ZP2 cleavage blocks polyspermy by modulating the architecture of the egg coat.

Following the fertilization of an egg by a single sperm, the egg coat or zona pellucida (ZP) hardens and polyspermy is irreversibly blocked. These events are associated with the cleavage of the N-terminal region (NTR) of glycoprotein ZP2, a major subunit of ZP filaments. ZP2 processing is thought to inactivate sperm binding to the ZP, but its molecular consequences and connection with ZP hardening are unknown. Biochemical and structural studies show that cleavage of ZP2 triggers its oligomerization. Moreover, the structure of a native vertebrate egg coat filament, combined with AlphaFold predictions of human ZP polymers, reveals that two protofilaments consisting of type I (ZP3) and type II (ZP1/ZP2/ZP4) components interlock into a left-handed double helix from which the NTRs of type II subunits protrude. Together, these data suggest that oligomerization of cleaved ZP2 NTRs extensively cross-links ZP filaments, rigidifying the egg coat and making it physically impenetrable to sperm.

Egg envelope formation of medaka Oryzias latipes requires ZP proteins originating from both the liver and ovary.

Teleost oocytes are surrounded by a structure called chorion or egg envelopes, which is composed of zona pellucida (ZP) proteins. As a result of the gene duplication in teleost, the expression site of the zp genes, coding the major component protein of egg envelopes, changed from the ovary to the maternal liver. In Euteleostei, there are three liver-expressed zp genes, named choriogenin (chg) h, chg hm, and chg l, and the composition of the egg envelope is mostly made up of these Chgs. In addition, ovary-expressed zp genes are also conserved in the medaka genomes, and their proteins have also been found to be minor components of the egg envelopes. However, the specific role of liver-expressed versus ovary-expressed zp genes was unclear. In the present study, we showed that ovary-synthesized ZP proteins first form the base layer of the egg envelope and then Chgs polymerize inwardly to thicken the egg envelope. To analyze the effects of dysfunction of the chg gene, we generated some chg knockout medaka. All knockout females failed to produce normally fertilized eggs by the natural spawning. The egg envelopes lacking Chgs were significantly thinner, but layers formed by ZP proteins synthesized in the ovary were found in the thin egg envelope of knockout as well as wildtype eggs. These results suggest that the ovary-expressed zp gene is well conserved in all teleosts, including those species in which liver-derived ZP proteins are the major component, because it is essential for the initiation of egg envelope formation.

Cryo-EM structure of native human uromodulin, a zona pellucida module polymer.

Assembly of extracellular filaments and matrices mediating fundamental biological processes such as morphogenesis, hearing, fertilization, and antibacterial defense is driven by a ubiquitous polymerization module known as zona pellucida (ZP) "domain". Despite the conservation of this element from hydra to humans, no detailed information is available on the filamentous conformation of any ZP module protein. Here, we report a cryo-electron microscopy study of uromodulin (UMOD)/Tamm-Horsfall protein, the most abundant protein in human urine and an archetypal ZP module-containing molecule, in its mature homopolymeric state. UMOD forms a one-start helix with an unprecedented 180-degree twist between subunits enfolded by interdomain linkers that have completely reorganized as a result of propeptide dissociation. Lateral interaction between filaments in the urine generates sheets exposing a checkerboard of binding sites to capture uropathogenic bacteria, and UMOD-based models of heteromeric vertebrate egg coat filaments identify a common sperm-binding region at the interface between subunits.

Domain Expansion and Functional Diversification in Vertebrate Reproductive Proteins.

The rapid evolution of fertilization proteins has generated remarkable diversity in molecular structure and function. Glycoproteins of vertebrate egg coats contain multiple zona pellucida (ZP)-N domains (1-6 copies) that facilitate multiple reproductive functions, including species-specific sperm recognition. In this report, we integrate phylogenetics and machine learning to investigate how ZP-N domains diversify in structure and function. The most C-terminal ZP-N domain of each paralog is associated with another domain type (ZP-C), which together form a "ZP module." All modular ZP-N domains are phylogenetically distinct from nonmodular or free ZP-N domains. Machine learning-based classification identifies eight residues that form a stabilizing network in modular ZP-N domains that is absent in free domains. Positive selection is identified in some free ZP-N domains. Our findings support that strong purifying selection has conserved an essential structural core in modular ZP-N domains, with the relaxation of this structural constraint allowing free N-terminal domains to functionally diversify.

