Evidence that proteolysis of the surface is an initial step in the mechanism of formation of sperm cell surface domains

Review: The role of male reproductive tract secretions in ruminant fertility

Male fertility largely depends on the ability to produce sperm that can transmit the paternal information onto the next generation. However, the factors that are critical for sperm function and the subsequent development of healthy offspring are still not completely understood in ruminants. Importantly, sperm function is not completely encoded by germ cell DNA, but rather, depends on sequential acquisition, loss, and modification of elements through interaction with secretions from the testes, epididymides, and accessory glands (collectively termed seminal plasma). In addition, these secretions can play a role in the inheritance of paternal environmental effects by progeny. This is likely achieved directly, by the regulation of sperm epigenetic effectors, and indirectly, by altering the female environment in which the individual develops. This review will provide an overview of the different organs that contribute to seminal plasma in ruminants, and summarise how their secretions shape sperm function and modulate the female reproductive tract. Finally, some consideration will be given to the potential of paternal factors to affect embryo development and offspring health in ruminants.

Molecular perspective concerning fluoride and arsenic mediated disorders on epididymal maturation of spermatozoa: A concise review

Epididymis is a complex tubular structure of male reproductive system where spermatozoa undergo maturation and gain the fertilizing ability. Epididymal pseudostratified columnar epithelium with different cell types play imperative role by their secretory properties and enrich the luminal microenvironment necessary for achieving spermatozoal motility. During epididymal transit several secretory proteins like P26h, SPAG11, HSPD1 and many others are deposited on spermatozoal surface. At the same time spermatozoal proteins are also modified in this intraluminal milieu, which include cyritestin, fertilin, CE9 and others. Natural and anthropogenic activities disclose various environmental pollutants which affect different physiological systems of animals and human being. Likewise, reproductive system is also being affected. Fluoride causes structural alterations of caput and cauda segments of epididymis. Redox homeostasis and functional integrity are also altered due to diminished activities of SOD1, GR, Crisp2, Lrp2 and other important proteins. On the contrary arsenic affects mostly on cauda segment. Redox imbalance and functional amendment in epididymis have been observed with arsenic revelation as evidenced by altered genomic appearance of SOD, GST, catalase, Ddx3Y, VEGF and VEGFR2. This review is dealt with structure-function interplay in normal epididymal spermatozoal maturation along with subsequent complications developed under fluoride and arsenic toxicities.

Differential Expression in Testis and Liver Transcriptomes from Four Species of Peromyscus (Rodentia: Cricetidae)

The genus Peromyscus represents a rapidly diverged clade of Cricetid rodents that contains multiple cryptic species and has a propensity for morphologic conservation across its members. The unresolved relationships in previously proposed phylogenies reflect a suspected rapid adaptive radiation. To identify functional groups of genes that may be important in reproductive isolation in a reoccurring fashion across the Peromyscus phylogeny, liver and testis transcriptomes from four species (P. attwateri, P. boylii, P. leucopus, and P. maniculatus) were generated and differential expression (DE) tests were conducted. Taxa were selected to represent members diverged from a common ancestor: P. attwateri + P. boylii (clade A), and P. leucopus + P. maniculatus (clade B). Comparison of clades (A vs. B) suggested that 252 transcripts had significant DE in the liver data set, whereas significant DE was identified for 657 transcripts in the testis data set. Further, 45 genes had DE isoforms in the 657 testis transcripts and most of these functioned in major reproductive roles such as acrosome assembly, spermatogenesis, and cell cycle processes (meiosis). DE transcripts in the liver mapped to more broad gene ontology terms (metabolic processes, catabolic processes, response to chemical, and regulatory processes), and DE transcripts in the testis mapped to gene ontology terms associated with reproductive processes, such as meiosis, sperm motility, acrosome assembly, and sperm–egg fusion. These results suggest that a suite of genes that conduct similar functions in the testes may be responsible for the adaptive radiation events and potential reoccurring speciation of Peromyscus in terms of reproduction through varying expression levels.

SPATC1L maintains the integrity of the sperm head-tail junction

Spermatogenesis is a tightly regulated process involving germ cell-specific and germ cell-predominant genes. Here we investigate a novel germ cell-specific gene, Spatc1l (spermatogenesis and centriole associated 1 like). Expression analyses show that SPATC1L is expressed in mouse and human testes. We find that mouse SPATC1L localizes to the neck region in testicular sperm. Moreover, SPATC1L associates with the regulatory subunit of protein kinase A (PKA). Using CRISPR/Cas9-mediated genome engineering, we generate mice lacking SPATC1L. Disruption of Spatc1l in mice leads to male sterility owing to separation of sperm heads from tails. The lack of SPATC1L is associated with a reduction in PKA activity in testicular sperm, and we identify capping protein muscle Z-line beta as a candidate target of phosphorylation by PKA in testis. Taken together, our results implicate the SPATC1L-PKA complex in maintaining the stability of the sperm head-tail junction, thereby revealing a new molecular basis for sperm head-tail integrity.

Characterization of MAGEG2 with testis-specific expression in mice

Male germ cell development is a well-defined process occurring in numerous seminiferous tubules of the testis. Uncovering testicular novel genes related to intrinsic regulation of spermatogenesis is essential for the understanding of spermatogenesis. In the present study, we investigated mouse Mageg2, which belongs to a group of melanoma-associated antigens (MAGEs). Mageg2 is transcribed in the testis specifically, and its expression level is increased at the pachytene spermatocyte stage, indicating that Mageg2 is expressed predominantly in germ cells. We generated an antibody against mouse MAGEG2 for further characterization at the protein level. Immunoblot analysis suggested that MAGEG2 has specific testicular expression and the expression primarily occurred in pachytene spermatocytes. Proteomic analyses demonstrated that mouse MAGEG2 binded to testicular germ cell-specific serine/threonine-protein kinase 31 (STK31) and heat shock protein 9 (HSPA9). Direct binding with both interaction partners was confirmed by co-immunoprecipitation. We found that STK31 and HSPA9 bind MAGEG2 directly but not with each other. Interestingly, MAGEG2 reduced the kinase activity of STK31. Our study suggests that mouse MAGEG2 has at least two functions, including chaperone activity related to HSPA9 and regulation of pachytene spermatocyte-specific kinase, STK31. Altogether, our results provide the first information about MAGEG2 at the transcript and protein levels and suggest its potential molecular functions.

Influence of antifertility agents Dutasteride and Nifedipine on CatSper gene level in epididymis during sperm maturation in BALB/c mice

Calcium (Ca²⁺) signaling is critical for successful fertilization. In spermatozoa, capacitation, hyperactivation of motility and the acrosome reaction are all mediated by increases in intracellular Ca²⁺ through CatSper (sperm-specific cation channel). The CatSper channel complex contains four pore-forming α subunits (CatSper1-4) and five accessory subunits called β, δ, ε, γ and ζ. Genetic deletion of any of the four CatSper genes in mice results in loss of hyperactivated motility and male infertility. Despite their vital role in male fertility, almost very little is known about influence of antifertility agents on CatSper gene expression in epididymis and epididymal spermatozoa. Therefore, we performed quantitative real-time qPCR analysis for CatSper expression in the epididymis and epididymal sperm of BALB/c mice after treatment with Dutasteride (DS), a dual 5-α reductase inhibitor and Nifedipine (NF) a calcium channel blocker as positive control. We observed that treatment with antifertility agents Dutasteride and Nifedipine induced significant decreases in the caput and cauda epididymal sperm counts, motility and fertility which could partly be attributed to alteration in the normal morphology of the sperm associated with downregulation/upregulation of CatSper mRNAs in epididymis and epididymal spermatozoa of male BALB/c mice. These can be explained on the basis of interference with mechanisms affecting calcium ion signaling resulting in changes in intracellular calcium required for sperm activity, finally affecting sperm maturation and fertility of male BALB/c mice. These studies provide some novel avenues for developing new male contraceptives in future.

