Novel mutations in ZP1, ZP2, and ZP3 cause female infertility due to abnormal zona pellucida formation

Cellular mechanisms of monozygotic twinning: clues from assisted reproduction

BACKGROUND

Monozygotic (MZ) twins are believed to arise from the fission of a single fertilized embryo at different stages. Monochorionic MZ twins, who share one chorion, originate from the splitting of the inner cell mass (ICM) within a single blastocyst. In the classic model for dichorionic MZ twins, the embryo splits before compaction, developing into two blastocysts. However, there are a growing number of ART cases where a single blastocyst transfer results in dichorionic MZ twins, indicating that embryo splitting may occur even after blastocyst formation.

OBJECTIVE AND RATIONALE

For monochorionic MZ twins, we conducted a comprehensive analysis of the cellular mechanisms involved in ICM splitting, drawing from both ART cases and animal experiments. In addition, we critically re-examine the classic early splitting model for dichorionic MZ twins. We explore cellular mechanisms leading to two separated blastocysts in ART, potentially causing dichorionic MZ twins.

SEARCH METHODS

Relevant studies including research articles, reviews, and conference papers were searched in the PubMed database. Cases of MZ twins from IVF clinics were found by using combinations of terms including 'monozygotic twins' with 'IVF case report', 'ART', 'single embryo transfer', or 'dichorionic'. The papers retrieved were categorized based on the implicated mechanisms or as those with unexplained mechanisms. Animal experiments relating to MZ twins were found using 'mouse embryo monozygotic twins', 'mouse 8-shaped hatching', 'zebrafish janus mutant', and 'nine-banded armadillo embryo', along with literature collected through day-to-day reading. The search was limited to articles in English, with no restrictions on publication date or species.

OUTCOMES

For monochorionic MZ twins, ART cases and mouse experiments demonstrate evidence that a looser ICM in blastocysts has an increased chance of ICM separation. Physical forces facilitated by blastocoel formation or 8-shaped hatching are exerted on the ICM, resulting in monochorionic MZ twins. For dichorionic MZ twins, the classic model resembles artificial cloning of mouse embryos in vitro, requiring strictly controlled splitting forces, re-joining prevention, and proper aggregation, which allows the formation of two separate human blastocysts under physiological circumstances. In contrast, ART procedures involving the transfer of a single blastocysts after atypical hatching or vitrified-warmed cycles might lead to blastocyst separation. Differences in morphology, molecular mechanisms, and timing across various animal model systems for MZ twinning can impede this research field. As discussed in future directions, recent developments of innovative in vitro models of human embryos may offer promising avenues for providing fundamental novel insights into the cellular mechanisms of MZ twinning during human embryogenesis.

WIDER IMPLICATIONS

Twin pregnancies pose high risks to both the fetuses and the mother. While single embryo transfer is commonly employed to prevent dizygotic twin pregnancies in ART, it cannot prevent the occurrence of MZ twins. Drawing from our understanding of the cellular mechanisms underlying monochorionic and dichorionic MZ twinning, along with insights into the genetic mechanisms, could enable improved prediction, prevention, and even intervention strategies during ART procedures.

REGISTRAITON NUMBER

N/A.

Novel Loss-of-function Variants of ZP3 Associated with Premature Ovarian Insufficiency

Premature ovarian insufficiency (POI) is one of the leading causes of female infertility. To date, the genetic etiology of POI has been elucidated in approximately 20-25% of the total cases. The human zona pellucida (ZP) plays an important role in the organization and differentiation of granulosa cells, follicle formation, and sperm recognition. Mutations in ZP1, ZP2, and ZP3 have been reported to cause female infertility due to oocyte degeneration, empty follicle, or in vitro fertilization failure. In this study, we identified three novel missense mutations in ZP3 (NM_001110354.2): c.643G > A (p.Asp215Asn), c.215 C > T (p.Thr72Ile), and c.152T > C (p.Leu51Pro) in three sporadic Han Chinese POI patients through whole-exome sequencing. These variants are absent from population databases and were predicted to be deleterious by multiple in silico tools. Structure prediction analysis showed that the affected amino acid altered the ZP3 protein structure. Western blot further confirmed that these ZP3 variants reduced the expression and secretion of ZP components. In summary, this study reports three novel deleterious variants in ZP3 associated with POI, thereby broadening the mutation spectrum of ZP3 in POI patients.

A Compound Heterozygous Pathogenic Variant in ZP2 Gene Causes Female Infertility

The oocyte maturation defect 6 is an autosomal recessive hereditary disease caused by a homozygous variant in ZP2 gene. It is characterized by female primary infertility due to an abnormally thin zona pellucida (ZP) and defective sperm binding. Here we identified a compound heterozygous variant (c.1924C > T and c.1695-2A > G) in ZP2 gene in a Chinese Han family. Quantitative real-time PCR showed that the variant c.1924C > T significantly decreased the expression of truncated ZP2 message RNA by the nonsense-mediated decay pathway. Minigene assays showed the c.1695-2A > G variant led to an extra-61-nt preservation of intron 15 at the junction between exons 15 and 16 during transcription. Both variants (c.1924C > T and c.1695-2A > G) resulted in truncated ZP2 proteins (p.R642X and p.C566Hfs*2) that lost the transmembrane domain, which prevented the secretion of the mutant ZP2 proteins and produced a structurally abnormal ZP, thus resulting in female infertility. This study further elucidated the pathogenic mechanism of these two variants and provided new support for the genetic diagnosis of female infertility.

A Novel Homozygous Missense ZP1 Variant Result in Human Female Empty Follicle Syndrome

Empty follicle syndrome (EFS) is a disorder characterised by the unsuccessful retrieval of oocytes from matured follicles following ovarian stimulation for in vitro fertilisation (IVF). Genetic factors significantly contribute to this pathology. To date, an increasing number of genetic mutations associated with GEFS have been documented, however, some cases still remain unexplained by these previously reported mutations. Here, we identified a novel homozygous missense ZP1 variant (c.1096 C > T, p.Arg366Trp) in a female patient with GEFS from a consanguineous family who failed to retrieve any oocytes during two cycles of IVF treatment. We conducted a molecular dynamics simulation analysis on the mutant ZP1 model, revealing that the mutant ZP1 protein has an altered 3D structure, lower fluctuation, higher compactness and higher instability than wild-type ZP1. Immunostaining, immunoblotting and co-immunoprecipitation results showed that the homozygous missense mutation in ZP1 impaired protein secretion and weakened interactions between ZP1 and other ZP proteins, which may affect the ZP assembly. This study contributes to a more comprehensive understanding of the genetic aetiopathogenesis of GEFS.

Advances in the genetic etiology of female infertility

Human reproduction is a complex process involving gamete maturation, fertilization, embryo cleavage and development, blastocyst formation, implantation, and live birth. If any of these processes are abnormal or arrest, reproductive failure will occur. Infertility is a state of reproductive dysfunction caused by various factors. Advances in molecular genetics, including cell and molecular genetics, and high-throughput sequencing technologies, have found that genetic factors are important causes of infertility. Genetic variants have been identified in infertile women or men and can cause gamete maturation arrest, poor quality gametes, fertilization failure, and embryonic developmental arrest during assisted reproduction technology (ART), and thus reduce the clinical success rates of ART. This article reviews clinical studies on repeated in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) failures caused by ovarian dysfunction, oocyte maturation defects, oocyte abnormalities, fertilization disorders, and preimplantation embryonic development arrest due to female genetic etiology, the accumulation of pathogenic genes and gene pathogenic loci, and the functional mechanism and clinical significance of pathogenic genes in gametogenesis and early embryonic development.

Single-cell RNA sequencing of human oocytes reveals a differential transcriptomic profile associated with agar-like zona pellucida

BACKGROUND

Agar-like zona pellucida (ZP) is the most common type of abnormal ZP, and is one of the causes of low fertility or infertility. However, the molecular mechanism of agar-like ZP is unclear. Single-cell RNA-sequencing (scRNA-seq) analysis was used to assess the cellular and molecular landscape of oocytes with agar-like ZP.

METHODS

Human metaphase I (MI) oocytes were collected from four patients with agar-like ZP and four healthy donors. Total RNA was isolated, cDNA was synthesized, and libraries were generated and subsequently sequenced on a HiSeq 2500 instrument. The scRNA-seq data were analyzed with R software.

