ZP2 pathogenic variants cause in vitro fertilization failure and female infertility

Novel PATL2 variants cause female infertility with oocyte maturation defect

PURPOSE

Oocyte maturation defect (OOMD) is a rare cause of in vitro fertilization failure characterized by the production of immature oocytes. Compound heterozygous or homozygous PATL2 mutations have been associated with oocyte arrest at the germinal vesicle (GV), metaphase I (MI), and metaphase II (MII) stages, as well as morphological changes.

METHODS

In this study, we recruited three OOMD cases and conducted a comprehensive multiplatform laboratory investigation.

RESULTS

Whole exome sequence (WES) revealed four diagnostic variants in PATL2, nonsense mutation c.709C > T (p.R237*) and frameshift mutation c.1486_1487delinsT (p.A496Sfs*4) were novel mutations that have not been reported previously. Furthermore, the pathogenicity of these variants was predicted using in silico analysis, which indicated detrimental effects. Molecular dynamic analysis suggested that the A496S variant disrupted the hydrophobic segment, leading to structural changes that affected the overall protein folding and stability. Additionally, biochemical and molecular experiments were conducted on cells transfected with wild-type (WT) or mutant PATL2 (p.R237* and p.A496Sfs*4) plasmid vectors.

CONCLUSIONS

The results demonstrated that PATL2A496Sfs*4 and PATL2R237* had impacts on protein size and expression level. Interestingly, expression levels of specific genes involved in oocyte maturation and early embryonic development were found to be simultaneously deregulated. The findings in our study expand the variation spectrum of the PATL2 gene, provide solid evidence for counseling on future pregnancies in affected families, strongly support the application of in the diagnosis of OOMD, and contribute to the understanding of PATL2 function.

Conserved genes regulating human sex differentiation, gametogenesis and fertilization

The study of the functional genome in mice and humans has been instrumental for describing the conserved molecular mechanisms regulating human reproductive biology, and for defining the etiologies of monogenic fertility disorders. Infertility is a reproductive disorder that includes various conditions affecting a couple's ability to achieve a healthy pregnancy. Recent advances in next-generation sequencing and CRISPR/Cas-mediated genome editing technologies have facilitated the identification and characterization of genes and mechanisms that, if affected, lead to infertility. We report established genes that regulate conserved functions in fundamental reproductive processes (e.g., sex determination, gametogenesis, and fertilization). We only cover genes the deletion of which yields comparable fertility phenotypes in both rodents and humans. In the case of newly-discovered genes, we report the studies demonstrating shared cellular and fertility phenotypes resulting from loss-of-function mutations in both species. Finally, we introduce new model systems for the study of human reproductive biology and highlight the importance of studying human consanguineous populations to discover novel monogenic causes of infertility. The rapid and continuous screening and identification of putative genetic defects coupled with an efficient functional characterization in animal models can reveal novel mechanisms of gene function in human reproductive tissues.

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.

Novel biallelic ASTL variants are associated with polyspermy and female infertility: A successful live birth following ICSI treatment

Fertilization of the egg by the sperm is the first vital stage of embryogenesis. In mammals, only one sperm is incorporated into the oocyte. Polyspermy is a key anomaly of fertilization that is generally lethal to the embryo. To date, only a few causative genes for polyspermy have been reported. In a recent study, a homozygous variant in astacin-like metalloendopeptidase (ASTL), which encodes the ovastacin enzyme that cleaves ZP2 to prevent polyspermy, was found to be associated with female infertility characterized by polyspermy in vitro. Herein, we identified two ASTL variants in a Chinese woman likely responsible for her primary infertility and polyspermy in in vitro fertilization. Both variants were located within the key catalytic domain and predicted to alter hydrogen bonds, potentially impairing protein stability. Moreover, expression and immunoblot analyses in CHO-K1 cells indicated abnormal ovastacin zymogen activation or decreased enzyme stability. Intracytoplasmic sperm injection treatment successfully bypassed the defect in polyspermy blocking and resulted in a live birth. Our study associates ASTL variants with human infertility and further supports the contribution of this gene to blocking polyspermy in humans. Our findings expand the spectrum of ASTL mutations and should facilitate the diagnosis of oocyte-borne polyspermy.

