http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:11890 Background: Spermatogenesis culminates in production of one of the most highly differentiated cells in biology, the spermatozoon. The gametes that emerge from the testes are, however, functionally immature and only acquire full functionality once they have completed a process of post-testicular maturation in the epididymis and female reproductive tract. Remarkably, this acquisition of sperm function occurs while these cells are transcriptionally and translationally silent and is therefore highly dependent on post-translational modifications to their existing protein complement. In this review, we consider the emerging roles of several prominent molecular chaperone families in orchestrating both the morphological differentiation of male germ cells during spermatogenesis and their functional transformation during sperm maturation. Methods: Journal databases were searched using key words, including chaperone, heat shock protein, testes, spermatogenesis, spermatozoa, epididymal maturation, capacitation and fertilization. Results: In the past two decades, molecular chaperones have been acknowledged to play key roles in controlling both the morphological transformation of germ cells during spermatogenesis and the post-testicular maturation of these cells as they transit the male and female reproductive tracts. Furthermore, there is mounting evidence that aberrant chaperone expression may be a major contributing factor to the defective sperm function seen in many cases of male infertility. Conclusions: Molecular chaperones are critically involved in all phases of sperm development. Targeted disruption of these proteins has the ability to arrest spermatogenesis, compromise sperm maturation and inhibit fertilization. These proteins therefore hold considerable promise as targets for novel contraceptive strategies and as diagnostic biomarkers for male infertility. 2012-11-01T04:43:43.354Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:11888 Sperm-oocyte interactions are among the most remarkable processes in cell biology. These cellular recognition events are initiated by an exquisitely specific adhesion of free-swimming spermatozoa to the zona pellucida, an acellular matrix that surrounds the ovulated oocyte. Decades of research focusing on this interaction have led to the establishment of a widely held paradigm that the zona pellucida receptor is a single molecular entity that is constitutively expressed on the sperm cell surface. In contrast, we have employed the techniques of blue native-polyacrylamide gel electrophoresis, far Western blotting, and proximity ligation to secure the first direct evidence in support of a novel hypothesis that zona binding is mediated by multimeric sperm receptor complex(es). Furthermore, we show that one such multimeric association, comprising the chaperonin-containing TCP1 complex (CCT/TRiC) and a zona-binding protein, zona pellucida-binding protein 2, is present on the surface of capacitated spermatozoa and could account for the zona binding activity of these cells. Collectively, these data provide an important biochemical insight into the molecular basis of sperm-zona pellucida interaction and a plausible explanation for how spermatozoa gain their ability to fertilize. 2012-11-01T04:26:24.449Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:11356 At the moment of insemination, millions of mammalian sperm cells are released into the female reproductive tract with the single goal of finding the oocyte. The spermatozoa subsequently ignore the thousands of cells they make contact with during their journey to the site of fertilization, until they reach the surface of the oocyte. At this point, they bind tenaciously to the acellular coat, known as the zona pellucida, which surrounds the oocyte and orchestrate a cascade of cellular interactions that culminate in fertilization. These exquisitely cell- and species- specific recognition events are among the most strategically important cellular interactions in biology. Understanding the cellular and molecular mechanisms that underpin them has implications for the etiology of human infertility and the development of novel targets for fertility regulation. Herein we describe our current understanding of the molecular basis of successful sperm–zona pellucida binding. 2012-08-27T03:58:47.317Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:11318 Infertility is a relatively common condition affecting approximately one in ten of the population. In half of these cases, a male factor is involved, making defective sperm function the largest single, defined cause of human infertility. Among other factors, recent data suggest that oxidative stress plays a major role in the etiology of this condition. Spermatozoa spontaneously produce a variety of reactive oxygen species (ROS) including the superoxide anion, hydrogen peroxide and nitric oxide. Produced in small amounts, ROS are functionally important in driving the tyrosine phosphorylation cascades associated with sperm capacitation. However, when ROS production exceeds the spermatozoa’s limited antioxidant defenses, a state of oxidative stress is induced characterized by peroxidative damage to the sperm plasma membrane and DNA strand breakage in the sperm nucleus. Such oxidative stress not only disrupts the fertilizing potential of human spermatozoa but also the ability of these cells to create a normal healthy embryo. As a result, DNA damage in human spermatozoa is correlated with an increased incidence of miscarriage and various kinds of morbidity in the offspring. These insights into the pathophysiology of defective sperm function have clear implications for the diagnosis and treatment of male infertility, particularly with respect to the potential importance of antioxidant therapy. These concepts may also be relevant to the design of novel approaches to male contraception that attempt to replicate the pathological situation. 2012-08-22T02:10:06.131Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:11205 The purpose of this study was to examine the impact of prolactin (PRL) on human sperm function, in light of a recent proteomic analysis indicating that these cells express the PRL receptor (PRLR). Immunocytochemical analyses confirmed the presence of PRLR in human spermatozoa and localized this receptor to the postacrosomal region of the sperm head as well as the neck, midpiece, and principal piece of the sperm tail. Nested PCR analysis indicated that these cells possess four splice variants of the PRLR: the long form and three short isoforms, one of which is reported for the first time. A combination of Western blot analyses and immunocytochemistry demonstrated that PRL inhibited sperm capacitation in a dose-dependent manner, suppressing SRC kinase activation and phosphotyrosine expression, two hallmarks of this process. The suppression of sperm capacitation was accompanied by a powerful prosurvival effect, supporting the prolonged motility of these cells and preventing the formation of spontaneous DNA strand breaks via mechanisms that involved the concomitant suppression of caspase activation. Western blot analyses indicated that the prosurvival effect of PRL on human spermatozoa involved the stimulation of Akt phosphorylation, whereas inhibitors of phosphatidylinositol-3-OH kinase and Akt negated this effect, as did the direct induction of sperm capacitation with cAMP analogues. We conclude that PRL is a prosurvival factor for human spermatozoa that prevents these cells from defaulting to an intrinsic apoptotic pathway associated with cell senescence. These findings have implications for preservation of sperm integrity in vivo and in vitro. 2012-08-08T23:02:49.678Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:10935 Following ejaculation, mammalian spermatozoa undergo an obligatory process known as capacitation, which enables these cells to bind to and fertilize an oocyte. Since spermatozoa are transcriptionally and translationally silent, the functional metamorphosis of these cells during capacitation is accomplished entirely by PTMs. Despite the importance of this process, very few studies have attempted to define the precise nature of the proteomic changes that allow spermatozoa to attain a capacitated state. Here we report the use of an IPG-strip pre-fractionation approach to isolate and purify tryptic peptides derived from mouse spermatozoa exhibiting varying degrees of capacitation. Following focusing, the strips were cut into 1 cm segments, the peptides extracted and run into a mass spectrometer. Label-free, quantitative analysis of proteomic changes associated with capacitation was then performed. In total, we found 210 significant peptide changes. Of these, we could conclusively interpret the tandem mass spectra of 71 peptides, corresponding to 52 protein changes during capacitation. Many proteins including VDAC2, Fascin-3 and sorbitol dehydrogenase (SORD) have not previously been implicated in this process. To validate our data, we were able to show significant upregulation of SORD activity during capacitation, suggesting that the polyol pathway is activated during this process. 