Recombinant human zona pellucida protein ZP3 produced by chinese hamster ovary cells induces the human sperm acrosome reaction and promotes sperm-egg fusion

The Relationships among Plasma Fetuin-B, Thyroid Autoimmunity, and Fertilization Rate In Vitro Fertilization and Embryo Transfer

OBJECTIVE

The objective of the study is to investigate the relationships between fetuin-B, thyroid autoimmunity (TAI), and pregnancy outcomes in women undergoing in vitro fertilization and embryo transfer (IVF-ET). Design, Patients, and Measurements. In this prospective study, 180 women who were preparing for pregnancy with IVF-ET were included. There were 120 women with TAI positive and 60 negative controls matched with age and BMI.

RESULTS

The 180 women had mean ± SD age of 31.4 ± 4.0 years, with a mean ± SD BMI of 21.0 ± 1.6 kg/m². There was a significant difference in the level of fetuin-B in women with TAI positive compared with TAI negative group (65.2 ± 18.5 vs. 76.4 ± 25.1, P=0.001). Fetuin-B had a negative relationship with thyroid antibodies even after adjusting for other variables (OR (95%CI) = 0.98 (0.96-0.99), P=0.002). Compared with women with TAI negative, those with TAI positive had a significantly higher risk of low fertilization (20.0% vs. 6.7%; P=0.035). And we found no difference in terms of pregnancy, abortion, implantation, and live birth rate between the two groups. Logistic regression analysis showed that both fetuin-B and TAI were the independent factors to lead the low fertilization of IVF-ET (OR (95%CI) = 0.96 (0.94-0.99) and 4.084 (1.39-15.30), P=0.004 and 0.019, respectively).

CONCLUSION

Fetuin-B was significantly associated with TAI and low fertilization rate in women undergoing IVF-ET. Decreased fetuin-B in women with TAI may be the underlying reason for the lower IVF-ET success rate.

CD147 deficiency is associated with impairedsperm motility/acrosome reaction and offersa therapeutic target for asthenozoospermia

Patients with asthenozoospermia often present multiple defects in sperm functions apart from a decrease in sperm motility. However, the etiological factors underlying these multifaceted defects remain mostly unexplored, which may lead to unnecessary treatment and unsatisfactory assisted reproductive technologies (ART) outcome. Here, we show that the protein levels of CD147 were lowered in sperm obtained from asthenozoospermic infertile patients exhibiting defects in both sperm motility and the acrosome reaction. Whereas CD147 maintained sperm motility before capacitation, female tract-derived soluble CD147 interacted with sperm-bound CD147 to induce an acrosome reaction in capacitated sperm. Soluble CD147 treatment restored the acrosome reaction and improved the fertility of sperm from patients with asthenozoospermia. Mechanistically, CD147 promotes sperm motility and acrosome reaction (AR) by eliciting Ca²⁺ influx through soluble CD147 binding to sperm-bound CD147. Notably, the level of soluble CD147 in seminal plasma was positively correlated with the fertilization rate and pregnancy outcome in infertile couples undergoing in vitro fertilization. Our study has identified a marker for the diagnosis and a therapeutic target for the defective AR capability in asthenozoospermia and a candidate for the prediction of in vitro fertilization outcomes for male infertile patients that facilitates the development of precision medicine in ART.

New Insights into the Mammalian Egg Zona Pellucida

Mammalian oocytes are surrounded by an extracellular coat called the zona pellucida (ZP), which, from an evolutionary point of view, is the most ancient of the coats that envelope vertebrate oocytes and conceptuses. This matrix separates the oocyte from cumulus cells and is responsible for species-specific recognition between gametes, preventing polyspermy and protecting the preimplantation embryo. The ZP is a dynamic structure that shows different properties before and after fertilization. Until very recently, mammalian ZP was believed to be composed of only three glycoproteins, ZP1, ZP2 and ZP3, as first described in mouse. However, studies have revealed that this composition is not necessarily applicable to other mammals. Such differences can be explained by an analysis of the molecular evolution of the ZP gene family, during which ZP genes have suffered pseudogenization and duplication events that have resulted in differing models of ZP protein composition. The many discoveries made in recent years related to ZP composition and evolution suggest that a compilation would be useful. Moreover, this review analyses ZP biosynthesis, the role of each ZP protein in different mammalian species and how these proteins may interact among themselves and with other proteins present in the oviductal lumen.

Human Zona Pellucida Glycoproteins: Binding Characteristics With Human Spermatozoa and Induction of Acrosome Reaction

Human zona pellucida (ZP) matrix is composed of four glycoproteins designated as ZP glycoprotein -1 (ZP1), -2 (ZP2), -3 (ZP3), and -4 (ZP4). Mutations in the genes encoding human ZP glycoproteins are one of the causative factors leading to abnormal ZP matrix and infertility in women. Relevance of the human ZP glycoproteins in 'sperm-oocyte' binding has been delineated by using either transgenic animal models expressing human zona proteins or purified native/recombinant human zona proteins. Studies based on the purified native/recombinant human zona proteins revealed that ZP1, ZP3, and ZP4 primarily bind to the capacitated acrosome-intact human spermatozoa whereas ZP2 binds to acrosome-reacted spermatozoa. On the contrary, human spermatozoa binds to the eggs obtained from transgenic mouse lines expressing human ZP2 but not to those expressing human ZP1, ZP3, and ZP4 suggesting that ZP2 has an important role in human 'sperm-oocyte' binding. Further studies using transgenic mouse lines showed that the N-terminus of human ZP2 mediate the taxon-specific human sperm-oocyte binding. Both glycans and protein-protein interactions have a role in human gamete interaction. Further studies have revealed that the purified native/recombinant human ZP1, ZP3, and ZP4 are competent to induce acrosome reaction. Human sperm binds to the mouse transgenic eggs expressing human ZP1-4 instead of mouse ZP1-3 proteins, penetrated the ZP matrix and accumulated in the perivitelline space, which were acrosome-reacted suggesting that human ZP2 in transgenic mouse model also induce acrosome reaction. In humans N-linked glycosylation of zona proteins have been shown to play an important role in induction of the acrosome reaction. Hence in humans, based on studies using transgenic mouse model as well as purified native/recombinant zona proteins, it is likely that more than one zona protein is involved in the 'sperm-oocyte' binding and induction of the acrosome reaction.

Mammalian spermatozoa and cumulus cells bind to a 3D model generated by recombinant zona pellucida protein-coated beads

The egg is a spherical cell encapsulated by the zona pellucida (ZP) which forms a filamentous matrix composed of several glycoproteins that mediate gamete recognition at fertilization. Studies on molecular mechanisms of sperm-egg binding are limited in many mammalian species by the scarcity of eggs, by ethical concerns in harvesting eggs, and by the high cost of producing genetically modified animals. To address these limitations, we have reproduced a three-dimensional (3D) model mimicking the oocyte's shape, by means of magnetic sepharose beads coated with recombinant ZP glycoproteins (B_ZP) and cumulus cells. Three preparations composed of either ZP2 (C and N-termini; B_ZP2), ZP3 (B_ZP3) or ZP4 (B_ZP4) were obtained and characterized by protein SDS-PAGE, immunoblot and imaging with confocal and electron microscopy. The functionality of the model was validated by adhesion of cumulus cells, the ability of the glycoprotein-beads to support spermatozoa binding and induce acrosome exocytosis. Thus, our findings document that ZP-beads provide a novel 3D tool to investigate the role of specific proteins on egg-sperm interactions becoming a relevant tool as a diagnostic predictor of mammalian sperm function once transferred to the industry.