Defects in phospholipase C zeta cause polyspermy and low fertilization after conventional IVF: not just ICSI failure

ABSTRACT

Phospholipase C zeta (PLCζ) is a key sperm-borne oocyte-activating factor that triggers Ca2+ oscillations and the subsequent block to polyspermy following gamete fusion. Mutations in PLCZ1, the gene encoding PLCζ, cause male infertility and intracytoplasmic sperm injection (ICSI) fertilization failure; and PLCζ expression and localization patterns are significantly correlated with ICSI fertilization rate (FR). However, in conventional in vitro fertilization (cIVF), whether and how sperm PLCζ affects fertilization remain unclear. Herein, we identified one previously reported and two novel PLCZ1 mutations associated with polyspermy in vitro that are characterized by excessive sperm-zona binding and a delay in pronuclei (PN) formation. Immunofluorescence staining and oocyte activation testing revealed that virtually all spermatozoa from patients lacked functional PLCζ and were thus unable to evoke Ca2+ oscillations. ICSI with an artificial oocyte activation treatment successfully rescued the polyspermic phenotype and resulted in a live birth. Furthermore, we analyzed PLCζ in an additional 58 males after cIVF treatment in the Reproductive and Genetic Hospital of CITIC-Xiangya (Changsha, China) between February 2019 and January 2022. We found that the proportion of spermatozoa that expressed PLCζ was positively correlated with both 2PN rate and total FR. The optimal cutoff value below which males were likely to experience low FR (total FR ≤30%) after cIVF was 56.7% for the proportion of spermatozoa expressing PLCζ. Our study expands the mutation and the phenotypic spectrum of PLCZ1 and further suggests that PLCζ constitutes a promising biomarker for identifying low FRs cases in cIVF due to sperm-related oocyte activation deficiency and that sperm PLCζ analysis may benefit the wider male population and not only men with ICSI failure.

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.

Dynein axonemal heavy chain 10 deficiency causes primary ciliary dyskinesia in humans and mice

Primary ciliary dyskinesia (PCD) is a congenital, motile ciliopathy with pleiotropic symptoms. Although nearly 50 causative genes have been identified, they only account for approximately 70% of definitive PCD cases. Dynein axonemal heavy chain 10 (DNAH10) encodes a subunit of the inner arm dynein heavy chain in motile cilia and sperm flagella. Based on the common axoneme structure of motile cilia and sperm flagella, DNAH10 variants are likely to cause PCD. Using exome sequencing, we identified a novel DNAH10 homozygous variant (c.589C > T, p.R197W) in a patient with PCD from a consanguineous family. The patient manifested sinusitis, bronchiectasis, situs inversus, and asthenoteratozoospermia. Immunostaining analysis showed the absence of DNAH10 and DNALI1 in the respiratory cilia, and transmission electron microscopy revealed strikingly disordered axoneme 9+2 architecture and inner dynein arm defects in the respiratory cilia and sperm flagella. Subsequently, animal models of Dnah10-knockin mice harboring missense variants and Dnah10-knockout mice recapitulated the phenotypes of PCD, including chronic respiratory infection, male infertility, and hydrocephalus. To the best of our knowledge, this study is the first to report DNAH10 deficiency related to PCD in human and mouse models, which suggests that DNAH10 recessive mutation is causative of PCD.

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.

Development and validation of a conventional in vitro total fertilization failure prediction model

BACKGROUND

Conventional total fertilization failure (TFF) is a challenging problem for clinicians. The predictive model developed in this study aims to predict the individual probability of conventional in vitro total fertilization failure.

METHODS

The prediction model was developed based on 1635 patients who underwent first-attempt in vitro fertilization (IVF) cycles from January 2018 to January 2020. Total fertilization failure and normal fertilization occurred in 218 and 1417 cycles, respectively. Multivariate logistic regression analyses were used to develop the prediction model. Performance of our model was evaluated using calibration (Hosmer-Lemeshow test) and discrimination (area under the receiver operating characteristic curve [AUC]).

RESULTS

Thirteen risk factors for TFF were included in the prediction model, as follows: female age; female body mass index; infertility duration; number of oocytes retrieved; stimulation protocol; infertility etiology; infertility diagnosis; male age; sperm concentration; total sperm motility; normal sperm morphology percentage; swim-up sperm motility; and swim-up sperm concentration. The AUC of our model was 0.815 (95% CI: 0.783-0.846), indicating satisfactory discrimination performance.

CONCLUSION

Considering female and male factors (especially sperm parameters), we established a model that predicts the probability of TFF in conventional IVF procedures that will be helpful in the laboratory supporting IVF to facilitate physicians in determining optimal treatment.

Dietary Soybean (Glycine max (L.) Merr.) Improved the ZP2 Expression in Female Swiss Mice

OBJECTIVE

This study aimed to determine the effects of soybean (Glycine max) administration on ZP2 expression in female mice.

METHODS

This research used Mus musculus, six-week-old female SWISS strain mice divided into three groups (group without soybean administration and groups with mixed feed with soybeans and pelleted 50:50 and 25:75). Soybean feed for mice was 360 grams per kilogram of mouse body weight for 2 weeks. The percentage of follicles was measured and analyzed using Hematoxylin-Eosin staining, and the expression of ZP2 was analyzed using immunohistochemistry. We assessed the data using one-way ANOVA and paired t-test using the SPSS 17.