2012-06-19T04:02:04.462Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:10106 Recent studies from within our laboratory have demonstrated a causal relationship between capacitation-associated surface phosphotyrosine expression and the ability of mouse spermatozoa to recognize the oocyte and engage in sperm–zona pellucida interaction. In the studies described herein we have sought to investigate the signaling pathways that underpin the tyrosine phosphorylation of sperm surface protein targets and validate the physiological significance of these pathways in relation to sperm–zona pellucida adhesion. Through selective pharmacological inhibition we have demonstrated that surface phosphotyrosine expression is unlikely to be mediated by the canonical cAMP-dependent protein kinase A (PKA) signaling cascade that has been most widely studied in relation to sperm capacitation. Rather, it appears to be primarily driven by the extracellular signal-regulated kinase (ERK) module of the mitogen-activated protein kinase (MAPK) pathway. Consistent with this notion, the main components of the ERK module (RAS, RAF1, MEK, and ERK1/2) were localized to the periacrosomal region of the head of mature mouse spermatozoa and their phosphorylation status within this region of the cell was positively modulated by capacitation. Furthermore, inhibition of several elements of this pathway suppressed sperm surface phosphotyrosine expression and induced a concomitant reduction sperm–zona pellucida interaction. Collectively, these data highlight a previously unappreciated role of the ERK module in the modification of the sperm surface during capacitation to render these cells functionally competent to engage in the process of fertilization. 2012-02-21T03:00:03.952Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9963 Before fertilization can occur, ejaculated mammalian spermatozoa must undergo a maturation process known as capacitation, which is dominated by post-translational modifications, particularly phosphorylation. Despite its biological importance, characterization of those proteins targeted for phosphorylation during capacitation remains ill-defined. Here, we report the isolation and purification of 288 phosphorylated peptides from rat spermatozoa using titanium dioxide columns in combination with nanoflow mass spectrometry. This equated to 120 identified phosphorylated proteins present in pure populations of spermatozoa. The MS survey scans of replicate titanium dioxide eluates, derived from both noncapacitated and capacitated sperm lysates, were then compared in silico using a virtual 2D PAGE format and DeCyderMS software. This analysis found 15 differentially phosphorylated proteins during capacitation. Included in this list were sperm qualifiers such as Izumo, a known sperm-oocyte fusion protein. To demonstrate that this label-free quantitative approach to phosphoprotein analysis was viable, we measured the enzymatic activity of 5′-nucleotidase, the phosphorylation status of which changed during capacitation. The results revealed, for the first time, that 5′-nucleotidase activity is up-regulated as sperm capacitate. This change, together with the other protein identifications reported in this study, constitute important new leads in elucidating the biochemical mechanisms by which spermatozoa attain a capacitated state. 2012-02-09T00:50:03.825Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7946 Background: In recent times there has been some controversy over the impact of electromagnetic radiation on human health. The significance of mobile phone radiation on male reproduction is a key element of this debate since several studies have suggested a relationship between mobile phone use and semen quality. The potential mechanisms involved have not been established, however, human spermatozoa are known to be particularly vulnerable to oxidative stress by virtue of the abundant availability of substrates for free radical attack and the lack of cytoplasmic space to accommodate antioxidant enzymes. Moreover, the induction of oxidative stress in these cells not only perturbs their capacity for fertilization but also contributes to sperm DNA damage. The latter has, in turn, been linked with poor fertility, an increased incidence of miscarriage and morbidity in the offspring, including childhood cancer. In light of these associations, we have analyzed the influence of RF-EMR on the cell biology of human spermatozoa in vitro. Principal Findings: Purified human spermatozoa were exposed to radio-frequency electromagnetic radiation (RF-EMR) tuned to 1.8 GHz and covering a range of specific absorption rates (SAR) from 0.4 W/kg to 27.5 W/kg. In step with increasing SAR, motility and vitality were significantly reduced after RF-EMR exposure, while the mitochondrial generation of reactive oxygen species and DNA fragmentation were significantly elevated (P<0.001). Furthermore, we also observed highly significant relationships between SAR, the oxidative DNA damage bio-marker, 8-OH-dG, and DNA fragmentation after RF-EMRexposure. Conclusions: RF-EMR in both the power density and frequency range of mobile phones enhances mitochondrial reactive oxygen species generation by human spermatozoa, decreasing the motility and vitality of these cells while stimulating DNA base adduct formation and, ultimately DNA fragmentation. These findings have clear implications for the safety of extensive mobile phone use by males of reproductive age, potentially affecting both their fertility and the health and wellbeing of their offspring. 2012-01-30T05:27:50.610Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7044 Mammalian spermatozoa acquire the ability to fertilize an oocyte as they ascend the female reproductive tract. This process is characterized by a complex cascade of biophysical and biochemical changes collectively know as “capacitation.” The attainment of a capacitated state is accompanied by a dramatic reorganization of the surface architecture to render spermatozoa competent to recognize the oocyte and initiate fertilization. Emerging evidence indicates that this process is facilitated by molecular chaperone-mediated assembly of a multimeric receptor complex on the sperm surface. However, the mechanisms responsible for gathering key recognition molecules within this putative complex have yet to be defined. In this study, we provide the first evidence that chaperones partition into detergent resistant membrane fractions (DRMs) within capacitated mouse spermatozoa and co-localize in membrane microdomains enriched with the lipid raft marker, GM1 ganglioside. During capacitation, these microdomains coalesce within the apical region of the sperm head, a location compatible with a role in sperm–zona pellucida interaction. Significantly, DRMs isolated from spermatozoa possessed the ability to selectively bind to the zona pellucida of unfertilized, but not fertilized, mouse oocytes. A comprehensive proteomic analysis of the DRM fractions identified a total of 100 proteins, a number of which have previously been implicated in sperm–oocyte interaction. Collectively, these data provide compelling evidence that mouse spermatozoa possess membrane microdomains that provide a platform for the assembly of key recognition molecules on the sperm surface and thus present an important mechanistic insight into the fundamental cell biological process of sperm–oocyte interaction. 2012-01-30T05:06:10.467Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9576 This article reports the results of the most recent in a series of EHSRE workshops designed to synthesize the current state of the field in Andrology and provide recommendations for future work (for details see Appendix). Its focus is on methods for detecting sperm DNA damage and potential application of new knowledge about sperm chromatin organization, vulnerability and repair to improve the diagnosis and treatment of clinical infertility associated with that damage. Equally important is the use and reliability of these tests to identify the extent to which environmental contaminants or pharmaceutical agents may contribute to the incidence of sperm DNA damage and male fertility problems. A working group (for workshop details, see Appendix) under the auspices of ESHRE met in May 2009 to assess the current knowledge base and suggest future basic and clinical research directions. This document presents a synthesis of the working group’s understanding of the recent literature and collective discussions on the current state of knowledge of sperm chromatin structure and function during fertilization. It highlights the biological, assay and clinical uncertainties that require further research and ends with a series of 5 key recommendations. 