Mouse sperm-egg plasma membrane interactions: analysis of roles of egg integrins and the mouse sperm homologue of PH-30 (fertilin) beta

Phylogeny and expression of ADAM10 and ADAM17 homologs in lamprey

The ADAMs (a disintegrin and metalloproteinase) play regulatory roles in cell adhesion, migration and proteolysis. To explore the origin and evolution of ADAMs, this study identified the homologs of adam10 and adam17 in Lampetra morii and Lampetra japonica. Sequence analysis revealed that they share the same genomic structures with their counterparts in jawed vertebrates. The putative proteins possess conserved motifs, including a furin cut site (RXXR) for precursor processing, an enzyme catalytic motif (HEXGEHXXGXXH) for hydrolysis, and a Ca²⁺-binding motif (CGNXXXEXGEXCD) for stabilizing protein structure. In addition, a substrate recognition domain is present at the membrane-proximal region of lamprey ADAM17. The cytoplasmic region of lamprey ADAM10 contains a potential threonine phosphorylation site which has been shown to be activated by protein kinase C (PKC) in mammals. Both the adam10 and adam17 genes were constitutively expressed in the brain, kidney, and gills and were differentially regulated in the primary blood leukocytes by lipopolysaccharide (LPS) and pokeweed mitogen (PWM). Adam10 was induced by LPS but not PWM; conversely, adam17 was induced by PWM but not LPS. Taken together, our results suggest that the activation pathways and functions of ADAM10 and ADAM17 are conserved in agnathans.

ADAM28: Another ambivalent protease in cancer

Emergence of novel therapeutic options in a perspective of personalized therapy of cancer relies on the discovery of precise molecular mechanisms involved in the switch from a localized tumor to invasive metastasis spread. Pro-tumor functions have been mostly ascribed to proteolytic enzymes from the metalloproteinase family including A Disintegrin And Metalloproteinases (ADAMs). Particularly, when expressed by cancer cells, ADAM28 protease supports cancer cell proliferation, survival and migration as well as metastatic progression. In sharp contrast, ADAM28 derived from the tumor microenvironment has shown to exert strong protective effects against deleterious metastasis dissemination. Indeed, depletion of host-derived ADAM28 (ADAM28 KO mice) accelerates colonization lung tissues, increases tumor foci implantation, and impairs T cell immune response. In this review, we outline specific ADAM28 functions when specifically expressed by carcinoma cells or by tumor microenvironment. Finally, we discuss about future research strategies that could be pursued to highlight new functions of this protease in cancer.

The evolution of ADAM gene family in eukaryotes

The ADAM (A Disintegrin And Metalloprotease) gene family encodes proteins with adhesion and proteolytic functions. ADAM proteins are associated with diseases like cancers. Twenty ADAM genes have been identified in humans. However, little is known about the evolution of the family. We analyzed the repertoire of ADAM genes in a vast number of eukaryotic genomes to clarify the main gene copy number expansions. For the first time, we provide compelling evidence that early-branching green algae (Mamiellophyceae) have ADAM genes, suggesting that they originated in the last common ancestor of eukaryotes, before the split of plants, fungi and animals. The ADAM family expanded in early metazoans, with the most significative gene expansion happening during the first steps of vertebrate evolution. We concluded that most of mammal ADAM diversity can be explained by gene duplications in early bone fish. Our data suggest that ADAM genes were lost early in green plant evolution.

Cut loose and run: The complex role of ADAM proteases during neural crest cell development

ADAM metalloproteases have been shown to play critical roles during development. In this review, we will describe functional evidence that implicates ADAM proteins during the genesis, migration and differentiation of neural crest cells. We will restrict our analysis to the transmembrane ADAMs as other reviews have addressed the role of extracellular metalloproteases (Christian et al. [2013] Critical Reviews in Biochemistry and Molecular Biology 48:544-560). This review will describe advances that have been obtained mainly through the use of two vertebrate model systems, the frog, and avian embryos. The role of the principal substrates of ADAMs, the cadherins, has been extensively described in other reviews, most recently in (Cousin [1997] Mechanisms of Development 148:79-88; Taneyhill and Schiffmacher [2017] Genesis, 55). The function of ADAMs in the migration of other cell types, including the immune system, wound healing and cancer has been described previously in (Dreymueller et al. [2017] Mediators of Inflammation 2017: 9621724). Our goal is to illustrate both the importance of ADAMs in controlling neural crest behavior and how neural crest cells have helped us understand the molecular interactions, substrates, and functions of ADAM proteins in vivo.

Characterization of Mammalian ADAM2 and Its Absence from Human Sperm

The members of the ADAM (a disintegrin and metalloprotease) family are membrane-anchored multi-domain proteins that play prominent roles in male reproduction. ADAM2, which was one of the first identified ADAMs, is the best studied ADAM in reproduction. In the male germ cells of mice, ADAM2 and other ADAMs form complexes that contribute to sperm-sperm adhesion, sperm-egg interactions, and the migration of sperm in the female reproductive tract. Here, we generated specific antibodies against mouse and human ADAM2, and investigated various features of ADAM2 in mice, monkeys and humans. We found that the cytoplasmic domain of ADAM2 might enable the differential association of this protein with other ADAMs in mice. Western blot analysis with the anti-human ADAM2 antibodies showed that ADAM2 is present in the testis and sperm of monkeys. Monkey ADAM2 was found to associate with chaperone proteins in testis. In humans, we identified ADAM2 as a 100-kDa protein in the testis, but failed to detect it in sperm. This is surprising given the results in mice and monkeys, but it is consistent with the failure of ADAM2 identification in the previous proteomic analyses of human sperm. These findings suggest that the reproductive functions of ADAM2 differ between humans and mice. Our protein analysis showed the presence of potential ADAM2 complexes involving yet-unknown proteins in human testis. Taken together, our results provide new information regarding the characteristics of ADAM2 in mammalian species, including humans.

A Disintegrin and Metalloprotease (ADAM): Historical Overview of Their Functions

Since the discovery of the first disintegrin protein from snake venom and the following identification of a mammalian membrane-anchored metalloprotease-disintegrin implicated in fertilization, almost three decades of studies have identified additional members of these families and several biochemical mechanisms regulating their expression and activity in the cell. Most importantly, new in vivo functions have been recognized for these proteins including cell partitioning during development, modulation of inflammatory reactions, and development of cancers. In this review, we will overview the a disintegrin and metalloprotease (ADAM) family of proteases highlighting some of the major research achievements in the analysis of ADAMs' function that have underscored the importance of these proteins in physiological and pathological processes over the years.

