Mechanism for procaine-mediated hyperactivated motility in guinea pig spermatozoa

Hyperglycemia adversely affects critical physiological events related to rat sperm capacitation

Hyperglycemia, the hallmark of diabetes mellitus (DM), is the main cause of DM-related systemic complications, including reproductive issues. Furthermore, the incidence of DM in males of reproductive ages is becoming an increasing concern, as the complexity of sperm capacitation (an essential process for fertilizing the egg) extends beyond conventional sperm parameters such as count, viability, and motility. Capacitation defects cause male infertility, and DM-related hyperglycemia may affect this process. We explore the effects of uncontrolled hyperglycemia on sperm using alloxan-induced hyperglycemic Wistar rats. In addition to assessing conventional sperm parameters, we also evaluated functional indicators, including hyperactivation (HA) with a pharmacological approach and assessed its effects with a computer-assisted sperm analysis (CASA); fluorescence indicators to monitor membrane potential (EmR, DiSC3(5)) and mitochondrial membrane potential (Ψ, JC-1); CatSper activity, using its ability to permeate Na+ ions, and ATP levels with the luciferin-luciferase reaction. We confirmed previous findings with our hyperglycemic model, which replicated the typical reduction on conventional sperm parameters. In sperm from hyperglycemic rats, we observed increased motility and HA levels after pharmacological treatment. Additionally, CatSper activity was unaffected by hyperglycemia, while EmR was hyperpolarized under non-capacitating condition. Finally, we noted a low percentage of hyperpolarized Ψ and reduced ATP content. This study highlights the significance of impact of hyperglycemia on sperm physiology and capacitation. We proposed that low ATP levels perturb energy state, signaling pathways, ion channels activity, motility, and HA. Our findings offer insight into DM-associated infertility and potential treatment strategies.

Update on mammalian sperm capacitation: how much does the horse differ from other species?

In contrast to various other mammalian species, conventional in vitro fertilization (IVF) with horse gametes is not reliably successful. In particular, stallion spermatozoa fails to penetrate the zona pellucida, most likely due to incomplete activation of stallion spermatozoa (capacitation) under in vitro conditions. In other mammalian species, specific capacitation triggers have been described; unfortunately, none of these is able to induce full capacitation in stallion spermatozoa. Nevertheless, knowledge of capacitation pathways and their molecular triggers might improve our understanding of capacitation-related events observed in stallion sperm. When sperm cells are exposed to appropriate capacitation triggers, several molecular and biochemical changes should be induced in the sperm plasma membrane and cytoplasm. At the level of the sperm plasma membrane, (1) an increase in membrane fluidity, (2) cholesterol depletion and (3) lipid raft aggregation should occur consecutively; the cytoplasmic changes consist of protein tyrosine phosphorylation and elevated pH, cAMP and Ca2+ concentrations. These capacitation-related events enable the switch from progressive to hyperactivated motility of the sperm cells, and the induction of the acrosome reaction. These final capacitation triggers are indispensable for sperm cells to migrate through the viscous oviductal environment, penetrate the cumulus cells and zona pellucida and, finally, fuse with the oolemma. This review will focus on molecular aspects of sperm capacitation and known triggers in various mammalian species. Similarities and differences with the horse will be highlighted to improve our understanding of equine sperm capacitation/fertilizing events.

Novel methods to detect capacitation-related changes in spermatozoa

Prior to interaction with the oocyte, spermatozoa must undergo capacitation, which involves a series of physio-chemical transformations that occur in the female tract. As capacitation is a pre-requisite for successful fertilisation, it is a topic of great interest for sperm biologists, but the complexity of the numerous biochemical and biophysical processes involved make it difficult to measure. Capacitation is an extremely complex event that encompasses numerous integrated processes that can occur concurrently during this window of time. The identification of techniques to accurately assess and quantify capacitation is therefore crucial to gain a meaningful insight into this fascinating sperm maturation event. Whilst there are extensive reviews in the literature that focus on the functional changes to spermatozoa during capacitation, few have examined the methods required to measure these changes. The aim of this review is to highlight frequently used methods to quantify different stages of capacitation and identify promising novel techniques. Factors that are able to modulate various capacitation processes will also be discussed. The overall outcome is to provide researchers with a toolbox of methods that can be used to gain a deeper understanding of the intricacies of capacitation in spermatozoa.

