Reduction of mouse egg surface integrin alpha9 subunit (ITGA9) reduces the egg's ability to support sperm-egg binding and fusion

Assessing genomic diversity and selective pressures in Bashan cattle by whole-genome sequencing data

Specific ecological environments and domestication have continuously influenced the physiological characteristics of Chinese indigenous cattle. Among them, Bashan cattle belongs to one of the indigenous breeds. However, the genomic diversity of Bashan cattle is still unknown. Published whole-genome sequencing (WGS) data of 13 Bashan cattle and 48 worldwide cattle were used to investigate the genetic composition and selection characteristics of Bashan cattle. The population structure analysis revealed that Bashan cattle harbored ancestries with East Asian taurine and Chinese indicine. Genetic diversity analysis implied the relatively high genomic diversity in Bashan cattle. Through the identification of containing >5 nsSNPs or frameshift mutations genes in Bashan cattle, a large number of pathways related to sensory perception were discovered. CLR, θπ ratio, FST, and XP-EHH methods were used to detect the candidate signatures of positive selection in Bashan cattle. Among the identified genes, most of the enriched signal pathways were related to environmental information processing, biological systems, and metabolism. We mainly reported genes related to the nervous system (HCN1, KATNA1, FSTL1, GRIK2, and CPLX2), immune (CD244, SLAMF1, LY9, and CD48), and reproduction (AKR1C1, AKR1C3, AKR1C4, and TUSC3). Our findings will be significant in understanding the molecular basis underlying phenotypic variation of breed-related traits and improving productivity in Bashan cattle.

Identification and Expression of Integrins during Testicular Fusion in Spodoptera litura

Integrin members are cell adhesion receptors that bind to extracellular matrix (ECM) proteins to regulate cell-cell adhesion and cell-ECM adhesion. This process is essential for tissue development and organogenesis. The fusion of two testes is a physiological phenomenon that is required for sperm production and effective reproduction in many Lepidoptera. However, the molecular mechanism of testicular fusion is unclear. In Spodoptera litura, two separated testes fuse into a single testis during the larva-to-pupa transformation. We identified five α and five β integrin subunits that were closely associated with testicular fusion. Integrin α1 and α2 belong to the position-specific 1 (PS1) and PS2 groups, respectively. Integrin α3, αPS1/αPS2, and αPS3 were clustered into the PS3 group. Integrin β1 belonged to the insect β group, and β2, β3, and β5 were clustered in the βν group. Among these integrins, α1, α2, α3, αPS1/PS2, αPS3, β1, and β4 subunits were highly expressed when the testes fused. However, their expression levels were much lower before and after the fusion of the testis. The qRT-PCR and immunohistochemistry analyses indicated that integrin β1 mRNA and the protein were highly expressed in the peritoneal sheath of the testis, particularly when the testes fused. These results indicate that integrins might participate in S. litura testicular fusion.

Detrimental effects of vitrification on integrin genes (α9 and β1) and in vitro fertilization in mouse oocytes

OBJECTIVE

Integrins are known as key molecules that importantly involve in fertilization. This study aimed to evaluate effects of vitrification on fertilization rate and expression of integrin genes, α9 and β1, on mice oocytes in GV and MІІ stages.

MATERIALS AND METHODS

From the ovarian tissue and fallopian tube of NMRI mice, germinal vesicle (GV, n = 200) and metaphase II (MII, n = 200) oocytes were obtained. Then, oocytes were distributed into 4 groups including non-vitrified GV, non-vitrified MII, vitrified GV, and vitrified MII. Cryotop method was used for vitrification and oocytes (for 4 weeks) were kept in liquid nitrogen. After that, by using an inverted microscope, the rate of survived oocytes was assessed. Also, in vitro fertilization (IVF) for oocytes, obtained from in vitro maturated MII and mice ovaries (ovulated MII), was done to assess embryos at differenced stages (2-cells, morula, and hatched). Finally, RT-qPCR was performed to investigate the mRNA expression of integrin genes (α9 and β1).

