The development of signal transduction pathways during epididymal maturation is calcium dependent

Capacitation has been correlated with the activation of a cAMP-PKA-dependent signaling pathway leading to protein tyrosine phosphorylation. The ability to exhibit this response to cAMP matures during epididymal maturation in concert with the ability of the spermatozoa to capacitate. In this study, we have addressed the mechanisms by which spermatozoa gain the potential to activate this signaling pathway during epididymal maturation. In a modified Tyrode's medium containing 1.7 mM calcium, caput spermatozoa had significantly higher [Ca2+]i than caudal cells and could not tyrosine phosphorylate in response to cAMP. However, in calcium-depleted medium both caput and caudal cells could exhibit a cAMP-dependent phosphorylation response. The inhibitory effect of calcium on tyrosine phosphorylation was also observed in caudal spermatozoa using thapsigargin, a Ca(2+)-ATPase inhibitor that increased [Ca2+]i and precipitated a corresponding decrease in phosphotyrosine expression. We also demonstrate that despite the activation of tyrosine phosphorylation in caput spermatozoa, these cells remain nonfunctional in terms of motility, sperm-egg recognition and acrosomal exocytosis. These results demonstrate that the signaling pathway leading to tyrosine phosphorylation in mouse spermatozoa is negatively regulated by [Ca2+]i, and that maturation mechanisms that control [Ca2+]i within the spermatozoon are critically important during epididymal transit.

Redox activity associated with the maturation and capacitation of mammalian spermatozoa

As rat spermatozoa undergo epididymal maturation, they acquire the ability to exhibit a spontaneous burst of luminol-peroxidase-dependent chemiluminescence when released into a simple, defined culture medium. This activity was suppressed by inhibitors of plasma membrane redox systems such as diphenylene iodonium, p-chloromercuribenzenesulfonic acid, and capsaicin, but was resistant to inhibition by resiniferatoxin and rotenone. The luminol-peroxidase signal was dependent on the presence of bicarbonate, enhanced by the substitution of fructose for glucose, and severely suppressed by desferoxamine, superoxide dimutase, and catalase. Both L- and D-arginine were stimulatory, suggesting the involvement of *NO in this spontaneous chemiluminescence activity. The L-arginine-dependent, but not the D-arginine-dependent, activity was significantly suppressed by an inhibitor of nitric oxide synthase (N(G)-nitro-L-arginine methyl ester). L- and D-arginine could also stimulate redox activity observed in immature caput epididymal cells, but only after prolonged incubation. The inhibitory effects of uric acid and ascorbate suggested the chemiluminescence signal might be induced by peroxynitrite. This conclusion was supported by confocal imaging of the cells following treatment with 4-amino-5-methylamino-2',7'-difluorofluorescein. Stimulation or suppression of the redox activity detected by luminol-peroxidase led to corresponding changes in the ability of the spermatozoa to exhibit acrosomal exocytosis, indicating that this pathway is of fundamental biological significance.

Identification of cytochrome P450-reductase as the enzyme responsible for NADPH-dependent lucigenin and tetrazolium salt reduction in rat epididymal sperm preparations

Lucigenin-dependent chemiluminescence and WST-1 reduction can be detected following addition of NADPH to many cell types, including rat epididymal sperm suspensions. Although many reports suggest that such a phenomenon is due to reactive oxygen species production, other probes-such as MCLA and luminol-that are capable of detecting reactive oxygen metabolites do not produce a chemiluminescent signal in this model system. Our aim was to purify and identify the enzyme catalyzing the NADPH-dependent lucigenin and WST-1 reduction from rat epididymal spermatozoa preparations. Here, we show the identity of this enzyme as cytochrome P450-reductase. In support of this, a homogenous preparation of this protein was capable of reducing lucigenin and WST-1 in the presence of NADPH. Moreover, COS-7 cells overexpressing cytochrome P450-reductase displayed a 3-fold increase in the aforementioned activity compared with mock-transfected cells. Immunolocalization studies and biochemical analysis suggest that the majority of the NADPH-lucigenin activity is localized to the epithelial cells present within the epididymis. These results emphasize the importance of the direct NADPH-dependent reduction of superoxide-sensitive probes by cytochrome P450-reductase even though this enzyme does not, on its own accord, produce reactive oxygen species.

