Changes in immunochemical localisation of acrosomal and sperm proteins in boar spermatozoa during capacitation and induced acrosome reaction

Fluorescent analysis of boar sperm capacitation process in vitro

BACKGROUND

Capacitation involves physiological changes that spermatozoa must undergo in the female reproductive tract or in vitro to obtain the ability to bind, penetrate and fertilize the egg. Up to date, several methods have been developed to characterize this complex biological process. The goal of the presented study is to mutually compare several fluorescent techniques, check their ability to detect changes in molecular processes during the capacitation progress and determine their ability to predict the percentage of acrosome reacted (AR) sperm after the exposure to solubilized zona pellucida (ZP). The capacitation process was analyzed using four fluorescent techniques: 1. chlortetracycline (CTC) staining, 2. anti-acrosin antibody (ACR.2) assay, 3. anti-phosphotyrosine (pY) antibody assay, 4. fluorescein isothiocyanate-conjugated phalloidin (FITC-phall) assay. All these methods were tested using fluorescent microscopy and flow cytometry.

RESULTS

All selected methods are capable to detect the capacitation progress of boar sperm in vitro, but there are significant differences in their outcome when using fluorescent microscopy or flow cytometry experimental arrangements and subsequent statistical analysis (KW-ANOVA). Also, the ability to predict the absolute numbers of sperm which will undergo ZP-induced AR differ significantly (CTC and ACR.2 gave the best predictions).

CONCLUSIONS

Our study compared four largely used methods used to characterize capacitation process, highlighted their differences and showed that all are able to detect capacitation progress, CTC and ACR.2 are furthermore able to accurately predict the percentage of AR sperm after ZP-induced AR.

Compartmentalization of the proteasome-interacting proteins during sperm capacitation

Ubiquitination is a stable, reversible posttranslational modification of target proteins by covalent ligation of the small chaperone protein ubiquitin. Most commonly ubiquitination targets proteins for degradation/recycling by the 26S proteasome in a well-characterized enzymatic cascade. Studies using human and non-human mammalian spermatozoa revealed the role of the ubiquitin-proteasome system (UPS) in the regulation of fertilization, including sperm-zona pellucida (ZP) interactions as well as the early events of sperm capacitation, the remodeling of the sperm plasma membrane and acrosome, and for the acquisition of sperm fertilizing ability. The present study investigated the activity of UPS during in vitro capacitation of fresh boar spermatozoa in relation to changes in sperm proteome. Parallel and sequential treatments of ejaculated and capacitated spermatozoa under proteasome permissive/inhibiting conditions were used to isolate putative sperm proteasome-associated sperm proteins in a compartment-specific manner. A differential proteomic approach employing 1D PAGE revealed differences in accumulated proteins at the molecular weights of 60, 58, 49, and 35 kDa, and MS analysis revealed the accumulation of proteins previously reported as proteasome co-purifying proteins, as well as some novel proteins. Among others, P47/lactadherin, ACRBP, ADAM5, and SPINK2 (alias SAAI) were processed by the proteasome in a capacitation dependent manner. Furthermore, the capacitation-induced reorganization of the outer acrosomal membrane was slowed down in the presence of proteasomal inhibitors. These novel results support the proposed role of UPS in sperm capacitation and open several new lines of inquiry into sperm capacitation mechanism.

Effect of estrogens on boar sperm capacitation in vitro

BACKGROUND

Mammalian sperm must undergo a series of controlled molecular processes in the female reproductive tract called capacitation before they are capable of penetrating and fertilizing the egg. Capacitation, as a complex biological process, is influenced by many molecular factors, among which steroidal hormone estrogens play their role. Estrogens, present in a high concentration in the female reproductive tract are generally considered as primarily female hormones. However, there is increasing evidence of their important impact on male reproductive parameters. The purpose of this study is to investigate the effect of three natural estrogens such as estrone (E1), 17beta-estradiol (E2) and estriol (E3) as well as the synthetical one, 17 alpha-ethynylestradiol (EE2) on boar sperm capacitation in vitro.

METHODS

Boar sperm were capacitated in vitro in presence of estrogens. Capacitation progress in control and experimental samples was analyzed by flow cytometry with the anti-acrosin monoclonal antibody (ACR.2) at selected times of incubation. Sperm samples were analyzed at 120 min of capacitation by CTC (chlortetracycline) assay, immunocytochemistry and flow cytometry with anti-acrosin ACR.2 antibody. Furthermore, sperm samples and capacitating media were analyzed by immunocytochemistry, ELISA with the ACR.2 antibody, and the acrosin activity assay after induced acrosomal reaction (AR).

