The mammalian spermatozoon: a model for the study of regional specificity in plasma membrane organization and function

The functional anatomy of the human spermatozoon: relating ultrastructure and function

The Internet, magazine articles, and even biomedical journal articles, are full of cartoons of spermatozoa that bear minimal resemblance to real spermatozoa, especially human spermatozoa, and this had led to many misconceptions about what spermatozoa look like and how they are constituted. This review summarizes the historical and current state of knowledge of mammalian sperm ultrastructure, with particular emphasis on and relevance to human spermatozoa, combining information obtained from a variety of electron microscopic (EM) techniques. Available information on the composition and configuration of the various ultrastructural components of the spermatozoon has been related to their mechanistic purpose and roles in the primary aspects of sperm function and fertilization: motility, hyperactivation, capacitation, the acrosome reaction and sperm-oocyte fusion.

Reproductive tract modifications of the boar sperm surface

The sperm cell has a unique, polarized, and segregated surface that is modified extensively by the changing environments in both the male and the female reproductive tracts. The sperm cannot refresh its surface, as protein translation and membrane recycling by intracellular vesicular transport have ceased upon its maturation. So, how is the sperm surface modified in the reproductive tracts and how do these processes affect fertilization? This review traces these modifications as boar sperm travels from their liberation from the Sertoli cell into the lumen of seminiferous tubules of the testis to the site of fertilization in the ampulla of the oviduct in the sow, via an artificial insemination route. The effect of sperm dilution for artificial insemination, as well as more extensive sperm processing for in vitro fertilization, cryopreservation, or sex sorting, are also discussed with respect to how these procedures affect sperm surface organization and fertilization capacity.

Reorganization of mouse sperm lipid rafts by capacitation

One of the hallmarks of mammalian sperm capacitation is the loss of cholesterol from the plasma membrane. Cholesterol has been associated with the formation of detergent insoluble membrane microdomains in many cell types, and sperm from several mammalian species have been shown to contain detergent-resistant membranes (DRMs). The change in cholesterol composition of the sperm plasma membrane during capacitation raises the question of whether the contents of DRMs are altered during this process. In this study, we investigated changes in protein composition of DRMs isolated from uncapacitated or capacitated mouse sperm. TX-100 insoluble membranes were fractionated by sucrose flotation gradient centrifugation and analyzed by Western and lectin blotting, and capacitation-related differences in protein composition were identified. Following capacitation, the detergent insoluble fractions moved to lighter positions on the sucrose gradients, reflecting a global change in density or composition. We identified several individual proteins that either became enriched or depleted in DRM fractions following capacitation. These data suggest that the physiological changes in sperm motility, ability to penetrate the zona pellucida (ZP), ZP responsiveness, and other capacitation-dependent changes, may be due in part to a functional reorganization of plasma membrane microdomains.

Optimizing and quantifying fusion of liposomes to mammalian sperm using resonance energy transfer and flow cytometric methods

BACKGROUND

Liposomes are used to carry pharmaceutical agents and to alter the lipid composition of cell membranes. This study compared resonance energy transfer (RET), fluorescence dequenching, and flow cytometry as monitors and quantifiers of fusion between liposomes and mammalian spermatozoa.

METHODS

Preliminary experiments used RET to determine the optimum sperm concentration for fusion of DL-alpha-phosphatidylcholine dipalmitoyl (PC)/DL-alpha-phosphatidylethanolamine dipalmitoyl (PE) liposomes at 35 degrees C +/- 5 mM Ca2+. Microscopy confirmed the fusion of liposomes, not just adhesion (n = 3). Dequenching tested the time-dependent fusion of liposomes of two different lipid compositions to sperm, both, (n = 3) +/- 1 mM Ca2+ and (n = 3) without Ca2+ at two sperm concentrations. Finally, flow cytometry absolutely quantified the percentage of sperm fusing to liposomes at different liposome-to-sperm ratios (n = 4) and with sperm from different donors (n = 3).

RESULTS

RET detected fusion of liposomes with sperm and microscopy confirmed the interaction to be true fusion. Dequenching detected more fusion of liposomes with sperm at 100 x 10(6) sperm per milliliter than at lower concentrations (P < 0.05). Fusion dynamics differed with lipid composition but Ca2+ had no effect. Flow cytometry reliably quantified the percentage of sperm fusing with liposomes, which varied from bull to bull (P < 0.05).

