Biallelic Mutations in PATL2 Cause Female Infertility Characterized by Oocyte Maturation Arrest

PATL2 mutations affect human oocyte maternal mRNA homeostasis and protein interactions in cell cycle regulation

BACKGROUND

Oocyte maturation defect (OMD) and early embryonic arrest result in female infertility. Previous studies have linked biallelic mutations in the PATL2 gene to OMD, yet the underlying mechanism remains largely unknown.

RESULTS

This study uncovers three novel mutations (c.1201G > T, c.1284delA and c.1613 + 2_1613 + 3insGT) and three reported mutations (c.1204 C > T, c.1271T > C, c.223 - 14_223-2delCCCTCCTGTTCCA) in the PATL2 gene across five unrelated individuals exhibiting OMD, oocyte death, and early embryonic arrest. RNA sequencing revealed that PATL2 mutations decreased mRNA storage in human germinal vesicle (GV) oocytes and impeded mRNA decay during maturation and in early embryos. We demonstrate that PATL2 interacts with CPEB1 and TUT7 in human oocytes to maintain mRNA homeostasis. Additionally, we observed a reduction in CCNB1 and CCNE1 mRNA levels in PATL2-mutant GV oocytes, which may be linked to GV arrest. Employing both wild-type and mutated PATL2V401F/R402W variants, we characterized the protein interactome of PATL2, identifying disruptions of PATL2V401F/R402W variants predominantly affecting cell cycle-related proteins, including CDC23, APC1 and MAD2L1. PATL2's interaction with and stabilization of CDC23 in oocytes may elucidate the mechanisms behind the mutation-induced MI arrest. PALT2 is required for the efficient mRNA translation and it maintains the protein level of CDC23, APC1 and MAD2L1 in mouse GV oocyte.

CONCLUSION

PATL2 plays a critical role in regulating mRNA accumulation and decay in human oocytes, potentially through interactions with CPEB1 and TUT7, respectively. Mutations in PATL2 lead to oocyte meiosis defects by affecting the mRNA accumulation, mRNA translation, and direct binding to and stabilizing proteins related to cell cycle regulation, such as CCNB1 and CDC23. This study expands the mutational spectrum of PATL2 and provides new insights into the molecular mechanisms underlying PATL2 mutation-associated oocyte maturation disorders.

Transcriptomic analysis and epigenetic regulators in human oocytes at different stages of oocyte meiotic maturation

Human oocytes are highly specialized cells with the capacity to store and regulate mRNAs during oocyte maturation, in preparation for post-fertilization steps. Here we performed single-oocyte transcriptomic analysis of human oocytes in three meitoic maturation stages - Germinal Vesicle (GV; n = 6), Metaphase I (MI; n = 6) and Metaphase II (MII; n = 7). Single-oocyte transcriptomic analysis revealed that the total number of expressed genes progressively decreased from GV to MII stages, with 9660 genes being transcribed in GV, 8734 in MI and 5889 in MII. The same tendency was observed for the number of uniquely expressed genes, with 1328 uniquely expressed genes in GV, 401 in MI and 72 in MII. GO analysis of the uniquely expressed genes showed distinct terms in GV oocytes such as transferase activity, organonitrogen compound metabolic process and ncRNA processing. Analysis of Differentially Expressed Genes (DEGs) between the three maturation stages revealed 1165 DEGs between GV and MII oocytes, with 635 being upregulated and 528 downregulated, 42 DEGs between GV and MI, with 38 being upregulated and 4 downregulated, and no significant changes in gene expression between MI and MII oocytes. Comprehensive analysis of epigenetic regulators showed high expression of several histone-modifying enzymes, namely deacetylases, acetylases, lysine demethylases and methyltransferases, and DNA methylation regulators, namely the maintenance methyltransferase DNMT1 and its co-regulators DPPA3 and UHRF1. Some of these epigenetic regulators were differentially expressed between maturation stages, namely SIRT3, SIRT6, KDM3AP1, KMT2E, DNMT1, DPPA3 and the MEST and RASGRF1 imprinted genes. Our study contributes with important information on the transcriptional landscape of human oocytes in different stages of meiotic maturation, providing important insights into candidate biomarkers of human oocyte quality.

Identification of a novel mutation in PATL2 gene associated with the germinal vesicle arrest of oocytes

The aim of this study was to investigate the genetic factors of a patient with germinal vesicle arrest in oocytes. Clinical data and blood samples were collected from the patient and some were amplified for high-throughput gene and Sanger sequencing. Several molecular and cellular experiments were performed to determine the association between the gene mutation and germinal vesicle arrest. Two mutation sites (c.1282G > T and c.1247C > A) were found in the PATL2 gene. The c.1282G > T mutation is associated with oocyte maturation abnormalities according to previous research, whereas c.1247C > A is a novel mutation of unknown clinical significance. In cell transfection experiments, qRT-PCR, immunofluorescence, and Western blotting revealed that the mRNA and protein levels of the PATL2 gene with the c.1247C > A mutation were reduced. Sanger sequencing suggested that the patient inherited the PATL2 mutations from her parents via a compound heterozygous mode of inheritance. Collectively, this study describes the PATL2-gene c.1247C > A mutation associated with germinal vesicle arrest in oocytes, providing a useful target for genetic and background tests for patients presenting with oocyte maturation abnormalities and/or germinal vesicle arrest following multiple unsuccessful attempts with assisted reproductive technology.

A heterozygous SPRY4 variant identified in female infertility characterized by reduced oocyte potential and early embryonic arrest

STUDY QUESTION

Can novel genetic factors contributing to early embryonic arrest in infertile patients be identified, along with the underlying mechanisms of the pathogenic variant?

SUMMARY ANSWER

We identified a heterozygous variant in the SPRY4 (sprouty RTK signaling antagonist 4) in infertile patients and conducted in vitro and in vivo studies to investigate the effects of the variant/deletion, highlighting its critical role in female reproductive health.

WHAT IS KNOWN ALREADY

SPRY4 acts as a negative regulator of receptor tyrosine kinases (RTKs) and functions as a tumor suppressor. Its abnormal expression can lead to recurrent miscarriage by affecting trophoblast function. In mice, Spry4 knockout (KO) leads to craniofacial anomalies and growth defects. A human study links the SPRY4 variant to a male patient with isolated hypogonadotropic hypogonadism (IHH), hypothetically impacting gonadotropin-releasing hormone (GnRH) neurons, and causing reproductive dysfunctions. SPRY4 is thus potentially integral in regulating endocrine homeostasis and reproductive function. To date, no study has reported SPRY4 variants associated with female fertility, and a causal relationship has not been established with functional evidence.