Expression of uncharacterized male germ cell-specific genes and discovery of novel sperm-tail proteins in mice

The identification and characterization of germ cell-specific genes are essential if we hope to comprehensively understand the mechanisms of spermatogenesis and fertilization. Here, we searched the mouse UniGene databases and identified 13 novel genes as being putatively testis-specific or -predominant. Our in silico and in vitro analyses revealed that the expressions of these genes are testis- and germ cell-specific, and that they are regulated in a stage-specific manner during spermatogenesis. We generated antibodies against the proteins encoded by seven of the genes to facilitate their characterization in male germ cells. Immunoblotting and immunofluorescence analyses revealed that one of these proteins was expressed only in testicular germ cells, three were expressed in both testicular germ cells and testicular sperm, and the remaining three were expressed in sperm of the testicular stages and in mature sperm from the epididymis. Further analysis of the latter three proteins showed that they were all associated with cytoskeletal structures in the sperm flagellum. Among them, MORN5, which is predicted to contain three MORN motifs, is conserved between mouse and human sperm. In conclusion, we herein identify 13 authentic genes with male germ cell-specific expression, and provide comprehensive information about these genes and their encoded products. Our finding will facilitate future investigations into the functional roles of these novel genes in spermatogenesis and sperm functions.

Proteome of the rete testis fluid from tropically-adapted Morada Nova rams

The rete testis has a close relationship with sperm development and may have other functions besides serving as an intercalated channel. The aim of this study was to identify and characterize the proteins of rete testis fluid (RTF) from tropically-adapted Morada Nova rams. Testicles obtained from six Morada Nova rams were dissected and the head of the epididymis was separated to access the efferent ducts. Rete testis fluid was obtained by gentle massage of the testis. The fluid was centrifuged to remove cell debris and sperm. RTF samples (containing 400μg protein) were separated by 2-D SDS-PAGE and gels, analyzed using PDQuest software (Bio Rad, USA). Proteins were identified using tandem mass spectrometry. Gene ontology and protein network were analyzed using the software tool for searching annotations of proteins (STRAP) and STRING database. Gels had, on average, 227±13.5 spots and 51% of the proteins were found above 40kDa, corresponding to 65% of the intensity of all spots detected. Based on gene ontology analysis, the most common biological processes associated with RTF proteins were regulation (24.3%) and cellular process (23.3%). Binding (27.3%) and catalytic activity (19.3%) corresponded to the most frequent molecular functions. Albumin, clusterin, serotransferrin, immunoglobulin gamma-1 chain and alpha-2-HS-glycoprotein were the most abundant proteins in the ram rete testis fluid. In conclusion, proteins identified in the ram rete testis fluid are linked to several physiological processes associated with sperm protection and spermatogenesis.

TEX13 is a novel male germ cell-specific nuclear protein potentially involved in transcriptional repression

The identification and characterization of male germ cell-specific genes is crucial to understanding the mechanisms of male germ cell development. In this study, we investigated the protein encoded by the novel mouse germ cell-specific gene testis-expressed gene 13 (Tex13). We found that TEX13 expression is testis- and germ cell-specific and is regulated in a stage-specific manner via translational repression. Immunostaining of testicular cells and sperm showed that TEX13 is localized in the nuclei of spermatogenic cells and the redundant nuclear envelope of mature sperm. Remarkably, we found that TEX13 possesses transcriptional repressor activity and that its overexpression in GC-2 cells altered the expression levels of 130 genes. Our results suggest that TEX13 has a potential role in transcriptional regulation during spermatogenesis.

Normal Fertility Requires the Expression of Carbonic Anhydrases II and IV in Sperm

HCO3 (-) is a key factor in the regulation of sperm motility. High concentrations of HCO3 (-) in the female genital tract induce an increase in sperm beat frequency, which speeds progress of the sperm through the female reproductive tract. Carbonic anhydrases (CA), which catalyze the reversible hydration of CO2 to HCO3 (-), represent potential candidates in the regulation of the HCO3 (-) homeostasis in sperm and the composition of the male and female genital tract fluids. We show that two CA isoforms, CAII and CAIV, are distributed along the epididymal epithelium and appear with the onset of puberty. Expression analyses reveal an up-regulation of CAII and CAIV in the different epididymal sections of the knockout lines. In sperm, we find that CAII is located in the principal piece, whereas CAIV is present in the plasma membrane of the entire sperm tail. CAII and CAIV single knockout animals display an imbalanced HCO3 (-) homeostasis, resulting in substantially reduced sperm motility, swimming speed, and HCO3 (-)-enhanced beat frequency. The CA activity remaining in the sperm of CAII- and CAIV-null mutants is 35% and 68% of that found in WT mice. Sperm of the double knockout mutant mice show responses to stimulus by HCO3 (-) or CO2 that were delayed in onset and reduced in magnitude. In comparison with sperm from CAII and CAIV double knockout animals, pharmacological loss of CAIV in sperm from CAII knockout animals, show an even lower response to HCO3 (-). These results suggest that CAII and CAIV are required for optimal fertilization.

Amyloid precursor protein interaction network in human testis: sentinel proteins for male reproduction

BACKGROUND

Amyloid precursor protein (APP) is widely recognized for playing a central role in Alzheimer's disease pathogenesis. Although APP is expressed in several tissues outside the human central nervous system, the functions of APP and its family members in other tissues are still poorly understood. APP is involved in several biological functions which might be potentially important for male fertility, such as cell adhesion, cell motility, signaling, and apoptosis. Furthermore, APP superfamily members are known to be associated with fertility. Knowledge on the protein networks of APP in human testis and spermatozoa will shed light on the function of APP in the male reproductive system.

RESULTS

We performed a Yeast Two-Hybrid screen and a database search to study the interaction network of APP in human testis and sperm. To gain insights into the role of APP superfamily members in fertility, the study was extended to APP-like protein 2 (APLP2). We analyzed several topological properties of the APP interaction network and the biological and physiological properties of the proteins in the APP interaction network were also specified by gene ontologyand pathways analyses. We classified significant features related to the human male reproduction for the APP interacting proteins and identified modules of proteins with similar functional roles which may show cooperative behavior for male fertility.

CONCLUSIONS

The present work provides the first report on the APP interactome in human testis. Our approach allowed the identification of novel interactions and recognition of key APP interacting proteins for male reproduction, particularly in sperm-oocyte interaction.

ADAM15 participates in fertilization through a physical interaction with acrogranin

Mammalian fertilization is completed by direct interaction between sperm and egg. This process is primarily mediated by both adhesion and membrane-fusion proteins found on the gamete surface. ADAM1, 2, and 3 are members of the ADAMs protein family, and have been involved in sperm–egg binding. In this study, we demonstrate the proteolytic processing of ADAM15 during epididymal maturation of guinea pig spermatozoa to produce a mature form a size of 45 kDa. We find that the size of the mature ADAM15, 45 kDa, in cauda epididymal spermatozoa indicates that the pro-domain and metalloprotease domain are absent. In addition, using indirect immunofluorescence, ADAM15 was found throughout the acrosome, at the equatorial region and along the flagellum of guinea pig spermatozoa. After acrosome reaction, ADAM15 is lost from the acrosomal region and retained in the equatorial region and flagellum. In this study, we also report the first evidence of a complex between ADAM15 and acrogranin. By immunoprecipitation, we detected a protein band of 65 kDa which co-immunoprecipated together ADAM15. Analysis of the N-terminal sequence of this 65 kDa protein has revealed its identity as acrogranin. In addition, using cell-surface labeling, ADAM15 was found to be present on the cell surface. Assays of heterologous fertilization showed that the antibody against acrogranin inhibited the sperm–egg adhesion. Interestingly, ADAM15 and acrogranin were also found associated in two breast cancer cell lines. In conclusion, our results demonstrated that ADAM15 and acrogranin are present on and associated with the surface of guinea pig spermatozoa; besides both proteins may play a role during sperm–egg binding.

