Tyrosine phosphorylation activates surface chaperones facilitating sperm-zona recognition

Reduced fertility in vitro in mice lacking the cystatin CRES (cystatin-related epididymal spermatogenic): rescue by exposure of spermatozoa to dibutyryl cAMP and isobutylmethylxanthine

The cystatin CRES (cystatin-related epididymal spermatogenic; Cst8) is the defining member of a reproductive subgroup of family 2 cystatins of cysteine protease inhibitors and is present in the epididymis and spermatozoa, suggesting roles in sperm maturation and fertilization. To elucidate the role of CRES in reproduction, mice lacking the Cst8 gene were generated and their fertility examined. Although both male and female Cst8(-/-) mice generated offspring in vivo, spermatozoa from Cst8(-/-) mice exhibited a profound fertility defect in vitro. Compared to spermatozoa from Cst8(+/+) mice, spermatozoa from Cst8(-/-) mice were unable to undergo a progesterone-stimulated acrosome reaction and had decreased levels of protein tyrosine phosphorylation, suggesting a defect in the ability of Cst8(-/-) spermatozoa to capacitate. Incubation of Cst8(-/-) spermatozoa with dibutyryl cAMP and 3-isobutyl-1-methylxanthine rescued the fertility defect, including the capacity for sperm protein tyrosine phosphorylation. Both untreated Cst8(+/+) and Cst8(-/-) spermatozoa, however, exhibited similar increased total levels of cAMP and protein kinase A (PKA) activity throughout the capacitation time course compared to spermatozoa incubated under noncapacitating conditions. Taken together, these results suggest that mice lacking CRES may have altered local levels of cAMP/PKA activity, perhaps because of improper partitioning or tethering of these signaling molecules, or that the CRES defect does not directly involve cAMP/PKA but other signaling pathways that regulate protein tyrosine phosphorylation and capacitation.

Protein tyrosine phosphorylation of the human sperm head during capacitation: immunolocalization and relationship with acquisition of sperm-fertilizing ability

The occurrence of tyrosine phosphorylation (TP) in the sperm head during capacitation has been poorly investigated, and no data exist on the relationship of its dynamics with the acquisition of sperm fertilizing ability. This study localized TP of head proteins in human spermatozoa during capacitation and explored its relationship with acquisition of the ability to display progesterone (P)-stimulated acrosome reactions (ARs) and to penetrate zona-free hamster oocytes. By immunofluorescence, TP immunoreactivity was revealed in the acrosomal region of formaldehyde-fixed/unpermeabilized samples, whereas it was abolished in fixed/permeabilized samples, in which TP immunoreactivity was high in the principal piece. No TP immunoreactivity was detectable in unfixed spermatozoa. Head TP immunoreactivity was localized externally to the acrosome, close to the cytoplasmic membrane, as assessed by transmission electron microscopy. The increase in head TP was an early event during capacitation, occurring within 1 h in capacitating conditions. At this time, the P-stimulated ARs were also increased, whereas egg penetration was as poor as in uncapacitated spermatozoa. At 5 h of capacitation, the extent of neither head TP nor the P-induced ARs were greater than that at 1 h, whereas egg penetration had significantly increased. Seminal plasma inhibited head TP, P-induced ARs and egg penetration. None of these inhibitory effects, unlike those on tail TP, were prevented by the cAMP analogue dbcAMP (N,2-O-dibutyryladenosine 3',5'-cyclic monophosphate). In conclusion, head TP is a subsurface event occurring early during capacitation and is closely related to acquisition of the ability to display P-stimulated ARs, whereas the ability to fuse with oolemma and to decondense is a later capacitation-related event.

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

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

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

Elucidation of the signaling pathways that underpin capacitation-associated surface phosphotyrosine expression in mouse spermatozoa

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.

