Molecular cloning and characterization of P47, a novel boar sperm-associated zona pellucida-binding protein homologous to a family of mammalian secretory proteins

A novel role for milk fat globule-EGF factor 8 protein (MFGE8) in the mediation of mouse sperm-extracellular vesicle interactions

Spermatozoa transition to functional maturity as they are conveyed through the epididymis, a highly specialized region of the male excurrent duct system. Owing to their transcriptionally and translationally inert state, this transformation into fertilization competent cells is driven by complex mechanisms of intercellular communication with the secretory epithelium that delineates the epididymal tubule. Chief among these mechanisms are the release of extracellular vesicles (EV), which have been implicated in the exchange of varied macromolecular cargo with spermatozoa. Here, we describe the optimization of a tractable cell culture model to study the mechanistic basis of sperm-extracellular vesicle interactions. In tandem with receptor inhibition strategies, our data demonstrate the importance of milk fat globule-EGF factor 8 (MFGE8) protein in mediating the efficient exchange of macromolecular EV cargo with mouse spermatozoa; with the MFGE8 integrin-binding Arg-Gly-Asp (RGD) tripeptide motif identified as being of particular importance. Specifically, complementary strategies involving MFGE8 RGD domain ablation, competitive RGD-peptide inhibition and antibody-masking of alpha V integrin receptors, all significantly inhibited the uptake and redistribution of EV-delivered proteins into immature mouse spermatozoa. These collective data implicate the MFGE8 ligand and its cognate integrin receptor in the mediation of the EV interactions that underpin sperm maturation.

Ligands and Receptors Involved in the Sperm-Zona Pellucida Interactions in Mammals

Sperm-zona pellucida (ZP) interaction, involving the binding of sperm surface ligands to complementary carbohydrates of ZP, is the first direct gamete contact event crucial for subsequent gamete fusion and successful fertilization in mammals. It is a complex process mediated by the coordinated engagement of multiple ZP receptors forming high-molecular-weight (HMW) protein complexes at the acrosomal region of the sperm surface. The present article aims to review the current understanding of sperm-ZP binding in the four most studied mammalian models, i.e., murine, porcine, bovine, and human, and summarizes the candidate ZP receptors with established ZP affinity, including their origins and the mechanisms of ZP binding. Further, it compares and contrasts the ZP structure and carbohydrate composition in the aforementioned model organisms. The comprehensive understanding of sperm-ZP interaction mechanisms is critical for the diagnosis of infertility and thus becomes an integral part of assisted reproductive therapies/technologies.

Porcine model for the study of sperm capacitation, fertilization and male fertility

Mammalian fertilization remains a poorly understood event with the vast majority of studies done in the mouse model. The purpose of this review is to revise the current knowledge about semen deposition, sperm transport, sperm capacitation, gamete interactions and early embryonic development with a focus on the porcine model as a relevant, alternative model organism to humans. The review provides a thorough overview of post-ejaculation events inside the sow's reproductive tract including comparisons with humans and implications for human fertilization and assisted reproductive therapy (ART). Porcine methodology for sperm handling, preservation, in vitro capacitation, oocyte in vitro maturation, in vitro fertilization and intra-cytoplasmic sperm injection that are routinely used in pig research laboratories can be successfully translated into ART to treat human infertility. Last, but not least, new knowledge about mitochondrial inheritance in the pig can provide an insight into human mitochondrial diseases and new knowledge on polyspermy defense mechanisms could contribute to the development of new male contraceptives.

Compartmentalization of the proteasome-interacting proteins during sperm capacitation

Ubiquitination is a stable, reversible posttranslational modification of target proteins by covalent ligation of the small chaperone protein ubiquitin. Most commonly ubiquitination targets proteins for degradation/recycling by the 26S proteasome in a well-characterized enzymatic cascade. Studies using human and non-human mammalian spermatozoa revealed the role of the ubiquitin-proteasome system (UPS) in the regulation of fertilization, including sperm-zona pellucida (ZP) interactions as well as the early events of sperm capacitation, the remodeling of the sperm plasma membrane and acrosome, and for the acquisition of sperm fertilizing ability. The present study investigated the activity of UPS during in vitro capacitation of fresh boar spermatozoa in relation to changes in sperm proteome. Parallel and sequential treatments of ejaculated and capacitated spermatozoa under proteasome permissive/inhibiting conditions were used to isolate putative sperm proteasome-associated sperm proteins in a compartment-specific manner. A differential proteomic approach employing 1D PAGE revealed differences in accumulated proteins at the molecular weights of 60, 58, 49, and 35 kDa, and MS analysis revealed the accumulation of proteins previously reported as proteasome co-purifying proteins, as well as some novel proteins. Among others, P47/lactadherin, ACRBP, ADAM5, and SPINK2 (alias SAAI) were processed by the proteasome in a capacitation dependent manner. Furthermore, the capacitation-induced reorganization of the outer acrosomal membrane was slowed down in the presence of proteasomal inhibitors. These novel results support the proposed role of UPS in sperm capacitation and open several new lines of inquiry into sperm capacitation mechanism.

The Proteome of Pig Spermatozoa Is Remodeled During Ejaculation

Proteins are essential for sperm function, including their fertilizing capacity. Pig spermatozoa, emitted in well-defined ejaculate fractions, vary in their functionality, which could be related to different sperm protein composition. This study aimed (i) to update the porcine sperm proteome and (ii) to identify proteins differentially expressed in mature spermatozoa from cauda epididymis and those delivered in separate ejaculate fractions. Ejaculates from nine mature and fertile boars were manually collected in three separate portions: the first 10 ml of the sperm-rich ejaculate fraction (SRF), the rest of the SRF and the post-SRF. The contents of cauda epididymides of the boars were collected post-mortem by retrograde duct perfusion, generating four different semen sources for each boar. Following centrifugation, the resulting pellets of each semen source were initially pooled and later split to generate two technical replicates per source. The resulting eight sperm samples (two per semen source) were subjected to iTRAQ-based 2D-LC-MS/MS for protein identification and quantification. A total of 1,723 proteins were identified (974 of Sus scrofa taxonomy) and 1,602 of them were also quantified (960 of Sus scrofa taxonomy). After an ANOVA test, 32 Sus scrofa proteins showed quantitative differences (p < 0.01) among semen sources, which was particularly relevant for sperm functionality in the post-SRF. The present study showed that the proteome of boar spermatozoa is remodeled during ejaculation involving proteins clearly implicated in sperm function. The findings provide valuable groundwork for further studies focused on identifying protein biomarkers of sperm fertility.