RESULTS

After vitrification, the rate of survived oocytes, 68.65%for GV and 65.07% % for MII, did not show a remarkable difference related to non-vitrified groups, while the fertilization rate in vitrified groups remarkably decrease compared to non-vitrified groups (p < 0.05). Also, the expression of α9 and β1 genes was significantly altered in vitrified groups when compared to non-vitrified groups (p < 0.05). There was no significant difference in embryo developmental rates for non-vitrified and vitrified groups.

CONCLUSION

Cryotop method for vitrification caused an alternation in oocyte quality by reducing fertilization rate and integrin gene expression.

Positive selection on ADAM10 builds species recognition in the synchronous spawning coral Acropora

The reef-building coral Acropora is a broadcast spawning hermaphrodite including more than 110 species in the Indo-Pacific. In addition, many sympatric species show synchronous spawning. The released gametes need to mate with conspecifics in the mixture of the gametes of many species for their species boundaries. However, the mechanism underlying the species recognition of conspecifics at fertilization remains unknown. We hypothesized that rapid molecular evolution (positive selection) in genes encoding gamete-composing proteins generates polymorphic regions that recognize conspecifics in the mixture of gametes from many species. We identified gamete proteins of Acropora digitifera using mass spectrometry and screened the genes that support branch site models that set the "foreground" branches showing strict fertilization specificity. ADAM10, ADAM17, Integrin α9, and Tetraspanin4 supported branch-site model and had positively selected site(s) that produced polymorphic regions. Therefore, we prepared antibodies against the proteins of A. digitifera that contained positively selected site(s) to analyze their functions in fertilization. The ADAM10 antibody reacted only with egg proteins of A. digitifera, and immunohistochemistry showed ADAM10 localized around the egg surface. Moreover, the ADAM10 antibody inhibited only A. digitifera fertilization but not the relative synchronous spawning species A. papillare. This study indicates that ADAM10 has evolved to gain fertilization specificity during speciation and contributes to species boundaries in this multi-species, synchronous-spawning, and species-rich genus.

Mysteries and unsolved problems of mammalian fertilization and related topics

Mammalian fertilization is a fascinating process that leads to the formation of a new individual. Eggs and sperm are complex cells that must meet at the appropriate time and position within the female reproductive tract for successful fertilization. I have been studying various aspects of mammalian fertilization over 60 years. In this review, I discuss many different aspects of mammalian fertilization, some of my laboratory's contribution to the field, and discuss enigmas and mysteries that remain to be solved.

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.

Partial Sperm beta1 Integrin Subunit Deletion Proves its Involvement in Mouse Gamete Adhesion/Fusion

We have previously shown, using antibodies, that the sperm alpha6beta1 integrin is involved in mouse gamete fusion in vitro. Here we report the conditional knockdown of the sperm Itgb1 gene. It induced a drastic failure of sperm fusogenic ability with sperm accumulation in the perivitelline space of in vitro inseminated oocytes deleted or not for the Itgb1 gene. These data demonstrate that sperm, but not oocyte, beta1 integrin subunit is involved in gamete adhesion/fusion. Curiously, knockdown males were fertile in vivo probably because of the incomplete Cre-mediated deletion of the sperm Itgb1 floxed gene. Indeed, this was shown by Western blot analysis and confirmed by both the viability and litter size of pups obtained by mating partially sperm Itgb1 deleted males with females producing completely deleted Itgb1 oocytes. Because of the total peri-implantation lethality of Itgb1 deletion in mice, we assume that sperm that escaped the Itgb1 excision seemed to be preferentially used to fertilize in vivo. Here, we showed for the first time that the deletion, even partial, of the sperm Itgb1 gene makes the sperm unable to normally fertilize oocytes. However, to elucidate the question of the essentiality of its role during fertilization, further investigations using a mouse expressing a recombinase more effective in male germ cells are necessary.