Lessons from reproductive technology research

A plethora of assisted reproductive technologies (ARTs) have come into routine use over the past half century. Some of these procedures were used much earlier experimentally. For example, Spallanzani performed artificial insemination in the dog in the late 1700s, and Heape did successful embryo transfer in the rabbit in 1890. Truly revolutionary tools and concepts important for ART occur at approximately half-decade intervals, for example, recombinant DNA procedures, transgenic technology, somatic cell nuclear transplantation, the polymerase chain reaction, and microRNAs. Similarly, obvious technologies sometimes take decades to come into practical use, such as sexing sperm and in vitro fertilization. I have categorized ARTs into five somewhat arbitrary categories in terms of perceived difficulty and feasibility: (a) when the seemingly possible turns out to be (essentially) impossible, e.g., homozygous, uniparental females; (b) when the seemingly impossible becomes possible, e.g., cryopreservation of embryos and transgenesis; (c) when the seemingly difficult turns out to be relatively easy, e.g., cryopreservation of sperm; (d) when the seemingly easy turns out to be difficult in key species, e.g., in vitro fertilization; and (e) when the seemingly difficult remains difficult, e.g., making true embryonic stem cells. The adage that "it is easy when you know how" applies repeatedly. The boundaries between what appears impossible/possible and difficult/easy change constantly owing to new tools and insights, one of the more important lessons learned. ARTs frequently are synergistic with each other. For example, somatic cell nuclear transplantation has made many kinds of experiments feasible that otherwise were impractical. Another example is that sexing sperm is useless for application without artificial insemination or in vitro fertilization. ARTs frequently are perceived as neat tricks and stimulate further thinking. This is useful for both teaching and research.

Reduced glutathione and procaine hydrochloride protect the nucleoprotein structure of boar spermatozoa during freeze–thawing by stabilising disulfide bonds

One important change the head of boar spermatozoa during freeze–thawing is the destabilisation of its nucleoprotein structure due to a disruption of disulfide bonds. With the aim of better understanding these changes in frozen–thawed spermatozoa, two agents, namely reduced glutathione (GSH) and procaine hydrochloride (ProHCl), were added at different concentrations to the freezing media at different concentrations and combinations over the range 1–2 mM. Then, 30 and 240 min after thawing, cysteine-free residue levels of boar sperm nucleoproteins, DNA fragmentation and other sperm functional parameters were evaluated. Both GSH and ProHCl, at final concentrations of 2 mM, induced a significant (P < 0.05) increase in the number of non-disrupted sperm head disulfide bonds 30 and 240 min after thawing compared with the frozen–thawed control. This effect was accompanied by a significant (P < 0.05) decrease in DNA fragmentation 240 min after thawing. Concomitantly, 1 and 2 mM GSH, but not ProHCl at any of the concentrations tested, partially counteracted the detrimental effects caused by freeze–thawing on sperm peroxide levels, motility patterns and plasma membrane integrity. In conclusion, the results show that both GSH and ProHCl have a stabilising effect on the nucleoprotein structure of frozen–thawed spermatozoa, although only GSH exerts an appreciable effect on sperm viability.

Behavioral mechanism during human sperm chemotaxis: involvement of hyperactivation

When mammalian spermatozoa become capacitated they acquire, among other activities, chemotactic responsiveness and the ability to exhibit occasional events of hyperactivated motility—a vigorous motility type with large amplitudes of head displacement. Although a number of roles have been proposed for this type of motility, its function is still obscure. Here we provide evidence suggesting that hyperactivation is part of the chemotactic response. By analyzing tracks of spermatozoa swimming in a spatial chemoattractant gradient we demonstrate that, in such a gradient, the level of hyperactivation events is significantly lower than in proper controls. This suggests that upon sensing an increase in the chemoattractant concentration capacitated cells repress their hyperactivation events and thus maintain their course of swimming toward the chemoattractant. Furthermore, in response to a temporal concentration jump achieved by photorelease of the chemoattractant progesterone from its caged form, the responsive cells exhibited a delayed turn, often accompanied by hyperactivation events or an even more intense response in the form of flagellar arrest. This study suggests that the function of hyperactivation is to cause a rather sharp turn during the chemotactic response of capacitated cells so as to assist them to reorient according to the chemoattractant gradient. On the basis of these results a model for the behavior of spermatozoa responding to a spatial chemoattractant gradient is proposed.