Immunocontraceptive target repertoire defined by systematic identification of sperm membrane alloantigens in a single species

Sperm competence in animal fertilization requires the collective activities of numerous sperm-specific proteins that are typically alloimmunogenic in females. Consequently, sperm membrane alloantigens are potential targets for contraceptives that act by blocking the proteins' functions in gamete interactions. Here we used a targeted proteomics approach to identify the major alloantigens in swine sperm membranes and lipid rafts, and thereby systematically defined the repertoire of these sperm-specific proteins in a single species. Gilts with high alloantibody reactivity to proteins in sperm membranes or lipid rafts produced fewer offspring (73% decrease) than adjuvant-only or nonimmune control animals. Alloantisera recognized more than 20 potentially unique sperm membrane proteins and five sperm lipid raft proteins resolved on two-dimensional immunoblots with or without prior enrichment by anion exchange chromatography. Dominant sperm membrane alloantigens identified by mass spectrometry included the ADAMs fertilin α, fertilin ß, and cyritestin. Less abundant alloantigens included ATP synthase F1 β subunit, myo-inositol monophosphatase-1, and zymogen granule membrane glycoprotein-2. Immunodominant sperm lipid raft alloantigens included SAMP14, lymphocyte antigen 6K, and the epididymal sperm protein E12. Of the fifteen unique membrane alloantigens identified, eleven were known sperm-specific proteins with uncertain functions in fertilization, and four were not previously suspected to exist as sperm-specific isoforms. De novo sequences of tryptic peptides from sperm membrane alloantigen "M6" displayed no evident homology to known proteins, so is a newly discovered sperm-specific gene product in swine. We conclude that alloimmunizing gilts with sperm membranes or lipid rafts evokes formation of antibodies to a relatively small number of dominant alloantigens that include known and novel sperm-specific proteins with possible functions in fertilization and potential utility as targets for immunocontraception.

Milk-fat globule epidermal growth factor 8 (MFGE8) is expressed at the embryo– and fetal–maternal interface in equine pregnancy

Milk-fat globule epidermal growth factor (EGF) 8 protein (MFGE8), also known as lactadherin, promotes cell adhesion in an Arg-Gly-Asp (RGD)-dependent modus via integrins. In the present study, the expression of MFGE8 was examined in equine endometrium during oestrus and at Days 12 and 16 after ovulation in pregnant and non-pregnant mares and in mares during the 5th month of gestation. Results demonstrated that MFGE8 is expressed at the embryo– and fetal–maternal interface in equine pregnancy. In non-pregnant endometrium its expression was upregulated by oestrogen, a finding that was confirmed using endometrial explant culture. MFGE8 was expressed at similar levels by conceptuses collected 13 and 14 days after ovulation and by allantochorion sampled during the 5th month of gestation. Pericytes of endometrial blood vessels displayed strong MFGE8 expression upon in situ hybridisation. During the 5th month of gestation, the fetal side of the allantochorionic villi in particular displayed pronounced staining upon in situ hybridisation, confirming that MFGE8 expression is not restricted to early pregnancy but persists and is present at the fetal–maternal interface. Potential roles of MFGE8 in equine pregnancy include mediating cell–cell adhesion, promotion of angiogenesis and placental transfer of fatty acids.

Sperm membrane proteins associated with the boar semen cryopreservation

This study aimed to define sperm membrane protein markers of semen freezability of boars with the aid of a proteomic approach. Semen from fourteen adult boars were subjected to slow freezing and rapid thawing. After thawing, sperm vigor and motility were analyzed, and based on these results, animals were separated into two groups: good (GFEs) and poor freezability (PFEs). Sperm membrane proteins were extracted and subjected to two-dimensional electrophoresis. Stained gels were analyzed by computerized resources to indicate differentially expressed protein spots, that were identified by mass spectrometry. Six animals showed good freezability with average sperm vigor and motility of 2.2±0.8 and 41.8±22.9, respectively, whereas eight boars showed poor freezability, with 1.9±0.6 and 26.8±17.5 of sperm vigor sperm motility, respectively. An average of 263±62.2 spots per gel and 234.2±54.6 of spots consistently present in all gels were detected. The intensities of five spots were significantly different between groups. Fc fragment of IgG binding protein and lactadherin were more intense in the PFE group, while Arylsulfatase A and F-actin capping protein subunit alpha 1 were more expressed in the GEF group. Based on their functions and interactions with other proteins, we conclude that these four sperm membrane proteins may act as potential markers of boar semen freezability.

Lactadherin is a candidate oviduct Lewis X trisaccharide receptor on porcine spermatozoa

A recent study has demonstrated that porcine spermatozoa recognize with high affinity carbohydrate structures containing Lewis X motifs. Sperm adhesion to Lewis X is proposed to mediate sperm binding to the oviduct epithelium to form a reservoir. The objective of this study was to identify Lewis X-binding proteins from porcine spermatozoa as candidate receptors for oviduct glycans. To identify low-abundance proteins typically masked by proteins originating from seminal fluid, Lewis X candidate receptors were enriched from cauda epididymal boar spermatozoa. Plasma membrane preparations from cauda epididymal spermatozoa were subjected to RP-HPLC and glycan blotting assays to isolate and detect proteins that bind Lewis X. Following bottom-up LC-MS/MS analysis, among the two bands that bound sulfated Lewis X, ADAM5, which spermatozoa, was confidently identified. ADAM family members have been established as contributors to sperm entry into the oviduct. A second sulfated Lewis X-binding protein identified was the peripheral membrane protein lactadherin (also known as P47, SED1 and MFG-E8 in different species). The interaction between Lewis X and lactadherin was functionally important because competitive inhibition by soluble recombinant lactadherin reduced sperm binding to the oviduct epithelium. Furthermore, far-western blotting demonstrated that purified lactadherin could bind oviduct cells. In summary, these findings reveal that, in addition to the previously reported glycan affinity of accessory gland proteins that adhere to spermatozoa, multiple proteins intrinsic to spermatozoa have affinity for a specific oviduct glycan. Further, in addition to binding to the zona pellucida, lactadherin is now implicated in binding to oviduct glycans to promote formation of the sperm reservoir.

Sperm proteome and reproductive technologies in mammals

Sperm is highly differentiated cell that can be easily obtained and purified. Mature sperm is considered to be transcriptionally and translationally silent and incapable of protein synthesis. Recently, a large number of proteins have been identified in sperm from different species by using the proteomic approaches. Clinically, sperm proteins can be used as markers for male infertility due to different protein profiles identified in sperm from fertile and infertile male animals. Recent evidences have shown that the conditions of sperm preservation in vitro can also change the sperm protein profiles. This paper reviews the recent scientific publications available to address sperm proteome and their relationship with sperm cryopreservation, capacitation, fertilization, and separation of X and Y sperm. Future directions in the application of sperm proteomics to develop or optimize reproductive technologies in mammals are also discussed.