Novel variants in ZP1, ZP2 and ZP3 associated with empty follicle syndrome and abnormal zona pellucida.

RESEARCH QUESTION: Which genetic variants might explain the causes of empty follicle syndrome (EFS) and abnormal zona pellucida (ZP) and affect the success of treatment with assisted reproductive technologies (ART)? DESIGN: Whole-exome sequencing was performed in probands with EFS and abnormal ZP. Sanger sequencing was used for variant validation. Using HEK-293T cells, the effects of ZP1 and ZP2 variants on protein expression were explored by western blotting, and the effect of the ZP1 variant on protein location was investigated via immunofluorescence. The protein structure was also analysed to investigate the pathogenicity of variants. RESULTS: A homozygous nonsense variant in ZP1 (c.874C>T, p.Gln292*) was detected in a patient with EFS. A novel homozygous frameshift variant in ZP2 (c.836_837delAG, p.Glu279Valfs*6) and a novel heterozygous missense variant in ZP3 (c.1159G>A, p.Val387Met) were identified in two patients with ZP morphological abnormalities, respectively. Western blotting and immunofluorescence analysis showed that the ZP1 variant results in a premature stop codon, leading to the truncated ZP1 protein. The ZP2 variant, which is situated in the N-terminus, triggers the degradation of a premature termination protein. Additionally, the patient with the ZP3 variant achieved clinical pregnancy following intracytoplasmic sperm injection treatment. CONCLUSIONS: These findings expand the mutational spectrum of ZP1, ZP2 and ZP3, and provide new evidence for genetic diagnosis of female infertility. The targeted genetic diagnosis of ZP genes is recommended to choose appropriate fertilization methods and improve success rates of treatment with ART.

Integrity of Narrow Epithelial Tubes in the C. elegans Excretory System Requires a Transient Luminal Matrix.

Most epithelial cells secrete a glycoprotein-rich apical extracellular matrix that can have diverse but still poorly understood roles in development and physiology. Zona Pellucida (ZP) domain glycoproteins are common constituents of these matrices, and their loss in humans is associated with a number of diseases. Understanding of the functions, organization and regulation of apical matrices has been hampered by difficulties in imaging them both in vivo and ex vivo. We identified the PAN-Apple, mucin and ZP domain glycoprotein LET-653 as an early and transient apical matrix component that shapes developing epithelia in C. elegans. LET-653 has modest effects on shaping of the vulva and epidermis, but is essential to prevent lumen fragmentation in the very narrow, unicellular excretory duct tube. We were able to image the transient LET-653 matrix by both live confocal imaging and transmission electron microscopy. Structure/function and fluorescence recovery after photobleaching studies revealed that LET-653 exists in two separate luminal matrix pools, a loose fibrillar matrix in the central core of the lumen, to which it binds dynamically via its PAN domains, and an apical-membrane-associated matrix, to which it binds stably via its ZP domain. The PAN domains are both necessary and sufficient to confer a cyclic pattern of duct lumen localization that precedes each molt, while the ZP domain is required for lumen integrity. Ectopic expression of full-length LET-653, but not the PAN domains alone, could expand lumen diameter in the developing gut tube, where LET-653 is not normally expressed. Together, these data support a model in which the PAN domains regulate the ability of the LET-653 ZP domain to interact with other factors at the apical membrane, and this ZP domain interaction promotes expansion and maintenance of lumen diameter. These data identify a transient apical matrix component present prior to cuticle secretion in C. elegans, demonstrate critical roles for this matrix component in supporting lumen integrity within narrow bore tubes such as those found in the mammalian microvasculature, and reveal functional importance of the evolutionarily conserved ZP domain in this tube protecting activity.

Histochemistry of the zona pellucida of the ovary of a species with natural polyovulation: Lagostomus maximus (Rodentia, Hystricomorpha, Chinchillidae).

This study reports the histochemistry and the distribution of glycoconjugates (GCs) in the zona pellucida (ZP) of preantral, secondary, tertiary, polyovulatory and atretic follicles of ovaries from non-pregnant (NPr) and pregnant (Pr) females of Lagostomus maximus. GCs were studied using histochemical and lectin histochemical methods. The viscacha ZP was positive to all the histochemical techniques. In addition, it was observed that the intensity of staining of the ZP was constant in the different follicular stages between both female groups. The lectin histochemical study revealed that ZP was positive for certain lectins (WGA, RCA-I and CON-A) and that the labelling did not vary between the different follicular stages, but between the two groups of females. By using both histochemical techniques, it was established that the GCs present in the ZP label the complexity of the area. These results allow us to increase our knowledge on the biology of the viscacha's ovary, particularly contributing to the study of polyovulation.

