Tetraspanin family protein CD9 in the mouse sperm: unique localization, appearance, behavior and fate during fertilization

The association of ODF4 with AK1 and AK2 in mice is essential for fertility through its contribution to flagellar shape

Normal sperm flagellar shape and movement are essential for fertilization. The integral protein outer dense fiber 4 (ODF4) localizes to ODFs, but its function remains unclear. Adenylate kinase (AK) is a phosphotransferase that catalyzes the interconversion and controls the concentration equilibrium of adenine nucleotides. AK shuttles ATP to energy-consuming sites. Here, we report on the relationship of flagellar shape and movement with ODF4, AK1 and AK2 by using Odf4-deletion (Odf4^-/-) mice. Soluble ODF4 is coimmunoprecipitated with AK1 and AK2 in Odf4^+/+ spermatozoa. ODF4, AK1 and AK2 localize to whole flagella (plasmalemma, mitochondria, ODFs, and residual cytoplasmic droplets (CDs)), principal pieces, and midpieces, respectively. Odf4^-/- sperm flagella lose ODF4 and reduce AK1 and AK2 but produce ATP. The flagellum is bent (hairpin flagellum) with a large CD in the midpiece. There is no motility in the midpiece, but the principal piece is motile. Odf4^-/- spermatozoa progress backward and fail to ascend in the uterus. Thus, Odf4^-/- males are infertile owing to abnormal flagellar shape and movement caused mainly by the loss of ODF4 with AK1 and AK2. This study is supported by the rescue experiment; the abnormalities and male infertility caused by Odf4 deletion were reversed by Odf4 restoration.

Significance of Complement Regulatory Protein Tetraspanins in the Male Reproductive System and Fertilization

Fertilization is a very sophisticated and unique process involving several key steps resulting in a zygote's formation. Recent research has indicated that some immune system-related cell surface molecules (CD molecules from the tetraspanin superfamily) may have a role in fertilization. Extracellular vesicles are undeniably involved in a variety of cellular functions, including reproduction. Tetraspanin proteins identified in extracellular vesicles are now used mostly as markers; mounting evidence indicates that they also participate in cell targeting, cargo selection, and extracellular vesicle formation. Their significance and potential in mammalian reproduction are currently being studied extensively. Despite the fact that the current data did not establish any theory, the crucial function of tetraspanins in the fertilization process was not ruled out, and the specific role of tetraspanins is still unknown. In this review, we bring insight into the existing knowledge regarding the expression of tetraspanins in spermatozoa and seminal fluid and their role in gamete binding and fusion.

Tetraspanin Cd9b plays a role in fertility in zebrafish

In mice, CD9 expression on the egg is required for efficient sperm-egg fusion and no effects on ovulation or male fertility are observed in CD9 null animals. Here we show that cd9b knockout zebrafish also appear to have fertility defects. In contrast to mice, fewer eggs were laid by cd9b knockout zebrafish pairs and, of the eggs laid, a lower percentage were fertilised. These effects could not be linked to primordial germ cell numbers or migration as these were not altered in the cd9b mutants. The decrease in egg numbers could be rescued by exchanging either cd9b knockout partner, male or female, for a wildtype partner. However, the fertilisation defect was only rescued by crossing a cd9b knockout female with a wildtype male. To exclude effects of mating behaviour we analysed clutch size and fertilisation using in vitro fertilisation techniques. Number of eggs and fertilisation rates were significantly reduced in the cd9b mutants suggesting the fertility defects are not solely due to courtship behaviours. Our results indicate that CD9 plays a more complex role in fish fertility than in mammals, with effects in both males and females.

