NLRP7 and KHDC3L, the two maternal-effect proteins responsible for recurrent hydatidiform moles, co-localize to the oocyte cytoskeleton

Genetics and Genomics of Gestational Trophoblastic Disease

This article focuses on hydatidiform mole (HM), which is the most common form of gestational trophoblastic disease and the most studied at the genomic and genetic levels. We summarize current laboratory methods to diagnose HM, discuss their limitations and advantages, and share the lessons we have learned. We also provide an overview of the history of recurrent HM, their known genetic etiologies, and the mechanisms of their formation.

Structural basis of the subcortical maternal complex and its implications in reproductive disorders

The subcortical maternal complex (SCMC) plays a crucial role in early embryonic development. Malfunction of SCMC leads to reproductive diseases in women. However, the molecular function and assembly basis for SCMC remain elusive. Here we reconstituted mouse SCMC and solved the structure at atomic resolution using single-particle cryo-electron microscopy. The core complex of SCMC was formed by MATER, TLE6 and FLOPED, and MATER embraced TLE6 and FLOPED via its NACHT and LRR domains. Two core complexes further dimerize through interactions between two LRR domains of MATERs in vitro. FILIA integrates into SCMC by interacting with the carboxyl-terminal region of FLOPED. Zygotes from mice with Floped C-terminus truncation showed delayed development and resembled the phenotype of zygotes from Filia knockout mice. More importantly, the assembly of mouse SCMC was affected by corresponding clinical variants associated with female reproductive diseases and corresponded with a prediction based on the mouse SCMC structure. Our study paves the way for further investigations on SCMC functions during mammalian preimplantation embryonic development and reveals underlying causes of female reproductive diseases related to SCMC mutations, providing a new strategy for the diagnosis of female reproductive disorders.

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.

NLRP7 participates in the human subcortical maternal complex and its variants cause female infertility characterized by early embryo arrest

Successful human reproduction requires normal oocyte maturation, fertilization, and early embryo development. Early embryo arrest is a common phenomenon leading to female infertility, but the genetic basis is largely unknown. NLR family pyrin domain-containing 7 (NLRP7) is a member of the NLRP subfamily. Previous studies have shown that variants of NLRP7 are one of the crucial causes of female recurrent hydatidiform mole, but whether NLRP7 variants can directly affect early embryo development is unclear. We performed whole-exome sequencing in patients who experienced early embryo arrest, and five heterozygous variants (c.251G > A, c.1258G > A, c.1441G > A, c. 2227G > A, c.2323C > T) of NLRP7 were identified in affected individuals. Plasmids of NLRP7 and subcortical maternal complex components were overexpressed in 293 T cells, and Co-IP experiments showed that NLRP7 interacted with NLRP5, TLE6, PADI6, NLRP2, KHDC3L, OOEP, and ZBED3. Injecting complementary RNAs in mouse oocytes and early embryos showed that NLRP7 variants influenced the oocyte quality and some of the variants significantly affected early embryo development. These findings contribute to our understanding of the role of NLRP7 in human early embryo development and provide a new genetic marker for clinical early embryo arrest patients. KEY MESSAGES: Five heterozygous variants of NLRP7 (c.1441G > A; 2227G > A; c.251G > A; c.1258G > A; c.2323C > T) were identified in five infertile patients who experienced early embryo arrest. NLRP7 is a component of human subcortical maternal complex. NLRP7 variants lead to poor quality of oocytes and early embryo development arrest. This study provides a new genetic marker for clinical early embryo arrest patients.

Gestational Trophoblastic Disease: Contemporary Diagnostic Approach

Pathologic diagnosis of gestational trophoblastic disease (GTD)-hydatidiform moles and gestational trophoblastic neoplasms-underwent a major shift in the past decade from morphology-based recognition to precise molecular genetic classification of entities, which also allows for prognostic stratification of molar gestations. This article highlights these recent advances and their integration into the routine pathology practice. The traditional gross and histomorphologic features of each entity are also reviewed with special focus on differential diagnoses and their clinical implications.

Novel genetic variants of KHDC3L and other members of the subcortical maternal complex associated with Beckwith-Wiedemann syndrome or Pseudohypoparathyroidism 1B and multi-locus imprinting disturbances

BACKGROUND

Beckwith-Wiedemann syndrome (BWS) and Pseudohypoparathyroidism type 1B (PHP1B) are imprinting disorders (ID) caused by deregulation of the imprinted gene clusters located at 11p15.5 and 20q13.32, respectively. In both of these diseases a subset of the patients is affected by multi-locus imprinting disturbances (MLID). In several families, MLID is associated with damaging variants of maternal-effect genes encoding protein components of the subcortical maternal complex (SCMC). However, frequency, penetrance and recurrence risks of these variants are still undefined. In this study, we screened two cohorts of BWS patients and one cohort of PHP1B patients for the presence of MLID, and analysed the positive cases for the presence of maternal variants in the SCMC genes by whole exome-sequencing and in silico functional studies.

RESULTS

We identified 10 new cases of MLID associated with the clinical features of either BWS or PHP1B, in which segregate 13 maternal putatively damaging missense variants of the SCMC genes. The affected genes also included KHDC3L that has not been associated with MLID to date. Moreover, we highlight the possible relevance of relatively common variants in the aetiology of MLID.

CONCLUSION

Our data further add to the list of the SCMC components and maternal variants that are involved in MLID, as well as of the associated clinical phenotypes. Also, we propose that in addition to rare variants, common variants may play a role in the aetiology of MLID and imprinting disorders by exerting an additive effect in combination with rarer putatively damaging variants. These findings provide useful information for the molecular diagnosis and recurrence risk evaluation of MLID-associated IDs in genetic counselling.