Down-regulation of the liver-derived plasma protein fetuin-B mediates reversible female infertility.

STUDY QUESTION: Does antisense oligonucleotide (ASO)-mediated down-regulation of serum fetuin-B cause infertility like fetuin-B gene deficiency in female mice? SUMMARY ANSWER: Pharmacological fetuin-B down-regulation by ASO therapy results in reversible infertility in female mice. WHAT IS KNOWN ALREADY: Female fetuin-B deficient (Fetub-/-) mice are infertile owing to premature zona pellucida (ZP) hardening. Enzyme activity studies demonstrated that fetuin-B is a potent and highly specific inhibitor of the zona proteinase ovastacin, which cleaves ZP protein 2 (ZP2) and thus mediates definitive ZP hardening. STUDY DESIGN, SIZE, DURATION: Ten fetuin-B ASO boli (100 mg/kg) were injected s.c. over 20 days in 12 female mice, and 10 phosphate-buffered saline (PBS)-treated mice were used as control. At day 20 females were mated to evaluate fetuin-B as a potential molecular target for contraception. ASO and PBS treatment was continued for ten injections. After treatment cessation at day 50, mating was continued to investigate if infertility was reversible. PARTICIPANTS/MATERIALS, SETTING, METHODS: We generated fetuin-B/ovastacin double deficient (Fetub-/-, Astl-/-) mice by conventional breeding to test if fertility of Fetub-/- female mice was restored when the target proteinase would likewise be deleted. At least five matings with each female genotype (Fetub-/- single deficient, Astl-/- single deficient, Fetub-/-, Astl-/- double deficient) were performed. To test the contraceptive effect of fetuin-B down-regulation, 22 female mice (6-13 weeks old) were treated with repetitive boli of 100 mg/kg fetuin-B ASO (n = 12) or PBS (n = 10) and mated continuously. Serum fetuin-B was determined by immunoblot before, during and after the ASO treatment. After 3 weeks of ASO treatment, in 6 females Fetub mRNA in liver was analyzed by PCR, and six PBS-treated females were used as control. Aspartate (AST) and alanine aminotransferase (ALT) were also measured in serum of six mice in each group. To determine the minimum permissive serum fetuin-B concentration required for successful fertilization IVF was performed in five fetuin-B ASO-treated mice. As a control, six females were injected with control oligonucleotides and six females were left untreated. MAIN RESULTS AND THE ROLE OF CHANCE: Fertility of Fetub-/- female mice was restored by additional ovastacin deficiency (Astl-/-). Unlike Fetub-/- mice, female Fetub-/-, Astl-/- mice were fertile, confirming ovastacin as a primary molecular target of fetuin-B. At day 20, after receiving 10 fetuin-B ASO boli, serum fetuin-B was down-regulated to 8 ± 6% (mean ± SD) of baseline level. Fetuin-B down-regulation was confirmed at the mRNA level. Fetuin-B ASO-treated females had 12.1 ± 3.1% of the liver Fetub mRNA level seen in PBS-treated females. In the following mating study, 11 out of 12 mated females failed to become pregnant during 50 days of ASO treatment and continuous mating from day 20 onwards. IVF of oocytes derived from ASO-treated females suggested that a serum fetuin-B level of less than 10 µg/ml was required to prevent pregnancy. Withdrawal of ASO treatment normalized serum fetuin-B and restored fertility; all female mice became pregnant and had litters within 60.3 ± 35.9 days after cessation of ASO treatment. The first litter was significantly smaller than that of control mice (4.6 ± 2.3 versus 6.7 ± 1.8 pups, n = 20, P = 0.04) but the smaller litter size was only temporary. The size of the second litter was similar to the first litter of control mice (7.6 ± 1.3 versus 6.7 ± 1.8 pups, n = 18, P = 0.25). LIMITATIONS, REASONS FOR CAUTION: The repeated dose of 100 mg/kg fetuin-B ASO boli caused an increased serum ALT and AST activity, suggesting hepatotoxicity. Daily vaginal plug checks indicated successful mating, but mating plugs in ASO-treated mice were less stable (vaginal tract not closed) than in control mice. WIDER IMPLICATIONS OF THE FINDINGS: Pharmacological fetuin-B down-regulation in mice caused reversible infertility. Control of ovastacin proteinase activity by fetuin-B is a necessary determinant of female fertility that can serve as a target for female contraception. Although promising in terms of human contraception, further studies analyzing the balance between sufficient fetuin-B down-regulation and tolerable side effects are required to improve safety before transfer into human reproductive biology can be considered. LARGE SCALE DATA: None. STUDY FUNDING AND COMPETING INTERESTS: The research was supported by a grant from Deutsche Forschungsgemeinschaft and by the START program of the Medical Faculty of RWTH Aachen University. The authors E.D., J.F. and W.J.-D. are named inventors on a patent application of RWTH Aachen University covering the use of fetuin-B in ovary and oocyte culture. No conflict of interest is declared by C.S. and A.C.