Role of Integrins in Sperm Activation and Fertilization

In mammals, integrins are heterodimeric transmembrane glycoproteins that represent a large group of cell adhesion receptors involved in cell-cell, cell-extracellular matrix, and cell-pathogen interactions. Integrin receptors are an important part of signalization pathways and have an ability to transmit signals into and out of cells and participate in cell activation. In addition to somatic cells, integrins have also been detected on germ cells and are known to play a crucial role in complex gamete-specific physiological events, resulting in sperm-oocyte fusion. The main aim of this review is to summarize the current knowledge on integrins in reproduction and deliver novel perspectives and graphical interpretations presenting integrin subunits localization and their dynamic relocation during sperm maturation in comparison to the oocyte. A significant part of this review is devoted to discussing the existing view of the role of integrins during sperm migration through the female reproductive tract; oviductal reservoir formation; sperm maturation processes ensuing capacitation and the acrosome reaction, and their direct and indirect involvement in gamete membrane adhesion and fusion leading to fertilization.

αV Integrin Expression and Localization in Male Germ Cells

Integrins are transmembrane receptors that facilitate cell adhesion and cell–extracellular matrix communication. They are involved in the sperm maturation including capacitation and gamete interaction, resulting in successful fertilization. αV integrin belongs to the integrin glycoprotein superfamily, and it is indispensable for physiological spermiogenesis and testosterone production. We targeted the gene and protein expression of the αV integrin subunit and described its membrane localization in sperm. Firstly, in mouse, we traced αV integrin gene expression during spermatogenesis in testicular fraction separated by elutriation, and we detected gene activity in spermatogonia, spermatocytes, and round spermatids. Secondly, we specified αV integrin membrane localization in acrosome-intact and acrosome-reacted sperm and compared its pattern between mouse, pig, and human. Using immunodetection and structured illumination microscopy (SIM), the αV integrin localization was confined to the plasma membrane covering the acrosomal cap area and also to the inner acrosomal membrane of acrosome-intact sperm of all selected species. During the acrosome reaction, which was induced on capacitated sperm, the αV integrin relocated and was detected over the whole sperm head. Knowledge of the integrin pattern in mature sperm prepares the ground for further investigation into the pathologies and related fertility issues in human medicine and veterinary science.

Suppression of Non-Random Fertilization by MHC Class I Antigens

Hermaphroditic invertebrates and plants have a self-recognition system on the cell surface of sperm and eggs, which prevents their self-fusion and enhances non-self-fusion, thereby contributing to genetic variation. However, the system of sperm–egg recognition in mammals is under debate. To address this issue, we explored the role of major histocompatibility complex class I (MHC class I, also known as histocompatibility 2-K^b or H2-K^b and H2-D^b in mice) antigens by analyzing H2-K^b-/-H2-D^b-/-β2-microglobulin (β2M)^-/- triple-knockout (T-KO) male mice with full fertility. T-KO sperm exhibited an increased sperm number in the perivitelline space of wild-type (WT) eggs in vitro. Moreover, T-KO sperm showed multiple fusion with zona pellucida (ZP)-free WT eggs, implying that the ability of polyspermy block for sperm from T-KO males was weakened in WT eggs. When T-KO male mice were intercrossed with WT female mice, the percentage of females in progeny increased. We speculate that WT eggs prefer fusion with T-KO sperm, more specifically X-chromosome-bearing sperm (X sperm), suggesting the presence of preferential (non-random) fertilization in mammals, including humans.

The Progresses of Spermatogonial Stem Cells Sorting Using Fluorescence-Activated Cell Sorting

In recent years, the research on stem cells has been more and more in-depth, and many achievements have been made in application. However, due to the small number of spermatogonial stem cells (SSCs) and deficiency of efficient markers, it is difficult to obtain very pure SSCs, which results in the research on them being hindered. In fact, many methods have been developed to isolate and purify SSCs, but these methods have their shortcomings. Fluorescence-activated cell sorting (FACS), as a method to enrich SSCs with the help of specific surface markers, has the characteristics of high efficiency and accuracy in enrichment of SSCs, thus it is widely accepted as an effective method for purification of SSCs. This review summarizes the recent studies on the application of FACS in SSCs, and introduces some commonly used markers of effective SSCs sorting, aiming to further optimize the FACS sorting method for SSCs, so as to promote the research of germline stem cells and provide new ideas for the research of reproductive biology.

