Voltage-dependent Ca(2+) channel subunit expression and immunolocalization in mouse spermatogenic cells and sperm

The Role of Sperm Membrane Potential and Ion Channels in Regulating Sperm Function

During the last seventy years, studies on mammalian sperm cells have demonstrated the essential role of capacitation, hyperactivation and the acrosome reaction in the acquisition of fertilization ability. These studies revealed the important biochemical and physiological changes that sperm undergo in their travel throughout the female genital tract, including changes in membrane fluidity, the activation of soluble adenylate cyclase, increases in intracellular pH and Ca2+ and the development of motility. Sperm are highly polarized cells, with a resting membrane potential of about -40 mV, which must rapidly adapt to the ionic changes occurring through the sperm membrane. This review summarizes the current knowledge about the relationship between variations in the sperm potential membrane, including depolarization and hyperpolarization, and their correlation with changes in sperm motility and capacitation to further lead to the acrosome reaction, a calcium-dependent exocytosis process. We also review the functionality of different ion channels that are present in spermatozoa in order to understand their association with human infertility.

Odorant and Taste Receptors in Sperm Chemotaxis and Cryopreservation: Roles and Implications in Sperm Capacitation, Motility and Fertility

Sperm chemotaxis, which guide sperm toward oocyte, is tightly associated with sperm capacitation, motility, and fertility. However, the molecular mechanism of sperm chemotaxis is not known. Reproductive odorant and taste receptors, belong to G-protein-coupled receptors (GPCR) super-family, cause an increase in intracellular Ca²⁺ concentration which is pre-requisite for sperm capacitation and acrosomal reaction, and result in sperm hyperpolarization and increase motility through activation of Ca²⁺-dependent Cl^¯ channels. Recently, odorant receptors (ORs) in olfactory transduction pathway were thought to be associated with post-thaw sperm motility, freeze tolerance or freezability and cryo-capacitation-like change during cryopreservation. Investigation of the roles of odorant and taste receptors (TRs) is important for our understanding of the freeze tolerance or freezability mechanism and improve the motility and fertility of post-thaw sperm. Here, we reviewed the roles, mode of action, impact of odorant and taste receptors on sperm chemotaxis and post-thaw sperm quality.

Sperm ion channels and transporters in male fertility and infertility

Mammalian sperm cells must respond to cues originating from along the female reproductive tract and from the layers of the egg in order to complete their fertilization journey. Dynamic regulation of ion signalling is, therefore, essential for sperm cells to adapt to their constantly changing environment. Over the past 15 years, direct electrophysiological recordings together with genetically modified mouse models and human genetics have confirmed the importance of ion channels, including the principal Ca²⁺-selective plasma membrane ion channel CatSper, for sperm activity. Sperm ion channels and membrane receptors are attractive targets for both the development of contraceptives and infertility treatment drugs. Furthermore, in this era of assisted reproductive technologies, understanding the signalling processes implicated in defective sperm function, particularly those arising from genetic abnormalities, is of the utmost importance not only for the development of infertility treatments but also to assess the overall health of a patient and his children. Future studies to improve reproductive health care and overall health care as a function of the ability to reproduce should include identification and analyses of gene variants that underlie human infertility and research into fertility-related molecules.

Human sperm ion channel (dys)function: implications for fertilization

BACKGROUND

Intensive research on sperm ion channels has identified members of several ion channel families in both mouse and human sperm. Gene knock-out studies have unequivocally demonstrated the importance of the calcium and potassium conductances in sperm for fertility. In both species, the calcium current is carried by the highly complex cation channel of sperm (CatSper). In mouse sperm, the potassium current has been conclusively shown to be carried by a channel consisting of the pore forming subunit SLO3 and auxiliary subunit leucine-rich repeat-containing 52 (LRRC52). However, in human sperm it is controversial whether the pore forming subunit of the channel is composed of SLO3 and/or SLO1. Deciphering the role of the proton-specific Hv1 channel is more challenging as it is only expressed in human sperm. However, definitive evidence for a role in, and importance for, human fertility can only be determined through studies using clinical samples.

OBJECTIVE AND RATIONALE

This review aims to provide insight into the role of sperm ion channels in human fertilization as evidenced from recent studies of sperm from infertile men. We also summarize the key discoveries from mouse ion channel knock-out models and contrast the properties of mouse and human CatSper and potassium currents. We detail the evidence for, and consequences of, defective ion channels in human sperm and discuss hypotheses to explain how defects arise and why affected sperm have impaired fertilization potential.

SEARCH METHODS

Relevant studies were identified using PubMed and were limited to ion channels that have been characterized in mouse and human sperm. Additional notable examples from other species are included as appropriate.

OUTCOMES

There are now well-documented fundamental differences between the properties of CatSper and potassium channel currents in mouse and human sperm. However, in both species, sperm lacking either channel cannot fertilize in vivo and CatSper-null sperm also fail to fertilize at IVF. Sperm-lacking potassium currents are capable of fertilizing at IVF, albeit at a much lower rate. However, additional complex and heterogeneous ion channel dysfunction has been reported in sperm from infertile men, the causes of which are unknown. Similarly, the nature of the functional impairment of affected patient sperm remains elusive. There are no reports of studies of Hv1 in human sperm from infertile men.

WIDER IMPLICATIONS

Recent studies using sperm from infertile men have given new insight and critical evidence supporting the supposition that calcium and potassium conductances are essential for human fertility. However, it should be highlighted that many fundamental questions remain regarding the nature of molecular and functional defects in sperm with dysfunctional ion channels. The development and application of advanced technologies remains a necessity to progress basic and clinical research in this area, with the aim of providing effective screening methodologies to identify and develop treatments for affected men in order to help prevent failed ART cycles. Conversely, development of drugs that block calcium and/or potassium conductances in sperm is a plausible strategy for producing sperm-specific contraceptives.

Molecular Basis of Human Sperm Capacitation

In the early 1950s, Austin and Chang independently described the changes that are required for the sperm to fertilize oocytes in vivo. These changes were originally grouped under name of “capacitation” and were the first step in the development of in vitro fertilization (IVF) in humans. Following these initial and fundamental findings, a remarkable number of observations led to characterization of the molecular steps behind this process. The discovery of certain sperm-specific molecules and the possibility to record ion currents through patch-clamp approaches helped to integrate the initial biochemical observation with the activity of ion channels. This is of particular importance in the male gamete due to the fact that sperm are transcriptionally inactive. Therefore, sperm must control all these changes that occur during their transit through the male and female reproductive tracts by complex signaling cascades that include post-translational modifications. This review is focused on the principal molecular mechanisms that govern human sperm capacitation with particular emphasis on comparing all the reported pieces of evidence with the mouse model.