Effects of hormones on the expression of matrix metalloproteinases and their inhibitors in bovine spermatozoa

Proteases and protease inhibitors play key roles in most physiological processes, including cell migration, cell signaling, and cell surface and tissue remodeling. Among these, the matrix metalloproteinase (MMPs) pathway is one of the most efficient biosynthetic pathways for controlling the activation of enzymes responsible for protein degradation. This also indicates the association of MMPs with the maturation of spermatozoa. In an attempt to investigate the effect of MMP activation and inhibitors in cultures with various hormones during sperm capacitation, we examined and monitored the localization and expression of MMPs (MMP-2 and MMP-9), tissue inhibitors of metalloproteinases (TIMP-2 and TIMP-3), as well as their expression profiles. Matured spermatozoa were collected from cultures with follicle-stimulating hormone (FSH), luteinizing hormone (LH), and Lutalyse at 1 h, 6 h, 18 h, and 24 h. ELISA detected the expression of MMP-2, MMP-9, TIMP-2, and TIMP-3 in all culture media, regardless of medium type (FSH-supplemented fertilization Brackett-Oliphant medium (FFBO), LH-supplemented FBO (LFBO), or Lutalyse-supplemented FBO (LuFBO)). TIMP-2 and TIMP-3 expression patterns decreased in LFBO and LuFBO. MMP-2 and MMP-9 activity in FBO and FFBO progressively increased from 1 h to 24 h but was not detected in LFBO and LuFBO. The localization and expression of TIMP-2 and TIMP-3 in sperm heads was also measured by immunofluorescence analysis. However, MMPs were not detected in the sperm heads. MMP and TIMP expression patterns differed according to the effect of various hormones. These findings suggest that MMPs have a role in sperm viability during capacitation. In conjunction with hormones, MMPs play a role in maintaining capacitation and fertilization by controlling extracellular matrix inhibitors of sperm.

Role of posttranslational protein modifications in epididymal sperm maturation and extracellular quality control

The epididymal lumen is a complex microenvironment in which spermatozoa acquire motility and fertility. Spermatozoa are synthetically inactive and therefore the maturation process requires their interaction with proteins that are synthesized and secreted in a highly regionalized manner by the epididymal epithelium. In addition to the integration of epididymal secretory proteins, posttranslational modifications of existing sperm proteins are important for sperm maturation and acquisition of fertilizing potential. Phosphorylation, glycosylation, and processing are several of the posttranslational modifications that sperm proteins undergo during epididymal transit resulting in changes in protein function and localization ultimately leading to mature spermatozoa. In addition to these well-characterized modifications, protein aggregation and cross-linking also occur within the epididymal lumen and may represent unique mechanisms for controlling protein function including that for maturation as well as for extracellular quality control.

Intracellular translocation and differential accumulation of cell-penetrating peptides in bovine spermatozoa: evaluation of efficient delivery vectors that do not compromise human sperm motility

STUDY QUESTION

Do cell penetrating peptides (CPPs) translocate into spermatozoa and, if so, could they be utilized to deliver a much larger protein cargo?

SUMMARY ANSWER

Chemically diverse polycationic CPPs rapidly and efficiently translocate into spermatozoa. They exhibit differential accumulation within intracellular compartments without detrimental influences upon cellular viability or motility but they are relatively ineffective in transporting larger proteins.

WHAT IS ALREADY KNOWN

Endocytosis, the prevalent route of protein internalization into eukaryotic cells, is severely compromised in mature spermatozoa. Thus, the translocation of many bioactive agents into sperm is relatively inefficient. However, the delivery of bioactive moieties into mature spermatozoa could be significantly improved by the identification and utility of an efficient and inert vectorial delivery technology.

STUDY DESIGN

CPP translocation efficacies, their subsequent differential intracellular distribution and the influence of peptides upon viability were determined in bovine spermatozoa. Temporal analyses of sperm motility in the presence of exogenously CPPs utilized normozoospermic human donor samples.

MATERIALS AND METHODS

CPPs were prepared by manual, automated and microwave-enhanced solid phase synthesis. Confocal fluorescence microscopy determined the intracellular distribution of rhodamine-conjugated CPPs in spermatozoa. Quantitative uptake and kinetic analyses compared the translocation efficacies of chemically diverse CPPs and conjugates of biotinylated CPPs and avidin. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) conversion assays were employed to analyse the influence of CPPs upon sperm cell viability and sperm class assays determined the impact of CPPs on motility in capacitated and non-capacitated human samples.

MAIN RESULTS

Chemically heterogeneous CPPs readily translocated into sperm to accumulate within discrete intracellular compartments. Mitoparan (INLKKLAKL(Aib)KKIL), for example, specifically accumulated within the mitochondria located in the sperm midpiece. The unique plasma membrane composition of sperm is a critical factor that directly influences the uptake efficacy of structurally diverse CPPs. No correlations in efficacies were observed when comparing CPP uptake into sperm with either uptake into fibroblasts or direct translocation across a phosphatidylcholine membrane. These comparative investigations identified C105Y (CSIPPEVKFNKPFVYLI) as a most efficient pharmacokinetic modifier for general applications in sperm biology. Significantly, CPP uptake induced no detrimental influence upon either bovine sperm viability or the motility of human sperm. As a consequence of the lack of endocytotic machinery, the CPP-mediated delivery of much larger protein complexes into sperm is relatively inefficient when compared with the similar process in fibroblasts.

LIMITATIONS, REASONS FOR CAUTION

It is possible that some CPPs could directly influence aspects of sperm biology and physiology that were not analysed in this study.

WIDER IMPLICATIONS OF THE FINDINGS

CPP technologies have significant potential to deliver selected bioactive moieties and so could modulate the biology and physiology of human sperm biology both prior- and post-fertilization.

Sperm Membrane Dynamics Assessed by Changes in Lectin Fluorescence Before and After Capacitation

Sperm capacitation is correlated with acquisition of fertilizing ability, and the molecular events underlying this process are only beginning to be understood. A number of membrane changes associated with capacitation have been documented. In this study we used lectin probes to identify changes in glycoprotein localization as a result of capacitation of mouse sperm. Eight lectins (LEA, PSA, PNA, AAA, UEA-1, WGA, STA, and TPA) stained regions of the mouse sperm head, tail, or both. No changes in tail staining patterns were detected when sperm were incubated under capacitating conditions. In contrast, 7 of 8 lectins tested showed clear shifts in staining patterns in the sperm head as a result of incubation under capacitating conditions. When staining patterns were quantified, a distinct heterogeneity within the sperm population was observed. Each lectin displayed 3 distinct staining patterns in both uncapacitated and capacitated sperm samples. The least common pattern represented the acrosome-reacted (AR) pattern, as independently assessed by lectin staining of ionophoretreated sperm that were >95% AR as judged by Coomassie staining. However, a reciprocal shift in the two predominant staining patterns was correlated with capacitation and suggests that changes in distribution of cell surface proteins during capacitation constitute part of the molecular changes which result in changes in sperm function acquired during this process.