DNA Methylation Dynamics in the Female Germline and Maternal-Effect Mutations That Disrupt Genomic Imprinting

Genomic imprinting is an epigenetic marking process that results in the monoallelic expression of a subset of genes. Many of these ‘imprinted’ genes in mice and humans are involved in embryonic and extraembryonic growth and development, and some have life-long impacts on metabolism. During mammalian development, the genome undergoes waves of (re)programming of DNA methylation and other epigenetic marks. Disturbances in these events can cause imprinting disorders and compromise development. Multi-locus imprinting disturbance (MLID) is a condition by which imprinting defects touch more than one locus. Although most cases with MLID present with clinical features characteristic of one imprinting disorder. Imprinting defects also occur in ‘molar’ pregnancies-which are characterized by highly compromised embryonic development-and in other forms of reproductive compromise presenting clinically as infertility or early pregnancy loss. Pathogenic variants in some of the genes encoding proteins of the subcortical maternal complex (SCMC), a multi-protein complex in the mammalian oocyte, are responsible for a rare subgroup of moles, biparental complete hydatidiform mole (BiCHM), and other adverse reproductive outcomes which have been associated with altered imprinting status of the oocyte, embryo and/or placenta. The finding that defects in a cytoplasmic protein complex could have severe impacts on genomic methylation at critical times in gamete or early embryo development has wider implications beyond these relatively rare disorders. It signifies a potential for adverse maternal physiology, nutrition, or assisted reproduction to cause epigenetic defects at imprinted or other genes. Here, we review key milestones in DNA methylation patterning in the female germline and the embryo focusing on humans. We provide an overview of recent findings regarding DNA methylation deficits causing BiCHM, MLID, and early embryonic arrest. We also summarize identified SCMC mutations with regard to early embryonic arrest, BiCHM, and MLID.

The subcortical maternal complex: emerging roles and novel perspectives

Since its recent discovery, the subcortical maternal complex (SCMC) is emerging as a maternally inherited and crucial biological structure for the initial stages of embryogenesis in mammals. Uniquely expressed in oocytes and preimplantation embryos, where it localizes to the cell subcortex, this multiprotein complex is essential for early embryo development in the mouse and is functionally conserved across mammalian species, including humans. The complex has been linked to key processes leading the transition from oocyte to embryo, including meiotic spindle formation and positioning, regulation of translation, organelle redistribution, and epigenetic reprogramming. Yet, the underlying molecular mechanisms for these diverse functions are just beginning to be understood, hindered by unresolved interplay of SCMC components and variations in early lethal phenotypes. Here we review recent advances confirming involvement of the SCMC in human infertility, revealing an unexpected relationship with offspring health. Moreover, SCMC organization is being further revealed in terms of novel components and interactions with additional cell constituents. Collectively, this evidence prompts new avenues of investigation into possible roles during the process of oogenesis and the regulation of maternal transcript turnover during the oocyte to embryo transition.

NLRP7 Promotes Choriocarcinoma Growth and Progression through the Establishment of an Immunosuppressive Microenvironment

The inflammatory gene NLRP7 is the major gene responsible for recurrent complete hydatidiform moles (CHM), an abnormal pregnancy that can develop into gestational choriocarcinoma (CC). However, the role of NLRP7 in the development and immune tolerance of CC has not been investigated. Three approaches were employed to define the role of NLRP7 in CC development: (i) a clinical study that analyzed human placenta and sera collected from women with normal pregnancies, CHM or CC; (ii) an in vitro study that investigated the impact of NLRP7 knockdown on tumor growth and organization; and (iii) an in vivo study that used two CC mouse models, including an orthotopic model. NLRP7 and circulating inflammatory cytokines were upregulated in tumor cells and in CHM and CC. In tumor cells, NLRP7 functions in an inflammasome-independent manner and promoted their proliferation and 3D organization. Gravid mice placentas injected with CC cells invalidated for NLRP7, exhibited higher maternal immune response, developed smaller tumors, and displayed less metastases. Our data characterized the critical role of NLRP7 in CC and provided evidence of its contribution to the development of an immunosuppressive maternal microenvironment that not only downregulates the maternal immune response but also fosters the growth and progression of CC.

Modulation of Bovine Endometrial Cell Receptors and Signaling Pathways as a Nanotherapeutic Exploration against Dairy Cow Postpartum Endometritis

Simple Summary

The provision of updated information on the molecular pathogenesis of bovine endometritis with host-pathogen interactions and the possibility of exploring the cellular sensors mechanism in a nanotechnology-based drug delivery system against persistent endometritis were reported in this review. The mechanism of Gram-negative bacteria and their ligands has been vividly explored, with the paucity of research detail on Gram-positive bacteria in bovine endometritis. The function of cell receptors, biomolecules proteins, and sensors were reportedly essential in transferring signals into cell signaling pathways to induce immuno-inflammatory responses by elevating pro-inflammatory cytokines. Therefore, understanding endometrial cellular components and signaling mechanisms across pathogenesis are essential for nanotherapeutic exploration against bovine endometritis. The nanotherapeutic discovery that could inhibit infectious signals at the various cell receptors and signal transduction levels, interfering with transcription factors activation and pro-inflammatory cytokines and gene expression, significantly halts endometritis.

Abstract

In order to control and prevent bovine endometritis, there is a need to understand the molecular pathogenesis of the infectious disease. Bovine endometrium is usually invaded by a massive mobilization of microorganisms, especially bacteria, during postpartum dairy cows. Several reports have implicated the Gram-negative bacteria in the pathogenesis of bovine endometritis, with information dearth on the potentials of Gram-positive bacteria and their endotoxins. The invasive bacteria and their ligands pass through cellular receptors such as TLRs, NLRs, and biomolecular proteins of cells activate the specific receptors, which spontaneously stimulates cellular signaling pathways like MAPK, NF-kB and sequentially triggers upregulation of pro-inflammatory cytokines. The cascade of inflammatory induction involves a dual signaling pathway; the transcription factor NF-κB is released from its inhibitory molecule and can bind to various inflammatory genes promoter. The MAPK pathways are concomitantly activated, leading to specific phosphorylation of the NF-κB. The provision of detailed information on the molecular pathomechanism of bovine endometritis with the interaction between host endometrial cells and invasive bacteria in this review would widen the gap of exploring the potential of receptors and signal transduction pathways in nanotechnology-based drug delivery system. The nanotherapeutic discovery of endometrial cell receptors, signal transduction pathway, and cell biomolecules inhibitors could be developed for strategic inhibition of infectious signals at the various cell receptors and signal transduction levels, interfering on transcription factors activation and pro-inflammatory cytokines and genes expression, which may significantly protect endometrium against postpartum microbial invasion.

The genetics of recurrent hydatidiform moles in Mexico: further evidence of a strong founder effect for one mutation in NLRP7 and its widespread

PURPOSE

To investigate the frequency of a founder mutation in NLRP7, L750V, in independent cohorts of Mexican patients with recurrent hydatidiform moles (RHMs).

METHODS

Mutation analysis was performed by Sanger sequencing on DNA from 44 unrelated Mexican patients with RHMs and seven molar tissues from seven additional unrelated patients.

RESULTS

L750V was present in homozygous or heterozygous state in 37 (86%) patients and was transmitted on the same haplotype to patients from different states of Mexico. We also identified a second founder mutation, c.2810+2T>G in eight (18.1%) patients, and a novel premature stop-codon mutation W653*.