Laminin-111 Inhibits Bovine Fertilization but Improves Embryonic Development in vitro, and Receptor Integrin-β1 is Involved in Sperm-Oocyte Binding

This study detected the distribution of laminin during embryonic formation by immunofluorescence. To determine the possible function of laminin on developmental ability of in vitro fertilized embryos, the presumptive zygotes were divided and transferred to CR1aa medium supplemented with different concentrations (0 μg/ml, 5 μg/ml, 10 μg/ml and 20 μg/ml) of laminin. To explore the association with sperm-oocyte fusion, oocytes and/or sperm were pre-incubated with laminin or anti-β1 antibody before insemination. Laminin was absent in mature oocytes and could be detected first at the 8-cell stage and then displayed an increasing tendency. Adding 10 μg/ml laminin to the culture medium improved embryonic development including cleavage rate, blastocyst rate, total cell numbers in the blastocyst and cell numbers in the inner cell mass. Laminin inhibited sperm-oocyte fusion when incubated with oocytes and/or sperm before in vitro fertilization, and only integrin-β1 of sperm was involved in sperm-oocyte binding. Inhibition may be caused by blocking β1, but why laminin inhibits fertilization is still unknown. The results suggest that laminin plays an important role during embryonic formation and has a negative function in sperm-oocyte fusion, but improves embryonic development. However, only integrin-β1 is involved in sperm-oocyte binding.

Integrin Adhesions Suppress Syncytium Formation in the Drosophila Larval Epidermis

Integrins are critical for barrier epithelial architecture. Integrin loss in vertebrate skin leads to blistering and wound healing defects. However, how integrins and associated proteins maintain the regular morphology of epithelia is not well understood. We found that targeted knockdown of the integrin focal adhesion (FA) complex components β-integrin, PINCH, and integrin-linked kinase (ILK) caused formation of multinucleate epidermal cells within the Drosophila larval epidermis. This phenotype was specific to the integrin FA complex and not due to secondary effects on polarity or junctional structures. The multinucleate cells resembled the syncytia caused by physical wounding. Live imaging of wound-induced syncytium formation in the pupal epidermis suggested direct membrane breakdown leading to cell-cell fusion and consequent mixing of cytoplasmic contents. Activation of Jun N-terminal kinase (JNK) signaling, which occurs upon wounding, also correlated with syncytium formation induced by PINCH knockdown. Further, ectopic JNK activation directly caused epidermal syncytium formation. No mode of syncytium formation, including that induced by wounding, genetic loss of FA proteins, or local JNK hyperactivation, involved misregulation of mitosis or apoptosis. Finally, the mechanism of epidermal syncytium formation following JNK hyperactivation and wounding appeared to be direct disassembly of FA complexes. In conclusion, the loss-of-function phenotype of integrin FA components in the larval epidermis resembles a wound. Integrin FA loss in mouse and human skin also causes a wound-like appearance. Our results reveal a novel and unexpected role for proper integrin-based adhesion in suppressing larval epidermal cell-cell fusion--a role that may be conserved in other epithelia.

Identification of putative drug targets for human sperm-egg interaction defect using protein network approach

BACKGROUND

Sperm-egg interaction defect is a significant cause of in-vitro fertilization failure for infertile cases. Numerous molecular interactions in the form of protein-protein interactions mediate the sperm-egg membrane interaction process. Recent studies have demonstrated that in addition to experimental techniques, computational methods, namely protein interaction network approach, can address protein-protein interactions between human sperm and egg. Up to now, no drugs have been detected to treat sperm-egg interaction disorder, and the initial step in drug discovery research is finding out essential proteins or drug targets for a biological process. The main purpose of this study is to identify putative drug targets for human sperm-egg interaction deficiency and consider if the detected essential proteins are targets for any known drugs using protein-protein interaction network and ingenuity pathway analysis.