Expression and function of the testis-predominant protein LYAR in mice

Mammalian spermatogenesis is a complex process involving an intrinsic genetic program of germ cell-specific and -predominant genes. In the present study, we analyzed the Ly-1 reactive clone (Lyar) gene in the mouse. Lyar, which is known to be expressed abundantly in the testis, encodes a nucleolar protein that contains a LYAR-type C2HC zinc finger motif and three nuclear localization signals. We herein confirmed that Lyar is expressed predominantly in the testis, and further showed that this expression is specific to germ cells. Protein analyses with an anti-LYAR antibody demonstrated that the LYAR protein is present in spermatocytes and spermatids, but not in sperm. To assess the functional role of LYAR in vivo, we used a genetrap mutagenesis approach to establish a LYAR-null mouse model. Lyar mutant mice were born live and developed normally. Male mutant mice lacking LYAR were fully fertile and showed intact spermatogenesis. Taken together, our results demonstrate that LYAR is strongly preferred in male germ cells, but has a dispensable role in spermatogenesis and fertility.

Glycocalyx characterisation and glycoprotein expression of Sus domesticus epididymal sperm surface samples

The sperm surface is covered with a dense coating of carbohydrate-rich molecules. Many of these molecules are involved in the acquisition of fertilising ability. In the present study, eight lectins (i.e. Arachis hypogae (peanut) agglutinin (PNA), Lens culimaris (lentil) agglutinin-A (LCA), Pisum sativum (pea) agglutin (PSA), Triticum vulgari (wheat) germ agglutinin (WGA), Helix pomatia agglutinin (HPA), Phaseolus vulgaris (red kidney bean) leucoagglutinin (PHA-L), Glycine max (soybean) agglutinin (SBA) and Ulex europaeus agglutinin I (UEA-I)) were investigated to identify changes in the nature and localisation of glycoproteins in boar spermatozoa migrating along the epididymal duct. Complementary procedures included measurement of global lectin binding over the surface of the viable sperm population by flow cytometry, analysis of lectin localisation on the membrane of individual spermatozoa using fluorescence microscopy and the electrophoretic characterisation of the major sperm surface glycoprotein receptors involved in lectin binding. A significant increase was found in sperm galactose, glucose/mannose and N-acetyl-d-glucosamine residues distally in the epididymis. Moreover, the sperm head, cytoplasmic droplet and midpiece were recognised by most of the lectins tested, whereas only HPA and WGA bound to the principal piece and end piece of the sperm tail. Fourteen sperm surface proteins were observed with different patterns of lectin expression between epididymal regions. The sperm glycocalyx modifications observed in the present study provide an insight into the molecular modifications associated with epididymal maturation, which may be correlated with the degree of maturation of ejaculated spermatozoa.

Identification and validation of mouse sperm proteins correlated with epididymal maturation

Sperm need to mature in the epididymis to become capable of fertilization. To understand the molecular mechanisms of mouse sperm maturation, we conducted a proteomic analysis using saturation dye labeling to identify proteins of caput and cauda epididymal sperm that exhibited differences in amounts or positions on two-dimensional gels. Of eight caput epididymal sperm-differential proteins, three were molecular chaperones and three were structural proteins. Of nine cauda epididymal sperm-differential proteins, six were enzymes of energy metabolism. To validate these proteins as markers of epididymal maturation, immunoblotting and immunofluorescence analyses were performed. During epididymal transit, heat shock protein 2 was eliminated with the cytoplasmic droplet and smooth muscle γ-actin exhibited reduced fluorescence from the anterior acrosome while the signal intensity of aldolase A increased, especially in the principal piece. Besides these changes, we observed protein spots, such as glutathione S-transferase mu 5 and the E2 component of pyruvate dehydrogenase complex, shifting to more basic isoelectric points, suggesting post-translational changes such dephosphorylation occur during epididymal maturation. We conclude that most caput epididymal sperm-differential proteins contribute to the functional modification of sperm structures and that many cauda epididymal sperm-differential proteins are involved in ATP production that promotes sperm functions such as motility.

Expression, immunolocalization and processing of fertilins ADAM-1 and ADAM-2 in the boar (Sus domesticus) spermatozoa during epididymal maturation

Fertilin alpha (ADAM-1) and beta (ADAM-2) are integral membrane proteins of the ADAM family that form a fertilin complex involved in key steps of the sperm-oocyte membrane interaction. In the present work, we analyzed the presence of ADAM-1 and ADAM-2 mRNAs, the spermatozoa proteins' processing and their sub-cellular localization in epididymal samples from adult boars. ADAM-1 and ADAM-2 mRNAs were highly produced in the testis, but also in the vas efferens and the epididymis. On immunoblots of sperm extracts, ADAM-1 subunit appeared as a main reactive band of ~50-55 kDa corresponding to occurrence of different isoforms throughout the epididymal duct, especially in the corpus region where isoforms ranged from acidic to basic pI. In contrast, ADAM-2 was detected as several bands of ~90 kDa, ~75 kDa, ~50-55 kDa and ~40 kDa. The intensity of high molecular mass bands decreased progressively in the distal corpus where lower bands were also transiently observed, and only the ~40 kDa was observed in the cauda. The presence of bands of different molecular weights likely results from a proteolytic processing occurring mainly in the testis for ADAM-1, and also throughout the caput epididymis for ADAM-2. Immunolocalization showed that fertilin migrates from the acrosomal region to the acrosomal ridge during the sperm transit from the distal corpus to the proximal cauda. This migration is accompanied by an important change in the extractability of a part of ADAM-1 from the sperm membrane. This suggests that the fertilin surface migration may be triggered by the biochemical changes induced by the epididymal post-translational processing of both ADAM1 and ADAM-2. Different patterns of fertilin immunolocalization then define several populations of spermatozoa in the cauda epididymis. Characterization of such fertilin complex maturation patterns is an important step to develop fertility markers based on epididymal maturation of surface membrane proteins in domestic mammals.

Impaired spermatogenesis and fertility in mice carrying a mutation in the Spink2 gene expressed predominantly in testes

Spermatogenesis is a complex process involving an intrinsic genetic program composed of germ cell-specific and -predominant genes. In this study, we investigated the mouse Spink2 (serine protease inhibitor Kazal-type 2) gene, which belongs to the SPINK family of proteins characterized by the presence of a Kazal-type serine protease inhibitor-pancreatic secretory trypsin inhibitor domain. We showed that recombinant mouse SPINK2 has trypsin-inhibitory activity. Distribution analyses revealed that Spink2 is transcribed strongly in the testis and weakly in the epididymis, but is not detected in other mouse tissues. Expression of Spink2 is specific to germ cells in the testis and is first evident at the pachytene spermatocyte stage. Immunoblot analyses demonstrated that SPINK2 protein is present in male germ cells at all developmental stages, including in testicular spermatogenic cells, testicular sperm, and mature sperm. To elucidate the functional role of SPINK2 in vivo, we generated mutant mice with diminished levels of SPINK2 using a gene trap mutagenesis approach. Mutant male mice exhibit significantly impaired fertility; further phenotypic analyses revealed that testicular integrity is disrupted, resulting in a reduction in sperm number. Moreover, we found that testes from mutant mice exhibit abnormal spermatogenesis and germ cell apoptosis accompanied by elevated serine protease activity. Our studies thus provide the first demonstration that SPINK2 is required for maintaining normal spermatogenesis and potentially regulates serine protease-mediated apoptosis in male germ cells.