CONCLUSION

Our data confirm the strong founder effect for L750V, which appears to be the most common mutation in NLRP7. We also report on six healthy live births to five patients with biallelic NLRP7 mutations, two from spontaneous conceptions and four from donated ovum and discuss our recommendations for DNA testing and genetic counseling.

The pivotal roles of the NOD-like receptors with a PYD domain, NLRPs, in oocytes and early embryo development†

Nucleotide-binding oligomerization domain (NOD)-like receptors with a pyrin domain (PYD), NLRPs, are pattern recognition receptors, well recognized for their important roles in innate immunity and apoptosis. However, several NLRPs have received attention for their new, specialized roles as maternally contributed genes important in reproduction and embryo development. Several NLRPs have been shown to be specifically expressed in oocytes and preimplantation embryos. Interestingly, and in line with divergent functions, NLRP genes reveal a complex evolutionary divergence. The most pronounced difference is the human-specific NLRP7 gene, not identified in rodents. However, mouse models have been extensively used to study maternally contributed NLRPs. The NLRP2 and NLRP5 proteins are components of the subcortical maternal complex (SCMC), which was recently identified as essential for mouse preimplantation development. The SCMC integrates multiple proteins, including KHDC3L, NLRP5, TLE6, OOEP, NLRP2, and PADI6. The NLRP5 (also known as MATER) has been extensively studied. In humans, inactivating variants in specific NLRP genes in the mother are associated with distinct phenotypes in the offspring, such as biparental hydatidiform moles (BiHMs) and preterm birth. Maternal-effect recessive mutations in KHDC3L and NLRP5 (and NLRP7) are associated with reduced reproductive outcomes, BiHM, and broad multilocus imprinting perturbations. The precise mechanisms of NLRPs are unknown, but research strongly indicates their pivotal roles in the establishment of genomic imprints and post-zygotic methylation maintenance, among other processes. Challenges for the future include translations of findings from the mouse model into human contexts and implementation in therapies and clinical fertility management.

A noncanonical role of NOD-like receptor NLRP14 in PGCLC differentiation and spermatogenesis

NOD-like receptors (NLRs) are traditionally recognized as key surveillance pattern recognition receptors (PRRs) during innate immune regulation. Several NLRs exhibit highly restricted expression in mammalian germline, where their physiological functions are largely unknown. Here we report that Nlrp14, an NLR specifically expressed in testis and ovary, plays a critical role in regulating germ cell differentiation and reproduction. Nlrp14 deficiency led to decreased primordial germ cell-like cell (PGCLC) differentiation in vitro and reproduction failure in both male and female mice in vivo. In the male mice, Nlrp14 knockout strongly compromised differentiation of spermatogonial stem cells and meiosis. Mechanistically, NLRP14 protected HSPA2 from proteasome-mediated degradation by recruiting BAG2, loss of which was further confirmed in a human mutation associated with male sterility.

NOD-like receptors (NLRs) are traditionally recognized as major inflammasome components. The role of NLRs in germ cell differentiation and reproduction is not known. Here, we identified the gonad-specific Nlrp14 as a pivotal regulator in primordial germ cell-like cell (PGCLC) differentiation in vitro. Physiologically, knock out of Nlrp14 resulted in reproductive failure in both female and male mice. In adult male mice, Nlrp14 knockout (KO) inhibited differentiation of spermatogonial stem cells (SSCs) and meiosis, resulting in trapped SSCs in early stages, severe oligozoospermia, and sperm abnormality. Mechanistically, NLRP14 promoted spermatogenesis by recruiting a chaperone cofactor, BAG2, to bind with HSPA2 and form the NLRP14−HSPA2−BAG2 complex, which strongly inhibited ChIP-mediated HSPA2 polyubiquitination and promoted its nuclear translocation. Finally, loss of HSPA2 protection and BAG2 recruitment by NLRP14 was confirmed in a human nonsense germline variant associated with male sterility. Together, our data highlight a unique proteasome-mediated, noncanonical function of NLRP14 in PGCLC differentiation and spermatogenesis, providing mechanistic insights of gonad-specific NLRs in mammalian germline development.

Human epidermal growth factor receptor 2 fluorescence in situ hybridization and P57KIP2 immunohistochemistry using tissue microarray: Improving histopathological subtyping of hydatidiform mole

INTRODUCTION

Trophoblastic neoplasia is detected in approximately 25% of complete hydatidiform moles (CMs) and 0.5% of partial hydatidiform moles (PMs). Hydatidiform mole (HM) subtyping is important to properly monitor and predict patient outcomes. Ploidy studies generally involve diploid CMs and triploid PMs. P57KIP2, expressed in the maternal genome, is usually not detected in CM. We determined whether HER2 FISH and p57 immunostaining contributed to the histopathological classification of HMs.

METHODS

This retrospective cohort study focused on patients diagnosed with HM by histopathological examination who were followed up at a trophoblastic disease center from 2002 to 2017. Pathological samples of 108 products of conception were reviewed and reclassified according to detailed criteria. Tissue microarray technology (TMA) was used for p57 KIP2 immunostaining and HER2 FISH analysis.

RESULTS

Histopathological review showed 57 (53%) CMs, 47 (43%) PMs and 4 (4%) inconclusive cases. P57 immunostaining revealed 59 (55%) negative and 22 (20%) positive specimens, and 27 (25%) were inadequate for analysis. FISH HER2 detected 68 (63%) diploid and 33 (30%) triploid cases; two (2%) had oncogene amplification. The three strategies led to a diagnostic change in 28 samples (26%). The final diagnosis was CM in 75 cases (70%) and PM in 30 (28%); three cases remained inconclusive.

DISCUSSION

TMA is a cost-saving method that allows the simultaneous study of large case series. The combination of histopathology, HER2 FISH and p57 tests can be useful for accurately differentiating CM and PM, thus providing additional information on disease prognosis.