Lipid modulation of calcium flux through CaV2.3 regulates acrosome exocytosis and fertilization

Membrane lipid regulation of cell function is poorly understood. In early development, sterol efflux and the ganglioside GM1 regulate sperm acrosome exocytosis (AE) and fertilization competence through unknown mechanisms. Here, we show that sterol efflux and focal enrichment of GM1 trigger Ca(2+) influx necessary for AE through CaV2.3, whose activity has been highly controversial in sperm. Sperm lacking CaV2.3's pore-forming α1E subunit showed altered Ca(2+) responses, reduced AE, and a strong subfertility phenotype. Surprisingly, AE depended on spatiotemporal information encoded by flux through CaV2.3, not merely the presence/amplitude of Ca(2+) waves. Using studies in both sperm and voltage clamp of Xenopus oocytes, we define a molecular mechanism for GM1/CaV2.3 regulatory interaction, requiring GM1's lipid and sugar components and CaV2.3's α1E and α2δ subunits. Our results provide a mechanistic understanding of membrane lipid regulation of Ca(2+) flux and therefore Ca(2+)-dependent cellular and developmental processes such as exocytosis and fertilization.

Participation of the Cl-/HCO(3)- exchangers SLC26A3 and SLC26A6, the Cl- channel CFTR, and the regulatory factor SLC9A3R1 in mouse sperm capacitation

Sperm capacitation is required for fertilization and involves several ion permeability changes. Although Cl(-) and HCO(3)(-) are essential for capacitation, the molecular entities responsible for their transport are not fully known. During mouse sperm capacitation, the intracellular concentration of Cl(-) ([Cl(-)](i)) increases and membrane potential (Em) hyperpolarizes. As in noncapacitated sperm, the Cl(-) equilibrium potential appears to be close to the cell resting Em, opening of Cl(-) channels could not support the [Cl(-)](i) increase observed during capacitation. Alternatively, the [Cl(-)](i) increase might be mediated by anion exchangers. Among them, SLC26A3 and SLC26A6 are good candidates, since, in several cell types, they increase [Cl(-)](i) and interact with cystic fibrosis transmembrane conductance regulator (CFTR), a Cl(-) channel present in mouse and human sperm. This interaction is known to be mediated and probably regulated by the Na(+)/H(+) regulatory factor-1 (official symbol, SLC9A3R1). Our RT-PCR, immunocytochemistry, Western blot, and immunoprecipitation data indicate that SLC26A3, SLC26A6, and SLC9A3R1 are expressed in mouse sperm, localize to the midpiece, and interact between each other and with CFTR. Moreover, we present evidence indicating that CFTR and SLC26A3 are involved in the [Cl(-)](i) increase induced by db-cAMP in noncapacitated sperm. Furthermore, we found that inhibitors of SLC26A3 (Tenidap and 5099) interfere with the Em changes that accompany capacitation. Together, these findings indicate that a CFTR/SLC26A3 functional interaction is important for mouse sperm capacitation.

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

A proper dialogue between spermatozoa and the egg is essential for conception of a new individual in sexually reproducing animals. Ca2+ is crucial in orchestrating this unique event leading to a new life. No wonder that nature has devised different Ca2+-permeable channels and located them at distinct sites in spermatozoa so that they can help fertilize the egg. New tools to study sperm ionic currents, and image intracellular Ca2+ with better spatial and temporal resolution even in swimming spermatozoa, are revealing how sperm ion channels participate in fertilization. This review critically examines the involvement of Ca2+ channels in multiple signaling processes needed for spermatozoa to mature, travel towards the egg, and fertilize it. Remarkably, these tiny specialized cells can express exclusive channels like CatSper for Ca2+ and SLO3 for K+, which are attractive targets for contraception and for the discovery of novel signaling complexes. Learning more about fertilization is a matter of capital importance; societies face growing pressure to counteract rising male infertility rates, provide safe male gamete-based contraceptives, and preserve biodiversity through improved captive breeding and assisted conception initiatives.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 4: intercellular bridges, mitochondria, nuclear envelope, apoptosis, ubiquitination, membrane/voltage-gated channels, methylation/acetylation, and transcription factors

As germ cells divide and differentiate from spermatogonia to spermatozoa, they share a number of structural and functional features that are common to all generations of germ cells and these features are discussed herein. Germ cells are linked to one another by large intercellular bridges which serve to move molecules and even large organelles from the cytoplasm of one cell to another. Mitochondria take on different shapes and features and topographical arrangements to accommodate their specific needs during spermatogenesis. The nuclear envelope and pore complex also undergo extensive modifications concomitant with the development of germ cell generations. Apoptosis is an event that is normally triggered by germ cells and involves many proteins. It occurs to limit the germ cell pool and acts as a quality control mechanism. The ubiquitin pathway comprises enzymes that ubiquitinate as well as deubiquitinate target proteins and this pathway is present and functional in germ cells. Germ cells express many proteins involved in water balance and pH control as well as voltage-gated ion channel movement. In the nucleus, proteins undergo epigenetic modifications which include methylation, acetylation, and phosphorylation, with each of these modifications signaling changes in chromatin structure. Germ cells contain specialized transcription complexes that coordinate the differentiation program of spermatogenesis, and there are many male germ cell-specific differences in the components of this machinery. All of the above features of germ cells will be discussed along with the specific proteins/genes and abnormalities to fertility related to each topic.

Male infertility caused by spermiogenic defects: lessons from gene knockouts

Spermiogenesis refers to the process by which postmeiotic spermatids differentiate into elongated spermatids and eventually spermatozoa. During spermiogenesis, round spermatids undergo dynamic morphologic changes, which include nuclear condensation and elongation, formation of flagella and acrosome, reorganization of organelles and elimination of cytoplasm upon spermiation. This cellular differentiation process is unique to male haploid germ cells, which may explain why approximately half of the testis-specific genes are exclusively expressed in spermiogenesis. The spermiogenesis-specific expression implies that these genes contribute to either structural or functional aspects of future sperm. Many such genes have been inactivated in mice and some of these gene knockout mice display male infertility due to nonfunctional sperm which display no or various degrees of structural abnormalities. Since the majority of these spermiogenesis-specific genes are highly conserved between mice and humans, findings from knockout mouse studies may be applicable to human infertility. Here, I briefly review some of these spermatid-specific gene knockouts. The mouse studies strongly suggest that sperm quality rather than quantity is a better indicator of male fertility and novel assays should be developed to determine sperm functionality.