Recombinant fetuin-B protein maintains high fertilization rate in cumulus cell-free mouse oocytes.

STUDY QUESTION: Does fetuin-B inhibit premature zona pellucida (ZP) hardening in mouse oocytes in vitro and thus increase IVF rate? SUMMARY ANSWER: Supplementation of oocyte in vitro maturation (IVM) media with recombinant mouse fetuin-B (rmFetuB) increased fertilization rate without affecting mouse embryo development into blastocysts. WHAT IS KNOWN ALREADY: Mice deficient in fetuin-B are infertile owing to premature ZP hardening. Premature ZP hardening also occurs during oocyte IVM leading to decreased fertilization rate. STUDY DESIGN, SIZE, DURATION: We fertilized batches of 20-30 mouse metaphase II (Mll) stage oocytes from C57BL/6 mice with fresh sperm, and studied early embryo development until blastocyst hatching. PARTICIPANTS/MATERIALS, SETTING, METHODS: Oocytes were maintained with or without rmFetuB during IVM and IVF. Exogenous rmFetuB was added to media prior to oocyte isolation. ZP hardening was quantified by chymotrypsin digestion timing and by counting attached sperm. MAIN RESULTS AND THE ROLE OF CHANCE: In the absence of cumulus cells, rmFetuB dose-dependently inhibited ZP hardening and increased IVF rate (P = 0.039). Fetuin-B at ≥0.03 mg/ml also inhibited physiological, fertilization-triggered ZP hardening (indicated by increased sperm binding, P = 0.0002), without increasing embryo death. Exogenous rmFetuB increased IVF rate for up to 5 hours of IVM (P = 0.02 at 1 hour, P = 0.01 at 5 hours of IVM). LIMITATIONS, REASONS FOR CAUTION: Mll stage oocytes in this study were isolated from the ampullae of fetuin-B expressing mice. Thus, oocytes were protected against premature ZP hardening by endogenous fetuin-B. In humans and livestock, oocytes are usually isolated by follicle puncture before ovulation. In this situation, the deprivation of endogenous fetuin-B would occur earlier and the effect of exogenous fetuin-B in the IVF medium may be even more pronounced. Fertilization-triggered ZP hardening is essential for embryo development but in this study the effect of fetuin-B supplementation was only studied to blastocyst stage. Any influence of added fetuin-B on later embryo development after transplantation remains to be determined. WIDER IMPLICATIONS OF THE FINDINGS: The astacin-type protease ovastacin triggers definitive ZP hardening by cleaving the zona pellucida protein 2. Animal sera are known to inhibit premature ZP hardening. The addition of rFetuB to the culture medium of oocytes could increase IVF rates by the inhibition of premature ZP hardening. In this regard, the results could be useful for clinical activity. LARGE SCALE DATA: None. STUDY FUNDING/COMPETING INTERESTS: The research was supported by a grant from Deutsche Forschungsgemeinschaft and by the START program of the Medical Faculty of RWTH Aachen University. The authors ED, JF and WJD are named inventors on a patent application of RWTH Aachen University covering the use of fetuin-B in ovary and oocyte culture.

Bidirectional Estrogen-Like Effects of Genistein on Murine Experimental Autoimmune Ovarian Disease.