Molecular chaperones and protein-folding catalysts as intercellular signaling regulators in immunity and inflammation

This review critically examines the hypothesis that molecular chaperones and protein-folding catalysts from prokaryotes and eukaryotes can be secreted by cells and function as intercellular signals, principally but not exclusively, for leukocytes. A growing number of molecular chaperones have been reported to function as ligands for selected receptors and/or receptors for specific ligands. Molecular chaperones initially appeared to act primarily as stimulatory signals for leukocytes and thus, were seen as proinflammatory mediators. However, evidence is now emerging that molecular chaperones can have anti-inflammatory actions or, depending on the protein and concentration, anti- and proinflammatory functions. Recasting the original hypothesis, we propose that molecular chaperones and protein-folding catalysts are "moonlighting" proteins that function as homeostatic immune regulators but may also under certain circumstances, contribute to tissue pathology. One of the key issues in the field of molecular chaperone biology relates to the role of microbial contaminants in their signaling activity; this too will be evaluated critically. The most fascinating aspect of molecular chaperones probably relates to evidence for their therapeutic potential in human disease, and ongoing studies are evaluating this potential in a range of clinical settings.

Caught with their PAMPs down? The extracellular signalling actions of molecular chaperones are not due to microbial contaminants

In recent years, it has been hypothesised that a new signalling system may exist in vertebrates in which secreted molecular chaperones form a dynamic continuum between the cellular stress response and corresponding homeostatic physiological mechanisms. This hypothesis seems to be supported by the finding that many molecular chaperones are released from cells and act as extracellular signals for a range of cells. However, this nascent field of biological research seems to suffer from an excessive criticism that the biological activities of molecular chaperones are due to undefined components of the microbial expression hosts used to generate recombinant versions of these proteins. In this article, a number of the proponents of the cell signalling actions of molecular chaperones take this criticism head-on. They show that sufficient evidence exists to support fully the hypothesis that molecular chaperones have cell-cell signalling actions that are likely to be part of the homeostatic mechanism of the vertebrate.

Multiple moonlighting functions of mycobacterial molecular chaperones

Molecular chaperones and protein folding catalysts are normally thought of as intracellular proteins involved in protein folding quality control. However, in the mycobacteria there is increasing evidence to support the hypothesis that molecular chaperones are also secreted intercellular signalling molecules or can control actions at the cell wall or indeed control the composition of the cell wall. The most recent evidence for protein moonlighting in the mycobacteria is the report that chaperonin 60.2 of Mycobacterium tuberculosis is important in the key event in tuberculosis - the entry of the bacterium into the macrophage. This brief overview highlights the potential importance of the moonlighting functions of molecular chaperones in the biology and pathobiology of the mycobacteria.

Sperm-zona pellucida interaction: molecular mechanisms and the potential for contraceptive intervention

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.

Heat shock proteins on the human sperm surface

The sperm plasma membrane is known to be critical to fertilization and to be highly regionalized into domains of head, mid- and principal pieces. However, the molecular composition of the sperm plasma membrane and its alterations during genital tract passage, capacitation and the acrosome reaction remains to be fully dissected. A two-dimensional gel-based proteomic study previously identified 98 human sperm proteins which were accessible for surface labelling with both biotin and radioiodine. In this report twelve dually labelled protein spots were excised from stained gels or PDVF membranes and analysed by mass spectrometry (MS) and Edman degradation. Seven members from four different heat shock protein (HSP) families were identified including HYOU1 (ORP150), HSPC1 (HSP86), HSPA5 (Bip), HSPD1 (HSP60), and several isoforms of the two testis-specific HSP70 chaperones HSPA2 and HSPA1L. An antiserum raised against the testis-specific HSPA2 chaperone reacted with three 65kDa HSPA2 isoforms and three high molecular weight surface proteins (78-79kDa, 84kDa and 90-93kDa). These proteins, together with seven 65kDa HSP70 forms, reacted with human anti-sperm IgG antibodies that blocked in vitro fertilization in humans. Three of these surface biotinylated human sperm antigens were immunoprecipitated with a rabbit antiserum raised against a linear peptide epitope in Chlamydia trachomatis HSP70. The results indicate diverse HSP chaperones are accessible for surface labelling on human sperm. Some of these share epitopes with C. trachomatis HSP70, suggesting an association between genital tract infection, immunity to HSP70 and reproductive failure.