Distribution profiles of transient receptor potential melastatin- and vanilloid-related channels in rat spermatogenic cells and sperm

In the present study, we aimed to investigate the expression and distribution of transient receptor potential melastatin (TRPM)- and vanilloid (TRPV)- related channels in rat spermatogenic cells and spermatozoa. Spermatogenic cells and spermatozoa were obtained from male Sprague-Dawley rats. Reverse transcription polymerase chain reaction (RT-PCR) were used to detect the expression of all TRPM and TRPV channel members with specific primers. Western blot analysis was applied for detecting the expression of TRPM and TRPV channel proteins. Immunohistochemistry staining for TRPM4, TRPM7 and TRPV5 was also performed in rat testis. The mRNAs of TRPM3, TRPM4, TRPM7 and TRPV5 were detected in the spermatogenic cells and spermatozoa in rat. Western blot analysis verified the expression of TRPM4, TRPM7 and TRPV5 in the rat spermatogenic cells and spermatozoa. Immunocytochemistry staining for TRPM and TRPV channel families indicated that TRPM4 and TRPM7 proteins were highly expressed in different stages of spermatogenic cells and spermatozoa, while TRPV5 protein was lowly expressed in these cells. Our results demonstrate that mRNAs or proteins for TRPM3, TRPM4, TRPM7 and TRPV5 exist in rat spermatogenic cells and spermatozoa. These data presented here may assist in elucidating the possible physiological function of TRPM and TRPV channels in spermatogenic cells and spermatozoa.

Expression, localization and functions in acrosome reaction and sperm motility of Ca(V)3.1 and Ca(V)3.2 channels in sperm cells: an evaluation from Ca(V)3.1 and Ca(V)3.2 deficient mice

In spermatozoa, voltage-dependent calcium channels (VDCC) have been involved in different cellular functions like acrosome reaction (AR) and sperm motility. Multiple types of VDCC are present and their relative contribution is still a matter of debate. Based mostly on pharmacological studies, low-voltage-activated calcium channels (LVA-CC), responsible of the inward current in spermatocytes, were described as essential for AR in sperm. The development of Ca(V)3.1 or Ca(V)3.2 null mice provided the opportunity to evaluate the involvement of such LVA-CC in AR and sperm motility, independently of pharmacological tools. The inward current was fully abolished in spermatogenic cells from Ca(V)3.2 deficient mice. This current is thus only due to Ca(V)3.2 channels. We showed that Ca(V)3.2 channels were maintained in sperm by Western-blot and immunohistochemistry experiments. Calcium imaging experiments revealed that calcium influx in response to KCl was reduced in Ca(V)3.2 null sperm in comparison to control cells, demonstrating that Ca(V)3.2 channels were functional. On the other hand, no difference was noticed in calcium signaling induced by zona pellucida. Moreover, neither biochemical nor functional experiments, suggested the presence of Ca(V)3.1 channels in sperm. Despite the Ca(V)3.2 channels contribution in KCl-induced calcium influx, the reproduction parameters remained intact in Ca(V)3.2 deficient mice. These data demonstrate that in sperm, besides Ca(V)3.2 channels, other types of VDCC are activated during the voltage-dependent calcium influx of AR, these channels likely belonging to high-voltage activated Ca(2+) channels family. The conclusion is that voltage-dependent calcium influx during AR is due to the opening of redundant families of calcium channels.

Expression of CatSper family transcripts in the mouse testis during post-natal development and human ejaculated spermatozoa: relationship to sperm motility

CatSper is a unique sperm cation channel-like protein family exclusively expressed in the testis and plays important roles in sperm functions. The temporal expression profiles of CatSper1-4 mRNAs in the mouse testis during post-natal development through adulthood were investigated using real-time RT-PCR. The CatSper2 transcript was present in the testis of the 8-day-old mice, and was repressed in the adult testis after two sharp up-regulations at day 18 and 35. CatSper1 and CatSper3, 4 mRNAs were detectable in the testis of 18-day and 15-day-old mice, respectively. After sharp up-regulation at day 25 and 35, respectively, they were maximal at the adult testis stage. The differences between the temporal expression profiles of the CatSper transcripts in post-natal mouse testis development suggest different regulation to their transcription, and potentially contribute to the possibility of forming heteromeric channels among these four CatSper family members. CatSper1-3 transcripts were identified to be present in the human ejaculated spermatozoa by RT-PCR. Significantly higher levels of CatSper2 and CatSper3 mRNAs revealed by real-time RT-PCR were observed in the high-motile spermatozoa than in the low-motile fraction and suggests that CatSper2 and CatSper3 transcripts in the human ejaculated spermatozoa could be the potential targets for further study and male infertility screening.

All four CatSper ion channel proteins are required for male fertility and sperm cell hyperactivated motility

Mammalian spermatozoa become motile at ejaculation, but before they can fertilize the egg, they must acquire more thrust to penetrate the cumulus and zona pellucida. The forceful asymmetric motion of hyperactivated spermatozoa requires Ca2+ entry into the sperm tail by an alkalinization-activated voltage-sensitive Ca2+-selective current (ICatSper). Hyperactivation requires CatSper1 and CatSper2 putative ion channel genes, but the function of two other related genes (CatSper3 and CatSper4) is not known. Here we show that targeted disruption of murine CatSper3 or CatSper4 also abrogated ICatSper, sperm cell hyperactivated motility and male fertility but did not affect spermatogenesis or initial motility. Direct protein interactions among CatSpers, the sperm specificity of these proteins, and loss of ICatSper in each of the four CatSper-/- mice indicate that CatSpers are highly specialized flagellar proteins.