Antioxidant strategies in the epididymis

Spermatozoa are very specialized cells, dedicated to fertilization of the oocyte. The attainment of this biological role is partly due to the fusogenic properties of the sperm plasma membrane, which is particularly rich in polyunsaturated fatty acids (PUFA). This predominance of PUFA renders spermatozoa highly susceptible to lipid peroxidation due to attacks from reactive oxygen species (ROS). These attacks ultimately lead to the impairment of sperm function through oxidative stress. Despite such disruptive effects, it should be also emphasized that these molecules also play an important positive, physiological role in the regulation of sperm physiology through their participation in apoptosis and the signal transduction cascades that control sperm maturation and capacitation. In this article, the different sources of ROS are examined and then the antioxidant strategies that protect these cells during epididymal transit are reviewed. While the major focus is on the involvement of glutathione peroxidase in this process, consideration will also be given to a range of additional antioxidant enzymes (catalase, indolamine dioxygenase and superoxide dismutase) that have evolved to protect spermatozoa during this extremely vulnerable phase in their life history. Besides the classical enzymatic roles of these enzymes in recycling ROS, additional features are discussed in the light of contraceptive development.

The importance of redox regulated pathways in sperm cell biology

Redox regulated events are fundamental to our understanding of many cellular pathways and pathological processes. On the one hand, production of reactive oxygen species by mammalian spermatozoa has been associated with a loss of cell function and DNA integrity as a consequence of oxidative stress. These cells are exquisitely sensitive to such damage as a consequence of their relative lack of cytosolic antioxidant enzymes and relative abundance of polyunsaturated fatty acids. Given this susceptibility, it is surprising to discover that spermatozoa are intensely redox active cells and professional generators of reactive oxygen species. The latter are physiologically important to the spermatozoa in regulating every aspect of sperm function examined, including their movement characteristics, capacitation, sperm-zona interaction, the acrosome reaction and sperm-oocyte fusion. The molecular basis of this redox drive is still poorly understood in terms of the source of the reactive oxygen species and the mechanisms by which these reactive metabolites enhance sperm function. Recent advances include the discovery of NOX5 in the male germ line and elucidation of the role of reactive oxygen species in controlling a unique signal transduction cascade associated with sperm capacitation. Given the central importance of redox chemistry in the control of sperm function further research in this area may uncover valuable targets for contraceptive intervention.

Cyclic AMP-dependent tyrosine phosphorylation in tammar wallaby (Macropus eugenii) spermatozoa

Despite considerable advances in our understanding of the molecular mechanisms regulating eutherian sperm function, there is a paucity of such knowledge for the Metatheria. In eutherian spermatozoa, the attainment of functional competence is associated with a redox-regulated, cAMP-mediated tyrosine phosphorylation cascade, activated during capacitation. In this report we investigate whether tammar wallaby (Macropus eugenii) spermatozoa possess a similar signal transduction pathway. Western blot analysis of phosphotyrosine expression in caudal and ejaculated populations of tammar spermatozoa revealed that elevation of intracellular cAMP levels, but not exposure to oxidants or NADPH, induced a dramatic increase in the overall level of tyrosine phosphorylation. Washed, ejaculated spermatozoa exhibited more pronounced increases in tyrosine phosphorylation than unwashed sperm populations. Localisation of tyrosine phosphorylation by immunocytochemistry showed that phosphotyrosine residues were principally located along the tammar sperm flagellum, and occasionally at a small region of the sperm head, adjacent to the acrosome. Associated with the tyrosine phosphorylation of tammar spermatozoa, was a change in sperm head conformation to a T-shaped orientation, further implying the importance of these pathways to normal tammar sperm function. Redox activity, as detected by lucigenin-dependent chemiluminescence, was stimulated by NADPH in caudal sperm preparations but not ejaculated spermatozoa. However, neither sperm population responded to treatment with NADPH with changes in intracellular cAMP or tyrosine phosphorylation. In conclusion, tammar spermatozoa possess the same cAMP-mediated, tyrosine phosphorylation-dependent signal transduction cascade that has been associated with capacitation in eutherian spermatozoa. However in Metatherian spermatozoa we could find no evidence that this pathway was redox regulated.