Phenotyping male infertility in the mouse: how to get the most out of a 'non-performer'

BACKGROUND

Functional male gametes are produced through complex processes that take place within the testis, epididymis and female reproductive tract. A breakdown at any of these phases can result in male infertility. The production of mutant mouse models often yields an unexpected male infertility phenotype. It is with this in mind that the current review has been written. The review aims to act as a guide to the ‘non-reproductive biologist’ to facilitate a systematic analysis of sterile or subfertile mice and to assist in extracting the maximum amount of information from each model.

METHODS

This is a review of the original literature on defects in the processes that take a mouse spermatogonial stem cell through to a fully functional spermatozoon, which result in male infertility. Based on literature searches and personal experience, we have outlined a step-by-step strategy for the analysis of an infertile male mouse line.

RESULTS

A wide range of methods can be used to define the phenotype of an infertile male mouse. These methods range from histological methods such as electron microscopy and immunohistochemistry, to hormone analyses and methods to assess sperm maturation status and functional competence.

CONCLUSION

With the increased rate of genetically modified mouse production, the generation of mouse models with unexpected male infertility is increasing. This manuscript will help to ensure that the maximum amount of information is obtained from each mouse model and, by extension, will facilitate the knowledge of both normal fertility processes and the causes of human infertility.

Cumulus-associated alpha2-macroglobulin derivative retains proconceptive glycodelin-C in the human cumulus matrix

BACKGROUND

Glycodelin-C is a glycodelin isoform isolated from the cumulus matrix. It stimulates spermatozoa-zona pellucida binding. Here, we report the isolation and characterization of a novel glycodelin interacting protein (GIP) from human cumulus matrix.

METHODS

GIP was purified by liquid chromatograph and identified by mass spectrometry. The interaction of GIP with glycodelin, matrix molecule and spermatozoa were investigated.

RESULTS

Mass spectrometry analysis suggested that GIP contained the N-terminal region of alpha2-macroglobulin, confirmed by western blot with anti-alpha2-macroglobulin antibody. GIP bound to native but not deglycosylated glycodelin-C in native gel electrophoresis, suggesting that the binding was glycosylation-dependent. GIP did not bind to capacitated and uncapacitated human spermatozoa. The cumulus cells could convert exogenous labeled alpha2-macroglobulin into GIP in vitro. GIP interacted with hyaluronic acid, a major component of the cumulus matrix. Glycodelin-C bound to hyaluronic acid-coated agarose beads in the presence of GIP. Human spermatozoa acquired the hyaluronic acid-GIP-bound glycodelin-C during incubation in vitro.

CONCLUSION

The hyaluronic acid-GIP complex formed in the cumulus matrix retains and concentrates glycodelin-C in the cumulus matrix for displacing sperm-bound glycodelin-A and -F and stimulating the zona binding activity of the spermatozoa traversing through the cumulus mass.

Unfolding the relationship between secreted molecular chaperones and macrophage activation states

Over the last 20 years, it has emerged that many molecular chaperones and protein-folding catalysts are secreted from cells and function, somewhat in the manner of cytokines, as pleiotropic signals for a variety of cells, with much attention being focused on the macrophage. During the last decade, it has become clear that macrophages respond to bacterial, protozoal, parasitic and host signals to generate phenotypically distinct states of activation. These activation states have been termed 'classical' and 'alternative' and represent not a simple bifurcation in response to external signals but a range of cellular phenotypes. From an examination of the literature, the hypothesis is propounded that mammalian molecular chaperones are able to induce a wide variety of alternative macrophage activation states, and this may be a system for relating cellular or tissue stress to appropriate macrophage responses to restore homeostatic equilibrium.

Changes in content and localization of proteins phosphorylated at tyrosine, serine and threonine residues during ram sperm capacitation and acrosome reaction

