Capacitation of bovine sperm by heparin

Capacitation of bovine sperm was evaluated by determining the ability of sperm to fertilize bovine oocytes in vitro and to undergo an acrosome reaction upon exposure to lysophosphatidylcholine (LC). Incubation of sperm with heparin (10 micrograms/ml) increased the percentage of oocytes fertilized, but this required exposing sperm to heparin for at least 4 h before adding them to oocytes. There was no effect on the percentage of motile or acrosome-reacted sperm after exposure of noncapacitated sperm to 100 micrograms/ml LC for 15 min. When sperm were incubated for 4 h with heparin, exposure to 100 micrograms/ml LC for 15 min had no effect on the percentage of sperm that were motile, but the percentage of acrosome-reacted sperm increased from less than 10% to over 70%. The acrosome reactions (ARs) induced by LC were synchronous, reached maximal levels within 15 min, and differed (p less than 0.001) between sperm incubated under capacitating (with heparin) and noncapacitating conditions (without heparin). The time course required for heparin to capacitate sperm as judged by in vitro fertilization and to render sperm sensitive to LC induction of the AR were found to be similar. The percentage of ARs induced by LC and percentage of oocytes fertilized by sperm were found to be heparin-dose-dependent, with the maximum responses occurring at 5-10 micrograms/ml heparin. The correlation between the mean fertilization and LC-induced AR percentages was 0.997 (p less than 0.01). These studies demonstrate capacitation of bovine sperm by heparin requires at least a 4-h exposure of sperm to heparin and suggest that plasma membrane changes prior to an AR can be detected by exposure of bovine sperm to LC.

Generation of reactive oxygen species, lipid peroxidation, and human sperm function

Recent studies have demonstrated that human spermatozoa are capable of generating reactive oxygen species and that this activity is significantly accelerated in cases of defective sperm function. In view of the pivotal role played by lipid peroxidation in mediating free radical damage to cells, we have examined the relationships between reactive oxygen species production, lipid peroxidation, and the functional competence of human spermatozoa. Using malondialdehyde production in the presence of ferrous ion promoter as an index of lipid peroxidation, we have shown that lipid peroxidation is significantly accelerated in populations of defective spermatozoa exhibiting high levels of reactive oxygen species production or in normal cells stimulated to produce oxygen radicals by the ionophore, A23187. The functional consequences of lipid peroxidation included a dose-dependent reduction in the ability of human spermatozoa to exhibit sperm oocyte-fusion, which could be reversed by the inclusion of a chain-breaking antioxidant, alpha-tocopherol. Low levels of lipid peroxidation also had a slight enhancing effect on the generation of reactive oxygen species in response to ionophore, without influencing the steady-state activity. At higher levels of lipid peroxidation, both the basal level of reactive oxygen species production and the response to A23187 were significantly diminished. In contrast, lipid peroxidation had a highly significant, enhancing effect on the ability of human spermatozoa to bind to both homologous and heterologous zonae pellucidae via mechanisms that could again be reversed by alpha-tocopherol. These results are consistent with a causative role for lipid peroxidation in the etiology of defective sperm function and also suggest a possible physiological role for the reactive oxygen species generated by human spermatozoa in mediating sperm-zona interaction.

Cellular basis of defective sperm function and its association with the genesis of reactive oxygen species by human spermatozoa

Addition of the divalent cation ionophore, A23187, to washed populations of human spermatozoa resulted in a sudden burst of production of reactive oxygen species which peaked within 3-5 min. This activity was dependent upon the presence of calcium in the external medium and was unaffected by the mitochondrial inhibitors, oligomycin, antimycin and rotenone. Studies with scavengers of reactive oxygen species revealed that, while reagents directed against singlet oxygen and the hydroxyl radical were without effect, cytochrome C reduced the response to A23187 by about 50%, suggesting that the superoxide anion radical is a major product of the activated human spermatozoon. The clinical implications of these studies stem from the considerable variation observed between individuals in the levels of reactive oxygen species produced by the spermatozoa. This variability was shown to be inversely related to the ability of the spermatozoa to exhibit sperm-oocyte fusion on exposure to A23187; defective samples exhibited a basal level of reactive oxygen species production which was 40 times that observed with normal functional cells.