CONCLUSION

Liposome fusion with mammalian sperm membranes can be quantified cytometrically and varies with lipid composition, sperm-to-liposome ratio, and individual animals.

Comparative distribution of short dystrophin superfamily products in various guinea pig spermatozoa domains

In this study, the presence and cellular distribution of dystrophin family products (i.e. Dp71d, Dp71f-like protein and dystrobrevin) was examined by indirect immunofluorescence and Western blotting in guinea pig spermatozoa. Two dystrophin-associated proteins, beta-dystroglycan and alpha-syntrophin, and nNOS a protein frequently associated with alpha-syntrophin, were determined. In spermatozoa lacking plasma membrane and acrosome, Dp71f-like protein was found in the postacrosomal perinuclear theca and also in the middle piece of the flagellum. In the flagellum, Dp71f-like protein is localized together with alpha-syntrophin and nNOS. Dp71d was present in the plasma membrane of the middle piece with beta-dystroglycan, alpha-syntrophin and nNOS. Dp71d was also present in plasma membrane of the post acrosomal region, but only with nNOS. Finally, dystrobrevin was located all along skeletal flagellum structures and in the subacrosomal hemisphere of the perinuclear theca. This distinct and complementary distribution in various domains of spermatozoa may reveal a specific function for each short dystrophin family product, in the stabilization of the domains where they are located.

Changes in lipid diffusibility in the hamster sperm head plasma membrane during capacitation in vivo and in vitro

The technique of fluorescence recovery after photobleaching (FRAP) was employed on spermatozoa labeled with the fluorescent lipid analogue C14dil to provide two measures of lateral diffusion in the plane of the sperm plasma membrane during capacitation in vivo and in vitro: the diffusion coefficient (D) for C14dil and the fraction of C14dil that is free to diffuse (%R) within the domain. To evaluate changes in lipid diffusibility during capacitation in vivo, spermatozoa were recovered from the uterus within 30 min after ejaculation or from the oviduct at 2, 4, 6 and 8 hr after mating. To compare the changes which occur in vivo with those which occur during capacitation in vitro, caudal epididymal spermatozoa were incubated under capacitating or non-capacitating (control) conditions for 4 hr. Although transient changes in D occurred during the course of capacitation, there was no net change in D for either anterior (AH) or posterior head (PH) domains following capacitation in vitro or in vivo. Significant differences in the lipid diffusion coefficient between the two head domains were observed during the course of capacitation. A transient decrease in %R was observed for the AH domain during capacitation in vitro and incubation under control conditions, but no significant change in %R was observed in the AH domain during capacitation in vivo. A significant decline in %R of the PH domain was observed for spermatozoa during capacitation in vivo, in vitro and following incubation under non-capacitating conditions. These data indicate that the changes in the lipid diffusibility of the AH and PH domains which occur during capacitation in vivo exhibit both similarities and differences to those which occur during capacitation in vitro.

Experimental hypercholesterolaemia in rabbits. Effect on lipid domains in homologous spermatozoa

The distribution of membrane filipin sterol complexes (FSC) in the plasma membrane of the acrosomal region (PMAR) of rabbit sperm from epididymis and testis, in normal and hypercholesterolaemic rabbits, was examined at ultrastructural level. Membrane FSG were quantitatively analysed on freeze fracture replicas of filipin-treated cells. Cauda epididymal sperm shows a significant increase in filipin sterol complexes concentration in PMAR of hypercholesterolaemic animals compared to normal rabbits. Hypercholesterolaemic animals had 0.53 +/- 0.08 FSC micron-2 in the marginal segment of PMAR and 0.26 +/- 0.03 FSC micron-2 for normal animals. In the principal piece we found 0.70 +/- 0.07 FSC micron-2 for hypercholesterolaemic and 0.43 +/- 0.03 FSC micron-2 for control animals. We also counted 0.58 +/- 0.04 FSC micron-2 in the equatorial segment of PMAR for hypercholesterolaemic and 0.38 +/- 0.03 FSC micron-2 for normal animals respectively. The FSC concentration of testicular sperm, like sperm from corpus and caput of epididymis in hypercholesterolaemic animals, did not differ from the controls. Cholesterol, phospholipids and cholesterol:phospholipid ratio in caudal epididymal sperm from treated males did not differ from controls. Only the sphingomyelin concentration decreases in cauda epididymal sperm from hypercholesterolaemic males compared to controls. The results presented in this paper suggest that the lipidic domains in PMAR of hypercholesterolaemic rabbits changes when the gametes go through the epididymis.

