Identification of the proteins present in the bull sperm cytosolic fraction enriched in tyrosine kinase activity: a proteomic approach

miR-124-3p regulates the involvement of Ptpn1 in testicular development and spermatogenesis in mouse

Testicular development and spermatogenesis in mouse are a complex process in which phosphorylation modifications and regulation of genes by non-coding RNAs play an important role. However, protein tyrosine phosphatase, non-receptor type 1 (Ptpn1) is widely expressed in mammalian tissues. In this study, we analyzed the expression of Ptpn1 mRNA and its encoded proteins in testicular tissues of juvenile and adult mice by using experimental techniques such as biological information, real-time fluorescence quantitative PCR (RT-qPCR), western blot (WB), immunofluorescence (IF) and transfection, and further analyzed the possible target-regulatory relationship and regulatory mechanisms of miR-124-3p and Ptpn1. We found that Ptpn1 mRNA and its encoded protein were up-regulated in adult mouse testis compared to juvenile mouse testis. The expression trend of miR-124-3p was opposite to that of Ptpn1. In other cell types, Ptpn1 protein is localized in cell membrane, cytoplasm, endoplasmic reticulum and cytoplasmic vesicles. Immunofluorescence showed that Ptpn1 protein was mainly localized in the cytoplasm of male germ cells and was expressed at a high level in early-stage cells (spermatogonia) and at a low level in late-stage cells (sperm). Transfection results showed that the expression levels of Ptpn1 mRNA and its protein were significantly down-regulated after miR-124-3p overexpression in mouse spermatogonia. Bioinformatics analysis showed that Ptpn1 can involved in biological processes such as protein kinase inactivation through peptidyl tyrosine dephosphorylation. The reduction of miR-124-3p may be a key factor in promoting the high expression of Ptpn1 in testicular tissues of adult mice. Increased miR-124-3p may be a key factor in suppressing Ptpn1 expression in the mouse spermatogonia mimics group. The differential expression results from the negative regulation of miR-124-3p.

Genome-wide association study reveals candidate markers related to field fertility and semen quality traits in Holstein-Friesian bulls

In vitro assessment of bull semen quality is routinely used in bull semen processing centres in order to ensure that semen destined to be used in the field has passed minimum standards. Despite these stringent quality control checks, individual bulls that pass the quality control checks can still vary in field fertility by up to 25%. A genome-wide association study was undertaken to determine genetic markers associated with prefreeze and post-thaw bull sperm quality traits as well as field fertility. Genome-wide association analysis was performed using a single nucleotide polymorphism (SNP) regression mixed linear model in WOMBAT. Genes within a 250 Kb span of a suggestive (P ≤ 1 × 10^-5) SNP were considered as candidate genes. One SNP was associated with adjusted pregnancy rate, and 21 SNPs were associated across the seven semen quality traits (P ≤ 1 × 10^-5). Functional candidate genes include SIPA1L2 which was associated with adjusted pregnancy rate. This encodes a Rap GTPase-activating protein involved in Rap1 signalling pathway and was previously found to play a role in the process of sperm differentiation. Gene ontology (GO) analysis also identified significantly enriched biological processes involved protein tyrosine kinase activity including genes such as DYRK1A, TEC and TXK that were associated with sperm motility prior to freezing. Another candidate gene associated with post-thaw sperm motility was FHDC1 which coordinates actin filament and microtubule dynamics. The induced 11 GO terms in the ejaculates rejected after freezing trait were related to ATPase, phosphatase and hydrolase activity. These results reveal novel specific genomic regions and candidate genes associated with economically important phenotypes such as field fertility and semen quality traits.