NLRP7 is expressed in the ovine ovary and associated with in vitro pre-implantation embryo development

NLRP (NACHT, LRR and PYD domain-containing proteins) family plays pivotal roles in mammalian reproduction. Mutation of NLRP7 is often associated with human recurrent hydatidiform moles. Few studies regarding the functions of NLRP7 have been performed in other mammalian species rather than humans. In the current study, for the first time, the function of NLRP7 has been explored in ovine ovary. NLRP7 protein was mainly located in ovarian follicles and in in vitro pre-implantation embryos. To identify its origin, 763 bp partial CDS of NLRP7 deriving from sheep cumulus oocyte complexes (COCs) was cloned, it showed a great homology with Homo sapiens. The high levels of mRNA and protein of NLRP7 were steadily expressed in oocytes, parthenogenetic embryos or IVF embryos. NLRP7 knockdown by the combination of siRNA and shRNA jeopardized both the parthenogenetic and IVF embryo development. These results strongly suggest that NLRP7 plays an important role in ovine reproduction. The potential mechanisms of NLRP7 will be fully investigated in the future.

Subcortical maternal complex (SCMC) expression during folliculogenesis is affected by oocyte donor age in sheep

PURPOSE

The age-associated decline in female fertility is largely ascribable to the decrease in oocyte quality. The subcortical maternal complex (SCMC) is a multiprotein complex essential for early embryogenesis and female fertility and functionally conserved across mammals. The present work evaluated expression dynamics of its components during folliculogenesis in relation to maternal age in sheep.

METHODS

The expression of the SCMC components (KHDC3/FILIA, NLRP2, NLRP5/MATER, OOEP/FLOPED, PADI6, TLE6 and ZBED3) was analyzed by real-time PCR in pools of growing oocytes (GO) of different diameters (70-90 μm (S), 90-110 μm (M), or 110-130 μm (L)) derived from non-hormonally treated adult (Ad; age < 4 years), prepubertal (Pr; age 40 days), or aged ewes (age > 6 years).

RESULTS

Specific expression patterns associated with donor age were observed during folliculogenesis for all genes, except ZBED3. In oocytes of adult donors, the synthesis of NLRP2, NLRP5, PADI6, and ZBED3 mRNAs was complete in S GO, while FILIA, TLE6, and OOEP were actively transcribed at this stage. Conversely, Pr GO showed active transcription of all mRNAs, except for ZBED3, during the entire window of oocyte growth. Notably, aged GO showed a completely inverse pattern, with a decrease of NLRP2, TLE6, FILIA, and PADI6 mRNA abundance during the latest stage of oocyte growth (L GO). Interestingly, MATER showed high expression variability, suggesting large inter-oocyte differences.

CONCLUSION

Our study describes the SCMC expression dynamics during sheep oogenesis and reports age-specific patterns that are likely involved in the age-related decline of oocyte quality.

Pregnancy after oocyte donation in a patient with NLRP7 gene mutations and recurrent molar hydatidiform pregnancies

Molar pregnancies are benign trophoblastic diseases associated with a risk of malignant transformation. If aetiology remains mostly unknown, the risk of recurrent molar pregnancy is around 1.5% after one molar pregnancy and around 25% after 2 molar pregnancies. In the later situation, genetic mutations have been described, increasing hugely this risk. In case of mutations, probability to obtain a normal pregnancy is estimated around 1.8%. We report the case of a Caucasian 30-year-old woman whose previous five spontaneous pregnancies had a negative outcome: a spontaneous miscarriage and then 4 complete hydatidiform moles. Genetic testing revealed that the patient carried two heterozygous mutations in the NLRP7 gene (c.2982-2A > G and Y318CfsX7). According to this, counselling was conducted to advocate for oocyte donation in order to obtain a normal pregnancy. This technique enabled a complication-free, singleton pregnancy that resulted in a healthy term live birth of a 2900 g female. Few months after delivery, the patient presented a new complete hydatidiform mole. Women presented with mutations in the NLRP7, KHDC3L or PADI6 genes are unlikely to obtain normal pregnancies, with a major risk of reproductive failure. In such a context, oocyte donation may be the best option. Only 4 normal pregnancies and deliveries have been published in this situation through this technique to our knowledge.

Identification of novel, clinically correlated autoantigens in the monogenic autoimmune syndrome APS1 by proteome-wide PhIP-Seq

The identification of autoantigens remains a critical challenge for understanding and treating autoimmune diseases. Autoimmune polyendocrine syndrome type 1 (APS1), a rare monogenic form of autoimmunity, presents as widespread autoimmunity with T and B cell responses to multiple organs. Importantly, autoantibody discovery in APS1 can illuminate fundamental disease pathogenesis, and many of the antigens found in APS1 extend to more common autoimmune diseases. Here, we performed proteome-wide programmable phage-display (PhIP-Seq) on sera from a cohort of people with APS1 and discovered multiple common antibody targets. These novel APS1 autoantigens exhibit tissue-restricted expression, including expression in enteroendocrine cells, pineal gland, and dental enamel. Using detailed clinical phenotyping, we find novel associations between autoantibodies and organ-restricted autoimmunity, including a link between anti-KHDC3L autoantibodies and premature ovarian insufficiency, and between anti-RFX6 autoantibodies and diarrheal-type intestinal dysfunction. Our study highlights the utility of PhIP-Seq for extensively interrogating antigenic repertoires in human autoimmunity and the importance of antigen discovery for improved understanding of disease mechanisms.

A novel NLRP7 protein-truncating mutation associated with discordant and divergent p57 immunostaining in diploid biparental and triploid digynic moles

NLRP7 is a maternal-effect gene that has a primary role in the oocyte. Its biallelic mutations are a major cause for recurrent diploid biparental hydatidiform moles (HMs). Here, we describe the full characterization of four HMs from a patient with a novel homozygous protein-truncating mutation in NLRP7. We found that some HMs have features of both complete and partial moles. Two HMs expressed p57 in the cytotrophoblast and stromal cells and exhibited divergent and discordant immunostaining. Microsatellite DNA-genotyping demonstrated that two HMs are diploid biparental and one is triploid digynic due to the failure of meiosis II. FISH analysis demonstrated triploidy in the cytotrophoblast and stromal cells in all villi. Our data highlight the atypical features of HM from patients with recessive NLRP7 mutations and the important relationship between NLRP7 defects in the oocyte and p57 expression that appear to be the main contributor to the molar phenotype regardless of the zygote genotype.

NLRP7 Is Involved in the Differentiation of the Decidual Macrophages

Macrophage polarization, regulated appropriately, may play important roles in successful pregnancy. In the face of the vital roles of decidua macrophages in pregnancy, it is insufficient to recognize the trigger of macrophage differentiation and polarization. We aimed to explore the link between the NLRP7 gene and macrophage polarization in human deciduas. Here, we enrolled the endometrial tissues from eight pregnant women in the first trimester. We found that NLRP7 was abundant in endometrial tissues and that NLRP7 was expressed in decidual macrophages of the first-trimester pregnancy. NLRP7 was predominately expressed in the decidual M2 macrophages, as compared with the M1 macrophages. Furthermore, our results suggest that NLRP7 is associated with decidual macrophage differentiation. NLRP7 over-expression suppresses the expression of M1 markers and enhances the expression of the M2 markers. Considering that NLRP7 relates to decidualization and macrophage differentiation, we propose that NLRP7 is a primate-specific multitasking gene to maintain endometrial hemostasis and reproductive success. This finding may pave the way for therapies of pathological pregnancies.