2011-12-02T04:50:12.752Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9572 Background: DNA damage in human spermatozoa is known to be associated with a variety of adverse clinical outcomes affecting both reproductive efficiency and the health and wellbeing of the offspring. However, the origin of this damage,its biochemical nature and strategies for its amelioration, still await resolution. Methods: Using novel methods to simultaneously assess DNA fragmentation (modified TUNEL assay), DNA-base adduct formation (8-hydroxy-2′-deoxyguanosine [8OHdG]) and cell vitality, spermatozoa from a cohort of 50 assisted conception patients were examined and compared with a group of donors. Receiver operating characteristic (ROC) curve analysis was then used to examine the frequency distribution of the data and to determine optimized thresholds for identifying patients exhibiting abnormally high levels of DNA damage. Results: 8OHdG formation and DNA fragmentation were highly correlated with each other and frequently associated with cell death. Percoll centrifugation improved sperm quality but, unexpectedly, increased 8OHdG formation in live cells, as did sperm fractionation using Puresperm® gradients. ROC analysis indicated that the frequency distribution of 8OHdG and DNA fragmentation data were significantly different between patients and donors (P < 0.001), permitting the development of thresholds that would allow the accurate diagnosis of DNA damage in the male germ line. Conclusion: The aetiology of DNA damage in spermatozoa involves a cascade of changes that progress from the induction of oxidative stress and oxidized DNA base adduct formation to DNA fragmentation and cell death. Preparation of spermatozoa on discontinuous density gradients aggravates the problem by stimulating the formation of 8OHdG in live cells. However, the development of novel methods and optimized thresholds for diagnosing oxidative DNA damage in human spermatozoa should assist in the clinical management of this pathology. 2011-12-02T04:50:04.957Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:8464 The rapid rise of proteomics has been driven by technological developments in high-throughput mass spectrometry that make protein sequencing feasible at a scale not remotely possible only a decade ago. Coupled with enhanced methods for protein prefractionation, such developments have enabled characterization of complex proteomes from various cell types, including the spermatozoa of a number of species. These studies have generated inventories consisting of thousands of sperm proteins and paved the way for significant advances that will now be driven by parallel improvements in our capacity to turn these protein inventories into meaningful functional insights. Specifically, there is a need to quantitatively compare proteomic profiles from spermatozoa in different functional states (immature vs. mature, uncapacitated vs. capacitated, fertile vs. infertile). Such comparisons will enable us to define which specific elements of the proteome are of functional significance and understand the cascade of posttranslational modifications (e.g., phosphorylation, glycosylation, proteolytic cleavage) involved in generating a functional spermatozoon. This fundamental information will then create a basis for identifying key points in the posttesticular maturation of spermatozoa that might be targeted for contraceptive purposes or implicated in the defective sperm function observed in a significant proportion of infertile males. 2011-07-29T06:51:07.461Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:8340 Understanding the cellular mechanisms that regulate mammalian sperm function is strategically important for both the management of male infertility and the development of novel approaches to male contraception. The spermatozoon is a transcriptionally and translationally suppressed cell that is released from the testes in a functionally inert state. Functional activation occurs in the epididymis and female tract via mechanisms that are entirely dependent on post-translational modifications. Proteomics is, therefore, the ideal technology to investigate this cell type. Herein, we comment on the proteomic analyses that have been applied to mammalian spermatozoa, including some concerns relating to data interpretation. Three comprehensive liquid chromatography–mass spectrometry lists of human, mouse and rat spermatozoa are then compared, insights into the molecular regulation of sperm function discussed and future directions speculated upon. 2011-07-19T23:10:03.574Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:8305 There is an urgent need to develop safe, effective, dual-purpose contraceptive agents that combine the prevention of pregnancy with protection against sexually transmitted diseases. Here we report the identification of a group of compounds that on contact with human spermatozoa induce a state of “spermostasis,” characterized by the extremely rapid inhibition of sperm movement without compromising cell viability. These spermostatic agents were more active and significantly less toxic than the reagent in current clinical use, nonoxynol 9, giving therapeutic indices (ratio of spermostatic to cytotoxic activity) that were orders of magnitude greater than this traditional spermicide. Although certain compounds could trigger reactive oxygen species generation by spermatozoa, this activity was not correlated with spermostasis. Rather, the latter was associated with alkylation of two major sperm tail proteins that were identified as A Kinase-Anchoring Proteins (AKAP3 and AKAP4) by mass spectrometry. As a consequence of disrupted AKAP function, the abilities of cAMP to drive protein kinase A-dependent activities in the sperm tail, such as the activation of SRC and the consequent stimulation of tyrosine phosphorylation, were suppressed. Furthermore, analysis of microbicidal activity using Chlamydia muridarum revealed powerful inhibitory effects at the same low micromolar doses that suppressed sperm movement. In this case, the microbicidal action was associated with alkylation of Major Outer Membrane Protein (MOMP), a major chlamydial membrane protein. Taken together, these results have identified for the first time a novel set of cellular targets and chemical principles capable of providing simultaneous defense against both fertility and the spread of sexually transmitted disease. 2011-07-18T06:00:03.507Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:8206 DNA damage in human spermatozoa has been associated with a range of adverse clinical outcomes, including infertility, abortion, and disease in the offspring. We have advanced a two-step hypothesis to explain this damage involving impaired chromatin remodeling during spermiogenesis followed by a free radical attack to induce DNA strand breakage. The objective of the present study was to test this hypothesis by determining whether impaired chromatin protamination is correlated with oxidative base damage and DNA fragmentation in human spermatozoa. DNA fragmentation, chromatin protamination, mitochondrial membrane potential, and formation of the oxidative base adduct, 8-hydroxy-2′-deoxyguanosine (8OHdG), were monitored by flow cytometry/fluorescence microscopy. Impairment of DNA protamination during late spermatogenesis was highly correlated (P < 0.001) with DNA damage in human spermatozoa. The disruption of chromatin remodeling also was associated with a significant elevation in the levels of 8OHdG (P < 0.001), and the latter was itself highly correlated with DNA fragmentation (P < 0.001). The significance of oxidative stress in 8OHdG formation was demonstrated experimentally using H₂O₂/Fe2⁺ and by the correlation observed between this base adduct and superoxide generation (P < 0.001). That 8OHdG formation was inversely associated with mitochondrial membrane potential (P < 0.001) suggested a possible role for these organelles in the creation of oxidative stress. These results clearly highlight the importance of oxidative stress in the induction of sperm DNA damage and carry significant implications for the clinical management of this condition. 2011-07-11T04:50:15.364Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7891 Upon ejaculation, spermatozoa undergo a series of post-translational modifications in a process known as capacitation in order to prepare for fertilization. In the absence of capacitation, fertilization cannot occur. Spermatozoa are unusual in that one of the hallmarks of capacitation is a global up-regulation in phosphotyrosine expression, which is known to be mediated upstream by PKA. Little is known about the signaling events downstream of PKA apart from the involvement of SRC, as a key mediator of PKA-induced tyrosine phosphorylation in the sperm tail. Here we describe the presence of c-Abl in mouse spermatozoa. In vitro analysis confirmed that PKA can up-regulate c-Abl kinase activity. In vivo, this tyrosine kinase was found to associate, and become threonine phosphorylated by PKA in the sperm flagellum. By treating spermatozoa with hemolysin we could demonstrate that a significant proportion of the tyrosine phosphorylation associated with capacitation could be suppressed by the c-Abl inhibitor, Gleevac. This is the first report of c-Abl being up-regulated by PKA for any cell type. We present a model, whereby these kinases may operate together with SRC to ensure optimal levels of tyrosine phosphorylation in the sperm flagellum during the attainment of a capacitated state. 