Sperm channel diversity and functional multiplicity

Ion channels are extraordinarily efficient machines that move ions in diversely controlled manners, allowing cells to rapidly exchange information with the outside world and with other cells. Communication is the currency of fertilization, as it is of most fundamental cell signaling events. Ion channels are deeply involved in the dialogue between sperm, its surroundings, and the egg. How sperm swim, find the egg and fertilize it depend on ion permeability changes modulated by environmental cues and components of the egg outer layer. Different ion channels distinctly localized in these tiny, amazing cells perform specific decoding functions that shape the sophisticated behavior of sperm. It is not surprising that certain sperm ion channels are turning out to be unique. New strategies to characterize sperm ion transport have opened exciting possibilities to dissect sperm-egg signaling and unveil novel contraception targets.

Effects of calcium channel blockers on the spermatogenesis and gene expression in peripubertal mouse testis

Treatment of Ca(2+) channel blockers (CCB) to relieve hypertension causes reversible male infertility, suggesting deregulation of Ca(2+) homeostasis in testis is closely related with male infertility. To investigate the possible toxicity of therapeutic application of CCB in childhood, the effect of nifedipine and ethosuximide, an L-type and T-type CCB, respectively, on the spermatogenesis and testicular gene expression was examined. Following the intraperitoneal injection of either drug for 7 days to 18 days on old mice, the paired testes weights were significantly lower in mice treated with nifedipine (> or = 10 mg/kg/day) or ethosuximide (100 mg/kg/day) than vehicle controls. In mice given high drug dosing (100 mg/kg), seminiferous tubules showed immaturity with spermatogenic arrest at elongating spermatid stage and poorly developed lumen. Unexpectedly, the expression of activator isoform of transcription factor cAMP-responsive element modulator (CREM) mRNA increased together with transition protein 2 and protamine 2 mRNA in drug-treated mice testes, suggesting that CCB may deregulate expression of activator isoform of CREM in male germ cells and that spermatogenic defect following CCB treatment may attribute to ectopic expression of CREM-dependent gene battery in testis. Therapeutic application of CCB in childhood should be cautious because of their potential to cause spermatogenic defect and altered gene expression in testis.

Role of the Na+/Ca2+ exchanger in calcium homeostasis and human sperm motility regulation

A number of cell functions, such as flagellar beating, swimming velocity, acrosome reaction, etc., are triggered by a Ca2+ influx across the cell membrane. For appropriate physiological functions, the motile human sperm maintains the intracellular free calcium concentration ([Ca2+]i) at a submicromolar level. The objective of this study was to determine the role of the Na+/Ca2+ exchanger (NCX) in the maintenance of [Ca2+]i in human spermatozoa. Spermatozoa maintained in extracellular medium containing>or=1 microM Ca2+ exhibited motility similar to that of the control. In addition to several calcium transport mechanisms described earlier, we provide evidence that the NCX plays a crucial role in the maintenance of [Ca2+]i. Three chemically unrelated inhibitors of the NCX (bepridil, DCB (3',4'-dichlorobenzamil hydrochloride), and KB-R7943) all blocked human sperm motility in a dose and incubation time dependent manner. The IC50 values for bepridil, DCB, and KB-R7943 were 16.2, 9.8, and 5.3 microM, respectively. The treatment with the above-mentioned blockers resulted in an elevated [Ca2+]i and a decreased [Na+]i. The store-operated calcium channel (SOCC) inhibitor SKF 96365 also blocked the sperm motility (IC50=2.44 microM). The presence of the NCX antigen in the human spermatozoa was proven by flow cytometry, confocal laser scanning microscopy, and immunoblotting techniques. Calcium homeostasis of human spermatozoa is maintained by several transport proteins among which the SOCC and the NCX may play a major role.

KATP channels in mouse spermatogenic cells and sperm, and their role in capacitation

Mammalian sperm must undergo a series of physiological changes after leaving the testis to become competent for fertilization. These changes, collectively known as capacitation, occur in the female reproductive tract where the sperm plasma membrane is modified in terms of its components and ionic permeability. Among other events, mouse sperm capacitation leads to an increase in the intracellular Ca(2+) and pH as well as to a hyperpolarization of the membrane potential. It is well known that ion channels play a crucial role in these events, though the molecular identity of the particular channels involved in capacitation is poorly defined. In the present work, we report the identification and potential functional role of K(ATP) channels in mouse spermatogenic cells and sperm. By using whole-cell patch clamp recordings in mouse spermatogenic cells, we found K(+) inwardly rectifying (K(ir)) currents that are sensitive to Ba(2+), glucose and the sulfonylureas (tolbutamide and glibenclamide) that block K(ATP) channels. The presence of these channels was confirmed using inhibitors of the ATP synthesis and K(ATP) channel activators. Furthermore, RT-PCR assays allowed us to detect transcripts for the K(ATP) subunits SUR1, SUR2, K(ir)6.1 and K(ir)6.2 in total RNA from elongated spermatids. In addition, immunoconfocal microscopy revealed the presence of these K(ATP) subunits in mouse spermatogenic cells and sperm. Notably, incubation of sperm with tolbutamide during capacitation abolished hyperpolarization and significantly decreased the percentage of AR in a dose-dependent fashion. Together, our results provide evidence for the presence of K(ATP) channels in mouse spermatogenic cells and sperm and disclose the contribution of these channels to the capacitation-associated hyperpolarization.

Calcium signalling in human spermatozoa: a specialized 'toolkit' of channels, transporters and stores

Ca(2+) is a ubiquitous intracellular messenger which encodes information by temporal and spatial patterns of concentration. In spermatozoa, several key functions, including acrosome reaction and motility, are regulated by cytoplasmic Ca(2+) concentration. Despite the very small size and apparent structural simplicity of spermatozoa, evidence is accumulating that they possess sophisticated mechanisms for regulation of cytoplasmic Ca(2+) concentration and generation of complex Ca(2+) signals. In this review, we consider the various components of the Ca(2+)-signalling 'toolkit' that have been characterized in somatic cells and summarize the evidence for their presence and activity in spermatozoa. In particular, data accumulated over the last few years show that spermatozoa possess one (and probably two) Ca(2+) stores as well as a range of plasma membrane pumps and channels. Selective regulation of the various components of the 'toolkit' by agonists probably allows spermatozoa to generate localized Ca(2+) signals despite their very small cytoplasmic volume, permitting the discrete and selective activation of cell functions.

