The human knockout phenotype ofPADI6is female sterility caused by cleavage failure of their fertilized eggs

Padi6 expression patterns in buffalo oocytes and preimplantation embryos

The subcortical maternal complex, which consists of maternal-effect genes, plays a crucial role in the development of oocytes and preimplantation embryo until the activation of the zygote genome. One such gene, known as peptidyl-arginine deiminase VI (Padi6), is involved in the oocyte maturation, fertilization and embryonic development. However, the precise function of Padi6 gene in buffalo is still unclear and requires further investigation. In this study, the sequence, mRNA and protein expression patterns of Padi6 gene were analyzed in oocytes, preimplantation embryos and somatic tissues of buffalo. The coding sequence of gene was successfully cloned and characterized. Real-time quantitative PCR results indicated an absence of Padi6 transcripts in somatic tissues. Notably, the expression levels of Padi6 in oocytes showed an increased from the germinal vesicle stage to metaphase II stage, followed by a rapid decrease during the morula and blastocyst stages. Immunofluorescence analysis confirmed these findings, revealing a noticeable decline in protein expression levels. Our research provides the initial comprehensive expression profile of Padi6 in buffalo oocytes and preimplantation embryos, serving as a solid foundation for further investigations into the functionality of maternal-effect genes in buffalo.

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.

Hydatidiform Mole-Between Chromosomal Abnormality, Uniparental Disomy and Monogenic Variants: A Narrative Review

A hydatidiform mole (HM) or molar pregnancy is the most common benign form of gestational trophoblastic disease characterized by a proliferation of the trophoblastic epithelium and villous edema. Hydatidiform moles are classified into two forms: complete and partial hydatidiform moles. These two types of HM present morphologic, histopathologic and cytogenetic differences. Usually, hydatidiform moles are a unique event, but some women present a recurrent form of complete hydatidiform moles that can be sporadic or familial. The appearance of hydatidiform moles is correlated with some genetic events (like uniparental disomy, triploidy or diandry) specific to meiosis and is the first step of embryo development. The familial forms are determined by variants in some genes, with NLRP7 and KHDC3L being the most important ones. The identification of different types of hydatidiform moles and their subsequent mechanisms is important to calculate the recurrence risk and estimate the method of progression to a malign form. This review synthesizes the heterogeneous mechanisms and their implications in genetic counseling.

PADI6: What we know about the elusive fifth member of the peptidyl arginine deiminase family

Peptidyl arginine deiminase 6 (PADI6) is a maternal factor that is vital for early embryonic development. Deletion and mutations of its encoding gene in female mice or women lead to early embryonic developmental arrest, female infertility, maternal imprinting defects and hyperproliferation of the trophoblast. PADI6 is the fifth and least well-characterized member of the peptidyl arginine deiminases (PADIs), which catalyse the post-translational conversion of arginine to citrulline. It is less conserved than the other PADIs, and currently has no reported catalytic activity. While there are many suggested functions of PADI6 in the early mouse embryo, including in embryonic genome activation, cytoplasmic lattice formation, maternal mRNA and ribosome regulation, and organelle distribution, the molecular mechanisms of its function remain unknown. In this review, we discuss what is known about the function of PADI6 and highlight key outstanding questions that must be answered if we are to understand the crucial role it plays in early embryo development and female fertility. This article is part of the Theo Murphy meeting issue 'The virtues and vices of protein citrullination'.

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.

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.

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.

Maternal effect genes: Update and review of evidence for a link with birth defects

Maternal effect genes (MEGs) encode factors (e.g., RNA) that are present in the oocyte and required for early embryonic development. Hence, while these genes and gene products are of maternal origin, their phenotypic consequences result from effects on the embryo. The first mammalian MEGs were identified in the mouse in 2000 and were associated with early embryonic loss in the offspring of homozygous null females. In humans, the first MEG was identified in 2006, in women who had experienced a range of adverse reproductive outcomes, including hydatidiform moles, spontaneous abortions, and stillbirths. Over 80 mammalian MEGs have subsequently been identified, including several that have been associated with phenotypes in humans. In general, pathogenic variants in MEGs or the absence of MEG products are associated with a spectrum of adverse outcomes, which in humans range from zygotic cleavage failure to offspring with multi-locus imprinting disorders. Although less established, there is also evidence that MEGs are associated with structural birth defects (e.g., craniofacial malformations, congenital heart defects). This review provides an updated summary of mammalian MEGs reported in the literature through early 2021, as well as an overview of the evidence for a link between MEGs and structural birth defects.

