Oocyte Maturation Arrest Research Articles

Homozygous missense variations of APC12 cause meiotic metaphase I arrest in oocytes and female infertility

Oocyte maturation arrest is a leading cause of female infertility. However, the genetic variables remain largely unknown. In oocytes, the activation of anaphase-promoting complex/cyclosome (APC/C) is a critical step in the transition from meiosis I to meiosis II. However, the causal relationship between variants in APC/C components and female infertility hasn't been completely investigated. This study aims to find a novel gene and its pathogenic mutation as a cause for metaphase I arrest in oocytes, thus introducing a new APC/C component for screening causes of female infertility. Whole-exome sequencing was performed on 30 infertile women with recurrent oocyte maturation arrest without known gene variants. A homozygous missense mutation in the APC12 gene (p.R8H) was identified as a candidate for oocyte metaphase I arrest in a consanguineous family member. The experiment was conducted in vitro with HEK293T cells and mouse oocytes. Methods such as oocyte microinjection, western blotting, co-immunoprecipitation, and immunofluorescence were used. A knockdown mouse model was generated to verify the function of Apc12 in causing oocyte metaphase I arrest. About 100 wild-type C57BL/6J mice and 50 gene-edited mice were used in this study. APC12 p.R8H was identified in an infertile woman with oocyte metaphase I arrest. Microinjection of Apc12 mutant cRNA in mouse oocytes caused a considerably higher rate of metaphase I stage arrest (65.21±5.64% vs. 30.86±1.74%, p<0.01) with decreased APC12 protein expression and Securin accumulation compared to the control group, while oocytes injected with Apc12 cRNA showed comparable metaphase I arrest rate (31.51±3.05%). This fit the phenotype we identified in our case and suggested that Apc12 p.R8H was a loss-of-function mutation leading to oocyte metaphase I arrest. The in-vitro experiments in HEK293T cells suggested that the APC12 p.R8H mutation disrupted the interaction between APC12 and APC6, as well as impaired APC/C activity by disrupting Securin ubiquitination. Knocking down APC12 with siRNA in mouse oocytes led to metaphase I arrest (41.65±6.10% vs. 24.20±2.19%, p<0.01). Oocytes from Apc12+/- mice exhibited metaphase I arrest compared with oocytes from wild-type mice (72.29±0.51% vs. 23.33±5.82%, p<0.01), which could be rescued by injecting Apc12 cRNA (53.44±1.20%). We identified a pathogenic mutation in APC12 in a female patient and confirmed its relevance as a causative factor for metaphase I arrest in oocytes, implying its importance as an APC/C component in the pathophysiology of oocyte maturation arrest, which caused female infertility.

COX15 deficiency causes oocyte ferroptosis

Mitochondria play diverse roles in mammalian physiology. The architecture, activity, and physiological functions of mitochondria in oocytes are largely different from those in somatic cells, but the mitochondrial proteins related to oocyte quality and reproductive longevity remain largely unknown. Here, using whole-exome sequencing data from 1,024 women (characterized by oocyte maturation arrest and degenerated or morphologically abnormal oocytes) and 2,868 healthy controls, we performed a population and gene-based burden test for mitochondrial genes and identified a candidate gene, cytochrome c oxidase assembly protein 15 (COX15). We report that biallelic COX15 pathogenic variants cause human oocyte ferroptosis and female infertility in a recessive inheritance pattern. COX15 variants impaired mitochondrial respiration in Saccharomyces cerevisiae and led to reduced protein levels in HeLa cells. Oocyte-specific deletion of Cox15 led to impaired Fe2+ and reactive oxygen species homeostasis that caused mitochondrial dysfunction and ultimately sensitized oocytes to ferroptosis. In addition, ferrostatin-1 (an inhibitor of ferroptosis) could rescue the oocyte ferroptosis phenotype in vitro and ex vivo. Our findings not only provide a genetic diagnostic marker for oocyte development defects but also expand the spectrum of mitochondrial disorders to female infertility and contribute to unique insights into the role of ferroptosis in human oocyte defects.