Regulation of Sperm Capacitation by the 26S Proteasome: An Emerging New Paradigm in Spermatology

The ubiquitin proteasome system (UPS) participates in many biological processes ranging from cell cycle and antigen processing to cellular defense and signaling. Work of the last decade has made it evident that the UPS is involved in many sperm-related processes leading up to and as part of fertilization. The current knowledge of UPS involvement and changes during sperm capacitation are reviewed together with a list of known proteasome-associated sperm proteins and a discussion of the relationships between these proteins and the proteasome. Proteasomal inhibitors such as MG-132 and epoxomicin significantly alter capacitation and prevent acrosome reaction. The 26S proteasome degrades AKAP3, an A-kinase anchoring protein, partially regulating the release of protein-kinase A (PKA), a vital component necessary for the steps leading up to capacitation. Further, changes occur in 20S core subunit localization and abundance throughout capacitation. Proteasome-interacting valosine-containing protein (VCP) undergoes tyrosine phosphorylation; however, its physiological roles in capacitation and fertilization remain unknown. The E1-type ubiquitin-activating enzyme (UBA1) inhibitor PYR-41 also alters acrosomal membrane remodeling during capacitation. Furthermore, after capacitation, the acrosomal proteasomes facilitate the degradation of zona pellucida glycoproteins leading up to fertilization. Methods to modulate the sperm proteasome activity during sperm storage and capacitation may translate to increased reproductive efficiency in livestock animals. Human male infertility diagnostics may benefit from incorporation of research outcomes built upon relationships between UPS and capacitation. Altogether, the studies reviewed here support the involvement of UPS in sperm capacitation and present opportunities for new discoveries.

Identification of bovine sperm acrosomal proteins that interact with a 32-kDa acrosomal matrix protein

Mammalian fertilization is accomplished by the interaction between sperm and egg. Previous studies from this laboratory have identified a stable acrosomal matrix assembly from the bovine sperm acrosome termed the outer acrosomal membrane-matrix complex (OMC). This stable matrix assembly exhibits precise binding activity for acrosin and N-acetylglucosaminidase. A highly purified OMC fraction comprises three major (54, 50, and 45 kDa) and several minor (38-19 kDa) polypeptides. The set of minor polypeptides (38-19 kDa) termed "OMCrpf polypeptides" is selectively solubilized by high-pH extraction (pH 10.5), while the three major polypeptides (55, 50, and 45 kDa) remain insoluble. Proteomic identification of the OMC32 polypeptide (32 kDa polypeptide isolated from high-pH soluble fraction of OMC) yielded two peptides that matched the NCBI database sequence of acrosin-binding protein. Anti-OMC32 recognized an antigenically related family of polypeptides (OMCrpf polypeptides) in the 38-19-kDa range with isoelectric points ranging between 4.0 and 5.1. Other than glycohydrolases, OMC32 may also be complexed to other acrosomal proteins. The present study was undertaken to identify and localize the OMC32 binding polypeptides and to elucidate the potential role of the acrosomal protein complex in sperm function. OMC32 affinity chromatography of a detergent-soluble fraction of bovine cauda sperm acrosome followed by mass spectrometry-based identification of bound proteins identified acrosin, lactadherin, SPACA3, and IZUMO1. Co-immunoprecipitation analysis also demonstrated the interaction of OMC32 with acrosin, lactadherin, SPACA3, and IZUMO1. Our immunofluorescence studies revealed the presence of SPACA3 and lactadherin over the apical segment, whereas IZUMO1 is localized over the equatorial segment of Triton X-100 permeabilized cauda sperm. Immunoblot analysis showed that a significant portion of SPACA3 was released after the lysophosphatidylcholine (LPC)-induced acrosome reaction, whereas the IZUMO1 and lactadherin polypeptides remain associated to the particulate fraction. Almost entire population of bovine sperm IZUMO1 relocates to the equatorial segment during the LPC-induced acrosome reaction. We propose that the interaction of OMC32 matrix polypeptide with detergent-soluble acrosomal proteins regulates the release of hydrolases/other acrosomal protein(s) during the acrosome reaction.

Proteomic Characterization of Pig Sperm Anterior Head Plasma Membrane Reveals Roles of Acrosomal Proteins in ZP3 Binding

The sperm anterior head plasma membrane (APM) is the site where sperm first bind to the zona pellucida (ZP). This binding reaches the maximum following the sperm capacitation process. To gain a better understanding of the sperm-ZP binding mechanisms, we compared protein profiles obtained from mass spectrometry of APM vesicles isolated from non-capacitated and capacitated sperm. The results revealed that ZP-binding proteins were the most abundant group of proteins, with a number of them showing increased levels in capacitated sperm. Blue native gel electrophoresis and far-western blotting revealed presence of high molecular weight (HMW) protein complexes in APM vesicles of both non-capacitated and capacitated sperm, but the complexes (∼750-1300 kDa) from capacitated sperm possessed much higher binding capacity to pig ZP3 glycoprotein. Proteomic analyses indicated that a number of proteins known for their acrosome localization, including zonadhesin, proacrosin/acrosin and ACRBP, were components of capacitated APM HMW complexes, with zonadhesin being the most enriched protein. Our immunofluorescence results further demonstrated that a fraction of these acrosomal proteins was transported to the surface of live acrosome-intact sperm during capacitation. Co-immunoprecipitation indicated that zonadhesin, proacrosin/acrosin and ACRBP interacted with each other and they may traffic as a complex from the acrosome to the sperm surface. Finally, the significance of zonadhesin in the binding of APM HMW complexes to pig ZP3 was demonstrated; the binding ability was decreased following treatment of the complexes with anti-zonadhesin antibody. Our results suggested that acrosomal proteins, especially zonadhesin, played roles in the initial sperm-ZP binding during capacitation.

MFG-E8 expression for progression of oral squamous cell carcinoma and for self-clearance of apoptotic cells

Milk fat globule--epidermal growth factor (EGF)--factor VIII (MFG-E8) is a secreted glycoprotein that promotes clearance of apoptotic cells by bridging phosphatidylserine on apoptotic cells and integrin αvβ3/5 on phagocytes. High expression of MFG-E8 has been reported in various types of cancer in humans. Apoptotic figures are frequently found in the surgical samples of oral squamous cell carcinoma (SCC) and carcinoma in situ, and we have often observed apoptotic carcinoma cells engulfed by macrophages or even by neighboring carcinoma cells. Thus we hypothesized that MFG-E8 might promote engulfment of apoptotic carcinoma cells by living carcinoma cells and that MFG-E8 expressed by carcinoma cells could contribute to tumor progression. The aim of this study was to elucidate the biological role of MFG-E8 in oral SCC. Fifty-three surgical specimens of oral SCC were used for immunohistochemistry for MFG-E8, and the expression profiles were correlated with clinicopathological properties. Also, we examined the MFG-E8 expression patterns and functions using three human oral SCC cell lines. Most of the cases had MFG-E8-positive SCC cells, and the expression of MFG-E8 was correlated with such clinicopathological features as tumor size, pathological stage, locoregional recurrence, scattering invasion pattern, and SCC cell figures engulfing apoptotic SCC cells. The MFG-E8 staining was enhanced in apoptotic SCC cells, some of which were apparently engulfed by the neighboring SCC cells. ZK-1 cells showed high MFG-E8 expression, and its localization was found in the cytoplasm and the cell surface. Transient MFG-E8 knockdown by siRNA in ZK-1 decreased cell proliferation and invasiveness and increased cell death. Thus we have demonstrated that MFG-E8 promotes tumor progression in oral SCC and that it might be involved in the clearance of apoptotic SCC cells by living SCC cells.