RESULTS

Estrogens stimulate sperm capacitation of boar sperm collected from different individuals. The stimulatory effect depends on capacitation time and is highly influenced by differences in the response to estrogens such as E2 by individual animals. Individual estrogens have relatively same effect on capacitation progress. In the boar samples with high estrogen responsiveness, estrogens stimulate the capacitation progress in a concentration-dependent manner. Furthermore, estrogens significantly increase the number of acrosome-reacted sperm after zona pellucida- induced acrosomal reaction.

CONCLUSIONS

We demonstrate here the stimulatory effect of four different estrogens on boar sperm capacitation in vitro. According to our results, there is significant difference in the response to tested estrogens at different capacitation time and among individual animals. In animals with a high response to estrogens, there is a concentration-dependent stimulation of capacitation and individual estrogens have relatively the same effect. Effects of individual estrogens, differences in the response to them by individual animals, their time and concentration-dependent outcomes further contribute to our knowledge about steroidal action in sperm.

Fine structure and morphology of sterlet (Acipenser ruthenus L. 1758) spermatozoa and acrosin localization

Ultrastructure of sterlet Acipenser ruthenus L. 1758 sperm was examined by scanning and transmission electron microscopy, which allowed us to use various methods for visualizations of different parts of sterlet spermatozoa. Sperm cells possess a head with a distinct acrosome, a midpiece and a single flagellum surrounded by the flagellar plasma membrane. The average length of the head including the acrosome and the midpiece was estimated as 5.14+/-0.42 microm. Nine to 10 posterolateral projections were derived from the acrosome. Three inter-twining endonuclear canals bounded by membranes traversed the nucleus in its whole length from the acrosome to the implantation fossa. Acrosin was located in all the three parts (acrosome, endonuclear canals and implantation fossa). The proximal and distal centrioles located in the midpiece compacted of nine peripheral triplets of microtubules. One cut of the midpiece contained from two to six mitochondria with area of 215+/-85 nm(2) in average. The flagellum was 42.47+/-1.89 microm in length with typical eukaryotic organization of one central pair and nine peripheral pairs of microtubules. It passed through a cytoplasmic channel in the midpiece, which was formed by an invagination at the plasmalemma. The flagellum gradually developed two lateral extensions of its plasma membrane, so-called "fins". Detected morphological variation can be described by four principal component axes corresponding to groups of individual morphometric characters defined on the sperm structures. Correlations among the characters indicate that the sperms are variable in their shape rather than size. Significant variation among examined fish individuals was found only in flagellum and nucleus length. Comparison between the present and previous studies of morphology of sturgeon spermatozoa confirmed large inter- and/or intra-specific differences that could be of substantial taxonomic value.

Immunolocalization of heat shock protein 70 (Hsp 70) in boar spermatozoa and its role during fertilization

The presence and cellular distribution of heat protein 70 (Hsp70) in ejaculated, capacitated, and acrosome-reacted boar spermatozoa was evaluated by immunofluorescence and Western blot; the role of Hsp70 during fertilization was also studied. In freshly ejaculated spermatozoa, Hsp70 immunoreactivity is present in a well-defined triangular-shaped area in the equatorial segment that seems to correspond to the equatorial sub-segment. The distribution of the fluorescent signal changes in capacitated sperm, that exhibit different patterns probably in relation to the stage of capacitation of individual cells; after acrosome reaction Hsp70 immunoreactivity is localized on both a thick sub-equatorial band and a triangle in the equatorial segment. In reacted spermatozoa, Hsp70 seems to be not only relocalized but also translocated from the inner to the outer leaflet of the sperm plasma membrane, as a significant (P < 0.05) increase in the proportion of unfixed cells showing the fluorescent signal has been recorded. No differences in Hsp70 amount between fresh, capacitated, and reacted semen were observed by Western blot. The presence of anti-Hsp70 antibody in the fertilization medium significantly reduced, in a concentration-dependent manner, the fertilization rate of both zona-intact and zona-free oocytes. The overall data demonstrate that Hsp70 is present on boar sperm with a dynamic redistribution as the sperm undergoes capacitation and acrosome reaction and suggest an important role of this protein during porcine gamete interaction.

Monoclonal Antibodies against Sperm Intra-acrosomal Antigens as Markers for Male Infertility Diagnostics and Estimation of Spermatogenesis

PROBLEM

To determine the ability of monoclonal antibodies (MoAbs) against acrosomal antigens to detect physiology and pathology of human spermatozoa and to detect spermatids in ejaculates of infertile male with azoospermia.