Repetitive calcium transients and the role of calcium in exocytosis and cell cycle activation in the mouse egg

The role of calcium in cortical granule exocytosis and activation of the cell cycle at fertilization was examined in the mouse egg using the calcium chelator BAPTA (1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) and the fluorescent calcium indicator fluo-3. BAPTA and fluo-3 were introduced into zona-free mouse eggs by a 30-min incubation with 0.01-50 microM BAPTA acetoxymethyl ester (AM) and/or 1-20 microM fluo-3 AM prior to in vitro fertilization. Incubation of eggs in greater than or equal to 5.0 microM BAPTA AM inhibited cortical granule exocytosis in all cases. Introduction of the calcium chelator into the egg blocked second polar body formation at greater than or equal to 1.0 microM BAPTA AM. Sperm entry occurred in all eggs regardless of the BAPTA AM concentration. Sperm induce a large transient increase in calcium lasting 2.3 +/- 0.6 min, followed by repetitive transients lasting 0.5 +/- 0.1 min and occurring at 3.4 +/- 1.4-min intervals. Incubation with greater than or equal to 5.0 microM BAPTA AM inhibited all calcium transients. Introduction of BAPTA also inhibited calcium transients, exocytosis, and the resumption of meiosis following application of the calcium ionophore A23187 or SrCl2, which activate eggs. These results demonstrate that the calcium increase at fertilization is required for cortical granule exocytosis and resumption of the cell cycle in a mammalian egg.

Mouse egg integrin alpha 6 beta 1 functions as a sperm receptor

Binding between sperm and egg plasma membranes is an essential step in fertilization. Whereas fertilin, a mammalian sperm surface protein, is involved in this crucial interaction, sperm receptors on the egg plasma membrane have not been identified. Because fertilin contains a predicted integrin ligand domain, we investigated the expression and function of integrin subunits in unfertilized mouse eggs. Polymerase chain reactions detected mRNAs for alpha 5, alpha 6, alpha v, beta 1, beta 3, and beta 5. Immunofluorescence revealed alpha 6 beta 1 and alpha v beta 3 on the plasma membrane. GoH3, a function-blocking anti-alpha 6 monoclonal antibody, abolished sperm binding, but a nonfunction-blocking anti-alpha 6 monoclonal antibody, a function-blocking anti-alpha v beta 3 polyclonal antibody, and an RGD peptide had no effect. Somatic cells bound sperm avidly, but only if they expressed alpha 6 beta 1. A peptide analog of the fertilin integrin ligand domain inhibited sperm binding to eggs and alpha 6 beta 1+ cells and diminished GoH3 staining of eggs. Our results indicate a novel role for the integrin alpha 6 beta 1 as a cell-cell adhesion receptor that mediates sperm-egg binding.

Redox regulation of tyrosine phosphorylation in human spermatozoa and its role in the control of human sperm function

The redox status of human spermatozoa was found to have a profound influence on the fertilizing potential of these cells in association with qualitative and quantitative changes in the patterns of tyrosine phosphorylation. In general, oxidizing conditions enhanced tyrosine phosphorylation and stimulated sperm function, whereas reducing conditions had the opposite effect. Unstimulated human spermatozoa exhibited low levels of spontaneous acrosomal exocytosis and sperm-oocyte fusion and minimal reactive oxygen species generation, while phosphotyrosine expression was largely confined to a single protein of 116 kDa. However, if the spermatozoa were exposed to oxidizing conditions through the addition of exogenous H2O2, or the stimulation of endogenous NADPH-dependent reactive oxygen species generation, then a dramatic increase in tyrosine phosphorylation was observed (major phosphotyrosyl bands at 222 kDa, 200 kDa, 159 kDa, 133 kDa, 116 kDa and 82 kDa) in concert with the functional activation of the spermatozoa. A causal association between reactive oxygen species generation, tyrosine phosphorylation and sperm function was indicated by studies with the ionophore, A23187, which induced high rates of spermoocyte fusion together with enhanced rates of reactive oxygen species production and the increased expression of phosphotyrosyl proteins. This functional response to A23187 could be abrogated, without any concomitant change in sperm motility or viability, by using membrane permeant thiols or catalase to suppress the reactive oxygen species-induced increase in phosphotyrosine expression. The fact that the biological responses of human spermatozoa to biological agonists (recombinant human ZP3 and progesterone) could also be inhibited by catalase indicated the general relevance of these findings.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of the relationship between defective sperm function and the generation of reactive oxygen species in cases of oligozoospermia