Novel biallelic mutations in PADI6 in patients with early embryonic arrest

Peptidyl arginine deiminase, type VI (PADI6) is a member of the subcortical maternal complex (SCMC), which plays vital roles in mammalian embryogenesis. Most mutations in SCMC members have been reported to cause human embryonic arrest, and a total of 15 mutations in PADI6 have been shown to be responsible for early embryonic arrest according to previous studies. However, the genetic factors behind this phenotype remain to be understood in further detail. Here, we identified 13 novel mutations and 4 previously reported mutations of PADI6 in 14 patients who were diagnosed with abnormal embryonic development caused by early arrest, embryonic fragmentation, and recurrent implantation failure. Most of the mutations were predicted by in silico analysis to be deleterious or damaging to the function of PADI6. In addition, the total and East Asian population frequencies of the mutations were low or absent in the gnomAD database. Our study expands the mutational spectrum in PADI6 and will provide precise targets for genetic counseling in the future.

The seminal plasma proteins Peptidyl arginine deaminase 2, rRNA adenine N (6)-methyltransferase and KIAA0825 are linked to better motility post thaw in stallions

Seminal plasma plays an important role in sperm physiology. Seminal plasma proteins vehiculated in microvesicles, carry RNAs and proteins with a potential role in early embryo development. Additionally, proteins present in seminal plasma participate in redox regulation and energy metabolism. In view of these facts, we hypothesized that differences in protein composition of the seminal plasma among stallions may help to explain differences in freeze-ability seen among them. Three independent ejaculates from 10 different stallions of varying breeds were frozen using standard protocols in our laboratory. Aliquots of the ejaculate were separated and stored at -80 °C until further proteomic analysis. Semen analysis was performed using computer assisted sperm analysis and flow cytometry. Significant differences in proteome composition of seminal plasma were observed in the group of stallions showing better motility post thaw. 3116 proteins were identified, and of these, 34 were differentially expressed in stallions with better motility post thaw, 4 of them were also differentially expressed in stallions with different percentages of linearly motile sperm post thaw and 1 protein, Midasin, was expressed in stallions showing high circular velocity post thaw. Seminal plasma proteins may play a major role in sperm functionality; being vehiculated through extracellular vesicles and participating in sperm physiology. Bioinformatic analysis identifies discriminant proteins able to predict the outcome of cryopreservation, identifying potential new biomarkers to assess ejaculate quality.

Lethal variants in humans: lessons learned from a large molecular autopsy cohort

BACKGROUND

Molecular autopsy refers to DNA-based identification of the cause of death. Despite recent attempts to broaden its scope, the term remains typically reserved to sudden unexplained death in young adults. In this study, we aim to showcase the utility of molecular autopsy in defining lethal variants in humans.

METHODS

We describe our experience with a cohort of 481 cases in whom the cause of premature death was investigated using DNA from the index or relatives (molecular autopsy by proxy). Molecular autopsy tool was typically exome sequencing although some were investigated using targeted approaches in the earlier stages of the study; these include positional mapping, targeted gene sequencing, chromosomal microarray, and gene panels.

RESULTS

The study includes 449 cases from consanguineous families and 141 lacked family history (simplex). The age range was embryos to 18 years. A likely causal variant (pathogenic/likely pathogenic) was identified in 63.8% (307/481), a much higher yield compared to the general diagnostic yield (43%) from the same population. The predominance of recessive lethal alleles allowed us to implement molecular autopsy by proxy in 55 couples, and the yield was similarly high (63.6%). We also note the occurrence of biallelic lethal forms of typically non-lethal dominant disorders, sometimes representing a novel bona fide biallelic recessive disease trait. Forty-six disease genes with no OMIM phenotype were identified in the course of this study. The presented data support the candidacy of two other previously reported novel disease genes (FAAH2 and MSN). The focus on lethal phenotypes revealed many examples of interesting phenotypic expansion as well as remarkable variability in clinical presentation. Furthermore, important insights into population genetics and variant interpretation are highlighted based on the results.

CONCLUSIONS

Molecular autopsy, broadly defined, proved to be a helpful clinical approach that provides unique insights into lethal variants and the clinical annotation of the human genome.