Size-specific follicle selection improves mouse oocyte reproductive outcomes

Encapsulated in vitro follicle growth (eIVFG) has great potential to provide an additional fertility preservation option for young women and girls with cancer or other reproductive health threatening diseases. Currently, follicles are cultured for a defined period of time and analyzed as a cohort. However, follicle growth is not synchronous, and culturing follicles for insufficient or excessive times can result in compromised gamete quality. Our objective is to determine whether the selection of follicles based on size, rather than absolute culture time, better predict follicle maturity and oocyte quality. Multilayer secondary mouse follicles were isolated and encapsulated in 0.25% alginate. Follicles were cultured individually either for defined time periods or up to specific follicle diameter ranges, at which point several reproductive endpoints were analyzed. The metaphase II (MII) percentage after oocyte maturation on day 6 was the highest (85%) when follicles were cultured for specific days. However, if follicles were cultured to a terminal diameter of 300-350 μm irrespective of absolute time in culture, 93% of the oocytes reached MII. More than 90% of MII oocytes matured from follicles with diameters of 300-350 μm showed normal spindle morphology and chromosome alignment, 85% of oocytes showed two pronuclei after IVF, 81% developed into the two-cell embryo stage and 38% developed to the blastocyst stage, all significantly higher than the percentages in the other follicle size groups. Our study demonstrates that size-specific follicle selection can be used as a non-invasive marker to identify high-quality oocytes and improve reproductive outcomes during eIVFG.

MAPK3/1 (ERK1/2) and Myosin Light Chain Kinase in Mammalian Eggs Affect Myosin-II Function and Regulate the Metaphase II State in a Calcium- and Zinc-Dependent Manner

Vertebrate eggs are arrested at metaphase of meiosis II, a state classically known as cytostatic factor arrest. Maintenance of this arrest until the time of fertilization and then fertilization-induced exit from metaphase II are crucial for reproductive success. Another key aspect of this meiotic arrest and exit is regulation of the metaphase II spindle, which must be appropriately localized adjacent to the egg cortex during metaphase II and then progress into successful asymmetric cytokinesis to produce the second polar body. This study examined the mitogen-activated protein kinases MAPK3 and MAPK1 (also known as ERK1/2) as regulators of these two related aspects of mammalian egg biology, specifically testing whether this MAPK pathway affected myosin-II function and whether myosin-II perturbation would produce some of the same effects as MAPK pathway perturbation. Inhibition of the MEK1/2-MAPK pathway with U0126 leads to reduced levels of phosphorylated myosin-regulatory light chain (pMRLC) and causes a reduction in cortical tension, effects that are mimicked by treatment with the myosin light chain kinase (MLCK) inhibitor ML-7. These data indicate that one mechanism by which the MAPK pathway acts in eggs is by affecting myosin-II function. We further show that MAPK or MLCK inhibition induces loss of normal cortical spindle localization or parthenogenetic egg activation. This parthenogenesis is dependent on cytosolic and extracellular calcium and can be rescued by hyperloading eggs with zinc, suggesting that these effects of inhibition of MLCK or the MAPK pathway are linked with dysregulation of ion homeostasis.

ADAM15 participates in fertilization through a physical interaction with acrogranin

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

SAS1B protein [ovastacin] shows temporal and spatial restriction to oocytes in several eutherian orders and initiates translation at the primary to secondary follicle transition

BACKGROUND

Sperm Acrosomal SLLP1 Binding (SAS1B) protein (ovastacin) is an oolemmal binding partner for the intra-acrosomal sperm protein SLLP1.

RESULTS

Immunohistochemical localization revealed that SAS1B translation is restricted among adult tissues to the ovary and oocytes, SAS1B appearing first in follicles at the primary-secondary transition. Quiescent oocytes within primordial follicles and primary follicles did not stain for SAS1B. Examination of neonatal rat ovaries revealed SAS1B expression first as faint signals in postnatal day 3 oocytes, with SAS1B protein staining intensifying with oocyte growth. Irrespective of animal age or estrus stage, SAS1B was seen only in oocytes of follicles that initiated a second granulosa cell layer. The precise temporal and spatial onset of SAS1B expression was conserved in adult ovaries in seven eutherian species, including nonhuman primates. Immunoelectron micrographs localized SAS1B within cortical granules in MII oocytes. A population of SAS1B localized on the oolemma predominantly in the microvillar region anti-podal to the nucleus in ovulated MII rat oocytes and on the oolemma in macaque GV oocytes.

CONCLUSIONS

The restricted expression of SAS1B protein in growing oocytes, absence in the ovarian reserve, and localization on the oolemma suggest this zinc metalloprotease deserves consideration as a candidate target for reversible female contraceptive strategies.

Involvement of the prostate and testis expression (PATE)-like proteins in sperm-oocyte interaction

BACKGROUND

The prostate and testis expression (PATE)-like family of proteins are expressed mainly in the male genital tract. They are localized in the sperm head and are homologous to SP-10, the acrosomal vesicle protein also named ACRV1. Our aim was to characterize the expression and functional role of three PATE-like proteins in the testis and ejaculated sperm.

METHODS

The expression and localization of PATE-like proteins in human testis biopsies (n= 95) and sperm cells were assessed by RT-PCR, immunohistochemistry and immunofluorescence staining (at least 600 sperm cells per specimen). The function of the PATE protein was tested by the hemizona assay and hamster egg penetration test (HEPT).

RESULTS

PATE and PATE-M genes and proteins were present almost exclusively in germ cells in the testis: immunoflourescence showed that the percentage of germ cells positive for PATE, PATE-M and PATE-B was 85, 50 and 2%, respectively. PATE and PATE-M proteins were localized in the equatorial segment of the sperm head, while PATE-B protein was localized in the post-acrosomal region. A polyclonal antibody (Ab, at 1:50 and 1:200 dilutions) against the PATE protein did not inhibit sperm-zona binding in the hemizona assay (hemizona index of 89.6 ± 10 and 87 ± 36%, respectively). However, there was inhibition of sperm-oolemma fusion and penetration in the HEPT (penetration index: without Ab 7 ± 3.9; Ab dilution of 1:100, 4 ± 3.5; Ab dilution of 1:20, 0.6 ± 1.2, P < 0.001).

CONCLUSIONS

Our data suggest that PATE protein is involved in sperm-oolemma fusion and penetration but not sperm-zona binding.

Oocyte specific oolemmal SAS1B involved in sperm binding through intra-acrosomal SLLP1 during fertilization

Molecular mechanisms by which fertilization competent acrosome-reacted sperm bind to the oolemma remain uncharacterized. To identify oolemmal binding partner(s) for sperm acrosomal ligands, affinity panning was performed with mouse oocyte lysates using sperm acrosomal protein, SLLP1 as a target. An oocyte specific membrane metalloproteinase, SAS1B (Sperm Acrosomal SLLP1 Binding), was identified as a SLLP1 binding partner. cDNA cloning revealed six SAS1B splice variants, each containing a zinc binding active site and a putative transmembrane domain, with signal peptides in three variants. SAS1B transcripts were ovary specific. SAS1B protein was first detected in early secondary follicles in day 3 ovaries. Immunofluorescence localized SAS1B to the microvillar oolemma of M2 oocytes. After fertilization, SAS1B decreased on the oolemma and became virtually undetectable in blastocysts. In transfected CHO-K1 cells SAS1B localized to the surface of unpermeabilized cells. Recombinant and native SLLP1 co-localized with SAS1B to the microvillar domain of ovulated M2 oocytes. Molecular interactions between mouse SLLP1 and SAS1B were demonstrated by surface plasmon resonance, far-western, yeast two-hybrid, recombinant- and native-co-IP analyses. SAS1B bound to SLLP1 with high affinity. SAS1B had protease activity, and SAS1B protein or antibody significantly inhibited fertilization. SAS1B knockout female mice showed a 34% reduction in fertility. The study identified SAS1B-SLLP1 as a pair of novel sperm-egg binding partners involving the oolemma and intra-acrosomal compartment during fertilization.

