Ethanol inhibits human and hamster sperm penetration of eggs

The effect of alcohol on the fertilizing ability of both human and hamster spermatozoa was examined by an in vitro fertilization assay using hamster ova. Spermatozoa were incubated in capacitating media for 3 hr (hamster sperm) and 4 hr (human sperm). Hamster ova were inseminated with preincubated sperm and were examined after 2 to 3 hr. Ethanol was added to the capacitating media at concentrations of 25, 50, 100, 200, and 400 mg%. Fertilization of zona-free hamster eggs by human spermatozoa was reduced from 49.6% in no alcohol to 16.7% in 400 mg% ethanol. Fertilization of hamster eggs by hamster sperm revealed a reduction from 63.6% to 33.7% in cumulus-intact eggs and from 65.8% to 10.8% in cumulus-free eggs in the presence of ethanol at 400 mg%. Hamster sperm acrosome reaction was reduced from 47% to 12%. When these hamster sperm with reduced acrosome reaction were placed with zona-free hamster eggs, the 100% fertilization rate was not reduced; however, the fertilization index, which reflects the number of swelling sperm heads per egg, was reduced from 8.5 to 1.8. This suggests that as little as 12% of the sperm with an acrosome reaction is sufficient to fertilize 100% of the zona-free eggs. If ethanol was added to the insemination media only, there was no inhibition of fertilization by human sperm or hamster sperm that had been previously capacitated in an ethanol-free media. Removal of the ethanol from the preincubated sperm produced fertilization at control levels; thus the inhibitory effect is reversible. These results indicate that ethanol may affect fertilization by an inhibition of the capacitation and/or acrosome reaction process.     

Role of the sperm proteasome during fertilization and gamete interaction in the mouse

In this work, we have investigated the role of the sperm proteasome during in vitro fertilization (IVF) and gamete interaction in the mouse. Proteasome activity was measured in extract and intact sperm using a specific substrate. In addition, sperm were treated with specific proteasome inhibitors and evaluated during IVF, binding to the zona pellucida, and progesterone- and zona pellucida-induced acrosome reactions. In other experiments, sperm membrane proteins were obtained resuspending them in Triton X-114, shaking vigorously and let standing by 4 hr. Soluble sperm proteins were partitioned in the aqueous phase and sperm membrane proteins in the detergent phase. In both phases, proteasome activity was measured. Labeling of cell surface sperm proteins was carried out with the cell-impermeable NHS-LC biotin, extracted with Triton X-114, and mixing with avidin-agarose beads. Nonpermeabilized sperm were incubated with an anti-proteasome monoclonal antibody and evaluated by indirect immunofluorescence. The results indicate that sperm extracts as well as intact sperm had proteasome activity; the sperm proteasome was involved in IVF, specifically during sperm-zona pellucida binding and the acrosome reaction; soluble sperm membrane proteins exhibited proteasome activity; biotin experiments indicated the presence of proteasomes on the sperm surface, which was corroborated by indirect immunofluorescence experiments. All these observations indicate that the mouse sperm proteasome participates in the binding to the zona pellucida and the acrosome reaction and that there is a pool of proteasomes located on the sperm head.     

Activation of phospholipase A2 of human spermatozoa by proteases

The effect of various proteases (kallikrein, plasmin, and trypsin) on sperm phospholipase A₂ activity (PA₂: EC 3.1.1.4) has been studied. The addition of trypsin to spermatozoa, isolated and washed in the presence of the protease inhibitor benzamidine, increased PA₂ activity optimally with trypsin concentrations of 1.0–1.5 units/assay. In kinetic studies, all of the above proteases stimulated the deacylation of phosphatidylcholine (PC); in fresh spermatozoa, trypsin showed a higher activation potential than kallikrein or plasmin. In the presence of benzamidine, the activity remained at basal levels. Endogenous protease activity due to acrosin (control) resulted in an increase in PC deacylation compared to the basal level. The maximum activation time of PA₂ activity by proteases was 30 min. Natural protease inhibitors (soybean trypsin inhibitor and aprotinin) kept the PA₂ activity at basal levels and a by-product of kallikrein, bradykinin, did not significantly affect the control level. Protein extracts of fresh spermatozoa exhibited the same pattern of PA₂ activation upon the addition of proteases, thus indicating that the increase in PA₂ activity was not merely due to the release of the enzyme from the acrosome. All of these findings suggest the presence of a precursor form of phospholipase A₂ that can be activated by endogenous proteases (acrosin) as well by exogenous proteases present in seminal plasma and in follicular fluid (plasmin, kallikrein). Thus, this interrelationship of proteases and prophospholipase A₂ could activate a dormant fusogenic system: the resulting effect would lead to membrane fusion by lysolipids, key components in the acrosome reaction.     