STUDY DESIGN, SIZE, DURATION

Whole-exome sequencing (WES) was performed in 392 infertile women who suffered from primary infertility of unknown reason, and the heterozygous SPRY4 variant were identified in one independent family. The infertile patients presenting were recruited from July 2017 to November 2023.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Women diagnosed with primary infertility were recruited from the Reproduction Center of Zhongshan Hospital, Fudan University. Genomic DNA was extracted from peripheral blood for WES analysis. The SPRY4 variant were identified through WES, in silico analysis, and variant screening. All variants were confirmed by Sanger sequencing. The effects of the variants were investigated in human embryonic kidney (HEK) 293T (HEK293T) cells via western blotting, and in mouse oocytes and embryos through complementary RNA (cRNA) injection, RNA sequencing, fluorescence, absorbance, and RT-qPCR assays. Gene function was further examined in Spry4 KO mice via histology, western blotting, ELISA, and RT-qPCR assays.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified a missense heterozygous pathogenic variant in SPRY4 (GRCh38, GenBank: NM_030964.5, c.157C>T p.(Arg53Trp), rs200531302) that reduces SPRY4 protein levels in HEK293T cells and disrupts the redox system and mitochondrial function in mouse oocyte, and perturbs developmental potential in mouse embryos. These phenotypes could be partially reversed by the exogenous addition of Nrf1 cRNA. Additionally, Spry4-/- mice exhibit ovarian oxidative stress and decreased ovarian function.

LIMITATIONS, REASONS FOR CAUTION

Due to the limited WES data and population, we identified only one family with a SPRY4 mutation. The deeper mechanism and therapeutic strategy should be further investigated through mutant mice and recovery experiment.

WIDER IMPLICATIONS OF THE FINDINGS

Our study has identified a pathogenic variant in SPRY4 associated with early embryonic arrest in humans. These findings enhance our understanding of the role of SPRY4 in early embryonic development and present a new genetic marker for female infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Natural Science Foundation of China (82071643 and 82171655) and Natural Science Foundation of Shanghai (22ZR1456200). None of the authors have any competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Identification of a novel splicing variant of thyroid hormone receptor interaction protein 13 (TRIP13) in female infertility characterized by oocyte maturation arrest

PURPOSE

As a cause of primary female infertility, oocyte maturation arrest (OMA) is characterized by failure to obtain mature oocytes due to abnormal meiosis. We aimed to identify pathogenic variants in two sisters with OMA phenotype from a non-consanguineous family.

METHODS

Whole-exome sequencing and Sanger sequencing were conducted to identify and validate the disease-causing gene variant. Additionally, we performed a minigene assay, quantitative reverse transcription PCR, and Western blotting to assess the effects of the variant.

RESULTS

We identified a novel homozygous splicing variant (c.1021-11T>C) in TRIP13, which followed a recessive inheritance pattern. Minigene assay showed that the variant could disrupt the integrity of TRIP13 mRNA, as evidenced by the production of an alternative transcript with intron10 intermediate retention of 79 bp. Compared to normal controls, the expression of TRIP13 mRNA and abundance of TRIP13 protein were also significantly decreased in Epstein-Barr virus-immortalized lymphoblastoid cells derived from affected individuals.

CONCLUSION

Our findings confirm the contribution of genetic factors to OMA and expand the mutation spectrum of TRIP13 in female infertility.

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.

Genetic factors of oocyte maturation arrest: an important cause for recurrent IVF/ICSI failures

Oocyte maturation arrest (OMA) is a common phenotype observed in IVF/ICSI cycles, characterized by the production of immature oocytes which lead to infertility. Previous studies have demonstrated that genetic factors play an important role in OMA, but the genetic mechanisms underlying a group of patients remain to be elucidated. In the recent issue of Journal of Assisted Reproduction and Genetics, Hu et al. and Wan et al. identified novel PATL2 or ZFP36L2 variants in OMA patients, respectively. By conducting in vitro experiments, they demonstrated the destructive effect of the variants on protein function. These findings expand the mutational spectrum of PATL2 and ZFP36L2, and provide precise reference for genetic counseling of OMA patients.

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.

Transcriptomic imputation of genetic risk variants uncovers novel whole-blood biomarkers of Parkinson's disease

Blood-based gene expression signatures could potentially be used as biomarkers for PD. However, it is unclear whether genetically-regulated transcriptomic signatures can provide novel gene candidates for use as PD biomarkers. We leveraged on the Genotype-Tissue Expression (GTEx) database to impute whole-blood transcriptomic expression using summary statistics of three large-scale PD GWAS. A random forest classifier was used with the consensus whole-blood imputed gene signature (IGS) to discriminate between cases and controls. Outcome measures included Area under the Curve (AUC) of Receiver Operating Characteristic (ROC) Curve. We demonstrated that the IGS (n = 37 genes) is conserved across PD GWAS studies and brain tissues. IGS discriminated between cases and controls in an independent whole-blood RNA-sequencing study (1176 PD, 254 prodromal, and 860 healthy controls) with mean AUC and accuracy of 64.8% and 69.4% for PD cohort, and 78.8% and 74% for prodromal cohort. PATL2 was the top-performing imputed gene in both PD and prodromal PD cohorts, whose classifier performance varied with biological sex (higher performance for males and females in the PD and prodromal PD, respectively). Single-cell RNA-sequencing studies (scRNA-seq) of healthy humans and PD patients found PATL2 to be enriched in terminal effector CD8+ and cytotoxic CD4+ cells, whose proportions are both increased in PD patients. We demonstrated the utility of GWAS transcriptomic imputation in identifying novel whole-blood transcriptomic signatures which could be leveraged upon for PD biomarker derivation. We identified PATL2 as a potential biomarker in both clinical and prodromic PD.

Identification novel mutations and phenotypic spectrum expanding in PATL2 in infertile women with IVF/ICSI failure

AIM

Abnormalities in oocyte maturation, fertilization, and early embryonic development are major causes of primary infertility in women who are undergoing IVF/ICSI attempts. Although many genetic factors responsible for these abnormal phenotypes have been identified, there are more additional pathogenic genes and variants yet to be discovered. Previous studies confirmed that bi-allelic PATL2 deficiency is an important factor for female infertility. In this study, 935 infertile patients with IVF/ICSI failure were selected for whole-exome sequencing, and 18 probands carrying PATL2 variants with a recessive inheritance pattern were identified.

METHODS

We estimated that the prevalence contributed by PATL2 was 1.93% (18/935) in our study cohort.

RESULTS

15 novel variants were found in those families, including c.1093C > T, c.1609dupA, c.1204C > T, c.643dupG, c.877-2A > G, c.1228C > G, c.925G > A, c.958G > A, c.4A > G, c.1258T > C, c.1337G > A, c.1264dupA, c.88G > T, c.1065-2A > G, and c.1271T > C. The amino acids altered by the corresponding variants were highly conserved in mammals, and in silico analysis and 3D molecular modeling suggested that the PATL2 mutants impaired the physiologic function of the resulting proteins. Diverse clinical phenotypes, including oocyte maturation defect, fertilization failure, and early embryonic arrest might result from different variants of PATL2.