Tetraspanins in mammalian reproduction: spermatozoa, oocytes and embryos

It is known that tetraspanin proteins are involved in many physiological somatic cell mechanisms. Additionally, research has indicated they also have a role in various infectious diseases and cancers. This review focuses on the molecular interactions underlying the tetraspanin web formation in gametes. Primarily, tetraspanins act in the reproductive tract as organizers of membrane complexes, which include the proteins involved in the contact and association of sperm and oocyte membranes. In addition, recent data shows that tetraspanins are likely to be involved in these processes in a complex way. In mammalian fertilization, an important role is attributed to CD molecules belonging to the tetraspanin superfamily, particularly CD9, CD81, CD151, and also CD63; mostly as part of extracellular vesicles, the significance of which and their potential in reproduction is being intensively investigated. In this article, we reviewed the existing knowledge regarding the expression of tetraspanins CD9, CD81, CD151, and CD63 in mammalian spermatozoa, oocytes, and embryos and their involvement in reproductive processes, including pathological events.

Expression and distribution of CD151 as a partner of alpha6 integrin in male germ cells

The physiological importance of CD151 tetraspanin is known from somatic cells and its outside-in signalling through integrins was described. In male germ cells, two tetraspanins, CD9 and CD81, are involved in sperm-egg membrane fusion, and similarly to integrins, they occupy characteristic regions. We report here on a newly discovered presence of CD151 in sperm, and present its expression and distribution during spermatogenesis and sperm transition during the acrosome reaction. We traced CD151 gene and protein expression in testicular cell subpopulations, with strong enrichment in spermatogonia and spermatids. The testicular and epididymal localization pattern is designated to the sperm head primary fusion site called the equatorial segment and when compared to the acrosome vesicle status, CD151 was located into the inner acrosomal membrane overlying the nucleus. Moreover, we show CD151 interaction with α6 integrin subunit, which forms a dimer with β4 as a part of cis-protein interactions within sperm prior to gamete fusion. We used mammalian species with distinct sperm morphology and sperm maturation such as mouse and bull and compared the results with human. In conclusion, the delivered findings characterise CD151 as a novel sperm tetraspanin network member and provide knowledge on its physiology in male germ cells.

CD9 and CD81 Interactions and Their Structural Modelling in Sperm Prior to Fertilization

Proteins CD9 and CD81 are members of the tetraspanin superfamily and were detected in mammalian sperm, where they are suspected to form an active tetraspanin web and to participate in sperm–egg membrane fusion. The importance of these two proteins during the early stages of fertilization is supported by the complete sterility of CD9/CD81 double null female mice. In this study, the putative mechanism of CD9/CD81 involvement in tetraspanin web formation in sperm and its activity prior to fertilization was addressed. Confocal microscopy and colocalization assay was used to determine a mutual CD9/CD81 localization visualised in detail by super-resolution microscopy, and their interaction was address by co-immunoprecipitation. The species-specific traits in CD9 and CD81 distribution during sperm maturation were compared between mice and humans. A mutual position of CD9/CD81 is shown in human spermatozoa in the acrosomal cap, however in mice, CD9 and CD81 occupy a distinct area. During the acrosome reaction in human sperm, only CD9 is relocated, compared to the relocation of both proteins in mice. The structural modelling of CD9 and CD81 homologous and possibly heterologous network formation was used to propose their lateral Cis as well as Trans interactions within the sperm membrane and during sperm–egg membrane fusion.

