Bi-allelic mutations in MOS cause female infertility characterized by preimplantation embryonic arrest

Bi-allelic missense variants in MEI4 cause preimplantation embryonic arrest and female infertility

Preimplantation embryonic arrest is an important pathogenesis of female infertility, but little is known about the genetic factors behind this phenotype. MEI4 is an essential protein for DNA double-strand break formation during meiosis, and Mei4 knock-out female mice are viable but sterile, indicating that MEI4 plays a crucial role in reproduction. To date, MEI4 has not been found to be associated with any human reproductive diseases. Here, we identified six compound heterozygous and homozygous MEI4 variants-namely, c.293C > T, p.(Ser98Leu), c.401C > G, p.(Pro134Arg), c.391C > G, p.(Pro131Ala), c.914A > T, p.(Tyr305Phe), c.908C > G, p.(Ala303Gly), and c.899A > T, p.(Gln300Leu)-in four independent families that were responsible for female infertility mainly characterized by preimplantation embryonic arrest. In vitro, we found that these variants reduced the interaction between MEI4 and DNA. In vivo, we generated a knock-in mouse model and demonstrated that female mice were infertile and were characterized by developmental defects during oogenesis. Our findings reveal the important roles of MEI4 in human reproduction and provide a new diagnostic marker for genetic counseling of clinical infertility patients.

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.

Evolution of tissue-specific expression of ancestral genes across vertebrates and insects

Regulation of gene expression is arguably the main mechanism underlying the phenotypic diversity of tissues within and between species. Here we assembled an extensive transcriptomic dataset covering 8 tissues across 20 bilaterian species and performed analyses using a symmetric phylogeny that allowed the combined and parallel investigation of gene expression evolution between vertebrates and insects. We specifically focused on widely conserved ancestral genes, identifying strong cores of pan-bilaterian tissue-specific genes and even larger groups that diverged to define vertebrate and insect tissues. Systematic inferences of tissue-specificity gains and losses show that nearly half of all ancestral genes have been recruited into tissue-specific transcriptomes. This occurred during both ancient and, especially, recent bilaterian evolution, with several gains being associated with the emergence of unique phenotypes (for example, novel cell types). Such pervasive evolution of tissue specificity was linked to gene duplication coupled with expression specialization of one of the copies, revealing an unappreciated prolonged effect of whole-genome duplications on recent vertebrate evolution.

Mitochondrial deoxyguanosine kinase is required for female fertility in mice

Mitochondrial homeostasis plays a pivotal role in oocyte maturation and embryonic development. Deoxyguanosine kinase (DGUOK) is a nucleoside kinase that salvages purine nucleosides in mitochondria and is critical for mitochondrial DNA replication and homeostasis in non-proliferating cells. Dguok loss-of-function mutations and deletions lead to hepatocerebral mitochondrial DNA deletion syndrome. However, its potential role in reproduction remains largely unknown. In this study, we find that Dguok knockout results in female infertility. Mechanistically, DGUOK deficiency hinders ovarian development and oocyte maturation. Moreover, DGUOK deficiency in oocytes causes a significant reduction in mitochondrial DNA copy number and abnormal mitochondrial dynamics and impairs germinal vesicle breakdown. Only few DGUOK-deficient oocytes can extrude their first polar body during in vitro maturation, and these oocytes exhibit irregular chromosome arrangements and different spindle lengths. In addition, DGUOK deficiency elevates reactive oxygen species levels and accelerates oocyte apoptosis. Our findings reveal novel physiological roles for the mitochondrial nucleoside salvage pathway in oocyte maturation and implicate DGUOK as a potential marker for the diagnosis of female infertility.