Characterization of mouse sperm TMEM190, a small transmembrane protein with the trefoil domain: evidence for co-localization with IZUMO1 and complex formation with other sperm proteins

TMEM190, a small transmembrane protein containing the trefoil domain, was previously identified by our proteomic analysis of mouse sperm. Two structural features of TMEM190, ‘trefoil domain’ and ‘small transmembrane protein’, led us to hypothesize that this protein forms a protein–protein complex required during fertilization, and we characterized TMEM190 by biochemical, cytological, and genetic approaches. We showed in this study that the mouse Tmem190 gene exhibits testis-specific mRNA expression and that the encoded RNA is translated into a 19-kDa protein found in both testicular germ cells and cauda epididymal sperm. Treatment of the cell surface with proteinase K, subcellular fractionation, and immunofluorescence assay all revealed that mouse TMEM190 is an inner-acrosomal membrane protein of cauda epididymal sperm. During the acrosome reaction, TMEM190 partly relocated onto the surface of the equatorial segment, on which sperm–oocyte fusion occurs. Moreover, TMEM190 and IZUMO1, which is an immunoglobulin-like protein required for gamete fusion, co-localized in mouse sperm both before and after the acrosome reaction. However, immunoprecipitates of TMEM190 contained several sperm proteins, but did not include IZUMO1. These findings suggest that a mouse sperm protein complex(es) including TMEM190 plays an indirect role(s) in sperm–oocyte fusion. The role(s), if any, is probably dispensable since Tmem190-null male mice were normally fertile.

The annulus of the mouse sperm tail is required to establish a membrane diffusion barrier that is engaged during the late steps of spermiogenesis

The annulus is a higher order septin cytoskeletal structure located between the midpiece and principal piece regions of the sperm tail. The annulus has been hypothesized to generate the diffusion barrier that exists between these two membrane domains. We tested this premise directly on septin 4 knockout mice, whose sperm are viable but lack an annulus, by following the diffusing membrane protein basigin. Basigin is normally confined to the principal piece domain on testicular and caput sperm, but undergoes relocation into the midpiece during sperm epididymal transit. On Sept4(-/-) sperm, domain confinement was lost, and basigin localized over the entire plasma membrane. Both immunofluorescence and immunoblotting further revealed reduced levels of basigin expression on sperm from the knockout. Testicular immunohistochemistry showed similar basigin expression and tail targeting in wild-type (WT) and Sept4(-/-) tubules until step 15 of spermatid development, at which point basigin was redistributed throughout the plasma membrane of Sept4(-/-) spermatids. The basigin outside of the tail was subsequently lost around the time of sperm release into the lumen. The redistribution in the knockout coincides with the time in WT sperm when the annulus completes its migration from the neck down to the midpiece-principal piece junction. We posit that basigin may not diffuse freely until after the annulus arrives at the midpiece-principal piece junction to restrict lateral movement. These results are the strongest evidence to date of a mammalian septin structure establishing a membrane diffusion barrier.

The glycosylphosphatidylinositol-anchored serine protease PRSS21 (testisin) imparts murine epididymal sperm cell maturation and fertilizing ability

An estimated 25%-40% of infertile men have idiopathic infertility associated with deficient sperm numbers and quality. Here, we identify the membrane-anchored serine protease PRSS21, also known as testisin, to be a novel proteolytic factor that directs epididymal sperm cell maturation and sperm-fertilizing ability. PRSS21-deficient spermatozoa show decreased motility, angulated and curled tails, fragile necks, and dramatically increased susceptibility to decapitation. These defects reflect aberrant maturation during passage through the epididymis, because histological and electron microscopic structural analyses showed an increased tendency for curled and detached tails as spermatozoa transit from the corpus to the cauda epididymis. Cauda epididymal spermatozoa deficient in PRSS21 fail to mount a swelling response when exposed to hypotonic conditions, suggesting an impaired ability to respond to osmotic challenges facing maturing spermatozoa in the female reproductive tract. These data suggest that aberrant regulation of PRSS21 may underlie certain secondary male infertility syndromes, such as "easily decapitated" spermatozoa in humans.

The epididymal influence on sperm maturation

Consideration of the function of the epididymis has undergone profound changes over the last century during which it has moved from a largely neglected male reproductive organ to one that is an increasingly exploited source of sperm for assisted reproduction strategies. From histological studies in the lizard1 it was considered that, ‘…the cells lining the epididymal canal produce a material necessary for the spermatozoa during their passage through the organ …’ whereas a fertility study with guinea-pigs stated boldly that, ‘… changes undergone [by spermatozoa in the epididymis] are not conditioned by some specific action of epididymal secretion …’. The former view found favour in a review of the literature which concluded that, ‘… there are specific epididymal secretions necessary for sperm maturation and survival …’, although the nature of the secretions were not then known. However, this concept, currently held by most of those studying the epididymis of animals, was again contradicted on the basis of clinical work: ‘… it certainly is possible for sperm that have never passed through any length of the epididymis at all to mature on their own …’.

Molecular biology of sperm maturation in the human epididymis

Male infertility is a frequent cause of childlessness, and, indeed, a comparison of the contributions to conception failure made by male and female factors shows them to be equally frequent. In practice, male infertility appears to be resistant to most treatments. However, the major reason for this may be that often attempts are carried out without knowing the cause of the problem. Unlike in women, obstructions and hormonal disorders are rare in male infertility. Rather, it would appear that sperm disorders are the most common cause, reflecting a variety of pathogenetic mechanisms. Defects in sperm morphology, defective sperm movement, deficient development or functional failure of the acrosome, and the excessive generation of reactive oxygen species are changes that are often seen in infertile semen, but little is known about their aetiology. In 5–10% of men being treated for infertilty, an autoimmune reaction against spermatozoa is observed. Although the correlation between the presence of systemic antisperm antibodies and fertility potential is poor, the appearance of sperm-bound antibodies of immunoglobulin class IgA in semen seems to be closely associated with infertility. Studies in laboratory animals and humans have shown that complementary adhesion molecules are located on the surface of oocytes and spermatozoa. These molecules interact and lead to gamete fusion. Abnormalities in these molecules on the sperm surface might be expected to contribute to male infertility. However, their clinical significance has not yet been documented, and the molecular basis of human gamete interaction is far from being understood. Therefore, the key to understanding male infertility may lie in basic research which directly targets the fundamental cellular and molecular biology of the human spermatozoon.

Polymeric ADAM protein mimics interrogate mammalian sperm-egg binding

The sperm proteins ADAM2 and ADAM3, members of the ADAM family of proteins, have been implicated in mammalian sperm-egg binding. However, elucidating their roles is complex because of the interdependence of ADAM protein expression in the testis. Hence, multivalent probes containing the three-amino acid binding sequence of ADAM2, glutamate-cysteine-aspartate (ECD), and ADAM3, glutamine-cysteine-aspartate (QCD), were designed, synthesized, and tested to investigate gamete interactions. In this work, ECD polymer mimics were synthesized by ring-opening metathesis polymerization with a faster initiating ruthenium catalyst than previously used. Polymers containing 100 copies of the ECD peptide mimic were found to be the best inhibitors of fertilization. The multivalent QCD polymers were also tested as inhibitors of fertilization. The structure-activity profile was the same as ECD polymers, but the overall potency was lower. Both ECD and QCD polymers require the presence of beta(1) integrin to inhibit fertilization. Next, triblock ABA and ABC copolymers containing both ECD and QCD ligands were synthesized with 96 monomer spacers as their B blocks. Although these polymers had lower densities of ECD and QCD peptides, their potencies correlated with the potencies of their corresponding homopolymers. In addition, no synergy between ECD and QCD mimics was observed. All the data suggest that QCD and ECD bind to the same complex of proteins that includes beta(1) integrin.

New insights into epididymal biology and function

BACKGROUND

The epididymis performs an important role in the maturation of spermatozoa including their acquisition of progressive motility and fertilizing ability. However, the molecular mechanisms that govern these maturational events are still poorly defined. This review focuses on recent progress in our understanding of epididymal function including its development, role of the luminal microenvironment in sperm maturation, regulation and novel mechanisms the epididymis utilizes to carry out some of its functions.