2011-06-20T00:00:12.145Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7528 The development of an embryo as male or female depends on differentiation of the gonads as either testes or ovaries. A number of genes are known to be important for gonadal differentiation, but our understanding of the regulatory networks underpinning sex determination remains fragmentary. To advance our understanding of sexual development beyond the transcriptome level, we performed the first global survey of the mouse gonad proteome at the time of sex determination by using two-dimensional nanoflow LC-MS/MS. The resulting data set contains a total of 1037 gene products (154 non-redundant and 883 redundant proteins) identified from 620 peptides. Functional classification and biological network construction suggested that the identified proteins primarily serve in RNA post-transcriptional modification and trafficking, protein synthesis and folding, and post-translational modification. The data set contains potential novel regulators of gonad development and sex determination not revealed previously by transcriptomics and proteomics studies and more than 60 proteins with potential links to human disorders of sexual development. 2011-05-03T00:10:18.283Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7489 DNA damage is a common feature of human spermatozoa with purported links to poor rates of conception, impaired embryonic development, an increased incidence of miscarriage and the appearance of various kinds of morbidity in the offspring including childhood cancer. However, difficulties in interpretation arise, because these associations are not consistently observed across all data sets. Such inconsistency reflects the inherent complexity of the reproductive process, large variations in sample size, differences in patient selection, inadequate study design as well as inter-individual differences in the type of DNA damage being detected and the effectiveness of repair mechanisms in the oocyte. This review considers the type, source and measurement of DNA damage in human spermatozoa. It also addresses the clinical utility of the information generated in such studies, and highlights areas where further research is needed to bridge the gap between an intriguing biological phenomenon and the evidence-based clinical management of male patients characterized by high levels of DNA damage in their spermatozoa. 2011-04-06T06:10:12.425Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:7212 As mammalian spermatozoa ascend the female reproductive tract, they acquire the ability to fertilize an oocyte via a complex cascade of biophysical and biochemical changes collectively know as ‘capacitation’. In virtually all species studied, capacitation is accompanied by dramatic remodeling of the surface architecture, in order to render spermatozoa competent to recognize the oocyte and initiate fertilization. Although the fundamental mechanisms that underpin the dynamic redistribution of sperm surface proteins are poorly understood, recent evidence indicates that this process may be facilitated, at least in part, by specialized membrane microdomains or lipid rafts. This notion is consistent with numerous demonstrations that lipid rafts contain a number of putative zona pellucida receptors, undergo a marked capacitation-associated lateral migration to the apical region of the sperm head, and possess the ability to selectively bind to the zona pellucida of unfertilized, but not fertilized oocytes. Accordingly, this review aims to cover the latest insights into sperm lipid raft research and considers the evidence that these microdomains serve as platforms for the assembly of key recognition molecules on the sperm surface during capacitation. 2011-02-14T01:30:36.840Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1032 2011-02-08T23:10:06.208Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4655 AB Immature spermatozoa are vulnerable to oxidative stress after their release from the testes, due in part to an innate deficiency in antioxidant enzymes. The male reproductive tract compensates for this deficiency by secreting antioxidant enzymes such as glutathione peroxidase 5 (Gpx5) into the epididymal lumen. In this issue of the JCI, Chabory et al. examined the phenotype of Gpx5⁻/⁻ mice and found that while deletion of this gene did not seem to affect fertility per se, it did influence the incidence of miscarriage and embryonic defects in mated wild-type female mice (see the related article beginning on page 2074). Importantly, the appearance of these problems was age dependent and associated with signs of oxidative stress in the spermatozoa. These results demonstrate the key importance of Gpx5 as an extracellular antioxidant designed to protect maturing mammalian spermatozoa from oxidative stress. 2010-09-27T04:50:01.569Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:6652 Spermatogenesis is an extremely active replicative process capable of generating approximately 1,000 sperm a second. The high rates of cell division inherent in this proccss simply correspondingly high rates of mitochondrial oxygen consumption by the germinal epirheliun. However, the poor vascularizarion of the testes means that oxygen tensions in this tissue are low and that competition for this vital element within the testes is extremely intense. Since both spermatogenesis and Leydig cell steroidogenesis are vunerable to oxidative stress, the low oxygen tension that characterizes this tissue may be an important component of the mechanisms by which the testes protects itself from free radical-mediated damage. In addition, the testes contain an elaborate array of antioxidant enzymes and free radical scavengers to ensure that the twin spermatogenic and steroidogenic functions of this organare are not impacted by oxidative stress. These antioxidant defence systems are of major importance because peroxidative damage is currently regarded as the single most important cause of imnpaired testicular function underpinning the pathological consequences of a wide range of conditions from testicular torsion to diabetes and xenobiotic exposure. This chapter sets out the specific nature of these antioxidant defence systems and also reviews the factors that have been found to impair their activity, precipitating a state of oxidative stress in the testes and impairing thetlatter's ability to produce viable spermatozoa capable of initiating and supporting embryonic development. 2010-09-10T02:00:07.847Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1273 In the tammar wallaby (Macropus eugenii), post-testicular acrosomal shaping involves a complex infolding and fusion of the anterior and lateral projections of the scoop-shaped acrosome into a compact button-like structure occupying the depression on the anterior end of the sperm nucleus. The present study has generated cytochemical and histological evidence to demonstrate that the occurrence of actin filaments (F-actin, labelled by Phalloidin-FITC) in the acrosome of tammar wallaby spermatozoa is temporally and spatially associated with the process of acrosomal shaping in the epididymis, through a pool of monomeric actin (G-actin, labelled by Rh-DNase I) present in the acrosome throughout all stages of epididymal maturation. F-actin was not detected in the acrosome of testicular spermatozoa, but was found in the infolding and condensing acrosome of caput and corpus epididymal spermatozoa. When the spermatozoa completed acrosome shaping in the cauda epididymidis, F-actin disappeared from the acrosomal area. The strong correlation between the occurrence of F-actin and the events of acrosomal shaping suggested that the post-testicular shaping of the acrosome might depend on a precise succession of assembly and disassembly of F-actin within the acrosome as the spermatozoa transit the epididymis. Thus, actin filaments might play a significant role in the acrosomal transformation, as they are commonly involved in morphological changes in somatic cells. 2010-04-27T06:54:54.610Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1286 Fertilization of the mammalian oocyte depends on the ability of spermatozoa to undergo a process known as capacitation as they ascend the female reproductive tract. A fundamental feature of this process is a marked increase in tyrosine phosphorylation by an unusual protein kinase A (PKA)-mediated pathway. To date, the identity of the intermediate PKA-activated tyrosine kinase driving capacitation is still unresolved. In this study, we have identified SRC as a candidate intermediate kinase centrally involved in the control of sperm capacitation. Consistent with this conclusion, the SRC kinase inhibitor SU6656 was shown to suppress both tyrosine phosphorylation and hyperactivation in murine spermatozoa. Moreover, SRC co-immunoprecipitated with PKA and this interaction was found to lead to an activating phosphorylation of SRC at position Y416. We have also used difference-in-2D-gel-electrophoresis (DIGE) in combination with mass spectrometry to identify a number of SRC substrates that become phosphorylated during capacitation including enolase, HSP90 and tubulin. Our data further suggest that the activation of SRC during capacitation is negatively controlled by C-terminal SRC kinase. The latter was localized to the acrosome and flagellum of murine spermatozoa by immunocytochemistry, whereas capacitation was associated with an inactivating serine phosphosphorylation of this inhibitory kinase. 