CONCLUSIONS

These results expand the spectrum of PATL2 variants and provide an important reference for genetic counseling for female infertility, and they increase our understanding of the mechanisms of oocyte maturation arrest caused by PATL2 deficiency.

Reduced PATL2 Impairs the Proliferation of Ovarian Granulosa Cells by Decreasing ADM2 Expression in Patients with PCOS

It is recognized that PCOS patients are often accompanied with aberrant follicular development, which is an important factor leading to infertility in patients. However, the relevant regulatory mechanisms of abnormal follicular development are not well understood. In the present study, by collecting human ovarian granulosa cells (GCs) from PCOS patients who underwent in vitro fertilization (IVF), we found that the proliferation ability of GCs in PCOS patients was significantly reduced. Surprisingly, PATL2 and adrenomedullin 2 (ADM2) were obviously decreased in the GCs of PCOS patients. To further explore the potential roles of PATL2 and ADM2 on GC, we transfected PATL2 siRNA into KGN cells to knock down the expression of PATL2. The results showed that the growth of GCs remarkably repressed after knocking down the PATL2, and ADM2 expression was also weakened. Subsequently, to study the relationship between PATL2 and ADM2, we constructed PATL2 mutant plasmid lacking the PAT construct and transfected it into KGN cells. The cells showed the normal PATL2 expression, but attenuated ADM2 expression and impaired proliferative ability of GCs. Finally, the rat PCOS model experiments further confirmed our findings in KGN cells. In conclusion, our study suggests that PATL2 promoted the proliferation of ovarian GCs by stabilizing the expression of ADM2 through "PAT" structure, which is beneficial to follicular development, whereas, in the ovary with polycystic lesions, reduction of PATL2 could result in the decreased expression of ADM2, subsequently weakened the proliferation ability of GCs and finally led to the occurrence of aberrant follicles.

Predicting Infertility: How Genetic Variants in Oocyte Spindle Genes Affect Egg Quality

Successful reproduction relies on the union of a single chromosomally normal egg and sperm. Chromosomally normal eggs develop from precursor cells, called oocytes, that have undergone accurate chromosome segregation. The process of chromosome segregation is governed by the oocyte spindle, a unique cytoskeletal machine that splits chromatin content of the meiotically dividing oocyte. The oocyte spindle develops and functions in an idiosyncratic process, which is vulnerable to genetic variation in spindle-associated proteins. Human genetic variants in several spindle-associated proteins are associated with poor clinical fertility outcomes, suggesting that heritable etiologies for oocyte dysfunction leading to infertility exist and that the spindle is a crux for female fertility. This chapter examines the mammalian oocyte spindle through the lens of human genetic variation, covering the genes TUBB8, TACC3, CEP120, AURKA, AURKC, AURKB, BUB1B, and CDC20. Specifically, it explores how patient-identified variants perturb spindle development and function, and it links these molecular changes in the oocyte to their cognate clinical consequences, such as oocyte maturation arrest, elevated egg aneuploidy, primary ovarian insufficiency, and recurrent pregnancy loss. This discussion demonstrates that small genetic errors in oocyte meiosis can result in remarkably far-ranging embryonic consequences, and thus reveals the importance of the oocyte's fine machinery in sustaining life.

Identification of nonfunctional PABPC1L causing oocyte maturation abnormalities and early embryonic arrest in female primary infertility

Oocyte maturation arrest, fertilization failure, and early embryonic arrest are important causes of female infertility, whereas the genetic events that contribute to these processes are largely unknown. Loss-of-function of PABPC1L in mice has been suggested to cause female infertility involved in the absence of mature oocytes or embryos in vivo or in vitro. However, the role of PABPC1L in human female reproduction remains largely elusive. In this study, we identified a homozygous missense mutation (c.536G>A, p.R179Q) and a compound heterozygous mutation (c.793C>T, p.R265W; c.1201C>T, p.Q401*) in PABPC1L in two unrelated infertile females characterized by recurrent oocyte maturation abnormalities and early embryonic arrest. These variants resulted in nonfunctional PABPC1L protein and were associated with impaired chromatin configuration and transcriptional silencing in GV oocytes. Moreover, the binding capacity of mutant PABPC1L to mRNAs related to oocyte maturation and early embryonic development was decreased significantly. Our findings revealed novel PABPC1L mutations causing oocyte maturation abnormalities and early embryonic arrest, confirming the essential role of PABPC1L in human female fertility.

Homozygous variants in CDC23 cause female infertility characterized by oocyte maturation defects

Oocyte maturation defects are major phenotypes resulting in female infertility. Although many genetic factors have been found to be responsible for these phenotypes, the underlying pathogenic genes and variants remain to be identified. The anaphase promoting complex or cyclosome (APC/C) is known to be essential in the metaphase-to-anaphase transition. In this study, we identified two homozygous missense variants (c.986A > G, p.Y329C and c.988C > T, p.R330C) in CDC23 that are responsible for female infertility characterized by oocyte maturation defects in three infertile individuals. CDC23 (cell division cycle 23) is one of the core subunits of the APC/C. In vitro experiments showed that the variant c.986A > G (p.Y329C) led to a decrease in CDC23 protein level and the variant c.988C > T (p.R330C) changed the localization of CDC23 in HeLa cells and mouse oocytes. In vivo studies showed that Cdc23Y329C/Y329C mice successfully mimicked the patients' phenotype by causing low expression of CDC23 and APC4 and the accumulation of securin and cyclin B1 in oocytes. AZ3146 treatment was able to rescue the phenotype. Taken together, our findings reveal the important roles of CDC23 in human oocyte maturation and provide a new genetic marker for female infertility.

Dual trigger for final oocyte maturation in expected normal responders with a high immature oocyte rate: a randomized controlled trial

Objective

To evaluate whether dual trigger could improve reproductive outcomes in women with low oocyte maturation rates compare to human chorionic gonadotropin (hCG) trigger.

Methods

This study included expected normal ovarian responders younger than 40 years old whose immature oocyte rate in the previous cycle was more than 50% at the reproductive center from July 2021 to November 2022. A total of 73 patients were enrolled at trigger, including 34 in the hCG trigger group and 39 in the dual trigger group (co-administration of gonadotrophin releasing hormone (GnRH) agonist and hCG, 40 and 34 h prior to oocyte retrieval, respectively). The primary outcome was oocyte maturation rate.