RESULTS

We identified 1320 genes that were differentially expressed between agar-like ZP oocytes and healthy donor oocytes. Gene Ontology term enrichment results showed that the genes downregulated in agar-like ZP oocytes were significantly related to extracellular matrix organization, while the genes upregulated in agar-like ZP oocytes were significantly related to the regulation of response to DNA damage stimulus. The Kyoto Encyclopedia of Genes and Genomes enrichment results showed that genes were enriched in the ECM-receptor interaction pathway and focal adhesion pathway. Other signaling pathways important in oocyte development were also enriched, such as PI3K-Akt. Differential expression analysis identified UBC, TLR4, RELA, ANXA5, CAV1, KPNA2, CCNA2, ACTA2, FYN and ITGB3 as genetic markers of oocytes with agar-like ZP.

CONCLUSIONS

Our findings suggest that agar-like ZP oocytes exhibit significant downregulation of genes involved in the ECM-receptor interaction signaling pathway and focal adhesion pathway, which could lead to aberrant ZP formation, while the upregulated genes were significantly related to regulation of the response to DNA damage stimulus. Agar-like ZP formation may interfere with the normal exchange of signals between oocytes and perivitelline granulosa cells, thereby preventing cumulus cells from participating in oocyte DNA damage repair and causing MI arrest.

ZP1-Y262C mutation causes abnormal zona pellucida formation and female infertility in humans

Defective oocyte maturation is a common cause of female infertility. The loss of the zona pellucida (ZP) represents a specific condition of impaired oocyte maturation. The extracellular matrix known as the ZP envelops mammalian oocytes and preimplantation embryos, exerting significant influence on oogenesis, fertilization, and embryo implantation. However, the genetic factors leading to the loss of the ZP in oocytes are not well understood. This study focused on patients who underwent oocyte retrieval surgery after ovarian stimulation and were found to have abnormal oocyte maturation without the presence of the ZP. Ultrasonography was performed during the surgical procedure to evaluate follicle development. Peripheral blood samples from the patient were subjected to exome sequencing. Here, a novel, previously unreported heterozygous mutation in the ZP1 gene was identified. Within the ZP1 gene, we discovered a novel heterozygous mutation (ZP1 NM_207341.4:c.785A>G (p.Y262C)), specifically located in the trefoil domain. Bioinformatics comparisons further revealed conservation of the ZP1-Y262C mutation across different species. Model predictions of amino acid mutations on protein structure and cell immunofluorescence/western blot experiments collectively confirmed the detrimental effects of the ZP1-Y262C mutation on the function and expression of the ZP1 protein. The ZP1-Y262C mutation represents the novel mutation in the trefoil domain of the ZP1 protein, which is associated with defective oocyte maturation in humans. Our report enhances comprehension regarding the involvement of ZP-associated genes in female infertility and offers enriched understanding for the genetic diagnosis of this condition.

Germline Exome Sequencing for Men with Testicular Germ Cell Tumor Reveals Coding Defects in Chromosomal Segregation and Protein-targeting Genes

BACKGROUND

Testicular germ cell tumor (TGCT) is the most common cancer among young White men. TGCT is highly heritable, although there are no known high-penetrance predisposition genes. CHEK2 is associated with moderate TGCT risk.

OBJECTIVE

To identify coding genomic variants associated with predisposition to TGCT.

DESIGN, SETTING, AND PARTICIPANTS

The study involved 293 men with familial or bilateral (high risk; HR)-TGCT representing 228 unique families and 3157 cancer-free controls.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

We carried out exome sequencing and gene burden analysis to identify associations with TGCT risk.

RESULTS AND LIMITATIONS

Gene burden association identified several genes, including loss-of-function variants of NIN and QRSL1. We identified no statistically significant association with the sex- and germ-cell development pathways (hypergeometric overlap test: p = 0.65 for truncating variants, p = 0.47 for all variants) or evidence of associations with the regions previously identified via genome-wide association studies (GWAS). When considering all significant coding variants together with genes associated with TGCT on GWAS, there were associations with three major pathways: mitosis/cell cycle (Gene Ontology identity GO:1903047: observed/expected variant ratio [O/E] 6.17, false discovery rate [FDR] 1.53 × 10-11), co-translational protein targeting (GO:0006613: O/E 18.62, FDR 1.35 × 10-10), and sex differentiation (GO:0007548: O/E 5.25, FDR 1.90 × 10-4).

CONCLUSIONS

To the best of our knowledge, this study is the largest to date on men with HR-TGCT. As in previous studies, we identified associations with variants for several genes, suggesting multigenic heritability. We identified associations with co-translational protein targeting, and chromosomal segregation and sex determination, identified via GWAS. Our results suggest potentially druggable targets for TGCT prevention or treatment.

PATIENT SUMMARY

We searched for gene variations that increase the risk of testicular cancer and found numerous new specific variants that contribute to this risk. Our results support the idea that many gene variants inherited together contribute to the risk of testicular cancer.

Embryological characteristics and clinical outcomes of oocytes with different degrees of abnormal zona pellucida during assisted reproductive treatment

Abnormalities in the zona pellucida (ZP) adversely affect oocyte maturation, embryo development and pregnancy outcomes. However, the assessment of severity is challenging. To evaluate the effects of different degrees of ZP abnormalities on embryo development and clinical outcomes, in total, 590 retrieval cycles were scored and divided into four categories (control, mild, moderate and severe) based on three parameters: perivitelline space, percentage of immature oocytes and percentage of oocytes with abnormal morphology. As the severity of abnormal ZP increased, both the number of retrieved oocytes and mature oocytes decreased. The fertilization rate did not differ significantly among groups. The rates of embryo cleavage and day-3 high-quality embryos in the mild group and the moderate group did not vary significantly between the two groups but were significantly higher than those in the severe group. The blastulation rates of the abnormal ZP groups were similar; however, they were lower than those of the control group. Moreover, the cycle cancellation rate of the severe abnormal ZP group was as high as 66.20%, which was significantly higher than that of the other three groups. Although the rates of cumulative clinical pregnancy and live births were lower than those in the control group, they were comparable among the abnormal ZP groups. There were no differences in the neonatal outcomes of the different groups. Together, ZP abnormalities show various degrees of severity, and in all patients regardless of the degree of ZP abnormalities who achieve available embryos, there will be an opportunity to eventually give birth.

Genetic mechanisms of fertilization failure and early embryonic arrest: a comprehensive review

BACKGROUND

Infertility and pregnancy loss are longstanding problems. Successful fertilization and high-quality embryos are prerequisites for an ongoing pregnancy. Studies have proven that every stage in the human reproductive process is regulated by multiple genes and any problem, at any step, may lead to fertilization failure (FF) or early embryonic arrest (EEA). Doctors can diagnose the pathogenic factors involved in FF and EEA by using genetic methods. With the progress in the development of new genetic technologies, such as single-cell RNA analysis and whole-exome sequencing, a new approach has opened up for us to directly study human germ cells and reproductive development. These findings will help us to identify the unique mechanism(s) that leads to FF and EEA in order to find potential treatments.

OBJECTIVE AND RATIONALE

The goal of this review is to compile current genetic knowledge related to FF and EEA, clarifying the mechanisms involved and providing clues for clinical diagnosis and treatment.

SEARCH METHODS

PubMed was used to search for relevant research articles and reviews, primarily focusing on English-language publications from January 1978 to June 2023. The search terms included fertilization failure, early embryonic arrest, genetic, epigenetic, whole-exome sequencing, DNA methylation, chromosome, non-coding RNA, and other related keywords. Additional studies were identified by searching reference lists. This review primarily focuses on research conducted in humans. However, it also incorporates relevant data from animal models when applicable. The results were presented descriptively, and individual study quality was not assessed.

OUTCOMES

A total of 233 relevant articles were included in the final review, from 3925 records identified initially. The review provides an overview of genetic factors and mechanisms involved in the human reproductive process. The genetic mutations and other genetic mechanisms of FF and EEA were systematically reviewed, for example, globozoospermia, oocyte activation failure, maternal effect gene mutations, zygotic genome activation abnormalities, chromosome abnormalities, and epigenetic abnormalities. Additionally, the review summarizes progress in treatments for different gene defects, offering new insights for clinical diagnosis and treatment.