KHDC3L mutation causes recurrent pregnancy loss by inducing genomic instability of human early embryonic cells

Recurrent pregnancy loss (RPL) is an important complication in reproductive health. About 50% of RPL cases are unexplained, and understanding the genetic basis is essential for its diagnosis and prognosis. Herein, we report causal KH domain containing 3 like (KHDC3L) mutations in RPL. KHDC3L is expressed in human epiblast cells and ensures their genome stability and viability. Mechanistically, KHDC3L binds to poly(ADP-ribose) polymerase 1 (PARP1) to stimulate its activity. In response to DNA damage, KHDC3L also localizes to DNA damage sites and facilitates homologous recombination (HR)-mediated DNA repair. KHDC3L dysfunction causes PARP1 inhibition and HR repair deficiency, which is synthetically lethal. Notably, we identified two critical residues, Thr145 and Thr156, whose phosphorylation by Ataxia-telangiectasia mutated (ATM) is essential for KHDC3L’s functions. Importantly, two deletions of KHDC3L (p.E150_V160del and p.E150_V172del) were detected in female RPL patients, both of which harbor a common loss of Thr156 and are impaired in PARP1 activation and HR repair. In summary, our study reveals both KHDC3L as a new RPL risk gene and its critical function in DNA damage repair pathways.

Recurrent pregnancy loss is an important complication in reproductive health, and about 50% of cases remain unexplained. This study shows that KHDC3L safeguards the genomic stability of human early embryonic cells, and damaging mutations in its gene cause recurrent pregnancy loss in humans.

Genetic diagnosis of subfertility: the impact of meiosis and maternal effects

During reproductive age, approximately one in seven couples are confronted with fertility problems. While the aetiology is diverse, including infections, metabolic diseases, hormonal imbalances and iatrogenic effects, it is becoming increasingly clear that genetic factors have a significant contribution. Due to the complex nature of infertility that often hints at a multifactorial cause, the search for potentially causal gene mutations in idiopathic infertile couples has remained difficult. Idiopathic infertility patients with a suspicion of an underlying genetic cause can be expected to have mutations in genes that do not readily affect general health but are only essential in certain processes connected to fertility. In this review, we specifically focus on genes involved in meiosis and maternal-effect processes, which are of critical importance for reproduction and initial embryonic development. We give an overview of genes that have already been linked to infertility in human, as well as good candidates which have been described in other organisms. Finally, we propose a phenotypic range in which we expect an optimal diagnostic yield of a meiotic/maternal-effect gene panel.

Hepatic toxicity following actinomycin D chemotherapy in treatment of familial gestational trophoblastic neoplasia: A case report

RATIONALE

Familial hydatidiform mole is extremely rare while familial gestational trophoblastic neoplasia (GTN) has never been reported. Inspired by 2 biological sisters with postmolar GTN and liver toxicity, we reviewed susceptible maternal-effect genes and explored the role of possible drug transporter genes in the development of GTN.

PATIENT CONCERNS

We reported one Chinese family where the two sisters developed postmolar GTN while experiencing fast remission and significant hepatic toxicity from actinomycin D chemotherapy.

DIAGNOSES

The index pregnancy was diagnosed with curettage. The following GTN was confirmed when there was a rise in beta-hCG for three consecutive weekly measurements over at least a period of 2 weeks. Computed tomography was used to identify lung metastasis. The elder sister was diagnosed with gestational trophoblastic neoplasia (III: 2) while the younger sister was diagnosed as III: 3 according to WHO scoring system.

INTERVENTIONS

Patients were treated with actinomycin D of 10 μg/kg intravenously for 5 days every 2 weeks. When hepatic toxicity was indicated, polyene phosphatidyl choline and magnesium isoglycyrrhizinate were prescribed.

OUTCOMES

Both patients responded extremely well to the 5-day actinomycin D regimen. Beta-hCG remained less than 2 mIU/ml after 5 cycles while computed tomography scan showed downsized pulmonary nodules. Both experienced significant rise in ALT and AST levels that could be ameliorated with corresponding medication. Monthly followed-up showed negative beta-hCG levels and normal liver enzyme levels.

LESSONS

We speculated that the known or unknown NLRP7 and KHDC3L mutations might be correlated with drug disposition in liver while liver drug transporters such as P-glycoprotein family that are also expressed in trophoblasts might be correlated to GTN susceptibility. Future genomic profiles of large samples alike using next generation sequencing are needed to confirm our hypothesis and discover yet unknown genes.

Recurrent complete hydatidiform mole: where we are, is there a safe gestational horizon? Opinion and mini-review

Benign hydatidiform mole, complete or partial, is the most common type of gestational trophoblastic disease (GTD) characterised by excessive trophoblastic proliferation and abnormal embryonic development. Although most complete hydatidiform moles (CHMs) are diploid androgenetic, a few cases of CHMs are biparental, characterised by recurrence and familial clustering. In these rare cases, mutations in NLRP7 or KHDC3L genes, associated with maternal imprinting defects, have been implicated. Current data regarding future pregnancy options in hydatidiform moles are discussed and our opinion is presented based on an incidence that took place in our hospital with a woman with consecutive molar pregnancies. In recurrent hydatidiform moles, DNA testing should be performed and when NLRP7 or KHDC3L mutation are detected, oocyte donation should be proposed as an option to maximise woman's chances of having a normal pregnancy.

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.

NLRPs, the subcortical maternal complex and genomic imprinting

Before activation of the embryonic genome, the oocyte provides many of the RNAs and proteins required for the epigenetic reprogramming and the transition to a totipotent state. Targeted disruption of a subset of oocyte-derived transcripts in mice results in early embryonic lethality and cleavage-stage embryonic arrest as highlighted by the members of the subcortical maternal complex (SCMC). Maternal-effect recessive mutations of NLRP7, KHDC3L and NLRP5 in humans are associated with variable reproductive outcomes, biparental hydatidiform moles (BiHM) and widespread multi-locus imprinting disturbances. The precise mechanism of action of these genes is unknown, but the maternal-effect phenomenon suggests a function during early pre-implantation development, while biochemical and genetic studies implement them as SCMC members or interacting partners. In this review article, we discuss the role of the NLRP family members and the SCMC proteins in the establishment of genomic imprints and post-zygotic methylation maintenance, the recent advances made in the understanding of the biology involved in BiHM formation and the wider roles of the SCMC in mammalian reproduction.