Review: Sperm-oocyte interactions and their implications for bull fertility, with emphasis on the ubiquitin-proteasome system

Fertilization is an intricate cascade of events that irreversibly alter the participating male and female gamete and ultimately lead to the union of paternal and maternal genomes in the zygote. Fertilization starts with sperm capacitation within the oviductal sperm reservoir, followed by gamete recognition, sperm-zona pellucida interactions and sperm-oolemma adhesion and fusion, followed by sperm incorporation, oocyte activation, pronuclear development and embryo cleavage. At fertilization, bull spermatozoon loses its acrosome and plasma membrane components and contributes chromosomes, centriole, perinuclear theca proteins and regulatory RNAs to the zygote. While also incorporated in oocyte cytoplasm, structures of the sperm tail, including mitochondrial sheath, axoneme, fibrous sheath and outer dense fibers are degraded and recycled. The ability of some of these sperm contributed components to give rise to functional zygotic structures and properly induce embryonic development may vary between bulls, bearing on their reproductive performance, and on the fitness, health, fertility and production traits of their offspring. Proper functioning, recycling and remodeling of gamete structures at fertilization is aided by the ubiquitin-proteasome system (UPS), the universal substrate-specific protein recycling pathway present in bovine and other mammalian oocytes and spermatozoa. This review is focused on the aspects of UPS relevant to bovine fertilization and bull fertility.

Reproductive tract modifications of the boar sperm surface

The sperm cell has a unique, polarized, and segregated surface that is modified extensively by the changing environments in both the male and the female reproductive tracts. The sperm cannot refresh its surface, as protein translation and membrane recycling by intracellular vesicular transport have ceased upon its maturation. So, how is the sperm surface modified in the reproductive tracts and how do these processes affect fertilization? This review traces these modifications as boar sperm travels from their liberation from the Sertoli cell into the lumen of seminiferous tubules of the testis to the site of fertilization in the ampulla of the oviduct in the sow, via an artificial insemination route. The effect of sperm dilution for artificial insemination, as well as more extensive sperm processing for in vitro fertilization, cryopreservation, or sex sorting, are also discussed with respect to how these procedures affect sperm surface organization and fertilization capacity.

Oviductosome-Sperm Membrane Interaction in Cargo Delivery: DETECTION OF FUSION AND UNDERLYING MOLECULAR PLAYERS USING THREE-DIMENSIONAL SUPER-RESOLUTION STRUCTURED ILLUMINATION MICROSCOPY (SR-SIM)

Oviductosomes ((OVS), exosomes/microvesicles), which deliver the Ca(2+) efflux pump, plasma membrane Ca(2+)ATPase 4 (PMCA4), to sperm are likely to play an important role in sperm fertilizing ability (Al-Dossary, A. A., Strehler, E. E., and Martin-DeLeon, P. A. (2013) PloS one 8, e80181). It is unknown how exosomes/microvesicles deliver transmembrane proteins such as PMCA4 to sperm. Here we define a novel experimental approach for the assessment of the interaction of OVS with sperm at a nanoscale level, using a lipophilic dye (FM4-64FX) and three-dimensional SR/SIM, which has an 8-fold increase in volumetric resolution, compared with conventional confocal microscopy. Coincubation assays detected fusion of prelabeled OVS with sperm, primarily over the head and midpiece. Immunofluorescence revealed oviductosomal delivery of PMCA4a to WT and Pmca4 KO sperm, and also endogenous PMCA4a on the inner acrosomal membrane. Fusion was confirmed by transmission immunoelectron microscopy, showing immunogold particles in OVS, and fusion stalks on sperm membrane. Immunofluorescence colocalized OVS with the αv integrin subunit which, along with CD9, resides primarily on the sperm head and midpiece. In capacitated and acrosome reacted sperm, fusion was significantly (p < 0.001) inhibited by blocking integrin/ligand interactions via antibodies, exogenous ligands (vitronectin and fibronectin), and their RGD recognition motif. Our results provide evidence that receptor/ligand interactions, involving αvβ3 and α5β1integrins on sperm and OVS, facilitate fusion of OVS in the delivery of transmembrane proteins to sperm. The mechanism uncovered is likely to be also involved in cargo delivery of prostasomes, epididymosomes, and uterosomes.