Detection of antibodies toward epididymal sperm antigens--an obligatory step in evaluation of human immunologic infertility?

PROBLEM

To test the relative impact of epididymal versus ejaculated sperm in immunologic infertility.

METHOD

Human antibody binding to epididymal and ejaculated spermatozoa was compared by flow cytometry (FCM) since it allows quantitative analysis of viable sperm while ignoring nonsperm cells. To select sera for FCM, GAT, TAT, and ELISA were applied on 145 sera from fertile men, idiopathically infertile and varicocele patients.

RESULTS

All GAT/TAT-positive infertile patients, a representative group of varicocele patients and the fertile control, were assessed by FCM. Higher reactivity toward epididymal sperm revealed 18/22 sera while only four out of them bound to ejaculated sperm stronger than the control. All varicocele sera were positive against epididymal while negative against ejaculated spermatozoa.

CONCLUSIONS

Epididymal sperm antigens may play a predominant role in some cases of immunologic infertility. Such patients might not be adequately diagnosed and respectively treated due to the limitations of diagnostic procedures applying only ejaculated spermatozoa.

Glycolipid migration from the apical to the equatorial subdomains of the sperm head plasma membrane precedes the acrosome reaction. Evidence for a primary capacitation event in boar spermatozoa

In order to extend the static information of immunolabelling sulphogalactolipids in fixed boar spermatozoa, a fluorescent sulphogalactolipid analogue, galactose(3-sulphate)-beta 1–1′[(N-lissamine rhodaminyl)-12-aminodode-canoyl]-sphingosine, was incorporated into plasma membranes of living spermatozoa and its lateral distribution over the sperm head was studied. The fluorescent lipid was enriched in the apical ridge subdomain of freshly ejaculated sperm cells. After sperm binding to the zona pellucida the lipid redistributed to the equatorial segment of the sperm surface. A similar shift occurred during capacitation in vitro with 2 mM CaCl2 or with 4% (w/v) bovine serum albumin. The desulphated derivative galactose-beta 1–1′[(N-lissamine rhodaminyl)-12-aminododecanoyl]-sphingosine was also incorporated into the plasma membrane of freshly ejaculated sperm cells and clearly stained the apical ridge subdomain and the (pre)-equatorial subdomains of the sperm heads. The desulphogalactolipid analogue showed a slightly faster migration to the equatorial segment of the sperm plasma membrane than did its sulphated counterpart. The measured fluorescence intensity distributions correlated linearly with the spatial probe distribution, which was checked by fluorescence lifetime imaging microscopy. The observed migration of the incorporated glycolipids precedes the acrosome reaction and is one of the underlying molecular events likely to be important in the process of sperm capacitation. The results of this study suggest that lipid phase segregation is an important driving force for the organization of the sperm head plasma membrane into subdomains.

Actin, alpha-actinin, and spectrin with specific associations with the postacrosomal and acrosomal domains of bovine spermatozoa

BACKGROUND

Characteristic membrane changes in spermatozoa culminating in acrosome reaction and sperm-egg fusion, and suspected involvement of actin-containing cytoskeleton in membrane changes in general, prompted us to investigate subcellular distribution of actin and actin-binding proteins in bovine spermatozoa subjected to various extractions which sequentially denude the sperm investments.

METHODS

Spermatozoa were treated with either 1% SDS, 0.1% Triton X-100, 0.1% Hyamine, or 1 M MgCl2 or were sonicated. Immunostaining of actin, alpha-actinin, spectrin, and acrosin as well as electron microscopic analysis of extracted spermatozoa were carried out.

RESULTS

Extractions caused evagination of the acrosomal lamina which retained focal contacts with the inner acrosomal membrane. Extractions further revealed lateral prongs at the anterior border of the postacrosomal sheath. Labeling for alpha-actinin and spectrin was localized in the acrosin-positive acrosomal lamina, neck, and principal piece, the latter containing also relatively extraction-resistant oligomeric or polymerized actin. In the postacrosomal area, actin was accumulated in the extraction-resistant posterior ring structure and anteriorly at the sites apparently related to the lateral prongs. Notably, spectrin reactivity was enhanced by MgCl2 in head, neck, and principal piece, and sonication abolished cytoskeletal immuno-reactivity in the head.