WIDER IMPLICATIONS

The information provided in this review will facilitate the development of more accurate molecular screening tools for diagnosing infertility using genetic markers and networks in human reproductive development. The findings will also help guide clinical practice by identifying appropriate interventions based on specific gene mutations. For example, when an individual has obvious gene mutations related to FF, ICSI is recommended instead of IVF. However, in the case of genetic defects such as phospholipase C zeta1 (PLCZ1), actin-like7A (ACTL7A), actin-like 9 (ACTL9), and IQ motif-containing N (IQCN), ICSI may also fail to fertilize. We can consider artificial oocyte activation technology with ICSI to improve fertilization rate and reduce monetary and time costs. In the future, fertility is expected to be improved or restored by interfering with or supplementing the relevant genes.

A tumor cell specific Zona Pellucida glycoprotein 3 RNA transcript encodes an intracellular cancer antigen

Background

Expression of Zona Pellucida glycoprotein 3 (ZP3) in healthy tissue is restricted to the extracellular Zona Pellucida layer surrounding oocytes of ovarian follicles and to specific cells of the spermatogenic lineage. Ectopic expression of ZP3 has been observed in various types of cancer, rendering it a possible therapeutic target.

Methods

To support its validity as therapeutic target, we extended the cancer related data by investigating ZP3 expression using immunohistochemistry (IHC) of tumor biopsies. We performed a ZP3 transcript specific analysis of publicly available RNA-sequencing (RNA-seq) data of cancer cell lines (CCLs) and tumor and normal tissues, and validated expression data by independent computational analysis and real-time quantitative PCR (qPCR). A correlation between the ZP3 expression level and pathological and clinical parameters was also investigated.

Results

IHC data for several cancer types showed abundant ZP3 protein staining, which was confined to the cytoplasm, contradicting the extracellular protein localization in oocytes. We noticed that an alternative ZP3 RNA transcript, which we term 'ZP3-Cancer', was annotated in gene databases that lacks the genetic information encoding the N-terminal signal peptide that governs entry into the secretory pathway. This explains the intracellular localization of ZP3 in tumor cells. Analysis of publicly available RNA-seq data of 1339 cancer cell lines (CCLs), 10386 tumor tissues (The Cancer Genome Atlas) and 7481 healthy tissues (Genotype-Tissue Expression) indicated that ZP3-Cancer is the dominant ZP3 RNA transcript in tumor cells and is highly enriched in many cancer types, particularly in rectal, ovarian, colorectal, prostate, lung and breast cancer. Expression of ZP3-Cancer in tumor cells was confirmed by qPCR. Higher levels of the ZP3-Cancer transcript were associated with more aggressive tumors and worse survival of patients with various types of cancer.

Conclusion

The cancer-restricted expression of ZP3-Cancer renders it an attractive tumor antigen for the development of a therapeutic cancer vaccine, particularly using mRNA expression technologies.

A heterozygous ZP2 mutation causes zona pellucida defects and female infertility in mouse and human

The zona pellucida (ZP) is an extracellular glycoprotein matrix surrounding mammalian oocytes. Recently, numerous mutations in genes encoding ZP proteins have been shown to be possibly related to oocyte abnormality and female infertility; few reports have confirmed the functions of these mutations in living animal models. Here, we identified a novel heterozygous missense mutation (NM_001376231.1:c.1616C>T, p.Thr539Met) in ZP2 from a primary infertile female. We showed that the mutation reduced ZP2 expression and impeded ZP2 secretion in cell lines. Furthermore, we constructed the mouse model with the mutation (Zp2T541M) using CRISPR-Cas9. Zp2WT/T541M female mice had normal fertility though generated oocytes with the thin ZP, whereas Zp2T541M female mice were completely infertile due to degeneration of oocytes without ZP. Additionally, ZP deletion impaired folliculogenesis and caused female infertility in Zp2T541M mice. Our study not only expands the spectrum of ZP2 mutation sites but also, more importantly, increases the understanding of pathogenic mechanisms of ZP2 mutations.

Case report: A novel homozygous variant in ZP3 is associated with human empty follicle syndrome

Empty follicle syndrome (EFS) is a rare condition in female infertility. It is characterized by the inability to retrieve oocytes from visibly large, normally developing follicles in the ovaries, despite ovarian stimulation. The genetic factors contributing to this syndrome remain unclear. This study focused on patients who underwent three consecutive ovarian stimulation procedures for oocyte retrieval but experienced unsuccessful outcomes, despite the presence of observable large follicles. Ultrasound examinations were conducted to assess follicular development during each procedure. In order to investigate potential genetic causes, we performed whole exome sequencing on peripheral blood samples from the patient. Interestingly, we identified that this patient carries a homozygous mutation in the ZP3 genes. Within the ZP3 gene, we identified a homozygous variant [NM_001110354.2, c.176T>A (p.L59H)] specifically located in the zona pellucida (ZP) domain. Further analysis, including bioinformatics methods and protein structure modeling, was carried out to investigate the conservation of the ZP3L59H variant across different species. This homozygous variant exhibited a high degree of conservation across various species. Importantly, the homozygous ZP3L59H variant was associated with the occurrence of empty follicle syndrome in affected female patients. The homozygous ZP3L59H variant represents a newly discovered genetic locus implicated in the development of human empty follicle syndrome. Our findings contribute to a deeper understanding of the role of zona pellucida-related genes in infertility and provide valuable insights for the genetic diagnosis of female infertility.

Ovastacin: An oolemma protein that cleaves the zona pellucida to prevent polyspermy

Monospermy occurs in the process of normal fertilization where a single sperm fuses with the egg, resulting in the formation of a diploid zygote. During the process of fertilization, the sperm must penetrate the zona pellucida (ZP), the outer layer of the egg, to reach the egg's plasma membrane. Once a sperm binds to the ZP, it undergoes an acrosomal reaction, which involves the release of enzymes from the sperm's acrosome that help it to penetrate the ZP. Ovastacin is one of the enzymes that is involved in breaking down the ZP. Studies have shown that ovastacin is necessary for the breakdown of the ZP and for successful fertilization to occur. However, the activity of ovastacin is tightly regulated to ensure that only one sperm can fertilize the egg. One way in which ovastacin helps to prevent polyspermy (the fertilization of an egg by more than one sperm) is by rapidly degrading the ZP after a sperm has penetrated it. This makes it difficult for additional sperm to penetrate the ZP and fertilize the egg. Ovastacin is also thought to play a role in the block to polyspermy, a mechanism that prevents additional sperm from fusing with the egg's plasma membrane after fertilization has occurred. In summary, the role of ovastacin in monospermic fertilization is to help ensure that only one sperm can fertilize the egg, while preventing polyspermy and ensuring successful fertilization.

A cryptic microdeletion del(12)(p11.21p11.23) within an unbalanced translocation t(7;12)(q21.13;q23.1) implicates new candidate loci for intellectual disability and Kallmann syndrome

In a patient diagnosed with both Kallmann syndrome (KS) and intellectual disability (ID), who carried an apparently balanced translocation t(7;12)(q22;q24)dn, array comparative genomic hybridization (aCGH) disclosed a cryptic heterozygous 4.7 Mb deletion del(12)(p11.21p11.23), unrelated to the translocation breakpoint. This novel discovery prompted us to consider the possibility that the combination of KS and neurological disorder in this patient could be attributed to gene(s) within this specific deletion at 12p11.21-12p11.23, rather than disrupted or dysregulated genes at the translocation breakpoints. To further support this hypothesis, we expanded our study by screening five candidate genes at both breakpoints of the chromosomal translocation in a cohort of 48 KS patients. However, no mutations were found, thus reinforcing our supposition. In order to delve deeper into the characterization of the 12p11.21-12p11.23 region, we enlisted six additional patients with small copy number variations (CNVs) and analyzed eight individuals carrying small CNVs in this region from the DECIPHER database. Our investigation utilized a combination of complementary approaches. Firstly, we conducted a comprehensive phenotypic-genotypic comparison of reported CNV cases. Additionally, we reviewed knockout animal models that exhibit phenotypic similarities to human conditions. Moreover, we analyzed reported variants in candidate genes and explored their association with corresponding phenotypes. Lastly, we examined the interacting genes associated with these phenotypes to gain further insights. As a result, we identified a dozen candidate genes: TSPAN11 as a potential KS candidate gene, TM7SF3, STK38L, ARNTL2, ERGIC2, TMTC1, DENND5B, and ETFBKMT as candidate genes for the neurodevelopmental disorder, and INTS13, REP15, PPFIBP1, and FAR2 as candidate genes for KS with ID. Notably, the high-level expression pattern of these genes in relevant human tissues further supported their candidacy. Based on our findings, we propose that dosage alterations of these candidate genes may contribute to sexual and/or cognitive impairments observed in patients with KS and/or ID. However, the confirmation of their causal roles necessitates further identification of point mutations in these candidate genes through next-generation sequencing.