Sperm acrosome reaction: its site and role in fertilization

Manner and roles of sperm acrosome reaction in a variety of animals were compared.

The Human Egg's Zona Pellucida

Human zona pellucida (ZP) matrix, a delicate network of thin interconnected filaments, is primarily composed of four glycoproteins, namely, ZP1, ZP2, ZP3, and ZP4. All four zona proteins share common structural elements such as signal peptide, "ZP domain," consensus furin cleavage site, transmembrane-like domain, and short cytoplasmic tail. In addition, ZP1 and ZP4 also have "Trefoil domain." Recombinant/native human zona proteins have been used to investigate their binding characteristics to the capacitated and/or acrosome-reacted spermatozoa. These investigations revealed that ZP1, ZP3, and ZP4 primarily bind to the head region of the capacitated human spermatozoa, whereas ZP2 binds to the acrosome-reacted sperm. However, using transgenic mice, N-terminal region of human ZP2 has also been shown to play an important role in binding of sperm to the egg. ZP1, ZP3, and ZP4 lead to dose-dependent increase in acrosome reaction, suggesting that in humans more than one ZP glycoprotein is responsible for induction of acrosome reaction. Glycosylation of these proteins, in particular, N-linked glycosylation as well as sialyl-Lewis^x, is essential for inducing acrosome reaction. Studies delineating downstream signaling events associated with induction of acrosome reaction reveal subtle differences between ZP3 and ZP1/ZP4 with respect to activation of Gi protein-coupled receptor and protein kinase A. The role of mutations in the zona proteins and ZP autoantibodies leading to infertility in women is suggestive and needs more rigorous experimentations for confirming their role in female infertility. The above-mentioned aspects of the human ZP glycoproteins have been discussed in this review.

The bioactivities of the central segment of Zp2 polypeptide

In order to understand the role of the protein zona pellucida 2 in fertilization, an antibody against a central segment of the zona pellucida 2 peptide, segment 190-505 (Z2eH), was prepared. The influence of the antibody on sperm-zona interaction was tested using the sperm-egg binding assay. The effect of the antibody on fertility was evaluated by passive immunization with anti-Z2eH antibody. Immunohistochemical assay showed that an antibody from rabbit reacted specifically with the natural zona pellucida on mouse ovarian sections. Immunofluorescence assay showed that the antibody bound specifically to the zonae pellucidae of the ovulated oocytes and 2-cell embryos after passive immunization. The antibody-treated oocytes bound capacitated sperm as control oocytes, passive immunization did not impede the action of sperm to fertilize the oocyte in vivo. These findings suggest that the central peptide of ZP2 (190-505) is immunogenic and contains zona pellucida-specific epitopes, however the central polypeptide might not be the crucial part from which to construct a functional domain to bind sperm.

A hybrid computational method for the discovery of novel reproduction-related genes

Uncovering the molecular mechanisms underlying reproduction is of great importance to infertility treatment and to the generation of healthy offspring. In this study, we discovered novel reproduction-related genes with a hybrid computational method, integrating three different types of method, which offered new clues for further reproduction research. This method was first executed on a weighted graph, constructed based on known protein-protein interactions, to search the shortest paths connecting any two known reproduction-related genes. Genes occurring in these paths were deemed to have a special relationship with reproduction. These newly discovered genes were filtered with a randomization test. Then, the remaining genes were further selected according to their associations with known reproduction-related genes measured by protein-protein interaction score and alignment score obtained by BLAST. The in-depth analysis of the high confidence novel reproduction genes revealed hidden mechanisms of reproduction and provided guidelines for further experimental validations.

Role of zona pellucida glycoproteins during fertilization in humans

In the last decade, scientific investigations pertaining to the role of zona pellucida (ZP) glycoproteins during fertilization in humans have led to new insights. This has been achieved using purified native/recombinant human zona proteins and transgenic mice expressing human ZP glycoproteins. The proposed model in mice of ZP glycoprotein-3 (ZP3) acting as primary sperm receptor and ZP glycoprotein-2 (ZP2) as secondary sperm receptor has been modified for sperm-egg binding in humans. ZP glycoprotein-1 (ZP1), ZP3, and ZP glycoprotein-4 (ZP4) have been shown to bind to the capacitated human sperm. ZP2 binds to the acrosome-reacted human spermatozoa. Further, the eggs obtained from transgenic mice expressing human ZP2 alone or in conjunction with other human instead of mouse zona proteins showed binding of human sperm, suggesting that ZP2 might also play a role in sperm-egg binding. This function has been mapped to a domain corresponding to amino acid residues 51-144 of ZP2. In contrast to mice, where ZP3 is the primary agonist for inducing the acrosome reaction, in humans, the acrosome reaction can be mediated by ZP1, ZP3, and ZP4. The effect of mutations in the genes encoding zona proteins on the ZP morphology and infertility has not been established. Further, the role of autoantibodies against ZP in women with 'unexplained infertility' leading to poor outcome of in vitro fertilization is currently controversial and needs further investigations. Understanding the role of ZP glycoproteins during human fertilization facilitates the development of new contraceptives and strategies to overcome the problem of infertility.

Stallion fertility: a focus on the spermatozoon

Stallion fertility is a vast subject, with a wide array of permutations that can impact reproductive performance in either positive or negative ways. This review is intended to address a mere segment of the male fertility issue, but the very essence of the male contribution to fertilisation, that of the spermatozoon. Spermatozoal ultrastructure and form-to-function are detailed and spermatozoal metabolism is discussed, with specific reference to distinctive characteristics of stallion spermatozoa. Lastly, methods for assessment of spermatozoal function are considered, with emphasis on spermatozoal motility, the acrosome reaction and spermatozoon-oocyte interactions. Closing comments address the need for development and standardisation of molecular-based assays for use with spermatozoa of stallions whose subfertility cannot be explained with conventional tests.

Hemizona assay and sperm penetration assay in the prediction of IVF outcome: a systematic review

The limited predictive value of semen analysis in achieving natural conception or in IVF outcome confirms the need for sperm function tests to determine optimal management. We reviewed HZA and SPA predictive power in IVF outcome, with statistical significance of diagnostic power of the assays. HZA was readily efficient in predicting IVF outcome, while evident inconsistency among the studies analysed framed the SPA's role in male fertility evaluation. Considerable variation was noted in the diagnostic accuracy values of SPA with wide sensitivity (52-100%), specificity (0-100%), and PPV (18-100%) and NPV (0-100%) together with fluctuation and notable differentiation in methodology and cutoff values employed by each group. HZA methodology was overall consistent with minor variation in cutoff values and oocyte source, while data analysis reported strong correlation between HZA results with IVF outcome, high sensitivity (75-100%), good specificity (57-100%), and high PPV (79-100%) and NPV (68-100%). HZA correlated well with IVF outcome and demonstrated better sensitivity/specificity and positive/negative predictive power. Males with normal or slightly abnormal semen profiles could benefit by this intervention and could be evaluated prior to referral to assisted reproduction. HZA should be used in a sequential fashion with semen analysis and potentially other bioassays in an IVF setting.