Identification and characterization of a novel splice variant of mouse and rat cytochrome b5/cytochrome b5 reductase

Cytochrome b5/cytochrome b5 reductase (cb5/cb5r) is a cytosolic fusion protein between the hemoprotein cytochrome b5 and the flavoprotein cytochrome b5 reductase. We describe the identification and characterization of a novel splice variant of cb5/cb5r in the mouse and rat and show that expression of the variant is conserved in both species but is not expressed in human tissue. Characterization of the exon structure of cb5/cb5r indicated that the variant was due to the deletion of the whole of exon 12, thus the variant was named cb5/cb5rdelta12. Exon 12 codes for the flavin-adenine dinucleotide binding domain of cb5/cb5r. Expression analysis revealed the transcript of cb5/cb5rdelta12 in mouse and rat testis, brain, and skeletal muscle and also in the male germ line. We postulate that cb5/cb5rdelta12 may function in a dominant negative fashion, limiting the amount of damage caused by the production of reactive oxygen species by cb5/cb5r.

The human spermatozoon--not waving but drowning

The poor quality of the human ejaculate sets man apart from all other mammalian species. Even in normal fertile men the ejaculate may contain up to 85% abnormal forms according to the World Heath Organization (1999). In the wake of this poor semen quality comes extremely poor fertility (Hull et al, 1985) and the highest rates of aneuploidy, pregnancy loss and birth defects in viviparous vertebrates. Thus, the poor quality of human spermatozoa is reflected in both their capacity for fertilization and their genetic integrity. The ultimate cause of defective sperm function is unknown. In certain patients a genetic basis for male infertility has been identified involving DNA deletions on the long arm of the Y chromosome. Such deletions might explain the impoverished semen quality seen in about 10-14% of men with severely impaired spermatogenesis, but fail to explain the infertility seen in most (>85%) cases of male infertility. One of the key attributes and probable causes of defective sperm function is oxidative stress created by excessive ROS generation by the spermatozoa and/or the disruption of antioxidant defence systems in the male reproductive tract. Excess free radical generation frequently involves an error in spermiogenesis resulting in the release of spermatozoa from the germinal epithelium exhibiting abnormally high levels of cytoplasmic retention. The excess cytoplasm contains enzymes that fuel the generation of ROS by the spermatozoa's plasma membrane redox systems. The consequences of such oxidative stress include a loss of motility and fertilizing potential and the induction of DNA damage in the sperm nucleus. The loss of sperm function is due to the peroxidation of unsaturated fatty acids in the sperm plasma membrane as a consequence of which the latter loses its fluidity and the cells lose their function. The causes and consequences of oxidative damage to the DNA in the sperm nucleus are still not known with certainty. The available evidence suggests that early pregnancy loss and morbidity in the offspring, including childhood cancer, are associated with such damage. Developing animal models with which to establish the validity of these relationships and identifying the environmental factors associated with the proposed 'testicular dysgenesis syndrome' will clearly be important tasks for the future.

Founders' Lecture. Human spermatozoa: fruits of creation, seeds of doubt

Deoxyribonucleic acid damage in the male germline is associated with defective fertilisation, impaired embryonic development, reduced implantation, abortion and childhood disease. Oxidative stress and the retention of excess residual cytoplasm by the spermatozoa are frequently associated with the induction of such damage. The redox cycling of xenobiotics by oxido-reductases in the germline, the patient’s age, the incidence of genital tract infections and Sertoli cell dysfunction are all possible contributors to DNA damage in germ cells. Collateral peroxidation of unsaturated fatty acids in the sperm plasma membrane generally ensures that spermatozoa experiencing severe oxidative DNA damage cannot participate in the process of fertilisation. The adaptive termination of pregnancy through the selective vulnerability of genes involved in placentation may also help prevent the vertical transmission of damaged DNA. However, the ultimate safeguard against this form of damage will be to understand the biochemical basis of oxidative stress in human spermatozoa, so that the underlying causative mechanisms can be addressed in a logical manner.

Oxidative stress and male reproductive biology

Spermatozoa were the first cell type in which the cellular generation of reactive oxygen was demonstrated. This activity has now been confirmed in spermatozoa from all mammalian species examined including the rat, mouse, rabbit, horse, bull and human being. Under physiological circumstances, cellular redox activity is thought to drive the cAMP-mediated, tyrosine phosphorylation events associated with sperm capacitation. In addition to this biological role, human spermatozoa also appear to suffer from oxidative stress, with impacts on the normality of their function and the integrity of their nuclear and mitochondrial DNA. Recent studies have helped to clarify the molecular basis for the intense redox activity observed in defective human spermatozoa, the nature of the subcellular structures responsible for this activity and possible mechanisms by which oxidative stress impacts on these cells. Given the importance of oxidative damage in the male germ line to the origins of male infertility, early pregnancy loss and childhood disease, this area of sperm biochemistry deserves attention from all those interested in improved methods for the diagnosis, management and prevention of male-mediated reproductive failure.