Identification of differentially expressed proteins in fresh and frozen–thawed boar spermatozoa by iTRAQ-coupled 2D LC–MS/MS

Cryodamage is a major problem in semen cryopreservation, causing changes in the levels of proteins that influence the function and motility of spermatozoa. In this study, protein samples prepared from fresh and frozen–thawed boar spermatozoa were compared using the isobaric tags for relative and absolute quantification (iTRAQ) labeling technique coupled to 2D LC–MS/MS analysis. A total of 41 differentially expressed proteins were identified and quantified, including 35 proteins that were present at higher levels and six proteins that were present at lower levels in frozen–thawed spermatozoa by at least a mean of 1.79-fold (P<0.05). On classifying into ten distinct categories using bioinformatic analysis, most of the 41 differentially expressed proteins were found to be closely relevant to sperm premature capacitation, adhesions, energy supply, and sperm–oocyte binding and fusion. The expression of four of these proteins, SOD1, TPI1, ODF2, and AKAP3, was verified by western blot analysis. We propose that alterations in these identified proteins affect the quality of cryopreserved semen and ultimately lower its fertilizing capacity. This is the first study to compare protein levels in fresh and frozen–thawed spermatozoa using the iTRAQ technology. Our preliminary results provide an overview of the molecular mechanisms of cryodamage in frozen–thawed spermatozoa and theoretical guidance to improve the cryopreservation of boar semen.

Characterization of sperm surface protein patterns of ejaculated and capacitated boar sperm, with the detection of ZP binding candidates

Complementary molecules on the surface of both gametes are responsible for the interaction of sperm protein receptors with zona pellucida (ZP) saccharide structures, and many primary sperm receptors for ZP glycoproteins have been disclosed in various mammals. For our study, proteins were obtained from the surface of ejaculated and in vitro capacitated boar sperm. The isolated proteins were characterized by 1D- and 2D-electrophoretic protein profiles, and by glycoprotein staining. Our results show quantitative and qualitative differences in protein and glycoprotein patterns between ejaculated and capacitated sperm. Far-western blotting with ZP glycoproteins identified 17 interactions in the subproteome of the ejaculated sperm and 14 interactions in the subproteome of the capacitated sperm. High-molecular-mass proteins, coincident with binding to ZP, were sequence-identified. Angiotensin-converting enzyme (ACE), polycystic kidney disease receptor and egg jelly receptor (PKDREJ), and acrosin precursor were successfully identified. This is the first time PKDREJ has been identified on the surface of boar spermatozoa.

The molecular basis of gamete recognition in mice and humans

Successful fertilization heralds the onset of development and requires both gamete recognition and a definitive block to polyspermy. Sperm initially bind and penetrate the extracellular zona pellucida (ZP) that surrounds ovulated eggs, but are unable to bind the zona surrounding preimplantation embryos. The ZP of humans is composed of four (ZP1-4) and that of mouse three (ZP1-3) glycoproteins. Models for gamete recognition developed in mice had proposed that sperm bind to ZP3 glycans. However, phenotypes observed in genetically engineered mice are not consistent with this widely accepted model. More recently, taking advantage of the observation that human sperm do not bind to mouse eggs, human ZP2 was defined as the zona ligand in transgenic mouse models using gain-of-function assays. The sperm-binding site is an N-terminal domain of ZP2 that is cleaved by ovastacin, a metalloendoprotease released from egg cortical granules following fertilization. Proteolysis of this docking site provides a definitive block to polyspermy as sperm bind to uncleaved, but not cleaved ZP2 even after fertilization and cortical granule exocytosis. While progress has been made in defining the ZP ligand, less headway has been made in identifying the cognate sperm receptor. Although a number of sperm receptor candidates have been documented to interact with specific proteins in the ZP in vitro, continued fertility after genetic ablation of the cognate gene indicates that none are essential for gamete recognition. These on-going investigations inform reproductive medicine and suggest new therapies to improve fertility and/or provide contraception, thus expanding reproductive choices for human couples.

Sperm surface changes and physiological consequences induced by sperm handling and storage

Spermatozoa interact with their immediate environment and this contact remodels the sperm surface in preparation for fertilisation. These fundamental membrane changes will be critically covered in this review with special emphasis on the very specific surface destabilisation event, capacitation. This process involves very subtle and intricate modifications of the sperm membrane including removal of suppression (decapacitation) factors and changes in the lateral organisation of the proteins and lipids of the sperm surface. Processing of sperm for assisted reproduction (storage, sex-sorting, etc.) subjects spermatozoa to numerous stressors, and it is possible that this processing overrides such delicate processes resulting in sperm instability and cell damage. To improve sperm quality, novel mechanisms must be used to stabilise the sperm surface during handling. In this review, different types of membrane stress are considered, as well as novel surface manipulation methods to improve sperm stability.

Exploring polymorphisms and effects of candidate genes on milk fat quality in dairy sheep

The aim of the present study was to investigate the genetic control of the fatty acid (FA) composition in milk from 3 breeds of sheep: Altamurana, Gentile di Puglia, and Sarda. Single nucleotide polymorphisms within genes, encoding enzymes putatively involved in the synthesis and metabolism of milk fat, were selected for analysis, and the allele substitution effects were determined for 16 genes, which were polymorphic in the 3 sheep breeds, upon the milk fat composition. Four genes (alpha-1-antichymotrypsin-2; diacylglycerol O-acyltransferase homolog-2; propionyl Coenzyme A carboxylase, beta polypeptide; and insulin-like growth factor-I) play a role in the desaturation of stearic FA into polyunsaturated fatty acids. Furthermore, 2 genes (growth hormone receptor and zona pellucida glycoprotein-2) affect the variability of the total fat content in addition to the butyric and stearic FA profile, and the fatty acid synthetase gene has an influence on the medium-chain FA. Milk FA profiles play an important role in dairy sheep farming because they have a large effect on cheese characteristics and also because sheep milk may be marketed as a source of nutraceuticals because it contains higher levels of conjugated linoleic acid than milk from other ruminants. The current study evaluated the global effects of a large number of single nucleotide polymorphisms and haplotypes on traits that are not commonly investigated in sheep but that are potentially very useful for improving milk quality.