Bovine sperm plasma membrane proteomics through biotinylation and subcellular enrichment

A significant proportion of mammalian fertilization is mediated through the proteomic composition of the sperm surface. These protein constituents can present as biomarkers to control and regulate breeding of agricultural animals. Previous studies have addressed the bovine sperm cell apical plasma membrane (PM) proteome with nitrogen cavitation enrichment. Alternative workflows would enable to expand the compositional data more globally around the entire sperm's surface. We used a cell surface biotin-labeling in combination with differential centrifugation to enrich sperm surface proteins. Using nano-LC MS/MS, 338 proteins were confidently identified in the PM-enriched proteome. Functional categories of sperm-egg interaction, protein turnover, metabolism as well as molecular transport, spermatogenesis, and signal transduction were represented by proteins with high quantitative signal in our study. A highly significant degree of enrichment was found for transmembrane and PM-targeted proteins. Among them, we also report proteins previously not described on bovine sperm (CPQ, CD58, CKLF, CPVL, GLB1L3, and LPCAT2B) of which CPQ and CPVL cell surface localization was further validated. A descriptive overview of the bovine sperm PM integral and peripheral proteins is provided to complement future studies on animal reproduction and its relation to sperm cell surface. All MS data have been deposited in the ProteomeXchange with identifier PXD001096 (http://proteomecentral.proteomexchange.org/dataset/PXD001096).

Analysis of the complexity of the sperm acrosomal membrane by super-resolution stimulated emission depletion microscopy compared with transmission electron microscopy

The acrosome is a Golgi-derived sperm cell organelle enclosed by a continuous acrosomal membrane. The acrosomal membrane complexes with surrounding matrices containing molecules necessary for fertilization; however, the complex of acrosomal membrane and associating matrices (CAMAM) has not been visualized in detail under living conditions. Here, we analyzed the CAMAM at the nanometer level using super-resolution stimulated emission depletion (STED) fluorescence microscopy and equatorin-enhanced green fluorescent protein transgenic mice. The STED images were compared with the corresponding images taken by immunoelectron microscopy. Consequently, the substructure of CAMAM could be differentiated at nanometer-scale resolution by STED microscopy without the need for sectioning. The information obtained in this study will be beneficial not only for understanding the molecular mechanism of fertilization but also for cell imaging under living conditions.

Integration of the mouse sperm fertilization-related protein equatorin into the acrosome during spermatogenesis as revealed by super-resolution and immunoelectron microscopy

Spermatids must precisely integrate specific molecules into structurally supported domains that develop during spermatogenesis. Once established, the architecture of the acrosome contributes to the acrosome reaction, which occurs prior to gamete interaction in mammals. The present study aims to clarify the morphology associated with the integration of the mouse fertilization-related acrosomal protein equatorin (mEQT) into the developing acrosome. EQT mRNA was first detected by in situ hybridization in round spermatids but disappeared in early elongating spermatids. The molecular size of mEQT was approximately 65 kDa in the testis. Developmentally, EQT protein was first detected on the nascent acrosomal membrane in round spermatids at approximately step 3, was actively integrated into the acrosomal membranes of round spermatids in the following step and then participated in acrosome remodeling in elongating spermatids. This process was clearly visualized by high-resolution fluorescence microscopy and super-resolution stimulated emission depletion nanoscopy by using newly generated C-terminally green-fluorescent-protein-tagged mEQT transgenic mice. Immunogold electron microscopy revealed that mEQT was anchored to the acrosomal membrane, with the epitope region observed as lying 5-70 nm away from the membrane and was associated with the electron-dense acrosomal matrix. This new information about the process of mEQT integration into the acrosome during spermatogenesis should provide a better understanding of the mechanisms underlying not only acrosome biogenesis but also fertilization and male infertility.

Involvement of sperm plasma membrane and cytoskeletal proteins in human male infertility

OBJECTIVE

To assess the physicochemical characteristics of sperm plasma membrane and to evaluate the immunohistochemical expression of transmembrane and cytoskeletal proteins in spermatozoa isolated from normospermic fertile donors and asthenozoospermic infertile patients.

DESIGN

Case-control study.

SETTING

Academic male infertility center.