CONCLUSIONS

Destabilization of membranes with selected extractions induces changes in the acrosomal lamina mimicking acrosomal vesicle formation. The lateral prongs and posterior ring structure, respectively, may serve as anterior and posterior anchors for the extraction-resistant post-acrosomal sheath. The lateral prongs may also be a merger zone for actin, alpha-actinin, and spectrin with important implication on sperm function. The latter two proteins may be involved in acrosomal vesicle formation. It is apparent that extractions have a significant effect on the detectability of sperm cytoskeletal elements.

Visualization and quantification of glycolipid polarity dynamics in the plasma membrane of the mammalian spermatozoon

Seminolipid (sulphogalactosylalkylacylglycerol), the glycolipid that is specific for mammalian germ cells, is located exclusively in the outer leaflet of the sperm plasma membrane. In this study the lateral distribution of seminolipid on sperm heads has been investigated by indirect immunofluorescence labelling and detection with digital imaging fluorescence microscopy. In freshly ejaculated sperm cells this glycolipid was present primarily at the apical ridge subdomain of the plasma membrane of the sperm head. After binding the sperm cells to zona-coated coverslips seminolipid migrated, in 40 minutes, from the apical ridge to the equatorial subdomain of the plasma membrane. A similar redistribution of seminolipid was observed during capacitation of sperm cells in vitro induced by Ca2+ or bovine serum albumin. Comparable migration of seminolipid was also found after prolonged storage of ejaculated sperm cells, albeit at a much slower rate. Addition of arylsulphatase A, an enzyme present in seminal plasma that desulphates seminolipid, significantly enhanced the migration of seminolipid during storage of sperm cells. Its breakdown product desulphoseminolipid (galactosylalkylacylglycerol) appeared highly specifically at the equatorial segment. The measured fluorescence intensity over the sperm head surface correlated linearly with the spatial probe distribution as was checked by fluorescence lifetime imaging microscopy. This paper demonstrates and quantifies for the first time the polarity of seminolipid on the surface of the sperm cell and the dynamic alterations that occur in this polarity during post-ejaculatory events.

Compartmentalization, processing and redistribution of the plasma membrane protein CE9 on rodent spermatozoa. Relationship of the annulus to domain boundaries in the plasma membrane of the tail

Western blotting, immunofluorescence and immunogold electron microscopy were used to examine the compartmentalization, processing and redistribution of the integral plasma membrane protein CE9 on the spermatozoa of rats, mice and hamsters. In each species examined, spermatozoal CE9 was found to undergo endoproteolytic processing followed by a net redistribution from the posterior-tail domain into the anterior-tail domain of the plasma membrane during epididymal maturation. Compared to spermatozoa of the rat and mouse, those of the hamster were found to express a greater proportion of their CE9 within the anterior-tail plasma membrane domain at all stages of maturation. As a consequence, CE9 was judged to be a suitable marker for two different spermatozoal plasma membrane domains: the posterior-tail plasma membrane domain (spermatozoa from the testis and caput epididymidis of the rat and mouse) and the anterior-tail domain (spermatozoa from the cauda epididymidis of the hamster). Immunogold electron microscopy was used to pinpoint the positions of the boundaries of these CE9-containing plasma membrane domains at a high level of resolution. In each case, the position of the CE9 domain boundary was found to be strongly correlated with that of the subplasmalemmal electron-dense ring known as the annulus. The precise spatial relationship between the CE9 domain boundary and the annulus was, however, found to differ significantly among species and/or as a function of maturation.

Morphometric analysis of intact sperm heads and of sperm nuclei in the mouse

A morphometric analysis of mouse sperm and of their nuclei was undertaken to investigate their respective post-testicular maturation. Sperm were collected from the testis, caput and cauda epididymidis, and their corresponding nuclei were isolated. Results indicate that the post-testicular maturation of sperm is distinct from that of nuclei. The size of intact sperm heads increases in the caput followed by a subsequent decrease in the cauda. In contrast, sperm nuclei decrease progressively in size. In general, a greater magnitude and number of alterations in intact heads and nuclei occur while in transit from the testis to the caput than during passage to the cauda epididymis. These results suggest that the period immediately following their release from the testis is crucial to the complete morphological maturation of sperm heads and nuclei.