Evidence for the inhibition of fertilization in vitro by anti-ZP3 antisera derived from DNA vaccine

Previously we have found that DNA vaccine, pCMV4-rZPC' can generate specific antibodies against rabbit ZPC (amino acid 263-415, rZPC'), which binds to ovarian ZP and leads to a significant reduction of fertility in vivo. The purpose of this study was to evaluate the effect of antisera from pCMV4-rZPC(')-immunized mice on sperm-oocyte interaction in vitro. The effect of antisera from DNA vaccine-immunized mice on fertilization and early embryonic development was studied using an in vitro fertilization system. The results showed that the antisera supplemented in fertilization medium (10%, v/v) significantly decreased the rate of fertilization compared to that of control groups (P<0.05); whereas the antisera showed no significant effect on the rate of fertilization when ZP-free eggs were used. Moreover, the antisera pre-neutralized with mouse soluble zona pellucida lost the capacity to inhibit fertilization when compared with that of control groups. In addition, the antisera showed no detrimental effect on early developmental potential of mouse embryos in vitro. Taken together, our study provided herein direct evidence showing that antisera generated by DNA vaccine can block sperm-egg recognition during fertilization via targeting the oocyte ZP proteins.

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.

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.

Establishment of the mammalian membrane block to polyspermy: evidence for calcium-dependent and -independent regulation

One crucial result of egg activation is the establishment of blocks on the zona pellucida and the egg plasma membrane to prevent fertilization by additional sperm. The mechanism(s) by which a mammalian egg regulates the establishment of the membrane block to polyspermy is largely unknown. Since Ca(2+) signaling regulates several egg activation events, this study investigates how sperm-induced Ca(2+) transients affect the membrane block to polyspermy, building on our previous work (Biology of Reproduction 67:1342). We demonstrate that mouse eggs that experience only one sperm-induced Ca(2+) transient establish a membrane block that is less effective, than in eggs that experience normal sperm-induced Ca(2+) transients but that is more effective than in eggs with completely suppressed [Ca(2+)](cyt) increases. Sperm-induced increases in [Ca(2+)](cyt) regulate the timing of membrane block establishment, as this block is established more slowly in eggs that experience one or no sperm-induced Ca(2+) transients. Finally, our studies produce the intriguing discovery that there is also a Ca(2+)-independent event that is associated with fertilization in the pathway leading to membrane block establishment. Taken together, these data indicate that Ca(2+) plays a role in facilitating membrane block establishment by regulating the timing with which this change in egg membrane function occurs, and also that the membrane block differs from other post-fertilization egg activation responses as Ca(2+) is not the only stimulus. The membrane block to polyspermy in mammalian eggs is likely to be the culmination of multiple post-fertilization events that together modify the egg membrane's receptivity to sperm.

Alpha6beta1 integrin expressed by sperm is determinant in mouse fertilization

Background

Based on inhibition tests, the alpha6beta1 integrin was suggested to be a sperm receptor, but further experiments using gene deletion techniques have shown that neither oocyte alpha6, nor beta1 integrin subunits were essential for mouse fertilization.

Results

Using Western blot analysis and immunofluorescence, we showed that the mouse sperm expresses the alpha6beta1 integrin. As for oocyte, binding of GoH3 anti-alpha6 antibody to sperm induces a specific inhibition of sperm fertilizing ability. Comparing zona-intact and zona-free eggs in fusion tests, we showed that the removal of the zona pellucida by acid treatment bypasses fertilizing oocyte alpha6beta1 integrin's function in the adhesion/fusion process.

Conclusion

These findings show that alpha6beta1 integrin is expressed by both gametes and is functional in their membranes interaction. These results and previous reports, about fertilization of alpha6 or beta1 integrin subunits deleted oocytes by wild type sperm, suggest that the presence of alpha6beta1 integrin on one of the two gamete membranes can rescue the fertilization process. This hypothesis is further supported by the exchange of membrane fragments occurring between gametes prior to fusion that we recently reported.

Influence of calcium on lipid mixing mediated by influenza hemagglutinin

We studied the influence of calcium on lipid mixing mediated by influenza hemagglutinin (HA). Lipid mixing between HA-expressing cells and liposomes containing disialoganglioside, influenza virus receptor, was studied at 37 degrees C and neutral pH after a low-pH pulse at 4 degrees C. With DSPC/cholesterol liposomes, calcium present after raising the temperature significantly promoted lipid mixing only when it was triggered by a short low-pH application. In case of DOPC/cholesterol liposomes, calcium promotion was observed regardless of the duration of the low-pH pulse. Calcium present during a short, but not long, low-pH application to HA-expressing cells with bound DSPC/cholesterol liposomes at 4 degrees C inhibited subsequent lipid mixing. We hypothesize that calcium influences lipid mixing because it binds to a vestigial esterase domain of hemagglutinin or causes expulsion of the fusion peptide from an electronegative cavity. We suggest that calcium promotes the transition from early and reversible conformation(s) of low pH-activated HA towards an irreversible conformation that underlies both HA-mediated lipid mixing and HA inactivation.

Calcium and sperm components in the establishment of the membrane block to polyspermy: studies of ICSI and activation with sperm factor

One important result of egg activation is the establishment of blocks to prevent polyspermic fertilization; these blocks are established on the zona pellucida and the egg plasma membrane. This study examines what the sperm brings to the egg to induce the establishment of the membrane block to polyspermy, building on past evidence that membrane block establishment does not occur in response to parthenogenetic stimuli that induce a single transient increase in cytosolic Ca2+ or intracytoplasmic sperm injection (ICSI). We test the hypotheses that (i) sperm-associated Ca2+ release activity triggers membrane block establishment; (ii) introduction of sperm contents via variations on ICSI protocols (resulting in improved Ca2+ transients, egg activation and embryo development over traditional ICSI protocols) triggers membrane block establishment and (iii) sperm adhesion [binding of an extracellular sperm ligand(s) to an egg receptor(s)] combined with sperm-associated Ca2+ release activity triggers membrane block establishment. Interestingly, none of these stimuli induced establishment of the membrane block to polyspermy in mouse eggs. However, the sperm-associated remodeling of the egg cortical cytoskeleton differs between conventionally fertilized and ICSI-fertilized eggs; taken with our previous data implicating actin microfilaments in membrane block establishment, this raises the possibility that cortical reorganization may be a contributing factor. In sum, fertilization-like Ca2+ transients, either alone or combined with sperm-egg binding, are not sufficient for membrane block establishment, but that an event(s) associated with gamete interaction plays a role in this membrane function change.