PADI6 Regulates Trophoblast Cell Migration-Invasion Through the Hippo/YAP1 Pathway in Hydatidiform Moles

Purpose

Peptidyl arginine deiminase, type VI (PADI6), a member of the subcortical maternal complex, plays an important role in oocyte growth and the development of fertilized oocytes. Human patients with PADI6 mutations can suffer from multiple reproductive deficiencies including hydatidiform moles and miscarriages. Recent studies have demonstrated that the Hippo signaling pathway plays a central role in the specification of the first cell fates and the maintenance of the human placental trophoblast epithelium. The present study aimed to verify the hypothesis that PADI6 regulates the biological functions of trophoblast cells by targeting YAP1 and to explore the mechanism by which PADI6 accomplishes this in trophoblast cells.

Methods

Villi from HMs and human trophoblast cell lines were used to identify the localization of PADI6 and YAP1 by immunohistochemistry and immunocytochemistry. PADI6 overexpression and knockdown were induced in human trophoblast cells. Co-immunoprecipitation was used to explore the interaction between PADI6 and YAP1. Wound healing, Transwell and EdU staining assays were used to detect migration, invasion and proliferation. Flow cytometric analysis was used to analyze the cell cycle and apoptosis. β-Tubulin and F-actin levels were determined by Western blot, quantitative real-time PCR and phalloidin staining.

Results

The results showed that PADI6 and YAP1 had the same expression pattern in villi and colocalized in the cytotrophoblast. An interaction between PADI6 and YAP1 was also confirmed in human trophoblast cell lines. We found that PADI6 positively regulated the expression of YAP1. Functionally, overexpression of PADI6 promoted cell cycle progression and enhanced migration, invasion, proliferation and apoptosis, whereas downregulation of PADI6 showed the opposite effects.

Conclusion

This study demonstrates that YAP1 is a novel target of PADI6 that serves as an important regulator of trophoblast dysfunction. The crosstalk between the Hippo/YAP1 pathway and the SCMC might be a new topic to explore to uncover the pathological mechanisms of HMs.

Two novel mutations in PADI6 and TLE6 genes cause female infertility due to arrest in embryonic development

Purpose

This study aims to identify genetic causes of female infertility associated with recurrent failure of assisted reproductive technology (ART) characterized by embryonic developmental arrest.

Methods

We recruited infertile patients from two consanguineous families from the Reproductive Medicine Center of Guizhou Provincial People’s Hospital. Peripheral blood was collected for genomic DNA extraction. Two affected individuals and their family members were performed with whole-exome sequencing and Sanger validation in order to identify possible causative genes. For further analyzing the effect of splicing mutation on mRNA integrity in vivo, TLE6 cDNA from the peripheral blood lymphocyte of the affected individual was sequenced. In addition, the possible impact of the pathogenic mutation on the structure and function of the protein were also assessed.

Results

Two novel homozygous mutations in the peptidylarginine deiminase type VI (PADI6) and the transducin-like enhancer of split 6 (TLE6) genes were identified in the two families. One patient carried the frameshift deletion mutation c.831_832del:p.S278Pfs^*59 of the PADI6 gene and the other patient carried the splicing mutation c.1245-2 A>G of the TLE6 gene. The analysis of the mRNA from the proband’s peripheral blood leukocytes confirmed aberrant splicing.

Conclusions

Our findings expand the mutational spectrum of PADI6 and TLE6 associated with embryonic developmental arrest and deepen our understanding of the genetic causes of infertility with recurrent ART failure.

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

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

Deimination, Intermediate Filaments and Associated Proteins

Deimination (or citrullination) is a post-translational modification catalyzed by a calcium-dependent enzyme family of five peptidylarginine deiminases (PADs). Deimination is involved in physiological processes (cell differentiation, embryogenesis, innate and adaptive immunity, etc.) and in autoimmune diseases (rheumatoid arthritis, multiple sclerosis and lupus), cancers and neurodegenerative diseases. Intermediate filaments (IF) and associated proteins (IFAP) are major substrates of PADs. Here, we focus on the effects of deimination on the polymerization and solubility properties of IF proteins and on the proteolysis and cross-linking of IFAP, to finally expose some features of interest and some limitations of citrullinomes.