Advances in the study of genetic factors and clinical interventions for fertilization failure

Fertilization failure refers to the failure in the pronucleus formation, evaluating 16-18 h post in vitro fertilization or intracytoplasmic sperm injection. It can be caused by sperm, oocytes, and sperm-oocyte interaction and lead to great financial and physical stress to the patients. Recent advancements in genetics, molecular biology, and clinical-assisted reproductive technology have greatly enhanced research into the causes and treatment of fertilization failure. Here, we review the causes that have been reported to lead to fertilization failure in fertilization processes, including the sperm acrosome reaction, penetration of the cumulus and zona pellucida, recognition and fusion of the sperm and oocyte membranes, oocyte activation, and pronucleus formation. Additionally, we summarize the progress of corresponding treatment methods of fertilization failure. This review will provide the latest research advances in the genetic aspects of fertilization failure and will benefit both researchers and clinical practitioners in reproduction and genetics.

Risk factors for low oocyte retrieval in patients with polycystic ovarian syndrome undergoing in vitro fertilization

BACKGROUND

The number of oocytes retrieved does not always coincide with the number of follicles aspirated in in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) treatment. Patients with high expectation of retrieval sometimes obtain few oocytes, which may be induced by improper operation or therapeutic factors. The purpose of this study was to evaluate the distribution data of oocyte retrieval rate (ORR) and to explore the risk factors for low ORR in patients with polycystic ovary syndrome (PCOS) undergoing IVF/ICSI.

METHODS

A total of 2478 patients with PCOS undergoing IVF/ICSI were involved in this retrospective case-control study from March 2016 to October 2021. The oocyte retrieval rate was calculated as the ratio of the number of obtained oocytes to the number of follicles (≥ 12 mm) on the trigger day. Patients were divided into a low ORR and a normal ORR group with the boundary of one standard deviation from the mean value of ORR. The patient characteristics, treatment protocols, serum hormone levels, and embryonic and pregnancy outcomes were analyzed.

RESULTS

The ORR exhibited a non-normal distribution, with a median of 0.818. The incidence of complete empty follicle syndrome was 0.12% (3/2478). The proportion of patients in the low ORR group who received the progestin-primed protocol was significantly higher than that in the normal ORR group (30.30% vs. 17.69%). A logistic regression analysis showed that the serum estradiol level/follicle (≥ 12 mm) ratio (OR: 0.600 (0.545-0.661)) and progesterone level (OR: 0.783 (0.720-0.853)) on the trigger day were significant factors in the development of a low ORR, with optimal cutoff values of 172.85 pg/ml and 0.83 ng/ml, respectively, as determined by receiver operating curve. Fewer high-quality embryos (2 vs. 5) and more cycles with no available embryos (5.42% vs. 0.43%) were found in the low ORR group.

CONCLUSIONS

For patients with PCOS, low estradiol levels/follicles (≥ 12 mm) and progesterone levels on the trigger day and the use of the progestin-primed protocol could be risk factors for low ORR, which leads to a limited number of embryos and more cycle cancellations.

Zona pellucida family genes in Chinese pond turtle: identification, expression profiles, and role in the spermatozoa acrosome reaction†

The zona pellucida (ZP) is an extracellular matrix that surrounds all vertebrate eggs, and it is involved in fertilization and species-specific recognition. Numerous in-depth studies of the ZP proteins of mammals, birds, amphibians, and fishes have been conducted, but systematic investigation of the ZP family genes and their role during fertilization in reptiles has not been reported to date. In this study, we identified six turtle ZP (Tu-ZP) gene subfamilies (Tu-ZP1, Tu-ZP2, Tu-ZP3, Tu-ZP4, Tu-ZPD, and Tu-ZPAX) based on whole genome sequence data from Mauremys reevesii. We found that Tu-ZP4 had large segmental duplication and was distributed on three chromosomes, and we also detected gene duplication in the other Tu-ZP genes. To evaluate the role of Tu-ZP proteins in sperm-egg binding, we assessed the expression pattern of these Tu-ZP proteins and their ability to induce the spermatozoa acrosome reaction in M. reevesii. In conclusion, this is the first report of the existence of gene duplication of Tu-ZP genes and that Tu-ZP2, Tu-ZP3, and Tu-ZPD can induce acrosome exocytosis of spermatogenesis in the reptile.

Inhibition of the NF-κB signaling pathway affects gonadal differentiation and leads to male bias in Paramisgurnus dabryanus

In recent years, sex-controlled breeding has emerged as an effective strategy to enhance the yields of economic animals with different growth characteristics, while increasing the economic benefits of aquaculture. It is known that the NF-κB pathway participates in gonadal differentiation and reproduction. Therefore, we used the large-scale loach as a research model for the present study and selected an effective inhibitor of the NF-κB signaling pathway (QNZ). This, to investigates the impacts of the NF-κB signaling pathway on gonadal differentiation during a critical period of gonad development and after maturation. Simultaneously, the sex ratio bias and the reproductive capacities of adult fish were analyzed. Our results indicated that the inhibition of the NF-κB signaling pathway influenced the expression of genes related to gonad development, regulated the gene expression related to the brain-gonad-liver axis of juvenile loaches, and finally impacted the gonadal differentiation of the large-scale loach and promoted a male-biased sex ratio. Meanwhile, high QNZ concentrations affected the reproductive abilities of adult loaches and inhibited the growth performance of offspring. Thus, our results deepened the exploration of sex control in fish and provided a certain research basis for the sustainable development of the aquaculture industry.

Identification of zona pellucida defects revealed a novel loss-of-function mutation in ZP2 in humans and rats

Introduction

Human zona pellucida (ZP) plays an important role in reproductive process. Several rare mutations in the encoding genes (ZP1, ZP2, and ZP3) have been demonstrated to cause women infertility. Mutations in ZP2 have been reported to cause ZP defects or empty follicle syndrome. We aimed to identify pathogenic variants in an infertile woman with a thin zona pellucida (ZP) phenotype and investigated the effect of ZP defects on oocyte gene transcription.

Methods

We performed whole-exome sequencing and Sanger sequencing of genes were performed for infertilite patients characterized by fertilization failure in routine in vitro fertilization (IVF). Immunofluorescence (IF) and intracytoplasmic sperm injection (ICSI) were used in the mutant oocytes. Single-cell RNA sequencing was used to investigate transcriptomes of the gene-edited (Zp2mut/mut) rat model. Biological function enrichment analysis, quantitative real-time PCR (qRT-PCR), and IF were performed.

Results

We identified a novel homozygous nonsense mutation of ZP2 (c.1924C > T, p.Arg642X) in a patient with non-consanguineous married parents. All oocytes showed a thin or no ZP under a light microscope and were fertilized after ICSI. The patient successfully conceived by receiving the only two embryos that developed to the blastocyst stage. The immunofluorescence staining showed an apparently abnormal form of the stopped oocytes. We further demonstrated a total of 374 differentially expressed genes (DEGs) in the transcriptome profiles of Zp2mut/mut rats oocytes and highlighted the signal communication between oocytes and granulosa cells. The pathway enrichment results of DEGs showed that they were enriched in multiple signaling pathways, especially the transforming growth factor-β (TGF-β) signaling pathway in oocyte development. qRT-PCR, IF, and phosphorylation analysis showed significantly downregulated expressions of Acvr2b, Smad2, p38MAPK, and Bcl2 and increased cleaved-caspase 3 protein expression.

Discussion

Our findings expanded the known mutational spectrum of ZP2 associated with thin ZP and natural fertilization failure. Disruption of the integrity of the ZP impaired the TGF-β signaling pathway between oocytes and surrounding granulosa cells, leading to increased apoptosis and decreased developmental potential of oocytes.