Results

There was no significant difference in the number of oocytes retrieved between the two study groups, but the oocyte maturation rate was higher in dual trigger group (84.0% [14.0%] vs. 55.5% [19.8%], p < 0.001). Moreover, there were also higher cumulative pregnancy rate (69.4% vs. 40.0%, p = 0.035) and cumulative live birth rate (66.7% vs. 36.0%, p = 0.022) in dual trigger group.

Conclusion

For normal responders with low oocyte maturation rates, the dual trigger may be more effective than the conventional hCG trigger.

Clinical trial registration

ClinicalTrials.gov, identifier ChiCTR2100049292.

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.

Genetic variants underlying developmental arrests in human preimplantation embryos

Developmental arrest in preimplantation embryos is one of the major causes of assisted reproduction failure. It is briefly defined as a delay or a failure of embryonic development in producing viable embryos during ART cycles. Permanent or partial developmental arrest can be observed in the human embryos from one-cell to blastocyst stages. These arrests mainly arise from different molecular biological defects, including epigenetic disturbances, ART processes, and genetic variants. Embryonic arrests were found to be associated with a number of variants in the genes playing key roles in embryonic genome activation, mitotic divisions, subcortical maternal complex formation, maternal mRNA clearance, repairing DNA damage, transcriptional, and translational controls. In this review, the biological impacts of these variants are comprehensively evaluated in the light of existing studies. The creation of diagnostic gene panels and potential ways of preventing developmental arrests to obtain competent embryos are also discussed.

Biallelic variants in MAD2L1BP (p31comet) cause female infertility characterized by oocyte maturation arrest

Human oocyte maturation arrest represents one of the severe conditions for female patients with primary infertility. However, the genetic factors underlying this human disease remain largely unknown. The spindle assembly checkpoint (SAC) is an intricate surveillance mechanism that ensures accurate segregation of chromosomes throughout cell cycles. Once the kinetochores of chromosomes are correctly attached to bipolar spindles and the SAC is satisfied, the MAD2L1BP, best known as p31comet, binds mitosis arrest deficient 2 (MAD2) and recruits the AAA+-ATPase TRIP13 to disassemble the mitotic checkpoint complex (MCC), leading to the cell-cycle progression. In this study, by whole-exome sequencing (WES), we identified homozygous and compound heterozygous MAD2L1BP variants in three families with female patients diagnosed with primary infertility owing to oocyte metaphase I (MI) arrest. Functional studies revealed that the protein variants resulting from the C-terminal truncation of MAD2L1BP lost their binding ability to MAD2. cRNA microinjection of full-length or truncated MAD2L1BP uncovered their discordant roles in driving the extrusion of polar body 1 (PB1) in mouse oocytes. Furthermore, the patient's oocytes carrying the mutated MAD2L1BP resumed polar body extrusion (PBE) when rescued by microinjection of full-length MAD2L1BP cRNAs. Together, our studies identified and characterized novel biallelic variants in MAD2L1BP responsible for human oocyte maturation arrest at MI, and thus prompted new therapeutic avenues for curing female primary infertility.

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.

LSM14B is an Oocyte-Specific RNA-Binding Protein Indispensable for Maternal mRNA Metabolism and Oocyte Development in Mice

Mammalian oogenesis features reliance on the mRNAs produced and stored during early growth phase. These are essential for producing an oocyte competent to undergo meiotic maturation and embryogenesis later when oocytes are transcriptionally silent. The fate of maternal mRNAs hence ensures the success of oogenesis and the quality of the resulting eggs. Nevertheless, how the fate of maternal mRNAs is determined remains largely elusive. RNA-binding proteins (RBPs) are crucial regulators of oogenesis, yet the identity of the full complement of RBPs expressed in oocytes is unknown. Here, a global view of oocyte-expressed RBPs is presented: mRNA-interactome capture identifies 1396 RBPs in mouse oocytes. An analysis of one of these RBPs, LSM family member 14 (LSM14B), demonstrates that this RBP is specific to oocytes and associated with many networks essential for oogenesis. Deletion of Lsm14b results in female-specific infertility and a phenotype characterized by oocytes incompetent to complete meiosis and early embryogenesis. LSM14B serves as an interaction hub for proteins and mRNAs throughout oocyte development and regulates translation of a subset of its bound mRNAs. Therefore, RNP complexes tethered by LSM14B are found exclusively in oocytes and are essential for the control of maternal mRNA fate and oocyte development.

High carrier frequency of pathogenic PATL2 gene mutations predicted in population: a bioinformatics-based approach

Topoisomerase II homologue 2 (PATL2) has been confirmed to be a key gene that contributes to oocyte maturation. However, the allele distribution and carrier frequency of these mutations remain uncharacterized. So a bioinformatics subcategory analysis of PATL2 mutations from outcome data and Single Nucleotide Polymorphism (SNP) databases was conducted. Altogether, the causative PATL2 mutation number detected in patients with oocyte maturation defects in the clinical studies and pathogenic PATL2 mutation sites predicted by software based on the database was approximately 53. The estimated carrier frequency of pathogenic mutation sites was at least 1.14‰ based on the gnomAD and ExAC database, which was approximately 1/877. The highest frequency of mutations detected in the independent patients was c.223-14_223-2del13. The carrier frequency of this mutation in the population was 0.25‰, which may be a potential threat to fertility. Estimated allele and carrier frequency are relatively higher than those predicted previously based on clinical ascertainment. A review of PATL2 mutation lineage identified in 34 patients showed that 53.81%, 9.22% and 14.72% of the oocytes with PATL2 mutations were arrested at the germinal vesicle (GV) stage, metaphase I (MI) stage and first polar body stage, respectively. Oocytes that could develop to the first polar body stage were extremely rare to fertilise, and their ultimate fate was early embryonic arrest. Phenotypic variability is related to the function of the regions and degree of loss of function of PATL2 protein. A 3D protein structure changes predicted by online tools, AlphaFold, showed aberrations at the mutation sites, which may explain partially the function loss. When the mutated and wild-type proteins are not in the same amino acid category, the protein structure will be considerably unstable. The integration of additional mutation sites with phenotypes is helpful in drawing a complete picture of the disease. Bioinformatics analysis of PATL2 mutations will help reveal molecular epidemiological characteristics and provide an important reference for new mutation assessment, genetic counselling and drug research.

Understanding the genetics of human infertility

Reproduction involves a wide range of biological processes, including organ formation and development, neuroendocrine regulation, hormone production, and meiosis and mitosis. Infertility, the failure of reproduction, has become a major issue for human reproductive health and affects up to one in seven couples worldwide. Here, we review various aspects of human infertility, including etiology, mechanisms, and treatments, with a particular emphasis on genetics. We focus on gamete production and gamete quality, which is the core of successful reproduction. We also discuss future research opportunities and challenges to further expand our understanding of human infertility and improve patient care by providing precision diagnosis and personalized treatments.

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.