Maternal heterozygous NLRP7 variant results in recurrent reproductive failure and imprinting disturbances in the offspring

It has been shown previously that homozygous and compound-heterozygous variants affecting protein function in the human NLRP genes impact reproduction and/or fetal imprinting patterns. These variants represent so-called 'maternal effect mutations', that is, although female variant carriers are healthy, they are at risk of reproductive failure, and their offspring may develop aberrant methylation and imprinting disorders. In contrast, the relevance to reproductive failure of maternal heterozygous NLRP7 variants remains unclear. The present report describes the identification of a heterozygous NLRP7 variant in a healthy 28-year-old woman with a history of recurrent reproductive failure, and the molecular findings in two of the deceased offspring. Next-generation sequencing (NGS) for NLRP variants was performed. In the tissues of two offspring (one fetus; one deceased premature neonate) methylation of imprinted loci was tested using methylation-specific assays. Both pregnancies had been characterized by the presence of elevated human chorionic gonadotropin (hCG) levels and ovarian cysts. In the mother, a heterozygous nonsense 2-bp deletion in exon 5 of the NLRP7 gene was identified (NM_001127255.1:c.2010_2011del, p.(Phe671Glnfs*18)). In the two investigated offspring, heterogeneous aberrant methylation patterns were detected at imprinted loci. The present data support the hypothesis that heterozygous NLRP7 variants contribute to reproductive wastage, and that these variants represent autosomal dominant maternal effect variants which lead to aberrant imprinting marks in the offspring. Specific screening and close prenatal monitoring of NLRP7 variant carriers is proposed. Egg donation might facilitate successful pregnancy in heterozygous NLRP7 variant carriers.

Pathogenic variant in NLRP7 (19q13.42) associated with recurrent gestational trophoblastic disease: Data from early embryo development observed during in vitro fertilization

Objective

To describe in vitro development of human embryos derived from an individual with a homozygous pathogenic variant in NLRP7 (19q13.42) and recurrent hydatidiform mole (HM), an autosomal recessive condition thought to occur secondary to an oocyte defect.

Methods

A patient with five consecutive HM pregnancies was genomically evaluated via next generation sequencing followed by controlled ovarian hyperstimulation, in vitro fertilization (IVF) with intracytoplasmic sperm injection, embryo culture, and preimplantation genetic screening. Findings in NLRP7 were recorded and embryo culture and biopsy data were tabulated as a function of parental origin for any identified ploidy error.

Results

The patient was found to have a pathogenic variant in NLRP7 (c.2810+2T>G) in a homozygous state. Fifteen oocytes were retrieved and 10 embryos were available after fertilization via intracytoplasmic sperm injection. Developmental arrest was noted for all 10 embryos after 144 hours in culture, thus no transfer was possible. These non-viable embryos were evaluated by karyomapping and all were diploid biparental; two were euploid and eight had various aneuploidies all of maternal origin.

Conclusion

This is the first report of early human embryo development from a patient with any NLRP7 mutation. The pathogenic variant identified here resulted in global developmental arrest at or before blastocyst stage. Standard IVF should therefore be discouraged for such patients, who instead need to consider oocyte (or embryo) donation with IVF as preferred clinical methods to treat infertility.

Maternally expressed NLRP2 links the subcortical maternal complex (SCMC) to fertility, embryogenesis and epigenetic reprogramming

Mammalian parental genomes contribute differently to early embryonic development. Before activation of the zygotic genome, the maternal genome provides all transcripts and proteins required for the transition from a highly specialized oocyte to a pluripotent embryo. Depletion of these maternally-encoded transcripts frequently results in failure of preimplantation embryonic development, but their functions in this process are incompletely understood. We found that female mice lacking NLRP2 are subfertile because of early embryonic loss and the production of fewer offspring that have a wide array of developmental phenotypes and abnormal DNA methylation at imprinted loci. By demonstrating that NLRP2 is a member of the subcortical maternal complex (SCMC), an essential cytoplasmic complex in oocytes and preimplantation embryos with poorly understood function, we identified imprinted postzygotic DNA methylation maintenance, likely by directing subcellular localization of proteins involved in this process, such as DNMT1, as a new crucial role of the SCMC for mammalian reproduction.

ECAT1 is essential for human oocyte maturation and pre-implantation development of the resulting embryos

ECAT1 is a subunit of the subcortical maternal complex that is required for cell cycle progression during pre-implantation embryonic development; however, its exact function remains to be elucidated. Here we investigated the expression of ECAT1 in human ovarian tissue, oocytes and pre-implantation embryos and assessed its function by using RNA interference (RNAi) in oocytes. ECAT1 mRNA was highly expressed in human oocytes and zygotes, as well as in two-cell, four-cell and eight-cell embryos, but declined significantly in morulae and blastocysts. ECAT1 was expressed in the cytoplasm of oocytes and pre-implantation embryos and was localized more specifically in the cortical region than in the inner cytoplasm. RNAi experiments demonstrated that down-regulation of ECAT1 expression not only impaired spindle assembly and reduced maturation and fertilization rates of human oocytes but also decreased the cleavage rate of the resulting zygotes. In conclusion, our study indicates that ECAT1 may play a role in meiotic progression by maintaining the accuracy of spindle assembly in human oocytes, thus promoting oocyte maturation and subsequent development of the embryo.

Two novel mutations in the KHDC3L gene in Asian patients with recurrent hydatidiform mole

Recurrent hydatidiform mole (RHM) is defined by the occurrence of repeated molar pregnancies in affected women. Two genes, NLRP7 and KHDC3L, play a causal role in RHM and are responsible for 48-80% and 5% of cases, respectively. Here, we report the results of screening these two genes for mutations in one Iranian and one Indian patient with RHM. No mutations in NLRP7 were identified in the two patients. KHDC3L sequencing identified two novel protein-truncating mutations in a homozygous state, a 4-bp deletion, c.17_20delGGTT (p.Arg6Leufs*7), in the Iranian patient and a splice mutation, c.349+1G>A, that affects the invariant donor site at the junction of exon 2 and intron 2 in the Indian patient. To date, only four mutations in KHDC3L have been reported. The identification of two additional mutations provides further evidence for the important role of KHDC3L in the pathophysiology of RHM and increases the diversity of mutations described in Asian populations.