Previously, we reported the involvement of tyrosine phosphorylation in events that lead to ram sperm capacitation. In this study, we carried out a comparative analysis of the localization of tyrosine, serine and threonine phosphoproteins in different functional stages of ram spermatozoa (after the swim-up procedure,in vitrocapacitation, and ionophore-induced acrosome reaction) by immunofluorescence, immunocytochemistry and confocal microscopy. Capacitation increased protein tyrosine, serine and threonine phosphorylation whereas the induction of the acrosome reaction resulted in significantly decreased phosphorylation, mainly in those proteins that increased following capacitation. Control samples showed tyrosine-phosphorylated proteins restricted to the head, mainly distributed at the equatorial region with some cells also displaying an acrosomal and/or post-acrosomal localization.In vitrocapacitation promoted both tail and acrosome phosphorylation, and the acrosome reaction induced the loss of labeling on the acrosome and the subsequent increase in the post-acrosomal region and flagellum. The preferential localization of serine- and threonine-phosphorylated proteins in the equatorial and acrosomal regions found in control samples changed during capacitation, which induced tail phosphorylation in a sequential manner. After the acrosome reaction, the labeling of both phosphoamino acids decreased in the acrosome and increased in the post-acrosome. The obtained results were proved by two immunodetection techniques and strengthened by confocal microscopy, and indicate that changes in phosphorylated proteins during capacitation and acrosome reaction of ram spermatozoa may have physiological significance in consolidating certain phosphorylated proteins to specific sperm regions involved in acrosomal exocytosis and zona pellucida recognition, binding and penetration.

Glucose-regulated protein 78 (Grp78/BiP) is secreted by human oviduct epithelial cells and the recombinant protein modulates sperm-zona pellucida binding

OBJECTIVE

To determine the secretion of Grp78 by human oviduct epithelial cells, its association to spermatozoa, and its involvement in gamete interaction.

DESIGN

Prospective study.

SETTING

Basic research laboratory.

SUBJECT(S)

Semen samples obtained from normozoospermic volunteers. Tubal tissue provided by patients undergoing hysterectomies. Oocytes collected from women undergoing IVF-ET.

INTERVENTION(S)

Analysis of Grp78 expression and secretion by oviductal tissue. Gamete incubation with recombinant Grp78 (rec-Grp78).

MAIN OUTCOME MEASURE(S)

Assessment of protein expression and secretion by immunohistochemistry and Western immunoblotting, respectively. Evaluation of rec-Grp78 binding to human spermatozoa by immunocytochemistry, and analysis of its effect upon gamete interaction using the hemizona assay.

RESULT(S)

Grp78 was found in the surface of oviduct epithelial cells. Soluble Grp78 was detected in oviductal fluids from women in the periovulatory period and in oviductal tissue conditioned medium. Rec-Grp78 was able to bind to the sperm acrosomal cap, and its presence during gamete interaction led to a decrease in the number of spermatozoa bound to the zona pellucida (ZP). When calcium ions from the incubation medium were replaced by strontium, rec-Grp78 enhanced sperm-ZP interaction.

CONCLUSION(S)

Grp78 is expressed and secreted by oviduct epithelial cells. The protein would bind to the gametes and may modulate their interaction in a calcium-dependent manner.

The CAP superfamily: cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins--roles in reproduction, cancer, and immune defense

The cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins (CAP) superfamily members are found in a remarkable range of organisms spanning each of the animal kingdoms. Within humans and mice, there are 31 and 33 individual family members, respectively, and although many are poorly characterized, the majority show a notable expression bias to the reproductive tract and immune tissues or are deregulated in cancers. CAP superfamily proteins are most often secreted and have an extracellular endocrine or paracrine function and are involved in processes including the regulation of extracellular matrix and branching morphogenesis, potentially as either proteases or protease inhibitors; in ion channel regulation in fertility; as tumor suppressor or prooncogenic genes in tissues including the prostate; and in cell-cell adhesion during fertilization. This review describes mammalian CAP superfamily gene expression profiles, phylogenetic relationships, protein structural properties, and biological functions, and it draws into focus their potential role in health and disease. The nine subfamilies of the mammalian CAP superfamily include: the human glioma pathogenesis-related 1 (GLIPR1), Golgi associated pathogenesis related-1 (GAPR1) proteins, peptidase inhibitor 15 (PI15), peptidase inhibitor 16 (PI16), cysteine-rich secretory proteins (CRISPs), CRISP LCCL domain containing 1 (CRISPLD1), CRISP LCCL domain containing 2 (CRISPLD2), mannose receptor like and the R3H domain containing like proteins. We conclude that overall protein structural conservation within the CAP superfamily results in fundamentally similar functions for the CAP domain in all members, yet the diversity outside of this core region dramatically alters target specificity and, therefore, the biological consequences.