Identification of voltage-dependent Ca2+channels in sea urchin sperm

Functional evidence indicates that voltage-dependent Ca2+ (Cav) channels participate in sea urchin sperm motility and the acrosome reaction (AR), however, their molecular identity remains unknown. We have identified transcripts for two Ca2+ channel alpha1 subunits in sea urchin testis similar in sequence to Cav1.2 and Cav2.3. Antibodies against rat Cav1.2 and Cav2.3 channels differentially label proteins in the flagella and acrosome of mature sea urchin sperm. The Cav channel antagonists nifedipine and nimodipine, which inhibit the AR, diminish the intracellular Ca2+ elevation induced by a K+-induced depolarization in valinomycin-treated sperm. These findings reveal that Cav1.2 and Cav2.3 channels could participate in motility and/or the AR in sea urchin sperm.

Identical phenotypes of CatSper1 and CatSper2 null sperm

Among several candidate Ca(2+) entry channels in sperm, only CatSper1 and CatSper2 are known to have required roles in male fertility. Past work with CatSper1 null sperm indicates that a critical lesion in hyperactivated motility underlies the infertility phenotype and is associated with an absence of depolarization-evoked Ca(2+)entry. Here we show that failure of hyperactivation of CatSper2 null sperm similarly correlates with an absence of depolarization evoked Ca(2+) entry. Additional shared aspects of the phenotypes of CatSper1 and -2 null sperm include unperturbed regional distributions of conventional voltage-gated Ca(2+) channel proteins and robust acceleration of the flagellar beat by bicarbonate. Further study reveals that treatment of both wild-type and CatSper2 null sperm with procaine increases beat asymmetry, a characteristic of the flagellar waveform of hyperactivation. This partial rescue of the loss-of-hyperactivation phenotype suggests that an absence of CatSper2 precludes hyperactivation by preventing delivery of needed Ca(2+) messenger rather than by preventing flagellar responses to Ca(2+). CatSper2 null sperm also have an increased basal cAMP content and beat frequency. Protein kinase A inhibitor H89 lowers beat frequency to that of wild-type sperm, suggesting that CatSper2 is required for protein kinase A-mediated, tonic control of resting cAMP content. Relative to wild-type testis, CatSper1 and -2 null testes contain normal amounts of CatSper2 and -1 transcripts, respectively. However, CatSper1 null sperm lack CatSper2 protein and CatSper2 null sperm lack CatSper1 protein. Hence, stable expression of CatSper1 protein requires CatSper2 and vice versa. This co-dependent expression dictates identical loss-of-function sperm phenotypes for CatSper1 and -2 null mutants.

Molecular physiology and pathology of Ca2+-conducting channels in the plasma membrane of mammalian sperm

Current evidence indicates that mechanisms controlling the intracellular Ca2+concentration play pivotal roles in determining sperm fertilizing ability. Multiple Ca2+-permeable channels have been identified and characterized in the plasma membrane and in the acrosome membrane of mammalian sperm. This review summarizes the recent findings and assesses the evidence suggesting that these channels play roles in controlling a host of sperm functions ranging from motility to the acrosome reaction, and describes recent advances in the identification of the underlying gene defects of inherited sperm Ca2+channelopathies.

Deletions in L-type calcium channel α1 subunit testicular transcripts correlate with testicular cadmium and apoptosis in infertile men with varicoceles

OBJECTIVE

To identify and understand predictors of successful varicocelectomy.

DESIGN

Examination of testicular L-type voltage-dependent calcium channel (L-VDCC) mRNAs and proteins in testis biopsies and comparison of presence and absence of various mRNAs with testicular cadmium levels, with apoptosis, and with sperm count change after varicocelectomy.

SETTING

University clinical urology practice and research laboratories.

PATIENT(S)

Infertile men with varicocele (left varicocele only, n = 18; bilateral varicoceles, n = 26) and controls (men with obstructive azoospermia undergoing testicular sperm extraction before intracytoplasmic sperm injection; n = 7).

INTERVENTION(S)

Left testis biopsies by percutaneous needle aspiration biopsy. Varicocele repair by subinguinal approach.

MAIN OUTCOME MEASURE(S)

Calcium channel mRNA sequence by reverse transcription-polymerase chain reaction and amplicon analysis; calcium channel protein distribution by immunocytochemistry; cadmium levels by atomic absorption and apoptosis by deoxynucleotidyl transferase labeling; and sperm counts in the ejaculate before and after varicocelectomy.

RESULT(S)

Calcium channel mRNAs are polymorphic in human testis biopsies from different men. Proteins from sequence-deleted exons 7 and/or 8 localize to germ cell membranes. Expression of undeleted L-type calcium channel mRNAs correlates with normal testes cadmium and increased sperm count after varicocelectomy. Apoptosis is lower in such cases.

CONCLUSION(S)

Expression of normal testicular L-VDCC sequence in exons 7-8 predicts postvaricocelectomy sperm count increase. Deletions may alter calcium channel function and affect testicular cadmium and apoptosis.

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.

Ryanodine receptors are expressed and functionally active in mouse spermatogenic cells and their inhibition interferes with spermatogonial differentiation

Ryanodine receptors (RyRs) are intracellular calcium release channels that are highly expressed in striated muscle and neurons but are also detected in several non-excitable cells. We have studied the expression of the three RyR isoforms in male germ cells at different stages of maturation by western blot and RT-PCR. RyR1 was expressed in spermatogonia, pachytene spermatocytes and round spermatids whereas RyR2 was found only in 5- to 10-day-old testis but not in germ cells. RyR3 was not revealed at the protein level, although its mRNA was detected in mixed populations of germ cells. Caffeine, a known agonist of RyRs, was able to induce release of Ca2+ from intracellular stores in spermatogonia, pachytene spermatocytes and round spermatids, but not spermatozoa. Treatment with high doses of ryanodine, which are known to block RyR channel activity, reduced spermatogonial proliferation and induced meiosis in in vitro organ cultures of testis from 7-day-old mice. In conclusion, the results presented here indicate that RyRs are present in germ cells and that calcium mobilization through RyR channels could participate to the regulation of male germ maturation.