The subcortical maternal complex: multiple functions for one biological structure?

The subcortical maternal complex (SCMC) is a multiprotein complex uniquely expressed in mammalian oocytes and early embryos, essential for zygote progression beyond the first embryonic cell divisions. Similiar to other factors encoded by maternal effect genes, the physiological role of SCMC remains unclear, although recent evidence has provided important molecular insights into different possible functions. Its potential involvement in human fertility is attracting increasing attention; however, the complete story is far from being told. The present mini review provides an overview of recent findings related to the SCMC and discusses its potential physiological role/s with the aim of inspiring new directions for future research.

Characterization and quantification of proteins secreted by single human embryos prior to implantation

The use of in vitro fertilization (IVF) has revolutionized the treatment of infertility and is now responsible for 1–5% of all births in industrialized countries. During IVF, it is typical for patients to generate multiple embryos. However, only a small proportion of them possess the genetic and metabolic requirements needed in order to produce a healthy pregnancy. The identification of the embryo with the greatest developmental capacity represents a major challenge for fertility clinics. Current methods for the assessment of embryo competence are proven inefficient, and the inadvertent transfer of non-viable embryos is the principal reason why most IVF treatments (approximately two-thirds) end in failure. In this study, we investigate how the application of proteomic measurements could improve success rates in clinical embryology. We describe a procedure that allows the identification and quantification of proteins of embryonic origin, present in attomole concentrations in the blastocoel, the enclosed fluid-filled cavity that forms within 5-day-old human embryos. By using targeted proteomics, we demonstrate the feasibility of quantifying multiple proteins in samples derived from single blastocoels and that such measurements correlate with aspects of embryo viability, such as chromosomal (ploidy) status. This study illustrates the potential of high-sensitivity proteomics to measure clinically relevant biomarkers in minute samples and, more specifically, suggests that key aspects of embryo competence could be measured using a proteomic-based strategy, with negligible risk of harm to the living embryo. Our work paves the way for the development of “next-generation” embryo competence assessment strategies, based on functional proteomics.

Causes and Consequences of Multi-Locus Imprinting Disturbances in Humans

Eight syndromes are associated with the loss of methylation at specific imprinted loci. There has been increasing evidence that these methylation defects in patients are not isolated events occurring at a given disease-associated locus but that some of these patients may have multi-locus imprinting disturbances (MLID) affecting additional imprinted regions. With the recent advances in technology, methylation profiling has revealed that imprinted loci represent only a small fraction of the methylation differences observed between the gametes. To figure out how imprinting anomalies occur at multiple imprinted domains, we have to understand the interplay between DNA methylation and histone modifications in the process of selective imprint protection during pre-implantation reprogramming, which, if disrupted, leads to these complex imprinting disorders (IDs).

Expressional and Bioinformatic Analysis of Bovine Filia/Ecat1/Khdc3l Gene: A Comparison with Ovine Species

Maternal effect genes have highly impressive effects on pre-implantation development. Filia/Ecat1/Khdc3l is a maternal effect gene found in mouse oocytes and embryos, loss of which causes a 50% decrease in fertility. In the present study, we investigated Filia mRNA expression in bovine oviduct, 30- to 40-day fetus, liver, heart, lung, and oocytes (as a positive control), by RT-PCR and detected it only in oocytes. A 443 bp fragment was amplified only in oocytes and was sequenced as a part of bovine predicted Filia mRNA. We analyzed bovine and ovine Filia N-terminal peptide sequence in PHYRE2, and a KH domain was predicted. Protein alignment using ClustalW indicated a highly identical N-terminal extention between the 2 species. Immunohistochemical analysis using anti-bovine Filia antibody showed the expression of Filia protein in the zone surrounding the nuclear membrane, and in the subcortex of ovine oocytes of primary and antral follicles. However, in the bovine, Filia has been found through the oocyte cytoplasm of antral follicles, and here it is further confirmed in the primary follicles. Our data suggests a difference in Filia expression pattern between cow and sheep, although the sequence is highly conserved.

The genomic architecture of NLRP7 is Alu rich and predisposes to disease-associated large deletions

NLRP7 is a major gene responsible for recurrent hydatidiform moles. Here, we report 11 novel NLRP7 protein truncating variants, of which five deletions of more than 1-kb. We analyzed the transcriptional consequences of four variants. We demonstrate that one large homozygous deletion removes NLRP7 transcription start site and results in the complete absence of its transcripts in a patient in good health besides her reproductive problem. This observation strengthens existing data on the requirement of NLRP7 only for female reproduction. We show that two other variants affecting the splice acceptor of exon 6 lead to its in-frame skipping while another variant affecting the splice donor site of exon 9 leads to an in-frame insertion of 54 amino acids. Our characterization of the deletion breakpoints demonstrated that most of the breakpoints occurred within Alu repeats and the deletions were most likely mediated by microhomology events. Our data define a hotspot of Alu instability and deletions in intron 5 with six different breakpoints and rearrangements. Analysis of NLRP7 genomic sequences for repetitive elements demonstrated that Alu repeats represent 48% of its intronic sequences and these repeats seem to have been inserted into the common NLRP2/7 primate ancestor before its duplication into two genes.

Chromosomal instability in mammalian pre-implantation embryos: potential causes, detection methods, and clinical consequences

Formation of a totipotent blastocyst capable of implantation is one of the first major milestones in early mammalian embryogenesis, but less than half of in vitro fertilized embryos from most mammals will progress to this stage of development. Whole chromosomal abnormalities, or aneuploidy, are key determinants of whether human embryos will arrest or reach the blastocyst stage. Depending on the type of chromosomal abnormality, however, certain embryos still form blastocysts and may be morphologically indistinguishable from chromosomally normal embryos. Despite the implementation of pre-implantation genetic screening and other advanced in vitro fertilization (IVF) techniques, the identification of aneuploid embryos remains complicated by high rates of mosaicism, atypical cell division, cellular fragmentation, sub-chromosomal instability, and micro-/multi-nucleation. Moreover, several of these processes occur in vivo following natural human conception, suggesting that they are not simply a consequence of culture conditions. Recent technological achievements in genetic, epigenetic, chromosomal, and non-invasive imaging have provided additional embryo assessment approaches, particularly at the single-cell level, and clinical trials investigating their efficacy are continuing to emerge. In this review, we summarize the potential mechanisms by which aneuploidy may arise, the various detection methods, and the technical advances (such as time-lapse imaging, "-omic" profiling, and next-generation sequencing) that have assisted in obtaining this data. We also discuss the possibility of aneuploidy resolution in embryos via various corrective mechanisms, including multi-polar divisions, fragment resorption, endoreduplication, and blastomere exclusion, and conclude by examining the potential implications of these findings for IVF success and human fecundity.