The ability of human spermatozoa to exhibit sperm-oocyte fusion in response to the ionophore, A23187, was examined in relation to the capacity of these cells to generate reactive oxygen species. In 70 fertile control donors, there was an overwhelming pattern of high levels of sperm-oocyte fusion associated with low levels of reactive oxygen species production. By contrast, 88% of the 74 oligozoospermic patients exhibited less than 25% oocyte penetration in response to A23187 and 58% exhibited no penetration whatsoever. Of the 40 oligozoospermic patients who failed to respond to A23187, nine had low levels of reactive oxygen species production in association with impaired liquefaction of seminal plasma. Of the remainder, 17 (55%) exhibited defective sperm function together with elevated production of reactive oxygen species. These observations, which are the first to describe a biochemical defect in the spermatozoa of oligozoospermic patients, may carry significant implications for the etiology and treatment of this condition.

Use of a xanthine oxidase free radical generating system to investigate the cytotoxic effects of reactive oxygen species on human spermatozoa

The reaction between xanthine and xanthine oxidase results in the univalent and divalent reduction of dioxygen to generate superoxide (O2-.) and hydrogen peroxide (H2O2), respectively. With the aid of this system, the direct effect of reactive oxygen species (ROS) on human sperm function has been investigated. A protocol involving the addition of xanthine oxidase to the reaction mixture at 0 and 15 min resulted in a loss of motility involving every component of sperm movement examined. Lower doses of xanthine oxidase, which did not influence sperm motility, were also found to suppress the competence of human spermatozoa to exhibit oocyte fusion in response to the ionophore, A23187. The reactive oxygen species responsible for the disruption of human sperm function was not influenced by the presence of superoxide dismutase (SOD) or scavengers of hypochlorous acid or hydroxyl radicals. However, the cytotoxic species was shown to be extremely stable and could be completely eliminated by catalase, which selectively eliminates H2O2. Confirmation that it is H2O2, and not O2-., which is cytotoxic to human spermatozoa was obtained in studies in which the direct addition of this oxidant was shown to influence both the movement of human spermatozoa and their competence for oocyte fusion. These results carry implications for the diagnosis of defective sperm function and the design of optimized culture media for the treatment of male factor infertility.

Identification of a binding site in the disintegrin domain of fertilin required for sperm-egg fusion

Fertilization and certain later stages in mammalian embryonic development require fusion between membranes of individual cells. The mechanism of eukaryotic cell-cell fusion is unknown, and no surface molecules required for this process have been unequivocally identified. The role of the sperm surface protein fertilin in sperm-egg fusion was tested by using peptide analogues of a potential integrin binding site in the fertilin beta subunit. Peptide analogues that include a TDE sequence from the disintegrin region of fertilin beta are able to bind to the egg plasma membrane and strongly inhibit sperm-egg fusion. These results show that the disintegrin domain of fertilin beta binds to the egg plasma membrane and that this binding is required for membrane fusion.

Receptor function of mouse sperm surface galactosyltransferase during fertilization

Past studies from this laboratory have suggested that mouse sperm binding to the egg zona pellucida is mediated by a sperm galactosyltransferase (GalTase), which recognizes and binds to terminal N-acetylglucosamine (GlcNAc) residues in the zona pellucida (Shur, B. D., and N. G. Hall, 1982, J. Cell Biol. 95:567-573; 95:574-579). We now present evidence that directly supports this mechanism for gamete binding. GalTase was purified to homogeneity by sequential affinity-chromatography on GlcNAc-agarose and alpha-lactalbumin-agarose columns. The purified enzyme produced a dose-dependent inhibition of sperm binding to the zona pellucida, relative to controls. To inhibit sperm/zona binding, GalTase had to retain its native conformation, since neither heat-inactivated nor Mn++-deficient GalTase inhibited sperm binding. GalTase inhibition of sperm/zona binding was not due to steric blocking of an adjacent sperm receptor on the zona, since GalTase could be released from the zona pellucida by forced galactosylation with UDPGal, and the resulting galactosylated zona was still incapable of binding sperm. In control experiments, when UDPGal was replaced with the inappropriate sugar nucleotide, UDPglucose, sperm binding to the zona pellucida remained normal after the adsorbed GalTase was washed away. The addition of UDPGal produced a dose-dependent inhibition of sperm/zona binding, and also dissociated preformed sperm/zona adhesions by catalyzing the release of the sperm GalTase from its GlcNAc substrate in the zona pellucida. Under identical conditions, UDP-glucose had no effect on sperm binding to the zona pellucida. The ability of UDPGal to dissociate sperm/zona adhesions was both time- and temperature-dependent. UDPGal produced nearly total inhibition of sperm/zona binding when the zonae pellucidae were first galactosylated to reduce the number of GalTase binding sites. Finally, monospecific anti-GalTase IgG and its Fab fragments produced a dose-dependent inhibition of sperm/zona binding and concomitantly blocked sperm GalTase catalytic activity. Preimmune IgG or anti-mouse brain IgG, which also binds to the sperm surface, had no effect. The sperm GalTase was localized by indirect immunofluorescence to a discrete plasma membrane domain on the dorsal surface of the anterior head overlying the intact acrosome. These results, along with earlier studies, show clearly that sperm GalTase serves as a principal gamete receptor during fertilization.