Enhancement of sperm-zona pellucida (ZP) binding capacity by activation of protein kinase A and C pathways in certain infertile men with defective sperm-ZP binding

BACKGROUND

Defective sperm-zona pellucida (ZP) binding (DSZPB) is a common cause of failure of fertilization in vitro. This study was to determine if DSZPB is caused by defective pathways upstream of protein kinase A (PKA) and C (PKC), or reduced protein tyrosine phosphorylation (TP).

METHODS

Infertile men with DSZPB and either normal sperm morphology (NSM) > or = 14% (n = 15) or < or =5% (n = 15) were studied. Sperm-ZP binding test was performed by incubation of motile sperm with oocytes for 2 h with or without dibutyryl cyclic AMP (dbcAMP, PKA activator) or phorbol myristate acetate (PMA, PKC activator). TP of capacitated sperm in medium was assessed by immunofluorescence with an anti-phosphotyrosine monoclonal antibody.

RESULTS

For normal sperm with normal sperm-ZP binding, both PMA and dbcAMP significantly enhanced sperm-ZP binding in a dose-response manner. Only dbcAMP, but not PMA, significantly increased TP of capacitated sperm. In DSZPB men with severe teratozoospermia (NSM < or = 5%), neither PMA nor dbcAMP enhanced sperm-ZP binding, despite dbcAMP significantly increasing the TP of capacitated sperm for all samples. In contrast, for DSZPB with NSM > or = 14%, PMA caused significantly increased sperm binding up to normal levels (> or =40 sperm bound/ZP) in five men, and dbcAMP had a similar result in two men. Again TP was significantly enhanced only by dbcAMP, but not by PMA.

CONCLUSIONS

There is defective signalling in pathways upstream of PKC and PKA in some men with DSZPB and normal semen analysis. Stimulation of TP by dbcAMP does not enhance sperm-ZP binding capacity in DSZPB men with low TP, regardless of sperm morphology.

Morphological and biochemical alterations of abalone testicular germ cells and spawned sperm and their fertilizing ability

In this study, we aimed to detect morphological and biochemical changes in developing germ cells (Gc), testicular sperm (Tsp), and spawned sperm (Ssp) using capacitation-associated characteristics. Gradual changes in the profiles of two membrane proteins, namely NaCl- and detergent-extractable proteins, were observed as compared Gc with Tsp and Tsp with Ssp. These membrane modifications were accomplished mostly through the introduction of new protein sets, both peripheral and integral, into Tsp and Ssp membranes. Activation of serine proteases, particularly in Ssp detergent-extracted proteins with the molecular masses of 38-130 kDa was evident and marked a major difference between Ssp and Tsp. An increase in the level of tyrosine phosphorylation of the proteins ranging from 15 to 20 kDa was noted in Tsp and remained constant in Ssp. Specifically, these three capacitation-associated characteristics could be detected in Ssp, possessing full fertilizing capacity. The lack of an activated proteolytic activity in Tsp resulted in a delayed fertilization, but not affected fertilizing ability. We believe that these characteristics should be advantageous in predicting abalone sperm fertilizing capability, particularly in cases when isolated germ cells or purified Tsp are used in place of spawned sperm in abalone aquaculture.

Increased activity of the human sperm tyrosine kinase SRC by the cAMP-dependent pathway in the presence of calcium

SRC-related tyrosine kinases are suggested to play a role in the increase of sperm protein phosphotyrosine content that occurs during capacitation. In our laboratory, we previously demonstrated that the SRC-related tyrosine kinase YES1 (also known as c-YES) is present in human spermatozoa. However, since it is negatively regulated by Ca(2+), whose intracellular concentration increases during capacitation, another kinase would most likely be involved in the capacitation-related increase in sperm protein tyrosine phosphorylation. The present study represents the first direct assessment of SRC tyrosine kinase activity in ejaculated mammalian sperm. By immunohistochemistry on human testis sections, it is clearly shown that SRC is expressed during spermatogenesis, mainly in round and elongating spermatids. Using an indirect immunofluorescence approach, SRC is detected in the acrosomal region of the head and in the sperm flagellum of ejaculated sperm. This tyrosine kinase is associated with the plasma membrane and with cytoskeletal elements, as suggested by its partial solubility in nonionic detergents. Despite its partial solubility, SRC kinase activity was assayed after immunoprecipitation using acid-denatured enolase as a substrate. It is clearly demonstrated that SRC activity is inhibited by SU6656 and PP1, selective SRC family tyrosine kinase inhibitors, and activated in a Ca(2+)-dependent manner. Furthermore, it is shown that SRC is activated in a cAMP/PRKA-dependent manner; SRC coimmunoprecipitates with the catalytic subunit of the cAMP-dependent protein kinase (PRKAC) and is phosphorylated by this latter kinase, resulting in an increase in enolase phosphorylation. All these results support the involvement of the tyrosine kinase SRC in the increase in sperm protein phosphotyrosine content observed during capacitation.