RESULTS

Some of the follicles in the ovaries do not develop until their final stage of follicle maturation. The administration of soybean before and after treatment in all groups was not significantly different, but the numbers of atretic follicles in groups 1 and 2 were significantly different. Soybean administration at a ratio of 50:50 has the effect of increasing the percentage of the ZP2 expression in tertiary follicles (p=0.001), whereas soybean administration at a ratio of 25:75 was not able to maintain or increase the formation of ZP2 in tertiary follicles (p=0.77).

CONCLUSION

Soybean administration with a ratio of 50:50 significantly increased the percentage of the ZP2 expression in tertiary follicles.

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.

Female infertility from oocyte maturation arrest: assembling the genetic puzzle

Assisted reproduction procedures often encounter an issue called oocyte maturation arrest (OMA), which is manifested as failed IVF/ICSI attempts using oocytes from some infertile women. In this issue of EMBO Molecular Medicine, Wang et al identify infertile women bearing novel DNA sequence variants in a gene called PABPC1L, which is essential for translation of maternal mRNAs. By conducting a series of in vitro and in vivo experiments, they demonstrated certain variants as being causal for OMA, confirming a conserved requirement for PABPC1L in human oocyte maturation. This study offers a promising therapeutic target for treating OMA patients.

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.

Bi-allelic pathogenic variants in PABPC1L cause oocyte maturation arrest and female infertility

Oocyte maturation arrest is one of the important causes of female infertility, but the genetic factors remain largely unknown. PABPC1L, a predominant poly(A)-binding protein in Xenopus, mouse, and human oocytes and early embryos prior to zygotic genome activation, plays a key role in translational activation of maternal mRNAs. Here, we identified compound heterozygous and homozygous variants in PABPC1L that are responsible for female infertility mainly characterized by oocyte maturation arrest in five individuals. In vitro studies demonstrated that these variants resulted in truncated proteins, reduced protein abundance, altered cytoplasmic localization, and reduced mRNA translational activation by affecting the binding of PABPC1L to mRNA. In vivo, three strains of Pabpc1l knock-in (KI) female mice were infertile. RNA-sequencing analysis showed abnormal activation of the Mos-MAPK pathway in the zygotes of KI mice. Finally, we activated this pathway in mouse zygotes by injecting human MOS mRNA, and this mimicked the phenotype of KI mice. Our findings reveal the important roles of PABPC1L in human oocyte maturation and add a genetic potential candidate gene to be screened for causes of 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.

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 novel homozygous C-terminal deletion in BTG4 causes zygotic cleavage failure and female infertility

PURPOSE

We aimed to identify pathogenic variants in a female patient with primary infertility and recurrent failure of in vitro fertilization with zygotic cleavage failure.

METHODS

The genomic DNA from the affected individual was subjected to whole-exome sequencing and the variant was confirmed by Sanger sequencing. The functional effect of the identified variant was further investigated in 293 T cells.

RESULTS

We identified a novel homozygous deletion in BTG4 (c.580_616del) in the affected individual. The deletion results in frameshift and replacement of the last 29 residues (aa195-223) with 66 random amino acids. The mutated amino acid residues are highly conserved among mammalian species. Co-immunoprecipitation in 293 T cells showed that the mutation abolished the interaction between BTG4 and PABPN1L.

CONCLUSION

This study conforms previous studies and expands the mutational spectrum of BTG4. Our findings prove the functional importance of the C-terminal of BTG4. BTG4 is a potential diagnostic and therapeutic target for patients suffering from zygotic cleavage failure.

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.

Common dysmorphic oocytes and embryos in assisted reproductive technology laboratory in association with gene alternations

Amorphic or defected oocytes and embryos are commonly observed in assisted reproductive technology (ART) laboratories. It is believed that a proper gene expression at each stage of embryo development contributes to the possibility of a decent-quality embryo leading to successful implantation. Many studies reported that several defects in embryo morphology are associated with gene expressions during in vitro fertilization (IVF) treatment. There is lacking literature review on summarizing common morphological defects about gene alternations. In this review, we summarized the current literature. We selected 64 genes that have been reported to be involved in embryo morphological abnormalities in animals and humans, 30 of which were identified in humans and might be the causes of embryonic changes. Five papers focusing on associations of multiple gene expressions and embryo abnormalities using RNA transcriptomes were also included during the search. We have also reviewed our time-lapse image database with over 3000 oocytes/embryos to show morphological defects possibly related to gene alternations reported previously in the literature. This holistic review can better understand the associations between gene alternations and morphological changes. It is also beneficial to select important biomarkers with strong evidence in IVF practice and reveal their potential application in embryo selection. Also, identifying genes may help patients with genetic disorders avoid unnecessary treatments by providing preimplantation genetic testing for monogenic/single gene defects (PGT-M), reduce embryo replacements by less potential, and help scientists develop new methods for oocyte/embryo research in the near future.