Tyrosine phosphorylation of HSP-90 during mammalian sperm capacitation

The process of sperm capacitation is correlated with activation of a signal transduction pathway leading to protein tyrosine phosphorylation. Whereas phosphotyrosine expression is an essential prerequisite for fertilization, the proteins that are phosphorylated during capacitation have not yet been identified. In the present study, we observed that a major target of this signaling pathway is the molecular chaperone protein, heat shock protein (HSP)-86, a member of the HSP-90 family of HSPs. We used cross-immunoprecipitation experiments to confirm the tyrosine phosphorylation of HSP-86, a process that is not inhibited by the ansamycin antibiotic, geldanamycin. The general significance of these findings was confirmed by studies in which HSP-90 was also found to be tyrosine phosphorylated in human and rat spermatozoa when incubated under conditions that support capacitation. To our knowledge, these results represent the first report of a protein that undergoes tyrosine phosphorylation during mouse sperm capacitation and the first study implicating molecular chaperones in the processes by which mammalian spermatozoa gain the ability to fertilize the oocyte.

Adenylyl cyclase isoforms in rat testis and spermatozoa from the cauda epididymidis

Expression of adenylyl cyclase genes in rat testis and spermatozoa from the cauda epididymidis was investigated using RT-PCR analysis. Genes encoding the transmembrane adenylyl cyclases (tmAC) II, III, IV, V, VI, VII, and VIII were expressed in the testis, whereas only the gene for tmAC III was expressed in caudal spermatozoa. Immunocytochemistry was used to investigate which tmAC were translated into putative, functional proteins in spermatozoa. Indirect immunofluorescence localized the tmAC II enzyme to a region on the head occupied by the acrosome. The tmAC III enzyme was localized to the posterior margin of the head and to the flagellum, whereas tmAC V and/or VI was localized to the region where the ventral surface of the acrosomal equatorial segment is located. The tmAC VII and VIII enzymes were localized to the convex margin of the head, covering the dorsal region of the acrosomal crescent. To our knowledge, this is the first demonstration that five apparently different tmAC enzymes are localized to discrete subcellular regions of mammalian spermatozoa. These findings provide a fundamental basis for future studies, to determine the physiological roles of tmAC in testis and mature spermatozoa.

Quantitative analysis of gene-specific DNA damage in human spermatozoa

Recent studies have suggested that human spermatozoa are highly susceptible to DNA damage induced by oxidative stress. However, a detailed analysis of the precise nature of this damage and the extent to which it affects the mitochondrial and nuclear genomes has not been reported. To induce DNA damage, human spermatozoa were treated in vitro with hydrogen peroxide (H2O2; 0-5 mM) or iron (as Fe(II)SO4, 0-500 microM). Quantitative PCR (QPCR) was used to measure DNA damage in individual nuclear genes (hprt, beta-pol and beta-globin) and mitochondrial DNA. Single strand breaks were also assessed by alkaline gel electrophoresis. H2O2 was found to be genotoxic toward spermatozoa at concentrations as high as 1.25 mM, but DNA damage was not detected in these cells with lower concentrations of H2O2. The mitochondrial genome of human spermatozoa was significantly (P<0.001) more susceptible to H2O2-induced DNA damage than the nuclear genome. However, both nDNA and mtDNA in human spermatozoa were significantly (P<0.001) more resistant to damage than DNA from a variety of cell lines of germ cell and myoblastoid origin. Interestingly, significant DNA damage was also not detected in human spermatozoa treated with iron. These studies report, for the first time, quantitative measurements of DNA damage in specific genes of male germ cells, and challenge the commonly held belief that human spermatozoa are particularly vulnerable to DNA damage.

Contraceptive vaccines

The control of human fertility would be revolutionised by the development of a safe, effective, long-acting contraceptive vaccine. The pursuit of this objective has involved the selection of appropriate targets within the reproductive process that are amenable to interference with antibodies. To date, three major targets have been researched. The zona pellucida (ZP) plays key roles in folliculogenesis, fertilisation and early development, and is comprised of powerful cell-specific antigens. The induction of infertility requires high ZP antibody titres that are difficult to maintain without inducing ovarian pathology characterised by a premature loss of primordial follicles. As a premature menopause would be a high price to pay for long-term contraception, this approach to a vaccine cannot progress until the cause of the ovarian pathology has been resolved. Sperm surface antigens represent another promising approach to contraceptive vaccine development. While there is some clinical data to support the likely efficacy of this strategy, none of the gamete-specific molecules characterised to date have fulfilled this promise. Anti-human chorionic gonadotropin (hCG) vaccines terminate pregnancy by preventing the maternal recognition of pregnancy. This vaccine has reached the stage of clinical trials, and preliminary indications are that the approach is safe and potentially effective. However, reliability may be an issue, given the observed inter-individual variability in antibody generation. The future of contraceptive vaccine development will clearly involve a continuation of the intense search for suitable targets and the development of improved immunisation procedures that exploit the latest innovations in vaccine technology.