Localization of wheat germ agglutinin and antibody binding sites on the plasma membranes of sea urchin sperm heads as revealed by label-fracture and fracture-flip

Freeze-fracture electron microscopy reveals that intramembrane particles are concentrated in a band encircling the posterior portion of the acrosome of Strongylocentrotus purpuratus sperm. Two colloidal gold labeling methods, label-fracture and replica-staining fracture-flip, were employed to show that the plant lectin wheat germ agglutinin, which recognizes a 210 kDa sperm surface glycoprotein, binds to this localized band of intramembrane particles. Monoclonal antibody J18/2, which also recognizes the 210 kDa surface glycoprotein, shows this localized binding in approximately 20% of the sperm observed in this study. The majority of sperm displayed a uniform distribution of receptor sites for monoclonal antibody J18/2. Since wheat germ agglutinin and monoclonal antibody J18/2 are known to agglutinate Strongylocentrotus purpuratus sperm but not sperm of another sea urchin, Lytechinus pictus, similar determinations were made for the latter species. Lytechinus pictus sperm are not labeled with wheat germ agglutinin and are only sparsely labeled with monoclonal antibody J18/2. The acrosomal localizations of wheat germ agglutinin and monoclonal antibody J18/2 receptors in Strongylocentrotus purpuratus sperm are consistent with the involvement of the 210 kDa surface glycoprotein in an egg jelly-induced sperm acrosome reaction. Low-temperature post-embed labeling of thin sections with wheat germ agglutinin and monoclonal antibody J18/2 show concentrations of label within the acrosomal vesicle of Strongylocentrotus purpuratus sperm, suggesting the presence of an intracellular storage site for the 210 kDa glycoprotein.

Topographical rearrangement of a plasma membrane antigen during capacitation of rat spermatozoa in vitro

We have previously described an antigen (termed 2B1) on rat spermatozoa that is present on the plasma membrane overlying the tail domain. The antigen is mobile within the plane of the plasma membrane and a mAb to it blocks fertilization in vitro. In the present study we describe some dynamic properties of this antigen in relation to its topographical distribution. When spermatozoa were incubated in vitro in a capacitation medium and stained with 2B1 mAb/FITC-rabbit anti-mouse F(ab')2, strong fluorescence appeared over the acrosomal domain. Acute exposure of fresh spermatozoa to dissociating reagents (1 M NaCl or 5 mM 2-mercaptoethanol) or inducers of the acrosome reaction (lysolecithin + Ca2+ or A23187 + Ca2+) failed to mimic these effects. Spermatozoa prelabeled with FITC-2B1 IgG and then capacitated in the presence of excess "cold" 2B1 IgG also showed accumulation of fluorescence on the acrosomal domain, suggesting that the antigen had migrated from the tail. Migration was selective and Ca2(+)- and temperature-dependent but was not inhibited by metabolic poisons (NaF or NaN3). Motility was not obligatory for migration. Immunogold-labeling studies at the ultrastructural level showed that 2B1 antigen was restricted to the surface membrane over both the tail and the acrosomal domains and that during migration it did not change the type of membrane into which it was inserted. From a quantitative analysis of fluorescence on spermatozoa prelabeled with FITC-2B1 IgG and then capacitated, the amount of antigen that appeared on the acrosomal domain was approximately equivalent to that lost from the midpiece domain. The Mr of 2B1 antigen extracted from capacitated spermatozoa was 300-500 Da less than that extracted from noncapacitated cells, suggesting that the molecule had undergone processing concomitant with migration. These results are discussed in relation to mechanisms for targeting antigens to sites where they become physiologically active and are correctly positioned to participate in gamete recognition processes.