The sperm-induced Ca2+ wave following fertilization of the Xenopus egg requires the production of Ins(1, 4, 5)P3

We used fluorescence ratio imaging of fura-2 in the egg of Xenopus laevis to study the initiation and propagation of the wave of increased free Ca2+ that is normally triggered at fertilization. Naturally matured, jellied eggs were injected with fura-2 and ratio-imaged with fluorescence excitation at 350 and 385 nm while sperm were added. The [Ca2+]i rise normally begins as a small spot near the surface of the egg, remains fairly localized for 20-60 sec, and then spreads more rapidly across the egg at 7.5 +/- 0.05 microns/sec to reach the antipode about 5 min after fertilization. The [Ca2+]i wave velocity is slowed by increasing the concentration of fura-2 in the cytoplasm to 100 microM, and 250 microM fura-2 blocks wave propagation. The peak [Ca2+]i in a sperm-activated wave is 2.2 +/- 0.1 microM and [Ca2+]i returns to preactivation levels within 21 +/- 0.7 min after fertilization. We further studied the mechanism by which sperm trigger the Ca2+ wave by injecting substances that interfere with Ins(1,4,5)P3-induced Ca2+ release or Ca(2+)-induced Ca2+ release (CICR). Heparin (3 kDa) inhibits sperm-induced egg activation in a manner that is linearly proportional to its cytoplasmic concentration. At 130 microM (390 micrograms/ml), sperm-induced activation is completely blocked and at 75 microM (225 micrograms/ml) activation of half of the eggs is inhibited. All eggs injected with 130 microM heparin are polyspermic as verified using Hoechst dye to label nuclear DNA. Imaging eggs injected with 75 microM heparin revealed multiple, transient "spots" of increased [Ca2+]i that failed to spread across the egg. Injection of a monoclonal antibody to PIP2 (0.2 microM), kt3g, blocked sperm-induced egg activation in 73% of the 30 eggs injected, suggesting that activation requires the hydrolysis of PIP2 in the membranes of the egg rather than simply the introduction of Ins(1,4,5)P3 from the sperm. This sperm-induced egg activation is not blocked by either of two CICR inhibitors, procaine (10 mM) or ruthenium red (30 microM), and egg activation is not triggered by either of two stimulators of CICR, caffeine (10 mM) or ryanodine (50 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of Human Spermatozoa with Progesterone Gradients to Simulate Approach to the Oocyte

Progesterone is present at micromolar concentrations in the cumulus matrix, which surrounds mammalian oocytes. Exposure of human spermatozoa to a concentration gradient of progesterone (0-3 microM) to simulate approach to the oocyte induced a slowly developing increase in [Ca(2+)](i) upon which, in many cells, slow oscillations were superimposed. [Ca(2+)](i) oscillations often started at very low progesterone (<10 nm), and their frequency did not change during the subsequent rise in concentration. Oscillations also occurred, but in a much smaller proportion of cells, in response to stepped application of progesterone (3 microM). When progesterone was removed, [Ca(2+)](i) oscillations often persisted or quickly resumed. Superfusion with low-Ca(2+) bathing medium (no added Ca(2+)) did not prevent [Ca(2+)](i) oscillations, but they could be abolished by addition of EGTA or La(3+). Inhibitors of sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPases or inositol trisphosphate signaling had no effect on [Ca(2+)](i) oscillations, but pharmacological manipulation of ryanodine receptors affected both their frequency and amplitude. Staining of live spermatozoa with BODIPY FL-X ryanodine showed localization of ryanodine binding primarily to the caudal part of the head and mid-piece. [Ca(2+)](i) oscillations did not induce acrosome reaction, but in cells generating oscillations, the flagellar beat mode alternated in synchrony with the oscillation cycle. Flagellar bending and lateral movement of the sperm head during [Ca(2+)](i) peaks were markedly increased compared with during [Ca(2+)](i) troughs. This alternating pattern of activity is likely to facilitate zona penetration. These observations show that progesterone initiates unusual and complex store-mediated [Ca(2+)](i) signaling in human spermatozoa and identify a previously unrecognized effect of progesterone in regulating sperm "behavior" during fertilization.