The stallion sperm acrosome: Considerations from a research and clinical perspective

During the fertilization process, the interaction between the sperm and the oocyte is mediated by a process known as acrosomal exocytosis (AE). Although the role of the sperm acrosome on fertilization has been studied extensively over the last 70 years, little is known about the molecular mechanisms that govern acrosomal function, particularly in species other than mice or humans. Even though subfertility due to acrosomal dysfunction is less common in large animals than in humans, the evaluation of sperm acrosomal function should be considered not only as a complementary but a routine test when individuals are selected for breeding potential. This certainly holds true for stallions, which might display lower levels of fertility in the face of "acceptable" sperm quality parameters determined by conventional sperm assays. Nowadays, the use of high throughput technologies such as flow cytometry or mass spectrometry-based proteomic analysis is commonplace in the research arena. Such techniques can also be implemented in clinical scenarios of males with "idiopathic" subfertility. The current review focuses on the sperm acrosome, with particular emphasis on the stallion. We aim to describe the physiological events that lead to the acrosome formation within the testis, the role of very specific acrosomal proteins during AE, the methods to study the occurrence of AE under in vitro conditions, and the potential use of molecular biology techniques to discover new markers of acrosomal function and subfertility associated with acrosomal dysfunction in stallions.

Genome-wide association study to identify genomic regions and positional candidate genes associated with male fertility in beef cattle

Fertility plays a key role in the success of calf production, but there is evidence that reproductive efficiency in beef cattle has decreased during the past half-century worldwide. Therefore, identifying animals with superior fertility could significantly impact cow-calf production efficiency. The objective of this research was to identify candidate regions affecting bull fertility in beef cattle and positional candidate genes annotated within these regions. A GWAS using a weighted single-step genomic BLUP approach was performed on 265 crossbred beef bulls to identify markers associated with scrotal circumference (SC) and sperm motility (SM). Eight windows containing 32 positional candidate genes and five windows containing 28 positional candidate genes explained more than 1% of the genetic variance for SC and SM, respectively. These windows were selected to perform gene annotation, QTL enrichment, and functional analyses. Functional candidate gene prioritization analysis revealed 14 prioritized candidate genes for SC of which MAP3K1 and VIP were previously found to play roles in male fertility. A different set of 14 prioritized genes were identified for SM and five were previously identified as regulators of male fertility (SOD2, TCP1, PACRG, SPEF2, PRLR). Significant enrichment results were identified for fertility and body conformation QTLs within the candidate windows. Gene ontology enrichment analysis including biological processes, molecular functions, and cellular components revealed significant GO terms associated with male fertility. The identification of these regions contributes to a better understanding of fertility associated traits and facilitates the discovery of positional candidate genes for future investigation of causal mutations and their implications.

Identification of Bovine Sperm Surface Proteins Involved in Carbohydrate-mediated Fertilization Interactions

Glycan-protein interactions play a key role in mammalian fertilization, but data on the composition and identities of protein complexes involved in fertilization events are scarce, with the added complication that the glycans in such interactions tend to differ among species. In this study we have used a bovine model to detect, characterize and identify sperm lectins relevant in fertilization. Given the complexity of the sperm-toward-egg journey, two important aspects of the process, both primarily mediated by protein-sugar interactions, have been addressed: (1) formation of the sperm reservoir in the oviductal epithelium, and (2) gamete recognition (oocyte-sperm interaction). Using whole sperm cells and a novel affinity capture method, several groups of proteins with different glycan specificities, including 58 hitherto unreported as lectins, have been identified in sperm surface, underscoring both the efficacy of our selective approach and the complex composition and function of sperm. Based on these results and previous data, we suggest that sperm surface proteins play significant roles in fertilization events such as membrane remodeling, transport, protection and function, thus supporting the hypothesis that rather than a simple lock-and-key model, mammalian fertilization relies on a complex interactome involving multiple ligands/receptors and recognition/binding events.