Effect of the site of assisted hatching on vitrified-warmed blastocyst transfer cycles: a prospective randomized study

PURPOSE

To assess the effect of assisted hatching (AH) site on the clinical outcomes in vitrified-warmed blastocyst transfer cycles.

METHODS

A total of 160 women who underwent vitrified-warmed blastocyst transfer cycles were randomized to either the ICM group (AH performing at the site near the inner cell mess, ICM), or the TE group (AH performing at the site opposite to the ICM). AH with laser zona drilling was performed 20 or 30 min after thawing once the ICM can be detected. Clinical pregnancy rate, implantation rate, live birth rate and the occurrence rate of monozygotic twins (MZT) pregnancy after transfer of these two groups were compared.

RESULTS

No significant difference was found in the clinical pregnancy rate (63.8% vs. 67.5%), implantation rate (51.7% vs. 53.6%) and live birth rate (57.5% vs. 62.5%) between the ICM group and the TE group. The occurrence rate of MZT was comparable between the two groups (3.9% vs. 5.6%).

CONCLUSIONS

The site of assisted hatching has no influence on the implantation, pregnancy and live birth rate in human vitrified-warmed blastocyst transfer cycles.

Mammalian zona pellucida glycoproteins: structure and function during fertilization

Zona pellucida (ZP) is a glycoproteinaceous translucent matrix that surrounds the mammalian oocyte and plays a critical role in the accomplishment of fertilization. In humans, it is composed of 4 glycoproteins designated as ZP1, ZP2, ZP3 and ZP4, whereas mouse ZP is composed of ZP1, ZP2 and ZP3 (Zp4 being a pseudogene). In addition to a variable sequence identity of a given zona protein among various species, human ZP1 and ZP4 are paralogs and mature polypeptide chains share an identity of 47%. Employing either affinity purified native or recombinant human zona proteins, it has been demonstrated that ZP1, ZP3 and ZP4 bind to the capacitated human spermatozoa and induce an acrosome reaction, whereas in mice, ZP3 acts as the putative primary sperm receptor. Human ZP2 only binds to acrosome-reacted spermatozoa and thus may be acting as a secondary sperm receptor. In contrast to O-linked glycans of ZP3 in mice, N-linked glycans of human ZP3 and ZP4 are more relevant for induction of the acrosome reaction. Recent studies suggest that Sialyl-Lewis(x) sequence present on both N- and O-glycans of human ZP play an important role in human sperm-egg binding. There are subtle differences in the downstream signaling events associated with ZP3 versus ZP1/ZP4-mediated induction of the acrosome reaction. For example, ZP3 but not ZP1/ZP4-mediated induction of the acrosome reaction is dependent on the activation of the Gi protein-coupled receptor. Thus, various studies suggest that, in contrast to mice, in humans more than one zona protein binds to spermatozoa and induces an acrosome reaction.

Immunoregulation of follicular renewal, selection, POF, and menopause in vivo, vs. neo-oogenesis in vitro, POF and ovarian infertility treatment, and a clinical trial

The immune system plays an important role in the regulation of tissue homeostasis ("tissue immune physiology"). Function of distinct tissues during adulthood, including the ovary, requires (1) Renewal from stem cells, (2) Preservation of tissue-specific cells in a proper differentiated state, which differs among distinct tissues, and (3) Regulation of tissue quantity. Such morphostasis can be executed by the tissue control system, consisting of immune system-related components, vascular pericytes, and autonomic innervation. Morphostasis is established epigenetically, during morphogenetic (developmental) immune adaptation, i.e., during the critical developmental period. Subsequently, the tissues are maintained in a state of differentiation reached during the adaptation by a "stop effect" of resident and self renewing monocyte-derived cells. The later normal tissue is programmed to emerge (e.g., late emergence of ovarian granulosa cells), the earlier its function ceases. Alteration of certain tissue differentiation during the critical developmental period causes persistent alteration of that tissue function, including premature ovarian failure (POF) and primary amenorrhea. In fetal and adult human ovaries the ovarian surface epithelium cells called ovarian stem cells (OSC) are bipotent stem cells for the formation of ovarian germ and granulosa cells. Recently termed oogonial stem cells are, in reality, not stem but already germ cells which have the ability to divide. Immune system-related cells and molecules accompany asymmetric division of OSC resulting in the emergence of secondary germ cells, symmetric division, and migration of secondary germ cells, formation of new granulosa cells and fetal and adult primordial follicles (follicular renewal), and selection and growth of primary/preantral, and dominant follicles. The number of selected follicles during each ovarian cycle is determined by autonomic innervation. Morphostasis is altered with advancing age, due to degenerative changes of the immune system. This causes cessation of oocyte and follicular renewal at 38 +/-2 years of age due to the lack of formation of new granulosa cells. Oocytes in primordial follicles persisting after the end of the prime reproductive period accumulate genetic alterations resulting in an exponentially growing incidence of fetal trisomies and other genetic abnormalities with advanced maternal age. The secondary germ cells also develop in the OSC cultures derived from POF and aging ovaries. In vitro conditions are free of immune mechanisms, which prevent neo-oogenesis in vivo. Such germ cells are capable of differentiating in vitro into functional oocytes. This may provide fresh oocytes and genetically related children to women lacking the ability to produce their own follicular oocytes. Further study of "immune physiology" may help us to better understand ovarian physiology and pathology, including ovarian infertility caused by POF or by a lack of ovarian follicles with functional oocytes in aging ovaries. The observations indicating involvement of immunoregulation in physiological neo-oogenesis and follicular renewal from OSC during the fetal and prime reproductive periods are reviewed as well as immune system and age-independent neo-oogenesis and oocyte maturation in OSC cultures, perimenopausal alteration of homeostasis causing disorders of many tissues, and the first OSC culture clinical trial.

Defective protein kinase A and C pathways are common causes of disordered zona pellucida (ZP)--induced acrosome reaction in normozoospermic infertile men with normal sperm-ZP binding

OBJECTIVE

To determine association between defective protein kinases C (PKC) and A (PKA) and disordered zona pellucida (ZP)-induced acrosome reaction (DZPIAR) in normozoospermic infertile men with normal sperm-ZP binding.

DESIGN

Sperm from DZPIAR infertile men were treated without (control) or with (test) phorbol myristate acetate (PMA, PKC activator) or dibutyryl cyclic AMP (dbcAMP, PKA activator) under in vitro standard culture condition. The ZP-induced AR was assessed and compared between control and test.

SETTING

Public and private hospital-based clinical assisted reproduction technology (ART) centers.

PATIENT(S)

A total of 51 DZPIAR infertile men were involved in this study.

INTERVENTION(S)

None.

MAIN OUTCOMES MEASURE(S)

Sperm-ZP binding and the ZP-induced IAR.

RESULT(S)

Both PMA and dbcAMP enhanced ZP-induced AR up to a normal level (≥25%) in some subjects with DZPIAR: 29 (57%) with PMA and 27 (53%) with dbcAMP. Overall 35 (69%) had the ZP-induced AR enhanced to normal by PMA or dbcAMP but 16 (31%) had little or no response to either agent. Fourteen men responded to the two activators differently: 8 effective only with PMA and 6 effective only with dbcAMP.