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

BACKGROUND

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

OBJECTIVE AND RATIONALE

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

SEARCH METHODS

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

OUTCOMES

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

WIDER IMPLICATIONS

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

NLRP14 deficiency causes female infertility with oocyte maturation defects and early embryonic arrest by impairing cytoplasmic UHRF1 abundance

Oocyte maturation is vital to attain full competence required for fertilization and embryogenesis. NLRP14 is preferentially expressed in mammalian oocytes and early embryos. Yet, the role and molecular mechanism of NLRP14 in oocyte maturation and early embryogenesis are poorly understood, and whether NLRP14 deficiency accounts for human infertility is unknown. Here, we found that maternal loss of Nlrp14 resulted in sterility with oocyte maturation defects and early embryonic arrest (EEA). Nlrp14 ablation compromised oocyte competence due to impaired cytoplasmic and nuclear maturation. Importantly, we revealed that NLRP14 maintained cytoplasmic UHRF1 abundance by protecting it from proteasome-dependent degradation and anchoring it from nuclear translocation in the oocyte. Furthermore, we identified compound heterozygous NLRP14 variants in women affected by infertility with EEA, which interrupted the NLRP14-UHRF1 interaction and decreased UHRF1 levels. Our data demonstrate NLRP14 as a cytoplasm-specific regulator of UHRF1 during oocyte maturation, providing insights into genetic diagnosis for female infertility.

Cordycepin delays postovulatory aging of oocytes through inhibition of maternal mRNAs degradation via DCP1A polyadenylation suppression

Postovulatory aging leads to the decline in oocyte quality and subsequent impairment of embryonic development, thereby reducing the success rate of assisted reproductive technology (ART). Potential preventative strategies preventing oocytes from aging and the associated underlying mechanisms warrant investigation. In this study, we identified that cordycepin, a natural nucleoside analogue, promoted the quality of oocytes aging in vitro, as indicated by reduced oocyte fragmentation, improved spindle/chromosomes morphology and mitochondrial function, as well as increased embryonic developmental competence. Proteomic and RNA sequencing analyses revealed that cordycepin inhibited the degradation of several crucial maternal proteins and mRNAs caused by aging. Strikingly, cordycepin was found to suppress the elevation of DCP1A protein by inhibiting polyadenylation during postovulatory aging, consequently impeding the decapping of maternal mRNAs. In humans, the increased degradation of DCP1A and total mRNA during postovulatory aging was also inhibited by cordycepin. Collectively, our findings demonstrate that cordycepin prevents postovulatory aging of mammalian oocytes by inhibition of maternal mRNAs degradation via suppressing polyadenylation of DCP1A mRNA, thereby promoting oocyte developmental competence.

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.

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.

Mutations in OOEP and NLRP5 identified in infertile patients with early embryonic arrest

The subcortical maternal complex (SCMC), composed of several maternal-effect genes, is vital for the development of oocytes and early embryos. Variants of SCMC-encoding genes (NLRP2, NLRP5, TLE6, PADI6, and KHDC3L, but not OOEP and ZBED3) are associated with human oocyte maturation dysfunction, fertilization failure, and early embryonic arrest. In this study, we enrolled 118 Chinese patients who experienced recurrent preimplantation embryonic arrest during assisted reproductive technology treatments and performed whole-exome sequencing. We discovered compound heterozygous missense variants (c.110G>C and c.109C>G) in the OOEP gene in one patient who experienced recurrent preimplantation embryonic arrest. Arrested embryos from this affected patient were analyzed by single-cell RNA sequencing, which showed a downregulated transcriptome. In addition, six novel NLRP5 variants (c.971T>A, c.3341T>C, c.1575_1576delAG, c.1830_1831delGT, c.1202C>T, and c.2378T>G) were identified in four patients with arrested and severely fragmented embryos. These suspicious mutations were examined by in vitro studies in HEK293T cells. Western blot analysis and immunofluorescence experiments showed that OOEP and partial NLRP5 mutations caused decreased protein levels. Our findings first demonstrated that biallelic variants in OOEP gene could also cause human early embryonic arrest, similar to other SCMC components. We expanded the genetic mutation spectrum of SCMC genes related to early embryogenesis in humans, especially early embryonic arrest.

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.

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.