2010-04-27T06:54:49.101Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1294 The control of primordial follicle recruitment into the growing follicle population is a major limiting process in female reproduction. In order to gain insight into the molecular processes occurring at the time of primordial follicle activation, a subtractive hybridization analysis was performed between cDNAs prepared from temporally distinct mouse neonatal ovarian tissues that differed according to the state of primordial follicle activation. One highly represented clone associated with activation was an Mt retrotransposon-like sequence designated Mtfull, which was subsequently cloned and determined to be novel and restricted in expression to the ovary. The polyadenylated 1684-bp sequence has long terminal repeats, is predicted to be noncoding, and is the predominant Mti-related sequence present in the mouse ovary. In situ hybridization further localized Mtfull expression to the oocyte and confirmed that expression is concomitant with follicle activation. Together with in silico data, we predict Mtfull plays an essential role in folliculogenesis through regulation of gene expression. 2010-04-27T06:54:31.859Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3007 The objectives of this study were to map the ontogeny of tyrosine phosphorylation signal transduction pathways during germ cell development and to determine their association with the differentiation of a functional gamete. Until testicular germ cells differentiate into spermatozoa, cAMP-induced tyrosine phosphorylation is not detectable. Entry of these cells into the epididymis is accompanied by sudden activation of the tyrosine phosphorylation pathway, initially in the principal piece of the cell and subsequently in the midpiece. In the caput and corpus epididymides, the potential to express this pathway is inhibited by the presence of calcium in the extracellular medium. However, calcium has no effect on the expression of this pathway in caudal epididymal sperm. The competence of these cells to phosphorylate the entire sperm tail, from the neck to the tail-end piece, is accompanied by a capacity to exhibit hyperactivated motility on stimulation with cAMP. A distinctly different pattern of tyrosine phosphorylation, involving the acrosomal domain of the sperm head, is invoked as spermatozoa enter the caput epididymis, and phosphorylation remains high until these cells enter the distal corpus and cauda. The proportion of cells exhibiting this form of tyrosine phosphorylation is not affected by extracellular calcium or cAMP but is negatively correlated (R² = 0.99) with their ability to acrosome-react. However, this relationship is not causative. Our findings indicate that the development of functional spermatozoa is accompanied by carefully orchestrated changes in tyrosine phosphorylation, controlled by independent regulatory mechanisms in distinct subcellular compartments of these highly specialized cells. 2010-04-27T06:47:09.439Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:987 The molecular mechanisms behind the entry of the primordial follicle into the growing follicle pool remain poorly understood. To investigate this process further, a microarray-based comparison was undertaken between 2-day postpartum mouse ovaries consisting of primordial follicles/naked oocytes only and those with both primordial follicles and newly activated follicles (7-day postpartum). Gene candidates identified included the chemoattractive cytokine stromal derived factor-1 (SDF1) and its receptor CXCR4. SDF1 and CXCR4 have been implicated in a variety of physiological processes including the migration of embryonic germ cells to the gonads. SDF1-α expression increased with the developmental stage of the follicle. Embryonic expression was found to be dichotomous post-germ cell migration, with low expression in the female. Immunohistochemical studies nonetheless indicate that the autocrine pattern of expression ligand and receptor begins during embryonic life. Addition of recombinant SDF1-α to neonatal mouse ovaries in vitro resulted in significantly higher follicle densities than for control ovaries. TUNEL analysis indicated no detectable difference in populations of apoptotic cells of treated or control ovaries. Treated ovaries also contained a significantly lower percentage of activated follicles as determined by measurement of oocyte diameter and morphological analysis. Treatment of cultured ovaries with an inhibitor of SDF1-α, AMD3100, ablated the effect of SDF1-α. By retaining follicles in an unactivated state, SDF1/CXCR4 signaling may play an important role in maintaining the size and longevity of the primordial follicle pool. 2010-04-27T06:43:12.253Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1016 The molecular mechanisms leading to male infertility in vitamin A deficient (VAD) rodents have never been fully elucidated. Here, we report an interaction between BMP4 and retinoid signaling pathways in germ cells that may help clarify the biochemical basis of VAD. Adult germ cells, in particular spermatogonia, expressed BMP4 at both the mRNA and protein levels. BMP4 expression was significantly up-regulated in the testes of VAD mice and was down-regulated in freshly isolated germ cells and VAD testes by retinol, but not retinoic acid. The retinoid-responsive gene, RARβ, was not induced in germ cells following retinoid treatment. Examination of BMP4 promoter usage in spermatogonia and the VAD testis revealed that germ cells utilize the recently characterized BMP4 intron 2 promoter, in addition to the classical 1A and 1B promoters. The observed decrease in BMP4 in response to retinol was mediated by the 1A and intron 2 promoters of the BMP4 gene. Our results reflect a direct requirement for retinoids by germ cells for the resumption of spermatogenesis in VAD animals via mechanisms that involve the suppression of BMP4 expression. 2010-04-27T06:41:27.965Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:908 Mammalian spermatozoa undergo a series of molecular and biochemical changes collectively termed capacitation prior to acquiring the ability to fertilise the oocyte. Although phosphorylation of sperm proteins on tyrosine residues has been recognised as an important component of this process, the precise relationship between the phosphorylation status of mammalian spermatozoa and their capacity for fertilisation has remained unclear. In this study we demonstrate a causal relationship between tyrosine phosphorylation in spermatozoa and sperm-zona interaction. The phosphotyrosine expression associated with sperm capacitation localised to internal flagellar structures in permeabilised cells but could also be detected on the exterior surface of the sperm head in live cells. Importantly, almost all spermatozoa bound to the zona pellucida demonstrated this pattern of phosphoprotein localisation, compared to fewer than 15% of the free-swimming population. These data suggest that tyrosine phosphorylation plays a significant role in remodelling the sperm surface, so that these cells are able to recognise the zona pellucida. Phosphoproteome analysis yielded the first evidence of molecular chaperones, endoplasmin (erp99) and heat shock protein 60 (hsp60), as targets for phosphorylation on the surface of mouse spermatozoa, whereas immunofluorescence localised these proteins to the precise region of the sperm head that participates in zona recognition. Based on these results, we propose a novel mechanism for mammalian gamete interaction whereby the activation of sperm-surface chaperones by tyrosine phosphorylation during capacitation may trigger conformational changes facilitating the formation of a functional zona pellucida receptor complex on the surface of mammalian spermatozoa. 2010-04-27T06:40:19.528Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1202 Mammalian spermatozoa must undergo capacitation before acquiring the ability to fertilize the oocyte. This process is believed to be initiated following the release of surface-associated decapacitation factors that are elaborated by both the epididymis and the male accessory organs. Herein, we report the identification of a number of proteins that are actively released from the surface of mouse spermatozoa during capacitation in vitro. As anticipated, the addition of these factors back to suspensions of mouse spermatozoa was shown to suppress several correlates of the capacitation process. Specifically, they induced a significant, dose-dependent inhibition of the ability of spermatozoa to undergo a progesterone-induced acrosome reaction and to bind to the zona pellucida in vitro. Inhibition of these functions was associated with the suppression of tyrosine phosphorylation in the sperm plasma membrane but had no effect on the phosphorylation of internal proteins in either the sperm head or tail. This inhibitory activity was attributed to a subset of the isolated proteins compromising at least four putative decapacitation factors. These proteins were identified via tandem-mass spectrometry amino acid sequence analysis as plasma membrane fatty acid binding protein, cysteine-rich secretory protein 1 (CRISP1), phosphatidylethanolamine binding protein 1 (PBP), and an unnamed protein product that we have termed decapacitation factor 10 (DF10). Of these proteins, PBP was identified as a primary candidate for a decapacitation factor. 