Boar sperm membranes antigens. I. Topography of a mobile glycoprotein of the sperm cell membrane

A monoclonal antibody, designated mAb P86/5, was generated by immunization of female Balb/c mice with a membrane vesicle fraction composed of the outer acrosomal membrane and plasma membrane (PM-OAM). As determined by fluorescence microscopy and electron microscopy P86/5 recognizes a sperm plasma membrane antigen that is restricted to the sperm head. In intact spermatozoa the P86/5-antigen is distributed over the surface of the sperm head with the exception of the rostral region. By comparing the antibody binding pattern generated at 4 degrees C and 25 degrees C, it could be shown that the P86/5-antigen is capable to diffuse freely within the cell membrane overlying the acrosome whereas its lateral mobility is restricted to the post-acrosomal region. The P86/5-antigen had a molecular weight of about 78 kDa as revealed by SDS-PAGE and western blotting. The glycoprotein nature of the P86/5-antigen was established by lectin affinity chromatography.

Cytochalasin D inhibits penetration of hamster eggs by guinea pig and human spermatozoa

Fertilization experiments using zona-free hamster eggs and spermatozoa from both guinea pig and human were conducted in the presence of cytochalasin D to evaluate the possible role of actin filaments in fertilization processes. When the actin filament inhibitor, cytochalasin D, was added to fertilization media at concentrations of 10 to 30 microM, penetration of eggs was significantly inhibited. Preincubation of the eggs with cytochalasin D and washing prior to addition of spermatozoa had no effect on penetration as quantitated by the number of swollen heads in the egg cytoplasm. However, spermatozoa preincubated with cytochalasin D and subsequently washed prior to egg addition showed reduced penetration of the same magnitude as when spermatozoa and eggs were coincubated with cytochalasin D. Both the percentage of zona-free eggs showing decondensed sperm heads and the penetration indices (total decondensed spermatozoa/total eggs) were significantly affected when spermatozoa were exposed to cytochalasin D. The DMSO vehicle used to dissolve cytochalasin D had little effect on the number of decondensed heads. When the concentration of cytochalasin D was increased (DMSO remaining constant) in human sperm experiments, percent penetration decreased and progressively fewer decondensed spermatozoa were recorded, indicating dose-responsiveness to cytochalasin D. Motility parameters of human spermatozoa were not altered at any of the concentrations of cytochalasin D tested. Neither guinea pig sperm motility nor acrosome reaction was altered significantly by cytochalasin D or the DMSO vehicle. These experiments suggest that cytochalasin D may be an inhibitor of some fertilization processes such as sperm penetration or sperm head decondensation.

Identification of calcium conducting channels in isolated boar sperm plasma membranes

Ion channel recordings were obtained from liposomes containing purified boar sperm plasma membrane proteins using a tip-dip method. Liposomes prepared in HEPES-TRIS and clamped by electrodes containing Ba-HEPES displayed channel activity that was partially inhibited by verapamil or nitrendipine and completely inhibited by La3+. Reversal of current at pipette negative voltages was observed only when Ba2+ ions were also present in the bath solution. These data indicate that channels capable of carrying calcium currents are prominent components of the plasma membrane of mammalian sperm.

Characterization of the maturation-associated galactose oxidase-sensitive glycoproteins of rat caudal sperm plasma membrane and epididymal fluid

This paper explores the relationship between the galactose oxidase-sensitive glycoproteins from rat caudal epididymal sperm and fluid and, in addition, their relatedness to the 32,000-Da major acidic secretory glycoproteins of caudal epididymal fluid. The major acidic secretory glycoproteins were purified by a combination of high-resolution anion-exchange (Mono Q) and gel permeation (Bio-Sil TSK 125) chromatographic steps. Immunoprecipitation studies, peptide mapping, and the inability to label the purified glycoprotein by galactose oxidase/sodium boro[3H]hydride clearly established that the galactose oxidase-sensitive fluid and membrane glycoproteins were not related to these acidic secretory glycoproteins. Membrane and fluid tritium-labeled glycoproteins were shown to be closely related, but not identical, polypeptides. Sugar analysis indicated that both glycoproteins contain N- and O-linked saccharide chains and that the galactose oxidase-sensitive residue was present only on O-linked sugars. It was also found that efficient labeling of the 32,000-Da fluid glycoprotein was possible only if protease inhibitors were omitted from all buffers used in the isolation of caudal epididymal fluid and subsequent labeling procedures. This suggests that the fluid glycoprotein was acquired by the unintentional proteolysis of the membrane glycoprotein. Polyclonal antibodies raised against caput sperm plasma membranes immunoprecipitated tritium-labeled glycoproteins from both caudal epididymal fluid and sperm membrane, suggesting that a precursor form of the caudal galactose oxidase-sensitive glycoprotein may be present on caput sperm.