Expression and differential cell distribution of low-threshold Ca2+ channels in mammalian male germ cells and sperm

Numerous sperm functions including the acrosome reaction (AR) are associated with Ca(2+) influx through voltage-gated Ca(2+) (Ca(V)) channels. Although the electrophysiological characterization of Ca(2+) currents in mature sperm has proven difficult, functional studies have revealed the presence of low-threshold (Ca(V)3) channels in spermatogenic cells. However, the molecular identity of these proteins remains undefined. Here, we identified by reverse transcription polymerase chain reaction the expression of Ca(V)3.3 mRNA in mouse male germ cells, an isoform not previously described in these cells. Immunoconfocal microscopy revealed the presence of the three Ca(V)3 channel isoforms in mouse spermatogenic cells. In mature mouse sperm only Ca(V)3.1 and Ca(V)3.2 were detected in the head, suggesting its participation in the AR. Ca(V)3.1 and Ca(V)3.3 were found in the principal and the midpiece of the flagella. All Ca(V)3 channels are also present in human sperm, but only to a minor extent in the head. These findings were corroborated by immunogold transmission electron microscopy. Tail localization of Ca(V)3 channels suggested they may participate in motility, however, mibefradil and gossypol concentrations that inhibit Ca(V)3 channels did not significantly affect human sperm motility. Only higher mibefradil doses that can block high-threshold (HVA) Ca(V) channels caused small but significant motility alterations. Antibodies to HVA channels detected Ca(V)1.3 and Ca(V)2.3 in human sperm flagella.

CatSper1 required for evoked Ca2+ entry and control of flagellar function in sperm

CatSper family proteins are putative ion channels expressed exclusively in membranes of the sperm flagellum and required for male fertility. Here, we show that mouse CatSper1 is essential for depolarization-evoked Ca2+ entry and for hyperactivated movement, a key flagellar function. CatSper1 is not needed for other developmental landmarks, including regional distributions of CaV1.2, CaV2.2, and CaV2.3 ion channel proteins, the cAMP-mediated activation of motility by HCO3-, and the protein phosphorylation cascade of sperm capacitation. We propose that CatSper1 functions as a voltage-gated Ca2+ channel that controls Ca2+ entry to mediate the hyperactivated motility needed late in the preparation of sperm for fertilization.

Calcium regulation of the soluble adenylyl cyclase expressed in mammalian spermatozoa

In mammals, Ca2+ and HCO3- ions play a critical role in the regulation of sperm function, most likely by regulation of cAMP levels. Mammalian germ cells contain a soluble adenylyl cyclase (sAC) with properties distinct from the well characterized membrane-bound enzymes Here we investigated whether the cyclase expressed in mature spermatozoa has the properties of sAC and whether it is regulated by Ca2+. In addition to an HCO3--dependent activation, the cyclase endogenous to human spermatozoa is stimulated 2- to 3-fold by Ca2+ in a concentration-dependent manner (EC50 approximately 400 nM). In a similar fashion, Ca2+ activates the recombinant rat and human full-length sAC with similar EC50 values. The Ca2+ stimulation was also observed when sAC was activated with HCO3-, was independent of calmodulin, and was associated with an increase in Vmax without changes in Km for ATP-Mg2+. An increase in intracellular Ca2+ by ionophore or by a muscarinic cholinergic receptor agonist increases cAMP in cells transfected with FL-hsAC, but not in mock-transfected cells. Similarly, both Ca2+ and HCO3- stimulate cAMP accumulation in human spermatozoa. These findings provide evidence that human spermatozoa express a cyclase with the properties of sAC and that Ca2+ can substitute for HCO3- in the stimulation of this enzyme, underscoring an important role for sAC in the control of sperm functions.

Identification of human and mouse CatSper3 and CatSper4 genes: characterisation of a common interaction domain and evidence for expression in testis

BACKGROUND

CatSper1 and CatSper2 are two recently identified channel-like proteins, which show sperm specific expression patterns. Through targeted mutagenesis in the mouse, CatSper1 has been shown to be required for fertility, sperm motility and for cAMP induced Ca2+ current in sperm. Both channels resemble a single pore forming repeat from a four repeat voltage dependent Ca2+ /Na+ channel. However, neither CatSper1 or CatSper2 have been shown to function as cation channels when transfected into cells, singly or in conjunction. As the pore forming units of voltage gated cation channels form a tetramer it has been suggested that the known CatSper proteins require additional subunits and/or interaction partners to function.

RESULTS

Using in silico gene identification and prediction techniques, we have identified two further members of the CatSper family, CatSper3 and Catsper4. Each carries a single channel-forming domain with the predicted pore-loop containing the consensus sequence TxDxW. Each of the new CatSper genes has evidence for expression in the testis. Furthermore we identified coiled-coil protein-protein interaction domains in the C-terminal tails of each of the CatSper channels, implying that CatSper channels 1,2,3 and 4 may interact directly or indirectly to form a functional tetramer.

CONCLUSIONS

The topological and sequence relationship of CatSper1 and CatSper2 to the four repeat Ca2+ /Na+ channels suggested other members of this family may exist. We have identified a further two novel CatSper genes, conserved in both the human and mouse genomes. Furthermore, all four of the CatSper proteins are predicted to contain a common coiled-coil protein-protein interaction domain in their C-terminal tail. Coupled with expression data this leads to the hypothesis that the CatSper proteins form a functional hetero-tetrameric channel in sperm.

Gadolinium, a mechano-sensitive channel blocker, inhibits osmosis-initiated motility of sea- and freshwater fish sperm, but does not affect human or ascidian sperm motility

Exposure to hypo-osmotic or hyperosmotic environment triggers the initiation of fish sperm motility. In this article, we report that calcium and potassium channel blockers do not influence motility of puffer fish sperm but calmodulin antagonists reversibly decrease it, suggesting that calmodulin-Ca(2+) interactions are prerequisite for the initiation of sperm motility in this species. Gadolinium (a stretch activated ion channel blocker) decreased the motility of puffer fish sperm from 92 +/- 3% to 6 +/- 3% and that of carp sperm from 91 +/- 7% to 3.5 +/- 4.3% in a dose-dependent manner (10-40 micro M). The effect of gadolinium was reversible, suggesting that stretch activated ion channels participate in the initiation of sperm motility of the two species. Gadolinium inhibits changes in the isoelectric point of certain proteins of puffer fish sperm, which occur when sperm motility is initiated in a hypertonic solution. Anisotropy measurements showed that hypo-osmotic treatment, which initiates carp sperm motility, increased membrane fluidity. When hypo-osmotic treatment was given in the presence of gadolinium, the sperm membrane remained as rigid as in quiescent cells, while motility was blocked. By contrast, gadolinium did not influence the motility parameters of Ciona or human sperm. Based on these lines of evidence, we suggest that conformational changes of mechanosensitive membrane proteins are involved in osmolality-dependent but not osmolality-independent sperm.