PATIENT(S)

Twenty-five infertile patients affected by idiopathic asthenozoospermia and 21 age-matched normospermic fertile donors.

INTERVENTION(S)

Sperm parameters were evaluated; membrane fluidity and hydration studies, and immunohistochemical analysis were performed in isolated spermatozoa.

MAIN OUTCOME MEASURE(S)

Semen analyses to ascertain volume, sperm count, motility, and morphology; then membrane fluidity and hydration studies and immunohistochemical analysis were performed on isolated spermatozoa.

RESULT(S)

Spermatozoa from the asthenozoospermic group exhibited a reduced fluidity at the lipid-water interface level, an increased fluidity of the deeper portion of the bilayer, and a lower plasma membrane hydration than normospermic cells. Moreover, the immunohistochemical expression of ezrin, Cdc42, CD9, F-actin, and β-tubulin was higher in normospermic samples.

CONCLUSION(S)

Our results together assume that a cytoskeletal reorganization induced by a disturbance in the physicochemical features of sperm plasma membrane, and potentially mediated by ezrin, Cdc42, and tetraspanin CD9, could have a role in idiopathic asthenozoospermia.

CD81 and CD9 work independently as extracellular components upon fusion of sperm and oocyte

When a sperm and oocyte unite into one cell upon fertilization, membranous fusion between the sperm and oocyte occurs. In mice, Izumo1 and a tetraspanin molecule CD9 are required for sperm-oocyte fusion as one of the oocyte factors, and another tetraspanin molecule CD81 is also thought to involve in this process. Since these two tetraspanins often form a complex upon cell-cell interaction, it is probable that such a complex is also formed in sperm-oocyte interaction; however, this possibility is still under debate among researchers. Here we assessed this problem using mouse oocytes. Immunocytochemical analysis demonstrated that both CD9 and CD81 were widely distributed outside the oocyte cell membrane, but these molecules were separate, forming bilayers, confirmed by immunobiochemical analysis. Electron-microscopic analysis revealed the presence of CD9- or CD81-incorporated extracellular structures in those bilayers. Finally, microinjection of in vitro-synthesized RNA showed that CD9 reversed a fusion defect in CD81-deficient oocytes in addition to CD9-deficient oocytes, but CD81 failed in both oocytes. These results suggest that both CD9 and CD81 independently work upon sperm-oocyte fusion as extracellular components.

Membrane transfer from oocyte to sperm occurs in two CD9-independent ways that do not supply the fertilising ability of Cd9-deleted oocytes

Spermatozoa undergo regulation of their functions along their lifespan through exchanges via vesicles or interactions with epithelial cells, in the epididymis, in the seminal fluid and in the female genital tract. Two different ways of oocyte membrane transfer to spermatozoa have been described: trogocytosis and exosomes. We here report an analysis of in vitro exchanges between the membranes of unfertilised oocytes and capacitated spermatozoa. We showed that optimum conditions are fulfilled when unfertilised oocytes interact with acrosome-reacted spermatozoa, a scenario mimicking the events occurring when the fertilising spermatozoon is inside the perivitelline space. Although CD9 tetraspanin is an essential molecule for fertilisation, exosome and trogocytosis transfer persists in Cd9-null oocytes in spite of their dramatic fusion failure. These exchanges are CD9 tetraspanin independent. We also confirm that mice sperm express CD9 tetraspanin and that when Cd9-null oocytes were inseminated with sperm covered with oocyte membrane materials, including CD9 tetraspanin, no rescue of the oocytes' fertilisability could be obtained. Thus, the existence of two ways of exchange between gametes during fertilisation suggests that these events could be of a physiological importance in this process.