This study was to investigate the bidirectional estrogen-like effects of genistein on murine experimental autoimmune ovarian disease (AOD). Female BALB/c mice were induced by immunization with a peptide from murine zona pellucida. The changes of estrous cycle, ovarian histomorphology were measured, and the levels of serum sex hormone were analyzed using radioimmunoassay. Proliferative responses of the ovary were also determined by immunohistochemistry. Administration of 25 or 45 mg/kg body weight genistein enhanced ovary development with changes in serum sex hormone levels and proliferative responses. Meanwhile, the proportions of growing and mature follicles increased and the incidence of autoimmune oophoritis decreased, which exhibited normal ovarian morphology in administration of 25 or 45 mg/kg body weight genistein, while a lower dose (5 mg/kg body weight genistein) produced the opposite effect. These findings suggest that genistein exerts bidirectional estrogen-like effects on murine experimental AOD, while a high dose (45 mg/kg body weight) of genistein may suppress AOD.

Cysteine analogs with a free thiol group promote fertilization by reducing disulfide bonds in the zona pellucida of mice.

Archives of cryopreserved sperm harvested from genetically engineered mice, in mouse resource centers, are a readily accessible genetic resource for the scientific community. We previously reported that exposure of oocytes to reduced glutathione (GSH) greatly improves the fertilization rate of frozen-thawed mouse sperm. Application of GSH to in vitro fertilization techniques is widely accepted as a standard protocol to produce sufficient numbers of mice from cryopreserved sperm. However, the detailed mechanism of the enhancement of fertilization mediated by GSH in vitro is not fully understood. Here we focused on the chemical by determining the effects of its amino acid constituents and cysteine analogs on the fertilization of oocytes by frozen-thawed sperm. Furthermore, we determined the stability of these compounds in aqueous solution. We show here that l-cysteine (l-Cys), d-cysteine (d-Cys), or N-acetyl-l-cysteine (NAC) increased the rate of fertilization when added to the medium but did not adversely affect embryo development in vitro or in vivo. The levels of thiol groups of proteins in the zona pellucida (ZP) and the expansion of the ZP were increased by l-Cys, d-Cys, and NAC. These effects were abrogated by the methylation of the thiol group of l-Cys. NAC was the most stable of these compounds in the fertilization medium at 4°C. These results suggest that the thiol groups of cysteine analogs markedly enhance the fertilization rate of mouse oocytes.

Structural studies of "aggregation-prone" peptide-analogues of teleostean egg chorion ZPB proteins.

Egg envelopes of vertebrates are composed of a family of proteins called zona pellucida (ZP) proteins, which are distinguished by the presence of a common structural polymerizing motif, known as ZP domain. Teleostean fish chorion is a fibrous structure, consisting of protein members of the ZPB/ZP1 and the ZPC/ZP3 families, which are incorporated as tandemly repeating heterodimers inside chorion fibers. Computational analysis of multiple ZPB/ZP1 proteins from several teleostean species, reveals two potential "aggregation-prone" sequence segments, forming a specific polymerization interface (AG interface). These two peptides were synthesized and results are presented in this work from transmission electron microscopy, Congo red staining, X-ray fiber diffraction and ATR FT-IR, which clearly display the ability of these peptides to self-aggregate, forming amyloid-like fibrils. This, most probably implies that the AG interface of ZPB/ZP1 proteins plays an important role for the formation of the repeating ZPB-ZPC heterodimers, which constitute teleostean chorion fibrils.

ZP2 and ZP3 cytoplasmic tails prevent premature interactions and ensure incorporation into the zona pellucida.

The zona pellucida contains three proteins (ZP1, ZP2, ZP3), the precursors of which possess signal peptides, 'zona' domains and short (9-15 residue) cytoplasmic tails downstream of a transmembrane domain. The ectodomains of ZP2 and ZP3 are sufficient to form the insoluble zona matrix and yet each protein traffics through oocytes without oligomerization. ZP2 and ZP3 were fluorescently tagged and molecular interactions were assayed by fluorescent complementation in CHO cells and growing oocytes. ZP2 and ZP3 traffic independently, but colocalize at the plasma membrane. However, protein-protein interactions were observed only after release and incorporation of ZP2 and ZP3 into the extracellular matrix surrounding mouse oocytes. In the absence of their hydrophilic cytoplasmic tails, ZP2 and ZP3 interacted within the cell and did not participate in the zona pellucida. A heterologous GPI-anchored 'zona' domain protein fused with the cytoplasmic tails was integrated into the zona matrix. We conclude that the cytoplasmic tails are sufficient and necessary to prevent intracellular oligomerization while ensuring incorporation of processed ZP2 and ZP3 into the zona pellucida.