Identification of kinases, phosphatases, and phosphorylation sites in human and porcine spermatozoa

Multiple inter-connected signaling pathways, involving kinases and phosphatases, form a framework that controls sperm motility, function, and fertilizing ability. Methods that give a broad view of the proteomic landscape may prove valuable in uncovering new crosstalk connections, as well as in discovering new proteins within this regulatory framework. A multi-immunoblotting strategy was utilized to evaluate this concept on human and porcine spermatozoa samples. In human and porcine spermatozoa, a diversity of kinases were identified including protein kinase A (PKA), protein kinase B (PKB), isoforms of protein kinase C (PKC), calmodulin-dependent kinases (CAMK), casein kinase (CK), and isoforms of glycogen synthase kinase (GSK3). Several phosphatases, such as protein phosphatase (PP)-1, PP2A, PP2C, and mitogen activated protein kinase (MAPK) phosphatase (MKP-1), were identified in human spermatozoa. The phosphorylation epitopes recognized belonged to members of the MAPK family, in addition to α and β isoforms of GSK3 and cAMP response element binding protein (CREB). Proteomic approaches that allow a broad view may aid in understanding the crosstalk between signaling systems in spermatozoal physiology.

Profiling signaling proteins in human spermatozoa: biomarker identification for sperm quality evaluation

OBJECTIVE

To determine the correlation between semen basic parameters and the expression and activity of signaling proteins.

DESIGN

In vitro studies with human spermatozoa.

SETTING

Academic research institute.

PATIENT(S)

Thirty-seven men provided semen samples for routine analysis.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Basic semen parameters tracked included sperm DNA fragmentation (SDF), the expression levels of 75 protein kinases, and the phosphorylation/cleavage patterns of 18 signaling proteins in human spermatozoa.

RESULT(S)

The results indicated that the phosphorylated levels of several proteins (Bad, GSK-3β, HSP27, JNK/SAPK, mTOR, p38 MAPK, and p53), as well as cleavage of PARP (at D214) and Caspase-3 (at D175), were significantly correlated with motility parameters. Additionally, the percentage of morphologically normal spermatozoa demonstrated a significant positive correlation with the phosphorylated levels of p70 S6 kinase and, in turn, head defects and the teratozoospermia index (TZI) showed a significant negative correlation with the phosphorylated levels of Stat3. There was a significant positive correlation between SDF and the teratozoospermia index, as well as the presence of head defects. In contrast, SDF negatively correlated with the percentage of morphologically normal spermatozoa and the phosphorylation of Akt and p70 S6 kinase. Subjects with varicocele demonstrated a significant negative correlation between head morphological defects and the phosphorylated levels of Akt, GSK3β, p38 MAPK, and Stat1. Additionally, 34 protein kinases were identified as expressed in their total protein levels in normozoospermic samples.

CONCLUSION(S)

This study contributed toward establishing a biomarker "fingerprint" to assess sperm quality on the basis of molecular parameters.

Sperm phosphoproteomics: historical perspectives and current methodologies

Mammalian sperm are differentiated germ cells that transfer genetic material from the male to the female. Owing to this essential role in the reproductive process, an understanding of the complex mechanisms that underlie sperm function has implications ranging from the development of novel contraceptives to the treatment of male infertility. While the importance of phosphorylation in sperm differentiation, maturation and fertilization has been well established, the ability to directly determine the sites of phosphorylation within sperm proteins and to quantitate the extent of phosphorylation at these sites is a recent development that has relied almost exclusively on advances in the field of proteomics. This review will summarize the work that has been carried out to date on sperm phosphoproteomics and discuss how the resulting qualitative and quantitative information has been used to provide insight into the manner in which protein phosphorylation events modulate sperm function. The authors also present the proteomics process as it is most often utilized for the elucidation of protein expression, with a particular emphasis on the way in which the process has been modified for the analysis of protein phosphorylation in sperm.

Functional human sperm capacitation requires both bicarbonate-dependent PKA activation and down-regulation of Ser/Thr phosphatases by Src family kinases