Oxidative stress in the male germ line and its role in the aetiology of male infertility and genetic disease

The human male is characterized by extremely poor semen quality as reflected in the number, morphology and motility of the spermatozoa and a high incidence of nuclear and mitochondrial DNA damage. As a consequence of these factors, defective sperm function is thought to be a major contributor to the aetiology of human infertility, as well as childhood diseases including dominant genetic mutations such as achondroplasia and cancer. Factors associated with the origin of poor semen quality include: (i) a lack of selection pressure for high fecundity genes in developed countries, (ii) an evolutionary lineage associated with the deterioration of several male fertility genes in humans and their close ancestors, (iii) genetic factors including, but not limited to, Y-chromosome deletions (iv) paternal age and (v) environmental factors. A model is proposed whereby factors such as ageing or environmental toxicants initiate DNA strand breakage in the spermatozoa of affected males, eventually leading to a mutation in the embryo. This hypothesis stresses the importance of discovering the identity of those environmental factors that are capable of damaging DNA integrity in the male germ line. Such information could make an important contribution to understanding of the origins of both male infertility and a variety of pathological conditions that affect humans, including cancer and dominant genetic disease.

Endogenous redox activity in mouse spermatozoa and its role in regulating the tyrosine phosphorylation events associated with sperm capacitation

We investigated the role of endogenous redox activity in regulating the signal transduction pathway leading to tyrosine phosphorylation in mouse spermatozoa. Endogenous redox activity was monitored using a luminol-peroxidase chemiluminescent probe. Chemiluminescence increased in spermatozoa that were actively undergoing cAMP-mediated tyrosine phosphorylation events associated with capacitation and was inhibited in a dose-dependent manner by addition of catalase or diphenylene iodonium, both of which also inhibited tyrosine phosphorylation within the cell at points downstream of cAMP. Excluding bicarbonate from the incubation medium reduced the redox activity of sperm by 80-90% and dramatically reduced tyrosine phosphorylation. This study provides the first evidence that tyrosine phosphorylation associated with capacitation in mouse spermatozoa is redox regulated by a flavinoid-containing enzyme involving mediation by hydrogen peroxide. Bicarbonate regulated the redox activity of mouse spermatozoa, and this regulation may contribute to the impact of this anion on tyrosine phosphorylation during capacitation of mouse spermatozoa.

Biochemical entities involved in reactive oxygen species generation by human spermatozoa

Spermatozoa were the first cell type suggested to generate reactive oxygen species. However, a lack of standardization in sperm preparation techniques and the obfuscating impact of contaminating cell types in human ejaculates have made it difficult to confirm that mammalian germ cells do, in fact, make such reactive metabolites. By identifying, on a molecular level, those entities involved in reactive oxygen species generation and demonstrating their presence in spermatozoa, the role of redox chemistry in the control of sperm function can be elucidated. Two major proteins have apparently been identified in this context, namely, NOX5, a calcium-activated NADPH oxidase, and nitric oxide synthase. Understanding the involvement of these enzymes in sperm physiology is essential if we are to understand the causes of oxidative stress in the male germ line.

Development of the signalling pathways associated with sperm capacitation during epididymal maturation

