Changes in exposed membrane proteins during in vitro capacitation of boar sperm

ILA 147 immunoreactivity of the bull spermatozoa membrane during epididymal maturation

A cytochemical quantitative study was carried out to detect immunostaining of bull spermatozoa during epididymal maturation using an ILA 147 monoclonal antibody and a standard immunoperoxidase method. This antibody recognizes a bovine panleukocyte determinant. Microdensitometric measurements were made on spermatozoa collected from different sites of the male genital tract (caput, corpus and cauda epididymidis and ductus deferens). On the basis of ILA 147 staining, at least 5 subpopulations of sperm cells from each site of the genital tract were found. These subpopulations showed: 1) immunostaining in the acrosome domain and in the cytoplasmic droplet in a proximal position; 2) immunostaining in the acrosome domain and in the distal cytoplasmic droplet; 3) immunostaining in the acrosomal region and lack of a cytoplasmic droplet; 4) immunostaining only in the cytoplasmic droplet; 5) lack of a cytoplasmic droplet and absence of staining of the head. The possible relationship between the presence of ILA 147 on the sperm head and the maturation process was evaluated, and we suggest that the most significant changes in ILA 147 expression occur in the corpus epididymidis. The absence of immunocytochemical staining in some spermatozoa may be related to plasma membrane damage due to spontaneous peroxidative damage of lipids.

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.

The storage of pure ram semen at room temperature results in capacitation of a subpopulation of spermatozoa

We investigated whether storage of pure ram semen at room temperature would facilitate the sperm capacitation process, as assessed by means of the chlortetracycline method. Objective motility, membrane integrity and ability of spermatozoa to undergo acrosome reaction induced by A23187 for 15 min were simultaneously evaluated to gain further insight into this process. Storage for 4 h at room temperature had a clear capacitating effect in approximately 50% of spermatozoa and increased their ability to respond to A23187. Beyond that time, the percentage of motility and membrane integrity remained unchanged. Moreover, storage did not alter the ability of those spermatozoa that remained noncapacitated under these conditions to become capacitated in SOF-m medium. Storage for 4 h increased the percentage of spermatozoa showing swelling of the apical ridge from 3 to 13%. In conclusion, storage of ram semen at room temperature for 4 h in the dark has a marked capacitating effect on a subpopulation of spermatozoa, without changes in motility or membrane integrity, and a low effect on the appearance of the acrosome. Since semen storage is generally included in different IVF protocols, the results presented here contribute toward a clearer understanding of its role in these procedures.

Monoclonal antibodies reacting against capacitated but not with freshly ejaculated boar spermatozoa

PROBLEM

The involvement of individual sperm proteins in differentiation of antigenically specific and functionally defined regions on sperm membrane has not yet been completely elucidated.

METHOD

BALB/c mice were immunized with live capacitated boar spermatozoa and used for production of monoclonal antibodies (MAbs). ELISA, IIF, SDS-PAGE, IVF, and cytologic methods were used for selection and biological characterization of MAbs as well as for identification of corresponding antigens.

RESULTS

MAb1F10, MAb2E2, and MAb4B12 react with antigens in the acrosome portion of live capacitated spermatozoa, MAb 1F10 reacted with human sperm cells along with those from bull, ram, mouse, dog, whereas MAb2E2--with mouse's spermatozoa and MAB4B12-with bull's, mouse's, and dog's spermatozoa. Some glycolytic enzymes seemed to reduce mildly the reactions of the MAbs with enzyme treated sperm cells; proteolytic enzymes eliminated the binding of MAbs to the sperm acrosome. These MAbs have no sperm agglutinating and/or sperm-immobilizing activities and reduced the number of spermatozoa binding to zona pellucida.

CONCLUSIONS

MAb1F10, MAb2E2, and MAb4B12 seemed to recognize membrane associated antigens with potential role in the initial stages of fertilization, specific for capacitated but not for freshly ejaculated spermatozoa.

A 70 kDa protein is transferred from the outer acrosomal to the plasma membrane during capacitation

Bull sperm plasma and outer acrosomal membranes were analyzed by SDS-PAGE. Analysis of the plasma membrane proteins revealed the presence of a 70 kDa band the prominence of which is enhanced after capacitation. This protein was found to bind to zona pellucida intact oocytes. PAGE analysis of outer acrosomal membrane proteins also reveals the presence of a 70 kDa band, but its prominence decreases after capacitation. This protein also binds to zona pellucida intact oocytes. Furthermore, the 70 kDa outer acrosomal membrane protein is recognized in Western blot analysis by antibodies to plasma membrane proteins and vice versa. The results indicate that the 70 kDa acrosomal and plasma membrane proteins are the same. This 70 kDa protein would thus be a zona pellucida binding protein which is initially stored in the outer acrosomal membrane and transferred to the plasma membrane during capacitation, enabling it to function in egg-sperm binding.

Electron microscopic study of human sperm membrane isolation

OBJECT

Our purpose was to isolated pure, homogeneous human sperm membranes, free of cellular contaminants.