Dose-response effects of estrogenic mycotoxins (zearalenone, alpha- and beta-zearalenol) on motility, hyperactivation and the acrosome reaction of stallion sperm

BACKGROUND

The aim of this study was to investigate the in vitro effects of the Fusarium fungus-derived mycotoxin, zearalenone and its derivatives alpha-zearalenol and beta-zearalenol on motility parameters and the acrosome reaction of stallion sperm. Since the toxic effects of zearalenone and its derivatives are thought to result from their structural similarity to 17beta-estradiol, 17beta-estradiol was used as a positive control for 'estrogen-like' effects.

METHODS

Stallion spermatozoa were exposed in vitro to zearalenone, alpha-zearalenol, beta-zearalenol or 17beta-estradiol at concentrations ranging from 1 pM - 0.1 mM. After 2 hours exposure, motility parameters were evaluated by computer-assisted analysis, and acrosome integrity was examined by flow cytometry after staining with fluoroscein-conjugated peanut agglutinin.

RESULTS

Mycotoxins affected sperm parameters only at the highest concentration tested (0.1 mM) after 2 hours exposure. In this respect, all of the compounds reduced the average path velocity, but only alpha-zearalenol reduced percentages of motile and progressively motile sperm. Induction of motility patterns consistent with hyperactivation was stimulated according to the following rank of potency: alpha-zearalenol > 17beta-estradiol > zearalenone = beta-zearalenol. The hyperactivity-associated changes observed included reductions in straight-line velocity and linearity of movement, and an increase in the amplitude of lateral head displacement, while curvilinear velocity was unchanged. In addition, whereas alpha- and beta- zearalenol increased the percentages of live acrosome-reacted sperm, zearalenone and 17beta-estradiol had no apparent effect on acrosome status. In short, alpha-zearalenol inhibited normal sperm motility, but stimulated hyperactive motility in the remaining motile cells and simultaneously induced the acrosome reaction. Beta-zearalenol induced the acrosome reaction without altering motility. Conversely, zearalenone and 17beta-estradiol did not induce the acrosome reaction but induced hyperactive motility albeit to a different extent.

CONCLUSIONS

Apparently, the mycotoxin zearalenone has 17beta-estradiol-like estrogenic activity that enables it to induce hyperactivated motility of equine sperm cells, whereas the zearalenol derivatives induce premature completion of the acrosome reaction and thereby adversely affect stallion sperm physiology. The alpha form of zearalenol still possessed the estrogenic ability to induce hyperactivated motility, whereas its beta stereo-isomere had lost this property.

Effect of procaine, pentoxifylline and trolox on capacitation and hyperactivation of stallion spermatozoa

Reasons for low in vitro fertilisation rates in the horse include the difficulties in inducing capacitation and/or hyperactivation of stallion spermatozoa. The aim of this study was to analyse the effect of noncapacitating and capacitating modified Whitten's (MW) and modified Tyrode's medium (MT) and treatment with procaine (5 mmol), pentoxifylline (3.5 mmol) and trolox (120 mmol) on motility (CASA), capacitation, acrosomal status, viability and mitochondrial membrane potential of stallion spermatozoa (n = 4). While there was no influence of MW and MT on sperm motility, a significant increase in the percentage of viable-capacitated spermatozoa was observed after incubation in capacitating MW (P < 0.05). Pentoxifylline showed no significant effect on the motility pattern but increased the proportion of live-capacitated spermatozoa (P < 0.05). Trolox had no detectable effect on either capacitation or hyperactivation. Procaine was the only agent that induced hyperactivation in terms of a reduced proportion of progressively motile spermatozoa, straight line velocity, straightness, linearity and beat-cross frequency and an increase in the amplitude of lateral head displacement (P < 0.05). The combination of capacitating Whitten's medium and procaine showed the best results for the induction of capacitation and hyperactivation in stallion spermatozoa; this was possible even after short-term incubation.