RESULTS

We have created human sperm-egg protein interaction networks with high confidence, including 106 nodes and 415 interactions. Through topological analysis of the network with calculation of some metrics, such as connectivity and betweenness centrality, we have identified 13 essential proteins as putative drug targets. The potential drug targets are from integrins, fibronectins, epidermal growth factor receptors, collagens and tetraspanins protein families. We evaluated these targets by ingenuity pathway analysis, and the known drugs for the targets have been detected, and the possible effective role of the drugs on sperm-egg interaction defect has been considered. These results showed that the drugs ocriplasmin (Jetrea©), gefitinib (Iressa©), erlotinib hydrochloride (Tarceva©), clingitide, cetuximab (Erbitux©) and panitumumab (Vectibix©) are possible candidates for efficacy testing for the treatment of sperm-egg interaction deficiency. Further experimental validation can be carried out to confirm these results.

CONCLUSION

We have identified the first potential list of drug targets for human sperm-egg interaction defect using the protein interaction network approach. The essential proteins or potential drug targets were found using topological analysis of the protein network. These putative targets are promising for further experimental validation. These study results, if validated, may develop drug discovery techniques for sperm-egg interaction defect and also improve assisted reproductive technologies to avoid in-vitro fertilization failure.

Detection of selective sweeps in cattle using genome-wide SNP data

Background

The domestication and subsequent selection by humans to create breeds and biological types of cattle undoubtedly altered the patterning of variation within their genomes. Strong selection to fix advantageous large-effect mutations underlying domesticability, breed characteristics or productivity created selective sweeps in which variation was lost in the chromosomal region flanking the selected allele. Selective sweeps have now been identified in the genomes of many animal species including humans, dogs, horses, and chickens. Here, we attempt to identify and characterise regions of the bovine genome that have been subjected to selective sweeps.

Results

Two datasets were used for the discovery and validation of selective sweeps via the fixation of alleles at a series of contiguous SNP loci. BovineSNP50 data were used to identify 28 putative sweep regions among 14 diverse cattle breeds. Affymetrix BOS 1 prescreening assay data for five breeds were used to identify 85 regions and validate 5 regions identified using the BovineSNP50 data. Many genes are located within these regions and the lack of sequence data for the analysed breeds precludes the nomination of selected genes or variants and limits the prediction of the selected phenotypes. However, phenotypes that we predict to have historically been under strong selection include horned-polled, coat colour, stature, ear morphology, and behaviour.

Conclusions

The bias towards common SNPs in the design of the BovineSNP50 assay led to the identification of recent selective sweeps associated with breed formation and common to only a small number of breeds rather than ancient events associated with domestication which could potentially be common to all European taurines. The limited SNP density, or marker resolution, of the BovineSNP50 assay significantly impacted the rate of false discovery of selective sweeps, however, we found sweeps in common between breeds which were confirmed using an ultra-high-density assay scored in a small number of animals from a subset of the breeds. No sweep regions were shared between indicine and taurine breeds reflecting their divergent selection histories and the very different environmental habitats to which these sub-species have adapted.

Critical role of exosomes in sperm-egg fusion and virus-induced cell-cell fusion

In mammals, two integral membrane proteins, sperm IZUMO1 and egg CD9, regulate sperm-egg fusion, and their roles are critical, but yet unclear. Recent studies, however, indicate interesting connections between the sperm-egg fusion and virus-induced cell-cell fusion. First, CD9-containing exosome-like vesicles, which are released from wild-type eggs, can induce the fusion between sperm and CD9-deficient egg, even though CD9-deficient eggs are highly refractory to the fusion with sperm. This finding provides strong evidence for the involvement of CD9-containing, fusion-facilitating vesicles in the sperm-egg fusion. Secondly, there are similarities between the generation of retroviruses in the host cells and the formation of small cellular vesicles, termed exosomes, in mammalian cells. The exosomes are involved in intercellular communication through transfer of proteins and ribonucleic acids (RNAs) including mRNAs and microRNAs. These collective studies provide an insight into the molecular mechanism of membrane fusion events.