Sperm motility hyperactivation facilitates penetration of the hamster zona pellucida

These experiments were conducted to determine whether or not sperm motility hyperactivation facilities penetration of the zona pellucida of the oocyte. Two approaches were used. For the first, hamster sperm were incubated for 4.0-4.25 h in a capacitating medium that contained either 2.9 or 25.0 mM sodium bicarbonate. In these media, sperm became equally capacitated as evidenced by their ability to undergo the acrosome reaction when exposed to lysophosphatidyl choline or intact zonae pellucidae; however, sperm became hyperactivated only in the medium containing 25.0 mM bicarbonate. When these sperm were added to cumulus-free oocytes in vitro, only 2 of 88 oocytes were penetrated by sperm preincubated in 2.9 mM bicarbonate, while 31 of 86 oocytes were penetrated by sperm in 25.0 mM bicarbonate. It was found that equal numbers of sperm were bound to the oocytes and that equal numbers were acrosome-reacted on the surface of the zonae in the two media. For the second approach, sperm were incubated in a capacitating medium containing 25 mM bicarbonate. When > 70% were hyperactivated, aliquots were added to three sets of oocytes. After 10 min had been allowed for sperm to attach and acrosome-react, inhibitors of hyperactivation were added and the sperm and oocytes were incubated for an additional 20 min before fixation and examination for zona penetration. In the dishes treated with the inhibitors verapamil or Cd2+, 1 of 42 and 0 of 42 oocytes were penetrated, respectively, compared with 25 of 40 in controls. Therefore, it appears that hyperactivation facilitates penetration of the hamster zona pellucida.

Sulfated polysaccharides from the egg jelly layer are species-specific inducers of acrosomal reaction in sperms of sea urchins

We have characterized the fine structure of sulfated polysaccharides from the egg jelly layer of three species of sea urchins and tested the ability of these purified polysaccharides to induce the acrosome reaction in spermatozoa. The sea urchin Echinometra lucunter contains a homopolymer of 2-sulfated, 3-linked alpha-L-galactan. The species Arbacia lixula and Lytechinus variegatus contain linear sulfated alpha-L-fucans with regular tetrasaccharide repeating units. Each of these sulfated polysaccharides induces the acrosome reaction in conspecific but not in heterospecific spermatozoa. These results demonstrate that species specificity of fertilization in sea urchins depends in part on the fine structure of egg jelly sulfated polysaccharide.

Bicarbonate-induced membrane processing in sperm capacitation

During capacitation, major changes take place in the sperm plasma membrane so as to render it fusogenic and responsive to zona pellucida glycoproteins. However, the mechanisms involved have not been defined. As bicarbonate is known to be the key component that induces capacitation, we have investigated the bicarbonate-dependent changes in the boar sperm's plasma membrane architecture. We have discovered that bicarbonate induces a rapid collapse of phospholipid transverse asymmetry, exposing phosphatidylethanolamine and phosphatidylserine at the outer surface of the lipid bilayer. The collapse, which is reversible, is brought about as a result of activation of the phospholipid scramblase that exchanges phospholipids in a non-specific fashion between the two leaflets of the lipid bilayer. The activation takes place via a cyclic AMP-protein kinase A-dependent pathway and is initiated via stimulation of the so-called 'soluble' adenylyl cyclase in the sperm cell by bicarbonate. As a result of the collapse and the concurrent increase in phospholipid exchange, removal of cholesterol by albumin is facilitated (perhaps due to increased lipid packing disorder). This finding is in conflict with earlier surmises that cholesterol loss precedes activation of the cyclic AMP-protein kinase A axis. We have noted that not all cells in a given sperm population show rapid changes in response to bicarbonate stimulation; samples from individual boars also differ in their response. Maturation differences between cells have been found to play an important role in such functional heterogeneity.