Two distinct Ca(2+) signaling pathways modulate sperm flagellar beating patterns in mice

Hyperactivation, a swimming pattern of mammalian sperm in the oviduct, is essential for fertilization. It is characterized by asymmetrical flagellar beating and an increase of cytoplasmic Ca(2+). We observed that some mouse sperm swimming in the oviduct produce high-amplitude pro-hook bends (bends in the direction of the hook on the head), whereas other sperm produce high-amplitude anti-hook bends. Switching direction of the major bends could serve to redirect sperm toward oocytes. We hypothesized that different Ca(2+) signaling pathways produce high-amplitude pro-hook and anti-hook bends. In vitro, sperm that hyperactivated during capacitation (because of activation of CATSPER plasma membrane Ca(2+) channels) developed high-amplitude pro-hook bends. The CATSPER activators procaine and 4-aminopyridine (4-AP) also induced high-amplitude pro-hook bends. Thimerosal, which triggers a Ca(2+) release from internal stores, induced high-amplitude anti-hook bends. Activation of CATSPER channels is facilitated by a pH rise, so both Ca(2+) and pH responses to treatments with 4-AP and thimerosal were monitored. Thimerosal triggered a Ca(2+) increase that initiated at the base of the flagellum, whereas 4-AP initiated a rise in the proximal principal piece. Only 4-AP triggered a flagellar pH rise. Proteins were extracted from sperm for examination of phosphorylation patterns induced by Ca(2+) signaling. Procaine and 4-AP induced phosphorylation of proteins on threonine and serine, whereas thimerosal primarily induced dephosphorylation of proteins. Tyrosine phosphorylation was unaffected. We concluded that hyperactivation, which is associated with capacitation, can be modulated by release of Ca(2+) from intracellular stores to reverse the direction of the dominant flagellar bend and, thus, redirect sperm.

Control of hyperactivation in sperm

BACKGROUND

Sperm hyperactivation is critical to fertilization, because it is required for penetration of the zona pellucida. Hyperactivation may also facilitate release of sperm from the oviductal storage reservoir and may propel sperm through mucus in the oviductal lumen and the matrix of the cumulus oophorus. Hyperactivation is characterized by high amplitude, asymmetrical flagellar bending.

METHODS

This is a review of the original literature on the mechanisms that regulate hyperactivation, including physiological factors and signaling pathways.

RESULTS

Computer-assisted semen analysis systems can be used to identify hyperactivated sperm by setting minimum thresholds for curvilinear velocity (VSL) and lateral head movement and a maximum threshold for path linearity. Hyperactivation is triggered by a rise in flagellar Ca(2+) resulting from influx primarily through plasma membrane CatSper channels and possibly also by release of Ca(2+) from a store in the redundant nuclear envelope. It requires increased pH and ATP production. The physiological signals that trigger the rise in Ca(2+) remain elusive, but there is evidence that the increased Ca(2+) acts through a calmodulin/calmodulin kinase pathway. Hyperactivation is considered part of the capacitation process; however, the regulatory pathway that triggers hyperactivation can operate independently from that which prepares sperm to undergo the acrosome reaction. Hyperactivation may be modulated by chemotactic signals to turn sperm toward the oocyte.

CONCLUSIONS

Little is known about exactly what triggers hyperactivation in human sperm. This information could enable clinicians to develop reliable fertility assays to assess normal hyperactivation in human sperm samples.