Research Progress on Emerging Polysaccharide Materials Applied in Tissue Engineering

The development and application of polysaccharide materials are popular areas of research. Emerging polysaccharide materials have been widely used in tissue engineering fields such as in skin trauma, bone defects, cartilage repair and arthritis due to their stability, good biocompatibility and reproducibility. This paper reviewed the recent progress of the application of polysaccharide materials in tissue engineering. Firstly, we introduced polysaccharide materials and their derivatives and summarized the physicochemical properties of polysaccharide materials and their application in tissue engineering after modification. Secondly, we introduced the processing methods of polysaccharide materials, including the processing of polysaccharides into amorphous hydrogels, microspheres and membranes. Then, we summarized the application of polysaccharide materials in tissue engineering. Finally, some views on the research and application of polysaccharide materials are presented. The purpose of this review was to summarize the current research progress on polysaccharide materials with special attention paid to the application of polysaccharide materials in tissue engineering.

Novel RSPH4A Variants Associated With Primary Ciliary Dyskinesia–Related Infertility in Three Chinese Families

Background: The radial spoke head component 4A (RSPH4A) is involved in the assembly of radial spokes, which is essential for motile cilia function. Asthenoteratozoospermia in primary ciliary dyskinesia (PCD) related to RSPH4A variants has not been reported.

Materials and Methods:RSPH4A variants were identified and validated using whole-exome and Sanger sequencing in three unrelated Chinese families. High-speed video microscopy analysis (HSVA) was performed to measure the beating frequency and pattern of nasal cilia of the patients and healthy control. Papanicolaou staining and computer-aided sperm analysis were performed to analyze the morphology and motility of the sperm in patient 1. Immunofluorescence was adopted to confirm the structure deficiency of sperm and nasal cilia.

Results: Patient 1 from family 1 is a 22-year-old unmarried male presented with bronchiectasis. Semen analysis and sperm Papanicolaou staining confirmed asthenoteratozoospermia. Novel compound heterozygous RSPH4A variants c.2T>C, p.(Met1Thr) and c.1774_1775del, p.(Leu592Aspfs*5) were detected in this patient. Patients 2 and 3 are from two unrelated consanguineous families; they are both females and exhibited bronchiectasis and infertility. Two homozygous RSPH4A variants c.2T>C, p.(Met1Thr) and c.351dupT, p.(Pro118Serfs*2) were detected, respectively. HSVA showed that most of the cilia in patients 1 and 3 were with abnormal rotational movement. The absence of RSPH4A and RSPH1 in patient 1’s sperm and patient 3’s respiratory cilia was indicated by immunofluorescence. Patient 2 died of pulmonary infection and respiratory failure at the age of 35 during follow-up.

Conclusion: Dysfunctional sperm flagellum and motile cilia in the respiratory tract and the fallopian tube were found in patients with RSPH4A variants. Our study enriches the genetic spectrum and clinical phenotypes of RSPH4A variants in PCD, and c.2T>C, p.(Met1Thr) detected in our patients may be a hotspot RSPH4A variant in Chinese.

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.

CatSper and its CaM-like Ca2+ sensor EFCAB9 are necessary for the path chirality of sperm

Successful fertilization depends on sperm motility adaptation. Ejaculated and activated sperm beat symmetrically in high frequency, move linearly, and swim with clockwise chirality. After capacitation, sperm beat asymmetrically with lower amplitude and a high lateral head excursion. This motility change called hyperactivation requires CatSper activation and an increase in intracellular Ca²⁺ . However, whether CatSper-mediated Ca²⁺ influx participates in controlling the swim path chirality is unknown. In this study, we show that the clockwise path chirality is preserved in mouse sperm regardless of capacitation state but is lost in the sperm either lacking the entire CatSper channel or its Ca²⁺ sensor EFCAB9. Pharmacological inhibition of CatSper with either mibefradil or NNC 55-0396 leads to the same loss in swim path chirality. Exposure of sperm to the recombinant N-terminal part of the zona pellucida protein 2 randomizes chirality in capacitated cells, but not in non-capacitated ones. We conclude that Ca²⁺ sensitive regulation of CatSper activity orchestrates clockwise swim path chirality of sperm and any substantial change, such as the physiological stimulus of zona pellucida glycoproteins, results in a loss of chirality.

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.

Molecular tools for the genomic assessment of oocyte’s reproductive competence

The most important factor associated with oocytes' developmental competence has been widely identified as the presence of chromosomal abnormalities. However, growing application of genome-wide sequencing (GS) in population diagnostics has enabled the identification of multifactorial genetic predispositions to sub-lethal pathologies, including those affecting IVF outcomes and reproductive fitness. Indeed, GS analysis in families with history of isolated infertility has recently led to the discovery of new genes and variants involved in specific human infertility endophenotypes that impact the availability and the functionality of female gametes by altering unique mechanisms necessary for oocyte maturation and early embryo development. Ongoing advancements in analytical and bioinformatic pipelines for the study of the genetic determinants of oocyte competence may provide the biological evidence required not only for improving the diagnosis of isolated female infertility but also for the development of novel preventive and therapeutic approaches for reproductive failure. Here, we provide an updated discussion and review of the progresses made in preconception genomic medicine in the identification of genetic factors associated with oocyte availability, function, and competence.