Expanding the genetic and phenotypic spectrum of the subcortical maternal complex genes in recurrent preimplantation embryonic arrest

The subcortical maternal complex (SCMC) is an oocyte-to-embryo-specific maternal functional module. Some variants of SCMC genes that contribute to preimplantation embryonic arrest have been identified. However, more novel variants should be identified to broaden the genetic and phenotypic spectrum of SCMC genes and establish their roles in embryonic development. We identified 13 novel variants in the SCMC genes, TLE6, NLRP5, NLRP2, and PADI6, from 10 of a total of 50 infertile females with recurrent preimplantation embryonic arrest. Six variants in TLE6 were found in five patients with embryonic arrest, accompanied by direct cleavage and severe fragmentation at the cleavage stage. Three patients carried NLRP5 variants, and one patient each who carried NLRP2 and PADI6 variants had subsequent poor or failed fertilization and cleavage arrest with a relatively lower ratio of severely fragmented embryos. Our findings expand the genetic and phenotypic spectrum of SCMC genes associated with human embryogenesis and might help lay the foundation for the genetic diagnosis of female infertility.

Loss-of-function maternal-effect mutations of PADI6 are associated with familial and sporadic Beckwith-Wiedemann syndrome with multi-locus imprinting disturbance

BACKGROUND

PADI6 is a component of the subcortical maternal complex, a group of proteins that is abundantly expressed in the oocyte cytoplasm, but is required for the correct development of early embryo. Maternal-effect variants of the subcortical maternal complex proteins are associated with heterogeneous diseases, including female infertility, hydatidiform mole, and imprinting disorders with multi-locus imprinting disturbance. While the involvement of PADI6 in infertility is well demonstrated, its role in imprinting disorders is less well established.

RESULTS

We have identified by whole-exome sequencing analysis four cases of Beckwith-Wiedemann syndrome with multi-locus imprinting disturbance whose mothers are carriers of PADI6 variants. In silico analysis indicates that these variants result in loss of function, and segregation analysis suggests they act as either recessive or dominant-negative maternal-effect mutations. Genome-wide methylation analysis revealed heterogeneous and extensively altered methylation profiles of imprinted loci in the patients, including two affected sisters, but not in their healthy siblings.

CONCLUSION

Our results firmly establish the role of PADI6 in imprinting disorders. We report loss-of-function maternal-effect variants of PADI6 that are associated with heterogeneous multi-locus imprinting disturbances in the progeny. The rare finding of two siblings affected by Beckwith-Wiedemann syndrome suggests that in some cases, familial recurrence risk of these variants may be high. However, the heterogeneous phenotypes of the other pedigrees suggest that altered oocyte PADI6 function results in stochastic maintenance of methylation imprinting with unpredictable consequences on early embryo health.

A novel homozygous variant in NLRP5 is associate with human early embryonic arrest in a consanguineous Chinese family

Early embryonic arrest is one of the major causes of recurrent assisted reproduction failure. It is characterized by delayed embryonic development and failure to form viable eight-cell stage embryos on day 3 of an assisted reproduction cycle. A recent study reported that biallelic mutations in NLRP5 can cause early embryonic arrest. NLRP5 is a member of subcortical maternal complex, which plays a significant role in embryogenesis. In this study, we described a female in a consanguineous Chinese family who displayed clinical features of early embryonic arrest and identified a novel homozygous variant c.1061C>T (p.Pro354Leu) in NLRP5. This is the second report of the biallelic NLRP5 variant that associates with early embryonic arrest in humans, further confirming the role of NLRP5 variants in early embryonic arrest and expanding the spectrum of known pathogenic variants in NLRP5.

A genomics approach to females with infertility and recurrent pregnancy loss

Infertility affects 10% of reproductive-age women and is extremely heterogeneous in etiology. The genetic contribution to female infertility is incompletely understood, and involves chromosomal and single-gene defects. Our aim in this study is to decipher single-gene causes in infertile women in whom endocrinological, anatomical, and chromosomal causes have been excluded. Our cohort comprises women with recurrent pregnancy loss and no offspring from spontaneous pregnancies (RPL, n = 61) and those who never achieved clinical pregnancy and were referred for in vitro fertilization [primary infertility (PI), n = 14]. Whole-exome sequencing revealed candidate variants in 14, which represents 43% of those with PI and 13% of those with RPL. These include variants in previously established female infertility-related genes (TLE6, NLRP7, FSHR, and ZP1) as well as genes with only tentative links in the literature (NLRP5). Candidate variants in genes linked to primary ciliary dyskinesia (DNAH11 and CCNO) were identified in individuals with and without systemic features of the disease. We also identified variants in genes not previously linked to female infertility. These include one homozygous variant each in CCDC68, CBX3, CENPH, PABPC1L, PIF1, PLK1, and REXO4, which we propose as candidate genes for infertility based on their established biology or compatible animal models. Our study expands the contribution of single genes to the etiology of PI and RPL, improves the precision of disease classification at the molecular level, and offers the potential for future treatment and development of human genetics-inspired fertility regulators.