METHODS

A systematic search of Pubmed was carried out using the search term 'epididymis'. Articles that were published in the English language until the end of August 2008 and that focused on the specific topics described above were included. Additional papers cited in the primary reference were also included.

RESULTS

While the majority of these findings were the result of studies in animal models, recent studies in the human epididymis are also presented including gene profiling studies to examine regionalized expression in normal epididymides as well as in those from vasectomized patients.

CONCLUSIONS

Significant progress has been made in our understanding of epididymal function providing new insights that ultimately could improve human health. The data also indicate that the human epididymis plays an important role in sperm maturation but has unique properties compared with animal models.

Comprehensive analysis of reproductive ADAMs: relationship of ADAM4 and ADAM6 with an ADAM complex required for fertilization in mice

A Disintegrin And Metalloprotease (ADAM) family members expressed in male reproductive tissues are divided phylogenetically into three major groups. In the present study, we analyzed six ADAMs in one of the groups (ADAMs 4, 6, 24, 26, 29, and 30) of which function is largely unknown. Our results showed that most of the ADAMs undergo unique processing during sperm maturation and are located at the surface of sperm head. We found that the levels of ADAM4 and ADAM6 are dramatically reduced in Adam2 and Adam3 knockout sperm defective in various fertilization processes. We observed premature processing of ADAM4 in the Adam3-null mice. Furthermore, we obtained a result showing complex formation of ADAM6 with ADAM2 and ADAM3 in testis. Taken together, these results disclose involvement of ADAM4 and ADAM6 in a reproductive ADAM system that functions in fertilization.

A novel germ cell-specific protein, SHIP1, forms a complex with chromatin remodeling activity during spermatogenesis

To determine the mechanisms of spermatogenesis, it is essential to identify and characterize germ cell-specific genes. Here we describe a protein encoded by a novel germ cell-specific gene, Mm.290718/ZFP541, identified from the mouse spermatocyte UniGene library. The protein contains specific motifs and domains potentially involved in DNA binding and chromatin reorganization. An antibody against Mm.290718/ZFP541 revealed the existence of the protein in testicular spermatogenic cells (159 kDa) but not testicular and mature sperm. Immunostaining analysis of cells at various stages of spermatogenesis consistently showed that the protein is present in spermatocytes and round spermatids only. Transfection assays and immunofluorescence studies indicate that the protein is localized specifically in the nucleus. Proteomic analyses performed to explore the functional characteristics of Mm.290718/ZFP541 showed that the protein forms a unique complex. Other major components of the complex included histone deacetylase 1 (HDAC1) and heat-shock protein A2. Disappearance of Mm.290718/ZFP541 was highly correlated with hyperacetylation in spermatids during spermatogenesis, and specific domains of the protein were involved in the regulation of interactions and nuclear localization of HDAC1. Furthermore, we found that premature hyperacetylation, induced by an HDAC inhibitor, is associated with an alteration in the integrity of Mm.290718/ZFP541 in spermatogenic cells. Our results collectively suggest that the Mm.290718/ZFP541 complex is implicated in chromatin remodeling during spermatogenesis, and we provide further information on the previously unknown molecular mechanism. Consequently, we re-designate Mm.290718/ZFP541 as "SHIP1" representing spermatogenic cell HDAC-interacting protein 1.

Characterization of eight novel proteins with male germ cell-specific expression in mouse

BACKGROUND

Spermatogenesis and fertilization are highly unique processes. Discovery and characterization of germ cell-specific genes are important for the understanding of these reproductive processes. We investigated eight proteins encoded by novel spermatogenic cell-specific genes previously identified from the mouse round spermatid UniGene library.

METHODS

Polyclonal antibodies were generated against the novel proteins and western blot analysis was performed with various protein samples. Germ cell specificity was investigated using testes from germ cell-less mutant mice. Developmental expression pattern was examined in testicular germ cells, testicular sperm and mature sperm. Subcellular localization was assessed by cell surface biotin labeling and trypsinization. Protein localization and properties in sperm were investigated by separation of head and tail fractions, and extractabilities by a non-ionic detergent and urea.

RESULTS

The authenticity of the eight novel proteins and their specificity to spermatogenic cells were confirmed. In examining the developmental expression patterns, we found the presence of four proteins only in testicular germ cells, a single protein in testicular germ cells and testicular sperm, and three proteins in the testicular stages and mature sperm from the epididymis. Further analysis of the three proteins present in sperm disclosed that one is located at the surface of the acrosomal region and the other two are associated with cytoskeletal structures in the sperm flagellum. We name the genes for these sperm proteins Shsp1 (Sperm head surface protein 1), Sfap1 (Sperm flagellum associated protein 1) and Sfap2 (Sperm flagellum associated protein 2).

CONCLUSION

We analyzed eight novel germ cell-specific proteins, providing new and inclusive information about their developmental and cellular characteristics. Our findings will facilitate future investigation into the biological roles of these novel proteins in spermatogenesis and sperm functions.

Presence, processing, and localization of mouse ADAM15 during sperm maturation and the role of its disintegrin domain during sperm–egg binding

Successful fertilization requires gametes to complete several stages, beginning with maturation and transport along the male and female reproductive tracts and ending with the interaction between the sperm and the egg. This last step involves sperm–egg adhesion and membrane fusion. ADAMs (disintegrin and metalloprotease domain proteins) are a family of membrane-anchored glycoproteins that are thought to play diverse roles in cell–cell adhesion through their interaction with integrins. This study analyzes the presence, location, processing, and possible role of ADAM15 in mouse sperm. The presence of ADAM15 in mouse spermatozoa was detected by Western blotting, which revealed that ADAM15 is post-translationally processed, during epididymal sperm maturation and the acrosome reaction. The 35 kDa antigen present in the acrosome-reacted sperm is the last proteolytic product of the 110/75 kDa ADAM15 found in non-capacitated sperm. This 35 kDa protein contains the disintegrin domain. By indirect immunofluorescence, ADAM15 was identified in the acrosomal region and along the flagellum of mouse spermatozoa. In acrosome-reacted sperm, ADAM15 was lost from the acrosomal region, but remained diffusely distributed throughout the head and flagellum. Furthermore, the ADAM15 disintegrin domain (RPPTDDCDLPEF) partially inhibited fusion and almost completely inhibited sperm–oolemma adhesion. In conclusion, our data indicate that ADAM15 is present in the testis and in spermatozoa from the caput, corpus, and cauda epididymis, as well as in non-capacitated and acrosome-reacted gametes. Results also indicate that ADAM15 is processed during epididymal maturation and acrosome reaction and that it may play a role during sperm–egg binding.

Integrative characterization of germ cell-specific genes from mouse spermatocyte UniGene library

Background

The primary regulator of spermatogenesis, a highly ordered and tightly regulated developmental process, is an intrinsic genetic program involving male germ cell-specific genes.

Results

We analyzed the mouse spermatocyte UniGene library containing 2155 gene-oriented transcript clusters. We predict that 11% of these genes are testis-specific and systematically identified 24 authentic genes specifically and abundantly expressed in the testis via in silico and in vitro approaches. Northern blot analysis disclosed various transcript characteristics, such as expression level, size and the presence of isoform. Expression analysis revealed developmentally regulated and stage-specific expression patterns in all of the genes. We further analyzed the genes at the protein and cellular levels. Transfection assays performed using GC-2 cells provided information on the cellular characteristics of the gene products. In addition, antibodies were generated against proteins encoded by some of the genes to facilitate their identification and characterization in spermatogenic cells and sperm. Our data suggest that a number of the gene products are implicated in transcriptional regulation, nuclear integrity, sperm structure and motility, and fertilization. In particular, we found for the first time that Mm.333010, predicted to contain a trypsin-like serine protease domain, is a sperm acrosomal protein.