Heparin-binding proteins from seminal plasma bind to bovine spermatozoa and modulate capacitation by heparin

Bovine spermatozoa that have been exposed to seminal plasma possess more binding sites for heparin than sperm from the cauda epididymis that have not been exposed to accessory sex gland secretions. Seminal plasma exposure enables sperm, following incubation with heparin, to undergo zonae pellucidae-induced exocytosis of the acrosome. In this study, the regulatory role of seminal plasma heparin-binding proteins in capacitation of bovine spermatozoa by heparin was investigated. Plasma membranes from sperm exposed to seminal plasma in vivo or in vitro contained a series of acidic 15-17 kDa proteins not found in cauda epididymal sperm. Western blots of membrane proteins indicated that these 15-17 kDa proteins bound [125I]-heparin. Heparin-binding proteins were isolated by heparin affinity chromatography from seminal plasma from vasectomized bulls. Gel electrophoresis indicated that the heparin-binding peaks contained 14-18 kDa proteins with isoelectric variation, a basic 24 kDa protein, and a 31 kDa protein. Western blots probed with [125I]-heparin confirmed the ability of each of these proteins to bind heparin. Each of these proteins, as well as control proteins, bound to epididymal sperm. The seminal plasma proteins were peripherally associated with sperm since they were removed by hypertonic medium and did not segregate into the detergent phase of Triton X-114. Seminal plasma heparin-binding proteins potentiated zonae pellucidae-induced acrosome reactions in epididymal sperm. However, seminal plasma proteins that did not bind to the heparin affinity column were unable to stimulate zonae-sensitivity. Control proteins, including lysozyme--which binds to both heparin and sperm, were ineffective at enhancing zonae-induced acrosome reactions. These data provide evidence for a positive regulatory role of seminal plasma heparin-binding proteins in capacitation of bovine spermatozoa.

Involvement of trypsin-like activity in binding of mouse spermatozoa to zonae pellucidae

Work from a number of laboratories has shown that fertilization is blocked in the presence of protease inhibitors, although the specific site of inhibition has not been identified. The present experiments were designed to discriminate between sperm binding to zonae pellucidae as opposed to sperm penetration through zonae, so as to assess the effect of protease inhibitors on these two distinct events. Exposure of capacitated mouse spermatozoa to a variety of protease inhibitors directed against trypsin blocked sperm binding to zonae in a concentration-dependent manner. A chymotrypsin-directed inhibitor was not capable of blocking sperm binding to zonae. The trypsin inhibitors did not affect sperm penetration though zonae nor gamete membrane fusion if the sperm had established a firm association with the zona surface before addition of the inhibitors. Previous incubation of zona-intact eggs with the inhibitors did not lead to a reduction in sperm binding, indicating that the activity affected by the inhibitors is borne by spermatozoa. Interaction between spermatozoa and the zona surface appeared to be the specific locus of inhibition; sperm binding to zona-free eggs (i.e., binding to the egg plasma membrane) was unaltered by the trypsin inhibitors. These results suggest a reevaluation of the function of proteases in fertilization focusing on their role in initial sperm contact with the zona pellucida.

Gender-specific glycosylation of human glycodelin affects its contraceptive activity

We have recently demonstrated that a human amniotic fluid-derived glycoprotein, glycodelin-A (GdA; previously known as PP14 or PAEP), potently inhibits gamete binding in an established sperm-egg binding system and expresses immunosuppressive activities directed against a variety of different immune cell types. GdA has high mannose-, hybrid-, and complex-type biantennary oligosaccharides including structures with fucosylated or sialylated N, N'-diacetyllactosediamine (GalNAcbeta1-4GlcNAc) sequences, which are rare in other human glycoproteins. We now report the characterization of glycodelin-S (GdS). This is a human seminal plasma glycoprotein that is immunologically indistinguishable from GdA, but unlike the latter, does not inhibit human sperm-zona pellucida binding under hemizona assay conditions. Analysis of the N-glycans of GdS by mass spectrometry revealed that all glycoforms of GdS are different from those of GdA. GdS glycans are unusually fucose-rich, and the major complex-type structures are biantennary glycans with Lewisx (Galbeta1-4(Fucalpha1-3)GlcNAc) and Lewisy (Fucalpha1-2Galbeta1-4(Fucalpha1-3)GlcNAc) antennae. It is probable that these highly fucosylated epitopes contribute to the immunosuppressive activity of human seminal plasma and to the low immunogenicity of sperm. This study provides the first evidence for gender-specific glycosylation that may serve to regulate key processes involved in human reproduction.