In all mammalian species studied so far, sperm capacitation correlates with an increase in protein tyrosine (Tyr) phosphorylation mediated by a bicarbonate-dependent cAMP/protein kinase A (PKA) pathway. Recent studies in mice revealed, however, that a Src family kinase (SFK)-induced inactivation of serine/threonine (Ser/Thr) phosphatases is also involved in the signaling pathways leading to Tyr phosphorylation. In view of these observations and with the aim of getting a better understanding of the signaling pathways involved in human sperm capacitation, in the present work we investigated the involvement of both the cAMP/PKA and SFK/phosphatase pathways in relation to the capacitation state of the cells. For this purpose, different signaling events and sperm functional parameters were analyzed as a function of capacitation time. Results revealed a very early bicarbonate-dependent activation of PKA indicated by the rapid (1 min) increase in both phospho-PKA substrates and cAMP levels (P < 0.05). However, a complete pattern of Tyr phosphorylation was detected only after 6-h incubation at which time sperm exhibited the ability to undergo the acrosome reaction (AR) and to penetrate zona-free hamster oocytes. Sperm capacitated in the presence of the SFK inhibitor SKI606 showed a decrease in both PKA substrate and Tyr phosphorylation levels, which was overcome by exposure of sperm to the Ser/Thr phosphatase inhibitor okadaic acid (OA). However, OA was unable to induce phosphorylation when sperm were incubated under PKA-inhibitory conditions (i.e. in the absence of bicarbonate or in the presence of PKA inhibitor). Moreover, the increase in PKA activity by exposure to a cAMP analog and a phosphodiesterase inhibitor did not overcome the inhibition produced by SKI606. Whereas the presence of SKI606 during capacitation produced a negative effect (P < 0.05) on sperm motility, progesterone-induced AR and fertilizing ability, none of these inhibitions were observed when sperm were exposed to SKI606 and OA. Interestingly, different concentrations of inhibitors were required to modulate human and mouse capacitation revealing the species specificity of the molecular mechanisms underlying this process. In conclusion, our results describe for the first time the involvement of both PKA activation and Ser/Thr phosphatase down-regulation in functional human sperm capacitation and provide convincing evidence that early PKA-dependent phosphorylation is the convergent regulatory point between these two signaling pathways.

Mechanism of sperm capacitation and the acrosome reaction: role of protein kinases

Mammalian sperm must undergo a series of biochemical and physiological modifications, collectively called capacitation, in the female reproductive tract prior to the acrosome reaction (AR). The mechanisms of these modifications are not well characterized though protein kinases were shown to be involved in the regulation of intracellular Ca(2+) during both capacitation and the AR. In the present review, we summarize some of the signaling events that are involved in capacitation. During the capacitation process, phosphatidyl-inositol-3-kinase (PI3K) is phosphorylated/activated via a protein kinase A (PKA)-dependent cascade, and downregulated by protein kinase C α (PKCα). PKCα is active at the beginning of capacitation, resulting in PI3K inactivation. During capacitation, PKCα as well as PP1γ2 is degraded by a PKA-dependent mechanism, allowing the activation of PI3K. The activation of PKA during capacitation depends mainly on cyclic adenosine monophosphate (cAMP) produced by the bicarbonate-dependent soluble adenylyl cyclase. This activation of PKA leads to an increase in actin polymerization, an essential process for the development of hyperactivated motility, which is necessary for successful fertilization. Actin polymerization is mediated by PIP(2) in two ways: first, PIP(2) acts as a cofactor for phospholipase D (PLD) activation, and second, as a molecule that binds and inhibits actin-severing proteins such as gelsolin. Tyrosine phosphorylation of gelsolin during capacitation by Src family kinase (SFK) is also important for its inactivation. Prior to the AR, gelsolin is released from PIP(2) and undergoes dephosphorylation/activation, resulting in fast F-actin depolymerization, leading to the AR.

ATP-binding cassette transporter G2 activity in the bovine spermatozoa is modulated along the epididymal duct and at ejaculation