Screening of an antigen target for immunocontraceptives from cross-reactive antigens between human sperm and Ureaplasma urealyticum

Epidemiologic studies indicated that some infertile men who were infected with Ureaplasma urealyticum displayed positive antisperm antibodies in their serum and/or semen. The purpose of this study was to investigate the possible mechanism of antisperm antibodies production after infection with U. urealyticum and to analyze the relationship between U. urealyticum and infertility. The existence of cross-reactive antigens (61, 50, and 25 kDa) between U. urealyticum and human sperm membrane proteins was confirmed. Among the cross-reactive antigens, the urease complex component UreG of U. urealyticum was determined. By searching the Swiss-Prot protein database, a pentapeptide identity (IERLT) between UreG and human nuclear autoantigenic sperm protein (NASP) was found. Furthermore, using Western blot analysis and enzyme-linked immunosorbent assay, the cross-reaction between the NASP and UreG was verified. Both anti-rUreG antibody and the antiserum against the synthetic peptide NASP393-408 containing the pentapeptide inhibited mouse sperm egg binding and fusion. After immunization by rUreG or the synthetic peptide, 81.2 and 75% female mice became sterile, respectively. The effect on fertility in mice immunized with the synthetic peptide was reversible. These findings proved for the first time that it was feasible to screen antigens for immunocontraceptives from cross-reactive antigens between sperm and microorganisms which induce infertility.

Possible involvement of integrin-mediated signalling in oocyte activation: evidence that a cyclic RGD-containing peptide can stimulate protein kinase C and cortical granule exocytosis in mouse oocytes

BACKGROUND

Mammalian sperm-oocyte interaction at fertilization involves several combined interactions between integrins on the oocyte and integrin ligands (disintegrins) on the sperm. Recent research has indicated the ability of peptides containing the RGD sequence that characterized several sperm disintegrins, to induce intracellular Ca2+ transients and to initiate parthenogenetic development in amphibian and bovine oocytes. In the present study, we investigate the hypothesis that an integrin-associated signalling may participate in oocyte activation signalling by determining the ability of a cyclic RGD-containing peptide to stimulate the activation of protein kinase C (PKC) and the exocytosis of cortical granules in mouse oocytes.

METHODS

An In-Vitro-Fertilization assay (IVF) was carried in order to test the condition under which a peptide containing the RGD sequence, cyclo(Arg-Gly-Asp-D-Phe-Val), was able to inhibit sperm fusion with zona-free mouse oocytes at metaphase II stage. PKC activity was determined by means of an assay based on the ability of cell lysates to phosphorylate MARKS peptide, a specific PKC substrate. Loss of cortical granules was evaluated by measuring density in the oocyte cortex of cortical granules stained with LCA-biotin/Texas red-streptavidin. In all the experiments, effects of a control peptide containing a non RGD sequence, cyclo(Arg-Ala-Asp-D-Phe-Val), were evaluated.

RESULTS

The IVF assay revealed that the fusion rate declined significantly when insemination was carried out in the presence of cyclic RGD peptide at concentrations > or = 250 microM (P < 0.05, Student-Newman-Keuls Method). When the peptide was applied to the oocytes at these concentrations, a dose-dependent increase of PKC activity was observed, in association with a loss of cortical granules ranging from 38+/-2.5 % to 52+/-5.4 %. Evaluation of meiotic status revealed that cyclic RGD peptide was ineffective in inducing meiosis resumption under conditions used in the present study.

CONCLUSION

The presents results provide evidence that a cyclic RGD peptide highly effective in inhibiting sperm-oocyte interaction stimulates in mouse oocytes the activation of PKC and the exocytosis of cortical granules. These data support the view that RGD-binding receptors may function as signalling receptors giving rise integrated signalling not sufficient for a full oocyte activation response. This study may contribute to the understanding of possible negative effects of skipping gamete interaction in IVF techniques.

Multivalent fertilinbeta oligopeptides: the dependence of fertilization inhibition on length and density

The sperm protein fertilinbeta, a member of the ADAM family of proteins, is implicated in sperm-egg binding in all mammals studied to date. Multivalent inhibitors containing the three amino acid binding sequence of fertilinbeta, ECD, have been shown previously to be more effective inhibitors of fertilization than their monovalent counterparts. Here, we probed sperm-egg interactions with ruthenium-catalyzed ring-opening metathesis polymers that contained from 3 to 70 ECD pharmacophores in densities ranging from 10% to 100%. Evaluation of the polymer potencies, and synthesis of a triblock copolymer from two building blocks, revealed that two multivalent contacts are sufficient for maximal inhibition, and that the distance between ECD pharmacophores required is 7-9 monomers spanning 4-5 nm. We conclude that inhibition requires recruitment of two receptors on the egg surface into an inhibitory complex.

Targeted disruption of tyrosylprotein sulfotransferase-2, an enzyme that catalyzes post-translational protein tyrosine O-sulfation, causes male infertility

Tyrosine O-sulfation is a post-translational modification mediated by one of two Golgi tyrosylprotein sulfotransferases (TPST-1 and -2) expressed in all mammalian cells. Tyrosine sulfation plays an important role in the function of some known TPST substrates by enhancing protein-protein interactions. To explore the role of these enzymes in vivo and gain insight into other potential TPST substrates, TPST-2-deficient mice were generated by targeted disruption of the Tpst2 gene. Tpst2(+/-) mice appear normal and, when interbred, yield litters of normal size with a Mendelian distribution of the targeted mutation. Tpst2(-/-) mice have moderately delayed growth but appear healthy and attain normal body weight by 10 weeks of age. In contrast to Tpst1(-/-) males that have normal fertility, Tpst2(-/-) males are infertile. Tpst2(-/-) sperm are normal in number, morphology, and motility in normal media and appear to capacitate and undergo acrosomal exocytosis normally. However, they are severely defective in their motility in viscous media and in their ability to fertilize zona pellucida-intact eggs. Adhesion of Tpst2(-/-) sperm to the egg plasma membrane is reduced compared with wild type sperm, but sperm-egg fusion is similar or even increased. These data strongly suggest that tyrosine sulfation of unidentified substrate(s) play a crucial role in these processes and document for the first time the critical importance of post-translational tyrosine sulfation in male fertility.