Large-scale analysis of de novo mutations identifies risk genes for female infertility characterized by oocyte and early embryo defects

BACKGROUND

Oocyte maturation arrest and early embryonic arrest are important reproductive phenotypes resulting in female infertility and cause the recurrent failure of assisted reproductive technology (ART). However, the genetic etiologies of these female infertility-related phenotypes are poorly understood. Previous studies have mainly focused on inherited mutations based on large pedigrees or consanguineous patients. However, the role of de novo mutations (DNMs) in these phenotypes remains to be elucidated.

RESULTS

To decipher the role of DNMs in ART failure and female infertility with oocyte and embryo defects, we explore the landscape of DNMs in 473 infertile parent-child trios and identify a set of 481 confident DNMs distributed in 474 genes. Gene ontology analysis reveals that the identified genes with DNMs are enriched in signaling pathways associated with female reproductive processes such as meiosis, embryonic development, and reproductive structure development. We perform functional assays on the effects of DNMs in a representative gene Tubulin Alpha 4a (TUBA4A), which shows the most significant enrichment of DNMs in the infertile parent-child trios. DNMs in TUBA4A disrupt the normal assembly of the microtubule network in HeLa cells, and microinjection of DNM TUBA4A cRNAs causes abnormalities in mouse oocyte maturation or embryo development, suggesting the pathogenic role of these DNMs in TUBA4A.

CONCLUSIONS

Our findings suggest novel genetic insights that DNMs contribute to female infertility with oocyte and embryo defects. This study also provides potential genetic markers and facilitates the genetic diagnosis of recurrent ART failure and female infertility.

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.

Remodeling of maternal mRNA through poly(A) tail orchestrates human oocyte-to-embryo transition

Poly(A)-tail-mediated post-transcriptional regulation of maternal mRNAs is vital in the oocyte-to-embryo transition (OET). Nothing is known about poly(A) tail dynamics during the human OET. Here, we show that poly(A) tail length and internal non-A residues are highly dynamic during the human OET, using poly(A)-inclusive RNA isoform sequencing (PAIso-seq). Unexpectedly, maternal mRNAs undergo global remodeling: after deadenylation or partial degradation into 3'-UTRs, they are re-polyadenylated to produce polyadenylated degradation intermediates, coinciding with massive incorporation of non-A residues, particularly internal long consecutive U residues, into the newly synthesized poly(A) tails. Moreover, TUT4 and TUT7 contribute to the incorporation of these U residues, BTG4-mediated deadenylation produces substrates for maternal mRNA re-polyadenylation, and TENT4A and TENT4B incorporate internal G residues. The maternal mRNA remodeling is further confirmed using PAIso-seq2. Importantly, maternal mRNA remodeling is essential for the first cleavage of human embryos. Together, these findings broaden our understanding of the post-transcriptional regulation of maternal mRNAs during the human OET.

Genetic screening and analysis of TUBB8 variants in females seeking ART

RESEARCH QUESTION

More than 100 variants have been identified in the TUBB8 gene, which account for approximately 30% of infertile women with oocyte maturation defects. But what is the correlation between the highly phenotypic diversity and genetic variability? Are there other variants in TUBB8 related to female infertility?

DESIGN

TUBB8 resequencing was performed in 80 female subjects who were experiencing infertility and were seeking treatment with assisted reproductive technologies (ART), or had ever experienced ART failure due to oocyte maturation defects. All variants were evaluated with pedigree analysis, population frequency, in-silico analysis and molecular modelling. The effects of the variants on oocytes/arrested embryos were assessed by morphological observations, immunostaining, embryo biopsies and chromosome euploidy analysis.

RESULTS

Nine missense variants and two frameshift variants from an additional 15 families were identified, including four novel variants and seven previously reported recurrent variants. These TUBB8 variants were related to highly variable phenotypes, including abnormalities in oocyte maturation or morphology, fertilization failure, embryonic development abnormalities and implantation failure. Also further clarified were the incomplete penetrance of heterozygous p.E108K, the likely benign significance of heterozygous p.A313V and the clinical effect of a novel variant of p.R380C.

CONCLUSIONS

This study significantly expands the variant spectrum of the TUBB8 gene and, together with the available findings on TUBB8 variants and female infertility, will potentially facilitate the genetic counselling of infertile women in future.

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.

MOS mutation causes female infertility with large polar body oocytes

The Moloney sarcoma oncogene (MOS) encodes a protein serine/threonine kinase and MOS is expressed at high levels in oocytes undergoing meiotic maturation. The MOS/MAPK pathway is normally required for the maintenance of microtubules and chromatin in a metaphasic state during the meiotic divisions. To determine the pathogenic genes in a female infertile patient due to large polar body oocytes, whole-exome sequencing was performed on the patient and available family members. We identified a novel homozygous missense mutation c.591T > G in MOS. Bioinformatics analysis showed that the mutation is harmful. These findings suggest that MOS mutation results in oocytes with a large polar body and poor embryonic development in patients. The MOS variant may regulate oocyte asymmetric division by MAPK/WAVE2/Arp2/3/actin signaling pathway. This will help to understand the comprehensive role of MOS in early human reproductive process and provide genetic markers for future genetic counseling for more individualized treatments.

Oocyte phenotype, genetic diagnosis, and clinical outcome in case of patients with oocyte maturation arrest

Background

oocyte maturation arrest (OMA) is currently one of the major causes of in vitro fertilization (IVF) failure, and several gene mutations were found to be associated with OMA. The purpose of this study was to identify the oocyte phenotype, genetic diagnosis, and clinical outcomes of patients with OMA and explore their possible interrelationships, thus providing a more individualized and efficient treatment strategy guidance accordingly.

Methods

A retrospective study was conducted, involving 28 infertile women with OMA in the Reproductive Medicine Center of Tongji Hospital from 2018 to 2021. Whole-exome sequencing was performed for the detection of gene mutations. Patients were classified into three groups based on their oocyte phenotype, and for each group, the immature oocytes were cultured in vitro and mature oocytes were fertilized to evaluate both the maturation capacity and developmental potential. The clinical outcomes of OMA patients with different gene mutations or from different groups were further analyzed and compared.

Results

Twenty-eight women with OMA were evaluated in this study. According to the stage of OMA, 14 (50.0%) women were classified as OMA Type-1 (GV arrest), 5 (17.9%) were OMA Type-2 (MI arrest), and 9 (32.1%) were OMA Type-3 (with both GV and MI arrest). Immature oocytes from OMA patients exhibited significantly lower maturation rates even after IVM, compared to those in general patients. Seven patients (25.0%) were detected to have deleterious variations in two genes (PATL2 and TUBB8), known to be associated with the OMA phenotype. Patients with identified mutations were found to have little opportunity to obtain offspring with their own oocytes. Among the patients without mutations identified, those classified as OMA Type-1 or Type-3 still had a chance to obtain offspring through IVF or natural pregnancy, while all patients in the Type-2 group failed to obtain live birth.