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

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

Flavopiridol inhibits oocyte maturation, reduces oocyte quality and blocks cumulus cell function

Flavopiridol (FP) is a plant-derived flavonoidis and used to treat cancers, fungal infections and inflammation-related diseases. However, it is not clear whether it has side effects on the female reproductive system. In this study, we aimed to investigate the toxic effects and potential underlying mechanisms of FP on oocyte maturation and cumulus cell expansion in mice. Cumulus-oocyte complexes (COCs) were cultured in vitro with FP of gradient concentration (50–1000 nM), according to the plasma concentration of FP in the clinical trial. The maturation rate and cumulus expansion index of oocytes were counted and studied by immunofluorescence staining, qRT-PCR, oocyte chromosome preparation and so on. The results showed that the FP-exposed COCs inhibited the oocyte maturation and cumulus cell expansion, leading to cell apoptosis in a dose dependent way. Oocytes exposed to 500 nM FP showed abnormalities in the spindle structure and chromosome arrangement, ultimately leading to the oocyte maturation arrest and aneuploidy. This may be due to the excessive oxidative stress caused by mitochondrial membrane potential damage and mislocalization. Therefore, when FP is used for cancer treatment, its side effects on the female reproductive system should be seriously considered.

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.

O-057 Newly identified female mutations causing failed fertilization

Abstract Over the past decade, advancements in next-generation sequencing technology, alongside reduced costs, and the rising demand for infertility medical care, have resulted in the discovery of new genes and genetic variants linked to infertility conditions. Phenotypes of ICSI failure, such as oocyte maturation arrest (OMA), fertilization failure (FF) and embryo developmental arrest (EDA), can now be attributed to male or female genetic causes. This represents a transformative shift in patient treatment, allowing the identification of some cases previously classified as unexplained infertility, thereby reducing patient stress. Moreover, it facilitates personalized treatment recommendations, as well as paves the way for the exploration of novel treatment options, thus expanding research opportunities. This talk will review the genetic causes of FF following ICSI, with the main focus on the newly identified female causes, as well as give an update on current diagnostic tests and treatment options for this infertility condition. FF after ICSI still occurs in 1-3% of ICSI cycles, primarily due to oocyte activation deficiency (OAD). Defects in the male PLCζ protein, responsible of inducing calcium oscillations during oocyte activation, have long been known as the leading cause of OAD. Recent discoveries have identified genetic variants in the male genes ACTL7A, ACTL9 and IQCN, which also reduce PLCζ protein content in sperm cells and thus, contribute to FF after ICSI. Additionally, for the first time in 2018, mutations in a female gene (WEE2) crucial for oocyte activation were identified. WEE2 is an oocyte kinase that acts downstream the calcium release during fertilization. Interestingly, genetic variants in other female genes, such as PATL2, TUBB8 and CDC20 associated mainly to OMA and TLE6 and NLRP5 associated mainly to EDA, have also been described to cause failed fertilization in some patients. Determining whether the deficiency lies in sperm- or oocyte-related genes is crucial for tailoring the most effective treatment for FF after ICSI. For sperm-related factors, assisted oocyte activation (AOA), which consists in the artificial induction of calcium oscillations using calcium ionophores, has proven highly beneficial. However, most patients with oocyte-factors do not benefit from AOA (e.g. patients with WEE2 variants). In this regard, wild-type cRNA injection of the defected protein has been shown to rescue fertilization. A more generalist approach, such as maternal spindle transfer, which consists in replacing poor-quality oocyte cytoplasm with healthy cytoplasm from a donor oocyte, represents a potential treatment for these patients, as recently demonstrated in infertile females with repeated IVF failures. Nevertheless, further research into the safety of these procedures is needed before clinical application, and for now, gamete donation should be considered when facing female-related FF.

P-506 Oocyte/zygote/embryo maturation arrest: a functional and clinical study expanding the phenotype of NOBOX variants