Bicarbonate actions on flagellar and Ca2+ -channel responses: initial events in sperm activation

At mating, mammalian sperm are diluted in the male and female reproductive fluids, which brings contact with HCO(3)(-) and initiates several cellular responses. We have identified and studied two of the most rapid of these responses. Stop-motion imaging and flagellar waveform analysis show that for mouse epididymal sperm in vitro, the resting flagellar beat frequency is 2-3 Hz at 22-25 degrees C. Local perfusion with HCO(3)(-) produces a robust, reversible acceleration to 7 Hz or more. At 15 mM the action of HCO(3)(-) begins within 5 seconds and is near-maximal by 30 seconds. The half-times of response are 8.8+/-0.2 seconds at 15 mM HCO(3)(-) and 17.5+/-0.4 seconds at 1 mM HCO(3)(-). Removal of external HCO(3)(-) allows a slow return to basal beat frequency over approximately 10 minutes. Increases in beat symmetry accompany the accelerating action of HCO(3)(-). As in our past work, HCO(3)(-) also facilitates opening of voltagegated Ca(2+) channels, increasing the depolarization-evoked rate of rise of intracellular Ca(2+) concentration by more than fivefold. This action also is detectable at 1 mM HCO(3)(-) and occurs with an apparent halftime of approximately 60 seconds at 15 mM HCO(3)(-). The dual actions of HCO(3)(-) respond similarly to pharmacological intervention. Thus, the phosphodiesterase inhibitor IBMX promotes the actions of HCO(3)(-) on flagellar and channel function, and the protein kinase A inhibitor H89 blocks these actions. In addition, a 30 minute incubation with 60 micro M cAMP acetoxylmethyl ester increases flagellar beat frequency to nearly 7 Hz and increases the evoked rates of rise of intracellular Ca(2+) concentration from 17+/-4 to 41+/-6 nM second(-1). However, treatment with several other analogs of cAMP produces only scant evidence of the expected mimicry or blockade of the actions of HCO(3)(-), perhaps as a consequence of limited permeation. Our findings indicate a requirement for cAMP-mediated protein phosphorylation in the enhancement of flagellar and channel functions that HCO(3)(-) produces during sperm activation.

Scorpion toxins that block T-type Ca2+ channels in spermatogenic cells inhibit the sperm acrosome reaction

The acrosome reaction (AR) is a Ca(2+)-dependent event required for sperm to fertilize the egg. The activation of T-type voltage-gated Ca(2+) channels plays a key role in the induction of this process. This report describes the actions of two toxins from the scorpion Parabuthus granulatus named kurtoxin-like I and II (KLI and KLII, respectively) on sperm Ca(2+) channels. Both toxins decrease T-type Ca(2+) channel activity in mouse spermatogenic cells and inhibit the AR in mature sperm. Saturating concentrations of the toxins inhibited at most approximately 70% of the whole-cell Ca(2+) current, suggesting the presence of a toxin-resistant component. In addition, both toxins inhibited approximately 60% of the AR, which is consistent with the participation of T-type Ca(2+) channels in the sperm AR.

Ion channels in small cells and subcellular structures can be studied with a smart patch-clamp system

We have developed a scanning patch-clamp technique that facilitates single-channel recording from small cells and submicron cellular structures that are inaccessible by conventional methods. The scanning patch-clamp technique combines scanning ion conductance microscopy and patch-clamp recording through a single glass nanopipette probe. In this method the nanopipette is first scanned over a cell surface, using current feedback, to obtain a high-resolution topographic image. This same pipette is then used to make the patch-clamp recording. Because image information is obtained via the patch electrode it can be used to position the pipette onto a cell with nanometer precision. The utility of this technique is demonstrated by obtaining ion channel recordings from the top of epithelial microvilli and openings of cardiomyocyte T-tubules. Furthermore, for the first time we have demonstrated that it is possible to record ion channels from very small cells, such as sperm cells, under physiological conditions as well as record from cellular microstructures such as submicron neuronal processes.

Identification and localization of T-type voltage-operated calcium channel subunits in human male germ cells. Expression of multiple isoforms

Low voltage activated, voltage-operated Ca(2+) channels are expressed in rodent male germ cells and are believed to be pivotal in induction of the acrosome reaction in mouse spermatozoa. However, in humans, very little is known about expression of voltage-operated Ca(2+) channels in male germ cells or their function. We have used reverse transcription-polymerase chain reaction, in situ hybridization, and patch clamp recording to investigate the expression of low voltage activated voltage-operated Ca(2+) channels in human male germ cells. We report that full-length transcripts for both alpha(1G) and alpha(1H) low voltage activated channel subunits are expressed in human testis. Multiple isoforms of alpha(1G) are present in the testis and at least two isoforms of alpha(1H), including a splice variant not previously described in the human. Transcripts for all the isoforms of both alpha(1G) and alpha(1H) were detected by reverse transcription-polymerase chain reaction on mRNA isolated from human spermatogenic cells. In situ hybridization for alpha(1G) and alpha(1H) localized transcripts both in germ cells and in other cell types in the testis. Within the seminiferous tubules, alpha(1H) was detected primarily in germ cells. Using the whole cell patch clamp technique, we detected T-type voltage-operated Ca(2+) channel currents in isolated human male germ cells, although the current amplitude and frequency of occurrence were low in comparison to the occurrence of T-currents in murine male germ cells. We conclude that low voltage activated voltage-operated Ca(2+) channels are expressed in cells of the human male germ line.

Ion transport in sperm signaling

Ion channels and transporters, key elements in sperm-egg signaling and environmental sensing, are essential for fertilization. External cues and components from the outer envelopes of the egg influence sperm ion permeability and behavior. Combining in vivo measurements of membrane potential, intracellular ions, and second messengers with new molecular approaches and reconstitution strategies are revealing how sperm ion channels participate in motility, sperm maturation, and the acrosome reaction. Sperm are tiny differentiated terminal cells unable to synthesize proteins and difficult to characterize electrophysiologically. Spermatogenic cells, the progenitors of sperm, have become useful tools for probing sperm ion channels since they are larger and molecular biology techniques can be applied. These complementary strategies are opening new avenues to determine how sperm ion channels function in gamete signaling.