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.

Gene mutations associated with fertilization failure after in vitro fertilization/intracytoplasmic sperm injection

Fertilization failure during assisted reproductive technologies (ART) is often unpredictable, as this failure is encountered only after in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) have been performed. The etiology of fertilization failure remains elusive. More and more mutations of genes are found to be involved in human fertilization failure in infertile patients as high throughput sequencing techniques are becoming widely applied. In this review, the mutations of nine important genes expressed in sperm or oocytes, PLCZ1, ACTL7A, ACTL9, DNAH17, WEE2, TUBB8, NLRP5, ZP2, and TLE6, were summarized and discussed. These abnormalities mainly have shown Mendelian patterns of inheritance, including dominant and recessive inheritance, although de novo mutations were present in some cases. The review revealed the crucial roles of each reported gene in the fertilization process and summarized all known mutations and their corresponding phenotypes. The review suggested the mutations might become promising targets for precision treatments in reproductive medicine. Moreover, our work will provide some helpful clues for genetic counseling, risk prediction, and optimizing clinical treatments for human infertility by supplying the useful and timely information on the genetic causes leading to fertilization failure.

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.

CFAP65 is required in the acrosome biogenesis and mitochondrial sheath assembly during spermiogenesis

Asthenoteratospermia is a common cause of male infertility. Recent studies have revealed that CFAP65 mutations lead to severe asthenoteratospermia due to acrosome hypoplasia and flagellum malformations. However, the molecular mechanism underlying CFAP65-associated sperm malformation is largely unclear. Here, we initially examined the role of CFAP65 during spermiogenesis using Cfap65 knockout (Cfap65-/-) mice. The results showed that Cfap65-/- male mice exhibited severe asthenoteratospermia characterized by morphologically defective sperm heads and flagella. In Cfap65-/- mouse testes, hyper-constricted sperm heads were apparent in step 9 spermatids accompanied by abnormal manchette development, and acrosome biogenesis was abnormal in the maturation phase. Moreover, subsequent flagellar elongation was also severely affected and characterized by disrupted assembly of the mitochondrial sheath (MS) in Cfap65-/- male mice. Furthermore, the proteomic analysis revealed that the proteostatic system during acrosome formation, manchette organization, and MS assembly was disrupted when CFAP65 was lost. Importantly, endogenous immunoprecipitation and immunostaining experiments revealed that CFAP65 may form a cytoplasmic protein network comprising MNS1, RSPH1, TPPP2, ZPBP1, and SPACA1. Overall, these findings provide insights into the complex molecular mechanisms of spermiogenesis by uncovering the essential roles of CFAP65 during sperm head shaping, acrosome biogenesis, and MS assembly.

Case Report: A Novel Heterozygous ZP3 Deletion Associated With Empty Follicle Syndrome and Abnormal Follicular Development

Background: Empty follicle syndrome (EFS) is defined as the complete failure to retrieve oocytes after ovarian stimulation. Although several mutations in ZP1, ZP2, ZP3, and LHCGR have been identified as genetic causes of EFS, its pathogenesis is still not well-understood.

Methods: Whole-exome sequencing (WES) was employed to identify the candidate pathogenic mutations, which were then verified by Sanger sequencing. A study in CHO-K1 cells was performed to analyze the effect of the mutation on protein expression. Additionally, immunohistochemistry (IHC) staining was used to examine follicular development and zona pellucida (ZP) assembly in the ovary of an EFS patient.

Results: A novel heterozygous deletion in ZP3 (c.565_579del[p.Thr189_Gly193del]) was identified in the EFS patient. It was inherited dominantly and resulted in significant degradation of the ZP3 protein. Oocytes with degenerated cytoplasm and abnormal ZP assembly were observed in follicles up to the secondary stage, and many empty follicle-like structures were present.

Conclusion: We identified a novel ZP3 mutation that expands the mutational spectrum associated with human EFS. We also showed the abnormal follicular development and ZP assembly of the EFS patient with the heterozygous ZP3 mutation, which provides new insights into the pathogenesis of EFS.

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.