Effects of arginine-glycine-aspartic acid (RGD) containing snake venom peptides on parthenogenetic development and in vitro fertilization of bovine oocytes

The ability of synthetic arginine-glycine-aspartic acid (RGD)-containing peptides to induce intracellular calcium transients similar to those observed at fertilization by spermatozoa in the bovine has been reported (Campbell et al., 2000: Biol Reprod 62:1702-1709; Sessions et al., 2006. Mol Reprod Dev). These results also indicated the ability of synthetic RGD-containing peptides to induce activation and subsequent parthenogenetic development to the blastocyst stage, although, at numbers lower than observed with control in vitro fertilization (IVF). Evidence has been provided indicating the important effect of surrounding regions on the biological activity of the RGD sequence (Zhu and Evans, 2002; Sessions et al., 2006). The current experiments were designed to use natural RGD-containing sequences (disintegrins) to understand their effects. A total of three RGD-containing snake venom peptides (Kistrin (K), Elegantin (Ele), and Echistatin (Ech)) and one nonRGD-containing venom (Erabutoxin B (EB; control) were used at three concentrations (0.1, 1, and 10 micro g /ml) to induce parthenogenetic development to the blastocyst stage and in conjunction (1.0, 5.0, and 10 micro g/ml) with spermatozoa to evaluate competitive inhibition of fertilization and subsequent development. A (P < 0.01) higher number of bovine oocytes developed to the blastocyst stage after incubation with K, Ele and Ech at 1.0 micro g/ml, and was not different (P > 0.01) from IVF control. Fertilization was significantly reduced (P < 0.01) at all concentrations of K, Ele and Ech as compared to IVF control. No reduction (P > 0.05) was observed in EB (nonRGD) treated oocytes. These results support the involvement of a disintegrin-integrin interaction at fertilization in the bovine resulting in activation and subsequent development.

ADAM-9 (MDC-9/meltrin-gamma), a member of the a disintegrin and metalloproteinase family, regulates myeloma-cell-induced interleukin-6 production in osteoblasts by direct interaction with the alpha(v)beta5 integrin

ADAM-9, a member of the a disintegrin and metalloproteinase family, contains both metalloproteinase and disintegrin domains. Myeloma cell lines express ADAM-9; however, its function and role in the pathophysiology of multiple myeloma is unknown. The aim of this study was to establish whether primary myeloma cells express ADAM-9, whether ADAM-9 regulates IL-6 production in human osteoblasts (hOBs), whether ADAM-9 interacts with specific integrin heterodimers, and the identity of downstream signaling pathways. Primary myeloma cells demonstrated increased expression of ADAM-9 (P < .01). ADAM-9 promoted a 5-fold increase in IL-6, but not IL-1beta mRNA, and a dose- and time-dependent increase in IL-6 production by hOBs (P < .01). IL-6 induction was inhibited by an antibody to the alpha(v)beta5 integrin (P < .01) but not by antibodies to other integrin heterodimers. ADAM-9 was shown to bind directly to the alpha(v)beta5 integrin on hOBs. Antibodies to ADAM-9 and alpha(v)beta5 integrin inhibited myeloma cell-induced IL-6 production by hOBs (P < .01). Furthermore, inhibitors of p38 MAPK and cPLA2, but not NF-kappaB and JAK2, signaling pathways inhibited ADAM-9-induced IL-6 production by hOBs (P < .01). These data demonstrate that ADAM-9, expressed by myeloma cells, stimulates IL-6 production in hOBs by binding the alpha(v)beta5 integrin. This may have important consequences for the growth and survival of myeloma cells in bone.

Cyclin A2-CDK2 regulates embryonic gene activation in 1-cell mouse embryos

Recruitment of maternal mRNA in mice appears essential for embryonic gene activation (EGA) that is initiated in the 1-cell stage. The identity of which recruited mRNAs is responsible, however, is not known. We report here that recruitment of cyclin A2 mRNA may be critical for EGA. Cyclin A2 protein accumulates in pronuclei between 6 and 12 h after fertilization, the time when EGA is initiated. This cyclin A2 may be generated from maternally recruited cyclin A2 mRNA because its accumulation was inhibited by 3'-deoxyadenosine, which inhibits mRNA polyadenylation. When CDK2 activity or pronuclear accumulation of cyclin A2 was inhibited with CDK2 inhibitors or by microinjected siRNAs, respectively, DNA replication was not inhibited but the increase of transcriptional activity was prevented. In addition, microinjection of recombinant cyclin A2-CDK2 protein increased transcriptional activity. Cyclin A2-CDK2 is activated following egg activation, because an increase in phosphorylation of retinoblastoma protein was observed using antibodies that recognize site-specific phosphorylation catalyzed by this kinase and treatment with a CDK2 inhibitor or microinjection with cyclin A2 siRNAs prevented the increase in retinoblastoma protein phosphorylation. These results suggest that recruitment of maternal cyclin A2 mRNA following egg activation is linked to EGA.

Cyclic FEE peptide increases human gamete fusion and potentiates its RGD-induced inhibition

BACKGROUND

Alpha6beta1 integrin has been proposed to act as a sperm receptor on the mouse oocyte by interacting with spermatozoon fertilin beta. We investigated, in humans, whether oocyte integrins could act similarly in gamete fusion, using a cyclic peptide containing the putative disintegrin-binding domain of human fertilin beta [cyclic FEE (cFEE)] and RGD peptide.

METHODS

Zona-free eggs were inseminated in the absence or presence of peptides. To maintain the membrane protein pattern, the zona pellucida was removed by microdissection. Immunofluorescence and confocal microscopy were used to detect integrin subunits on the oocyte.

RESULTS

Unexpectedly, cFEE alone increased human gamete fusion by 94% instead of inhibiting fertilization. Furthermore, cFEE together with RGD potentiated the RGD-induced inhibition of fertilization in a dose-dependent manner. The data suggested the hypothesis of integrin cross-talk, further supported by the co-localization of alpha6beta1 and alphavbeta3 integrins, the putative receptors of cFEE and RGD peptides, respectively.

CONCLUSIONS

RGD-sensitive and -insensitive integrins may be associated in a multimolecular complex working as a sperm receptor on the human oocyte membrane. Supplementation of human IVF culture medium with cFEE peptide might improve fertilization rates in ART.

Combinatorial peptide library binding of mammalian spermatozoa identifies a ligand (HIPRT) in the axin protein: putative identification of a sperm surface axin binding protein and intriguing developmental implications

The identification of components in cell-cell interactions is an important research goal in reproductive and developmental biology. Such interactions are critical to gamete development, fertilization, implantation and basic development. Several proteins involved with sperm-oocyte interaction and other developmentally important phenomena have been identified. However, these are obviously only a subset of the molecular components involved in such complex cell-cell interactions. One method that has been used to identify binding partners for particular molecular targets is the use of combinatorial libraries accessible on phage surfaces. For the most part, this technique has mainly been applied to screen specific target moieties. However, in some cases whole-cell screening has been attempted. This study describes the first report of screening intact, living mammalian gametes using a proprietary whole-cell combinatorial library binding and analysis protocol. Results from the first screening protocol of mouse spermatozoa strongly identified a putative sperm-binding ligand using proprietary bioinformatic analysis. This amino acid sequence (HIPRT) precisely corresponds with a previously characterized highly conserved protein-protein interaction site in the axin protein. This sequence is found within the binding site for a known sperm surface protein, glycogen synthase kinase-3. This result not only provides proof of the utility of this technique to identify cell surface ligands in mammalian gametes, but it also suggests a potential role for spermatozoa in facilitating developmental axis formation in mammalian embryos.