A novel compound heterozygous mutation in TUBB8 causing early embryonic developmental arrest

PURPOSE

Mutations in the β-tubulin isotype, TUBB8, can cause female infertility. Although several mutations of TUBB8 have been reported, the full spectrum for guiding genetics counseling still needs to be further explored. Here, we sought to identify novel variants in TUBB8 and their phenotypic effects on microtubule network structure in vitro.

METHODS

Whole-exome sequence analysis was performed in two families with infertility to detect pathogenic variants, with validation by Sanger sequencing. All gene variants and protein structures were predicted in silico. Cells were transfected with wild-type and mutants, and immunofluorescence analysis was performed to visualize microtubule network changes.

RESULTS

We detected a novel compound heterozygous mutation, c.915_916delCC (p.Arg306Serfs*21) and c.82C > T (p.His28Tyr), and a benign heterozygous variant c.1286C > T (p.Thr429Met) in TUBB8 in the two families. Female patients with p.Arg306Serfs*21 and p.His28Tyr were infertile with early embryonic developmental arrest. The female patient with p.Thr429Met gave birth to a healthy baby in the second in vitro fertilization frozen embryo transfer cycle. The p.Arg306Serfs*21 mutation was predicted to cause large structural alteration in the TUBB8 protein and was confirmed to produce a truncated and trace protein by western blot analysis. Immunofluorescence analysis of transfected HeLa cells showed that p.Arg306Serfs*21 significantly disrupted microtubule structure.

CONCLUSIONS

Our findings expand the known mutational spectrum of TUBB8 associated with early embryonic developmental arrest and female infertility.

A microdeletion del(12)(p11.21p11.23) with a cryptic unbalanced translocation t(7;12)(q21.13;q23.1) implicates new candidate loci for intellectual disability and Kallmann syndrome

In an apparently balanced translocation t(7;12)(q22;q24)dn exhibiting both Kallmann syndrome (KS) and intellectual disability (ID), we detected a cryptic heterozygous 4.7 Mb del(12)(p11.21p11.23) unrelated to the translocation breakpoint. This new finding raised the possibility that KS combined with neurological disorder in this patient could be caused by gene(s) within this deletion at 12p11.21-12p11.23 instead of disrupted or dysregulated genes at the genomic breakpoints. Screening of five candidate genes at both breakpoints in 48 KS patients we recruited found no mutation, corroborating our supposition. To substantiate this hypothesis further, we recruited six additional subjects with small CNVs and analyzed eight individuals carrying small CNVs in this region from DECIPHER to dissect 12p11.21-12p11.23. We used multiple complementary approaches including a phenotypic-genotypic comparison of reported cases, a review of knockout animal models recapitulating the human phenotypes, and analyses of reported variants in the interacting genes with corresponding phenotypes. The results identified one potential KS candidate gene ( TSPAN11 ), seven candidate genes for the neurodevelopmental disorder ( TM7SF3 , STK38L , ARNTL2 , ERGIC2 , TMTC1 , DENND5B , and ETFBKMT ), and four candidate genes for KS with ID ( INTS13 , REP15 , PPFIBP1 , and FAR2 ). The high-level expression pattern in the relevant human tissues further suggested the candidacy of these genes. We propose that the dosage alterations of the candidate genes may contribute to sexual and/or cognitive impairment in patients with KS and/or ID. Further identification of point mutations through next generation sequencing will be necessary to confirm their causal roles.

Landscape of pathogenic mutations in premature ovarian insufficiency

Premature ovarian insufficiency (POI) is a major cause of female infertility due to early loss of ovarian function. POI is a heterogeneous condition, and its molecular etiology is unclear. To identify genetic variants associated with POI, here we performed whole-exome sequencing in a cohort of 1,030 patients with POI. We detected 195 pathogenic/likely pathogenic variants in 59 known POI-causative genes, accounting for 193 (18.7%) cases. Association analyses comparing the POI cohort with a control cohort of 5,000 individuals without POI identified 20 further POI-associated genes with a significantly higher burden of loss-of-function variants. Functional annotations of these novel 20 genes indicated their involvement in ovarian development and function, including gonadogenesis (LGR4 and PRDM1), meiosis (CPEB1, KASH5, MCMDC2, MEIOSIN, NUP43, RFWD3, SHOC1, SLX4 and STRA8) and folliculogenesis and ovulation (ALOX12, BMP6, H1-8, HMMR, HSD17B1, MST1R, PPM1B, ZAR1 and ZP3). Cumulatively, pathogenic and likely pathogenic variants in known POI-causative and novel POI-associated genes contributed to 242 (23.5%) cases. Further genotype-phenotype correlation analyses indicated that genetic contribution was higher in cases with primary amenorrhea compared to that in cases with secondary amenorrhea. This study expands understanding of the genetic landscape underlying POI and presents insights that have the potential to improve the utility of diagnostic genetic screenings.

Zona pellucida glycoproteins: Relevance in fertility and development of contraceptive vaccines

Mammalian zona pellucida (ZP) is composed of three to four glycoproteins, which plays an important role during fertilization. Mutations in the genes encoding zona proteins are reported in women with empty follicle syndrome, degenerated oocytes and those with an abnormal or no ZP further emphasizing their relevance during fertility. Immunization with either native or recombinant ZP glycoproteins/proteins leads to curtailment of fertility in various animal species. Observed infertility is frequently associated with ovarian pathology characterized by follicular atresia and degenerative changes in ZP, which may be due to oophoritogenic T cell epitope(s) within ZP glycoproteins. To avoid ovarian dystrophy, B cell epitopes of ZP glycoproteins have been mapped by using bio-effective monoclonal antibodies. Immunization with the immunogens encompassing the mapped B cell epitopes by and large led to amelioration of follicular atresia. However, their use for human application will require more rigorous research to establish their safety and reversibility of the contraceptive effect. Nonetheless, to minimize human-animal conflicts, ZP-based contraceptive vaccines have been used successfully in the population management of free-ranging animal species such as feral horses, white-tailed deer and elephants. To control zoonotic diseases, attempts are also underway to control the population of other animal species including stray dogs, which acts as one of the major vectors for the rabies virus.

Effect of In Vitro Maturation of Human Oocytes Obtained After Controlled Ovarian Hormonal Stimulation on the Expression of Development- and Zona Pellucida-Related Genes and Their Interactions

In an in vitro fertilization program, approximately 10-15% of oocytes obtained after controlled ovarian stimulation are immature, with germinal vesicles (GVs). These oocytes are usually discarded in clinical practice; however, an in vitro maturation (IVM) procedure can be applied to mature them. There are scarce data in the literature on the effect of IVM on the expression of important development- and zona pellucida (ZP)-related genes in human oocytes; therefore, we wanted to determine this. One hundred nine human oocytes were collected from patients enrolled in an intracytoplasmic sperm injection program. The expression of the BMP4, GDF9, ZP1, ZP2, ZP3, and ZP4 genes was analyzed using RT-qPCR in oocytes matured in vitro with different reproductive hormones in the IVM medium (AMH, FSH + hCG, FSH + hCG + AMH), in in vivo matured oocytes and in immature oocytes with GVs. No statistically significant differences in the expression of selected genes in oocytes were observed among groups with different reproductive hormones in IVM medium. However, several interesting significant correlations were found between BMP4 and GDF9, and ZP1 and ZP4; between GDF9 and ZP1, and ZP2 and ZP4; and between ZP1 and ZP3 and ZP4 in the in vitro matured oocytes, while no such correlations were present in other groups of oocytes. The type of reproductive hormone in the maturation medium does not affect the expression of the analyzed genes in oocytes during the maturation process. However, the in vitro maturation procedure itself generated correlations among analyzed genes that were otherwise not present in in vivo matured and immature oocytes.

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.

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.

Translational Bioinformatics for Human Reproductive Biology Research: Examples, Opportunities and Challenges for a Future Reproductive Medicine

Since 1978, with the first IVF (in vitro fertilization) baby birth in Manchester (England), more than eight million IVF babies have been born throughout the world, and many new techniques and discoveries have emerged in reproductive medicine. To summarize the modern technology and progress in reproductive medicine, all scientific papers related to reproductive medicine, especially papers related to reproductive translational medicine, were fully searched, manually curated and reviewed. Results indicated whether male reproductive medicine or female reproductive medicine all have made significant progress, and their markers have experienced the progress from karyotype analysis to single-cell omics. However, due to the lack of comprehensive databases, especially databases collecting risk exposures, disease markers and models, prevention drugs and effective treatment methods, the application of the latest precision medicine technologies and methods in reproductive medicine is limited.