Inferring the evolution of teleostean zp genes based on their sites of expression.

Fish egg envelopes consist of several glycoproteins, called zona pellucida (ZP) proteins, which are conserved among chordates. Euteleosts synthesize ZP proteins in the liver, while elopomorphs synthesize them in the ovaries. In Cypriniformes, zp genes are expressed in the ovaries. We investigated the zp genes of two Otocephalan orders: Clupeiformes (Pacific herring and Japanese anchovy) and Gonorynchiformes (milkfish), which diverged earlier than Cypriniformes. cDNA cloning of zp gene homologs revealed that Pacific herring and Japanese anchovy possessed both ovary- and liver-expressed zp genes; however, the zp genes of milkfish were only expressed in the ovaries. Molecular phylogenetic analysis showed that ovary- and liver-expressed zpc genes of two the Clupeiformes formed independent clades. Based on this, we hypothesized the evolution of teleostean zp genes, focusing on the organ expressing zp gene. As in other chordates, the original site of expression of zp genes was likely the ovary. In the early stage of teleostean evolution, the ancestral zp genes acquired the ability to express in the liver. Later, one of the two expression sites became dominant. The liver-expressed zp genes are component proteins of the egg envelope in the Euteleostei. In Otocephala, Clupeiformes possess both ovary- and liver-expressed genes that presumably participate in egg envelope formation, whereas the Gonorynchiformes and Cypriniformes have primarily preserved ovary expressed zp genes.

Identification of sperm head proteins involved in zona pellucida binding.

STUDY QUESTION: Which human sperm proteins interact with zona pellucida (ZP) glycoproteins, ZPA/2, ZPB/4 and ZPC/3? SUMMARY ANSWER: Co-precipitation experiments with recombinant human ZP (rhZP) coated beads demonstrated interactions with various proteins, including glutathione S-transferase M3 (GSTM) with ZPB/4 and voltage-dependent anion channel 2 (VDAC2) with ZPA/2 and ZPC/3. WHAT IS KNOWN ALREADY: Regarding sperm-ZP binding, several target spot/proteins have been detected in several species, but not all have been characterized. The limit of these studies was that a mixture of the different ZP glycoproteins was used and did not allow the identification of the specific ZP glycoprotein (ZPA/2, ZPC/3 or ZPB/4) involved in the interaction with the sperm proteins. STUDY DESIGN, SIZE, DURATION: To identify the human sperm proteins interacting with the oocyte ZP, we combined two approaches: immunoblot of human spermatozoa targeted by antisperm antibodies (ASAs) from infertile men and far western blot of human sperm proteins overlayd by each of the rhZP proteins. MATERIALS, SETTING, METHODS: We used rhZP expressed in Chinese hamster ovary (CHO) cells and ASA eluted from infertile patients undergoing IVF failure. Sperm proteins separated by two-dimensional (2D) electrophoresis recognized by both sperm-eluted ASAs from infertile patients and rhZP were identified by mass spectrometry (MALDI-MS/MS). Some of these proteins were further validated by co-precipitation experiments with rhZP and functional zona binding tests. MAIN RESULTS AND THE ROLE OF CHANCE: We identified proteins that are glycolytic enzymes such as pyruvate kinase 3, enolase 1, glyceraldehyde-3-phosphate dehydrogenase, aldolase A, triosephosphate isomerase, detoxification enzymes such as GSTM or phospholipid hydroperoxide glutathione peroxidase, ion channels such as VDAC2 and structural proteins such as outer dense fibre 2. Several of the proteins were localized on the sperm head. However, these proteins have also been described to exert other functions in the flagellum. Co-precipitation experiments with rhZP-coated beads confirmed the direct interaction of GSTM with ZP4 and of VDAC2 with ZP2 and ZP3. LIMITATIONS, REASONS FOR CAUTION: We used recombinant ZP in place of native ZP. Thus, the post-translational modifications of the proteins, such as glycosylations, can be different and can influence their function. However, CHO cell-expressed rhZP are functional, e.g. can bind human spermatozoa and induce the acrosome reaction. Moreover, the identification of relevant proteins was limited by the need for sufficient amounts of proteins on the preparative 2D-gel to be subsequently analysed in MALDI-TOF MS/MS. WIDER IMPLICATIONS OF THE FINDINGS: Our results bring new insights on the ability of sperm proteins to exert several functions depending on their sub-cellular localization, either the head or flagellum. Their multiple roles suggest that these sperm proteins are multifaceted or moonlighting proteins. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the grant ReproRio (CNRS, INRA, INSERM and CEA) and the Société d'Andrologie de Langue Française. TRIAL REGISTRATION NUMBER: Not applicable.