Differentiation of murine male germ cells to spermatozoa in a soft agar culture system

Establishment of an in vitro system that allows the development of testicular germ cells to sperm will be valuable for studies of spermatogenesis and future treatments for male infertility. In the present study, we developed in vitro culture conditions using three-dimensional agar culture system (SACS), which has the capacity to induce testicular germ cells to reach the final stages of spermatogenesis, including spermatozoa generation. Seminiferous tubules from testes of 7-day-old mice were enzymatically dissociated, and intratubular cells were cultured in the upper layer of the SACS in RPMI medium supplemented with fetal calf serum (FCS). The lower layer of the SACS contained only RPMI medium supplemented with FCS. Colonies in the upper layer were isolated after 14 and 28 days of culture and were classified according to their size. Immunofluorescence and real-time PCR were used to analyse specific markers expressed in undifferentiated and differentiated spermatogonia (Vasa, Dazl, OCT-4, C-Kit, GFR-α-1, CD9 and α-6-integrin), meiotic cells (LDH, Crem-1 and Boule) and post-meiotic cells (Protamine-1, Acrosin and SP-10). Our results reveal that it is possible to induce mouse testicular pre-meiotic germ cell expansion and induce their differentiation to spermatozoa in SACS. The spermatozoa showed normal morphology and contained acrosomes. Thus, our results demonstrate that SACS could be used as a novel in vitro system for the maturation of pre-meiotic mouse germ cells to post-meiotic stages and morphologically-normal spermatozoa.

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.

Dynamics of the mammalian sperm membrane modification leading to fertilization: a cytological study

Fertilization occurs when the sperm penetrates the egg, resulting in the combination of paternal and maternal genomes for the propagation of generations. To perform the task, the mammalian sperm membrane system, constructed during spermatogenesis, undergoes biochemical and cytological modifications. In this review, the following three points are discussed: (i) the nature of the acrosomal membrane disclosed by various types of microscopy, including transmission electron microscopy and the recently developed high-resolution fluorescence microscopy, (ii) the nascent acrosomal membrane dysfunction during acrosome biogenesis and (iii) the modification of the sperm membrane during sperm-egg interaction.

Fertilization and the oocyte-to-embryo transition in C. elegans

Fertilization is a complex process comprised of numerous steps. During fertilization, two highly specialized and differentiated cells (sperm and egg) fuse and subsequently trigger the development of an embryo from a quiescent, arrested oocyte. Molecular interactions between the sperm and egg are necessary for regulating the developmental potential of an oocyte, and precise coordination and regulation of gene expression and protein function are critical for proper embryonic development. The nematode Caenorhabditis elegans has emerged as a valuable model system for identifying genes involved in fertilization and the oocyte-to-embryo transition as well as for understanding the molecular mechanisms that govern these processes. In this review, we will address current knowledge of the molecular underpinnings of gamete interactions during fertilization and the oocyte-to-embryo transition in C. elegans. We will also compare our knowledge of these processes in C. elegans to what is known about similar processes in mammalian, specifically mouse, model systems.

Cumulus cell gene expression following the LH surge in bovine preovulatory follicles: potential early markers of oocyte competence

Cumulus cells (CCs) are essential for oocytes to reach full development competency and become fertilized. Many major functional properties of CCs are triggered by gonadotropins and governed by the oocyte. Consequently, cumulus may reflect oocyte quality and is often used for oocyte selection. The most visible function of CCs is their ability for rapid extracellular matrix expansion after the LH surge. Although unexplained, LH induces the final maturation and improves oocyte quality. To study the LH signaling and gene expression cascade patterns close to the germinal vesicle breakdown, bovine CCs collected at 2 h before and 6 h after the LH surge were hybridized to a custom-made microarray to better understand the LH genomic action and find differentially expressed genes associated with the LH-induced oocyte final maturation. Functional genomic analysis of the 141 overexpressed and 161 underexpressed clones was performed according to their molecular functions, gene networks, and cell compartments. Following real-time PCR validation of our gene lists, some interesting pathways associated with the LH genomic action on CCs and their possible roles in oocyte final maturation, ovulation, and fertilization are discussed. A list of early potential markers of oocyte competency in vivo and in vitro is thereafter suggested. These early biomarkers are a preamble to understand the LH molecular pathways that trigger the final oocyte competence acquisition process in bovine.