Evolution of genes involved in gamete interaction: evidence for positive selection, duplications and losses in vertebrates

Genes encoding proteins involved in sperm-egg interaction and fertilization exhibit a particularly fast evolution and may participate in prezygotic species isolation [1], [2]. Some of them (ZP3, ADAM1, ADAM2, ACR and CD9) have individually been shown to evolve under positive selection [3], [4], suggesting a role of positive Darwinian selection on sperm-egg interaction. However, the genes involved in this biological function have not been systematically and exhaustively studied with an evolutionary perspective, in particular across vertebrates with internal and external fertilization. Here we show that 33 genes among the 69 that have been experimentally shown to be involved in fertilization in at least one taxon in vertebrates are under positive selection. Moreover, we identified 17 pseudogenes and 39 genes that have at least one duplicate in one species. For 15 genes, we found neither positive selection, nor gene copies or pseudogenes. Genes of teleosts, especially genes involved in sperm-oolemma fusion, appear to be more frequently under positive selection than genes of birds and eutherians. In contrast, pseudogenization, gene loss and gene gain are more frequent in eutherians. Thus, each of the 19 studied vertebrate species exhibits a unique signature characterized by gene gain and loss, as well as position of amino acids under positive selection. Reflecting these clade-specific signatures, teleosts and eutherian mammals are recovered as clades in a parsimony analysis. Interestingly the same analysis places Xenopus apart from teleosts, with which it shares the primitive external fertilization, and locates it along with amniotes (which share internal fertilization), suggesting that external or internal environmental conditions of germ cell interaction may not be the unique factors that drive the evolution of fertilization genes. Our work should improve our understanding of the fertilization process and on the establishment of reproductive barriers, for example by offering new leads for experiments on genes identified as positively selected.

The newcomer in the integrin family: integrin α9 in biology and cancer

Integrins are heterodimeric transmembrane receptors regulating cell-cell and cell-extracellular matrix interactions. Of the 24 integrin heterodimers identified in humans, α9β1 integrin is one of the least studied. α9, together with α4, comprise a more recent evolutionary sub-family of integrins that is only found in vertebrates. Since α9 was thought to have similar functions as α4, due to many shared ligands, it was a rather overlooked integrin until recently, when its importance for survival after birth was highlighted upon investigation of the α9 knockout mouse. α9β1 is expressed on a wide variety of cell types, interacts with many ligands for example fibronectin, tenascin-C and ADAM12, and has been shown to have important functions in processes such as cell adhesion and migration, lung development, lymphatic and venous valve development, and in wound healing. This has sparked an interest to investigate α9β1-mediated signaling and its regulation. This review gives an overview of the recent progress in α9β1-mediated biological and pathological processes, and discusses its potential as a target for cancer diagnosis and therapy.

Sperm-egg interaction

A crucial step of fertilization is the sperm-egg interaction that allows the two gametes to fuse and create the zygote. In the mouse, CD9 on the egg and IZUMO1 on the sperm stand out as critical players, as Cd9(-/-) and Izumo1(-/-) mice are healthy but infertile or severely subfertile due to defective sperm-egg interaction. Moreover, work on several nonmammalian organisms has identified some of the most intriguing candidates implicated in sperm-egg interaction. Understanding of gamete membrane interactions is advancing through characterization of in vivo and in vitro fertilization phenotypes, including insights from less robust phenotypes that highlight potential supporting (albeit not absolutely essential) players. An emerging theme is that there are varied roles for gamete molecules that participate in sperm-egg interactions. Such roles include not only functioning as fusogens, or as adhesion molecules for the opposite gamete, but also functioning through interactions in cis with other proteins to regulate membrane order and functionality.