During their epididymal maturation, stabilizing factors such as cholesterol sulfate are associated with the sperm plasma membrane. Cholesterol is sulfated in epididymal spermatozoa by the enzyme estrogen sulfotransferase. Because of its role in the efflux of sulfate conjugates formed intracellularly by sulfotransferases, the ATP-binding cassette membrane transporter G2 (ABCG2) might have a role in the translocation of this compound across the plasma membrane. In the present study we showed that ABCG2 is present in the plasma membrane overlaying the acrosomal region of spermatozoa recovered from testis, epididymis, and after ejaculation. Although ABCG2 is also present in epididymosomes, the transporter is not transferred to spermatozoa via this mechanism. Furthermore, although epididymal sperm ABCG2 was shown to be functional, as determined by its ability to extrude Hoechst 33342 in the presence of the specific inhibitor Fumitremorgin C, ABCG2 present in ejaculated sperm was found to be nonfunctional. Additional experiments demonstrated that phosphorylation of ABCG2 tyrosyl residues, but not its localization in lipid rafts, is the mechanism responsible for its functionality. Dephosphorylation of ABCG2 in ejaculated spermatozoa is proposed to cause a partial protein relocalization to other intracellular compartments. Prostasomes are proposed to have a role in this process because incubation with this fraction of seminal plasma induces a decrease in the amount of ABCG2 in the associated sperm membrane fraction. These results demonstrate that ABCG2 plays a role in epididymal sperm maturation, but not after ejaculation. The loss of ABCG2 function after ejaculation is proposed to be regulated by prostasomes.

Delivering value from sperm proteomics for fertility

Fertilization of an egg by a spermatozoon sets the stage for mammalian development. Viable sperm are a prerequisite for successful fertilization and beyond. Spermatozoa have a unique cell structure where haploid genomic DNA is located in a tiny cytoplasmic space in the head, mitochondria in the midpiece and then the tail, all enclosed by several layers of membrane. Proteins in sperm play vital roles in motility, capacitation, fertilization, egg activation and embryo development. Molecular defects in these proteins are associated with low fertility or in some cases, infertility. This review will first summarize genesis, molecular anatomy and physiology of spermatozoa, fertilization, embryogenesis and then those proteins playing important roles in various aspects of sperm physiology.

Relationship of protein tyrosine phosphorylation state with tolerance to frozen storage and the potential to undergo cyclic AMP-dependent hyperactivation in the spermatozoa of Japanese Black bulls

The aim of this study was to elucidate the relationship between protein tyrosine phosphorylation state and sperm characteristics in frozen-stored spermatozoa of Japanese Black bulls. The spermatozoa were washed with PBS containing polyvinyl alcohol and then incubated with cell-permeable cAMP analog cBiMPS to induce flagellar hyperactivation. Before and after incubation, the spermatozoa were used for immunodetection of tyrosine-phosphorylated proteins, assessment of morphological acrosome condition and evaluation of motility. In bulls whose frozen-stored spermatozoa were classified as having a high-grade acrosome condition before incubation, sperm tyrosine-phosphorylated proteins, including the 33-kDa tyrosine-phosphorylated SPACA1 protein, were localized in the anterior region of the acrosome and equatorial subsegment. The immunodetection level of the 41- and 33-kDa sperm tyrosine-phosphorylated proteins in the Western blots and the immunofluorescence of tyrosine-phosphorylated proteins and SPACA1 proteins in the anterior region of the sperm acrosome were lower in bulls whose frozen-stored sperm were classified as having a low-grade acrosome condition. On the other hand, after incubation with cBiMPS, immunodetection levels of at least 10 tyrosine-phosphorylated proteins increased in the connecting and principal pieces of spermatozoa, coincident with the induction of flagellar hyperactivation. Many of the spermatozoa also exhibited detection patterns similar to those of boar hyperactivated spermatozoa. These results are consistent with the suggestion that immunodetection levels of tyrosine-phosphorylated proteins are valid markers that can predict the level of tolerance to frozen storage and the potential to undergo cAMP-dependent hyperactivation for the spermatozoa of individual Japanese Black bulls.

Testicular postgenomics: targeting the regulation of spermatogenesis

Sperm are, arguably, the most differentiated cells produced within the body of any given species. This is owing to the fact that spermatogenesis is an intricate and highly specialized process evolved to suit the individual particularities of each sexual species. Despite a vast diversity in method, the aim of spermatogenesis is always the same, the idealized transmission of genetic patrimony. Towards this goal certain requirements must always be met, such as a relative twofold reduction in ploidy, repackaging of the chromatin for transport and specialized enhancements for cell motility, recognition and fusion. In the past 20 years, the study of molecular networks coordinating male germ cell development, particularly in mammals, has become more and more facilitated thanks to large-scale analyses of genome expression. Such postgenomic endeavors have generated landscapes of data for both fundamental and clinical reproductive biology. Continuous, large-scale integration analyses of these datasets are undertaken which provide access to very precise information on a myriad of biomolecules. This review presents commonly used transcriptomic and proteomic workflows applied to various testicular germ cell studies. We will also provide a general overview of the technical possibilities available to reproductive genomic biologists, noting the advantages and drawbacks of each technique.