METHODS

Donor semen samples collected after masturbation were stored at -70 degrees C and eventually pooled. Each attempt at sperm membrane isolation required 800 x 10(6) spermatozoa which were sonicated by ultrasound (40% output; Vibra Cell). The effect of sonication time (3 x 5, 3 x 15, and 180 sec) on membrane isolation was investigated. Sonicated samples were centrifuged (500 g, 5 min) and the supernatant was pipetted off. The supernatant of the centrifuged sample was layered on either a sucrose cushion (supernatant on 1.6 M sucrose) or a discontinuous sucrose gradient and centrifuged (100,000 g, 1 hr). Contents of supernatants of sonicated samples and fractions (sucrose interfaces) were then fixed in 1.0% tannic acid and 2.5% buffered glutaraldehyde and examined electron microscopically using standard procedures.

RESULTS

(1) The optimal sonification time was found to be 3 x 15 sec. (2) Membrane isolation using a sucrose cushion was found to be inadequate, showing significant cellular contamination. (3) Sperm membrane isolation from the sucrose interface between 0.75 and 1.05 M sucrose was found to be most effective.

CONCLUSION

The advantage of this method is its simplicity. The drawback of this method is the large number of spermatozoa required for membrane purification.

Localisation and capacitation-dependent loss of buffalo sperm-coating antigens shared with rat sperm

The heterodimeric sperm-coating protein CFS was previously localised on the middle-piece region of rat spermatozoa by anti-CFS rabbit antibodies. CFS-immunorelated antigens were detected in the secretion of the water buffalo seminal vesicle by protein electrophoresis and Western blotting. Spermatozoa from buffalo epididymal cauda were incubated with the rat antigen and, upon immunostaining with anti-CFS antibodies and goat anti-rabbit fluorescein isothiocyanate (FITC)-conjugated IgGs, CFS was found attached on both the post-acrosomal region and the tail. Indirect immunofluorescence analysis permitted the localisation of CFS-related antigens on the same domains of buffalo ejaculated spermatozoa. These results suggest that the buffalo antigens not only share some epitopes with the homologous rat antigen but may also have some of its functional properties. Ejaculated spermatozoa were capacitated in vitro and then assayed for their content of CFS-like antigens. An inverse relationship was found between the levels of capacitation and the amounts of antigens detected, thus suggesting that the in vitro treatment was effective at removing CFS-related proteins from the cell surface. Titration of these proteins to monitor plasma membrane changes during sperm manipulation or to evaluate sperm quality is proposed.

Adsorption of oviductal fluid proteins by the bovine sperm membrane during in vitro capacitation

125I-labeled oviductal fluid (ODF) proteins and antiserum to ODF were used to determine whether ODF proteins associate with the sperm membrane during in vitro capacitation. Luteal and nonluteal pools of ODF were obtained from oviduct catheters during the estrous cycle. Washed sperm (50 x 10(6) sperm/ml) were incubated up to 4 h in a protein-free modified Tyrode's medium (MTM), or MTM supplemented with 40% ODF, or 0.5 ng 125I-labeled ODF proteins. Solubilized sperm membrane proteins and incubation media containing ODF proteins were separated by gel electrophoresis. Membranes isolated from bovine sperm, previously incubated with ODF, adsorbed five 125I-proteins: A doublet at 85-95 kDa, and others at 24, 34, 53, and 66 kDa. The amount of 66 kDA 125I-protein associated with the sperm decreased during the incubation, whereas the amount of 85 to 95-kDa protein did not. Western blot analyses also detected the presence of ODF proteins (53, 66, 85-95, and 116 kDa) in solubilized membranes from sperm incubated in ODF. The 85 to 95-kDa protein in ODF decreased in apparent molecular weight by 5 kDa when associated with the sperm membrane. At 53 kDa, ODF proteins which associated with sperm were transformed from two to three separate proteins. These studies indicate that the surface of sperm is modified by adsorption of ODF proteins to the membrane during in vitro capacitation.

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

A group of low Mr (16 kDa-23 kDa) glycoproteins on ejaculated boar spermatozoa have been shown to have high affinity for homologous zona pellucida glycoproteins (ZPGPs). These ZPGP binding proteins are derived from seminal plasma as shown by their absence from epididymal spermatozoa and their presence in seminal plasma as identified by N-terminal amino acid sequence analysis. They bind to ZPGPs by a polysulphate recognition mechanism similar to that found for proacrosin-ZPGP interactions. The haemagglutination activity of boar seminal plasma is also associated with these low Mr glycoproteins. It is suggested that they play a role in regulating the rate of sperm capacitation and survival in the female reproductive tract.

Detection of a sperm-coating antigen in the semen of Bubalus bubalis

1. Surface antigens of B. bubalis spermatozoa were solubilized by Triton X-100 and EDTA; the sperm extract was used to raise antibodies in rabbits. 2. Two major polypeptides, immunoprecipitated from the seminal plasma by the antibodies against the sperm extract, exhibited the same electrophoretic mobilities of two immunorelated sperm surface antigens. 3. The two polypeptides were isolated from the seminal plasma, by a multi-step chromatographic procedure, and found subunits of a single protein (MW 30,000), called SP 30. 4. The SP 30 protein bound in vitro to the postacrosomal region of homologous spermatozoa from cauda epididymis. 5. The localization of the sperm-coating antigen on the cell surface is compatible with a role in the fertilization process.