Zona pellucida glycoprotein 3 (pZP3) and integrin β2 (ITGB2) mRNA and protein expression in porcine oocytes after single and double exposure to brilliant cresyl blue test

Brilliant cresyl blues (BCB) staining test is a useful tool in assessing the competence of cumulus-oocyte-complexes (COCs) in several mammalian species. It is mostly used to select gametes after they are recovered from the ovary or before and after IVM to isolate those oocytes that reach developmental competency. However, there is evidence that double exposure to BCB test may lead to impaired fertilization or even have a toxic effect on cells. The aim of the present study was to investigate the expression pattern of sperm-egg interaction molecules in oocytes after single and double exposure to BCB test. Follicles were dissected from porcine ovaries after slaughter and aspirated COCs were cultured in standard porcine IVM culture medium (TCM 199) for 44 h. The BCB test was applied to COCs before and after IVM. In developmentally competent oocytes, assessed by determining the activity of glucose-6-phosphate dehydrogenase (G6PDH; BCB test), real-time quantitative PCR reaction methods, western blot and confocal microscopy analysis were applied to determine the transcript levels of porcine zona pellucida glycoprotein 3 (pZP3), and integrin beta 2 (ITGB2), as well as the levels of pZP3 and ITGB2 proteins. In the control group, assessment of the expression of the investigated genes was performed before and after IVM without BCB test. We observed a significantly higher level of pZP3 mRNA in oocytes after single exposure to BCB test compared to control before and after IVM (P < 0.001), and to double staining (P < 0.05). The level of ITGB2 mRNA was also increased in gametes after single exposure to BCB test as compared to control before and after IVM (P < 0.001, P < 0.01, respectively), and double staining (P < 0.05). Western blot analysis demonstrated a higher level of pZP3 protein in oocytes after single staining with BCB as compared to control both before and after IVM (P < 0.001, P < 0.05, respectively) and double staining (P < 0.05). Confocal microscopic observations have revealed the same pattern of increased level of pZP3 and ITGB2 expression after single exposure to BCB test. In both cases we detected specific cytoplasmic localization of both proteins. The ITGB2 protein has zona pellucida and membrane localization in control oocytes before IVM. After IVM and after single exposure to BCB, ITGB2 was also strongly detected in the cytoplasm. In both cases, after double exposure to BCB both proteins were detected only partially in the cytoplasm. Our results suggest that (i) single exposure to BCB increased the expression of sperm-oocyte interaction genes, (ii) double exposure to BCB leads to only partial expression of pZP3 and ITGB2 in oocyte cytoplasm, (iii) the BCB staining test itself may be a cause of specific pZP3 translocation from the zona pellucida to the cytoplasm, and that (iv) in vitro maturation of oocytes may increase ITGB2 expression and translocation from the zona pellucida to the cytoplasm.

ADAM2 interactions with mouse eggs and cell lines expressing α4/α9 (ITGA4/ITGA9) integrins: implications for integrin-based adhesion and fertilization

BACKGROUND

Integrins are heterodimeric cell adhesion molecules, with 18 α (ITGA) and eight β (ITGB) subunits forming 24 heterodimers classified into five families. Certain integrins, especially the α(4)/α(9) (ITGA4/ITGA9) family, interact with members of the ADAM (a disintegrin and metalloprotease) family. ADAM2 is among the better characterized and also of interest because of its role in sperm function. Having shown that ITGA9 on mouse eggs participates in mouse sperm-egg interactions, we sought to characterize ITGA4/ITGA9-ADAM2 interactions.

METHODOLOGY/PRINCIPAL FINDINGS

An anti-β(1)/ITGB1 function-blocking antibody that reduces sperm-egg binding significantly inhibited ADAM2 binding to mouse eggs. Analysis of integrin subunit expression indicates that mouse eggs could express at least ten different integrins, five in the RGD-binding family, two in the laminin-binding family, two in the collagen-binding family, and ITGA9-ITGB1. Adhesion assays to characterize ADAM2 interactions with ITGA4/ITGA9 family members produced the surprising result that RPMI 8866 cell adhesion to ADAM2 was inhibited by an anti-ITGA9 antibody, noteworthy because ITGA9 has only been reported to dimerize with ITGB1, and RPMI 8866 cells lack detectable ITGB1. Antibody and siRNA studies demonstrate that ITGB7 is the β subunit contributing to RPMI 8866 adhesion to ADAM2.