The "switching on" of mammalian spermatozoa: molecular events involved in promotion and regulation of capacitation

Following the discovery of mammalian sperm capacitation and its fundamental importance for the acquisition of fertilizing potential, it has gradually become possible to identify some specific molecules and molecular events that play pivotal roles in the "switching on" of spermatozoa. These are discussed in the context of the promotion and regulation of capacitation, emphasizing differences between commonly used conditions in vitro and the environment in vivo where spermatozoa normally undergo capacitation. Although typical culture media used in vitro do support capacitation, they do not prevent capacitated cells from undergoing spontaneous acrosome reactions and so losing fertilizing potential. This is not a problem in vitro, but could be in vivo where few spermatozoa reach the site of fertilization. Several small molecules, known to be present in vivo, have been shown in vitro to bind to spermatozoa and to regulate capacitation, first accelerating capacitation and then inhibiting spontaneous acrosome reactions, by regulating cAMP production. Since spermatozoa would contact these molecules during and after ejaculation, it is plausible that they serve a similar function in vivo. The mechanisms whereby the presence or absence of decapacitation factors might alter plasma membrane architecture and so alter functionality of a number of membrane-associated enzymes involved in capacitation are also considered. Finally, several unresolved issues relating to events during capacitation are discussed.

Glucose-regulated protein precursor (GRP78) and tumor rejection antigen (GP96) are unique to hamster caput epididymal spermatozoa

The immotile testicular mammalian spermatozoon gets transformed into a motile spermatozoon during 'epididymal maturation'. During this process, the spermatozoa transit from the caput to the cauda epididymis and undergo a number of distinct morphological, biophysical and biochemical changes, including changes in protein composition and protein modifications, which may be relevant to the acquisition of motility potential. The present proteome-based study of the hamster epididymal spermatozoa of caput and cauda led to the identification of 113 proteins spots using Matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS) analysis. Comparison of these 113 protein spots indicated that 30 protein spots (corresponding to 20 proteins) were significantly changed in intensity. Five proteins were increased and eleven were decreased in intensity in the cauda epididymal spermatozoa. In addition, two proteins, glucose-regulated protein precursor (GRP78) and tumor rejection antigen (GP96), were unique to the caput epididymal spermatozoa, while one protein, fibrinogen-like protein 1, was unique to cauda epididymal spermatozoa. A few of the five proteins, which increased in intensity, were related to sperm metabolism and ATP production during epididymal maturation. The changes in intensity of a few proteins such as ERp57, GRP78, GP96, Hsp60, Hsp70, and dihydrolipoamide S-acetyltransferase were validated by immunoblotting. The present study provides a global picture of the changes in protein composition occurring during hamster sperm epididymal maturation, besides being the first ever report on the proteome of hamster spermatozoa.

Sperm surface proteomics: from protein lists to biological function

Proteomics technologies have matured significantly in recent years and proteomics driven research articles in reproductive biology and medicine are increasingly common. The key challenge is to move from lists of identified proteins to informed understanding of biological function. This review introduces the range of proteomics workflows most commonly used for protein identification before focusing on the mammalian sperm cell at fertilization as an exemplar for proteomic studies. We review the work of others on entire cells but then argue that proper subcellular fractionation and proper solubilization strategies offers critical advantages to achieving increased biological understanding. In relation to understanding initial gamete recognition events at fertilization (capacitation, zona binding and acrosomal exocytosis) it is imperative to study the sperm surface proteome by using purified plasma membrane fractions. Although this task is challenging there are now strategies at our disposal to achieve comprehensive coverage of the proteins at the sperm surface. Within this context it is also important to understand the milieu of the sperm cell during transit from the testis to the oviduct as proteins (or other entities) from the genital tract epithelia and fluids may also affect the composition and organization of proteins on the sperm surface. Finally the arguments presented for studying the cell plasma membrane proteome to understand the role of the cell surface equally apply to all cell types with important roles in reproductive function.