Localization of Janus Kinase 2 to the Nuclei of Mature Oocytes and Early Cleavage Stage Mouse Embryos

Jak2, which is a member of the Janus tyrosine kinase family, plays essential roles in cytokine signal transduction and in the regulation of cell growth and gene expression. To investigate the involvement of Jak2 in the regulation of early preimplantation development, we examined the expression of Jak2 in mouse embryos. Reverse transcription-polymerase chain reaction assays revealed that the relative amount of Jak2 mRNA was highest in unfertilized oocytes, gradually decreased until the four-cell stage, and remained at low levels until the blastocyst stage. Immunocytochemistry showed that Jak2 was localized predominantly to the female pronucleus in one-cell embryos. The immunofluorescence signal was very weak or undetectable in the male pronucleus. In unfertilized oocytes and one-cell embryos at M phase, Jak2 was localized to the chromosomes. After cleavage to the two-cell stage, the intensity of the immunofluorescence signal decreased in the nucleus while the embryos were in late G2. This decrease was independent of DNA synthesis because it was not affected by inhibition of DNA replication. However, inhibition of protein synthesis repressed the disappearance of Jak2 from the nucleus. These results suggest a novel function for Jak2 in the regulation of early preimplantation development.

Calreticulin on the mouse egg surface mediates transmembrane signaling linked to cell cycle resumption

Calreticulin, a protein best known as an endoplasmic reticulum chaperone, also is found on the extracellular plasma membrane surface of many cell types where it serves as a mediator of adhesion and as a regulator of the immune response. In this report, we demonstrate that calreticulin is present on the extracellular surface of the mouse egg plasma membrane and is increased in the perivitelline space after egg activation. The extracellular calreticulin appears to be secreted by vesicles in the egg cortex that are distinct from cortical granules. An anticalreticulin antibody binds to extracellular calreticulin on live eggs and inhibits sperm-egg binding but not fusion. In addition, engagement of cell surface calreticulin by incubation of mouse eggs in the presence of anticalreticulin antibodies results in alterations in the localization of cortical actin and the resumption of meiosis as indicated by alterations in chromatin configuration, decreases in cdc2/cyclin B1 and MAP kinase activities, and pronuclear formation. These events occur in the absence of any observable alterations in intercellular calcium. These data demonstrate that calreticulin functionally interacts with the egg cytoskeleton and can mediate transmembrane signaling linked to cell cycle resumption. These studies suggest a role for calreticulin as a lectin that may be involved in signal transduction events during or after sperm-egg interactions at fertilization.

Requirements for glucose beyond sperm capacitation during in vitro fertilization in the mouse

In both the mouse and the human, it is a point of controversy whether glucose is necessary for in vitro fertilization. Some of this controversy has resulted from a failure to distinguish between requirements for glucose during sperm capacitation versus requirements during the multistage process of fertilization. Using the mouse as a model, we performed a series of experiments designed to identify specific processes that might require glucose. We observed a positive correlation between increasing glucose concentrations during capacitation and fertilization, and increasing fertilization of zona pellucida (ZP)-intact eggs. These data supported a requirement for glucose in the fertilization medium even when sperm were first capacitated in the presence of 5.5 mM glucose. This glucose requirement was observed for both ZP-intact and ZP-free eggs. During ZP-free in vitro fertilization, some binding and fusion between the plasma membrane of the sperm and egg occurred in the absence of glucose and at concentrations less than 1 mM, suggesting that this substrate is not absolutely required. However, glucose concentrations of 1 mM or higher greatly facilitated both binding and fusion under these conditions. These subtle distinctions suggest that during ZP-free in vitro fertilization, 1 mM glucose represents a threshold level that facilitates binding and fusion. Taken as a whole, the data suggest requirements for glucose during both capacitation and fertilization under normal physiologic conditions.

None of the integrins known to be present on the mouse egg or to be ADAM receptors are essential for sperm-egg binding and fusion

Antibody inhibition and alpha6beta1 ligand binding experiments indicate that the egg integrin alpha6beta1 functions as a receptor for sperm during gamete fusion; yet, eggs null for the alpha6 integrin exhibit normal fertilization. Alternative integrins may be involved in sperm-egg binding and fusion and could compensate for the absence of alpha6beta1. Various beta1 integrins and alphav integrins are present on mouse eggs. Some of these integrins are also reported to be receptors for ADAMs, which are expressed on sperm. Using alpha3 integrin null eggs, we found that the alpha3beta1 integrin was not essential for sperm-egg binding and fusion. Oocyte-specific, beta1 integrin conditional knockout mice allowed us to obtain mature eggs lacking all beta1 integrins. We found that the beta1 integrin null eggs were fully functional in fertilization both in vivo and in vitro. Furthermore, neither anti-mouse beta3 integrin function-blocking monoclonal antibody (mAb) nor alphav integrin function-blocking mAb inhibited sperm binding to or fusion with beta1 integrin null eggs. Thus, function of beta3 or alphav integrins does not seem to be involved in compensating for the absence of beta1 integrins. These results indicate that none of the integrins known to be present on mouse eggs or to be ADAM receptors are essential for sperm-egg binding/fusion, and thus, egg integrins may not play the role in gamete fusion previously attributed to them.

Identification and characterization of ADAM32 with testis-predominant gene expression

Members of the ADAM (A Disintegrin And Metalloprotease) family of cell surface proteins have been discovered in a variety of tissues and species. We have cloned and sequenced a mouse cDNA encoding a novel member of the ADAM family. This mouse ADAM gene was named ADAM32 after an human homologue previously sequenced but not characterized. The cDNA sequence of ADAM32 has an open reading frame which encodes 750 (mouse ADAM32) and 787 (human ADAM32) amino acids, sharing 69% homology between the two species. The deduced amino acid sequences of mouse and human ADAM32 cDNAs contain all of the domains common to ADAM family members. Comparison of amino acid sequences showed that ADAM32 is highly homologous to ADAM2 and ADAM3, sperm surface proteins required for fertilization. We found that the ADAM32 gene is expressed predominantly in the testis. Examination of transcription in pre-pubertal and adult mouse testes revealed that expression of ADAM32 begins during meiotic prophase, in pachytene spermatocytes. These results suggest a potential role for ADAM32 in sperm development or fertilization. Genome database searches revealed that the mouse and human ADAM32 genes are located on chromosomes 8 and 8q11, respectively. The ADAM32 gene covers a relatively large region of the genome (120 kb for mouse ADAM32 and 180 kb for human ADAM32) and consists of multiple small exons (at least 22 exons in mouse ADAM32 and 25 exons in human ADAM32).