Observations on the acrosome reaction of human sperm in vitro

Human sperm were incubated in vitro in serum or the defined medium TMPA and were periodically assessed for acrosome reactions using two new methods of assay. The first method, FITC-RCA labeling, was previously shown to be valid for estimating the percentage of normal acrosome reactions of human sperm. The second method, a triple staining technique, is shown in this study to give results comparable to those obtained with FITC-RCA labeling. The percentage of acrosome-reacted sperm was determined at 0, 2.5, 5, and 7 hr of incubation. In both media, some sperm had reacted by 2.5 hr; a maximum percentage of reactions occurred between 5 and 7 hr. The maximum percentage never exceeded 20–25%, which represents only one-third of the live sperm, ie, those potentially able to undergo normal acrosome reactions. It will be important in future studies to determine if this low-peak percentage is due to the fact that: (1) Commonly used culture media are suboptimal or (2) only about 25% of the sperm in a human ejaculate are capable of undergoing normal acrosome reactions.     

Cytochemical localization of membrane-bound Mg2+-dependent ATPase activity in guinea pig sperm head before and during the acrosome reaction

The distribution of ATPase activity in the heads of uncapacitated, capacitated, and acrosome-reacting guinea-pig spermatozoa was examined cytochemically using the Wachstein-Meisel's technique. In uncapacitated spermatozoa, the reaction products of the enzyme activity were localized on both the inner surface of the plasma membrane and the outer surface of the outer acrosomal membrane. The activity was Mg²⁺-dependent and inhibited by both Ca²⁺ and SH-blocking agents. This Mg²⁺-dependent ATPase activity was also demonstrated at the same sites in capacitated spermatozoa, whereas it was completely absent in acrosome-reacting spermatozoa. Although we did not determine the exact time of inactivation of the enzyme, it appeared to occur before the plasma membrane fused with the underlying outer acrosomal membrane. The abrupt loss of the Mg²⁺-dependent ATPase activity in the plasma and outer acrosomal membranes immediately before the onset of the acrosome reaction seems to suggest that inactivation of this enzyme by Ca²⁺ is one of the important biochemical events involved in the acrosome reaction.     

Localization and roles in fertilization of sperm proteasomes in the ascidian Halocynthia roretzi

We previously reported that sperm proteasome is responsible for degradation of the ubiquitinated vitelline-coat during fertilization in the ascidian Halocynthia roretzi. Here, we report the roles in fertilization and localization in the sperm cell surface of H. roretzi sperm proteasome. An anti-proteasome antibody, as well as the proteasome inhibitors MG115 and MG132, inhibited the fertilization, indicating that the sperm proteasome functions extracellularly in ascidian fertilization. In order to further assess this issue, the sperm surface proteasome activity was labeled with a cell-impermeable labeling reagent, NHS-LC-biotin, extracted with 0.1% CHAPS, and was subjected to a pull-down assay with avidin-agarose beads. It was found that a substantial amount of sperm proteasome is exposed to the cell surface. Partition analysis with Triton X-114 also revealed that a considerable amount of the sperm proteasome activity is partitioned into a lipid layer. Localization of the proteasome activity was investigated by fluorescence microscopy with succinyl-Leu-Leu-Val-Tyr-4-methylcoumaryl-7-amide as a substrate. The sperm proteasome activity was specifically detected in the sperm head region, and it was markedly activated upon sperm activation. The membrane-associated proteasome was purified from the membrane fraction of H. roretzi sperm by affinity chromatography using an anti-20S proteasome antibody-immobilized Sepharose column. SDS-PAGE of the purified preparation showed a similar pattern of subunit composition to that of the 26S proteasome of mammalian origin. Taken together, these results indicate that H. roretzi sperm has the membrane-associated proteasome on its head, which is activated upon sperm activation, and that sperm proteasome plays an essential role in H. roretzi fertilization.     