Sperm and oocyte treatments to improve the formation of male and female pronuclei and subsequent development following intracytoplasmic sperm injection into bovine oocytes

This study assessed pronuclear formation, the chromosomal constitution, and the developmental capacity of bovine zygotes formed by intracytoplasmic injection of oocytes with sperm, treated or not with dithiothreitol (DTT). Oocytes were matured in vitro for 22-24 h and then centrifuged so that sperm, prepared by swim-up in the presence or absence of 5 mM DTT, could be injected into the cleared area of the ooplasm. Injected oocytes were activated by treatment with 5 microM ionomycin (5 min) and, after a 3-h interval, with 1.9 mM 6-dimethylaminopurine (DMAP) for 3 h. They were then cocultured with bovine oviductal epithelial cells in M199. Sperm treatment resulted in a significantly higher proportion of male pronucleus formation 16 h after injection (40% vs. 11%; p < 0.0001) and a significantly higher rate of blastocyst development (24% vs. 10%; p < 0.005). Sixty-one percent of blastocysts produced with treated sperm were diploid. Of 12 blastocysts produced with treated sperm and sexed by a polymerase chain reaction, 4 were male and 7 female, and in one a definite diagnosis could not be made. Embryo transfer (2 embryos per heifer) resulted in pregnancies in 6 of 16 recipients at Day 49, but none was carried to term. These results show that the efficiency of bovine intracytoplasmic sperm injection can be improved by sperm pretreatment with DTT and by oocyte activation with ionomycin plus DMAP, although the developmental capacity of the resulting embryos remains limited.

Minimum and maximum extracellular Ca2+ requirements during mouse sperm capacitation and fertilization in vitro

The minimum and maximum extracellular Ca2+ concentrations required to promote capacitation, the acrosome reaction, hyperactivated motility, zona penetration and gamete fusion in the mouse have been established. The traces of free calcium in Ca2+-deficient medium were shown not to enhance capacitation since the inclusion of EGTA to chelate free ions during a 120 min preincubation failed to alter the kinetics of capacitation from those observed in the absence of EGTA; 1 h after addition of 1.80 mM-Ca2+, both suspensions were highly fertile. Complete capacitation, when suspensions were immediately functional upon the addition of 1.80 mM-Ca2+, required the presence of greater than or equal to 90 microM-Ca2. Considerably higher concentrations were required to initiate optimal sperm responses: acrosome reaction, 900 microM; gamete fusion, 900 microM; hyperactivated motility, 1.80 mM; zona penetration, 1.80 mM. None of these changes was effected when Ca2+ was less than 450 microM. The responses to elevated Ca2+ were dependent on the length of incubation, being initially positive and then negative. A short (30 min) exposure to 3.40 mM-Ca2+ (x 2 the standard) accelerated capacitation, as evidenced by significantly increased acrosome loss, precocious expression of hyperactivated motility and enhanced fertilizing ability when Ca2+ was reduced to 1.80 mM. However, extended (120 min) preincubation irreversibly damaged sperm function. In the presence of 7.20 mM-Ca2+ (x 4), fertilizing ability was inhibited at both 30 and 120 min, despite a high incidence of acrosome loss. The primary deleterious effect appeared to be on motility which was judged to be more erratic than in 1.80 mM-Ca2+, possibly due to elevated intracellular Ca2+. Because of the considerable difference in threshold Ca2+ concentrations, it is now possible to dissociate the Ca2+-dependent events of capacitation from those of the acrosome reaction and motility changes.