Loss of SED1/MFG-E8 results in altered luminal physiology in the epididymis

SED1/MFG-E8, herein referred to as SED1, is a bimotif adhesive protein with ascribed functions in a range of cell-cell interactions, including sperm-egg binding. In the male reproductive tract, SED1 is secreted by the initial segment of the epididymis, where it coats sperm and subsequently facilitates binding to the egg zona pellucida. We have recently reported that SED1-null epididymides show an unexpected incidence of spermatic granulomas, reflecting breakdown of the epithelium and a consequent autoimmune response against sperm antigens. However, spermatic granulomas are most often manifest in the distal segments of the epididymis, whereas the bulk of SED1 is expressed in the proximal epididymis. In some models, the presence of granulomas in the distal epididymis is associated with an underlying defect in the maintenance of luminal fluid homeostasis. Herein, we report that SED1-null epididymal fluid is both hypo-osmotic and alkaline, relative to wildtype epididymal fluid. Furthermore, the SED1-null epididymal epithelium exhibits various hallmarks of disrupted fluid reabsorption and pH regulation, including altered morphology of clear cells, increased intracellular vesicles, and apical distribution of VATPase. Results indicate that the SED1-null epididymal pathologies are not the secondary consequences of defective testes or efferent ducts or of improper epididymal differentiation, unlike that seen in other epididymal models. The expression and distribution of various ion exchangers, channels, and enzymes that mediate fluid transport and pH regulation are examined in wildtype and SED1-null epididymides, and models to account for how SED1 functions in luminal fluid dynamics are discussed.

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.

SED1/MFG-E8: a bi-motif protein that orchestrates diverse cellular interactions

MFG-E8 was initially identified as a principle component of the Milk Fat Globule, a membrane-encased collection of proteins and triglycerides that bud from the apical surface of mammary epithelia during lactation. It has since been independently identified in many species and by many investigators and given a variety of names, including p47, lactadherin, rAGS, PAS6/7, and BA-46. The acronym SED1 was proposed to bring cohesion to this nomenclature based upon it being a Secreted protein that contains two distinct functional domains: an N-terminal domain with two EGF-repeats, the second of which has an integrin-binding RGD motif, and a C-terminal domain with two Discoidin/F5/8C domains that bind to anionic phospholipids and/or extracellular matrices. SED1/MFG-E8 is now known to participate in a wide variety of cellular interactions, including phagocytosis of apoptotic lymphocytes and other apoptotic cells, adhesion between sperm and the egg coat, repair of intestinal mucosa, mammary gland branching morphogenesis, angiogenesis, among others. This article will explore the various roles proposed for SED1/MFG-E8, as well as its provocative therapeutic potential.

A novel role for SED1 (MFG-E8) in maintaining the integrity of the epididymal epithelium

The epididymis is a highly convoluted tubule that connects the testis with the vas deferens, and in which mammalian sperm acquire the ability to fertilize eggs. The most proximal portion of the epididymis, or initial segment, secretes numerous factors that are critical for sperm maturation and storage. One such factor is SED1 (also known as MFG-E8) a bi-motif protein composed of two N-terminal EGF domains, the second of which contains an RGD motif, and two C-terminal discoidin domains (also known as F5/8 type C domains). Previous studies have reported that SED1 is secreted into the epididymal lumen, where it coats sperm and later facilitates sperm-egg binding. Herein, we report that SED1-null males also harbor unexpected epididymal pathologies, including detached epithelia and spermatic granulomas. We therefore examined whether SED1 has a tissue-intrinsic role in the epididymis, in addition to its role in sperm-egg adhesion. Improved fixation protocols revealed that SED1 is found in the basolateral domains of epididymal epithelial cells in vivo, and similarly, SED1 is secreted both apically and basally from polarized epididymal cells in vitro. The basolateral distribution of SED1 suggests that it may play a novel role in epididymal cell adhesion. Consistent with this, in vitro assays showed that SED1 supports epididymal cell adhesion via RGD binding to alphaV integrin receptors on epididymal epithelial cells. Finally, epididymal cells from SED1-null males showed reduced adhesion in vitro, a phenotype that can be rescued with exogenous SED1. These results suggest that SED1 facilitates epididymal cell adhesion, and that its loss leads to breakdown of the epididymal epithelium and consequent development of spermatic granulomas.

Reassessing the role of protein-carbohydrate complementarity during sperm-egg interactions in the mouse

Despite years of intense study by many investigators, it may appear that we have made little progress towards a molecular understanding of mammalian sperm binding to the egg zona pellucida. An abundance of evidence derived from in vitro assays suggests that sperm-zona pellucida binding is dependent upon sperm recognition of specific glycan moieties on the zona pellucida glycoproteins. However, there is considerable disagreement regarding the identity of the zona pellucida sugars thought to mediate sperm binding, as well as disagreement over the identity of the sperm receptors themselves. Moreover, results from in vivo gene-targeting strategies fail to support a role for many, if not all, of the sperm receptors and their zona pellucida ligands implicated from in vitro assays. Nevertheless, a retrospective view of the literature suggests that some common principles are emerging regarding the molecular basis of mammalian sperm-zona binding, both with respect to the nature of the components that mediate binding, as well as the involvement of distinct receptor-ligand interactions, that involve both protein- and carbohydrate-dependent mechanisms of binding.

The involvement of beta-1,4-Galactosyltransferase and N-Acetylglucosamine residues in fertilization has been lost in the horse

BACKGROUND

In human and rodents, sperm-zona pellucida binding is mediated by a sperm surface Galactosyltransferase that recognizes N-Acetylglucosamine residues on a glycoprotein ZPC. In large domestic mammals, the role of these molecules remains unclear: in bovine, they are involved in sperm-zona pellucida binding, whereas in porcine, they are not necessary. Our aim was to clarify the role of Galactosyltransferase and N-Acetylglucosamine residues in sperm-zona pellucida binding in ungulates. For this purpose, we analyzed the mechanism of sperm-zona pellucida interaction in a third ungulate: the horse, since the Galactosyltransferase and N-Acetylglucosamine residues have been localized on equine gametes.

METHODS

We masked the Galactosyltransferase and N-Acetylglucosamine residues before the co-incubation of gametes. Galactosyltransferase was masked either with an anti-Galactosyltransferase antibody or with the enzyme substrate, UDP Galactose. N-Acetylglucosamine residues were masked either with a purified Galactosyltransferase or with an anti-ZPC antibody.

RESULTS AND DISCUSSION

The number of spermatozoa bound to the zona pellucida did not decrease after the masking of Galactosyltransferase or N-Acetylglucosamine. So, these two molecules may not be necessary in the mechanism of in vitro sperm-zona pellucida interaction in the horse.

CONCLUSION

The involvement of Galactosyltransferase and N-Acetylglucosamine residues in sperm-zona pellucida binding may have been lost during evolution in some ungulates, such as porcine and equine species.