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.

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.

The influence of fluorides on mouse sperm capacitation

Increasing infertility, due to pathological changes on sperm, has become a serious issue. Eco-toxicological effect of rising concentration of fluorides can be enhanced in the presence of aluminium ions by forming fluorometallic complexes, analogues of phosphate groups that interfere with the activity of G-proteins and P-type ATPases, which are part of several signalling pathways during sperm maturation. In order for sperm to gain fertilizing ability, they must undergo in the female reproductive tract, capacitation that includes tyrosine phosphorylation and consequent actin polymerization. The present paper reports the findings of 3-month oral toxicity in mice of fluorides at the concentrations 0, 1, 10, and 100ppm and their synergic action with aluminium at dose of 10ppm. There were no mortalities, clinical signs of discomfort or body weight loss during the experiment. The analysis revealed, for the concentrations of 10 and 100ppm, abnormalities of spermatogenesis and ability of epididymal spermatozoa to capacitate in vitro, as the result of decreased sperm head tyrosine phosphorylation and actin polymerization. The enhancing overload caused by fluorides represents a potential factor, having an impact on function of sperm, hence contributing to a growing infertility in the human population.

Proteomic changes in mammalian spermatozoa during epididymal maturation

Epididymal maturation is associated with the activation of a cAMP-induced tyrosine phosphorylation cascade, which is ultimately associated with the expression of capacitation-dependent sperm functions, such as hyperactivated movement and acrosomal exocytosis. As spermatozoa progress through the epididymis they first acquire the capacity to phosphorylate tyrosine on targets on the principal piece, followed by the midpiece. By the time these cells have reached the cauda epididymidis they can phosphorylate the entire tail from neck to endpiece. This particular pattern of phosphorylation is associated with the ontogeny of fully functional spermatozoa that are capable of fertilizing the oocyte. Proteomic analyses indicate that this change is associated with the phosphorylation of several mitochondrial proteins, creation of a mitochondrial membrane potential and activation of mitochondrial free radical generation. At least in rodent species, activation of sperm mitochondria appears to be a particularly important part of epididymal maturation.

Protein tyrosine phosphorylation of a heparin-binding sperm membrane mitogen (HBSM) is associated with capacitation and acrosome reaction

Protein tyrosine phosphorylation in spermatozoa is associated with epididymal maturation and though to be central for attainment of a capacitated state and expression of hyperactivated motility. Heparin, the most highly sulfated glycosaminoglycans, was also the most potent at stimulating the acrosomal reaction in bovine epididymal spermatozoa. Studies using radiolabeled inorganic phosphate showed 11-fold increase (32)Pi incorporation in heparin-binding sperm membrane protein (HBSM) during spermatozoal capacitation, and the phosphorylation occurs at the tyrosine residue. Epididymal spermatozoa were induced to undergo capacitation and acrosome reaction by 70% when the cells were incubated in BWW medium supplemented with heparin. The spermatozoa pre-treated with anti-HBSM antibody showed 46% reduction in the hyperactivated motility and lowers the acrosome reaction. This was confirms by measuring the hydrolysis of benzoyl-l-arginine ethyl ether (BAEE) by the acrosomal enzyme; acrosin. The preliminary finding suggests that HBSM may play an important role in the sperm capacitation and acrosome reaction.