Conclusions

Three different phenotypes were observed in patients with OMA. The clinical outcomes of patients were associated with the presence of gene mutations and the classification of oocyte phenotype, thus a reasonable triage system was proposed to optimize the allocation of health care resources and maximize patient benefit.

The physiological and pathological mechanisms of early embryonic development

Early embryonic development is a complex process. The zygote undergoes several rounds of division to form a blastocyst, and during this process, the zygote undergoes the maternal-to-zygotic transition to gain control of embryonic development and makes two cell fate decisions to differentiate into an embryonic and two extra-embryonic lineages. With the use of new molecular biotechnologies and animal models, we can now further study the molecular mechanisms of early embryonic development and the pathological causes of early embryonic arrest. Here, we first summarize the known molecular regulatory mechanisms of early embryonic development in mice. Then we discuss the pathological factors leading to the early embryonic arrest. We hope that this review will give researchers a relatively complete view of the physiology and pathology of early embryonic development.

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.

Disrupted expression of long non-coding RNAs in the human oocyte: the possible epigenetic culprits leading to recurrent oocyte maturation arrest

PURPOSE

To depict the lncRNA expression during human oocyte maturation and explore the lncRNAs leading to recurrent oocyte maturation arrest.

METHODS

LncRNA sequencing was performed on pooled RNA from 20 oocytes of each group (recurrent oocyte maturation arrest (ROMA), of germinal vesicle (GV), metaphase I (MI), or metaphase II (MII) stages. Bioinformatics software was deployed to compare the lncRNA differential expression between the normal and ROMA oocytes. The co-expression of lncRNA/mRNA was illustrated with the Cytoscape software. The pooled RNA from every 10 oocytes of each group (ROMA, GV, MI, MII) was extracted for further qPCR validation.

RESULTS

There were 17 downregulated and 3 upregulated lncRNAs in the ROMA oocyte. Among them, co-expression analysis indicated that NEAT1 and NORAD were both downregulated. Basing on the KEGG enrichment analysis, PRCKA and JAK3 might be the target genes in the PI3K-Akt pathway and modulated by NEAT1 and NORAD. As validated by qPCR, the expressional levels of lncRNA candidates (NEAT1 and NORAD) and their target genes (PRKCA and JAK3) were confirmed to be extremely lower in the ROMA oocyte than in the normal oocyte.

CONCLUSION

By targeting the PI3K-Akt pathway genes PRKCA and JAK3, the abnormal expression of NEAT1 and NORAD is suggested to impede oocyte maturation and impair oocyte genome integrity.

Gene mutations impede oocyte maturation, fertilization, and early embryonic development

Reproductive diseases are a long-standing problem and have become more common in the world. Currently, 15% of the world's population suffers from infertility, and half of them are women. Maturation of oocytes, successful fertilization, and high-quality embryos are prerequisites for pregnancy. With the development of assisted reproductive technology and advanced genetic assays, we have found that infertility in many young female patients is caused by mutations in various developmental regulators. These pathogenic factors may result in impediment of oocyte maturation, failure of fertilization or early embryonic development arrest. In this review, we categorize these clinically-identified, mutated genetic factors by their molecular characteristics: nuclear factors (PALT2, TRIP13, WEE2, TBPL2, REC114, MEI1 and CDC20), cytoplasmic factors (TLE6, PADI6, NLRP2/5, FBXO43, MOS and BTG4), a factor unique to primates (TUBB8), cell membrane factor (PANX1), and zona pellucida factors (ZP1-3). We compared discrepancies observed in phenotypes between human and mouse models to provide clues for clinical diagnosis and treatment of related reproductive diseases.

Microtubule-severing protein Fidgetin-like 1 promotes spindle organization during meiosis of mouse oocytes

Microtubule-severing proteins (MTSPs) play important roles in mitosis and interphase. However, to the best of our knowledge, no previous studies have evaluated the role of MTSPs in female meiosis in mammals. It was found that FIGNL1, a member of MTSPs, was predominantly expressed in mouse oocytes and distributed at the spindle poles during meiosis in the present study. FIGNL1 was co-localized and interacted with γ-tubulin, an important component of the microtubule tissue centre (MTOC). Fignl1 knockdown by specific small interfering RNA caused spindle defects characterized by an abnormal length:width ratio and decreased microtubule density, which consequently led to aberrant chromosome arrangement, oocyte maturation and fertilization obstacles. In conclusion, the present results suggested that FIGNL1 may be an essential factor in oocyte maturation by influencing the meiosis process via the formation of spindles.

Heterozygous loss-of-function variants in LHX8 cause female infertility characterized by oocyte maturation arrest

PURPOSE

The genetic causes of oocyte maturation arrest leading to female infertility are largely unknown, and no population-based genetic analysis has been applied in cohorts of patients with infertility. We aimed to identify novel pathogenic genes causing oocyte maturation arrest by using a gene-based burden test.

METHODS

Through comparison of exome sequencing data from 716 females with infertility characterized by oocyte maturation arrest and 3539 controls, we performed a gene-based burden test and identified a novel pathogenic gene LHX8. Splicing event was evaluated using a minigene assay, expression of LHX8 protein was assessed in HeLa cells, and nuclear subcellular localization was determined in both HeLa cells and mouse oocytes.

RESULTS

A total of 5 heterozygous loss-of-function LHX8 variants were identified from 6 independent families (c.389+1G>T, c.412C>T [p.Arg138∗], c.282C>A [p.Cys94∗]; c.257dup [p.Tyr86∗]; and c.180del, [p.Ser61Profs∗30]). All the identified variants in LHX8 produced truncated LHX8 protein and resulted in loss of LHX8 nuclear localization in both HeLa cells and mouse oocytes.

CONCLUSION

By combining genetic evidence and functional evaluations, we identified a novel pathogenic gene LHX8 and established the causative relationship between LHX8 haploinsufficiency and female infertility characterized by oocyte maturation arrest.

Identification and characterization of a novel homozygous splice site variant of PATL2 causing female infertility due to oocyte germinal vesicle arrest

Background: This study aims to describe clinical and diagnostic phenotype and identify pathogenic variants of a female with unknown causes of infertility.

Methods: Clinical assessment was performed for the phenotype diagnosis. Whole-exome sequencing (WES) and the followed cDNA-PCR sequencing were applied to identify the pathogenic variant and investigate the potentially aberrant mRNA splicing event. The pathogenicity of the variant was analysed using multiple in silico prediction tools, including the 3D protein remodelling. Quantitative RT-PCR (qRT-PCR) was performed to measure PATL2 mRNA expression in the peripheral blood leukocytes of the proband and controls.