Sperm Motility Defects and Infertility in Male Mice with a Mutation in Nsun7, a Member of the Sun Domain-Containing Family of Putative RNA Methyltransferases1

Poor sperm quality is the major cause of infertility in humans. Other than sex-linked factors, the genetic basis for male infertility is poorly defined, largely due to practical difficulties in studying the inheritance of this trait in humans. As an alternative, we have conducted forward genetic screens in mice to generate relevant models. We report on the identification and characterization of a chemically-induced mutation, Ste5Jcs1, which causes affected male mice to be sterile or subfertile. Mutant sperm exhibited depressed progressive motility associated with a rigid flagellar midpiece (but not principal piece) segment, which could not be rescued by treatment with agents that stimulate cAMP or calcium signaling pathways. Overall mutant sperm ultrastructure appeared normal, including the axoneme, although the midpiece mitochondrial sheath showed abnormal electron density patterns. Positional cloning of Ste5Jcs1 led to the identification of a mutation in a novel gene called Nsun7, which encodes a protein with a Sun domain that is homologous to tRNA and rRNA cytosine methyltransferases. Therefore, Ste5Jcs1 mutation uncovers a previously unrecognized biological process in sperm that underscores the functional compartmentalization of the midpiece and principal piece of the flagellum.

Bovine Sperm Hyperactivation Is Promoted by Alkaline-Stimulated Ca2+ Influx1

Sperm hyperactivated motility is characterized by high flagellar bend amplitude and asymmetrical beating, which are detected by computer-assisted sperm motility analysis as increased curvilinear velocity and lateral head movement. It is required for sperm penetration of the oocyte zona pellucida during fertilization and is induced by an increase in flagellar Ca(2+). Our objective was to determine whether pH plays a role in promoting Ca signaling of hyperactivated motility. The cell-permeant weak base NH(4)Cl increased curvilinear velocity and amplitude of lateral head movement of bovine sperm, indicative of hyperactivation. Fluorometric recordings of sperm loaded with BCECF-AM or fluo3-AM, revealed that NH(4)Cl evoked elevations of intracellular pH and Ca(2+), respectively, with the rise in pH occurring more rapidly than that of Ca(2+). Single-cell image analysis showed increased Ca(2+) levels in the flagellum in response to NH(4)Cl. When extracellular Ca(2+) was lowered with BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) prior to treatment with NH(4)Cl, intracellular pH was increased, but elevation of Ca(2+) and hyperactivation were diminished. This suggests that the rise in intracellular pH precedes an influx of Ca(2+). The Ca(2+) channel blocker Ni(2+) also diminished NH(4)Cl stimulation of hyperactivation, demonstrating that Ca(2+) entry is required for maximal expression of hyperactivation. Ca(2+) ionophore produced an increase in Ca(2+) that was 3-fold greater than that produced by NH(4)Cl; however, it produced a weaker hyperactivation response. These results indicate that a rise in pH increases intracellular Ca(2+)and promotes hyperactivation primarily by stimulating Ca(2+) influx, but also by other mechanisms.

F-actin involvement in guinea pig sperm motility

Sperm motility is a must for natural fertilization to occur. During their travel through the epididymis, mammalian spermatozoa gradually acquire the ability to move. This is accomplished through a sliding movement of the outer doublet microtubules of the axoneme which is energized by the dynein ATPase. Within its complex structure, the mammalian sperm flagellum contains F-actin and thus, we decided to test in the guinea pig sperm flagellum the role of F-actin in motility. During maturation, capacitation, and the acrosome reaction, a gradual decrease of the relative concentration of F-actin was observed. Motility increased as spermatozoa became able to fertilize. Gelsolin, phalloidin, and KI inhibited sperm motility. Gelsolin canceled sperm motility within 20 min of treatment while 0.6 M KI had immediate effects. Phalloidin diminished hyperactive sperm motility slightly. All three compounds significantly increased the relative concentration of F-actin. Latrunculins are conventional drugs that destabilize the F-actin cytoskeleton. Latrunculin A (LAT A) did not affect sperm motility; but significantly increased F-actin relative concentration. The results suggested that in guinea pig spermatozoa, randomly severing F-actin filaments inhibits flagellar motility; while end filament alteration does not. Thus, specific filament regions seem to be important for sperm motility.