The human is an exception to the evolutionarily-conserved phenomenon of pre-fertilization zona pellucida resistance to proteolysis induced by oviductal fluid.

STUDY QUESTION: Is zona pellucida (ZP) resistance to proteolysis, induced by oviductal fluid (OF), a mechanism common to species other than the pig and cow? SUMMARY ANSWER: ZP resistance to proteolysis induced by OF was observed in the mouse, rat, hamster, rabbit, sheep, goat, pig and cow, but not in humans. WHAT IS KNOWN ALREADY: Oviductal ZP resistance to proteolysis occurs in the pig and cow where it influences the incidence of fertilization and polyspermy. The effect is observed after incubation of ZP in OFs from pig (pOF), cow (cOF), rabbit (rOF) and sheep (sOF). STUDY DESIGN, SIZE, DURATION: Oocytes from nine different species, including ungulates, rodents, lagomorphs and primates were incubated in rOF, sOF, gOF, cOF, pOF and human oviductal fluid (hOF). ZP digestion times for the matured oocytes of these nine species, without any treatment or incubated in 5 (mouse, rat, hamster, rabbit, cow, ewe and goat) or 6 (pig and humans) of the OFs collected were compared using three replicates per treatment and at least three oocytes per replicate. MATERIALS, SETTING, METHODS: In vivo matured oocytes from rat, hamster, mouse, rabbit and humans, in vitro matured oocytes from cow, goat, ewe and pig and rOF, cOF, gOF, sOF, pOF and human (hOF) were collected and processed for the study. Oocytes from each species were incubated in the different OFs for 30 min. The resistance of the ZP of the oocytes to enzymatic digestion in a pronase solution (0.5% in PBS) was measured and registered as ZP digestion time. MAIN RESULTS AND THE ROLE OF CHANCE: rOF increased ZP resistance to proteolytic digestion in the range of between 96 and 720 h for any of the species tested, whereas the corresponding increase in human ZP was only 1 min. OFs from the remaining species also had a significant effect, with variations among the cross-species experiments (P < 0.05). hOF, which was only tested on human and porcine oocytes, had no effect on ZP chemical hardening. Measurements of ZP digestion times are not of extreme accuracy and errors of a few seconds can be assumed in the experimental data. However, when differences are in the range of hours among treatments, variations measured in seconds do not alter the robustness of the findings. LIMITATIONS, REASONS FOR CAUTION: Human oocytes and OF were of limited access, compared with oocytes from species collected in slaughterhouses. OFs from mouse, rat and hamster were not tested due to the small size of the genital tract in these species and the small volume of fluid available. WIDER IMPLICATIONS OF THE FINDINGS: Since oviductal modification of ZP resistance to proteolytic digestion has been demonstrated to influence fertilization and this pre-fertilization mechanism is considered to contribute to the control of polyspermy, the apparent absence of this mechanism in humans suggests that the regulation of polyspermy depends mainly on other mechanisms, most probably of cortical granule origin. Investigation into a possible relationship between the lack of oviductal ZP hardening in human oocytes and the existence of tubal ectopic pregnancies in this species is proposed. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the Spanish Ministry of Science and Innovation and FEDER, Grant AGL2009-12512-C02-01-02. The authors declare no competing interest.

Viscoelastic Properties of Zona Pellucida of Oocytes Characterized by Transient Electrical Impedance Spectroscopy.