Unraveling the Balance between Genes, Microbes, Lifestyle and the Environment to Improve Healthy Reproduction

Humans’ health is the result of a complex and balanced interplay between genetic factors, environmental stimuli, lifestyle habits, and the microbiota composition. The knowledge about their single contributions, as well as the complex network linking each to the others, is pivotal to understand the mechanisms underlying the onset of many diseases and can provide key information for their prevention, diagnosis and therapy. This applies also to reproduction. Reproduction, involving almost 10% of our genetic code, is one of the most critical human’s functions and is a key element to assess the well-being of a population. The last decades revealed a progressive decline of reproductive outcomes worldwide. As a consequence, there is a growing interest in unveiling the role of the different factors involved in human reproduction and great efforts have been carried out to improve its outcomes. As for many other diseases, it is now clear that the interplay between the underlying genetics, our commensal microbiome, the lifestyle habits and the environment we live in can either exacerbate the outcome or mitigate the adverse effects. Here, we aim to analyze how each of these factors contribute to reproduction highlighting their individual contribution and providing supporting evidence of how to modify their impact and overall contribution to a healthy reproductive status.

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.

Mutations in ZP4 are associated with abnormal zona pellucida and female infertility

BACKGROUND

The zona pellucida (ZP) of human oocytes plays essential protective roles in sperm-egg interactions during fertilisation and embryo development. ZP4-null female rabbits exhibit a thin and irregular ZP, which severely impairs embryo development and fertility. However, the effects of ZP4 defect on human female reproduction remain unknown.

METHODS AND RESULTS

We performed whole-exome sequencing in 26 female patients with abnormal (thin and irregular) ZP and identified heterozygous variants in ZP4 (OMIM: 613514) from 3 patients (approximately 11%). No ZP4 variant was found in the 30 control women with proven fertility. We constructed ZP4-mutated plasmids and found that the variants reduced the secretion of ZP4 in vitro. Lower suction pressure facilitated egg retrieval, and intracytoplasmic sperm injection (ICSI) was a desirable treatment for ZP4-mutated patients with abnormal ZP.

CONCLUSIONS

We identified ZP4 as a novel gene for human abnormal ZP and found that lower suction pressure and ICSI are efficient treatment strategies.

Bi-allelic BRWD1 variants cause male infertility with asthenoteratozoospermia and likely primary ciliary dyskinesia

Genetics-associated asthenoteratozoospermia is often seen in patients with multiple morphological abnormalities of the sperm flagella (MMAF). Although 24 causative genes have been identified, these explain only approximately half of patients with MMAF. Since sperm flagella and motile cilia (especially respiratory cilia) have similar axonemal structures, many patients with MMAF also exhibit respiratory symptoms, such as recurrent airway infection, chronic sinusitis, and bronchiectasis, which are frequently associated with primary ciliary dyskinesia (PCD), another recessive disorder. Here, exome sequencing was conducted to evaluate the genetic cause in 53 patients with MMAF and classic PCD/PCD-like symptoms. Two homozygous missense variants and a compound-heterozygous variant in the BRWD1 gene were identified in three unrelated individuals. BRWD1 staining was detected in the whole flagella and respiratory cilia of normal controls but was absent in BRWD1-mutated individuals. Transmission electron microscopy and immunostaining demonstrated that BRWD1 deficiency in human affected respiratory cilia and sperm flagella differently, as the absence of outer and inner dynein arms in sperm flagellum and respiratory cilia, while with a decreased number and outer doublet microtubule defects of respiratory cilia. To our knowledge, this is the first report of a BRWD1-variant-related disease in humans, manifesting as an autosomal recessive form of MMAF and PCD/PCD-like symptoms. Our data provide a basis for further exploring the molecular mechanism of BRWD1 gene during spermatogenesis and ciliogenesis.

A novel homozygous frameshift mutation in MNS1 associated with severe oligoasthenoteratozoospermia in humans

Oligoasthenoteratozoospermia (OAT) refers to the combination of various sperm abnormalities, including a decreased sperm count, reduced motility, and abnormal sperm morphology. Only a few genetic causes have been shown to be associated with OAT. Herein, we identified a novel homozygous frameshift mutation in meiosis-specific nuclear structural 1 (MNS1; NM_018365: c.603_604insG: p.Lys202Glufs*6) by whole-exome sequencing in an OAT proband from a consanguineous Chinese family. Subsequent variant screening identified four additional heterozygous MNS1 variants in 6/219 infertile individuals with oligoasthenospermia, but no MNS1 variants were observed among 223 fertile controls. Immunostaining analysis showed MNS1 to be normally located in the whole-sperm flagella, but was absent in the proband's sperm. Expression analysis by Western blot also confirmed that MNS1 was absent in the proband's sperm. Abnormal flagellum morphology and ultrastructural disturbances in outer doublet microtubules were observed in the proband's sperm. A total of three intracytoplasmic sperm injection cycles were carried out for the proband's wife, but they all failed to lead to a successful pregnancy. Overall, this is the first study to report a loss-of-function mutation in MNS1 causing OAT in a Han Chinese patient.

The critical role of ZP genes in female infertility characterized by empty follicle syndrome and oocyte degeneration

OBJECTIVE

To identify the major causative gene(s) of genuine empty follicle syndrome (GEFS) characterized by oocyte degeneration.