In guinea pig spermatozoa, the procaine-promoted synchronous acrosome reaction results in highly fertile cells exhibiting normal F-actin distribution

In guinea pig spermatozoa, procaine induces Ca(2+) independent hyperactivated motility suggestive of sperm capacitation. Nonetheless, in the presence of high extracellular Ca(2+), procaine increases cytoplasmic Ca(2+). We analyze the procaine effect on the acrosome reaction (AR) processes in guinea pig spermatozoa. Results indicated that: (i) in spermatozoa pre-incubated 5-30 min in MCM-PLG medium, procaine produced synchronous AR, (ii) the acrosome-reacted sperm number increased with the capacitation period before procaine treatment and with procaine concentration, (iii) acrosome reaction was blocked when Ca(2+) was omitted, (iv) plasma membrane-outer acrosomal membrane fusion started within 2 min after procaine treatment, (v) in acrosome-reacted spermatozoa, actin polymerization occurred and F-actin was located in the equatorial and post-acrosomal regions and (vi) procaine treatment resulted in highly fertile acrosome-reacted spermatozoa. This is the first report indicating that procaine promotes synchronic AR in mammalian spermatozoa. If procaine promotes premature AR of spermatozoa in vivo, it might be a factor for infertility in patients exposed to this local anesthetic.

Calcium Channels and Ca2+ Fluctuations in Sperm Physiology

Generating new life in animals by sexual reproduction depends on adequate communication between mature and competent male and female gametes. Ion channels are instrumental in the dialogue between sperm, its environment, and the egg. The ability of sperm to swim to the egg and fertilize it is modulated by ion permeability changes induced by environmental cues and components of the egg outer layer. Ca(2+) is probably the key messenger in this information exchange. It is therefore not surprising that different Ca(2+)-permeable channels are distinctly localized in these tiny specialized cells. New approaches to measure sperm currents, intracellular Ca(2+), membrane potential, and intracellular pH with fluorescent probes, patch-clamp recordings, sequence information, and heterologous expression are revealing how sperm channels participate in fertilization. Certain sperm ion channels are turning out to be unique, making them attractive targets for contraception and for the discovery of novel signaling complexes.

Different signaling pathways in bovine sperm regulate capacitation and hyperactivation

Hyperactivated sperm motility is characterized by high-amplitude and asymmetrical flagellar beating that assists sperm in penetrating the oocyte zona pellucida. Other functional changes in sperm, such as activation of motility and capacitation, involve cross talk between the cAMP/PKA and tyrosine kinase/phosphatase signaling pathways. Our objective was to determine the role of the cAMP/protein kinase A (PKA) signaling pathway in hyperactivation. Western blot analyses of detergent extracts of whole sperm and flagella were performed using antiphosphotyrosine antibody. Bull sperm capacitated by 10 microg/ml heparin and/or 1 mM dibutyryl-cAMP plus 100 microM 3-isobutyl-1-methylxanthine exhibited increased protein tyrosine phosphorylation without becoming hyperactivated. Procaine (5 mM) or caffeine (10 mM) immediately induced hyperactivation in nearly 100% of motile sperm but did not increase protein tyrosine phosphorylation. After 4 h of incubation with caffeine, sperm expressed capacitation-associated protein tyrosine phosphorylation but hyperactivation was significantly reduced. Sperm initially hyperactivated by procaine or caffeine remained hyperactivated for at least 4 h in the presence of Rp-cAMPS (cAMP antagonist) or PKA inhibitors H-89 or H-8. Pretreatment with inhibitors also failed to block induction of hyperactivation; however, the inhibitors did block protein tyrosine phosphorylation when sperm were incubated with capacitating agents, thereby verifying inhibition of the cAMP/PKA pathway. While induction of hyperactivation did not depend on cAMP/PKA, it did require extracellular Ca(2+). These findings indicate that hyperactivation is mediated by a Ca(2+) signaling pathway that is separate or divergent from the pathway associated with acquisition of acrosomal responsiveness and does not involve protein tyrosine phosphorylation downstream of the actions of procaine or caffeine.

