nucleotide sequence analysis of the 645-bp SPMI cDNA predicts a coded polypeptide of 137 amino acid residues which includes a 21-residue signal peptide and a 116-residue secreted protein. The amino acid sequence of SPMI was found to be highly homologous to AQN-3, a member of spermadhesin family proteins of boar that bind to spermatozoa. Expression of the boar SPMI gene detected by Northern blot analysis revealed that its expression is very abundant in seminal vesicles and specific to this tissue.

Characterization of two glycosylated boar spermadhesins

Boar spermadhesins AQN-1, AQN-3 and AWN form a recently described protein family, synthesized by the sexual accessory glands, and become associated with the sperm head upon ejaculation. They contain 109-133 amino acid residues, two conserved disulphide bridges, are not glycosylated, and have 40-60% primary structure identity. These boar polypeptides are multifunctional proteins, which possess heparin-, serine-protease-inhibitor- and/or zona-pellucida-glycoprotein-binding capability and have, therefore, been implicated in sperm capacitation and sperm-oocyte attachment. AQN-2 (18-20 kDa), however, is unique among boar spermadhesins in that it is the only member of the family which is known to be glycosylated and which possesses weak zona-pellucida-binding but not seminal-plasma-inhibitor-binding ability. In this study we report the structural and functional characterization of the two glycoproteins contained in the AQN-2 fraction. One component is identical with PSP-I, a major porcine seminal plasma protein whose function has not yet been identified, while the second protein is a glycosylated isoform of AQN-3. Here we show that the inability of the glycosylated boar spermadhesins to bind seminal-plasma protease inhibitors as well as the weak binding of glycosylated AQN-3 to zona pellucida glycoproteins is due to the presence of the oligosacharide chain on a conserved asparagine residue. This indicates that modification of a spermadhesin polypeptide framework may serve to modulate its ligand-binding capabilities.

Porcine zona pellucida ZP3 alpha glycoprotein mediates binding of the biotin-labeled M(r) 55,000 family (ZP3) to boar sperm membrane vesicles

The two M(r) 55,000 glycoproteins, ZP3 alpha and ZP3 beta, of porcine zona pellucida copurify as a preparation designated ZP3. Gamete binding assays have implicated ZP3 alpha, but not ZP3 beta, as participating in sperm-zona recognition events. We now report that boar sperm contain membrane-associated binding sites with specificity for ZP3 alpha. Biotin-labeled (b-) preparations of ZP3 bind to intact boar sperm in a saturable manner, with localization on the anterior head region. Membrane vesicles obtained from capacitated sperm by nitrogen cavitation retain b-ZP3 binding sites as determined by an enzyme-linked method employing alkaline phosphatase-conjugated strepavidin. In competitive binding assays using b-ZP3 (0.1 microgram/ml) as probe, heat-solubilized zonae and ZP3 were effective competitors, whereas the nonzona molecules fetuin and fucoidin were not. Digestion of ZP3 with endo-beta-galactosidase, an enzyme that trims polylactosamines, enhanced its affinity for membrane receptors. In contrast treatments such as chemical deglycosylation, pronase digestion, or disruption of disulfide bonds abolished the ligand activity of ZP3. Finally, purified ZP3 alpha was an at least 100-fold better antagonist than purified ZP3 beta. The results demonstrate that binding of b-ZP3 to isolated boar sperm membranes is mediated by sperm receptors with specificity for the ZP3 alpha macromolecular component and reveal a complex contribution of both carbohydrate and protein moieties toward the ligand activity of this sperm adhesive zona molecule.

Molecular cloning and sequence analysis of two porcine seminal proteins, PSP-I and PSP-II: new members of the spermadhesin family

Two full-length cDNAs encoding porcine seminal proteins, PSP-I and PSP-II, have been isolated from a porcine seminal vesicle cDNA library. Nucleotide sequence analysis of the 706-bp PSP-I cDNA predicts a precursor protein of 133 amino acid residues, which includes a 21-residue signal peptide and a 112-residue secreted protein. On the other hand, the complete sequence of the 686-bp PSP-II cDNA reveals a coding sequence for a 21-residue signal peptide and a 116-residue secreted protein. The predicted amino acid sequences agree very well with those determined by conventional amino acid sequence analysis. Alignment of the two cDNA sequences shows an overall 66% sequence homology throughout their entire length. However, the sequence homology is much higher in the 3' untranslated region (72%) than in the coding region (61%). This suggests that these two genes evolved by duplication and divergence from a common ancestral gene. They share about 50% amino acid sequence homology and a similar overall structure with three members of the spermadhesin family.

Binding characteristics and immunolocalization of porcine seminal protein, PSP-I

PSP-I, a 13 kDa protein purified from boar seminal plasma, was found to have about 50% amino acid sequence homology with a family of zona pellucida-binding proteins known as spermadhesins. These proteins are produced by the accessory gland(s) of the male reproductive tract and coat the spermatozoa during ejaculation. In this study, we have investigated the possible biological functions of PSP-I using a solid-phase protein binding assay and its site of synthesis using both Western blot and immunocytochemical analyses. PSP-I was found to bind a number of proteins including endo-beta-galactosidase digested ZP3, soybean trypsin inhibitor, IgA, IgG and alpha-casein, indicating that it may have multiple functions. The protein or carbohydrate structures were not critical in the binding, since polyvinyl sulfate could effectively inhibit the binding of PSP-I to these proteins. Western blot analysis using specific antiserum to PSP-I showed that the protein was present in the seminal vesicle but not in the testes, epididymis or prostate. The protein was revealed by immunocytochemical analysis in the epithelium of seminal vesicles but not in the testes or the epididymis. It is concluded that PSP-I is synthesized by the epithelium of the seminal vesicles, secreted into the semen during ejaculation, and may be involved in various reproductive functions, such as preventing premature acrosome reaction and immunosuppression.