Monoclonal antibody G3 epitope location on Guinea pig sperm membrane protein, sperad

A protein isolated from guinea pig testes was purified, characterized as having a molecular weight of 34 kDa, and subjected to amino acid sequencing. A monoclonal antibody to the protein (G11) was found to cross-react with a second monoclonal antibody (G3). Two peptide sequences derived from the purified protein, labeled as 34 kDa G11, show sequence homology with sperad. Sperad is a transmembrane protein present in the peri-acrosomal plasma membrane of guinea pig spermatozoa. Both G11 and G3 monoclonal antibodies recognise antigens on the equatorial segment plasma membrane of guinea pig spermatozoa following the acrosome-reaction. Therefore, experiments were designed to check whether monoclonal antibody G3 epitope is present on the sperad. The intra-cytoplasmic domain and the extra-cytoplasmic domain of sperad was amplified from a guinea pig testes cDNA expression library by polymerase chain reaction and cloned into pGEM T-Easy vector. The recombinant pGEM T-Easy plasmids were subjected to in vitro transcription and translation by rabbit reticulocyte lysate system. The resulting translated products were immunoprecipitated with monoclonal antibody G3. The results obtained from this study confirmed that monoclonal antibody G3 epitope is located on the extra-cytoplasmic domain but not on the intra-cytoplasmic domain of sperad.

Positive selection within sperm-egg adhesion domains of fertilin: an ADAM gene with a potential role in fertilization

Genes with a role in fertilization show a common pattern of rapid evolution. The role played by positive selection versus lack of selective constraints has been more difficult to establish. One problem arises from attempts to detect selection in an overall gene sequence analysis. I have analyzed the pattern of molecular evolution of fertilin, a gene coding for a heterodimeric sperm protein belonging to the ADAM (A disintegrin and A metalloprotease) gene family. A nonsynonymous to synonymous rate ratio (d(N)/d(S)) analysis for different protein domains of fertilin alpha and fertilin beta showed d(N)/d(S) < 1, suggesting that purifying selection has shaped fertilin's evolution. However, an analysis of the distribution of single positively selected codon sites using phylogentic analysis by maximum likelihood (PAML) showed sites within adhesion domains (disintegrin and cysteine-rich) of fertilin beta evolving under positive selection. The region 3' to the EGF-like domain of fertilin alpha, where the transmembrane and cytoplasmic tail regions are supposed to be localized, showed higher d(N) and d(S) than any other fertilin alpha region. However, it was not possible to identify positively selected codon sites due to ambiguous alignments of the carboxy-end region (ClustalX vs. DiAlign2). When this region was excluded from the PAML analysis, most single positively selected codon sites were concentrated within adhesion domains (cysteine-rich and EGF-like). The use of an ancestral sequence prior to a recent duplication event of fertilin alpha among non-Hominidae primates (Macaca, Papio, and Saguinus) revealed that the duplication is partially responsible for masking the detection of positively selected sites within the disintegrin domain. Finally, most ADAM genes with a potential role in sperm maturation and/or fertilization showed significantly higher d(N) estimates than other ADAM genes.

Regulation of cellular adhesion molecule expression in murine oocytes, peri-implantation and post-implantation embryos

Expression of the adhesion molecules, ICAM-1, VCAM-1, NCAM, CD44, CD49d (VLA-4, alpha chain), and CD11a (LFA-1, alpha chain) on mouse oocytes, and pre- and peri-implantation stage embryos was examined by quantitative indirect immunofluorescence microscopy. ICAM-1 was most strongly expressed at the oocyte stage, gradually declining almost to undetectable levels by the expanded blastocyst stage. NCAM, also expressed maximally on the oocyte, declined to undetectable levels beyond the morula stage. On the other hand, CD44 declined from highest expression at the oocyte stage to show a second maximum at the compacted 8-cell/morula. This molecule exhibited high expression around contact areas between trophectoderm and zona pellucida during blastocyst hatching. CD49d was highly expressed in the oocyte, remained significantly expressed throughout and after blastocyst hatching was expressed on the polar trophectoderm. Like CD44, CD49d declined to undetectable levels at the blastocyst outgrowth stage. Expression of both VCAM-1 and CD11a was undetectable throughout. The diametrical temporal expression pattern of ICAM-1 and NCAM compared to CD44 and CD49d suggest that dynamic changes in expression of adhesion molecules may be important for interaction of the embryo with the maternal cellular environment as well as for continuing development and survival of the early embryo.

Identification of the 48-kDa G11 protein from guinea pig testes as sperad

A protein found specifically in the membrane of spermatozoa called G11 has been implicated in sperm-egg binding and fusion. This study describes purification and identification of the G11 antigen. The G11 protein was purified using anion exchange chromatography, immunoaffinity chromatography and preparative SDS-PAGE and was subjected to amino acid microsequencing by tandem mass spectrometry. Internal amino acid sequence data derived from the 48-kDa G11 protein revealed that G11 is the recently discovered guinea pig sperm protein, sperad. Sperad is a transmembrane protein present in the periacrosomal plasma membrane of guinea pig sperm. The cytoplasmic domain of sperad was amplified from a guinea pig testes cDNA expression library by polymerase chain reaction and cloned into a prokaryotic gene expression vector, pGEX-2T. The recombinant glutathione S-transferase fusion protein was immunoblotted with monoclonal antibody G11. The results obtained from this study confirmed the monoclonal antibody G11 epitope location on the cytoplasmic domain of sperad.

Involvement of Calcium Signaling and the Actin Cytoskeleton in the Membrane Block to Polyspermy in Mouse Eggs1

This study examines the effects of actin microfilament-disrupting drugs on events of fertilization, with emphasis on gamete membrane interactions. Mouse eggs, freed of their zonae pellucidae, were treated with drugs that perturb the actin cytoskeleton by different mechanisms (cytochalasin B, cytochalasin D, jasplakinolide, latrunculin B) and then inseminated. Cytochalasin B, jasplakinolide, and latrunculin B treatments resulted in a decrease in the percentage of eggs fertilized and the average number of sperm fused per egg. However, cytochalasin D treatment resulted in an increase in the average number of sperm fused per egg and the percentage of polyspermic eggs. This increase in polyspermy occurred despite the observation that cytochalasin D treatment caused a decrease in sperm-egg binding and did not affect spontaneous acrosome reactions or sperm motility. This suggested that cytochalasin D-treated eggs had an impaired ability to establish a block to polyspermy at the level of the plasma membrane. The effect of cytochalasin D on the block to polyspermy was not due to a general disruption of egg activation because sperm-induced calcium oscillations and cortical granule exocytosis were similar in cytochalasin D-treated and control eggs. However, buffering of intracellular calcium levels with the calcium chelator BAPTA-AM resulted in an increase in polyspermy. Together, these data suggest that a postfertilization decrease in egg membrane receptivity to sperm requires functions of the egg actin cytoskeleton that are disrupted by cytochalasin D. Furthermore, egg activation-associated increased intracellular calcium levels are necessary but not sufficient to affect postfertilization membrane dynamics that contribute to a membrane block to polyspermy.