Disturbed genomic imprinting and its relevance for human reproduction: causes and clinical consequences

BACKGROUND

Human reproductive issues affecting fetal and maternal health are caused by numerous exogenous and endogenous factors, of which the latter undoubtedly include genetic changes. Pathogenic variants in either maternal or offspring DNA are associated with effects on the offspring including clinical disorders and nonviable outcomes. Conversely, both fetal and maternal factors can affect maternal health during pregnancy. Recently, it has become evident that mammalian reproduction is influenced by genomic imprinting, an epigenetic phenomenon that regulates the expression of genes according to their parent from whom they are inherited. About 1% of human genes are normally expressed from only the maternally or paternally inherited gene copy. Since numerous imprinted genes are involved in (embryonic) growth and development, disturbance of their balanced expression can adversely affect these processes.

OBJECTIVE AND RATIONALE

This review summarises current our understanding of genomic imprinting in relation to human ontogenesis and pregnancy and its relevance for reproductive medicine.

SEARCH METHODS

Literature databases (Pubmed, Medline) were thoroughly searched for the role of imprinting in human reproductive failure. In particular, the terms ‘multilocus imprinting disturbances, SCMC, NLRP/NALP, imprinting and reproduction’ were used in various combinations.

OUTCOMES

A range of molecular changes to specific groups of imprinted genes are associated with imprinting disorders, i.e. syndromes with recognisable clinical features including distinctive prenatal features. Whereas the majority of affected individuals exhibit alterations at single imprinted loci, some have multi-locus imprinting disturbances (MLID) with less predictable clinical features. Imprinting disturbances are also seen in some nonviable pregnancy outcomes, such as (recurrent) hydatidiform moles, which can therefore be regarded as a severe form of imprinting disorders. There is growing evidence that MLID can be caused by variants in the maternal genome altering the imprinting status of the oocyte and the embryo, i.e. maternal effect mutations. Pregnancies of women carrying maternal affect mutations can have different courses, ranging from miscarriages to birth of children with clinical features of various imprinting disorders.

WIDER IMPLICATIONS

Increasing understanding of imprinting disturbances and their clinical consequences have significant impacts on diagnostics, counselling and management in the context of human reproduction. Defining criteria for identifying pregnancies complicated by imprinting disorders facilitates early diagnosis and personalised management of both the mother and offspring. Identifying the molecular lesions underlying imprinting disturbances (e.g. maternal effect mutations) allows targeted counselling of the family and focused medical care in further pregnancies.

New biallelic mutations in PADI6 cause recurrent preimplantation embryonic arrest characterized by direct cleavage

PURPOSE

To investigate the pathogenesis of the recurrent preimplantation embryonic arrest characterized by direct cleavage.

METHODS

Two affected individuals underwent time-lapse imaging to observe the cleavage behaviors in their final ICSI attempts. In addition, both patients were subjected to whole-exome sequencing. After the identification of possible causative genes, molecular modeling analyses were used to evaluate the possible effects of candidate mutations on protein secondary structure.

RESULTS

All the bipronucleated (2PN) zygotes from both individuals presented multiple abnormal cleavage behaviors, particularly direct cleavage (DC) and subsequent cleavage arrest. Mutation analysis identified one new frameshift mutation c.1521dupC (p.S508Qfs*5) and two missense mutations c.A1117C and c.C1708T (p.T373P and p.R570C, respectively) of the PADI6 gene, which were in the protein-arginine deiminase (PAD) domain and highly conserved.

CONCLUSION

This study expands the mutation spectrum of PADI6 and is the first to propose that the preimplantation embryonic arrest with concomitant abnormal cleavage behaviors, especially DC, maybe associated with PADI6 mutations.