Cumulus oophorus-associated glycodelin-C displaces sperm-bound glycodelin-A and -F and stimulates spermatozoa-zona pellucida binding

Spermatozoa have to swim through the oviduct and the cumulus oophorus before fertilization in vivo. In the oviduct, spermatozoa are exposed to glycodelin-A and -F that inhibit spermatozoa-zona pellucida binding. In this study, we determined whether these glycodelins would inhibit fertilization. The data showed that the spermatozoa without previous exposure to glycodelin-A and -F acquired glycodelin immunoreactivity during their passage through the cumulus oophorus. On the other hand, when glycodelin-A or -F-pretreated spermatozoa were exposed to the cumulus oophorus, the zona pellucida binding inhibitory activity of glycodelin-A and -F was not only removed, but the spermatozoa acquired enhanced zona pellucida binding ability. These actions of the cumulus oophorus were due to the presence of a cumulus isoform of glycodelin, designated as glycodelin-C. The cumulus cells could convert exogenous glycodelin-A and -F to glycodelin-C, which was then released into the surrounding medium. The protein core of glycodelin-C was identical to that in other glycodelin isoforms, as demonstrated by mass spectrum, peptide mapping, and affinity to anti-glycodelin antibody recognizing the protein core of glycodelin. In addition to having a smaller size and a higher isoelectric point, glycodelin-C also had lectin binding properties different from other isoforms. Glycodelin-C stimulated spermatozoazona pellucida binding in a dose-dependent manner, and it effectively displaced sperm-bound glycodelin-A and -F. In conclusion, the cumulus cells transform glycodelin-A and -F to glycodelin-C, which in turn removes the spermatozoazona binding inhibitory glycodelin isoforms and enhances the zona binding capacity of spermatozoa passing through the cumulus oophorus.

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

Numerous sperm proteins have been identified on the basis of their increase in tyrosine phosphorylation during capacitation. However, the tyrosine kinases present in spermatozoa that are responsible for this phosphorylation remain unknown. As spermatozoa are devoid of transcriptional and translational activities, molecular biology approaches might not reflect the transcriptional pattern in mature spermatozoa. Working directly with the proteins present in ejaculated spermatozoa is the most reliable approach to identify the tyrosine kinases potentially involved in the capacitation-associated increase in protein tyrosine phosphorylation. A combination of tyrosine kinase assays and proteomic identification tools were used as an approach to identify sperm protein tyrosine kinases. Fractionation by nitrogen cavitation showed that the majority of tyrosine kinase activity is present in the cytosolic fraction of bovine spermatozoa. By the use of Poly-Glu:Tyr(4:1)-agarose affinity chromatography, we isolated a fraction enriched in tyrosine kinase activity. Proteomics approaches permitted the identification of tyrosine kinases from three families: Src (Lyn), Csk, and Tec (Bmx, Btk). We also identified proteins implicated in different cellular events associated with sperm capacitation and acrosome reaction. These results confirm the implication of tyrosine phosphorylation in some aspects of capacitation/acrosome reaction and reveal the identity of new players potentially involved in these processes.

Ontogeny of Tyrosine Phosphorylation-Signaling Pathways During Spermatogenesis and Epididymal Maturation in the Mouse1

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.

Identification of SRC as a key PKA-stimulated tyrosine kinase involved in the capacitation-associated hyperactivation of murine spermatozoa

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.

The Identification of Mouse Sperm-Surface-Associated Proteins and Characterization of Their Ability to Act as Decapacitation Factors1

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.

Evidence for the involvement of PECAM-1 in a receptor mediated signal-transduction pathway regulating capacitation-associated tyrosine phosphorylation in human spermatozoa

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.

Tyrosine phosphorylation on capacitated human sperm tail detected by immunofluorescence correlates strongly with sperm-zona pellucida (ZP) binding but not with the ZP-induced acrosome reaction

BACKGROUND

Protein tyrosine phosphorylation (TP) of human sperm is related to sperm capacitation and zona pellucida (ZP) binding. The aim of this study was to determine whether the TP of capacitated sperm is a useful marker for the ability of sperm to bind to the ZP and undergo the ZP-induced acrosome reaction (AR).