Low-voltage-activated calcium channels are not involved in capacitation and biological response to progesterone in human sperm

The involvement of voltage-dependent calcium channels in the biological effects exerted by progesterone (P) on human spermatozoa is still a controversial issue. We have investigated the involvement of T-type calcium channels [voltage-operated calcium channels (VOCCT)] in two biological functions of human sperm, responsiveness to P and capacitation, by employing three different pharmacological antagonists of VOCCT, namely mibefradil (Ro 5967), pimozide and amiloride. Intracellular calcium [Ca(2+)]i increase in response to P was essentially unaffected by pre-treatment with mibefradil and pimozide at concentrations previously shown to prevent [Ca(2+)]i increase in response to zona proteins. Amiloride could not be tested in these experiments because it was found to interfere with fura-2 fluorescence. The increase in tyrosine phosphorylation stimulated by P in a protein of about 97 kDa was unaffected by the three antagonists. Acrosome reaction (AR) induced by P was also unaffected by mibefradil or pimozide but was significantly inhibited by amiloride at high concentrations (100 and 500 but not 10 microM). At 100 and 500 microM amiloride also inhibited Na/H exchanger as assessed by a fluorimetric method. We conclude that VOCCT are not involved in calcium increase and AR stimulated by P in human sperm. We next investigated the effect of the three VOCCT inhibitors on sperm capacitation by evaluating tyrosine phosphorylation and AR in basal conditions and in response to P. We found that the presence of pimozide and amiloride during capacitation stimulated a higher increase of tyrosine phosphorylation, whereas mibefradil was less effective. The ability of P to induce the AR, considered an index of occurrence of capacitation, was not affected by pimozide and mibefradil, whereas was inhibited by amiloride at concentrations that inhibit Na/H exchanger. In conclusion, our results do not support a major role of low-voltage-activated calcium channels in capacitation and response to P of human spermatozoa.

Identification of mouse trp homologs and lipid rafts from spermatogenic cells and sperm

Intracellular Ca(2+) has an important regulatory role in the control of sperm motility, capacitation, and the acrosome reaction (AR). However, little is known about the molecular identity of the membrane systems that regulate Ca(2+) in sperm. In this report, we provide evidence for the expression of seven Drosophila transient receptor potential homolog genes (trp1-7) and three of their protein products (Trp1, Trp3 and Trp6) in mouse sperm. Allegedly some trps encode capacitative Ca(2+) channels. Immunoconfocal images showed that while Trp6 was present in the postacrosomal region and could be involved in sperm AR, expression of Trp1 and Trp3 was confined to the flagellum, suggesting that they may serve sperm to regulate important Ca(2+)-dependent events in addition to the AR. Likewise, one of these proteins (Trp1) co-immunolocalized with caveolin-1, a major component of caveolae, a subset of lipid rafts potentially important for signaling events and Ca(2+) flux. Furthermore, by using fluorescein-coupled cholera toxin B subunit, which specifically binds to the raft component ganglioside GM1, we identified caveolin- and Trp-independent lipid rafts residing in the plasma membrane of mature sperm. Notably, the distribution of GM1 changes drastically upon completion of the AR.

Analysis of Ca(2+) currents in spermatocytes from mice lacking Ca(v)2.3 (alpha(1E)) Ca(2+) channel

In mammalian male germ-line cells, low-voltage-activated (LVA) Ca(2+) current has been identified and its electrophysiological properties have been studied. To investigate whether alpha(1)2.3 (alpha(1E)) subunit of the voltage-dependent Ca(2+) channel codes for the LVA current, whole-cell patch clamp and following reverse transcription-polymerase chain reaction (RT-PCR) experiments were performed in pachytene spermatocytes from Ca(v)2.3+/+ and Ca(v)2.3-/- mice. Whole-cell current in acutely dissociated pachytene spermatocytes from Ca(v)2.3+/+ and Ca(v)2.3-/- mice displayed a typical profile of LVA Ca(2+) currents and kinetics with no significant differences. Single-cell RT-PCR revealed the expression of Cacna1g in the pachytene spermatocytes from Ca(v)2.3+/+ and Ca(v)2.3-/- mice in which LVA Ca(2+) currents were actually recorded. These results suggest that the Ca(v)2.3 channel makes no detectable contribution to the LVA Ca(2+) current in the pachytene spermatocyte. Instead, Ca(v)3 family such as Ca(v)3.1 may be the likely candidates responsible for the LVA currents in pachytene spermatocytes.

A voltage-gated ion channel expressed specifically in spermatozoa

Calcium ions play a primary role in the regulation of sperm cell behavior. We report finding a voltage-gated ion channel (CatSper2) that is expressed in male germ cells but not in other cells. The putative channel contains 6 transmembrane segments, making it more similar to the voltage-gated potassium channels, but the ion selectivity pore domain sequence resembles that of a Ca(v) channel. The mRNA is expressed during the meiotic or postmeiotic stages of spermatogenesis, and the protein is localized to the sperm flagellum, suggesting a role in the regulation of sperm motility. The mRNA for the channel is present in mouse, rat, and human sperm cells, and the gene is found on chromosome 2 E5-F1 in the mouse and 15q13 in the human. Recently, another voltage-gated channel (CatSper) that has features similar to the one reported here was discovered. It also is expressed within the flagellum and is required for normal fertility of mice. However, expression of CatSper2 alone or coexpression with CatSper in cultured cells, or attempts to coimmunoprecipitate the two proteins from germ cells failed to demonstrate that these two unique but similar alpha-like subunits form either a homo- or heterotetramer. It is possible, therefore, that two independent alpha subunits, different from other known voltage-gated channels, regulate sperm motility.

A sperm ion channel required for sperm motility and male fertility

Calcium and cyclic nucleotides have crucial roles in mammalian fertilization, but the molecules comprising the Ca2+-permeation pathway in sperm motility are poorly understood. Here we describe a putative sperm cation channel, CatSper, whose amino-acid sequence most closely resembles a single, six-transmembrane-spanning repeat of the voltage-dependent Ca2+-channel four-repeat structure. CatSper is located specifically in the principal piece of the sperm tail. Targeted disruption of the gene results in male sterility in otherwise normal mice. Sperm motility is decreased markedly in CatSper-/- mice, and CatSper-/- sperm are unable to fertilize intact eggs. In addition, the cyclic-AMP-induced Ca2+ influx is abolished in the sperm of mutant mice. CatSper is thus vital to cAMP-mediated Ca2+ influx in sperm, sperm motility and fertilization. CatSper represents an excellent target for non-hormonal contraceptives for both men and women.