Abstract Study question Are pathogenic NOBOX variants causal for oocyte/zygote/embryo maturation arrest (OZEMA) and what is their molecular mechanism? Summary answer Expression analysis of NOBOX target genes indicates that the examined variants do not influence early folliculogenesis, suggesting a potential involvement in later developmental stages. What is known already Primary ovarian insufficiency (POI) affects around 1% of women under 40 with pathogenic variants in the transcription factor NOBOX being causal in 5-7% of cases. Historically, NOBOX has been linked to premature oocyte depletion. Functional studies in female Nobox knockout (-/-) mice reveal a substantial disruption in germ cell cyst breakdown. This disruption impairs the formation of primordial follicles and the subsequent transition from primordial to primary stages, leading to the early loss of all oocytes. Study design, size, duration Three OZEMA families are presented with two distinct NOBOX variants. A functional study is conducted to explore alterations in mRNA expression associated with the investigated NOBOX variants. Participants/materials, setting, methods Three infertile women with OZEMA underwent multiple in vitro fertilization cycles. Subsequent, exome analysis targeting fertility-related genes revealed the presence of distinct NOBOX variants. To assess their impact on NOBOX target gene expression, we generated mutant NOBOX expressing plasmids via site-directed mutagenesis and transfected them into HEK293T cells. The expression of known NOBOX target genes was monitored by RT-qPCR. Main results and the role of chance We examined three families affected by OZEMA, in which the affected women were heterozygous for NOBOX variants. In one family, we found a heterozygous paternally inherited NM_001080413.3(NOBOX): c.1797_1798delCT, p.(Arg600Aspfs*6) variant in a female with oocyte maturation arrest. In two other families, a heterozygous probably pathogenic paternally inherited NM_001080413.3(NOBOX): c.1849C&amp;gt;T, p.(His617Tyr) variant was detected in females experiencing embryo maturation arrest. Analysis of NOBOX target genes in HEK293T cells revealed that both variants had no impact on the mRNA expression of MOS and OCT4, both of which are implicated in early folliculogenisis. Since both MOS and OCT4 are implicated in earlier folliculogenesis stages, this supports that NOBOX might also be implicated in later stages. Contrastingly, a known pathogenic NOBOX variant, used as a positive control, showed decreased MOS and OCT4 expression. Limitations, reasons for caution Verification of our findings is necessary, given that this is the first report of NOBOX variants in individuals with OZEMA. The precise molecular mechanism underlying OZEMA remains undisclosed at this stage. These results warrant the need of genome-wide mRNASeq to confirm and expand our findings. Wider implications of the findings Since NOBOX pathogenic variants are typically linked to POI, our findings suggest a broader clinical impact, where NOBOX plays a role in oocyte maturation and early embryo development. Hence, the investigation of NOBOX variants is advisable for individuals diagnosed with OZEMA. Trial registration number Not applicable

Follicular fluid-derived exosomal LncRNA LIPE-AS1 modulates steroid metabolism and survival of granulosa cells leading to oocyte maturation arrest in polycystic ovary syndrome.

Women who are of reproductive age can suffer from polycystic ovary syndrome (PCOS), an endocrine disorder. Anovulatory infertility is mostly caused by aberrant follicular development, which is seen in PCOS patients. Due to the dysfunction of reproductive and endocrine function in PCOS patients, assisted reproduction treatment is one of the main means to obtain clinical pregnancy for PCOS patients. Long non-coding RNA (lncRNA) as a group of functional RNA molecules have been found to participate in the regulation of oocyte function, hormone metabolism, and proliferation and apoptosis of granulosa cells. In this study, we investigated the role of lncRNAs in follicular fluid-derived exosomes and the underlying mechanism of lncRNA LIPE-AS1. We used RNA sequencing to analyze the lncRNA profiles of follicular fluid-derived exosomes in PCOS patients and controls. RT-qPCR was performed to detect the expression levels of these lncRNAs in control (n = 30) and PCOS (n = 30) FF exosome samples. Furthermore, we validated the performance of lncRNA LIPE-AS1 in oocyte maturation by in vitro maturation (IVM) experiments in mouse and steroid metabolism in granulosa cells. We found 501 lncRNAs were exclusively expressed in the control group and another 273 lncRNAs were found to be specifically expressed in the PCOS group. LncRNA LIPE-AS1, highly expressed in PCOS exosomes, was related to a poor oocyte maturation and embryo development in PCOS patients. Reduced number of MII oocytes were observed in the LIPE-AS1 group by in vitro maturation (IVM) experiments in mouse. LIPE-AS1 was also shown to modulate steroid metabolism and granulosa cell proliferation and apoptosis by LIPE-AS1/miR-4306/LHCGR axis. These findings suggested that the increased expression of LIPE-AS1, facilitated by follicular fluid exosomes, had a significant impact on both oocyte maturation and embryo development. We demonstrated the ceRNA mechanism involving LIPE-AS1, miR-4306, and LHCGR as a regulator of hormone production and metabolism. These findings indicate that LIPE-AS1 is essential in PCOS oocyte maturation and revealed a ceRNA network of LIPE-AS1 and provided new information on abnormal steroid metabolism and oocyte development in PCOS.