METHOD OF STUDY

Sperm antigens detected with prepared MoAbs were partially characterized by biochemical and immunocytochemical methods. The acrosomal status of spermatozoa was compared in men with normal and pathological spermiograms and in sperm before and after induced acrosome reaction (AR). Ejaculates from patients were tested for the presence of spermatids.

RESULTS

MoAbs specifically bind to intra-acrosomal sperm antigens with quantitative difference between ejaculates with normal and pathological spermiograms. These antigens are released from the acrosome after induced AR. MoAbs labeled acrosomal proteins in round and elongated spermatids in the ejaculates of patients with azoospermia.

CONCLUSION

MoAbs against intra-acrosomal sperm antigens are useful for human sperm diagnosis and prediction of spermatogenesis. The spermatids can be utilized in assisted reproduction.

Identification and isolation of boar sperm specific antigens with potential role in sperm-egg interaction

Investigations on specific and functionally active sperm antigens would bring about the elucidation of the mechanisms of gamete interaction and help the search to new approaches for prognosis and regulation of fertility. Previously, we have produced a polyclonal rabbit anti-boar spermatozoa antibody (RABSA) that might affect the fertilizing capacity of boar spermatozoa. The sperm specificity of RABSA was demonstrated by double immunodiffusion, immunoelectrophoresis and ELISA against boar spermatozoa, as well as against saline extracts of boar reproductive and somatic organs. Using indirect immunofluorescence (IIF) test, here we provide evidence that RABSA stained the acrosomes of ejaculated and capacitated boar and human spermatozoa, the fluorescence being intensified on the equatorial region after the acrosome reaction. The RABSA cognate antigen/s is a subject of interest because of their specific localization in sperm structures, which is shown to be a binding and/or fusion competence region. Using ion-exchange (Heparin-Sepharose) chromatography, we eluted an antigen with molecular mass 60 kDa (Ag60) in SDS-PAGE from NP40 extracts of capacitated boar spermatozoa. In Western blot, RABSA recognized specifically this antigen. The Ag60 did not affect the sperm-ligand activity of zona pellucida in a porcine sperm-zona binding assay. IIF experiments showed that zona-free porcine oocytes preincubated with Ag60 and RABSA presented fluorescent labeling over the entire egg surface. The biological and IIF experiments provide evidence supporting the involvement of Ag60 in functional steps required for sperm-egg binding and/or fusion, but not sperm-zona pellucida binding.

Effect of an endocrine disruptor on mammalian fertility. Application of monoclonal antibodies against sperm proteins as markers for testing sperm damage

PROBLEM

To determine the influence of an endocrine disruptor [bisphenol-A (BPA)] on the integrated reproductive process as well as on individual reproductive organs and gametes in order to select suitable markers for testing sperm damage.

METHOD OF STUDY

The effect of BPA on fertility in vivo in multigenerational studies in an outbred stock of mice was studied. Damage of reproductive organs was assessed by histochemical methods and damage of spermatozoa by means of a panel of monoclonal antibodies (MoAbs) against intra-acrosomal sperm proteins.

RESULTS

BPA had a negative influence on offspring born of mice, on reproductive organs, and on acrosome integrity of mice spermatozoa. Selected MoAbs against intra-acrosomal mammalian sperm proteins, cross-reacted with mouse spermatozoa, were used for determination of the acrosome integrity. BPA had no effect on body weight and testicle weight of males.

CONCLUSIONS

The present results demonstrate that BPA has a negative effect on in vivo fertility of mice, with impact on spermatogenesis and sperm quality. Monoclonal antibodies against intra-acrosomal sperm proteins can be used for detecting sperm damage.

Differential subcellular distribution of tubulin epitopes in boar spermatozoa: recognition of class III beta-tubulin epitope in sperm tail

The exposure of tubulin epitopes was studied in ejaculated boar spermatozoa using a panel of four monoclonal antibodies specific to the N-terminal or C-terminal structural domains of tubulin and three monoclonal antibodies against class III beta-tubulin. The specificity of the antibodies was confirmed by immunoblotting. Immunocytochemical staining showed that antibodies discriminated between various parts of a spermatozoon, and that epitopes of class III beta-tubulin were present in the flagellum. A tubulin epitope from the C-terminal domain of beta-tubulin was detected in the triangular segment of the postacrosomal part of the sperm head. Its distribution changed after an A23187 ionophore-induced acrosome reaction, indicating that tubulin participates in the early stages of fertilization. Three monoclonal antibodies, TU-20, SDL.3D10, and TUJ1 directed against epitopes on the C-terminal end of neuron-specific class III beta-tubulin that is widely used as a neuronal marker, stained the flagella. The reactivity of TU-20 was further confirmed by absorbing the antibody with the immunizing peptide and by immunoelectron microscopy. Immunoblotting after two-dimensional electrophoresis revealed that the corresponding epitope was not present on all beta-tubulin isoforms. These results suggest that various tubulins are involved in the functional organization of the mammalian sperm flagellum and head.