The success rate in vitro fertilization is significantly linked to the quality of the oocytes. The oocyte's membrane is encapsulated by a shell of gelatinous extracellular matrix, called zona pellucida, which undergoes dynamic changes throughout the reproduction cycle. During the window of highest fertility, the zona pellucida exhibits a softening phase, while it remains rigid during oocyte maturation and again after fertilization. These variations in mechanical properties facilitate or inhibit sperm penetration. Since successful fertilization considerably depends on the state of the zona pellucida, monitoring of the hardening process of the zona pellucida is vital. In this study, we scrutinized two distinct genetic mouse models, namely, fetuin-B wild-type and fetuin-B/ovastacin double deficient with normal and super-soft zona pellucida, respectively. We evaluated the hardening with the help of a microfluidic aspiration-assisted electrical impedance spectroscopy system. An oocyte was trapped by a microhole connected to a microfluidic channel by applying suction pressure. Transient electrical impedance spectra were taken by microelectrodes surrounding the microhole. The time-depending recovery of zona pellucida deflections to equilibrium was used to calculate the Young's modulus and, for the first time, absolute viscosity values. The values were obtained by fitting the curves with an equivalent mechanical circuit consisting of a network of dashpots and springs. The observer-independent electrical readout in combination with a fitting algorithm for the calculation of the viscoelastic properties demonstrates a step toward a more user-friendly and easy-to-use tool for the characterizing and better understanding of the rheological properties of oocytes.

A ZP1 gene mutation in a patient with empty follicle syndrome: A case report and literature review.

Genuine empty follicle syndrome (gEFS) is a rare cause of female infertility; it is defined as the presence of cumulus-oocyte complexes (COCs) in follicular fluid but the absence of oocytes after denudation in an in vitro fertilization (IVF) programme. Mutations in one of the four genes encoding zona pellucida (ZP) proteins have been implicated in gEFS. The objectives of the present study were to explore the molecular basis of idiopathic infertility in a 35-year-old woman with gEFS (observed after four ovarian retrievals), compare her phenotype and genotype with those of other patients described in the literature, and discuss therapeutic approaches that could be adopted by reproductive health centres in this situation. Sequencing of the ZP genes revealed a new homozygous missense variant in ZP1: c.1097G > A;p.(Arg366Gln). The variant is located in the ZP-N domain, which is essential for ZP protein polymerization. An immunohistochemical assessment of an ovarian biopsy confirmed the absence of ZP1 protein. The novel variant appears to prevent ZP assembly, which would explain the absence of normal oocytes after denudation in our patient (and despite the retrieval of COCs). ZP gene sequencing should be considered for patients with a phenotype suggestive of gEFS. An etiological genetic diagnosis enables appropriate genetic counselling and a switch to an IVF programme (with a suitable denudation technique) or an oocyte donation programme.

The molecular basis of sex: linking yeast to human.

Species-specific recognition between egg and sperm, a crucial event that marks the beginning of fertilization in multicellular organisms, mirrors the binding between haploid cells of opposite mating type in unicellular eukaryotes such as yeast. However, as implied by the lack of sequence similarity between sperm-binding regions of invertebrate and vertebrate egg coat proteins, these interactions are thought to rely on completely different molecular entities. Here, we argue that these recognition systems are, in fact, related: despite being separated by 0.6-1 billion years of evolution, functionally essential domains of a mollusc sperm receptor and a yeast mating protein adopt the same 3D fold as egg zona pellucida proteins mediating the binding between gametes in humans.

Efficient biofunctionalization of polysilicon barcodes for adhesion to the zona pellucida of mouse embryos.

Cell tracking is an emergent area in nanobiotechnology, promising the study of individual cells or the identification of populations of cultured cells. In our approach, microtools designed for extracellular tagging are prepared, because using biofunctionalized polysilicon barcodes to tag cell membranes externally avoids the inconveniences of cell internalization. The crucial covalent biofunctionalization process determining the ultimate functionality was studied in order to find the optimum conditions to link a biomolecule to a polysilicon barcode surface using a self-assembled monolayer (SAM) as the connector. Specifically, a lectin (wheat germ agglutinin, WGA) was used because of its capacity to recognize some specific carbohydrates present on the surface of most mammalian cells. Self-assembled monolayers were prepared on polysilicon surfaces including aldehyde groups as terminal functions to study the suitability of their covalent chemical bonding to WGA. Some parameters, such as the polysilicon surface roughness or the concentration of WGA, proved to be crucial for successful biofunctionalization and bioactivity. The SAMs were characterized by contact angle measurements, time-of-flight secondary ion mass spectrometry (TOF-SIMS), laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS), and atomic force microscopy (AFM). The biofunctionalization step was also characterized by fluorescence microscopy and, in the case of barcodes, by adhesion experiments to the zona pellucida of mouse embryos. These experiments showed high barcode retention rates after 96 h of culture as well as high embryo viability to the blastocyst stage, indicating the robustness of the biofunctionalization and, therefore, the potential of these new microtools to be used for cell tagging.