Acrosome reaction in sperm of the toad,bufo bufo japonicus

The acrosome in the sperm of the toad, Bufo bufo japonicus, consists of a membrane-limited acrosomal cap and a fibrous perforatorium. When sperm are incubated with the oviducal pars recta extract (PRE) for 30–60 min, the outer acrosomal membrane fuses with the overlying plasma membrane at several points with concomitant loss of the contents of the acrosomal cap. The inner acrosomal membrane thus exposed fuses with the plasma membrane at the caudal end of the acrosomal region. This PRE-induced acrosome reaction is completely inhibited by soybean trypsin inhibitor. Sperm found in the innermost jelly layer of inseminated eggs possess an intact acrosome, but those either passing through the vitelline coat or localizing in the perivitelline space are acrosome-reacted in the same manner as when treated with PRE. These observations, combined with recent evidence showing involvement of the pars recta substance in fertilization, indicate that the acrosome reaction occurring in a fertilizing sperm at or near the surface of the vitelline coat is a response to a substance that is derived from the pars recta and deposited in the vitelline coat.     

Alteration of sperm thiol-disulfide status and capacitation in the guinea pig

Epididymal spermatozoa of the guinea pig were incubated under conditions known to promote a rapid synchronous capacitation in a large proportion of the spermatozoa (Ca²⁺-free medium with lysophosphatidylcholine, LC) or in Ca ²⁺-free medium without LC. To study the effects of altered thiol-disulfide status and content, incubations were conducted with reagents that maintain and increase thiol groups (DTT, GSH), maintain and increase disulfide groups (diamide, GSSG), or which irreversibly block thiol groups by alkylation (NEM). The permeable DTT inhibited LC-induced capacitation and at high concentrations diminished the percentage of acrosome reactions in capacitated spermatozoa. The permeable diamide exhibited a stimulatory effect upon capacitation. The largely impermeable GSH and GSSG exhibited effects similar to their respective permeable counterparts but their effects were moderate and required extremely high concentrations. The DTT inhibition of LC-induced capacitation was reversible by washing and a further 1 hr incubation. In this final incubation after removal of DTT by washing, LC was absent too so its stimulatory effect must have been accomplished prior to washing and in the presence of DTT. NEM-alkylation of the existing thiol population did not affect LC-induced capacitation but alkylation of the increased thiol population after prior DTT treatment was inhibitory of capacitation. These results suggest that the maintenance and/or formation of disulfide groups on enzymes or structural proteins may be a component of the capacitation process. In contrast, the formation and maintenance by alkylation of increased thiol groups but not the maintenance of existing thiol groups, is inhibitory of capacitation. The relevance of these findings to a role for a thiol-sensitive proteinase in capacitation is discussed.     

Induction of the acrosome reaction in human spermatozoa by a fraction of human follicular fluid

Human ejaculated spermatozoa were washed through a Percoll gradient, preincubated for 10 hr in a defined medium containing serum albumin, and then induced to undergo rapid acrosome reactions by addition of human follicular fluid or a Sephadex G-75 column fraction of the fluid. Induction by follicular fluid did not occur when the spermatozoa were preincubated for only 0 or 5 hr. The reactions were detected by indirect immunofluorescence using a monoclonal antibody directed against the human sperm acrosomal region. The percentage of acrosomal loss counted by transmission electron microscopy agreed with that counted by immunofluorescence. The apparent molecular weight of the Sephadex G-75 fraction containing the peak of acrosome reaction-inducing activity was 45,000 ± 4,200 (SD). The occurrence of physiological acrosome reactions was supported by: assessing motility (no significant loss of motility occurred during the treatment period when sperm were preincubated with bovine serum albumin), transmission electron microscopy (the ultrastructural criteria for the acrosome reaction were met), and zona-free hamster oocyte binding and penetration (spermatozoa pretreated with the active fraction of follicular fluid, then washed and incubated with oocytes, showed significantly greater binding to and penetration of oocytes). The stimulation of the acrosome reaction by follicular fluid is apparently not due to blood serum contamination; treatment of preincubated spermatozoa with sera from the follicular fluid donors had no effect on the spermatozoa. The nature of the active component(s) in that fraction is currently being investigated.     

Effect of cholesterol and other sterols on human sperm acrosomal responsiveness

Human sperm become responsive to inducers of the acrosome reaction when they are washed free of seminal plasma and incubated in an appropriate medium. Previous work has shown that cholesterol-enriched medium prevents sperm from becoming responsive to the inducer, progesterone. Sperm that were incubated 24 hr in cholesterol-enriched medium and then treated with progesterone showed no evidence of membrane fusion, indicating that cholesterol acts at a stage before the earliest morphological change. Inhibition of acrosomal responsiveness by cholesterol was reversible. Among other sterols reported in mammalian sperm, desmosterol and cholesterol sulfate also inhibited sperm from becoming responsive, but cholesterol palmitate did not. Our results support a model in which sperm unesterified cholesterol, or a molecule in equilibrium with it, suppresses acrosomal responsiveness. Cholesterol-enriched medium also prevented sperm from becoming responsive to the calcium/proton exchanging ionophore, ionomycin, suggesting that cholesterol's effect may be, at least in part, at a point in the signal transduction pathway subsequent to the rise in intracellular-free calcium. © 1996 Wiley-Liss, Inc.     