CONCLUSION(S)

Defective upstream of PKC and PKA pathways are highly associated with disordered ZPIAR in normozoospermic infertile men with normal sperm-ZP binding.

Embryos generated from oocytes lacking complex N- and O-glycans have compromised development and implantation

Female mice generating oocytes lacking complex N- and O-glycans (double mutants (DM)) produce only one small litter before undergoing premature ovarian failure (POF) by 3 months. Here we investigate the basis of the small litter by evaluating ovulation rate and embryo development in DM (Mgat1(F/F)C1galt1(F/F):ZP3Cre) and Control (Mgat1(F/F)C1galt1(F/F)) females. Surprisingly, DM ovulation rate was normal at 6 weeks, but declined dramatically by 9 weeks. In vitro development of zygotes to blastocysts was equivalent to Controls although all embryos from DM females lacked a normal zona pellucida (ZP) and ∼30% lacked a ZP entirely. In contrast, in vivo preimplantation development resulted in less embryos recovered from DM females compared with Controls at 3.5 days post coitum (dpc) (3.2±1.3 vs 7.0±0.6). Furthermore, only 45% of mated DM females contained embryos at 3.5 dpc. Of the preimplantation embryos collected from DM females, approximately half were morulae unlike Controls where the majority were blastocysts, indicating delayed embryo development in DM females. Post-implantation development in DM females was analysed to determine whether delayed preimplantation development affected subsequent development. In DM females at 5.5 dpc, only ∼40% of embryos found at 3.5 dpc had implanted. However, at 6.5 dpc, implantation sites in DM females corresponded to embryo numbers at 3.5 dpc indicating delayed implantation. At 9.5 dpc, the number of decidua corresponded to embryo numbers 6 days earlier indicating that all implanted embryos progress to midgestation. Therefore, a lack of complex N- and O-glycans in oocytes during development impairs early embryo development and viability in vivo leading to delayed implantation and a small litter.

Mapping of epitopes relevant for induction of acrosome reaction on human zona pellucida glycoprotein-4 using monoclonal antibodies

PROBLEM

To decipher structural and functional aspects of human zona pellucida glycoprotein-4 (ZP4), the epitopes recognized by monoclonal antibodies (MAbs) have been mapped.

METHOD OF STUDY

Recombinant human ZP4-mediated induction of acrosome reaction in human sperm was studied in the absence and presence of ZP4-specific MAbs. The epitopes of MAbs were mapped using recombinant peptides expressed in Escherichia coli.

RESULTS

Monoclonal antibodies (MA-1662, MA-1671) against human ZP4 showed specific binding to ZP matrix of human eggs in an indirect immunofluorescence assay. Both the antibodies showed significant (P < 0.05) inhibition in the baculovirus-expressed recombinant ZP4-mediated acrosome reaction. MA-1671 recognized N-terminal fragment of ZP4 and minimal epitope mapped to amino acid residues 126-130 (PARDR), whereas MA-1662 reacted to C-terminal fragment and minimal epitope mapped to amino acid residues 256-260 (ENELV).

CONCLUSIONS

The epitopes corresponding to both N- and C-terminal parts of human ZP4 may be relevant for its biological activity.

Acrosome reaction in the cumulus oophorus revisited: involvement of a novel sperm-released factor NYD-SP8

Fertilization is a process involving multiple steps that lead to the final fusion of one sperm and the oocyte to form the zygote. One of the steps, acrosome reaction (AR), is an exocytosis process, during which the outer acrosome membrane fuses with the inner sperm membrane, leading to the release of acrosome enzymes that facilitate sperm penetration of the egg investments. Though AR has been investigated for decades, the initial steps of AR in vivo, however, remain largely unknown. A well elucidated model holds the view that AR occurs on the surface of the zona pellucida (ZP), which is triggered by binding of sperm with one of the ZP glycosylated protein, ZP3. However, this model fails to explain the large number of 'falsely' acrosome-reacted sperms found within the cumulus layer in many species examined. With the emerging evidence of cross-talk between sperm and cumulus cells, the potential significance of AR in the cumulus oophorus, the outer layer of the egg, has been gradually revealed. Here we review the acrosome status within the cumulus layer, the cross-talk between sperm and cumulus cells with the involvement of a novel sperm-released factor, NYD-SP8, and re-evaluate the importance and physiological significance of the AR in the cumulus in fertilization.

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.

Assisted hatching in assisted reproduction: a state of the art

The World Health Organization estimates that one in six couples experience some delay in conception and an increasing number require treatment by the assisted conception (AC) procedures of in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI).The implantation rate of embryos resulting from in vitro fertilization cycles is generally less than 20%. The exposure of oocytes and embryos to the artificial conditions of in vitro culture may have negative effects on the embryo's ability to undergo normal hatching, resulting in low rates of implantation following IVF and embryo transfer. Human embryos resulting from superovulation develop more slowly in vitro compared to embryos in vivo, manifest a relatively high degree of cytogenetic abnormalities and undergo cellular fragmentation. Artificially disrupting the zona pellucida is known as assisted hatching (AH) and there is some evidence that embryos that have undergone zona manipulation for assisted hatching tend to implant one day earlier than unhatched embryos. A variety of techniques have since been employed to assist embryo hatching, including partial mechanical zona dissection, zona drilling and zona thinning, making use of acid tyrodes, proteinases, piezon vibrator manipulators and lasers. This review will consider the impact of IVF conditions on zona pellucida physiology, zona hardening, different techniques of assisted hatching, who may benefit from assisted hatching and potential hazards.

The mammalian zona pellucida: a matrix that mediates both gamete binding and immune recognition?

The crucial cell adhesion events required for mammalian fertilization commence when spermatozoa bind to the specialized extracellular matrix of the oocyte, known as the zona pellucida (ZP). Bound gametes then undergo a signal transduction cascade known as acrosomal exocytosis that enables them to penetrate this matrix and fuse with the oocyte to create a new individual. The ZP is therefore the target of intense investigation in the mouse, pig, bovine, and human models. Major goals in such studies are to define the adhesion molecules, signal transduction pathways, and the molecular basis for the species-restricted binding of gametes. Evidence exists indicating that protein-carbohydrate and to a lesser extent protein-protein interactions play a role in the initial gamete binding. More recent findings in an unusual sperm-somatic cell adhesion system indicate that tri- and tetraantennary N-glycans mediate initial sperm-oocyte binding in both the murine and porcine models, but conflicting data exist. A novel paradigm designated the "domain specific model" will be presented that could explain these inconsistencies. Another potential functional role of the ZP is immune recognition. Both spermatozoa and oocytes lack major histocompatibility (MHC) class I molecules that mediate the recognition of self in the immune system. This absence makes gametes less susceptible to class I restricted cytotoxic T lymphocytes, but more vulnerable to natural killer (NK) cells. Therefore a "fail safe" system for NK cell recognition should exist on both types of gametes. Another issue is that oocytes could begin to express paternal major histocompatibility antigens during the blastocyst stage prior to hatching, and thus mechanisms could also be in place to block the development of maternal adaptive immune responses. An enhanced understanding of these issues could facilitate the development of superior infertility treatments and contraceptive strategies, and define central operating principles of immune recognition in the female reproductive system.