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

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

Pathogenic missense variation in PABPC1L/EPAB causes female infertility due to oocyte maturation arrest at the germinal vesicle stage.

Women undergoing controlled ovarian hyperstimulation prior to in vitro fertilization (IVF) are treated using various protocols to induce multiple follicular growths. Complete failure of all oocytes to mature during IVF cycles is rare; however, it is a known cause of primary female infertility. Recently, pathogenic variations in a few genes have been identified in women with oocyte maturation defects; however, the underlying genetic causes remain largely unknown.This study included a Turkish family comprising three sisters with recurring oocyte maturation arrest at the germinal vesicle stage after multiple ovarian stimulations. Exome sequencing revealed a homozygous missense variant (c.1037C>T, p.Ala346Val) in the EPAB gene (also known as PABPC1L) in all three affected sisters, which was either absent or heterozygous in the unaffected family members. Functional experiments confirming the pathogenicity of the variant were performed by transfecting HEK293T cells and demonstrated the instability and increased rate of proteolysis of the mutated PABPC1L/EPAB protein. The identified variant, located in the well-conserved fourth RNA recognition motif (RRM4), in silico 3D modelling suggested changes in the physical properties of the pathogenic variant of PABPC1L/EPAB.Our findings validate PABPC1L/EPAB as an essential genetic contributor to the oocyte maturation process in humans and have direct implications for the genetic counselling of patients and their family members.

Global crotonylome identifies EP300-regulated ANXA2 crotonylation in cumulus cells as a regulator of oocyte maturation

Lysine crotonylation (Kcr), a newly discovered post-translational modification, played a crucial role in physiology and disease progression. However, the roles of crotonylation in oocyte meiotic resumption remain elusive. As abnormal cumulus cell development will cause oocyte maturation arrest and female infertility, we report that cumulus cells surrounding human meiotic arrested oocytes showed significantly lower crotonylation, which was associated with decreased EP300 expression and blocked cumulus cell expansion. In cultured human cumulus cells, exogenous crotonylation or EP300 activator promoted cell proliferation and reduced cell apoptosis, whereas EP300 knockdown induced the opposite effect. Transcriptome profiling analysis in human cumulus cells indicated that functions of crotonylation were associated with activation of epidermal growth factor receptor (EGFR) pathway. Importantly, we characterized the Kcr proteomics landscape in cumulus cells by LC-MS/MS analysis, and identified that annexin A2 (ANXA2) was crotonylated in cumulus cells in an EP300-dependent manner. Crotonylation of ANXA2 enhanced the ANXA2-EGFR binding, and then activated the EGFR pathway to affect cumulus cell proliferation and apoptosis. Using mouse oocytes IVM model and EP300 knockout mice, we further confirmed that crotonylation alteration in cumulus cells affected the oocyte maturation. Together, our results indicated that EP300-mediated crotonylation is important for cumulus cells functions and oocyte maturation.

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.

Novel variants in TUBB8 gene cause multiple phenotypic abnormalities in human oocytes and early embryos

BackgroundThe genotype-phenotype relationships between TUBB8 variants and female infertility are difficult to clearly define due to the complex inheritance patterns and the highly heterogeneous phenotypes. This study aims to identify novel TUBB8 variants and relevant phenotypes in more infertile females.MethodsA total of 35 females with primary infertility were recruited from two reproductive centers and investigated for identifying variants in TUBB8. Pedigree analysis, in-silico analysis and molecular remodeling were performed to assess their clinical significance. The effects of the variants on human oocytes and embryos as well as HeLa cells were analyzed by morphological observations, immunostaining and Western blot.ResultsWe totally identified five novel variants (p.G13R, p.Y50C, p.T136I, p.F265V and p.T366A) and five previously reported variants (p.I4L, p.L42V, p.Q134*, p.V255M and p.V349I) in TUBB8 from 9 unrelated females with primary infertility. These variants were rare and highly conserved among different species, and were inherited in autosomal dominant/recessive patterns, or occurred de novo. In vitro functional assays in HeLa cells revealed that exogenous expression of mutant TUBB8 proteins caused different degrees of microtubule structural disruption. The existence of these pathogenic TUBB8 variants finally induced oocyte maturation arrest or morphological abnormalities, fertilization failure, cleavage failure, embryonic development defects and implantation failure in the affected females.ConclusionThese findings enriched the variant spectrum of TUBB8 gene and could contribute to optimize genetic counselling and clinical management of females with primary infertility.