A novel variant in TLE6 is associated with embryonic developmental arrest (EDA) in familial female infertility

This study aims to identify genetic causes of familial female infertility characterized by embryonic developmental arrest (EDA) and repeated implantation failure (RIF) with oocyte donation IVF cycle. We used Whole-exome sequencing and Sanger validation to find causative genes in an Iranian consanguineous family that had 3 infertile daughters, 4 fertile daughters, and 2 fertile sons. All patients in this consanguineous family exhibited typical manifestations of unexplained RIF and EDA. Genetic analysis identified a homozygous missense variant (c.G1054C:p.G352R) in exon 13 of the TLE6 gene that cosegregated with the EDA phenotype in an autosomal recessive pattern. Other members of the family, the gene carriers, remain clinically asymptomatic and fertile. Our findings identify a novel nonsynonymous variant, c.G1054C:p.G352R, in the TLE6 gene within a consanguineous Iranian family with autosomal-recessive female infertility and broaden the genetic spectrum of TLE6-associated EDA.

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.

Biallelic variants in MOS cause large polar body in oocyte and human female infertility

STUDY QUESTION

What is the genetic basis of female infertility involving abnormal oocyte morphology with the production of a large first polar body (PB1)?

SUMMARY ANSWER

The homozygous missense variant (c.791C>G) and compound missense variants (c.596A>T and c.875C>T) in MOS proto-oncogene, serine/threonine kinase (MOS) (Online Mendelian Inheritance in Man (OMIM) reference: 190060; NM_005372.1) are responsible for abnormal oocyte morphology with the production of a large PB1 to cause infertility in women.

WHAT IS KNOWN ALREADY

MOS, an oocyte-specific gene, encodes a serine/threonine-protein kinase that directly phosphorylates mitogen-activated protein kinase (MAPK) kinase (MEK) to activate MAPK (also called extracellular-signal-regulated kinase (ERK)) signal cascade in the oocyte. Female mice lacking Mos remained viable, but infertile because of oocyte symmetric division, spontaneous parthenogenetic activation and early embryonic arrest. Recently, two independent studies demonstrated that female infertility with early embryonic arrest and fragmentation can be caused by biallelic mutations in MOS. However, so far, MOS variants have not been associated with the phenotype of large PB1 extrusion in human oocytes to contribute to female infertility.

STUDY DESIGN, SIZE, DURATION

Two independent infertile families characterized by the presence of large PB1 in oocytes were recruited between December 2020 and February 2022.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Genomic DNA was extracted from the peripheral blood samples of the subjects for whole-exome sequencing. Pedigree analysis was validated by Sanger sequencing. Then, the pathogenic effects of the MOS variants on MOS protein properties and ERK1/2 activation were determined in HEK293 cells and mouse oocytes.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified three rare missense variants in MOS, including a homozygous missense variant (c.791C>G) from Patient 1 in Family 1 and two compound missense variants (c.596A>T and c.875C>T) from twin sisters in Family 2. The MOS variants followed a recessive inheritance pattern in infertile patients. All three patients displayed a high percentage of large PB1 extrusion in the oocytes. The three MOS variants could not activate MEK1/2 and ERK1/2 in oocytes and HEK293 cells. In addition, when compared with wild-type MOS, the MOS variants decreased the MOS protein level and attenuated the binding capacity with MEK1. Microinjection of wild-type human MOS complementary RNAs (cRNAs) reversed the symmetric division of oocytes after siMos treatment. In contrast, the three MOS variants demonstrated no rescuing ability.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Owing to the scarcity of human oocyte samples and the associated ethical restrictions, we could not perform the rescue attempt for the study patients.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings expand the genetic and phenotypic spectrum of MOS variants in causing female infertility. Our study findings facilitate the early genetic diagnosis of abnormal oocyte morphology characterized as large PB1 that eventually causes infertility in women.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Natural Science Foundation of China (82071640 and 82001633), Natural Science Foundation of Zhejiang Province (LD22C060001), the Key Projects Jointly Constructed by the Ministry and the Province of Zhejiang Medical and Health Science and Technology Project (WKJ-ZJ-2005), China Postdoctoral Science Foundation (2020M682575 and 2021T140198), the Changsha Municipal Natural Science Foundation (kq2007022) and Hunan Provincial Grant for Innovative Province Construction (2019SK4012). None of the authors declare any competing interests.

TRIAL REGISTRATION NUMBER

N/A.