Acrosome reaction: relevance of zona pellucida glycoproteins

During mammalian fertilisation, the zona pellucida (ZP) matrix surrounding the oocyte is responsible for the binding of the spermatozoa to the oocyte and induction of the acrosome reaction (AR) in the ZP-bound spermatozoon. The AR is crucial for the penetration of the ZP matrix by spermatozoa. The ZP matrix in mice is composed of three glycoproteins designated ZP1, ZP2 and ZP3, whereas in humans, it is composed of four (ZP1, ZP2, ZP3 and ZP4). ZP3 acts as the putative primary sperm receptor and is responsible for AR induction in mice, whereas in humans (in addition to ZP3), ZP1 and ZP4 also induce the AR. The ability of ZP3 to induce the AR resides in its C-terminal fragment. O-linked glycans are critical for the murine ZP3-mediated AR. However, N-linked glycans of human ZP1, ZP3 and ZP4 have important roles in the induction of the AR. Studies with pharmacological inhibitors showed that the ZP3-induced AR involves the activation of the G(i)-coupled receptor pathway, whereas ZP1- and ZP4-mediated ARs are independent of this pathway. The ZP3-induced AR involves the activation of T-type voltage-operated calcium channels (VOCCs), whereas ZP1- and ZP4-induced ARs involve both T- and L-type VOCCs. To conclude, in mice, ZP3 is primarily responsible for the binding of capacitated spermatozoa to the ZP matrix and induction of the AR, whereas in humans (in addition to ZP3), ZP1 and ZP4 also participate in these stages of fertilisation.

'ZP domain' of human zona pellucida glycoprotein-1 binds to human spermatozoa and induces acrosomal exocytosis

BACKGROUND

The human egg coat, zona pellucida (ZP), is composed of four glycoproteins designated as zona pellucida glycoprotein-1 (ZP1), -2 (ZP2), -3 (ZP3) and -4 (ZP4) respectively. The zona proteins possess the archetypal 'ZP domain', a signature domain comprised of approximately 260 amino acid (aa) residues. In the present manuscript, attempts have been made to delineate the functional significance of the 'ZP domain' module of human ZP1, corresponding to 273-551 aa fragment of human ZP1.

METHODS

Baculovirus-expressed, nickel-nitrilotriacetic acid affinity chromatography purified 'ZP domain' of human ZP1 was employed to assess its capability to bind and subsequently induce acrosomal exocytosis in capacitated human spermatozoa using tetramethyl rhodamine isothiocyanate conjugated Pisum sativum Agglutinin in absence or presence of various pharmacological inhibitors. Binding characteristics of ZP1 'ZP domain' were assessed employing fluorescein isothiocyanate (FITC) labelled recombinant protein.

RESULTS

SDS-PAGE and immunoblot characterization of the purified recombinant protein (both from cell lysate as well as culture supernatant) revealed a doublet ranging from ~35-40 kDa. FITC- labelled 'ZP domain' of ZP1 binds primarily to the acrosomal cap of the capacitated human spermatozoa. A dose dependent increase in acrosomal exocytosis was observed when capacitated sperm were incubated with recombinant 'ZP domain' of human ZP1. The acrosome reaction mediated by recombinant protein was independent of Gi protein-coupled receptor pathway, required extra cellular calcium and involved both T- and L-type voltage operated calcium channels.

CONCLUSIONS

Results described in the present study suggest that the 'ZP domain' module of human ZP1 has functional activity and may have a role during fertilization in humans.

Human zona pellucida glycoproteins: functional relevance during fertilization

The zona pellucida (ZP), a glycoproteinaceous matrix surrounding the mammalian oocyte plays an important role in species-specific sperm-egg binding, induction of acrosome reaction in the ZP-bound spermatozoa, avoidance of polyspermy and protection of the embryo prior to implantation. In contrast to mouse, human ZP matrix is composed of 4 glycoproteins designated as ZP1, ZP2, ZP3 and ZP4 (Zp4 pseudogene in mouse). Recent studies employing recombinant and immunoaffinity purified human zona proteins revealed that in addition to ZP3, capacitated acrosome-intact spermatozoa also bind ZP4. Human ZP2 primarily binds to the acrosome-reacted spermatozoa, supporting its role as secondary sperm receptor, as delineated in the murine model. For binding of human zona proteins to spermatozoa, glycosylation is not critical. Both human ZP3 and ZP4 induce dose-dependent acrosomal exocytosis in capacitated sperm. In contrast to the murine model, N-linked glycosylation is more critical for the human ZP3/ZP4 mediated induction of acrosomal exocytosis. Subtle differences in the downstream signaling events associated with ZP3 vs. ZP4 mediated induction of acrosomal exocytosis have been observed. To conclude, in humans, ZP3 and ZP4 are involved in binding of the spermatozoa to the egg and subsequent induction of acrosome reaction. The contribution, if any, of human ZP glycoprotein-1 (ZP1) during these stages of fertilization remains to be elucidated.

Role of proteasomal activity in the induction of acrosomal exocytosis in human spermatozoa

Sperm-associated proteasomes have been suggested to play an important role during fertilization in animals. To delineate the role of these proteasomes during fertilization in humans, the present study reports proteasomal proteolytic activity both in noncapacitated and capacitated human spermatozoa, which is not altered in the presence of baculovirus-expressed recombinant human zona pellucida glycoprotein-3 (ZP3) and zona pellucida glycoprotein-4 (ZP4). However, inhibition of proteasomal proteolytic activity by clasto-lactacystin beta-lactone (CLBL) and Z-Leu-Leu-Leu-CHO (MG132), which are specific inhibitors of the 20S proteasomal core proteases, led to a significant (P < 0.05) inhibition of induction of acrosome reaction mediated by both recombinant human ZP3 and ZP4. Both inhibitors, however, failed to inhibit the induction of acrosomal exocytosis mediated by pharmacological agonist, calcium ionophore (A23187). The binding of recombinant human ZP3 and ZP4, labelled with fluorescein isothiocyanate, to the capacitated spermatozoa was not affected in the presence of proteasomal inhibitors. These observations suggest a role of the sperm proteasome in the induction of ZP3- and ZP4-mediated acrosomal exocytosis upstream of calcium signalling in humans.

Production of monoclonal antibodies against recombinant human zona pellucida glycoproteins: utility in immunolocalization of respective zona proteins in ovarian follicles

The zona pellucida (ZP) glycoproteins play an important role in oocyte development and gamete biology. To analyze their expression in follicles during various developmental stages, murine monoclonal antibodies (MAbs) were generated against the baculovirus-expressed recombinant human ZP2, ZP3 and ZP4. A panel of MAbs specific for the respective zona protein in ELISA and Western blot, and devoid of cross-reaction with other zona proteins was selected. Immunohistochemistry has shown that ZP2 MAb, MA-1620, did not react with oocytes in resting primordial follicles but showed reactivity with degenerating oocytes in primordial follicles undergoing atresia, and with oocytes in growing and antral follicles. Three MAbs against ZP3 did not react with oocytes in primordial follicles, but reacted only with oocytes in growing and antral follicles. Out of four MAbs against ZP4, three MAbs reacted with oocytes in primordial, growing and antral follicles. No reactivity of these MAbs with other ovarian cell types and other tissues studied (endometrium, uterine cervix, fallopian tubes and kidney) was detected except for a strong reactivity of ZP2 MA-1620 with epithelial cells of the uterine ectocervix or endometrium in some samples investigated. Altogether, these studies document generation of MAbs exhibiting high specificity for human zona proteins, which will be useful reagents to study their immunobiology.