Results: The proband was diagnosed with the female infertility due to oocyte germinal vesicle (GV) arrest. A novel homozygous splice site variant of PATL2 (NM_001145112.2, c.871-1G&gt;A), inherited from her asymptomatic heterozygous parents, was detected by WES. Sequencing of cDNA amplification products demonstrated that this variant resulted in the exon 10 skipping and in-frame loss of 54 nucleotides in the PATL2 transcript. Quantitative RT-PCR suggested that the mutant transcript escape the mRNA degradation.

Conclusion: We identified a novel pathogenic homozygous splice site of PATL2 (c.871-1G&gt;A) underlying the oocyte GV arrest phenotype and elucidated its molecular mechanism. This study expands the variant spectrum of PATL2 and benefits our understanding of its genotype-phenotype correlations.

A novel heterozygous variant in PANX1 is associated with oocyte death and female infertility

PURPOSE

Oocyte death is a severe clinical phenotype that causes female infertility and recurrent in vitro fertilization and intracytoplasmic sperm injection failure. We aimed to identify pathogenic variants in a female infertility patient with oocyte death phenotype.

METHODS

Sanger sequencing was performed to screen PANX1 variants in the affected patient. Western blot analysis was used to check the effect of the variant on PANX1 glycosylation pattern in vitro.

RESULTS

We identified a novel PANX1 variant (NM_015368.4 c.86G > A, (p. Arg29Gln)) associated with the phenotype of oocyte death in a non-consanguineous family. This variant displayed an autosomal dominant inheritance pattern with reduced penetrance. Western blot analysis confirmed that the missense mutation of PANX1 (c.86G > A) altered the glycosylation pattern in HeLa cells. Moreover, the mutation effects on the function of PANX1 were weaker than recently reported variants.

CONCLUSION

Our findings expand the inheritance pattern of PANX1 variants to an autosomal dominant mode with reduced penetrance and enrich the variational spectrum of PANX1. These results help us to better understand the genetic basis of female infertility with oocyte death.

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.

Target-Sequencing of Female Infertility Pathogenic Gene Panel and a Novel TUBB8 Loss-of-Function Mutation

Genetic screening is an important approach for etiology determination and helps to optimize administration protocols in reproductive centers. After the first pathogenic gene of female infertility was reported in 2016, more and more new pathogenic genes were discovered, and we sought to develop an efficient and cost-effective method for genetic screening in patients. In this study, we designed a target-sequencing panel with 22 female infertility-related genes, namely, TUBB8, PATL2, WEE2, and PANX1 and sequenced 68 primary infertility (PI) and recurrent pregnancy loss (RPL) patients. We sequenced 68 samples reaching an average depth of 1559× and detected 3,134 variants. Among them, 62.2% were synonymous single-nucleotide variants (SNVs) and 36.3% were non-synonymous SNVs. The remaining 1.5% are indels (insertions and deletions) and stop-gains. DNAH11 and TUBB8 are the two genes that mutated most frequently. We also found a novel TUBB8 variant (c.898_900del; p.300_300del), proved its loss-of-function mechanism, and profiled the interactome of the wild-type (WT) and mutant TUBB8 proteins. Overall, this target-sequencing method provides an efficient and cost-effective approach for screening in IVF clinics and will support researchers for the discovery of new pathogenic variants.

A recurrent ZP1 variant is responsible for Oocyte Maturation Defect with degenerated oocytes in infertile females

A female factor is present in approximately 70% of couple infertility, often due to ovulatory disorders. In oocyte maturation defect (OMD), affected patients have a primary infertility with normal menstrual cycles but produce no oocyte, degenerated (atretic) or abnormal oocytes blocked at different stages of maturation. Four genes have so far been associated with OMD: PATL2, TUBB8, WEE2, and ZP1. In our initial study, 6 out of 23 OMD subjects were shown to carry the same PATL2 homozygous loss of function variant and one patient had a TUBB8 truncating variant. Here, we included four additional OMD patients and reanalyzed all 27 subjects. In addition to the seven patients with a previously identified defect, five carried the same deleterious homozygous ZP1 variant (c.1097G>A; p.Arg366Gln). All the oocytes from ZP1‐associated patients appeared shriveled and dark indicating that the abnormal ZP1 protein induced oocyte death and degeneration. Overall ZP1‐associated patients had degenerated or absent oocytes contrary to PATL2‐associated subjects who had immature oocytes blocked mainly at the germinal vesicle stage. In this cohort of North African OMD patients, whole exome sequencing permitted to diagnose 44% of the patients studied and to identify a new frequent ZP1 variant.

A proteomics approach identifies novel resident zebrafish Balbiani body proteins Cirbpa and Cirbpb

The Balbiani body (Bb) is the first marker of polarity in vertebrate oocytes. The Bb is a conserved structure found in diverse animals including insects, fish, amphibians, and mammals. During early zebrafish oogenesis, the Bb assembles as a transient aggregate of mRNA, proteins, and membrane-bound organelles at the presumptive vegetal side of the oocyte. As the early oocyte develops, the Bb appears to grow slowly, until at the end of stage I of oogenesis it disassembles and deposits its cargo of localized mRNAs and proteins. In fish and frogs, this cargo includes the germ plasm as well as gene products required to specify dorsal tissues of the future embryo. We demonstrate that the Bb is a stable, solid structure that forms a size exclusion barrier similar to other biological hydrogels. Despite its central role in oocyte polarity, little is known about the mechanism behind the Bb's action. Analysis of the few known protein components of the Bb is insufficient to explain how the Bb assembles, translocates, and disassembles. We isolated Bbs from zebrafish oocytes and performed mass spectrometry to define the Bb proteome. We successfully identified 77 proteins associated with the Bb sample, including known Bb proteins and novel RNA-binding proteins. In particular, we identified Cirbpa and Cirbpb, which have both an RNA-binding domain and a predicted self-aggregation domain. In stage I oocytes, Cirbpa and Cirbpb localize to the Bb rather than the nucleus (as in somatic cells), indicating that they may have a specialized function in the germ line. Both the RNA-binding domain and the self-aggregation domain are sufficient to localize to the Bb, suggesting that Cirbpa and Cirbpb interact with more than just their mRNA targets within the Bb. We propose that Cirbp proteins crosslink mRNA cargo and proteinaceous components of the Bb as it grows. Beyond Cirbpa and Cirbpb, our proteomics dataset presents many candidates for further study, making it a valuable resource for building a comprehensive mechanism for Bb function at a protein level.