Analysis of human sperm function following exposure to the ionophore A23187. Comparison of normospermic and oligozoospermic men

Time exposure photomicrography and interspecific in vitro fertilization techniques have been used to compare the responses to the divalent cation ionophore A23187 of spermatozoa from normal fertile and oligozoospermic men. The fertilizing capacity of spermatozoa from the fertile controls produced a bell-shaped dose response curve when assessed in the presence of ionophore. The optimal responses occurred in the presence of 50 and 100 microM A23187. At this concentration, a mean penetration rate of about 75%, in association with multiple polyspermy, was observed without significant changes in motility patterns. At higher doses of A23187, there was a decline in fertilization rates, an independent reduction in sperm motility, and a significant decrease in the amplitude of lateral sperm head displacement. In contrast to the fertile controls, spermatozoa recovered from patients with oligozoospermia failed to exhibit a significant change in their fertilizing potential following exposure to A23187. Calculations based on the Poisson distribution theory indicated that this lack of responsiveness was not related to any differences in the motility of the spermatozoa from the oligozoospermic patients compared to the controls. These results suggest that calcium ionophores may be of value in providing a rapid and sensitive indicator of the functional competence of human spermatozoa, which circumvents problems concerning the rate and efficiency of sperm capacitation encountered with conventional protocols.

Stimulation of rhesus monkey sperm capacitation by cyclic nucleotide mediators

Capacitation of rhesus monkey spermatozoa was assessed by monitoring sperm flagellar beat and trajectory changes during incubation in vitro and by determining sperm penetration into rhesus oocytes and hamster zona-free ova. Rhesus sperm capacitation in vitro depended on the addition to the culture medium of the cyclic nucleotide mediators, caffeine and dibutyryl cyclic AMP. Capacitation was correlated with the development of hyperactivated motility. Spermatozoa treated with the cyclic nucleotide mediators, and showing hyperactivated motility, penetrated 57.4% of all rhesus oocytes and fertilized 88.9% of mature rhesus oocytes that were morphologically normal. Control spermatozoa did not penetrate any of the eggs. Some sperm penetration into hamster ova occurred but was not statistically significant. These data provide a basis for achieving in-vitro fertilization in the rhesus monkey and information on specific sperm motility characteristics associated with fertilizing ability.

Characterization of the binding of recombinant mouse sperm fertilin beta subunit to mouse eggs: evidence for adhesive activity via an egg beta1 integrin-mediated interaction

The sperm protein fertilin (also known as PH-30) is a candidate for mediating the interactions between sperm and egg plasma membranes. Fertilin is a heterodimer. The beta subunit, which has a region with homology to the family of integrin ligands known as disintegrins, has been hypothesized to be involved in the binding of sperm to the egg surface. To investigate this hypothesis and determine what role fertilin beta plays in fertilization, we have expressed the putative extracellular domain of mouse fertilin beta in bacteria as a fusion protein with maltose-binding protein (hereafter referred to as recombinant fertilin beta-EC) and used two assays to characterize its binding to mouse eggs. Immunocytochemistry was used to examine the localization of recombinant fertilin beta-EC binding. A luminometric assay was also developed to quantify levels of binding of recombinant fertilin beta-EC to single eggs. We find that recombinant fertilin beta-EC binds to the region of the plasma membrane of the egg to which sperm bind, thus providing the first direct evidence that fertilin beta has adhesive properties. Peptides corresponding to the disintegrin domain of fertilin beta reduce its binding to eggs, suggesting that this domain is at least partially involved in the recognition of fertilin beta by binding sites on the egg. Treatment of zona pellucida-free eggs with chymotrypsin reduces the ability of the eggs to support the binding of recombinant fertilin beta-EC, implicating an egg surface protein as a binding site for recombinant fertilin beta-EC. Binding of recombinant fertilin beta-EC to eggs is also reduced in the absence of divalent cations and is supported by 2.0 mM Ca2+, Mg2+, or Mn2+. Furthermore, eggs incubated in recombinant fertilin beta-EC prior to in vitro fertilization show reduced levels of sperm binding. Finally, we have examined the possible role of integrins on eggs as receptors for fertilin beta, since an anti-alpha6 integrin subunit monoclonal antibody, GoH3, has been shown to inhibit sperm binding (E. A. C. Almeida et al. (1995) Cell 81, 1095-1104). We find that: (a) an increased amount of GoH3 epitope on the egg surface does not correlate with an increased ability of the eggs to bind sperm or recombinant fertilin beta-EC; (b) the GoH3 antibody has virtually no inhibitory effect on recombinant fertilin beta-EC binding; and (c) recombinant fertilin beta-EC binding is reduced in the presence of anti-beta1 integrin antibodies. These results suggest that a beta1-containing integrin participates in the binding of recombinant fertilin beta-EC to mouse eggs.