The mouse gamete adhesin, SED1, is expressed on the surface of acrosome-intact human sperm

OBJECTIVE

To determine whether SED1, a protein secreted by the mouse epididymis that coats sperm and participates in sperm adhesion to the zona pellucida, is present on human sperm and in human epididymal tissue.

DESIGN

SED1 expression was analyzed by immunoblot and indirect immunofluorescence assays.

SETTING

Academic clinical and research laboratories.

PATIENT(S)

Human breast milk was donated. Unused semen was donated by men presenting for semen analysis or in vitro fertilization (IVF). Cadaveric epididymal tissue was obtained from the institutional body donor program.

INTERVENTION(S)

Human milk fat globule membranes and human seminal plasma proteins were analyzed by immunoblot. Human sperm and epididymis were analyzed by indirect immunofluorescence microscopy. Acrosomal status was determined by staining with fluorescein isothiocyanate-Pisum sativum agglutinin.

MAIN OUTCOME MEASURE(S)

Immunoblot and indirect immunofluorescence assays.

RESULT(S)

Human SED1 is recognized by two different polyclonal anti-SED1 antisera. SED1 is localized to the plasma membrane of human sperm overlying the intact acrosome. In acrosome-reacted sperm, SED1 is localized to the equatorial segment. SED1 is expressed by the epithelium of the anterior caput epididymis.

CONCLUSION(S)

SED1 is expressed on the surface of acrosome-intact human sperm and in the anterior caput of the human epididymis, similar to that seen in mouse.

Transcriptomic analyses reveal novel genes with sexually dimorphic expression in the zebrafish gonad and brain

BACKGROUND

Our knowledge on zebrafish reproduction is very limited. We generated a gonad-derived cDNA microarray from zebrafish and used it to analyze large-scale gene expression profiles in adult gonads and other organs.

METHODOLOGY/PRINCIPAL FINDINGS

We have identified 116638 gonad-derived zebrafish expressed sequence tags (ESTs), 21% of which were isolated in our lab. Following in silico normalization, we constructed a gonad-derived microarray comprising 6370 unique, full-length cDNAs from differentiating and adult gonads. Labeled targets from adult gonad, brain, kidney and 'rest-of-body' from both sexes were hybridized onto the microarray. Our analyses revealed 1366, 881 and 656 differentially expressed transcripts (34.7% novel) that showed highest expression in ovary, testis and both gonads respectively. Hierarchical clustering showed correlation of the two gonadal transcriptomes and their similarities to those of the brains. In addition, we have identified 276 genes showing sexually dimorphic expression both between the brains and between the gonads. By in situ hybridization, we showed that the gonadal transcripts with the strongest array signal intensities were germline-expressed. We found that five members of the GTP-binding septin gene family, from which only one member (septin 4) has previously been implicated in reproduction in mice, were all strongly expressed in the gonads.

CONCLUSIONS/SIGNIFICANCE

We have generated a gonad-derived zebrafish cDNA microarray and demonstrated its usefulness in identifying genes with sexually dimorphic co-expression in both the gonads and the brains. We have also provided the first evidence of large-scale differential gene expression between female and male brains of a teleost. Our microarray would be useful for studying gonad development, differentiation and function not only in zebrafish but also in related teleosts via cross-species hybridizations. Since several genes have been shown to play similar roles in gonadogenesis in zebrafish and other vertebrates, our array may even provide information on genetic disorders affecting gonadal phenotypes and fertility in mammals.

Multiple proteins present in purified porcine sperm apical plasma membranes interact with the zona pellucida of the oocyte

An important step in fertilization is the recognition and primary binding of the sperm cell to the zona pellucida (ZP). Primary ZP binding proteins are located at the apical plasma membrane of the sperm head. In order to exclusively study primary zona binding proteins, plasma membranes of sperm heads were isolated, highly purified and subsequently solubilized with a mild or a strong solubilization procedure. Native, highly purified ZP ghosts were used as the binding substrate for solubilized sperm plasma membrane proteins, and a proteomic approach was employed to identify ZP binding proteins. Two-dimensional gel electrophoresis of ZP fragments with bound sperm proteins showed very reproducibly 24 sperm protein spots to be associated to the zona ghosts after mild plasma membrane solubilization whereas only three protein spots were detected after strong plasma membrane solubilization. This indicates the involvement of multiple sperm proteins in ZP binding. The three persistently bound proteins were identified by a tandem mass spectrometry as isoforms of AQN-3 and probably represent the main sperm protein involved in ZP binding. P47, fertilin beta and peroxiredoxin 5 were also conclusively identified. None of the identified proteins has a known acrosomal origin, which further indicated that there was no sample contamination with secondary ZP binding proteins from the acrosomal matrix. In this study, we showed and identified multiple zona binding proteins involved in primary sperm-zona binding. Although we were not able to identify all of the proteins involved, this is a first step in understanding the event of primary sperm-zona interactions and the relevance of this for fertilization is discussed.

The EGF repeat and discoidin domain protein, SED1/MFG-E8, is required for mammary gland branching morphogenesis

SED1, also known as MFG-E8, is a secreted protein composed of two EGF repeats (the second of which contains an RGD motif) and two discoidin/Factor V/VIII C domains. SED1 is expressed by a wide range of cell types, where it participates in diverse cellular interactions, such as sperm binding to the egg coat and macrophage recognition of apoptotic lymphocytes. Although SED1 was originally identified as a milk protein, its function in the mammary gland remains unclear; suggested functions include inhibition of viral infection and clearance of apoptotic cells during mammary gland involution. We report here that SED1 has an unexpected obligatory role during mammary gland development. Unlike that seen in WT glands, SED1-null glands show severely reduced branching from epithelial ducts and from terminal end buds, which are thin and poorly developed. SED1 is expressed by both luminal and myoepithelial cells in the developing epithelial duct, and binds to alpha(v) integrin receptors on myoepithelial cells leading to MAPK activation and cell proliferation. The absence of SED1 leads to greatly reduced levels of activated MAPK and a concomitant reduction in cell proliferation and branching throughout the epithelial tree. These results suggest that SED1 contributes, at least partly, to the intercellular signaling between luminal and myoepithelial cells that is required for branching morphogenesis.

Identification of novel gamete receptors that mediate sperm adhesion to the egg coat

Mammalian fertilization is initiated by the species-specific binding of sperm to the zona pellucida, or egg coat. Earlier studies suggested that sperm-egg adhesion in mouse is mediated by the binding of beta1,4-galactosyltransferase-I (GalT) on the sperm surface to specific glycoside ligands on the egg coat glycoprotein, ZP3. Binding of multiple ZP3 oligosaccharides induces GalT aggregation, triggering a pertussis toxin-sensitive G-protein cascade leading to induction of the acrosome reaction. Consistent with this, sperm bearing targeted deletions in GalT are unable to bind ZP3 nor undergo ZP3-dependent acrosomal exocytosis; however, GalT-null sperm are still able to bind to the egg coat. This indicates that sperm-egg binding requires at least two independent binding mechanisms: a GalT-ZP3-independent event that mediates initial adhesion, followed by a GalT-ZP3 interaction that facilitates acrosomal exocytosis. During the past few years, novel GalT-ZP3-independent gamete receptors have been identified that appear to participate in initial gamete adhesion. On such receptor is SED1, an EGF repeat and discoidin domain protein that coats sperm as they traverse through the epididymis, and which is required for sperm to bind the egg coat. Similarly, a novel egg coat ligand is present on ovulated oocytes, but not on ovarian eggs, and which also appears to function in initial sperm binding. The identification of novel gamete receptors that are required for sperm-egg binding opens up new avenues for the development of specific contraceptive strategies.