DESIGN

Genetic and functional studies.

SETTING

University-based reproductive medicine center.

PATIENT(S)

Thirty-five unrelated women with GEFS and oocyte degeneration.

INTERVENTION(S)

Whole-exome sequencing (WES) and targeted Sanger sequencing.

MAIN OUTCOME MEASURE(S)

Variants predicted by software and the functional effects of variants assessed via Western blot and immunofluorescence in Chinese hamster ovary (CHO) cells.

RESULT(S)

We identified zona pellucida (ZP) gene variants in 18 individuals, which included 20 variants in the ZP1 gene, two variants in the ZP2 gene, and one previously reported recurrent variant in the ZP3 gene. The women carrying ZP variants constituted 51.43% of the GEFS cohort. The ZP1 variants were inherited in an autosomal recessive pattern; the ZP2 and ZP3 variants were inherited in an autosomal dominant pattern. All variants were predicted to be deleterious. Studies in CHO cells suggested that most ZP1 variants led to increased intracytoplasmic protein and some variants influenced the intracellular transportation of other ZP proteins. Variant p.R642Q of ZP2 caused the secretion of ZP2 protein with an increased molecular weight, suggesting altered protein modification. Variant p.I619N of ZP2 resulted in increased ZP2 protein in cell lysate and decreased ZP2 protein in culture medium. These results showed that ZP variants might block the intracellular transportation and secretion of ZP proteins and disrupt the zona pellucida.

CONCLUSION(S)

We identified novel variants of ZP genes in more than half the cohort with GEFS and oocyte degeneration. Variants of ZP genes caused protein intracellular sequestration and failure to assemble the ZP filaments, resulting in EFS and female infertility. Our findings not only reveal the critical roles of ZP genes but also pave the way for the efficient genetic diagnosis of females with GEFS and oocyte degeneration.

Preconception genome medicine: current state and future perspectives to improve infertility diagnosis and reproductive and health outcomes based on individual genomic data

BACKGROUND

Our genetic code is now readable, writable and hackable. The recent escalation of genome-wide sequencing (GS) applications in population diagnostics will not only enable the assessment of risks of transmitting well-defined monogenic disorders at preconceptional stages (i.e. carrier screening), but also facilitate identification of multifactorial genetic predispositions to sub-lethal pathologies, including those affecting reproductive fitness. Through GS, the acquisition and curation of reproductive-related findings will warrant the expansion of genetic assessment to new areas of genomic prediction of reproductive phenotypes, pharmacogenomics and molecular embryology, further boosting our knowledge and therapeutic tools for treating infertility and improving women's health.

OBJECTIVE AND RATIONALE

In this article, we review current knowledge and potential development of preconception genome analysis aimed at detecting reproductive and individual health risks (recessive genetic disease and medically actionable secondary findings) as well as anticipating specific reproductive outcomes, particularly in the context of IVF. The extension of reproductive genetic risk assessment to the general population and IVF couples will lead to the identification of couples who carry recessive mutations, as well as sub-lethal conditions prior to conception. This approach will provide increased reproductive autonomy to couples, particularly in those cases where preimplantation genetic testing is an available option to avoid the transmission of undesirable conditions. In addition, GS on prospective infertility patients will enable genome-wide association studies specific for infertility phenotypes such as predisposition to premature ovarian failure, increased risk of aneuploidies, complete oocyte immaturity or blastocyst development failure, thus empowering the development of true reproductive precision medicine.

SEARCH METHODS

Searches of the literature on PubMed Central included combinations of the following MeSH terms: human, genetics, genomics, variants, male, female, fertility, next generation sequencing, genome exome sequencing, expanded carrier screening, secondary findings, pharmacogenomics, controlled ovarian stimulation, preconception, genetics, genome-wide association studies, GWAS.

OUTCOMES

Through PubMed Central queries, we identified a total of 1409 articles. The full list of articles was assessed for date of publication, limiting the search to studies published within the last 15 years (2004 onwards due to escalating research output of next-generation sequencing studies from that date). The remaining articles' titles were assessed for pertinence to the topic, leaving a total of 644 articles. The use of preconception GS has the potential to identify inheritable genetic conditions concealed in the genome of around 4% of couples looking to conceive. Genomic information during reproductive age will also be useful to anticipate late-onset medically actionable conditions with strong genetic background in around 2-4% of all individuals. Genetic variants correlated with differential response to pharmaceutical treatment in IVF, and clear genotype-phenotype associations are found for aberrant sperm types, oocyte maturation, fertilization or pre- and post-implantation embryonic development. All currently known capabilities of GS at the preconception stage are reviewed along with persisting and forthcoming barriers for the implementation of precise reproductive medicine.

WIDER IMPLICATIONS

The expansion of sequencing analysis to additional monogenic and polygenic traits may enable the development of cost-effective preconception tests capable of identifying underlying genetic causes of infertility, which have been defined as 'unexplained' until now, thus leading to the development of a true personalized genomic medicine framework in reproductive health.