Phenotypic variability in two female siblings with oocyte maturation arrest due to a TUBB8 variant

Tubulin beta-8 (TUBB8) is expressed exclusively in the oocyte and early embryo, encoding a beta-tubulin polypeptide that participates in the assembly of microtubules. TUBB8 was first attributed to being responsible for oocyte MI arrest. Further studies have demonstrated that patients with different pathogenic variants have variable phenotypes. We report a TUBB8 variant (c.10 A > C) in two siblings who presented different clinical features of primary infertility. The younger sister showed severe oocyte maturation arrest with abnormal morphology, whereas a few mature oocytes and zygotes could be retrieved from the older sister, but no embryo was available for transfer. This variant was previously reported without in vitro functional assays. In the present study, RT‒qPCR and western blot analyses revealed that c.10 A > C reduces TUBB8 mRNA and protein levels; however, immunofluorescence demonstrated that this variant does not change the localization of the protein. These findings confirm the pathogenicity of the c.10 A > C variant and support the relationship between the variant and phenotype in the patients.

Butylparaben weakens female fertility via causing oocyte meiotic arrest and fertilization failure in mice

Butylparaben is an ubiquitous environmental endocrine disruptor, that is commonly used in cosmetics and personal care product due to its anti-microbial properties. Butylparaben has been shown to cause developmental toxicity, endocrine and metabolic disorders and immune diseases. However, little is known about the impact on female fertility, especially oocyte quality. In the present study, we reported that butylparaben influenced female fertility by showing the disturbed oocyte meiotic capacity and fertilization potential. Specifically, butylparaben results in the oocyte maturation arrest by impairing spindle/chromosome structure and microtubule stability. Besides, butylparaben results in fertilization failure by impairing the dynamics of Juno and ovastacin and the sperm binding ability. Last, single-cell transcriptome analysis showed that butylparaben-induced oocyte deterioration was caused by mitochondrial dysfunction, which led to the accumulation of ROS and occurrence of apoptosis. Collectively, our study indicates that mitochondrial dysfunction and redox perturbation is the major cause of the weakened female fertility expoesd to butylparaben.

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.

Mutations in CCNB3 affect its location thus causing a multiplicity of phenotypes in human oocytes maturation by aberrant CDK1 activity and APC/C activity at different stages

BackgroundOocyte maturation arrest results in female infertility and the genetic etiology of this phenotype remains largely unknown. Previous studies have proven that cyclins play a significant role in the cell cycle both in meiosis and mitosis. Cyclin B3 (CCNB3) is one of the members of the cyclin family and its function in human oocyte maturation is poorly understood.Methods118 infertile patients were recruited and WES was performed for 68 independent females that experienced oocyte maturation arrest. Four mutations in CCNB3 were found and effects of these mutations were validated by Sanger sequencing and in vitro functional analyses.ResultsWe found these mutations altered the location of cyclin B3 which affected the function of cyclin dependent kinase 1 (CDK1) and led to mouse oocyte arrested at germinal vesicle (GV) stage. And then, low CDK1 activity influenced the degradation of cadherin 1 (CDH1) and the accumulation of cell division cycle 20 (CDC20) which are two types of anaphase-promoting complex/cyclosome (APC/C) activators and act in different stages of the cell cycle. Finally, APC/C activity was downregulated due to insufficient CDC20 level and resulted in oocyte metaphase I (MI) arrest. Moreover, we also found that the addition of PP1 inhibitor Okadic acid and CDK1 inhibitor Roscovitine at corresponding stages during oocyte in vitro maturation (IVM) significantly improved the maturation rates in CCNB3 mutant cRNAs injected oocytes. The above experiments were performed in mouse oocytes.ConclusionHere, we report five independent patients in which mutations in CCNB3 may be the cause of oocyte maturation arrest. Our findings shed lights on the critical role of CCNB3 in human oocyte maturation.