METHODS

Semen samples were obtained from 115 subfertile men with sperm count > or =20 x 10(6)/ml, motility > or =25% and variable morphology. Motile sperm (2 x 10(6)/ml) selected by swim-up were incubated with four oocytes for 2 h, and the number of sperm bound to the ZP and the ZP-induced AR was examined. TP of sperm tail was assessed by immunofluorescence (IF) with anti-phosphotyrosine monoclonal antibody. The time course and effects of dibutyryl cyclic adenosine monophosphate (dbcAMP) and phorbol myristate acetate (PMA) on TP were also studied.

RESULTS

TP was stimulated more by dbcAMP (P < 0.001) and less by PMA (P < 0.05). TP increased significantly with time of incubation of sperm. TP was not detectable on the surface of unfixed live sperm by either Dynabeads or IF. Sperm TP at 2, 4 and 20 h incubation was all significantly correlated with sperm-ZP binding but not with the ZP-induced AR.

CONCLUSION

Sperm TP detected by IF correlates strongly with sperm-ZP binding capacity but not with the ZP-induced AR. This simple IF assay of TP may be a clinically useful test of sperm function that is predictive of normal sperm ZP-binding capacity.

Dynamic quantification of the tyrosine phosphorylation of the sperm surface proteins during capacitation

BACKGROUND

Spermatozoa acquire active fertilizing competence only after deposition in the female tract and subsequent capacitation. Recent studies on the cellular location of major sperm phosphoproteins suggest that capacitation is associated with tyrosine phosphorylation of proteins exposed on the sperm surface. However, these changes have not yet been quantified objectively. A calcium influx seems to be required for the completion of tyrosine phosphorylation in some species; however, the exact temporal coordination between these processes is still poorly understood.

METHODS

Flow cytometry was used to quantify the degree of phosphorylation of the sperm surface proteins by probing with fluorescein isothiocyanate-conjugated anti-phosphotyrosine (pY) antibody raised in mouse. Dynamic changes in other sperm parameters (calcium influx, membrane integrity, and spontaneous acrosome reaction) were assessed to analyze their temporal coordination.

RESULTS

: The changes in specific phosphotyrosine (pY) fluorescence signal detected in live, nonpermeabilized boar cell suspensions were biphasic during incubation under capacitating conditions. After 120 min of incubation, the degree of pY fluorescence increased threefold, indicating the changes in proteins exposed on sperm surface. At the same time there was a gradual increase in cytosolic calcium ion levels with the maximal rate at 60 min of incubation. This rate slowed immediately before the onset of the massive rise in tyrosine phosphorylation and decreased by 90% after its completion. The integrity of plasma and acrosome membranes decreased only slowly, illustrating that the changes observed were not due to the process of spontaneous acrosome reaction.

CONCLUSIONS

These data provide quantitative evidence for the appearance of tyrosine-phosphorylated proteins on the surface of live boar spermatozoa during capacitation. An exact temporal coordination exists between cytosolic calcium ion content and protein tyrosine phosphorylation under these conditions. This novel approach has the advantage of making possible a precise quantification and kinetic comparison of molecular processes in different cell subpopulations.

FGFR-1 [corrected] signaling is involved in spermiogenesis and sperm capacitation

Cloning of the fibroblast growth factor receptor (FGFR) adaptor Snt-2 cDNA and the identification of FGFR-1 protein in association with sperm tails, suggested that FGFR-1 signaling was involved in either sperm tail development or function. This hypothesis was tested by the creation of transgenic mice that specifically expressed a dominant-negative variant of FGFR-1 in male haploid germ cells. Mating of transgenic mice showed a significant reduction in pups per litter compared with wild-type littermates. Further analysis demonstrated that this subfertility was driven by a combination of reduced daily sperm output and a severely compromised ability of those sperm that were produced to undergo capacitation prior to fertilization. An analysis of key signal transduction proteins indicated that FGFR-1 is functional on wild-type sperm and probably signals via the phosphatidylinositol 3-kinase pathway. FGFR-1 activation also resulted in the downstream suppression of mitogen activated protein kinase signaling. These data demonstrate the FGFR-1 is required for quantitatively and qualitatively normal spermatogenesis and has a key role in the regulation of the global tyrosine phosphorylation events associated with sperm capacitation.