Expression pattern of alphavbeta3 and alphavbeta5 integrin mRNA in mouse fetal gonads

The alphavbeta3 and alphavbeta5 integrins are known as transmembrane receptors capable of binding to the RGD amino acid peptide sequence. In mouse early gonadogenesis, some proteins containing the RGD sequence are deposited into extracellular space and participate in morphogenesis. We analyzed the expression patterns of the alphavbeta3 and alphavbeta5 integrins in mouse developing gonads (10.5-13.5 days post coitum) using whole-mount in situ hybridization. The alphav integrin mRNA was homogenously expressed in developing gonadal regions. On the other hand, the beta3 integrin mRNA was found only in large and round cells (presumptive germ cells), whereas beta5 integrin was localized in gonadal somatic cells, with the exception of coelomic epithelial cells. The beta3 integrin-expressed cells were determined to be primordial germ cells because the number of these cells was drastically reduced in busulfan-treated gonads. In this study, we demonstrated that the alphavbeta3 and alphavbeta5 integrins are widely localized in the mouse developing gonads and discussed their presumptive functions on mouse gonadogenesis.

Adhesion activity of fetal gonadal cells to EGF and discoidin domains of milk fat globule-EGF factor 8 (MFG-E8), a secreted integrin-binding protein which is transiently expressed in mouse early gonadogenesis

MFG-E8, a secreted integrin-binding protein, consists of two EGF domains containing a RGD motif and two discoidin domains. In mouse embryogenesis, MFG-E8 is highly expressed in gonadal stromal cells near mesonephros at 11.5-12.5 dpc, but its function in gonadogenesis has not been characterized. To clarify a possible role of MFG-E8 in developing gonads, we analyzed the adhesion activity of 10.5-15.5 dpc gonadal cells to recombinant proteins of EGF or discoidin domains of MFG-E8. In EGF-coated wells, the gonadal cells at 11.5-12.5 dpc revealed a significantly higher adhesion activity as compared to those at 10.5 and 15.5 dpc, while discoidin domains showed a constant number of the adhered cells throughout these stages. To identify the adhesive cells of 11.5-dpc gonads, immunohistochemistry with anti-SF1/Ad4Bp antibody (a specific marker for supporting, steroidogenic, and coelomic epithelial cells) and staining for alkaline phosphatase (a germ cell marker) were carried out. As a result, EGF domains, as well as discoidin domains, were capable of binding to all three groups of SF1/Ad4Bp-positive and negative somatic cells, and germ cells of 11.5-dpc gonads. These findings therefore suggest that MFG-E8 mediates the cell-to-cell interaction among several somatic cell types and germ cells in mouse early gonadogenesis.

SED1 function during mammalian sperm-egg adhesion

A prerequisite for successful fertilization is the species-specific binding of sperm to the extracellular coat of the egg. Gamete binding triggers the release of sperm hydrolytic enzymes that digest a path through the egg coat, thus bringing sperm into proximity with the egg plasma membrane where gamete fusion occurs. Although some components of the sperm membrane and the egg coat that participate in sperm-egg interactions have been identified, results from targeted deletions and gene substitutions indicate that other, as yet unidentified, gamete receptors must contribute to sperm-egg binding. Recent studies implicate the bi-motif protein, SED1, as being required for successful sperm-egg adhesion in mouse. SED1 contains Notch-like EGF repeats as well as discoidin/F5/8 complement domains--motifs that mediate a variety of cell-cell and cell-matrix interactions. SED1's ability to promote gamete adhesion resides within its two discoidin/F5/8C domains, which are able to dock to substrates as diverse as phospholipid membranes and extracellular matrices. SED1 is also expressed in a wide range of tissues and epithelia, where it may function similarly as an adhesive protein facilitating cell-cell and/or cell-matrix interactions.

Identification, proteomic profiling, and origin of ram epididymal fluid exosome-like vesicles

Small membranous vesicles, between 25- and 75-nm diameter, were collected by high-speed centrifugation from the ram cauda epididymal fluid and were found to be normal constituents of this fluid and of the seminal plasma. The SDS-PAGE protein pattern of these vesicles was specific and very different from that of the caudal fluid, seminal plasma, sperm extract, and cytoplasmic droplets. After two-dimensional electrophoresis separation and mass spectrometry analysis, several proteins were identified and grouped into i) membrane-linked enzymes, such as dipeptidyl peptidase IV (DPP-IV), neprilysin (NEP), phosphodiesterase-I (E-NPP3), and protein G-beta; ii) vesicle-associated proteins, such as lactadherin (MFEG8-PAS6/7) and vacuolar ATPase; iii) several cytoskeleton-associated proteins, such as actin, ezrin and annexin; and iv) metabolic enzymes. The presence of some of these proteins as well as several different hydrophobic proteins secreted by the epididymis was further confirmed by immunoblotting. These markers showed that the majority of the vesicles originated from the cauda epididymal region. The physical and biochemical characteristics of these vesicles suggest they are the equivalent of the exosomes secreted by several cell types and epithelium. The main membrane-linked proteins of the vesicles were not retrieved in the extract from cauda or ejaculated sperm, suggesting that these vesicles did not fuse with sperm in vivo.

Molecular genetic approaches to studying fertilization in model systems

In a wide range of experimental systems, a variety of both forward and reverse genetic approaches are becoming available for the study of the molecules involved in fertilization. An integration of these methods with the antibody-based and biochemical studies traditionally used in fertilization research is enabling rapid advancements in our understanding of this process. We highlight some of the recent advances resulting from these genetic methods and their applications in these systems.

X-linked retinoschisis: A clinical and molecular genetic review

X-linked retinoschisis is a leading cause of macular degeneration in male children. It is characterized by a high degree of clinical variability. Clinical features include a stellate foveal retinoschisis, with or without peripheral retinoschisis. The schisis occurs within the inner retina, primarily at the level of the nerve fiber layer. The disease-causing gene, X-linked retinoschisis 1, has recently been identified, and is expressed in photoreceptor and bipolar cells. This gene codes for retinoschisin, a secreted protein containing a discoidin domain which may be involved in cellular adhesion or cell-cell interactions. The identification of this gene allows for improved diagnosis and contributes to the understanding of this condition. Visual prognosis is variable, as X-linked retinoschisis exhibits a high degree of phenotypic variability. Although there is no treatment to halt the progressive maculopathy, clinical management is directed toward treatment of amblyopia and surgical correction of certain complications. X-linked retinoschisis is an important condition to study, both to improve the clinical management of this disorder, and to better understand retinal function and development. Herein, we review the clinical, histopathologic, and molecular genetic and treatment options of X-linked retinoschisis.