Characterization of the intracellular calcium store at the base of the sperm flagellum that regulates hyperactivated motility

Hyperactivated sperm motility is usually characterized by high-amplitude flagellar bends and asymmetrical flagellar beating. There is evidence that an inositol 1,4,5-trisphosphate (IP3) receptor-gated Ca2+ store in the base of the flagellum provides Ca2+ to initiate hyperactivation; however, the identity of the store was not known. Ca2+ stores are membrane-bounded organelles, and the only two membrane-bounded organelles found in this region of sperm are the redundant nuclear envelope (RNE) and mitochondria. Transmission electron micrographs revealed two different compartments of RNE, one enriched with nuclear pores and the other containing few pores but extensive membranous structures with enlarged cisternae. Immunolabeling showed that IP3 receptors and calreticulin are located in the region containing enlarged cisternae. In other cell types, mitochondria adjacent to Ca2+ stores are actively involved in modulating Ca2+ signals by taking up Ca2+ released from stores and also may respond by increasing production of NADH and ATP to support increased energy demand. Nevertheless, bull sperm did not show an increase in NADH when Ca2+ was released from intracellular stores by thapsigargin to induce hyperactivation. Consistently, no net increase in ATP production was detected when sperm were hyperactivated, although ATP was hydrolyzed at a greater rate. Furthermore, blocking Ca2+ efflux from mitochondria by CGP-37157, a specific inhibitor of the mitochondrial Na+/Ca2+ exchanger, did not inhibit the development of hyperactivated motility. We concluded that the intracellular Ca2+ store is the part of RNE that contains enlarged cisternae and that Ca2+ is released directly to the axoneme to trigger hyperactivated motility without the active participation of mitochondria.

Hyperactivated motility in sperm

Hyperactivation is a movement pattern seen in sperm at the site and time of fertilization in mammals. It may be critical to the success of fertilization, because it enhances the ability of sperm to detach from the wall of the oviduct, to move around in the labyrinthine lumen of the oviduct, to penetrate mucous substances and, finally, to penetrate the zona pellucida of the oocyte. The movement of hyperactivated sperm appears different under different physical conditions and in different species, but basically it involves an increase in flagellar bend amplitude and, usually, beat asymmetry. Presumably, a signal or signals exist in the oviduct to initiate hyperactivation at the appropriate time; however, none has yet been identified with certainty. While the signal transduction cascade regulating hyperactivation remains to be completely described, it is clear that calcium ions interact with the axoneme of the flagellum to switch on hyperactivation. Although hyperactivation often occurs during the process of capacitation, the two events are regulated by somewhat different pathways.

Unresolved Issues in Mammalian Fertilization

This review considers the role of the sperm in fertilization, addressing areas of misunderstanding and unfounded assumptions and taking particular advantage of the large body of data resulting from work with rodent species in vitro. Considerable attention is given to the appropriate use and interpretation of assays for capacitation, acrosomal exocytosis, hyperactivation, and sperm protein phosphorylation, as well as tests for sperm-zona and sperm-oocyte membrane interactions. The lack of general agreement on the means of sperm adhesion to and penetration of the zona pellucida is addressed, and the need for new approaches to this problem is pointed out. Some molecular advances in our understanding of specific steps in the process of fertilization are discussed in the context of intact cell-matrix and cell-cell interaction. This review should provide practical information for researchers just beginning the study of fertilization and interesting but not widely known observations to stimulate new ideas in experienced scientists.

A method for preparation, storage, and activation of large populations of immotile sea urchin sperm

Reversible protein phosphorylation is associated with initiation and modulation of sperm flagellar motility. Many studies aimed at examining the signal transduction mechanisms underlying the expression of motility have relied on detergent-permeabilized sperm reactivated with exogenous 32P-ATP. However, the reactivation conditions allow variable levels of motility to be expressed and phosphorylation of many proteins that appear to be unrelated to sperm motility. Thus, identification of the few relevant proteins is difficult. We have developed a method to collect and keep sperm immotile until reactivated for analysis to normal motility levels. Artificial sea water (ASW) buffered with 5 mM 2-[N-morpholino]ethanesulfonic acid at pH 6.0 and containing 50 mM KCl allows collection and storage of immotile sea urchin sperm for up to 96 h at 4-5 degrees C. Motility under these conditions is essentially zero, but sperm is rapidly reactivated to normal motility by diluting with ASW to standard pH (8.0) and KCl concentration (10 mM).