Relevance of glycosylation of human zona pellucida glycoproteins for their binding to capacitated human spermatozoa and subsequent induction of acrosomal exocytosis

To delineate the functional aspects of zona pellucida (ZP) glycoproteins during fertilization in human, in the present study, fluorochrome-conjugated Escherichia coli (E. coli)- and baculovirus-expressed recombinant human ZP glycoprotein-2 (ZP2), -3 (ZP3), and -4 (ZP4) were employed. In an immunofluorescence assay, capacitated human sperm exhibited binding of the baculovirus-expressed recombinant ZP3 as well as ZP4 to either acrosomal cap or equatorial region whereas acrosome-reacted sperm failed to show any binding to the acrosomal cap. Using double labeling experiments, simultaneous binding of ZP3 and ZP4 to the acrosomal cap was observed suggesting the possibility of different binding sites of these proteins on the sperm surface. No binding of ZP2 was observed to the capacitated sperm. However, acrosome-reacted sperm (20.00 +/- 1.93%) showed binding of ZP2 that was restricted to only equatorial region. Interestingly, E. coli-expressed recombinant human zona proteins also showed very similar binding profiles. Competitive inhibition studies with unlabeled recombinant human zona proteins revealed the specificity of the above binding characteristics. Binding characteristics have been further validated by an indirect immunofluorescence assay using native human heat solubilized isolated zona pellucida. Employing baculovirus-expressed recombinant ZP3 and ZP4 with reduced N-linked glycosylation and respective E. coli-expressed recombinant proteins, it was observed that glycosylation is required for induction of acrosomal exocytosis but its absence may not compromise on their binding ability. These studies have revealed the binding profile of individual human zona protein to spermatozoa and further strengthened the importance of glycosylation of zona proteins for acrosomal exocytosis in spermatozoa.

Biological Effects of Recombinant Human Zona Pellucida Proteins on Sperm Function1

The initial interaction between gametes takes place at the level of the sperm surface and the zona pellucida (ZP), the extracellular matrix of the egg in mammals. Successful fertilization requires the proper molecular recognition of the ZP by the sperm. Recently, human ZP was demonstrated to be composed of four proteins: ZP1, ZP2, ZP3, and ZP4. The goals of this study were to determine the effects of recombinant human ZP2, ZP3, and ZP4 on human sperm acrosomal exocytosis and sperm motility. Exposure of sperm to ZP proteins, alone or in combination, promoted acrosomal exocytosis in a time-dependent manner. This effect occurred in parallel with a considerable decrease in progressive motility, coincident with an increase in nonprogressive sperm motility. An analysis of kinetic parameters of ZP-treated sperm demonstrated that a characteristic motility pattern could be defined by values of curvilinear velocity > 63.9 mum/s and linearity <or= 15.5%. A strong correlation between curvilinear velocity and the amplitude of lateral head displacement was also observed. The incidence of sperm having these particular kinetic parameters increased after exposure to ZP proteins. These studies of two processes involved in sperm penetration through the ZP confirm that zona glycoproteins promote acrosomal exocytosis and now establish an additional role for these components as modifiers of sperm motility.

Tyrosine phosphorylation on capacitated human sperm tail detected by immunofluorescence correlates strongly with sperm-zona pellucida (ZP) binding but not with the ZP-induced acrosome reaction

BACKGROUND

Protein tyrosine phosphorylation (TP) of human sperm is related to sperm capacitation and zona pellucida (ZP) binding. The aim of this study was to determine whether the TP of capacitated sperm is a useful marker for the ability of sperm to bind to the ZP and undergo the ZP-induced acrosome reaction (AR).

METHODS

Semen samples were obtained from 115 subfertile men with sperm count > or =20 x 10(6)/ml, motility > or =25% and variable morphology. Motile sperm (2 x 10(6)/ml) selected by swim-up were incubated with four oocytes for 2 h, and the number of sperm bound to the ZP and the ZP-induced AR was examined. TP of sperm tail was assessed by immunofluorescence (IF) with anti-phosphotyrosine monoclonal antibody. The time course and effects of dibutyryl cyclic adenosine monophosphate (dbcAMP) and phorbol myristate acetate (PMA) on TP were also studied.

RESULTS

TP was stimulated more by dbcAMP (P < 0.001) and less by PMA (P < 0.05). TP increased significantly with time of incubation of sperm. TP was not detectable on the surface of unfixed live sperm by either Dynabeads or IF. Sperm TP at 2, 4 and 20 h incubation was all significantly correlated with sperm-ZP binding but not with the ZP-induced AR.

CONCLUSION

Sperm TP detected by IF correlates strongly with sperm-ZP binding capacity but not with the ZP-induced AR. This simple IF assay of TP may be a clinically useful test of sperm function that is predictive of normal sperm ZP-binding capacity.

Binding of recombinant human proacrosin/acrosin to zona pellucida (ZP) glycoproteins. I. Studies with recombinant human ZPA, ZPB, and ZPC

OBJECTIVE

To characterize proacrosin/acrosin interaction with isolated zona pellucida (ZP) components.

DESIGN

Prospective study.

SETTING

Basic research laboratory.

PATIENT(S)

Recombinant proteins derived from human proacrosin (Rec-40, Rec-30, Rec-20, Rec-10, and Rec-6) and from human ZP glycoproteins (rec-hZPA, ZPB, and ZPC).

INTERVENTION(S)

In vitro binding assay developed to assess proacrosin/acrosin-ZP interaction.

MAIN OUTCOME MEASURE(S)

Zona pellucida glycoprotein binding to proacrosin/acrosin; estimation of binding affinity.

RESULT(S)

Of all ZP proteins, rec-hZPA demonstrated the highest binding activity toward acrosin (Rec-30) (rec-hZPB: 42% of rec-hZPA; rec-hZPC: 39% of rec-hZPA; P<.0005). Rec-hZPA interaction was disturbed by dextran sulphate (75% inhibition with 10 microM), fucose (67% inhibition with 1.5 microM), and mannose (69% inhibition with 333 mM). Comparing binding activity of proacrosin with other N-terminal acrosin fragments, Rec-40 showed 2.6-3 times higher levels. Moreover, saturable high affinity binding of Rec-40 to ZP components was observed (Kd: 34 nM for rec-hZPA, 38 nM for rec-hZPB, 63 nM for rec-hZPC).

CONCLUSION(S)

The rec-hZPA is the major ZP ligand for human proacrosin/acrosin. The interaction involves mannosyl, fucosyl, and sulfated glycans. Binding sites for rec-hZP would be located both at the N- and C-terminus of proacrosin, revealing a key role of the proenzyme in the interaction.