2010-04-27T06:39:56.241Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1163 Context: Oxidative stress in the male germ line has been associated with poor fertility, impaired embryonic development, miscarriage, and childhood disease. Such stress is known to be associated with the peroxidation of unsaturated fatty acids in the sperm plasma membrane and oxidative DNA damage to both the nuclear and mitochondrial genomes. However, the source of the free radicals responsible for such damage is still unresolved. Objective: The objective of this study was to chemically validate the use of dihydroethidium (DHE) as a probe for detecting the generation of superoxide anion by human spermatozoa and to examine the relationship between this activity and defective sperm function. Method: DHE and SYTOX green were used in conjunction with flow cytometry and HPLC to investigate superoxide generation by human spermatozoa. Cause and effect relationships were established using menadione to artificially drive superoxide production by these cells. Results: HPLC, mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy, and spectrofluorometry were used to demonstrate that human spermatozoa generate the superoxide-specific product, 2-hydroxyethidium, from DHE. Spontaneous superoxide production by human spermatozoa was found to originate from a nonmitochondrial source and was inversely correlated with sperm motility. A causative relationship between superoxide generation and sperm function was demonstrated when the pharmacological stimulation of this activity with menadione was shown to result in both severe motility loss and DNA damage. Conclusions: These studies validate a methodology for investigating the origins of oxidative stress in the male germ line and demonstrate, for the first time, the significance of superoxide generation by human spermatozoa in the etiology of this condition. 2010-04-27T06:37:55.741Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1851 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. 2010-04-27T06:35:33.790Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1527 Mammalian spermatozoa must become `capacitated' in the female reproductive tract before they gain the ability to fertilize the oocyte. The attainment of a capacitated state has been correlated with a number of biochemical changes, the most notable of which is a dramatic increase in the tyrosine phosphorylation status of these cells. Despite its biological importance, the mechanisms responsible for initiating this tyrosine phosphorylation cascade in vivo are unknown. Here, we report that this signalling pathway can be elicited in a rapid, dose-dependent and lectin-specific manner by wheat germ agglutinin (WGA), but none of 18 other lectins assessed. This response was abrogated by prior enzymatic cleavage of either sialic acid or GlcNAc residues from the sperm surface and by treatment with a range of pharmacological inhibitors directed against protein kinase A, protein tyrosine kinases and intermediates including Src. Proteomic analysis of the WGA-binding sites on the sperm surface identified the putative cognate receptor as platelet cell adhesion molecule 1 (PECAM-1/CD31). This conclusion was supported by the following evidence: (i) anti-PECAM-1 antibodies identified a molecule of the correct molecular mass in human spermatozoa, (ii) PECAM-1 could be isolated from a pool of sperm surface proteins using WGA immobilized on a solid phase support, (iii) PECAM-1 and WGA co-localized to the sperm surface and (iv) anti-PECAM-1 antibodies could completely block the ability of WGA to stimulate tyrosine phosphorylation in these cells. Collectively, these data provide the first evidence that a receptor-mediated signal transduction pathway triggers human sperm capacitation and identifies PECAM-1 as the probable initiator of this second messenger cascade. 2010-04-27T06:29:31.513Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1595 Although the molecular basis of sperm-oocyte interaction is unclear, recent studies have implicated two chaperone proteins, heat shock protein 1 (HSPD1; previously known as heat shock protein 60) and tumor rejection antigen gp96 (TRA1; previously known as endoplasmin), in the formation of a functional zona-receptor complex on the surface of mammalian spermatozoa. The current study was undertaken to investigate the expression of these chaperones during the ontogeny of male germ cells through spermatogenesis, epididymal sperm maturation, capacitation, and acrosomal exocytosis. In testicular sections, both HSPD1 and TRA1 were closely associated with the mitochondria of spermatogonia and primary spermatocytes. However, this labeling pattern disappeared from the male germ line during spermiogenesis to become undetectable in testicular spermatozoa. Subsequently, these chaperones could be detected in epididymal spermatozoa and in previously unreported "dense bodies" in the epididymal lumen. The latter appeared in the precise region of the epididymis (proximal corpus), where spermatozoa acquire the capacity to recognize and bind to the zona pellucida, implicating these structures in the functional remodeling of the sperm surface during epididymal maturation. Both HSPD1 and TRA1 were subsequently found to become coexpressed on the surface of live mouse spermatozoa following capacitation in vitro and were lost once these cells had undergone the acrosome reaction, as would be expected of cell surface molecules involved in sperm-egg interaction. These data reinforce the notion that these chaperones are intimately involved in the mechanisms by which mammalian spermatozoa both acquire and express their ability to recognize the zona pellucida. 2010-04-27T06:28:50.133Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:2392 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. 2010-04-27T06:20:11.756Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:2302 During the past few decades, worries about environmental threats to human health have centred on the possible induction of cancers. Now risks to the male germ line, both real and potential, are also causing disquiet. 2010-04-27T06:19:44.455Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:2266 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/cb5rΔ12. Exon 12 codes for the flavin-adenine dinucleotide binding domain of cb5/cb5r. Expression analysis revealed the transcript of cb5/cb5rΔ12 in mouse and rat testis, brain, and skeletal muscle and also in the male germ line. We postulate that cb5/cb5rΔ12 may function in a dominant negative fashion, limiting the amount of damage caused by the production of reactive oxygen species by cb5/cb5r. 2010-04-27T06:19:30.336Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:2442 Mammalian spermatozoa undergo a series of molecular and biochemical changes collectively termed capacitation prior to acquiring the ability to fertilise the oocyte. Although phosphorylation of sperm proteins on tyrosine residues has been recognised as an important component of this process, the precise relationship between the phosphorylation status of mammalian spermatozoa and their capacity for fertilisation has remained unclear. In this study we demonstrate a causal relationship between tyrosine phosphorylation in spermatozoa and sperm-zona interaction. The phosphotyrosine expression associated with sperm capacitation localised to internal flagellar structures in permeabilised cells but could also be detected on the exterior surface of the sperm head in live cells. Importantly, almost all spermatozoa bound to the zona pellucida demonstrated this pattern of phosphoprotein localisation, compared to fewer than 15% of the free-swimming population. These data suggest that tyrosine phosphorylation plays a significant role in remodelling the sperm surface, so that these cells are able to recognise the zona pellucida. Phosphoproteome analysis yielded the first evidence of molecular chaperones, endoplasmin (erp99) and heat shock protein 60 (hsp60), as targets for phosphorylation on the surface of mouse spermatozoa, whereas immunofluorescence localised these proteins to the precise region of the sperm head that participates in zona recognition. Based on these results, we propose a novel mechanism for mammalian gamete interaction whereby the activation of sperm-surface chaperones by tyrosine phosphorylation during capacitation may trigger conformational changes facilitating the formation of a functional zona pellucida receptor complex on the surface of mammalian spermatozoa. 