O-304 Whole-exome sequencing in women with reproductive failure is a potentially useful diagnostic test in clinical practice

Abstract Study question Could whole-exome sequencing (WES) be useful in clinical practice for primary infertile female involving oocyte or embryo defects and unexplained recurrent miscarriage (RM) patients? Summary answer Identifying key genes involved in oocyte and embryo development helps explain approximately 17% cases of reproductive failure. WES results will help optimize clinical therapeutic treatment. What is known already Dozens of genes have been reported to be the genetic causes of human infertility. Variants in these genes have specific effects on certain processes of human early reproduction and result in a spectrum of phenotypes, such as oocyte maturation arrest, fertilization defects, cleavage failure, early embryonic lethality, and recurrent miscarriage. Study design, size, duration This retrospective cohort study was conducted from July 2020 to August 2022. A total of 129 affected females were enrolled. Most of them were primary infertile women who suffered repeated failure of in vitro fertilization (≥2 cycles) due to abnormal development of oocytes or embryos (PI group, n = 125). Our cohort also comprised a small number of unexplained RM subjects without offspring (RM group, n = 4). All patients and their spouses had normal karyotype. Participants/materials, setting, methods The peripheral blood samples from all the participants and all of their available family members were obtained for DNA extraction. Genomic DNA samples from the probands were subjected to WES to identify candidate variants. Subsequently, the variants were validated by Sanger sequencing or qPCR. Familial co-segregation analyses were then carried out within the family members. The relationship between phenotype and genotype by clinical tests and the clinical records of the patients was studied. Main results and the role of chance Firstly, variants that are potentially relevant to the phenotypes of female infertility were identified in 17.05% of cases (n = 22), including TUBB8 in 14 cases, PATL2 in 2 cases, ZP2, ZP3, PANX1, TLE6, NLRP2 and NLRP7 in 1 case for each. A breakdown by phenotype revealed that we identified variants in 16.00% (n = 20) of PI group and 50% (n = 2) of RM group. Secondly, 16 TUBB8 variants were identified in 14 cases, of which 8 were novel, 3 were previously reported, and 5 were novel amino acid change occurring at the same position as another previously reported change. We found 3 TUBB8 variants (p.C211R, p.T232I, p.A342T) in 3 embryonic arrest families and 1 TUBB8 mutation (p.A102V) in a RM family, which were maternally inherited. Thirdly, 75 patients in PI group without phenotypic variant underwent ≥1 cycles of ovulation and/or frozen embryo transfer after WES, and 49.33% had achieved clinical pregnancy (n = 37). Limitations, reasons for caution The genomic DNA of parents were not available in all these 22 families, so we cannot determine whether the variant is de novo or inherited in some cases. Additionally, further functional studies should be performed to prove that these novel mutations affect protein function. Wider implications of the findings The present study expands the kinds of variants and phenotypic spectrum of gene mutations with regard to female reproductive failure. Genetic tests for causative genes involved in oocyte and embryo defects were recommended for primary infertile patients who suffered from these conditions and for unexplained RM patients. Trial registration number not applicable

Novel mutations in TRIP13 lead to female infertility with oocyte maturation arrest.

Oocyte maturation arrest (OMA) refers to a rare clinical phenomenon of oocyte maturation disorder caused by abnormal meiosis, which is also one of the primary causes of female infertility. The clinical manifestations of these patients are often characterized with failure to obtain mature oocytes after repeated ovulation stimulation and/or induced in vitro maturation. To date, mutations in PATL2, TUBB8 and TRIP13 have been demonstrated to be associated with OMA, but studies on the genetic-based factors and mechanisms of OMA are still incomplete. In this study, peripheral blood from 35 primary infertile women characterized with recurrent OMA during assisted reproductive technology (ART) were subjected to whole-exome sequencing (WES). By using Sanger sequencing and co-segregated analysis, we identified four pathogenic variants in TRIP13. Proband 1 had a homozygous missense mutation of c.859A>G appeared on the 9th exon, which resulted in substitution of Ile287 to valine (p.Ile287Val); proband 2 had a homozygous missense mutation of c.77A>G on the 1st exon, which resulted in substitution of His26 to arginine (p.His26Arg); and proband 3 had compound heterozygous mutations of c.409G>A and c.1150A>G on the 4th and 12th exon, which resulted in the substitutions of Asp137 to asparagine (p.Asp137Asn) and Ser384 to glycine (p.Ser384Gly) in the encoded protein respectively. Three of these mutations have not been reported previously. Further, transfection of plasmids harboring the respective mutated TRIP13 in HeLa cells resulted in changes in TRIP13 expression and abnormal cell proliferation as demonstrated by western blotting and cell proliferation assay respectively. This study further summarizes the TRIP13 mutations reported previously and expands the mutation spectrum of TRIP13 pathogenic variants, thereby providing a valuable reference for further research on the pathogenic mechanism of OMA associated with TRIP13 mutations.

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.