Status of the rat acrosome during sperm-zona pellucida interactions

Over the past 40 years evidence from many sources has indicated that the mammalian acrosome reaction occurs within or near the cumulus oophorus. Recently, however, workers investigating in vitro fertilization in the mouse have concluded that in this system the acrosome reaction takes place on the surface of the zona pellucida. We have investigated the interaction of rat spermatozoa and the zona pellucida by using the scanning electron microscope (SEM) and two monoclonal antibodies which are directed to antigens of the rat sperm acrosome. When in vitro inseminated eggs from which the cumulus has been removed are viewed with the SEM some sperm heads on the surface of the zona pellucida appear unaltered whereas others appear to be undergoing changes. In vivo, all displayed altered head morphology. Using immunogold labeling we found that the two antibodies employed, 2C4 and 5B1, were directed to acrosomal content and vesiculating acrosomal membranes. Immunofluoresence staining of zonae pellucidae in in vitro fertilization studies revealed numerous small positive regions. These were presumably acrosomal content and membranes which had been left on the zona surface by spermatozoa which had been associated with the zona surface. Our results suggest that the rat acrosome interacts with the zona pellucida. During this interaction some acrosomal content and membranes detach from the spermatozoon and remain on the surface of the zona pellucida.     

In vitro capacitation and fertilizing ability of ejaculated rabbit sperm treated with lysophosphatidylcholine

Four experiments were replicated 1) to establish dose-response relationships between lysophosphatidylcholine (LPC), sperm motility, and the acrosome reaction (AR), 2) to evaluate the influence of rabbit serum (RS) on these endpoints, 3) to compare buck differences in induction of the AR, and 4) to examine fertilizing ability in vitro of sperm tested under the first three objectives. Semen was collected from Dutch-belted rabbits, washed once by centrifugation, resuspended, and preincubated for 2 or 4 hr in a chemically defined medium (DM), DM plus 20% RS, or BSA-free DM plus 20% RS at 37°C. At the end of preincubation LPC was added to the preincubated sperm at concentrations of from 0 to 100 μg/ml. Sperm were examined .5–4 hr later for AR and sperm motility. For in vitro fertilization, sperm and ova were coincubated in DM up to 24 hr after insemination and in a more complex medium for another 24 hr. Addition of LPC to 4-hr-preincubated sperm was more effective for inducing the AR than addition to 2-hr-preincubated sperm. A significant increase (P < .05) in the AR occurred in 15 and 30 min following exposure to 100 and 80 μg of LPC per ml, respectively, but the higher concentration of LPC decreased sperm motility. Addition of 20% RS to DM with or without BSA surprisingly inhibited the AR but maintained sperm motility, as expected. Bucks differed (P < .05) in the initial percentage and the induced percentage of AR sperm. For the AR the optimal concentration of LPC per ml was 80 μg, but for in vitro fertilization 60 μg tended to be superior.     

Effects of surfactants on the fertilizing capacity and acrosome reaction of sea urchin spermatozoa

The effects of seven surfactants on spermatozoa of the sea urchin, Hemicentrotus pulcherrimus, were studied. All these surfactants induced the acrosome reaction and inhibited the fertilizing capacity of spermatozoa. There was a statistically significant correlation between the concentrations that induce the acrosome reaction and inhibit fertilization. The critical micelle concentrations (CMC) of surfactants in sea water were almost even and these values, which are inherent physical properties of surfactants, did not provide a direct measure of their inhibitory effect of fertilization. Among seven surfactants, p-menthanyl-phenol polyoxyethylene (8.8) ether (TS-88) with a characteristic hydrophobes was the most potent both in the induction of acrosome reaction and in the inhibition of fertilization. Various ethylene oxide adducts to p-menthanyl-phenol were also tested for the purpose of comparison. It is suggested that the effects of surfactants on sea urchin spermatozoa at low concentrations reflect their activity associated with the hydrophobic group inherent in each surfactant.     