As spermatozoa mature within the epididymis they acquire the potential for capacitation and ultimately fertilization. In biochemical terms, the former is reflected in the progressive activation of a signal transduction pathway characterized by cAMP-mediated induction of phosphotyrosine expression on the sperm tail. In this study, we have examined the cellular mechanisms controlling this maturational event. Caput epididymal spermatozoa exhibited tyrosine phosphorylation on the sperm head that was largely unresponsive to cAMP and not significantly impaired by removal of extracellular HCO(3) (-). In contrast, caudal epididymal spermatozoa exhibited low levels of phosphorylation on the sperm head, yet responded dramatically to cAMP by phosphorylating a new set of proteins on the sperm tail via mechanisms that were highly dependent on extracellular HCO(3) (-). The impact of extracellular HCO(3) (-) depletion on caudal cells was not associated with a significant change in the redox regulation of cAMP but could be fully reversed by buffering the intracellular pH with N-Tris[Hydroxymethyl]methyl-3-amino-propanesulfonic acid (TAPS). The pattern of tyrosine phosphorylation was also profoundly influenced by the presence or absence of added extracellular calcium. In the presence of this cation, only caudal spermatozoa could respond to increased extracellular cAMP with tyrosine phosphorylation of the sperm tail. However, in calcium-depleted medium, this difference completely disappeared. Under these conditions, caput and caudal spermatozoa were equally competent to exhibit phosphotyrosine expression on the sperm tail in response to cAMP. These results emphasize the pivotal role played by calcium and HCO(3) (-) in modulating the changes in tyrosine phosphorylation observed during epididymal maturation.

Motility activation and second messenger signalling in spermatozoa from rat cauda epididymidis

This study examined molecular mechanisms involved in the activation of motility in spermatozoa from the cauda epididymidis of rats. A 1.05-fold dilution of semen from the cauda epididymidis with 300 mmol sucrose l(-1) did not activate motility in spermatozoa. Addition of dibutyryl cAMP, pentoxifylline or Ca(2+) to the sucrose activated motility in the short term (<30-60 min). A fivefold dilution of semen from the cauda epididymidis with a modified Tyrode's medium (BWW) activated and sustained vigorous motility that could not be attenuated with kinase inhibitors. This motility was associated with a transient increase in intracellular cAMP during the first 60 s of activation. Lower motility was activated in Ca(2+)-deficient media but this was not associated with an increase in cAMP. A fivefold dilution with plasma from the cauda epididymidis did not activate motility. The addition of Ca(2+) to the sucrose induced an increase in cAMP of similar duration but lower magnitude to that associated with dilution in BWW. The results from this study indicate that the cAMP and Ca(2+) signal transduction pathways are involved in activation of sperm motility, and that the increase in intracellular cAMP in rat spermatozoa from the cauda epididymidis undergoing motility activation is Ca(2+)-dependent. This is the first study to report a Ca(2+)-dependent increase in cAMP associated with motility activation in immotile mammalian spermatozoa. In light of these data, a model is proposed whereby cAMP and Ca(2+) act as synarchic messengers, initiating a signal transduction cascade, which is independent of protein kinase A-mediated phosphorylation of flagella proteins in immotile spermatozoa from the cauda epididymidis.

Immunocontraceptive vaccines for human use

The development of safe, effective, reversible contraceptive vaccines for the regulation of human fertility would be a significant addition to our contraceptive armamentarium. However, because we are such an out-bred species, immunological responsiveness to any given vaccine is certain to exhibit a high level of inter-individual variation that will impact upon the efficacy, reversibility and feasibility of the approach. Nevertheless a role for vaccines undoubtedly exists as an aid to birth spacing, particularly in developing countries, and as a non-surgical means of inducing sterility in men. Currently vaccines are being researched that target one of two strategic points in the reproductive process, fertilization and the maternal recognition of pregnancy. Our ability to engineer vaccines that target fertilization is hampered by deficiencies in our knowledge of the molecular mechanisms that regulate this process. However, anti-hCG vaccines have advanced to the stage of clinical trials and appear promising.

Induction of sperm maturation in vitro in epididymal cell cultures of the tammar wallaby (Macropus eugenii): disruption of motility initiation and sperm morphogenesis by inhibition of actin polymerization

A sperm-epididymal cell co-culture was shown to be capable of inducing the in vitro maturation of spermatozoa from a marsupial species, the tammar wallaby (Macropus eugenii). This system was able to maintain wallaby epididymal epithelial cells in vitro for more than 2 months. The system also enabled immature wallaby spermatozoa to differentiate from a T-shaped to a streamlined form, accompanied by the development of progressive motility after co-culture with epididymal cell monolayers that had been cultured for 7 days. The addition of inhibitors of actin polymerization (latrunculin A or B) to the co-culture system showed that wallaby sperm maturation was impaired by the interruption of actin organization within the immature spermatozoa. These results indicate that actin filaments play a significant role in sperm transformation during post-testicular maturation in marsupials. These observations also indicate that the marsupial co-culture system has the potential to greatly increase understanding of sperm-epididymal cell interactions and the mechanism of sperm maturation in these species.