Recombinant Porcine Zona Pellucida Glycoproteins Expressed in Sf9 Cells Bind to Bovine Sperm but Not to Porcine Sperm

The zona pellucida, which surrounds the mammalian oocyte, consists of the ZPA, ZPB, and ZPC glycoproteins and plays roles in species-selective sperm-egg interactions via its carbohydrate moieties. In the pig, this activity is conferred by tri- and tetraantennary complex type chains; in cattle, it is conferred by a chain of 5 mannose residues. In this study, porcine zona glycoproteins were expressed as secreted forms, using the baculovirus-Sf9 insect cell system. The sperm binding activities of the recombinant proteins were examined in three different assays. The assays clearly demonstrated that recombinant ZPB bound bovine sperm weakly but did not bind porcine sperm; when recombinant ZPC was also present, bovine sperm binding activity was greatly increased, but porcine sperm still was not bound. The major sugar chains of ZPB were pauci and high mannose type chains that were similar in structure to the major neutral N-linked chain of the bovine zona. In fact, the nonreducing terminal alpha-mannose residues were necessary for the sperm binding activity. These results show that the carbohydrate moieties of zona glycoproteins, but not the polypeptide moieties, play an essential role in species-selective recognition of porcine and bovine sperm. Moreover, Asn to Asp mutations at either of two of the N-glycosylation sites of ZPB, residue 203 or 220, significantly reduced the sperm binding activity of the ZPB/ZPC mixture, whereas a similar mutation at the third N-glycosylation site, Asn-333, had no effect on binding. These results suggest that the N-glycans located in the N-terminal half of the ZP domain of porcine ZPB are involved in sperm-zona binding.

Baculovirus-expressed recombinant human zona pellucida glycoprotein-B induces acrosomal exocytosis in capacitated spermatozoa in addition to zona pellucida glycoprotein-C

To facilitate our understanding of the role of zona pellucida glycoproteins during fertilization in humans, recombinant human zona pellucida glycoprotein-A (hZPA), -B (hZPB) and -C (hZPC) were obtained by using Escherichia coli and baculovirus expression systems. Analysis by SDS-PAGE and Western blot of the Ni-NTA affinity purified recombinant proteins revealed that the baculovirus-expressed hZPA, hZPB and hZPC have an apparent molecular weight of approximately 110, approximately 70-75 and approximately 65 kDa, respectively, as compared to approximately 80, approximately 65 and approximately 50 kDa of the respective E. coli-expressed proteins. Lectin binding studies revealed that the baculovirus-expressed recombinant zona proteins were glycosylated. Major oligosaccharides were represented by strong reactivity with Concanavalin A (mannose alpha 1-3 or mannose alpha 1-6 residues) and Jacalin (alpha-O glycosides of Gal or GalNAc moieties). A significant increase in acrosomal exocytosis was observed when capacitated human sperm were incubated in vitro with baculovirus-expressed hZPB (P=0.0005) and hZPC (P=0.0005) The E. coli-expressed hZPB, hZPC and baculovirus-expressed hZPA failed to induce any significant increase (P>0.05) in acrosome reaction. In contrast to hZPC, the acrosome reaction induced by recombinant hZPB was not inhibited by pertussis toxin. These studies, for the first time, have demonstrated that in humans, ZPB also induces acrosomal exocytosis through a Gi independent pathway.

Baculovirus expressed C-terminal fragment of bonnet monkey (Macaca radiata) zona pellucida glycoprotein-3 inhibits ZP3-mediated induction of acrosomal exocytosis

Zona pellucida glycoprotein-3 (ZP3) has been postulated as the primary sperm receptor in various mammalian species including bonnet monkey (Macaca radiata). However, information on the domain responsible for its binding to spermatozoa is inadequate. In the present study, bonnet monkey ZP3 (bmZP3), corresponding to amino acid (aa) residues 223-348 [bmZP3(223-348)] has been cloned and expressed using baculovirus expression system. SDS-PAGE and Western blot analysis of the purified renatured recombinant protein revealed it as a closely spaced doublet of approximately 25 kDa. Lectin-binding studies documented the presence of both O- as well as N-linked glycans. The biotinylated r-bmZP3(223-348) binds to the acrosomal region of the capacitated spermatozoa but fails to bind to the acrosome-reacted spermatozoa as investigated by immunofluorescence studies. In ELISA, nonbiotinylated r-bmZP3(223-348) and baculovirus expressed r-bmZP3, devoid of signal sequence and transmembrane-like domain [r-bmZP3(23-348)] competitively inhibit its binding to the capacitated spermatozoa. Interestingly, binding of biotinylated r-bmZP3(23-348) to the capacitated sperm is also inhibited by nonbiotinylated r-bmZP3(223-348). In contrast to r-bmZP3(23-348), r-bmZP3(223-348) failed to induce acrosomal exocytosis in the capacitated sperm. Interestingly, it competitively inhibits the acrosomal exocytosis induced by r-bmZP3(23-348). These studies, for the first time, identify a domain of ZP3 capable of binding to capacitated spermatozoa and inhibiting ZP3-mediated induction of acrosomal exocytosis furthering our understanding of mammalian fertilization.

Calcium Channels and Ca2+ Fluctuations in Sperm Physiology

Generating new life in animals by sexual reproduction depends on adequate communication between mature and competent male and female gametes. Ion channels are instrumental in the dialogue between sperm, its environment, and the egg. The ability of sperm to swim to the egg and fertilize it is modulated by ion permeability changes induced by environmental cues and components of the egg outer layer. Ca(2+) is probably the key messenger in this information exchange. It is therefore not surprising that different Ca(2+)-permeable channels are distinctly localized in these tiny specialized cells. New approaches to measure sperm currents, intracellular Ca(2+), membrane potential, and intracellular pH with fluorescent probes, patch-clamp recordings, sequence information, and heterologous expression are revealing how sperm channels participate in fertilization. Certain sperm ion channels are turning out to be unique, making them attractive targets for contraception and for the discovery of novel signaling complexes.

Clinical application of sperm-oocyte interaction tests in in vitro fertilization--embryo transfer and intracytoplasmic sperm injection programs

OBJECTIVE

To review the clinical value of sperm-oocyte interaction tests for the diagnosis and management of infertility by standard IVF or intracytoplasmic sperm injection (ICSI).

DESIGN

Review of recent publications on relationships among sperm-oocyte interaction tests, sperm characteristics, and results of IVF and determination of frequency of defective sperm-oocyte interaction in infertile men.

MAIN OUTCOME MEASURE(S)

Fertilization rates with IVF, sperm characteristics, sperm-zona pellucida (ZP) binding, ZP-induced acrosome reaction (AR), and sperm-ZP penetration.

RESULT(S)

Sperm defects associated with low sperm-ZP binding or impaired ZP-induced AR and sperm-ZP penetration are the major causes of failure of fertilization when all or most oocytes from a couple do not fertilize in standard IVF. There is a high frequency of defective sperm-ZP interaction in men with oligozoospermia (<20 x 10(6)/mL) and severe teratozoospermia (strict normal sperm morphology < or =5%). Sperm morphology correlates with sperm-ZP binding, and sperm concentration correlates with ZP-induced AR in infertile men with sperm concentrations >20 x 10(6)/mL. Defective ZP-induced AR may cause infertility in up to 25% men with idiopathic infertility. These patients require ICSI despite the normal standard semen analyses.