2010-04-27T06:12:22.955Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:1079 Context: Defective sperm function is the largest defined cause of human infertility; however, the etiology of this condition is poorly understood. Although oxidative stress is acknowledged as a key contributor to this pathology, there are also data indicating that defective human spermatozoa contain abnormally high amounts of cis-unsaturated fatty acids. This study investigated whether a causative relationship exists between these two attributes of impaired semen quality. Objective: The objective of this study was to determine whether polyunsaturated fatty acids can induce oxidative stress in human spermatozoa. Method: Dihydroethidium and SYTOX Green were used in conjunction with flow cytometry and HPLC to investigate reactive oxygen species (ROS) generation by human spermatozoa after fatty acid exposure. Results: Arachidonic acid (AA) induced a time- and dose-dependent increase in ROS generation by human spermatozoa that led to the promotion of peroxidative damage and a loss of sperm motility. This effect could not be blocked with inhibitors of the cyclooxygenase or lipoxygenase pathways of AA metabolism, rotenone, protein kinase C antagonists, or known inhibitors of plasma membrane redox systems. However, ROS generation could be triggered with other cis-unsaturated fatty acids including linoleic and docosahexaenoic acids. Saturated fatty acids, methyl esters of unsaturated fatty acids, or other amphiphiles were all ineffective. However in a cell-free system, AA could trigger a redox signal via mechanisms that were profoundly disrupted by diphenylene iodonium, a flavoprotein inhibitor. Conclusions: The presence of excess unsaturated fatty acids in defective human spermatozoa may precipitate the oxidative stress encountered in male infertility. 2010-04-27T06:06:49.822Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:2527 The capacitation of mammalian spermatozoa involves the activation of a cAMP-mediated signal transduction pathway that drives tyrosine phosphorylation via mechanisms that are unique to this cell type. Controversy surrounds the impact of extracellular calcium on this process, with positive and negative effects being recorded in independent publications. We clearly demonstrate that the presence of calcium in the external medium decreases tyrosine phosphorylation in both human and mouse spermatozoa. Under these conditions, a rise in intracellular pH was recorded, however, this event was not responsible for the observed changes in phosphotyrosine expression. Rather, the impact of calcium on tyrosine phosphorylation in these cells was associated with an unexpected change in the intracellular availability of ATP. Thus, the ATP content of both human and mouse spermatozoa fell significantly when these cells were incubated in the presence of external calcium. Furthermore, the removal of glucose, or addition of 2-deoxyglucose, decreased ATP levels within human spermatozoon populations and induced a corresponding decline in phosphotyrosine expression. In contrast, the mitochondrial inhibitor rotenone had no effect on either ATP levels or tyrosine phosphorylation. Addition of the affinity-labeling probe 8-N₃ ATP confirmed our prediction that spermatozoa have many calcium-dependent ATPases. Moreover, addition of the ATPase inhibitor thapsigargin, increased intracellular calcium levels, decreased ATP and suppressed tyrosine phosphorylation. Based on these findings, the present study indicates that extracellular calcium suppresses tyrosine phosphorylation by decreasing the availability of intracellular ATP, and not by activating tyrosine phosphatases or inhibiting tyrosine kinases as has been previously suggested. 2010-04-27T06:03:03.828Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:2526 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 Ca²⁺-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. 2010-04-27T06:02:52.907Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4594 Context: Male infertility has been linked with the excessive generation of reactive oxygen species (ROS) by defective spermatozoa. However, the subcellular origins of this activity are unclear. Objective: The objective of this study was to determine the importance of sperm mitochondria in creating the oxidative stress associated with defective sperm function. Method: Intracellular measurement of mitochondrial ROS generation and lipid peroxidation was performed using the fluorescent probes MitoSOX red and BODIPY C₁₁ in conjunction with flow cytometry. Effects on sperm movement were measured by computer-assisted sperm analysis. Results: Disruption of mitochondrial electron transport flow in human spermatozoa resulted in generation of ROS from complex I (rotenone sensitive) or III (myxothiazol, antimycin A sensitive) via mechanisms that were independent of mitochondrial membrane potential. Activation of ROS generation at complex III led to the rapid release of hydrogen peroxide into the extracellular space, but no detectable peroxidative damage. Conversely, the induction of ROS on the matrix side of the inner mitochondrial membrane at complex I resulted in peroxidative damage to the midpiece and a loss of sperm movement that could be prevented by the concomitant presence of α-tocopherol. Defective human spermatozoa spontaneously generated mitochondrial ROS in a manner that was negatively correlated with motility. Simultaneous measurement of general cellular ROS generation with dihydroethidium indicated that 68% of the variability in such measurements could be explained by differences in mitochondrial ROS production. Conclusion: We conclude that the sperm mitochondria make a significant contribution to the oxidative stress experienced by defective human spermatozoa. 2010-04-27T05:32:44.719Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3878 Reactive oxygen species (ROS) not only play a key role in mediating the pathological consequences of oxidative stress but also drive the biochemical pathways that are central to the regulation of normal cell function. Thus, ROS are a two-edged sword: a friend when produced in the small quantities needed to promote cellular processes such as apoptosis and signal transduction and, because of their promiscuous reactivity, a foe when generated in excess. In this review we shall examine both sides of these biologically important molecules in the context of sperm cell biology. However, in order to set the scene, we shall first overview the fundamental chemistry of ROS and consider the difficulties encountered in detecting these short-lived but highly reactive molecules. 2010-04-27T05:27:31.226Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4506 Mammalian spermatozoa must undergo epididymal maturation in the male reproductive tract and capacitation in the female tract before acquiring the ability to fertilize an oocyte. Previous studies from our laboratory have demonstrated a causal relationship between capacitation-associated surface phosphotyrosine expression and the ability of mouse spermatozoa to recognize the oocyte and engage in sperm-zona pellucida interaction. Our previous analyses of the surface phosphoproteome of capacitated murine spermatozoa identified two molecular chaperones, heat shock protein (HSP) D1 and HSP90B1, with well-characterized roles in protein folding and the assemblage of multimeric protein complexes. The expression of these chaperones was restricted to the rostral aspect of the sperm head, in an ideal position to mediate sperm-zona pellucida interaction. Herein, we report the characterization of an additional chaperone in this location, HSPE1 (chaperonin 10; HSP10). This chaperone was identified using a coimmunoprecipitation strategy employing HSPD1 as bait. The putative interaction between HSPE1 and HSPD1 was supported by reciprocal immunoprecipitation and colocalization studies, which demonstrated the coordinated appearance of both proteins on the surface of the sperm head during capacitation. However, the surface exposure of the protein was lost upon induction of acrosomal exocytosis, as would be expected of a protein potentially involved in sperm-zona pellucida interaction. Collectively, these data invite speculation that a number of molecular chaperones are involved in modification of the sperm surface during capacitation to render these cells functionally competent to engage the process of fertilization. 2010-04-27T05:11:26.527Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4868 Contraception-on-demand refers to contraceptive methods that are only employed when needed, such as barrier or postcoital methods, as opposed to technologies, such as the IUD or pill, where the exposure is continuous irrespective of the risk of pregnancy. The development of women-centered approaches to contraception-on-demand is a high priority in current contraceptive research, with emphasis on the 15- to 25-year-old demographic. Since this cohort of potential users is also at high risk of contracting sexually transmitted disease, topical methods that would provide simultaneous protection against both fertility and infection are of particular interest. This review examines the current strategies that are being pursued to achieve this objective. 2010-04-27T04:59:20.393Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4511 Contraceptives that are readily available and acceptable are required in many poorer countries to reduce population growth and in all countries to prevent maternal morbidity and mortality arising from unintended pregnancies. Most available methods use hormonal steroids or are variations of barrier methods. Reports from several fora over the last 12 years have emphasized the number of unwanted pregnancies and resultant abortions, which indicate an unmet need for safe, acceptable, and inexpensive contraceptive methods. This unmet need can be assuaged, in part, by development of new nonhormonal contraceptive methods. This Review addresses the contribution that the “omic” revolution can make to the identification of novel contraceptive targets, as well as the progress that has been made for different target molecules under development. 