Effects of exposure of epididymal boar spermatozoa to seminal plasma on the binding of zona pellucida proteins during in vitro capacitation

The purpose of the investigation was to determine whether seminal plasma plays a role in the increase during in vitro capacitation of the number of boar spermatozoa with enhanced binding of zona pellucida proteins. Ejaculated spermatozoa and spermatozoa collected from the caudae epididymides of boars were incubated at 39 degrees C in a Tyrode's IVF medium. During incubation, the zona binding ability of individual spermatozoa was assessed with fluorescein-conjugated solubilized zona pellucida proteins (FITC-sZP), using a flow cytometer. Propidium iodide (PI) was included to simultaneously monitor cell viability. During incubation of ejaculated spermatozoa, a percentage of the spermatozoa expressed enhanced binding of FITC-sZP. The percentage of viable spermatozoa with enhanced binding reached a maximum of 37% (S.D.=8, averaged over five boars) after 2-3 h. In epididymal sperm, a similar maximum was observed after incubation in vitro, but a longer time of incubation was needed (6 h). Also, the rate of cell death of epididymal sperm was much lower than that of ejaculated sperm. When epididymal spermatozoa was exposed to seminal plasma in vitro, the time needed to reach a maximal percentage of viable spermatozoa with enhanced FITC-sZP binding was similar to that in ejaculated semen. However, the rate of cell death was still much lower than in ejaculated sperm. We concluded that the binding sites on the sperm surface that are involved in the increased binding of zona proteins during incubation under IVF conditions were not derived from the seminal plasma. The cellular processes leading to the increased binding capacity were accelerated by exposure of the sperm to seminal plasma.

DNA microarray analysis of region-specific gene expression in the mouse epididymis

Microarray analysis was carried out to identify genes with enriched expression in the initial segment region of the mouse epididymis. A set of approximately 15 000 clones developed at the National Institutes for Aging and consisting of expressed sequence tags (ESTs) derived from pre- and peri-implantation embryos, Embryonic Day 12.5 female gonad/mesonephros, and newborn ovary were hybridized with probes generated against the initial segment (epididymal region 1) and the remainder of the epididymis (epididymal regions 2-5). The median values for the normalized ratios of region 1 to regions 2-5 from three independent experiments were averaged for each gene/EST using Genespring 5.0 software. The majority of clones showed a ratio of 1.0, suggesting they were expressed at similar levels in all epididymal regions. In addition, 123 clones exhibited 2-fold or higher expression in the initial segment, including Cres3, prostein, lipocalin 2, ALEX3, synaptotagmin-like 4, erm, and milk fat globule factor, whereas 216 clones, including elafin-like 1, lactotransferrin, Sin3B, zinc-finger protein 91, and membrane-type frizzled-related protein, showed 2-fold or higher expression in epididymal regions 2-5. Northern blot analyses of 12 clones predicted by microarray analysis to be either enriched in the initial segment (n = 8), enriched in epididymal regions 2-5 (n = 2), or similar in all regions (n = 2) were carried out. All clones exhibited the expected region-specific expression, thus confirming the microarray results. The studies presented here show a global survey of region-specific gene expression in the epididymis, identifying 15287 sequences, the majority of which have not previously been shown to be expressed in this organ.

Identification of mouse sperm SED1, a bimotif EGF repeat and discoidin-domain protein involved in sperm-egg binding

We report the identification of SED1, a protein required for mouse sperm binding to the egg zona pellucida. SED1 is homologous to a small group of secreted cell-matrix adhesive proteins that contain Notch-like EGF repeats and discoidin/F5/8 type C domains. SED1 is expressed in spermatogenic cells and is secreted by the initial segment of the caput epididymis, resulting in SED1 localization on the sperm plasma membrane overlying the acrosome. SED1 binds specifically to the zona pellucida of unfertilized oocytes, but not to the zona of fertilized eggs. Recombinant SED1 and anti-SED1 antibodies competitively inhibit sperm-egg binding, as do truncated SED1 proteins containing a discoidin/C domain. SED1 null males are subfertile and their sperm are unable to bind to the egg coat in vitro. These studies illustrate that Notch-like EGF and discoidin/C domains, protein motifs that facilitate a variety of cellular interactions, participate in gamete recognition as well.

Cloning and characterization of boar epididymal secretory proteins by homology to the human

Northern blot analysis suggested that the boar epididymis produces closely related counterparts to human epididymal proteins HE1, HE3, HE4, HE5 and HE12. 'Full-length' cloning by nucleic acid and amino acid sequence similarity was achieved by RT-PCR methods in the case of the porcine counterparts of HE3 and HE4, while the homologues of HE5 and HE12, despite their cross-hybridization during Northern blot analysis, have not yet been cloned. The two novel porcine cDNAs were derived from moderately abundant epididymal mRNAs that were 75 and 83% identical to HE3 and HE4 cDNAs, respectively. To emphasize their relationship to the corresponding HEs, they were named Se3 and Se4 cDNAs. Their open reading frames predicted small secretory proteins with 55% (Se3) and 76% (Se4) conserved amino acids. Monospecific antipeptide antibodies to HE secretory proteins identified He3- and HE12-related proteins on Western blots of porcine epididymal fluid and semen. Both Northern and Western analyses indicated that the Se proteins were produced in a regionalized pattern and accumulated in the cauda fluid.

Cell adhesion and fertilization: steps in oocyte transport, sperm-zona pellucida interactions, and sperm-egg fusion

Fertilization in mammals requires the successful completion of many steps, starting with the transport of gametes in the reproductive tract and ending with sperm-egg membrane fusion. In this minireview, we focus on three adhesion steps in this multistep process. The first is oocyte "pick-up," in which the degree of adhesion between the extracellular matrix of the cumulus cells and oviductal epithelial cells controls the successful pick-up of the oocyte-cumulus complex and its subsequent transfer into the oviduct. The second part of this review is concerned with the interaction between the sperm and the zona pellucida of the egg. Evidence is discussed that a plasma membrane form of galactosyltransferase on the surface of mouse sperm binds to ZP3 in the zona pellucida and initiates an acrosome reaction. Additional evidence raises the possibility that initial sperm binding to the zona pellucida is independent of ZP3. Last, we address the relationship between sperm adhesion to the egg plasma membrane and membrane fusion, especially the role of ADAM family proteins on the sperm surface and egg integrins.