CONCLUSION(S)

Sperm-oocyte interaction tests are useful for diagnosis of subtle sperm defects that cause infertility in men without severe abnormalities of semen analysis. Pre-IVF diagnosis of these sperm defects will assist in the clinical assignment of patients to treatment with either standard IVF or ICSI.

Efficacy of antibodies against a chimeric synthetic peptide encompassing epitopes of bonnet monkey (Macaca radiata) zona pellucida-1 and zona pellucida-3 glycoproteins to inhibit in vitro human sperm-egg binding

Immunocontraception achieved by immunization with zona pellucida (ZP) glycoproteins is invariably associated with ovarian dysfunction. Use of ZP glycoprotein-based synthetic peptides as immunogens has been proposed to overcome adverse side effects on ovaries. In the present study, a chimeric peptide encompassing the epitopes of bonnet monkey (Macaca radiata) ZP glycoprotein-1 (bmZP1; amino acid residues 251-273) and ZP glycoprotein-3 (bmZP3; amino acid residues 324-347), separated by a tri-glycine spacer, was synthesized and conjugated to diphtheria toxoid (DT). Immunization of female BALB/cJ mice and bonnet monkeys with the chimeric peptide led to generation of antibodies that reacted with the chimeric peptide, individual bmZP1 & bmZP3 peptides, and also recombinant bmZP1 and bmZP3 proteins expressed by E. coli in an ELISA. Indirect immunofluorescence studies revealed that the immune serum also recognized human as well as bonnet monkey ZP. A significant inhibition of human sperm binding to ZP was observed with antibodies generated against the chimeric peptide in mice (P = 0.0001) as well as monkeys (P = 0.0002) in a hemizona assay (HZA). The inhibition efficacy was significantly higher than that observed by using antibodies against the individual bmZP1 and bmZP3 peptides. Interestingly, no ovarian pathology was observed in female bonnet monkeys immunized with the chimeric peptide. These studies have demonstrated that the chimeric peptide encompassing peptides of multiple ZP glycoproteins may be a promising candidate antigen for designing immunocontraceptive vaccines.

Gp273, the ligand molecule for sperm-egg interaction in the bivalve mollusk, Unio elongatulus, binds to and induces acrosome reaction in human spermatozoa through a protein kinase C-dependent pathway

In a previous article, we suggested that gp273, the ligand molecule for sperm-egg interaction in the bivalve mollusk Unio elongatulus has functional carbohydrate epitopes in common with a human zona pellucida glycoprotein, probably ZP3. We demonstrated that: 1) anti-gp273-purified immunoglobulin G (IgG), which recognizes a carbohydrate gp273 epitope including a Lewisa-like structure, interacts with a zona pellucida protein; 2) human sperm specifically bind to gp273; and 3) binding is reversed by anti-gp273 IgG. In the present study, we confirm this suggestion by demonstrating that heat-solubilized zonae pellucidae reverse gp273-human sperm binding, that gp273-binding sites are restricted to the acrosomal region, and that gp273 induces the acrosome reaction in human sperm. We also demonstrated that gp273-binding sites on human sperm function as signaling receptors because exposure of spermatozoa to this glycoprotein results in significant stimulation of protein kinase C (PKC) activity. Because the PKC inhibitor, bisindolylmaleimide I, reverses both PKC activation and the acrosome reaction, this kinase is a key component of the signal transduction pathway activated by gp273 and leading to the exocytotic event.

Normal range and variation of the zona pellucida-induced acrosome reaction in fertile men

OBJECTIVE

To investigate the normal range of the zona pellucida (ZP)-induced acrosome reaction (AR) in fertile men.

DESIGN

A study of normative data.

SETTING

Academic research and teaching tertiary hospital.None.Fertile men (n = 111) who had children or whose female partner was currently pregnant. MAIN OUTCOME MEASURE (S): Semen analysis, sperm-ZP binding, and the ZP-induced AR.

RESULT(S)

There was wide range for the ZP-induced AR: 20%-98% with a mean of 48%. The ZP-induced AR was significantly correlated with sperm concentration and normal morphology. The ZP-induced AR was significantly lower in men with sperm concentration <or=60 x 10(6)/mL than those with sperm concentration >60 x 10(6)/mL. Similarly, men with normal sperm morphology >or=15% had significantly higher ZP-induced AR than men with normal morphology <15%.

CONCLUSION(S)

There is a wide range of the ZP-induced AR in fertile men that is correlated with sperm concentration and normal morphology.

Failed fertilization: is it predictable?

PURPOSE OF REVIEW

The purpose of this review is to critically examine the ability of screening tests to predict fertilization failure.

RECENT FINDINGS

Failed fertilization occurs in 5-10% of in-vitro fertilization cycles and 2-3% of intracytoplasmic sperm injection cycles. Failed fertilization may result from impaired spermatozoa, oocyte deficiencies or defects in the in-vitro sperm/oocyte medium. In the in-vitro fertilization setting most cases are caused by male factor deficiencies, whereas failure of oocyte activation is the most common cause of failed fertilization after intracytoplasmic sperm injection. Although the standard semen analysis has limited ability to predict fertilization failure, strict sperm morphology criteria, sperm-zona binding ratios and zona pellucida induced acrosome reaction tests provide increased capacity to avoid this outcome. The quality of the semen sample on the day of oocyte retrieval and fertilization performance in previous in-vitro fertilization cycles may also guide the appropriate use of intracytoplasmic sperm injection. However, the routine use of the latter technique in cases of non-male factor infertility is contraindicated.

SUMMARY

The ever improving techniques highlighted in this analysis offer improved ability to predict failed fertilization.

Identification of human sperm proteins involved in the interaction with homologous zona pellucida

OBJECTIVE

To identify human sperm proteins involved in homologous zona pellucida (ZP) interaction.

DESIGN

Prospective study.

SETTINGS

Basic research laboratory.

PATIENT(S)

Semen samples from normozoospermic donors, tissue sections from surgical pieces, and ZP from nonfertilized oocytes.

INTERVENTION(S)

Antibodies for sperm proteins (HSE; high salt extract) were developed (anti-HSE) and partially characterized. Participation of sperm proteins on ZP-interaction was tested with the hemizona assay (HZA). Antigens were immunolocalized in sperm and tissues.

MAIN OUTCOME MEASURE(S)

Sperm and tissue immunostaining; Western blotting; and number of sperm bound to the ZP.

RESULT(S)

Anti-HSE antibodies recognized several polypeptides in HSE (9 to 200 kd). Specific antibodies for 49 and 66 kd proteins (p49, p66) were obtained. Both (anti-p49 and anti-p66) stained the head of ejaculated and capacitated sperm. In the HZA, sperm preincubation with a mixture of anti-p49 and anti-p66 (100 micro g/mL) resulted in a decrease in the number of spermatozoa bound to the ZP. Presence of p66 (10 micro g/mL) inhibited sperm-ZP interaction. In contrast, p49 did not alter sperm binding to the ZP. Immunohistochemical analysis showed that p66 is present in the epididymis. No staining was observed in testicular sections.

CONCLUSION(S)

We found that p66 is an epididymal protein that participates in human sperm interaction with homologous ZP.