Can successful pregnancy be achieved and predicted from patients with identified ZP mutations? A literature review

BACKGROUND

In mammals, normal fertilization depends on the structural and functional integrity of the zona pellucida (ZP), which is an extracellular matrix surrounding oocytes. Mutations in ZP may affect oogenesis, fertilization and early embryonic development, which may cause female infertility.

METHODS

A PubMed literature search using the keywords 'zona pellucida', 'mutation' and 'variant' limited to humans was performed, with the last research on June 30, 2022. The mutation types, clinical phenotypes and pregnancy outcomes were summarized and analyzed. The naive Bayes classifier was used to predict clinical pregnancy outcomes for patients with ZP mutations.

RESULTS

A total of 29 publications were included in the final analysis. Sixty-nine mutations of the ZP genes were reported in 87 patients with different clinical phenotypes, including empty follicle syndrome (EFS), ZP-free oocytes (ZFO), ZP-thin oocytes (ZTO), degenerated and immature oocytes. The phenotypes of patients were influenced by the types and location of the mutations. The most common effects of ZP mutations are protein truncation and dysfunction. Three patients with ZP1 mutations, two with ZP2 mutations, and three with ZP4 mutations had successful pregnancies through Intracytoplasmic sperm injection (ICSI) from ZFO or ZTO. A prediction model of pregnancy outcome in patients with ZP mutation was constructed to assess the chance of pregnancy with the area under the curve (AUC) of 0.898. The normalized confusion matrix showed the true positive rate was 1.00 and the true negative rate was 0.38.

CONCLUSION

Phenotypes in patients with ZP mutations might be associated with mutation sites or the degree of protein dysfunction. Successful pregnancy outcomes could be achieved in some patients with identified ZP mutations. Clinical pregnancy prediction model based on ZP mutations and clinical characteristics will be helpful to precisely evaluate pregnancy chance and provide references and guidance for the clinical treatment of relevant patients.

Human Blastocyst Components Detection Using Multiscale Aggregation Semantic Segmentation Network for Embryonic Analysis

Infertility is one of the most important health concerns worldwide. It is characterized by not being successful of pregnancy after some periods of periodic unprotected sexual intercourse. In vitro fertilization (IVF) is an assisted reproduction technique that efficiently addresses infertility. IVF replaces the actual mode of reproduction through a manual procedure wherein embryos are cultivated in a controlled laboratory environment until they reach the blastocyst stage. The standard IVF procedure includes the transfer of one or two blastocysts from several blastocysts that are grown in a controlled environment. The morphometric properties of blastocysts with their compartments such as trophectoderm (TE), zona pellucida (ZP), inner cell mass (ICM), and blastocoel (BL), are analyzed through manual microscopic analysis to predict viability. Deep learning has been extensively used for medical diagnosis and analysis and can be a powerful tool to automate the morphological analysis of human blastocysts. However, the existing approaches are inaccurate and require extensive preprocessing and expensive architectures. Thus, to cope with the automatic detection of blastocyst components, this study proposed a novel multiscale aggregation semantic segmentation network (MASS-Net) that combined four different scales via depth-wise concatenation. The extensive use of depthwise separable convolutions resulted in a decrease in the number of trainable parameters. Further, the innovative multiscale design provided rich spatial information of different resolutions, thereby achieving good segmentation performance without a very deep architecture. MASS-Net utilized 2.06 million trainable parameters and accurately detects TE, ZP, ICM, and BL without using preprocessing stages. Moreover, it can provide a separate binary mask for each blastocyst component simultaneously, and these masks provide the structure of each component for embryonic analysis. Further, the proposed MASS-Net was evaluated using publicly available human blastocyst (microscopic) imaging data. The experimental results revealed that it can effectively detect TE, ZP, ICM, and BL with mean Jaccard indices of 79.08, 84.69, 85.88%, and 89.28%, respectively, for embryological analysis, which was higher than those of the state-of-the-art methods.

Advances in studying human gametogenesis and embryonic development in China

Reproductive medicine in China has developed rapidly since 1988 due to the support from the government and scientific exploration. However, the success rate of assisted reproduction technology (ART) is around 30-40% and many unknown "black boxes" in gametogenesis and embryo development are still present. With the development of single-cell and low-input sequencing technologies, the network of transcriptome and epigenetic regulation (DNA methylation, chromatin accessibility, and histone modifications) during the development of human primordial germ cells (PGCs), gametes and embryos has been investigated in depth. Furthermore, pre-implantation genetic testing (PGT) has also rapidly developed. In this review, we summarize and analyze China's outstanding progress in these fields.

Novel Heterozygous Mutations in ZP2 Cause Abnormal Zona Pellucida and Female Infertility

Zona pellucida (ZP) which is an extracellular matrix consisting of ZP1, ZP2, ZP3, and ZP4 plays a vital role in oocyte maturity, early embryonic development, and fertilization process. Any alterations of structure or function may lead to the abnormal formation of ZP and female infertility. Two novel heterozygous mutations c.1859G > A (p.Cys620Tyr) and c.1421 T > C (p.Leu474Pro) in ZP2 gene were recognized in three patients from two unrelated families with abnormal ZP and female infertility in this study. The expression constructs carrying wild-type ZP2 gene, c.1859G > A (p.Cys620Tyr) mutant ZP2 gene, and c.1421 T > C (p.Leu474Pro) mutant ZP2 gene were transfected into CHO cells respectively. There was a remarkable decrease in the expression of p.Cys620Tyr mutant protein with western blot. In addition, secretion of p.Leu474Pro mutant protein in the culture medium reduced markedly compared with that of wild-type ZP2 protein. Furthermore, co-immunoprecipitation showed that the p.Leu474Pro mutation affected the interaction between ZP2 and ZP3. Prediction of three-dimensional (3D) structure of the proteins showed that p.Cys620Tyr mutation altered the disulfide bond of ZP2 protein and may affect its function. These findings extend the ranges of mutations of ZP2 gene. Meanwhile, it will be helpful to the precise diagnosis of abnormal ZP.

Novel mutations in ZP2 and ZP3 cause female infertility in three patients

PURPOSE

The aim of this study was to identify the disease-causing mutations found in three infertile female patients who were diagnosed with abnormal zona pellucida (ZP) and empty follicle syndrome (EFS).

METHODS

We performed whole-exome sequencing and Sanger sequencing to identify and verify the disease-causing mutations. Additionally, we performed Western blotting and mini-gene splicing assay to assess the effects of the mutations.

RESULTS

We identified two novel compound heterozygous mutations in the ZP2 gene, a patient with an abnormal ZP carrying a novel compound heterozygous mutation (c.1695-2A>G and c.1831G>T, p.V611F) and a patient with EFS carrying a novel compound heterozygous mutation (c.1695-2A>G and c.1924 C>T, p.R642*). Furthermore, we identified a patient with typical abnormal ZP carrying a novel heterozygous mutation (c.400G>T, p.A134S) in the ZP3 gene. The splice site mutation (c.1695-2A>G) can cause abnormal pre-mRNA splicing that inserts an extra sequence of 61 bp in the mRNA of ZP2, and the missense mutation (c.1831G>T) can cause a decrease of ZP2 protein in HEK293 cells.

CONCLUSION

We identified three novel mutations in the ZP2 gene and the ZP3 gene in three Chinese female patients with infertility. Our study expands the spectrum of ZP gene mutations and phenotypes and thus is beneficial in the genetic diagnosis of infertility in females.