The status of acrosomal caps of hamster spermatozoa immediately before fertilization in vivo

Adult female golden hamsters were induced to superovulate. When they were mated several hours prior to ovulation or artificially inseminated about the time of ovulation, nearly 100% of their eggs were subsequently fertilized monospermically. During the progression of fertilization when the eggs were still surrounded by compact cumulus oophorus, the contents of the ampullary region of the oviducts were collected and spermatozoa moving in the ampullary fluid, within the cumulus and on/in the zonae pellucidae of unfertilized eggs, were examined by light and electron microscopy to evaluate the status of their acrosomal caps. Most spermatozoa swimming in the ampullary fluid had apparently intact acrosomal caps, while the vast majority moving within the cumulus had distinctly modified acrosomal caps. Most spermatozoa that had passed through the cumulus and reached the zona surfaces had remnants of their acrosomal caps (“acrosomal ghosts”). When the ghosts were present around the sperm heads on the zona, the heads pivoted about a point roughly corresponding to the places where the ghosts were located. The ghosts seemed to firmly attach to the zona surfaces, then were split open by the sperm heads and left behind as the sperm heads advanced into the zona. A few spermatozoa on the zona surfaces had no acrosomal ghosts (at least not detectable by light microscopy). In this case, the sperm head pivoted about either the inner acrosomal membrane or the equatorial segment of the acrosome. In no instance were spermatozoa with intact acrosomal caps found on zona surfaces. We infer from these observations that most spermatozoa in vivo initiate their acrosome reactions while they are advancing through the cumulus. When they arrive at the zona surfaces, acrosomal ghosts are generally present on the sperm heads. These ghosts appear to hold sperm heads to zona surfaces as well as to restrict the direction of advancement of sperm head through the zona. In a minority of cases, ghostless spermatozoa reach the zona surfaces. As these spermatozoa appear to be able to penetrate the zona successfully, structures other than the acrosomal ghost (ie, the inner acrosomal membrane and the plasma membrane over the equatorial segment of the acrosome) may also attach to zona surfaces before spermatozoa penetrate into the zona.     

Ultrastructural localization of proacrosin and acrosin in ram spermatozoa

Proacrosin and acrosin were localized immunocytochemically at the electron microscope level in ram spermatozoa undergoing an ionophore-induced acrosome reaction. Antigenicity was preserved after fixation with 0.5% w/v ethyl-(dimethylaminopropyl)-carbodimide, and an antibody preparation was used that reacted with all major forms of ram acrosin. All stages of the acrosome reaction could be observed in a single preparation. At the earliest stage, labeling was observed throughout the acrosomal contents, which were just beginning to disperse. As dispersal proceeded, labeling diminished, being associated only with visible remnants of the acrosomal matrix. By the time the acrosome had emptied, almost no labeling could be detected on the inner acrosomal membrane. The relationship between matrix dispersal and proacrosin activation was studied in isolated ram sperm heads. While proacrosin was prevented from activating, the acrosomal matrix remained compact; but as activation proceeded, the matrix decondensed and dispersed in close parallel. By the time proacrosin activation was complete, the acrosomal contents had almost entirely disappeared. We conclude that proacrosin is distributed throughout the acrosomal contents as an intrinsic constituent of the acrosomal matrix. During the acrosome reaction, proacrosin activation occurs, resulting directly in decondensation of the matrix. All the contents of the acrosome including acrosin disperse and, by the time the acrosome is empty and the acrosomal cap is lost, only occasional traces of acrosin remain on the inner acrosomal membrane. Since the acrosomal cap is normally lost during the earliest stages of zona penetration, acrosin's role in fertilization is unclear: it does not appear to be a zona lysin bound to the inner acrosomal membrane.     

Macaque sperm fusion with zona-free hamster oocytes

Abstract: Semen from six cynomolgus macaques was washed twice by centrifugation in BWW media and resuspended in 1:2 (vol:vol) of Tes-Tris-buffered eggyolk extract (EXT) diluent and BWW (EXT-BWW). Caffeine and dbcAMP were added to induce capacitation. Sperm were treated with calcium ionophore, A23187, followed by the addition of EXT to recover motility, then washed into BWW. The percent motile sperm was similar in ionophore-treated and control sperm suspensions, but motility of treated sperm decreased significantly by 20 min after treatment. The percentage of viable, acrosome-reacted sperm was 56.3% following ionophore treatment versus 4.0% in control suspensions. When ionophore-treated sperm were coincubated with zona-free hamster oocytes, 51 % of oocytes had evidence of sperm fusion and no oocytes were penetrated after incubation with control sperm. These results are consistent with the hypothesis that macaque sperm are capable of fusion with zona-free hamster oocytes if sperm are viable and acrosome-reacted.     