Phosphorylation and consequent stimulation of the tyrosine kinase c-Abl by PKA in mouse spermatozoa; its implications during capacitation

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.

The mouse sperm proteome characterized via IPG strip prefractionation and LC-MS/MS identification

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.

Comprehensive proteomic analysis of bovine spermatozoa of varying fertility rates and identification of biomarkers associated with fertility

BACKGROUND

Male infertility is a major problem for mammalian reproduction. However, molecular details including the underlying mechanisms of male fertility are still not known. A thorough understanding of these mechanisms is essential for obtaining consistently high reproductive efficiency and to ensure lower cost and time-loss by breeder.

RESULTS

Using high and low fertility bull spermatozoa, here we employed differential detergent fractionation multidimensional protein identification technology (DDF-Mud PIT) and identified 125 putative biomarkers of fertility. We next used quantitative Systems Biology modeling and canonical protein interaction pathways and networks to show that high fertility spermatozoa differ from low fertility spermatozoa in four main ways. Compared to sperm from low fertility bulls, sperm from high fertility bulls have higher expression of proteins involved in: energy metabolism, cell communication, spermatogenesis, and cell motility. Our data also suggests a hypothesis that low fertility sperm DNA integrity may be compromised because cell cycle: G2/M DNA damage checkpoint regulation was most significant signaling pathway identified in low fertility spermatozoa.

CONCLUSION

This is the first comprehensive description of the bovine spermatozoa proteome. Comparative proteomic analysis of high fertility and low fertility bulls, in the context of protein interaction networks identified putative molecular markers associated with high fertility phenotype.

Human spermatozoa contain multiple targets for protein S-nitrosylation: an alternative mechanism of the modulation of sperm function by nitric oxide?

Nitric oxide (NO) enhances human sperm motility and capacitation associated with increased protein phosphorylation. NO activates soluble guanylyl cyclase, but can also modify protein function covalently via S-nitrosylation of cysteine. Remarkably, this mechanism remains unexplored in sperm although they depend on post-translational protein modification to achieve changes in function required for fertilisation. Our objective was to identify targets for S-nitrosylation in human sperm. Spermatozoa were incubated with NO donors and S-nitrosylated proteins were identified using the biotin switch assay and a proteomic approach using MS/MS. 240 S-nitrosylated proteins were detected in sperm incubated with S-nitroso-glutathione. Minimal levels were observed in glutathione or untreated samples. Proteins identified consistently based on multiple peptides included established targets for S-nitrosylation in other cells e.g. tubulin, GST and HSPs but also novel targets including A-kinase anchoring protein (AKAP) types 3 and 4, voltage-dependent anion-selective channel protein 3 and semenogelin 1 and 2. In situ localisation revealed S-nitrosylated targets on the postacrosomal region of the head and throughout the flagellum. Potential targets for S-nitrosylation in human sperm include physiologically significant proteins not previously reported in other cells. Their identification will provide novel insight into the mechanism of action of NO in spermatozoa.

Counting sperm does not add up any more: time for a new equation?

Although sperm dysfunction is the single most common cause of infertility, we have poor methods of diagnosis and surprisingly no effective treatment (excluding assisted reproductive technology). In this review, we challenge the usefulness of a basic semen analysis and argue that a new paradigm is required immediately. We discuss the use of at-home screening to potentially improve the diagnosis of the male and to streamline the management of the sub-fertile couple. Additionally, we outline the recent progress in the field, for example, in proteomics, which will allow the development of new biomarkers of sperm function. This new knowledge will transform our understanding of the spermatozoon as a machine and is likely to lead to non-ART treatments for men with sperm dysfunction.