Conclusion

We identify 24 authentic genes with spermatogenic cell-specific expression, and provide comprehensive information about the genes. Our findings establish a new basis for future investigation into molecular mechanisms underlying male reproduction.

Identification of an ADAM2-ADAM3 complex on the surface of mouse testicular germ cells and cauda epididymal sperm

Male mice lacking ADAM2 (fertilin beta) or ADAM3 (cyritestin) are infertile; cauda epididymal sperm (mature sperm) from these mutant mice cannot bind to the egg zona pellucida. ADAM3 is barely present in Adam2-null sperm, despite normal levels of this protein in Adam2-null testicular germ cells (TGCs; sperm precursor cells). Here, we have explored the molecular basis for the loss of ADAM3 in Adam2-null TGCs to clarify the biosynthetic and functional linkage of ADAM2 and ADAM3. A small portion of total ADAM3 was found present on the surface of wild-type and Adam2(-/-) TGCs at similar levels. In the Adam2-null TGCs, however, surface-localized ADAM3 exhibited an increased amount of an endoglycosidase H-resistant form that may be related to instability of ADAM3. Moreover, we found a complex between ADAM2 and ADAM3 on the surface of TGCs and sperm. The intracellular chaperone calnexin was a component of the testicular ADAM2-ADAM3 complex. Our findings suggest that the association with ADAM2 is a key element for stability of ADAM3 in epididymal sperm. The presence of the ADAM2-ADAM3 complex in sperm also suggests a potential role of ADAM2 with ADAM3 in sperm binding to the egg zona pellucida.

Systematic identification and integrative analysis of novel genes expressed specifically or predominantly in mouse epididymis

Background

Maturation of spermatozoa, including development of motility and the ability to fertilize the oocyte, occurs during transit through the microenvironment of the epididymis. Comprehensive understanding of sperm maturation requires identification and characterization of unique genes expressed in the epididymis.

Results

We systematically identified 32 novel genes with epididymis-specific or -predominant expression in the mouse epididymis UniGene library, containing 1505 gene-oriented transcript clusters, by in silico and in vitro analyses. The Northern blot analysis revealed various characteristics of the genes at the transcript level, such as expression level, size and the presence of isoform. We found that expression of the half of the genes is regulated by androgens. Further expression analyses demonstrated that the novel genes are region-specific and developmentally regulated. Computational analysis showed that 15 of the genes lack human orthologues, suggesting their implication in male reproduction unique to the mouse. A number of the novel genes are putative epididymal protease inhibitors or β-defensins. We also found that six of the genes have secretory activity, indicating that they may interact with sperm and have functional roles in sperm maturation.

Conclusion

We identified and characterized 32 novel epididymis-specific or -predominant genes by an integrative approach. Our study is unique in the aspect of systematic identification of novel epididymal genes and should be a firm basis for future investigation into molecular mechanisms underlying sperm maturation in the epididymis.

Identification of a hyaluronidase, Hyal5, involved in penetration of mouse sperm through cumulus mass

A glycosylphosphatidylinositol (GPI)-anchored hyaluronidase, PH-20, on the sperm surface has long been believed to assist sperm penetration through the cumulus mass surrounding the eggs. However, mouse sperm lacking PH-20 were still capable of penetrating the cumulus mass despite a delayed dispersal of cumulus cells. Intriguingly, a 55-kDa hyaluronan-hydrolyzing protein was abundantly present in wild-type and PH-20-deficient mouse sperm. In this study, we purified the 55-kDa mouse protein from soluble protein extracts released from epididymal sperm by acrosome reaction and identified as a hyaluronidase, Hyal5. Hyal5 was exclusively expressed in the testis and formed a 160-kbp gene cluster together with Hyalp1, Hyal4, and Ph-20 on mouse chromosome 6. Hyal5 was a single-chain hyaluronidase present on the plasma and acrosomal membranes of sperm presumably as a GPI-anchored protein. Moreover, hyaluronan zymography revealed that Hyal5 is enzymatically active in the pH range 5-7 and inactive at pH 3 and 4. Both Hyal5-enriched PH-20-free soluble protein extracts and PH-20-deficient mouse sperm were capable of dispersing cumulus cells from the cumulus mass. Cumulus cell dispersal was strongly inhibited by the presence of a hyaluronidase inhibitor, apigenin. These results suggest that in the mouse, Hyal5 may function principally as a "cumulus matrix depolymerase" in the sperm penetration through the cumulus mass and in the local hyaluronan hydrolysis near or on the surface of the egg zona pellucida to enable the proximal region of sperm tail to move freely. PH-20 may compensate in part for the functional roles of Hyal5.

Molecular, biochemical, and cellular characterization of epididymal ADAMs, ADAM7 and ADAM28

The mammalian epididymis is critical for sperm to acquire motility and fertilizing capacity. This maturation process involves the interaction of epididymal secretory proteins with sperm. We analyzed mouse a disintegrin and metalloprotease (ADAMs) 7 and 28 expressed specifically or predominantly in the epididymis. We found that these ADAM genes are expressed in an epididymal region-specific manner and their gene expression is regulated by both androgen and testicular factors (ADAM7) or only testicular factors (ADAM28). We identified an ADAM28 transcript isoform that lacks the transmembrane domain. Protein analysis revealed that ADAM7, but not ADAM28, is transferred from the epididymis to the sperm surface and redistributed in the sperm head during acrosome reaction. These processes were shown to occur without processing of the protein. Taken together, our results indicate that the two epididymal ADAMs closely related in phylogeny are differential in various characteristics and ADAM7 has unique secretory feature and interactive relationship with sperm.

Defects in secretory pathway trafficking during sperm development in Adam2 knockout mice

Adam2-null and Adam3-null male mice exhibit reduced levels of one or more ADAM proteins on mature sperm, in addition to the loss of the genetically targeted protein. ADAM protein loss was believed to occur posttranslationally, although the timing of loss and the mechanism by which the loss occurred were not explored. In this study we have found that in Adam3-null mice, fertilin beta (also known as ADAM2) is lost during the formation of testicular sperm. In Adam2-null males, most cyritestin (ADAM3) protein is also lost at this stage, but 25% of cyritestin is lost later, during sperm passage through the epididymis. Although normal levels of cyritestin are synthesized and acquire Endoglycosidase H resistance, indicating transit through the Golgi, the protein does not reach the cell surface. We also discovered that the majority of both fertilin beta and cyritestin are found in a Triton X-100 insoluble compartment on testicular sperm, when most of the cyritestin was observed on the cell surface. This insoluble compartment may represent a sorting platform, because in Adam2-knockout cells, only a small fraction of the cyritestin becomes Triton X-100 insoluble. Thus, it appears that cyritestin loss in Adam2-knockout mice may result, at least in part, from a disruption in protein trafficking.

Contraceptive vaccines targeting sperm

Overpopulation is a global problem of significant magnitude, with grave implications for the future. Development of new contraceptives is necessary, as existing forms of birth control are unavailable, impractical and/or too expensive for many individuals due to sociological, financial or educational limitations. Immunocontraception and, in particular, the targeting of antibodies to sperm-specific antigens implicated in sperm-egg binding and fertilisation offers an attractive approach to control fertility. Sperm-specific antibodies may impair fertility by inhibiting sperm motility, by reducing penetration of the cervical mucus by sperm, or by interfering in sperm capacitation or the acrosome reaction; alternatively, antisperm antibodies may invoke the complement cascade, resulting in sperm lysis. The antibodies raised against sperm-specific antigens have proved to be extremely effective at reducing sperm-egg interactions in vitro; fertility trials in subhuman primates will eventually be needed to prove the effectiveness of the sperm antigens in terms of contraceptive efficacy before trials in humans can be justified. In addition, existing and emerging strategies (such as sperm proteomics, the determination of molecular and structural details of sperm proteins, and the modelling of protein-ligand interactions using X-ray and/or NMR structures to name a few) are expected to provide the experimental foundation for the design of small molecule inhibitors with antifertility effects. The technology underpinning vaccine development is constantly being developed and the introduction of DNA/RNA vaccines is certain to impact upon the field of immunocontraception.