Concanavalin A binding sites on the surface of Drosophila melanogaster sperm: a fluorescence and ultrastructural study

The distribution of alpha-D-mannose/alpha-D-glucose terminal residues in the plasma membrane of Drosophila melanogaster spermatozoon has been investigated by fluorescence and electron microscopy using concanavalin A (Con A) labeling. The results indicate the presence of distinct domains on the sperm surface. Intense binding of Con A to the plasma membrane is highly restricted to the acrosomal region and to the endpiece of the tail. In the former, Con A receptors are not homogeneously distributed, suggesting the presence of microdomains in the acrosomal area. The main part of the tail contains very few Con A binding sites, which are confined to specific areas of the membrane. The sperm surface overlying the nucleus is completely negative. The labeling pattern is unchanged after storage in the female before fertilization. A preliminary analysis of the surface of mature oocytes using fluorochrome-conjugated horseradish peroxidase indicates that D-mannose binding molecules are specifically associated with the chorion of the micropyle anterior part, which might therefore be the site of a preliminary interaction between egg and spermatozoon.

Widespread occurrence of calicin, a basic cytoskeletal protein of sperm cells, in diverse mammalian species

A novel cytoskeletal element consisting of dense webs of thin (3-14 nm) filaments surrounding the nucleus of the sperm head has recently been isolated and shown to be associated with certain major basic proteins. Using antibodies specific for calicin, a prominent Mr-60,000 cytoskeletal protein of the posterior calyx of bull sperm heads detected in immunoblotting on gel electrophoretically separated polypeptides as well as in immunofluorescence and immunoelectron microscopy, we show that the same--or an immunologically related--polypeptide occurs in sperm heads of other species with greatly different morphology, including human, boar, guinea pig, hamster, rat and mouse. The calicin localization in the various species is described and discussed in relation to the specific sperm morphology.

Maturation changes of the plasma membrane of rat spermatozoa observed by surface replica, rapid-freeze and deep-etch, and freeze-fracture methods

Rat spermatozoa from the epididymis and ductus deferens were observed by surface replica, rapid-freeze and deep-etch, and conventional freeze-fracture methods. By the surface replica method, parallel periodical ridges were observed in the acrosomal region of the spermatozoa from the distal part of the cauda epididymis (zone 6) and from the ductus deferens. The periodicity of the ridges forming a domain was about 35 nm. A quantitative analysis of the spermatozoa along the reproductive tract indicated that 39.4% and 73.5% of the population in zone 6 of the epididymis and in the ductus deferens, respectively, had the domain. None of the spermatozoa from zone 1 through zone 5 had the domain. The results of the rapid-freeze and deep-etch procedure showed that the ridges observed by the surface replica method consisted of linear arrangements of elliptical particles on the ES face of the plasma membrane. The particles were about 30 nm in length and 15 nm in width. On the corresponding PF face of the plasma membrane, linear arrangements of the intramembrane particles (IMPs) of about 8 nm in diameter were observed by both the deep-etch and freeze-fracture methods. The IMPs tended to run in paired parallel lines. A close relationship was observed between the lines of the elliptical particles on the ES and of the IMPs on the PF faces. The elliptical particle may be a protruded part of the IMP(s) or other protein(s) bound to the IMP(s).

Cytoskeletal assemblies of mammalian spermatozoa

It is becoming increasingly evident that the different domains of the mammalian spermatozoa possess distinct cytoskeletal assemblies. In this paper we have discussed three assemblies, found in the acrosomal, postacrosomal, and midpiece segment, respectively. Each has a distinct substructure and associates with specific sperm-membrane systems. Their protein compositions are currently unidentified, and they may be comprised of sperm-specific polypeptides. Analysis of their formation and fate during sperm-egg interaction should provide valuable insight into their role in the development of cell polarity and in the membrane-mediated steps of fertilization.

Actin and calmodulin coexist in the equatorial segment of ejaculated boar sperm

The direct overlay technique with iodinated calmodulin on boar sperm fractions evidenced a strong bond in the 45,000 molecular weight, which is the region recognized by anti-actin antibodies. This result and the close codistribution of the two staining patterns for calmodulin and actin with immunofluorescence and immunoelectronmicroscopy suggest a possible interaction between calmodulin and actin in boar sperm.