2010-04-27T04:57:22.178Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5193 The advent of enhanced methods for the pre-fractionation of proteins, improved high speed, high resolution, high sensitivity mass spectrometry hardware and superior informatics/bioformatics software is heralding a new era in our capacity to analyse the proteomic composition of human spermatozoa. Parallel improvements in our capacity to compare proteomic profiles from spermatozoa in different functional states (immature vs. mature, uncapacitated vs. capacitated, normal vs. defective) is also helping to define which specific elements of the proteome are of functional significance. The ultimate aim of such studies will be to integrate the proteome with the sperm metabolome so that we shall not only understand the cascade of post-translational modifications (e.g., phosphorylation, glycosylation, proteolytic cleavage) involved in generating a functional spermatozoon but also determine how these physiological changes are brought about. This fundamental information will then create a basis for identifying key points in the post-testicular maturation of spermatozoa that might be targeted for contraceptive purposes or implicated in the defective sperm function observed in a significant proportion of infertile males. 2010-04-27T04:47:19.539Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5181 Proteomic profiling of the mouse spermatozoon has generated a unique and valuable inventory of candidates that can be mined for potential contraceptive targets and to further our understanding of the PTMs that regulate the functionality of this highly specialized cell. Here we report the identification of 858 proteins derived from mouse spermatozoa, 23 of which demonstrated testis only expression. The list contained many proteins that are known constituents of murine spermatozoa including Izumo, Spaca 1, 3, and 5, Spam 1, Zonadhesin, Spesp1, Smcp, Spata 6, 18, and 19, Zp3r, Zpbp 1 and 2, Spa17, Spag 6, 16, and 17, CatSper4, Acr, Cylc2, Odf1 and 2, Acrbp, and Acrv1. Certain protein families were highly represented in the proteome. For example, of the 42 gene products classified as proteases, 26 belonged to the 26S-proteasome. Of the many chaperones identified in this proteome, eight proteins with a TCP-1 domain were found, as were seven Rab guanosine triphosphatases. Finally, our list yielded three putative seven-transmembrane proteins, two of which have no known tissue distribution, an extragenomic progesterone receptor and three unique testis-specific kinases all of which may have some potential in the future regulation of male fertility. 2010-04-27T04:46:46.379Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5006 A great deal of circumstantial evidence has linked DNA damage in human spermatozoa with adverse reproductive outcomes including reduced fertility and high rates of miscarriage. Although oxidative stress is thought to make a significant contribution to DNA damage in the male germ line, the factors responsible for creating this stress have not been elucidated. One group of compounds that are thought to be active in this context are the estrogens, either generated as a result of the endogenous metabolism of androgens within the male reproductive tract or gaining access to the latter as a consequence of environmental exposure. In this study, a wide variety of estrogenic compounds were assessed for their direct effects on human spermatozoa in vitro. DNA integrity was assessed using the Comet and TUNEL assays, lesion frequencies were quantified by QPCR using targets within the mitochondrial and nuclear (β-globin) genomes, DNA adducts were characterized by mass spectrometry and redox activity was monitored using dihydroethidium (DHE) as the probe. Of the estrogenic and estrogen analogue compounds evaluated, catechol estrogens, quercetin, diethylstilbestrol and pyrocatechol stimulated intense redox activity while genistein was only active at the highest doses tested. Other estrogens and estrogen analogues, such as 17β-estradiol, nonylphenol, bisphenol A and 2,3-dihydroxynaphthalene were inactive. Estrogen-induced redox activity was associated with a dramatic loss of motility and, in the case of 2-hydroxyestradiol, the induction of significant DNA fragmentation. Mass spectrometry also indicated that catechol estrogens were capable of forming dimers that can cross-link the densely packed DNA strands in sperm chromatin, impairing nuclear decondensation. These results highlight the potential importance of estrogenic compounds in creating oxidative stress and DNA damage in the male germ line and suggest that further exploration of these compounds in the aetiology of male infertility is warranted. 2010-04-27T04:45:37.791Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5003 The process of capacitation is a pre-requisite for mammalian spermatozoa allowing them to gain the ability to fertilize an oocyte. A fundamental part of this mechanism is a dramatic increase in the level of tyrosine phosphorylation. Implicated in this process is a unique cAMP/protein kinase A (PKA)-mediated pathway involving an intermediate PKA-activated tyrosine kinase suggested to be pp60c-src (SRC) in the mouse. This study has verified the importance of SRC as a key intermediate kinase in promoting the tyrosine phosphorylation events associated with human sperm capacitation. The presence of SRC in human spermatozoa was confirmed immunocytochemically and the kinase was localized to subcellular domains compatible with a role in tyrosine phosphorylation. Additionally SRC co-immunoprecipitated with PKA and became activated by phosphorylation of the Y416 residue during human sperm capacitation. Furthermore, the suppression of PKA and SRC through the application of specific inhibitors led to a dramatic decrease in tyrosine phosphorylation. However, although the inhibition of PKA was also accompanied by a suppression of sperm motility, SRC inhibition did not induce a similar response. 2010-04-27T04:45:32.521Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5508 Assisted reproductive technology (ART) has been responsible for the birth of over 3 million babies since the delivery of Louise Brown in the UK 28 years ago. Currently, one in 80–100 children born in the USA, one in 50 born in Sweden, one in 40 born in Australia and one in 24 born in Denmark are the product of this form of treatment. In 2003, more than 100,000 in vitro fertilization (IVF) cycles were reported from 399 clinics in the USA, resulting in the birth of more than 48,000 babies. Worldwide, this figure has now exceeded 200,000 births per annum and is continuing to rise. Indeed, it is a biological certainty that the more ART is used in one generation, the more it will be needed in the next. Given the cost of this form of treatment, and the fact that children born as a consequence of ART stand a 30–40% increased risk of birth defects , the current widespread use of assisted conception may constitute the beginnings of a serious public health problem. 2010-04-27T04:43:17.035Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5470 As clinical investigators and scientists in the Y chromosome deletion field, we wish to express our concern about the study by Feng et al. that purports to show a significantly increased risk of de novo Y chromosome deletions in children conceived by assisted reproductive technology (ART). We believe it has serious technical flaws and will serve to confuse and concern the readership. Several of us were involved in a previous study that looked in detail into this issue in a properly selected group of 86 severely infertile men who were thus candidates for intracytoplasmic sperm injection (ICSI), and we found no evidence for de novo chromosome deletions in their 99 ICSI- conceived male offspring. 2010-04-27T04:34:05.441Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5289 Proteomics represents a powerful tool for the analysis of mammalian spermatozoa, since these terminally differentiated cells are transcriptionally inactive and exhibit a limited dynamic range of protein expression. Here we report the identification of 5123 peptides, leading to 829 unambiguous and 2215 redundant gene products found to be present within rat spermatozoa derived from the cauda epididymis. Bioinformatics demonstrated that 60 proteins appeared to be specifically expressed in the genitourinary tract, including pyruvate dehydrogenase 1, ropporin, testis-specific serine kinase 4, testis-specific transporter, and retinol dehydrogenase 14. We also identified eight members of the ADAM family, seven of which have previously been detected in spermatozoa (ADAM2, -3, -4, -5, -6, -7, and -30) while ADAM34 has been identified in the sperm proteome for the first time. Approximately 21 gene products were found to possess isomerase activity including peptidylprolyl cis/trans isomerases that are known to be involved in germ cell differentiation and protein disulfide isomerases that have been implicated in sperm-oocyte fusion. Furthermore, 51 gene products clustered into ion-transporter activity. This inventory of gene products, the first ever 2-D LC-MS/MS analysis of rat spermatozoa, will be invaluable in directing future research into the molecular mechanisms that drive these highly specialized cells. 2010-04-27T04:33:33.437Z ]]>