Functional classification of ADAMs based on a conserved motif for binding to integrin alpha 9beta 1: implications for sperm-egg binding and other cell interactions

ADAMs (a disintegrin and metalloproteases) are members of the metzincin superfamily of metalloproteases. Among integrins binding to disintegrin domains of ADAMs are alpha(9)beta(1) and alpha(v)beta(3), and they bind in an RGD-independent and an RGD-dependent manner, respectively. Human ADAM15 is the only ADAM with the RGD motif in the disintegrin domain. Thus, both integrin alpha(9)beta(1) and alpha(v)beta(3) recognize the ADAM15 disintegrin domain. We determined how these integrins recognize the ADAM15 disintegrin domain by mutational analysis. We found that the Arg(481) and the Asp-Leu-Pro-Glu-Phe residues (residues 488-492) were critical for alpha(9)beta(1) binding, but the RGD motif (residues 484-486) was not. In contrast, the RGD motif was critical for alpha(v)beta(3) binding, but the other residues flanking the RGD motif were not. As the RX(6)DLPEF alpha(9)beta(1) recognition motif (residues 481-492) is conserved among ADAMs, except for ADAM10 and 17, we hypothesized that alpha(9)beta(1) may recognize disintegrin domains in all ADAMs except ADAM10 and 17. Indeed we found that alpha(9)beta(1) bound avidly to the disintegrin domains of ADAM1, 2, 3, and 9 but not to the disintegrin domains of ADAM10 and 17. As several ADAMs have been implicated in sperm-oocyte interaction, we tested whether the functional classification of ADAMs, based on specificity for integrin alpha(9)beta(1), applies to sperm-egg binding. We found that the ADAM2 and 15 disintegrin domains bound to oocytes, but the ADAM17 disintegrin domain did not. Furthermore, the ADAM2 and 15 disintegrin domains effectively blocked binding of sperm to oocytes, but the ADAM17 disintegrin domain did not. These results suggest that oocytes and alpha(9)beta(1) have similar binding specificities for ADAMs and that alpha(9)beta(1), or a receptor with similar specificity, may be involved in sperm-egg interaction during fertilization. As alpha(9)beta(1) is a receptor for many ADAM disintegrins and alpha(9)beta(1) and ADAMs are widely expressed, alpha(9)beta(1)-ADAM interaction may be of a broad biological importance.

Downregulated expression of ADAM9 in anterior polar cataracts

PURPOSE

To determine whether ADAM (a disintegrin and metalloproteinase) is regulated in lens epithelial cells (LECs) of patients with anterior polar cataracts and by transforming growth factor (TGF)-beta 1 in cultured LECs.

SETTING

Department of Ophthalmology and Visual Science, College of Medicine, The Catholic University of Korea, Seoul, Korea.

METHODS

Lens epithelial cells attached to the anterior capsules of human cataractous lenses with nuclear and anterior subcapsular cataracts and noncataractous lenses were analyzed by reverse transcribed-polymerase chain reaction for the expression of ADAMs. The effect of TGF-beta 1 on ADAM gene expression was also tested in mouse lens epithelial explants and cultured LEC lines (alpha TN-4 and HLE B-3).

RESULTS

Significantly reduced expression of mRNA for ADAM9 was observed in LECs from patients with anterior polar cataracts. The expression of mRNA for ADAM9 was downregulated by TGF-beta 1 in cultured human LECs. Treatment of cultured mouse LECs with TGF-beta 1 led to a reduction in ADAM1 mRNA.

CONCLUSIONS

ADAMs are expressed and regulated in LECs. The downregulated expression of ADAM9 may serve as a marker for anterior polar cataracts in addition to previously known proteins, fibronectin, alpha-SMA, and beta ig-h3. The functions of this protein in lens pathology require further investigation.

Analysis of the roles of RGD-binding integrins, alpha(4)/alpha(9) integrins, alpha(6) integrins, and CD9 in the interaction of the fertilin beta (ADAM2) disintegrin domain with the mouse egg membrane

Fertilin beta (also known as ADAM2), a mammalian sperm protein that mediates gamete cell adhesion during fertilization, is a member of the ADAM protein family whose members have disintegrin domains with homology to integrin ligands found in snake venoms. Fertilin beta utilizes an ECD sequence within its disintegrin domain to interact with the egg plasma membrane; the Asp is especially critical. Based on what is known about different integrin subfamilies and their ligands, we sought to characterize fertilin beta binding sites on mouse eggs, focusing on integrin subfamilies that recognize short peptide sequences that include an Asp residue: the alpha(5)/alpha(8)/alpha(v)/alpha(IIb) or RGD-binding subfamily (alpha(5)beta(1), alpha(8)beta(1), alpha(V)beta(1), alpha(V)beta(3), alpha(V)beta(5), alpha(V)beta(6), alpha(V)beta(8), and alpha(IIb)beta(3)) and the alpha(4)/alpha(9) subfamily (alpha(4)beta(1), alpha(9)beta(1), and alpha(4)beta(7)). We tested peptide sequences known to perturb interactions mediated by these integrins in two different assays for fertilin beta binding. Peptides with the sequence MLDG, which perturb alpha(4)/alpha(9) integrin-mediated interactions, significantly inhibit fertilin beta binding to eggs, which suggests a role for a member of this integrin subfamily as a fertilin beta receptor. RGD peptides, which perturb alpha(5)/alpha(8)/alpha(v)/alpha(IIb) integrin-mediated interactions, have partial inhibitory activity. The anti-alpha(6) antibody GoH3 has little or no inhibitory activity. An antibody to the integrin-associated tetraspanin protein CD9 inhibits the binding of a multivalent presentation of fertilin beta (immobilized on beads) but not soluble fertilin beta, which we speculate has implications for the role of CD9 in the strengthening of fertilin beta-mediated cell adhesion but not in initial ligand binding.

Non-functional fertility genes in humans: contributory factors in reduced male fertility?

Many of the mammalian sperm surface proteins that have been characterized in recent years have been implicated in sperm--egg interactions and subsequent fertilization. In particular, several members of the MDC protein family, most notably fertilin alpha, fertilin beta and cyritestin (also known as tMDC I), play an important role in sperm--egg interactions in rodents. In light of current data, it is proposed that many of these sperm proteins act co-operatively, and that the concerted effects of several proteins leads to 'maximum fertilizing ability', but that individual proteins are functionally redundant and are therefore not essential. Nevertheless, the co-operative nature of these interactions means that loss of individual proteins might lead to a concomitant reduction in fertilizing ability, a proposal that is supported by our recent finding of non-functional fertilin alpha and tMDC I genes in humans.