Establishment of pluripotent stem cell line induced by PATL2 heterozygous mutation in patients with oocyte maturation defect-4

Oocyte maturation defect-4 (OOMD4) is an autosomal recessive disease characterized by oocyte maturation arrest. On chromosome 15q21, the PATL2 gene is mutated, resulting in OOMD4 in either a homozygous or compound heterozygous form. Herein, the peripheral blood mononuclear cells (PBMCs) were obtained from a female patient who was heterozygous for OOMD4 due to a PALT2 gene mutation. Then we obtained the induced pluripotent stem cell (iPSC) by using episomal vectors with transcription factors for reprogramming. The teratoma assay revealed that the iPSC line exhibited pluripotency with the ability to differentiate into three germ layers, namely ectoderm, mesoderm, and endoderm, with positive expression of their markers, such as TUJ, SMA, and AFP, respectively. Furthermore, a normal karyotype (46, XX) was observed. In this view, iPSCs can be a valuable tool for conducting extensive research on the OOMD4, establishing models, and identifying potential therapeutic targets.

Mutation analysis of the TUBB8 gene in primary infertile women with oocyte maturation arrest

Background

Oocyte maturation arrest at metaphase I leads to fertilization failure in humans. In early embryos, the tubulin beta 8 class VIII (TUBB8) encodes a β-tubulin isotype and aids in the assembling of the human oocyte spindle. Mutations in the TUBB8 potentially interfere with human oocyte maturation—a crucial prerequisite for fertilization and subsequent embryonic development. This study aims to investigate the novel mutations in TUBB8 and their prevalence.

Results

Hundred fertile women (controls) and eleven infertile women with oocyte maturation arrest were chosen for the study. A total of five TUBB8 heterozygous/homozygous mutations were found in eleven infertile females (p.A313V, p.C239W, p.R251Q, p.P358L, and p.G96R). The Exome Aggregation Consortium (ExAC), SIFT, and PolyPhen-2 analyses revealed that p. A313V has unknown pathogenicity and p.C239W, p.R251Q, p.P358L, and p.G96R have possible pathogenicity. The wild-type (WT) and four mutant gene constructs were transfected to Hela cells. The Western blot analysis indicates that the TUBB8 expression of the p.C239W, p.R251Q, and p.G96R mutations was significantly decreased than that of WT. The immunofluorescence assay showed that the Hela cells transfected with either p.C239W, p.R251Q, or p.G96R mutations exhibited the disrupted microtubule structure, revealing a significant difference in the organization of the microtubule network compared to the WT.

Conclusions

We identified three novel variants and two reported variants out of 11 infertile women with oocyte metaphase I arrest. According to the present data, TUBB8 gene variants account for 31.96% of all participants (109/341) with oocyte maturation arrest.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13048-022-00971-9.

Oocyte maturation abnormalities - A systematic review of the evidence and mechanisms in a rare but difficult to manage fertility pheneomina

A small proportion of infertile women experience repeated oocyte maturation abnormalities (OMAS). OMAS include degenerated and dysmorphic oocytes, empty follicle syndrome, oocyte maturation arrest (OMA), resistant ovary syndrome and maturation defects due to primary ovarian insufficiency. Genetic factors play an important role in OMAS but still need specifications. This review documents the spectrum of OMAS and to evaluate the multiple subtypes classified as OMAS. In this review, readers will be able to understand the oocyte maturation mechanism, gene expression and their regulation that lead to different subtypes of OMAs, and it will discuss the animal and human studies related to OMAS and lastly the treatment options for OMAs. Literature searches using PubMed, MEDLINE, Embase, National Institute for Health and Care Excellence were performed to identify articles written in English focusing on Oocyte Maturation Abnormalities by looking for the following relevant keywords. A search was made with the specified keywords and included books and documents, clinical trials, animal studies, human studies, meta-analysis, randomized controlled trials, reviews, systematic reviews and options written in english. The search detected 3,953 sources published from 1961 to 2021. After title and abstract screening for study type, duplicates and relevancy, 2,914 studies were excluded. The remaining 1,039 records were assessed for eligibility by full-text reading and 886 records were then excluded. Two hundred and twenty seven full-text articles and 0 book chapters from the database were selected for inclusion. Overall, 227 articles, one unpublished and one abstract paper were included in this final review. In this review study, OMAS were classified and extensively evaluatedand possible treatment options under the light of current information, present literature and ongoing studies. Either genetic studies or in vitro maturation studies that will be handled in the future will lead more informations to be reached and may make it possible to obtain pregnancies.

Molecular determinants of the meiotic arrests in mammalian oocytes at different stages of maturation

Mammalian oocytes undergo two rounds of developmental arrest during maturation: at the diplotene of the first meiotic prophase and metaphase of the second meiosis. These arrests are strictly regulated by follicular cells temporally producing the secondary messengers, cAMP and cGMP, and other factors to regulate maturation promoting factor (composed of cyclin B1 and cyclin-dependent kinase 1) levels in the oocytes. Out of these normally appearing developmental arrests, permanent arrests may occur in the oocytes at germinal vesicle (GV), metaphase I (MI), or metaphase II (MII) stage. This issue may arise from absence or altered expression of the oocyte-related genes playing key roles in nuclear and cytoplasmic maturation. Additionally, the assisted reproductive technology (ART) applications such as ovarian stimulation and in vitro culture conditions both of which harbor various types of chemical agents may contribute to forming the permanent arrests. In this review, the molecular determinants of developmental and permanent arrests occurring in the mammalian oocytes are comprehensively evaluated in the light of current knowledge. As number of permanently arrested oocytes at different stages is increasing in ART centers, potential approaches for inducing permanent arrests to obtain competent oocytes are discussed.

Novel mutations in NLRP5 and PATL2 cause female infertility characterized by primarily oocyte maturation abnormality and consequent early embryonic arrest

PURPOSE

This study aims to identify the genetic causes of 12 women with primary infertility characterized by primarily oocyte maturation abnormality and consequent early embryonic arrest.

METHODS

Genomic DNA was isolated from peripheral blood samples. Whole-exome sequencing was performed on the probands, and the identified variants were confirmed by Sanger sequencing. The pathogenicity of the identified variants on the protein was accessed in silico. And we used qRT-PCR to detect the possible effects of the novel mutation on the mRNA level of NLRP5.

RESULTS

A novel homozygous frameshift variant (p.V429Efs*30) in NLRP5 and compound heterozygous variants with a novel frameshift variant (p.A297Efs*20) and a recurrent variant (c. 223-14_223-2delCCCTCCTGTTCCA) in PATL2 were identified in two unrelated affected individuals. qRT-PCR showed an obvious decrease of the mutant NLRP5 mRNA. In addition, the truncated proteins of NLRP5 and PATL2 were predicted to be non-functional due to the deletion of the most or the whole region of the critical functional domain(s) respectively.

CONCLUSIONS

This study identified novel mutations in NLRP5 and PATL2, further expanding the mutational and phenotypic spectrum of both genes. This is the first report of the NLRP5 mutations that associates with oocyte maturation abnormality in humans.