Ovarian Transcriptomic Analysis of Ninghai Indigenous Chickens at Different Egg-Laying Periods

Egg production is an essential indicator of poultry fertility. The ovary is a crucial organ involved in egg production; however, little is known about the key genes and signaling pathways involved in the whole egg-laying cycle of hens. In order to explore the mechanism of egg production at different stages of the egg-laying process, ovarian tissues from four chickens were randomly selected for transcriptome analysis at each of the three ages (145 d, 204 d, and 300 d in the early, peak, and late stages of egg laying). A total of 12 gene libraries were constructed, and a total of 8433 differential genes were identified from NH145d vs. NH204d, NH145d vs. NH300d and NH300d vs. NH204d (Ninghai 145-day-old, Ninghai 204-day-old, and Ninghai 300-day-old), with 1176, 1653 and 1868 up-regulated genes, and 621, 1955 and 1160 down-regulated genes, respectively. In each of the two comparison groups, 73, 1004, and 1030 differentially expressed genes were found to be co-expressed. We analyzed the differentially expressed genes and predicted nine genes involved in egg production regulation, including LRP8, BMP6, ZP4, COL4A1, VCAN, INHBA, LOX, PTX3, and IHH, as well as several essential egg production pathways, such as regulation adhesion molecules (CAMs), calcium signaling pathways, neuroactive ligand–receptor interaction, and cytokine–cytokine receptor interaction. Transcriptional analysis of the chicken ovary during different phases of egg-lay will provide a useful molecular basis for study of the development of the egg-laying ovary.

Gene Spectrum and Clinical Traits of Nine Patients With Oocyte Maturation Arrest

Background: Oocyte maturation arrest is a disease that produces immature oocytes and cannot be mature after culturing in vitro, which leads to female primary infertility. We aimed to summarize nine representative patients in our center to retrospectively analyze the genetic variants and clinical characteristics of oocyte maturation arrest.

Methods: This study examined and analyzed nine families with oocyte maturation arrest. Whole-exome sequencing (WES) of the probands was performed to detect the pathogenic variants. Sanger sequencing verified the WES findings in patients and available parents. ExAC database was used to search the variant frequency. The variants were assessed by pathogenicity and conservational property prediction analysis and according to the American College of Medical Genetics and Genomics (ACMG). Phenotypes of oocytes were evaluated by a light microscopy, and the phenotype-genotype correlation was also evaluated.

Results: Nine pathogenic variants in five genes were detected in nine patients, of which three were novel variants, including PATL2 [c.1374A > G (p. Ile458Met)] and [1289-1291del TCC (p. Leu430del)] and ZP2 [c.1543C > T (p. Pro515Ser)]. Nine variants were predicted to be pathogenic, resulting in different types of oocyte maturation arrest and clinical phenotypes.

Conclusion: Three novel pathogenic variants were identified, enabling the expansion of the gene variant spectrum. The related pathogenic mutations of the PATL2, TUBB8, and ZP1∼3 genes were highly suggestive of being causative of oocyte maturation arrest.

Novel expression of zona pellucida 3 protein in normal testis; potential functional implications

The expression of the zona pellucida glycoprotein 3 (ZP3), originally thought to be specific for oocytes, was recently extended to ovarian, prostate, colorectal and lung cancers. Earlier successful ZP3 immunization of a transgenic mouse model carrying a ZP3 positive ovarian tumor emphasized the suitability of ZP3 for cancer immunotherapy. This study was carried out to determine whether any other normal tissues besides the ovary in healthy human and mouse tissues may express ZP3, considered important to exclude off-target effects of ZP3 cancer immunotherapy. Strong ZP3 expression was found in normal human and mouse testis. ZP3 protein and mRNA transcripts were localized in spermatogonia, spermatocytes and round and elongated spermatids of both human and mouse testis, as well as in a mouse spermatogonial cell line, but absent in testicular Sertoli, Leydig, spermatogonial stem and progenitor cells. All other normal human and mouse tissues were ZP3 negative. This surprising testicular ZP3 expression has implications for the development of ZP3 cancer immunotherapies, and it also alludes to the potential of using ZP3 as a target for the development of a male immunocontraceptive.

Identification and in silico Characterization of Deleterious Single Nucleotide Variations in Human ZP2 Gene

ZP2, an important component of the zona matrix, surrounds mammalian oocytes and facilitates fertilization. Recently, some studies have documented the association of mutations in genes encoding the zona matrix with the infertile status of human females. Single nucleotide polymorphisms are the most common type of genetic variations observed in a population and as per the dbSNP database, around 5,152 SNPs are reported to exist in the human ZP2 (hZP2) gene. Although a wide range of computational tools are publicly available, yet no computational studies have been done to date to identify and analyze structural and functional effects of deleterious SNPs on hZP2. In this study, we conducted a comprehensive in silico analysis of all the SNPs found in hZP2. Six different computational tools including SIFT and PolyPhen-2 predicted 18 common nsSNPs as deleterious of which 12 were predicted to most likely affect the structure/functional properties. These were either present in the N-term region crucial for sperm-zona interaction or in the zona domain. 31 additional SNPs in both coding and non-coding regions were also identified. Interestingly, some of these SNPs have been found to be present in infertile females in some recent studies.

A novel gene mutation in ZP3 loop region identified in patients with empty follicle syndrome

The zona pellucida (ZP) is an extracellular matrix surrounding mammalian oocytes. It is composed of three to four glycoproteins, ZP1-ZP4. ZP3 is essential for sperm binding and zona matrix formation. Here, we identified a novel heterozygous mutation (NM_001110354.2:c.502_504delGAG) of ZP3, occurring in a pair of sisters with empty follicle syndrome (EFS). A mouse model with the same mutation was established using the CRISPR/Cas9 gene-editing system. As in the above family, F₀ -, F₁ -, and F₂ -generation female mice with the mutation were all infertile. Further analysis using the Chinese hamster ovary cells (CHO-K1) also showed that this mutation weakens the strength of binding between ZP3 and ZP2, which hinders the assembly of ZP and results in unstable ZP formation. Immunohistochemical analysis using ovarian serial sections in both humans and mice demonstrated that the ZP of preantral follicles was thinner than normal control, or even absent. Our study presents a new gene mutation that leads to EFS, providing new evidence and support for the genetic diagnosis of infertile individuals with similar phenotypes. Our results also show that the loop of ZP3 is not only a linker between two amphiphilic helices but may play a critical role in specifying the correct heterodimerization partner.

Novel WEE2 compound heterozygous mutations identified in patients with fertilization failure or poor fertilization

PURPOSE

To study associations between novel WEE2 mutations and patients with fertilization failure or poor fertilization.

METHODS

Thirty-one Chinese patients who underwent treatment with assisted reproductive technology and suffered from repeated (at least two times) total fertilization failure (TFF) or a low fertilization rate were enrolled. Genomic DNA was extracted from patients for whole-exome sequencing. Suspicious mutations were validated by Sanger sequencing. WEE2 protein levels in oocytes from affected patients were examined by immunofluorescence. Disruptive effects of mutations on WEE2 protein stability, subcellular localization, and kinase function were analyzed through western blotting, immunofluorescence, and flow cytometry in HeLa cells.

RESULTS

Three of thirty-one (9.6%) enrolled patients had six compound heterozygous mutations of the WEE2 gene, and three of them were reported here for the first time (c.115_116insT, c.756_758delTGA, and c.C1459T). Oocytes from affected patients showed decreased WEE2 immunofluorescence signals. In vitro experiments showed that the mutant WEE2 gene caused reduced WEE2 protein levels or cellular compartment translocation in HeLa cells, leading to decreased levels of the phosphorylated Cdc2 protein. Compared with the wild-type WEE2 protein, the mutant WEE2 proteins were also found to have different effects on the cell cycle.

CONCLUSION

Three novel compound heterozygous WEE2 variants were found in patients with pronucleus formation failure. This study provides new evidence that WEE2 mutations result in loss of function, which could result in fertilization failure.

ASTL is mutated in female infertility

Female infertility is a relatively common phenotype with a growing number of single gene causes although these account for only a minority of cases. Here, we report a consanguineous family in which adult females who are homozygous for a truncating variant in ASTL display markedly reduced fertility in a pattern strikingly similar to Astl^-/- female mice. ASTL encodes ovastacin, which is known to trigger zona pellucida hardening (ZPH) as part of the cortical reaction upon fertilization. ZPH is required for normal early embryonic development and its absence can be caused by pathogenic variants in other zona pellucida proteins that result in a similar infertility phenotype in humans and mouse. This is the first report of ASTL-related infertility in humans and suggests that the inclusion of ASTL in female infertility gene panels is warranted.