Biallelic PADI6 variants linking infertility, miscarriages, and hydatidiform moles

Recurrent hydatidiform moles (RHM) are aberrant human pregnancies characterized by absence of, or abnormal, embryonic development, hydropic degeneration of chorionic villi, and hyperproliferation of the trophoblast. Biallelic mutations in two maternal-effect genes, NLRP7 and KHDC3L, underlie the causation of RHM in 60% of patients. We performed exome sequencing on a patient with six pregnancy losses, two miscarriages and four HM, and found no variants that affect the functions of the known genes. We found biallelic missense variants that affect conserved amino acids in PADI6 and segregate with the disease phenotype in the family. PADI6 is another maternal-effect gene and a member of the subcortical maternal complex that has been shown to have recessive variants that affect the gene function in four unrelated women with infertility who also experienced early embryonic arrest during preimplantation development after IVF. We demonstrated that PADI6 co-localizes with NLRP7 in human oocytes and preimplantation embryos and reviewed the morphology and genotypes of four products of conception from our patient. Our data expand the involvement of PADI6 to other forms of reproductive loss and highlight the commonality between infertility, miscarriages, and molar pregnancies, in some cases.

Novel mutations in genes encoding subcortical maternal complex proteins may cause human embryonic developmental arrest

Successful human reproduction initiates from normal gamete formation, fertilization and early embryonic development. Abnormalities in any of these steps will lead to infertility. Many infertile patients undergo several failures of IVF and intracytoplasmic sperm injection (ICSI) cycles, and embryonic developmental arrest is a common phenotype in cases of recurrent failure of IVF/ICSI attempts. However, the genetic basis for this phenotype is poorly understood. The subcortical maternal complex (SCMC) genes play important roles during embryonic development, and using whole-exome sequencing novel biallelic mutations in the SCMC genes TLE6, PADI6 and KHDC3L were identified in four patients with embryonic developmental arrest. A mutation in TLE6 was found in a patient with cleaved embryos that arrested on day 3 and failed to form blastocysts. Two patients with embryos that arrested at the cleavage stage had mutations in PADI6, and a mutation in KHDC3L was found in a patient with embryos arrested at the morula stage. No mutations were identified in these genes in an additional 80 patients. These findings provide further evidence for the important roles of TLE6, PADI6 and KHDC3L in embryonic development. This work lays the foundation for the genetic diagnosis of patients with recurrent IVF/ICSI failure.

TDRD6 is associated with oligoasthenoteratozoospermia by sequencing the patient from a consanguineous family

Oligoasthenoteratozoospermia (OAT) is characterized as low sperm count, decreased sperm motility and structural abnormalities of the sperm head in the same patient. However, very few studies reported the genetic alterations associated with OAT. Here we report a 38-year-old patient with OAT from a consanguineous family, with 2-6 million/mL sperm density, 2.1-3.8% normal sperm morphology and immotile sperm. Whole-exome sequencing (WES) identified homozygous variant c.1259A>G:p.Y420C in the TDRD6 gene. TDRD6 is a testis-specific expressed protein that was localized to the chromatoid bodies in germ cells and played an important role in the nonsense-mediated decay pathway. This rare variant co-segregated with the OAT phenotype in this family. Bioinformatic analysis also suggested the variant a pathogenic mutation. Two intracytoplasmic sperm injection (ICSI) cycles were carried out in the patient's wife, but she did not become pregnant after embryo transfer. So the mutations in TDRD6 may be associated with human male infertility and early embryonic lethality.

Female Infertility Caused by Mutations in the Oocyte-Specific Translational Repressor PATL2

Infertility is a relatively common disorder of the reproductive system and remains unexplained in many cases. In vitro fertilization techniques have uncovered previously unrecognized infertility phenotypes, including oocyte maturation arrest, the molecular etiology of which remains largely unknown. We report two families affected by female-limited infertility caused by oocyte maturation failure. Positional mapping and whole-exome sequencing revealed two homozygous, likely deleterious variants in PATL2, each of which fully segregates with the phenotype within the respective family. PATL2 encodes a highly conserved oocyte-specific mRNP repressor of translation. Previous data have shown the strict requirement for PATL2 in oocyte-maturation in model organisms. Data gathered from the families in this study suggest that the role of PATL2 is conserved in humans and expand our knowledge of the factors that are necessary for female meiosis.