Possible involvement of CD81 in acrosome reaction of sperm in mice

Tetraspanin CD81 is closely homologous in amino acid sequence with CD9. CD9 is well known to be involved in sperm-egg fusion, and CD81 has also been reported to be involved in membrane fusion events. However, the function of CD81 as well as that of CD9 in membrane fusion remains unclear. Here, we report that disruption of the mouse CD81 gene led to a reduction in the fecundity of female mice, and CD81-/- eggs had impaired ability to fuse with sperm. Furthermore, we demonstrated that when CD81-/- eggs were incubated with sperm, some of the sperm that penetrated into the perivitelline space of CD81-/- eggs had not yet undergone the acrosome reaction, indicating that the impaired fusibility of CD81-/- eggs may be in part caused by failure of the acrosome reaction of sperm. In addition, we showed that CD81 was highly expressed in granulosa cells, somatic cells that surround oocytes. Our observations suggest that there is an interaction between sperm and CD81 on somatic cells surrounding eggs before the direct interaction of sperm and eggs. Our results may provide new clues for clarifying the cellular mechanism of the acrosome reaction, which is required for sperm-egg fusion.     

Comparative study of the biological activity of spermatozoa-zona pellucida binding inhibitory factors from human follicular fluid on various sperm function parameters.

Previous studies showed that human follicular fluid (hFF) from gonadotrophin stimulated cycles contained two glycoproteins, named as ZIF-1 and ZIF-2, that reduced the zona binding capacity of spermatozoa. The present study showed that the spermatozoa-zona pellucida binding inhibitory activity was also present in hFF from natural cycle. Using the hemizona binding assay, the inhibitory effect of ZIF-1 on the zona binding capacity of spermatozoa was dose-dependent. The effect of ZIF-2 was also dose-dependent, in the range of 10-100 ng/ml. The inhibitory effects of both ZIF-1 and -2 increased with the duration of the spermatozoa-ZIF interaction. The effect of the former was present up to 120 min incubation, whilst that of latter occurred for the first 90 min. The zona binding inhibitory effect of ZIF-1 and -2 was additive when they were used together to treat the spermatozoa. The biological activity of ZIFs on other sperm parameters that might affect spermatozoa-zona pellucida binding was also investigated. ZIF-1 did not affect the acrosomal status of human spermatozoa while ZIF-2 significantly increased the number of acrosome reacted spermatozoa in the range of 0.1-10 microg. However, the increase in the incidence of acrosome-reacted spermatozoa after ZIF-2 treatment could not totally account the inhibitory effect of ZIF-2 on zona binding. Both glycoproteins did not affect the motility of human spermatozoa. Radioactively-labelled ZIFs bound to human spermatozoa. Unlabelled ZIF displaced the bound radioactivity of spermatozoa treated with the corresponding labelled ZIF. These suggested the presence of specific binding sites of ZIFs on human spermatozoa.     

Giant,accordioned sperm acrosomes of the greater bulldog bat,Noctilio leporinus

Sperm of the greater bulldog bat Noctilio leporinus display an architecture that is totally unique among mammalian spermatozoa. The sperm head of Noctilio is extraordinarily large and flat and lies eccentrically with respect to the sperm tail. The major portion of the atypically large acrosome lies anterior to the nucleus and is shaped into a dozen accordionlike folds that run parallel to the long axis of the sperm. The ridge of each fold is shaped into ∼60 minute, evenly spaced rises that extend along the entire length of the fold. We speculate that acrosome ridges may serve to strengthen the sperm head during transport. Mol. Reprod. Dev. 48:90–94, 1997 © 1997 Wiley-Liss, Inc.     

Egg and sperm recognition systems during fertilization

Fertilization is a programmed process that has many molecules and sequential events amenable to study. The biochemistry of fertilization has identified cellular and acellular components fundamental to the interactions between sperm and egg. Recent studies highlight the molecular details of the species-specificity of fertilization that involve protein–protein and protein–carbohydrate interactions. Although the diversity of structure and mechanism may imply rapid evolution of fertilization proteins, understanding the structure–function relationships has become important. Here, we introduce the molecules controlling the sperm AR, sperm attachment to, and penetration through, the egg investments.