CONCLUSIONS/SIGNIFICANCE

These data indicate that a novel integrin α-β combination, ITGA9-ITGB7 (α(9)β(7)), in RPMI 8866 cells functions as a binding partner for ADAM2. ITGA9 had previously only been reported to dimerize with ITGB1. Although ITGA9-ITGB7 is unlikely to be a widely expressed integrin and appears to be the result of "compensatory dimerization" occurring in the context of little/no ITGB1 expression, the data indicate that ITGA9-ITGB7 functions as an ADAM binding partner in certain cellular contexts, with implications for mammalian fertilization and integrin function.

Multivariate analysis of male reproductive function in Inpp5b-/- mice reveals heterogeneity in defects in fertility, sperm-egg membrane interaction and proteolytic cleavage of sperm ADAMs

Past work indicated that sperm from mice deficient in the inositol polyphosphate 5-phosphatase Inpp5b have reduced ability to fertilize eggs in vitro and reduced epididymal proteolytic processing of the sperm protein A Disintegrin and A Metalloprotease 2 (ADAM2). On the basis of these data, our central working hypothesis was that reduced ADAM cleavage would correlate with reduced sperm-egg binding and fusion and in turn with reduced male fertility in Inpp5b(-/-) mice. Multiple endpoints of reproductive functions [mating trials, in vitro fertilization (IVF) assays and ADAM2 and ADAM3 cleavage] were investigated on a male-by-male basis, with pair-wise correlation analysis used to assess the relationships between these various parameters. Motile sperm from Inpp5b(-/-) mice showed significantly reduced fertilization of zona pellucida-free eggs due to reduced binding to the egg plasma membrane and subsequent fusion. Localization of a mouse sperm protein required for gamete fusion, IZUMO1, appears normal in Inpp5b-null sperm. To our surprise and differing from previous reports, we found that ADAM cleavage was only modestly impaired in numerous Inpp5b-null males and varied between individual animals. Performance in mating trials also differed from past reports. The pair-wise correlation analysis revealed that ADAM2 and ADAM3 cleavage was positively correlated, suggesting that processing of these proteins occurs by related/identical mechanisms, but otherwise, there were few correlations between the reproductive endpoints examined here. Nevertheless, this work provides detailed analysis of the Inpp5b(-/-) phenotype and also a blueprint for multivariate analysis to examine relationships between molecular characteristics and in vitro and in vivo physiological functions.

Sperm surface proteomics: from protein lists to biological function

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

Egg integrins: back in the game of mammalian fertilization

Recent data provide insights into the function of egg integrins in mammalian fertilization and address some of the controversies regarding the involvement of these molecules in sperm-egg interaction.

Beta1 integrin is an adhesion protein for sperm binding to eggs

We investigated the role of beta(1) integrin in mammalian fertilization and the mode of inhibition of fertilinbeta-derived polymers. We determined that polymers displaying the Glu-Cys-Asp peptide from the fertilinbeta disintegrin domain mediate inhibition of mammalian fertilization through a beta(1) integrin receptor on the egg surface. Inhibition of fertilization is a consequence of competition with sperm binding to the cell surface, not activation of an egg-signaling pathway. The presence of the beta(1) integrin on the egg surface increases the rate of sperm attachment but does not alter the total number of sperm that can attach or fuse to the egg. We conclude that the presence of beta(1) integrin enhances the initial adhesion of sperm to the egg plasma membrane and that subsequent attachment and fusion are mediated by additional egg and sperm proteins present in the beta(1) integrin complex. Therefore, the mechanisms by which sperm fertilize wild-type and beta(1) knockout eggs are different.