Expression and secretion of rat SPAM1(2B1 or PH-20) in the epididymis: role of testicular lumicrine factors

Rat sperm surface antigen Sperm Adhesion Molecule1, SPAM1 (a.k.a. 2B1 or PH-20) is a plasma membrane-bound glycoprotein with hyaluronidase activity and putative roles during fertilization. Previously the antigen was thought to be testis-specific but recently it has been shown to be synthesized in the epididymis (mouse, macaque and human). Using the efferent ductule ligated (EDL) rat as a model to produce a sperm-free androgen-maintained epididymis, we have examined the factors regulating the expression of epididymal 2B1. RT-PCR and in situ transcript hybridization (ISH) studies showed that 2B1 mRNA is transcribed in the principal cells in all three regions of the epididymis. Its cognate protein was also detected by Western blot analysis in sperm-free cytosols from normal epididymis and found to undergo endoproteolytic cleavage into 2 subunits of similar size to the sperm-bound form. Immunohistochemistry with a monoclonal antibody to 2B1 confirmed that the protein is present in the epididymal epithelium and luminal secretions. The intensity of staining was much stronger in the sperm-free EDL epididymis than that in the normal (sperm-present) epididymis. The protein was shown to have hyaluronidase activity at neutral pH and both its quantity and activity appeared to be greater in the EDL epididymis. It is suggested that a soluble form of SPAM1 glycoprotein is synthesized and released in the epididymis and that in addition to androgens, its regulation may involve a cross-talk between the tubule epithelium and lumicrine factors, the latter possibly of testicular origin.

Epididymal cell secretory activities and the role of proteins in boar sperm maturation

The final stages of sperm differentiation occur outside the gonad, in the epididymal tubule. These last maturation steps, essential to the quality of spermatozoa, are not under the genomic control of the germ cells. A series of sequential interactions with the epididymal fluid, mostly specific proteins present in the lumen of different regions, are believed to induce the final steps of sperm maturation. In order to provide the luminal changes required for this maturation to occur, the epithelium may resort to two basic mechanisms: absorption and secretion. Far from being a uniform channel, the epididymal duct is a canal with highly specialized regional differentiation of its epithelial ultrastructure and its secretory and absorptive functions. This review focuses on the ultrastructural characteristic of the epithelial cells, their specific secretory activity according to the epididymal regions and their eventual role in sperm maturation of the boar. The chronology of the changes that occur in and on the sperm and in the surrounding environment are described. Relationships between the highly regionalized epididymal activities, sperm characteristics linked to their survival and fertility potential are also presented in this review.

Effects of scrotal heating on sperm surface protein PH-20 expression in sheep

Sperm surface protein PH-20 expression was studied during spermatogenesis in pubertal and adult sheep, using molecular and histological methods. The effects of 24 hr of insulation raising scrotal temperatures to 39 degrees C on PH-20 expression in ejaculated sheep sperm were also determined. A 282 nt cDNA fragment of ovine PH-20 was identified in total RNA extracts of sheep testes, which exhibited 76% identity at the nucleotide level with the equivalent region of the human sequence. Ovine PH-20 mRNA and immunoreactivity were identified only in adult ram testis and not in peri-pubertal ram testis tubules lacking round spermatids, nor in adult sheep brain, pituitary, heart, spleen, lung, liver, kidney, epididymis, or ovary. Ovine PH-20 protein was distributed predominantly on the postacrosomal membrane and was also present on the anterior membrane of the sperm head in fresh, unheated sheep semen. Scrotal heating caused a significant, transient decrease in the percentage of PH-20 immunoreactive sperm, but did not change the pattern of PH-20 staining on the sperm head. The results strongly suggest that ovine PH-20 is postmeiotically expressed in haploid germ cells in sheep testis and is arrayed on the membrane of the mature ovine spermatozoon. Scrotal heating appears to have few effects on PH-20 expression and distribution on ejaculated sperm.

Possible function of the ADAM1a/ADAM2 Fertilin complex in the appearance of ADAM3 on the sperm surface

In mouse, two different isoforms of ADAM1 (fertilin alpha), ADAM1a and ADAM1b, are produced in the testis. ADAM1a is localized within the endoplasmic reticulum of testicular germ cells, whereas epididymal sperm contain only ADAM1b on the plasma membrane. In this study, we show that the loss of ADAM1a results in the male infertility because of the severely impaired ability of sperm to migrate from the uterus into the oviduct through the uterotubal junction. However, epididymal sperm of ADAM1a-deficient mice were capable of fertilizing cumulus-intact, zona pellucida-intact eggs in vitro despite the delayed dispersal of cumulus cells and the reduced adhesion/binding to the zona pellucida. Among testis (sperm)-specific proteins examined, only the level of ADAM3 (cyritestin) was strongly reduced in ADAM1a-deficient mouse sperm. Moreover, the appearance of ADAM3 on the sperm surface was dependent on the formation of a fertilin protein complex between ADAM1a and ADAM2 (fertilin beta) in testicular germ cells, although no direct interaction between the fertilin complex and ADAM3 was found. These results suggest that ADAM1a/ADAM2 fertilin may be implicated in the selective transport of specific sperm proteins including ADAM3 from the endoplasmic reticulum of testicular germ cells onto the cell surface. These proteins then can participate in sperm migration into the oviduct, the dispersal of cumulus cells, and sperm binding to the zona pellucida.

Assessment of contraceptive vaccines based on recombinant mouse sperm protein PH20

Mouse PH20 (mPH20), the mouse homologue to guinea pig hyaluronidase protein PH20 (gpPH20), was used to produce contraceptive vaccines that target both sexes of mice. Previously, immunization with a female gamete antigen (the zona pellucida subunit 3 protein) delivered in a recombinant murine cytomegalovirus (MCMV), or as a purified recombinant protein, has been shown to induce infertility in female mice. There is evidence, however, that sperm protein antigens could provide broader contraceptive coverage by affecting both males and females, and the most promising has been gpPH20 when tested in a guinea pig model. Mice were therefore either inoculated with a recombinant MCMV expressing mPH20 or immunized directly with purified recombinant mPH20 protein fused to maltose-binding protein. Mice treated with either vaccine formulation developed serum antibodies that cross-reacted to a protein band of 55 kDa corresponding to mPH20 in Western blots of mouse sperm. However, there was no significant reduction in the fertility of males or females compared with control animals with either formulation. We conclude from our data that recombinant mPH20 is not a useful antigen for inclusion in immunocontraceptive vaccines that target mice.

The spermatid plasma membrane comes of age

Spermiogenesis affords a unique opportunity to examine the formation of plasma membrane domains. Recent attempts to chart the life cycles of well-characterized integral plasma membrane proteins during spermiogenesis have suggested that spermatids are at least as adept as epithelial cells or neurons at establishing their plasma membrane domains. They appear to expand upon the standard recipe involving concurrent domain-specific protein targeting and diffusion barriers by using a combination of intracellular storage within the secretory pathway, developmentally-regulated delivery to provisional plasma membrane domains, large-scale redistributions of diffusion barriers and integral plasma membrane proteins, and the shedding of an entire plasma membrane domain.