Thoughts on the popularity of ICSI

Purpose

Intracytoplasmic sperm injection (ICSI) is the most widely utilized assisted reproductive technique (ART) worldwide. In this feature, we review the early assisted fertilization attempts that eventually led to the development of ICSI, and discuss its current utilization in cases of male and non-male factor infertility.

Methods

We researched the literature related to the development, indications, and current use of ICSI, such as sperm structural abnormalities, male genetic indications, surgically retrieved sperm, high sperm chromatin fragmentation, oocyte dysmorphism, and preimplantation genetic testing (PGT). We also describe the potential future applications of ICSI.

Results

This review summarizes the early micromanipulation techniques that led to the inception of ICSI. We also explore its current indications, including non-male factor infertility, where its use is more controversial. Finally, we consider the benefits of future advancements in reproductive biology that may incorporate ICSI, such as in vitro spermatogenesis, neogametogenesis, and heritable genome editing.

Conclusion

The versatility, consistency, and reliability of ICSI have made it the most prevalently utilized ART procedure worldwide.

A novel mutation in ZP3 causes empty follicle syndrome and abnormal zona pellucida formation

PURPOSE

To identify disease-causing genes involved in female infertility.

METHODS

Whole-exome sequencing and Sanger DNA sequencing were used to identify the mutations in disease-causing genes. We performed subcellular protein localization, western immunoblotting analysis, and co-immunoprecipitation analysis to evaluate the effects of the mutation.

RESULTS

We investigated 17 families with female infertility. Whole-exome and Sanger DNA sequencing were used to characterize the disease gene in the patients, and we identified a novel heterozygous mutation (p.Ser173Cys, c.518C > G) in the ZP3 gene in a patient with empty follicle syndrome. When we performed co-immunoprecipitation analysis, we found that the S173C mutation affected interactions between ZP3 and ZP2.

CONCLUSIONS

We identified a novel mutation in the ZP3 gene in a Chinese family with female infertility. Our findings thus expand the mutational and phenotypical spectrum of the ZP3 gene, and they will be helpful in precisely diagnosing this aspect of female infertility.

ZP1 mutations are associated with empty follicle syndrome: evidence for the existence of an intact oocyte and a zona pellucida in follicles up to the early antral stage. A case report

Empty follicle syndrome (EFS) is the complete failure to retrieve oocytes after ovarian stimulation. Although LHCGR and ZP3 were identified as causative genes, it is still unclear what happens to these patients' oocytes, and the pathogenesis of EFS remains obscure. Here, we identified six novel ZP1 mutations associated with EFS and female infertility that was inherited recessively in five unrelated families. Studies in CHO-K1 cells showed that these mutations resulted in either degradation or truncation of ZP1 protein. Immunohistochemistry using ovarian serial sections demonstrated that all preantral follicles had normal architecture, but with a thin ZP, lacking ZP1, surrounding the growing oocytes. The antral follicles were also defective in normal cumulus-oocyte complex organisation, leading us to speculate that the lack of ZP1 might lead to oocyte degeneration or increased fragility of the oocyte during follicular puncture, ultimately resulting in EFS. To our knowledge, this is the first study that presents morphological evidence showing normal preantral folliculogenesis with abnormal ZP assembly in EFS patients. Our data provides a better understanding of the biological functions of ZP1 in human ZP assembly and folliculogenesis and gives new insights into the pathogenesis of EFS and possible therapeutic developments.

Influence of mouse defective zona pellucida in folliculogenesis on apoptosis of granulosa cells and developmental competence of oocytes†

Zona pellucida (ZP), which enwraps the oocyte during folliculogenesis, initially forms in the primary follicle and plays an important role in female fertility. Here, we investigated a mouse strain ("mutant mice" for short) carrying two types of ZP defects in folliculogenesis, i.e., ZP thinned (but intact) and ZP cracked, caused by targeted mutation in the Zp1 gene. Using this mutant mouse strain and wild-type mouse as control, we studied the effects of the ZP defects on the development of oocytes and granulosa cells during folliculogenesis. For each ZP defect, we examined the morphology of transzonal projections and apoptosis of granulosa cells in the corresponding growing follicles, as well as the morphology of corresponding ovulated eggs and their abilities to develop into viable individuals. Our results suggested that ZP integrity rather than thickness or porosity is crucial for preventing the ectopia of granulosa cells, maintaining adequate routine bilateral signaling between oocyte and surrounding granulosa cells, and thus for ensuring the survival of granulosa cells and the establishment of the full developmental competence of oocytes. This is the first study to elucidate the effects of different degrees of ZP defects caused by the same gene mutation, on the apoptosis of granulosa cells and developmental competence of oocytes, and to explore the potential mechanisms underlying these effects.