Monoclonal antibodies to intra-acrosomal proteins inhibit gamete binding in vitro

The sperm-zona pellucida-binding assay in vitro was used as a functional test for zona pellucida-binding ability of boar spermatozoa after co-incubation with monoclonal antibodies against intra-acrosomal proteins. The effect of monoclonal antibodies ACR.2 against boar acrosin (55, 53, 45 and 38 kDa), and Hs-8 against boar intra-acrosomal protein (230, 110, 88, 60, 48 kDa) on boar spermatozoa-porcine oocyte binding was examined. The sperm-zona pellucida-binding was reduced when medium was supplemented with monoclonal antibodies during sperm-oocyte co-incubation, but not when capacitated spermatozoa were pretreated with monoclonal antibodies before incubation with oocytes. Our results show that the monoclonal antibodies (ACR.2, Hs-8) against intra-acrosomal proteins reduce the secondary sperm-zona pellucida-binding with statistically significant difference. This suggests the role of these proteins in the early phases of fertilization.

Characterization of boar spermadhesins by monoclonal and polyclonal antibodies and their role in binding to oocytes

PROBLEM

The role of Ala-Trp-Asn (AWN) and Ala-Gln-Asn (AQN) families of spermadhesive sperm proteins in fertilization.

METHOD OF STUDY

The preparation and characterization of polyclonal antibodies against AWN and AQN spermadhesins and one monoclonal antibody (MAb), designated Bo.5, against AWN spermadhesin. The use of biochemical and immunocytochemical methods for characterization of spermadhesins on the sperm membrane of boar spermatozoa and in the cryostat sections of boar reproductive organs.

RESULTS

Polyclonal anti-AWN and anti-AQN antibodies specifically reacted with AWN and AQN proteins, respectively. MAb Bo.5 detected the 17-, 16-, and 14-kDa protein members of AWN subfamily. The monoclonal, as well as the polyclonal, AWN antibodies remarkably decreased the sperm binding to the egg surface in an in vitro sperm zona pellucida binding assay.

CONCLUSIONS

Presented results demonstrate that polyclonal antibodies and MAb Bo.5 against spermadhesins specifically recognize the membrane-associated antigens and inhibit the binding of sperm to oocytes. Reduced binding of sperm to oocytes, due to the antibodies, indicates the role of these spermadhesins in sperm-egg primary binding.

Monoclonal antibodies to canine intra-acrosomal sperm proteins recognizing acrosomal status during capacitation and acrosome reaction

Monoclonal antibodies Ds-1 and Ds-2 specifically labelling dog sperm acrosome were prepared by immunization of mice with acetic acid extracts of dog spermatozoa. Electron microscopy and indirect immunofluorescence localized the site of Ds-1 and Ds-2 proteins inside the acrosomal vesicle. Ds-1 antibody detected 55, 76, 115, 120 and 190 kDa proteins under non-reducing conditions, and 73 kDa and 54 kDa proteins after reduction (p73/Ds-1 and p54/Ds-1). 92 kDa and 40 kDa proteins recognized by Ds-2 (p92/Ds-2 and p40/Ds-2) migrated at > 200 kDa in the absence of reducing agent. In vivo, p73/Ds-1 and p54/Ds-1 are therefore likely to be present both in free and complexed form, while all of p92/Ds-2 and p40/Ds-2 form disulfide-bonded complexes. Decrease in the rate of acrosomes stained with Ds-1 and Ds-2 was correlated with the progress of capacitation resulting in the increased rate of spontaneous acrosome reactions, as suggested by a dramatic effect of A23187. Monoclonal antibody to boar acrosin (ACR-2) recognized dog sperm acrosin homologue. A higher rate of ACR-2-negative spermatozoa was observed after capacitation and A23187 treatment compared to Ds-1 and Ds-2, indicating that proteins recognized by Ds-1 and Ds-2 are localized in a specific compartment of acrosome, distinct from acrosin and possibly representing fraction of acrosomal matrix.

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.