Empty Zona Pellucida Only Case: A Critical Review of the Literature

The presence of empty zona pellucida (EZP) in oocytes following oocyte retrieval (OR) during an in vitro fertilization (IVF) cycle presents a major clinical and laboratory challenge in assisted reproduction. It has been attributed to several factors such as the ovarian stimulation protocol employed, the damaging of the follicles during oocyte retrieval (OR) mainly through the high aspiration pressure, during the denudation technique, and the degeneration of oolemma within the zona pellucida (ZP) through apoptosis. The role of ZP is pivotal from the early stages of follicular development up to the preimplantation embryo development and embryo hatching. Polymorphisms or alterations on the genes that encode ZP proteins may contribute to EZP. We present a critical review of the published literature hitherto on EZP and available options when encountered with the phenomenon of EZP. Concerning the former, we found that there is rare data on this phenomenon that merits documentation. The latter includes technical, genetic, and pathophysiological perspectives, along with specific treatment options. In conclusion, we identify the lack of a definitive management proposal for couples presenting with this phenomenon, we underline the need for an algorithm, and indicate the questions raised that point towards our goal for a strategy when addressing a previous finding of EZP.

Zona Pellucida Genes and Proteins: Essential Players in Mammalian Oogenesis and Fertility

All mammalian oocytes and eggs are surrounded by a relatively thick extracellular matrix (ECM), the zona pellucida (ZP), that plays vital roles during oogenesis, fertilization, and preimplantation development. Unlike ECM surrounding somatic cells, the ZP is composed of only a few glycosylated proteins, ZP1–4, that are unique to oocytes and eggs. ZP1–4 have a large region of polypeptide, the ZP domain (ZPD), consisting of two subdomains, ZP-N and ZP-C, separated by a short linker region, that plays an essential role in polymerization of nascent ZP proteins into crosslinked fibrils. Both subdomains adopt immunoglobulin (Ig)-like folds for their 3-dimensional structure. Mouse and human ZP genes are encoded by single-copy genes located on different chromosomes and are highly expressed in the ovary by growing oocytes during late stages of oogenesis. Genes encoding ZP proteins are conserved among mammals, and their expression is regulated by cis-acting sequences located close to the transcription start-site and by the same/similar trans-acting factors. Nascent ZP proteins are synthesized, packaged into vesicles, secreted into the extracellular space, and assembled into long, crosslinked fibrils that have a structural repeat, a ZP2-ZP3 dimer, and constitute the ZP matrix. Fibrils are oriented differently with respect to the oolemma in the inner and outer layers of the ZP. Sequence elements in the ZPD and the carboxy-terminal propeptide of ZP1–4 regulate secretion and assembly of nascent ZP proteins. The presence of both ZP2 and ZP3 is required to assemble ZP fibrils and ZP1 and ZP4 are used to crosslink the fibrils. Inactivation of mouse ZP genes by gene targeting has a detrimental effect on ZP formation around growing oocytes and female fertility. Gene sequence variations in human ZP genes due to point, missense, or frameshift mutations also have a detrimental effect on ZP formation and female fertility. The latter mutations provide additional support for the role of ZPD subdomains and other regions of ZP polypeptide in polymerization of human ZP proteins into fibrils and matrix.

Genetic factors as potential molecular markers of human oocyte and embryo quality

Successful human reproduction requires gamete maturation, fertilization, and early embryonic development. Human oocyte maturation includes nuclear and cytoplasmic maturation, and abnormalities in the process will lead to infertility and recurrent failure of IVF/ICSI attempts. In addition, the quality of oocytes/embryos in the clinic can only be determined by morphological markers, and there is currently a lack of molecular markers for determining oocyte quality. As the number of patients undergoing IVF/ICSI has increased, many patients have been identified with recurrent IVF/ICSI failure. However, the genetic basis behind this phenotype remains largely unknown. In recent years, a few mutant genes have been identified by us and others, which provide potential molecular markers for determining the quality of oocytes/embryos. In this review, we outline the genetic determinants of abnormalities in the processes of oocyte maturation, fertilization, and early embryonic development. Currently, 16 genes (PATL2, TUBB8, TRIP13, ZP1, ZP2, ZP3, PANX1, TLE6, WEE2, CDC20, BTG4, PADI6, NLRP2, NLRP5, KHDC3L, and REC114) have been reported to be the causes of oocyte maturation arrest, fertilization failure, embryonic arrest, and preimplantation embryonic lethality. These abnormalities mainly have Mendelian inheritance patterns, including both dominant inheritance and recessive inheritance, although in some cases de novo mutations have also appeared. In this review, we will introduce the effects of each gene in the specific processes of human early reproduction and will summarize all known variants in these genes and their corresponding phenotypes. Variants in some genes have specific effects on certain steps in the early human reproductive processes, while other variants result in a spectrum of phenotypes. These variants and genetic markers will lay the foundation for individualized genetic counseling and potential treatments for patients and will be the target for precision treatments in reproductive medicine.

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.

Zp4 is completely dispensable for fertility in female rats†

Zona pellucida (ZP), which is composed of at most four extracellular glycoproteins (ZP1, ZP2, ZP3, and ZP4) in mammals, shelters the oocytes and is vital in female fertility. Several studies have identified the indispensable roles of ZP1-3 in maintaining normal female fertility. However, the understanding of ZP4 is still very poor because only one study on ZP4-associated infertility performed in rabbits has been reported up to date. Here we investigated the function of mammalian Zp4 by creating a knockout (KO) rat strain (Zp4-/- rat) using CRISPR-Cas9-mediated DNA-editing method. The influence of Zp4 KO on ZP morphology and some pivotal processes of reproduction, including oogenesis, ovulation, fertilization, and pup production, were studied using periodic acid-Schiff's staining, superovulation, in vitro fertilization, and natural mating. The ZP morphology in Zp4-/- rats was normal, and none of these pivotal processes was affected. This study renewed the knowledge of mammalian Zp4 by suggesting that Zp4 was completely dispensable for female fertility.

A novel homozygous nonsense mutation in zona pellucida 1 (ZP1) causes human female empty follicle syndrome

PURPOSE

To identify a pathogenic gene mutation in a female infertility proband characterized by empty follicle syndrome (EFS) and explore the genetic cause of EFS.

METHODS

Whole exome sequencing (WES) was performed to identify the candidate pathogenic mutation. Sanger sequencing was used to validate the mutation in family members. The pathogenicity of the identified variant and its possible effects on the protein were evaluated with in silico tools. Immunofluorescence staining was used to study the possible mechanism of the mutation on affected oocyte.

RESULTS

We identified a family with a novel homozygous nonsense mutation in zona pellucida 1 (ZP1) (c.199G > T [p.Glu67Ter]). Based on bioinformatics analysis, the mutation was predicted to be pathogenic. This variant generates a premature stop codon in exon 2 at the 199th nucleotide, and was inferred to result in a truncated ZP1 protein of 67 amino acids at the ZP-N1 domain. An in vitro study showed that the oocyte of the EFS proband was degenerated and the zona pellucida was absent. Additionally, the mutant ZP1 proteins were localized in the cytoplasm of the degenerated oocyte but not at the surface.

CONCLUSIONS

The novel mutation in ZP1 is a genetic cause of female infertility characterized by EFS. Our finding expands the genetic spectrum for EFS and will help justify the EFS diagnosis in patients.

A novel homozygous variant in ZP2 causes abnormal zona pellucida formation and female infertility

PURPOSE

We aimed to identify pathogenic variants in two infertile sisters in a family with a thin zona pellucida (ZP) phenotype.

METHODS

Whole-exome sequencing was performed in the two affected sisters, and Sanger sequencing was used to confirm the identified variants. The effects of the identified variant were further investigated in mouse oocytes and Chinese hamster ovary (CHO) cells.

RESULTS

We identified a novel homozygous frameshift variant in ZP2 (c.1235_1236del, p.Q412Rfs*17) in the two affected individuals. Immunoblotting demonstrated that the variant produced a truncated ZP2 protein that was expressed at low levels in CHO cells. Immunofluorescence in mouse oocytes confirmed the decreased protein level of mutant ZP2, although the subcellular localization was not affected. In addition, immunoprecipitation showed that the pathogenic variant reduced the interaction between ZP2 and ZP3.

CONCLUSION

This study identified a novel pathogenic variant in ZP2 that produces a truncated ZP2 protein. The variant might disrupt the assembly of ZP2-ZP3 dimers, thus resulting in a thin ZP and female infertility.

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.