Postovulatory aging affects dynamics of mRNA, expression and localization of maternal effect proteins, spindle integrity and pericentromeric proteins in mouse oocytes

STUDY QUESTION

Is the postovulatory aging-dependent differential decrease of mRNAs and polyadenylation of mRNAs coded by maternal effect genes associated with altered abundance and distribution of maternal effect and RNA-binding proteins (MSY2)?

SUMMARY ANSWER

Postovulatory aging results in differential reduction in abundance of maternal effect proteins, loss of RNA-binding proteins from specific cytoplasmic domains and critical alterations of pericentromeric proteins without globally affecting protein abundance.

WHAT IS KNOWN ALREADY

Oocyte postovulatory aging is associated with differential alteration in polyadenylation and reduction in abundance of mRNAs coded by selected maternal effect genes. RNA-binding and -processing proteins are involved in storage, polyadenylation and degradation of mRNAs thus regulating stage-specific recruitment of maternal mRNAs, while chromosomal proteins that are stage-specifically expressed at pericentromeres, contribute to control of chromosome segregation and regulation of gene expression in the zygote.

STUDY DESIGN, SIZE, DURATION

Germinal vesicle (GV) and metaphase II (MII) oocytes from sexually mature C57B1/6J female mice were investigated. Denuded in vivo or in vitro matured MII oocytes were postovulatory aged and analyzed by semiquantitative confocal microscopy for abundance and localization of polyadenylated RNAs, proteins of maternal effect genes (transcription activator BRG1 also known as ATP-dependent helicase SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily a, member 4 (SMARCA4) and NOD-like receptor family pyrin domain containing 5 (NLRP5) also known as MATER), RNA-binding proteins (MSY2 also known as germ cell-specific Y-box-binding protein, YBX2), and post-transcriptionally modified histones (trimethylated histone H3K9 and acetylated histone H4K12), as well as pericentromeric ATRX (alpha thalassemia/mental retardation syndrome X-linked, also termed ATP-dependent helicase ATRX or X-linked nuclear protein (XNP)). For proteome analysis five replicates of 30 mouse oocytes were analyzed by selected reaction monitoring (SRM).

MATERIAL AND METHODS

GV and MII oocytes were obtained from large antral follicles or ampullae of sexually mature mice, respectively. Denuded MII oocytes were aged for 24 h post ovulation. For analysis of distribution and abundance of polyadenylated RNAs fixed oocytes were in situ hybridized to Cy5 labeled oligo(dT)20 nucleotides. Absolute quantification of protein concentration per oocyte of selected proteins was done by SRM proteome analysis. Relative abundance of ATRX was assessed by confocal laser scanning microscopy (CLSM) of whole mount formaldehyde fixed oocytes or after removal of zona and spreading. MSY2 protein distribution and abundance was studied in MII oocytes prior to, during and after exposure to nocodazole, or after aging for 2 h in presence of H2O2 or for 24 h in presence of a glutathione donor, glutathione ethylester (GEE).

MAIN RESULTS AND ROLE OF CHANCE

The significant reduction in abundance of proteins (P < 0.001) translated from maternal mRNAs was independent of polyadenylation status, while their protein localization was not significantly changed by aging. Most of other proteins quantified by SRM analysis did not significantly change in abundance upon aging except MSY2 and GTSF1. MSY2 was enriched in the subcortical RNP domain (SCRD) and in the spindle chromosome complex (SCC) in a distinct pattern, right and left to the chromosomes. There was a significant loss of MSY2 from the SCRD (P < 0.001) and the spindle after postovulatory aging. Microtubule de- and repolymerization caused reversible loss of MSY2 spindle-association whereas H2O2 stress did not significantly decrease MSY2 abundance. Aging in presence of GEE decreased significantly (P < 0.05) the aging-related overall and cytoplasmic loss of MSY2. Postovulatory aging increased significantly spindle abnormalities, unaligned chromosomes, and abundance of acetylated histone H4K12, and decreased pericentromeric trimethylated histone H3K9 (all P < 0.001). Spreading revealed a highly significant increase in pericentromeric ATRX (P < 0.001) upon ageing. Thus, the significantly reduced abundance of MSY2 protein, especially at the SCRD and the spindle may disturb the spatial control and timely recruitment, deadenylation and degradation of developmentally important RNAs. An autonomous program of degradation appears to exist which transiently and specifically induces the loss and displacement of transcripts and specific maternal proteins independent of fertilization in aging oocytes and thereby can critically affect chromosome segregation and gene expression in the embryo after fertilization.

LIMITATION, REASONS FOR CAUTION

We used the mouse oocyte to study processes associated with postovulatory aging, which may not entirely reflect processes in aging human oocytes. However, increases in spindle abnormalities, unaligned chromosomes and H4K12 acetylated histones, as well as in mRNA abundance and polyadenylation have been observed also in aged human oocytes suggesting conserved processes in aging.

WIDER IMPLICATIONS OF THE FINDINGS

Postovulatory aging precociously induces alterations in expression and epigenetic modifications of chromatin by ATRX and in histone pattern in MII oocytes that normally occur after fertilization, possibly contributing to disturbances in the oocyte-to-embryo transition (OET) and the zygotic gene activation (ZGA). These observations in mouse oocytes are also relevant to explain disturbances and reduced developmental potential of aged human oocytes and caution to prevent oocyte aging in vivo and in vitro.

STUDY FUNDING/COMPETING INTERESTS

The study has been supported by the German Research Foundation (DFG) (EI 199/7-1 | GR 1138/12-1 | HO 949/21-1 and FOR 1041). There is no competing interest.

Absence of Maternal Methylation in Biparental Hydatidiform Moles from Women with NLRP7 Maternal-Effect Mutations Reveals Widespread Placenta-Specific Imprinting

Familial recurrent hydatidiform mole (RHM) is a maternal-effect autosomal recessive disorder usually associated with mutations of the NLRP7 gene. It is characterized by HM with excessive trophoblastic proliferation, which mimics the appearance of androgenetic molar conceptuses despite their diploid biparental constitution. It has been proposed that the phenotypes of both types of mole are associated with aberrant genomic imprinting. However no systematic analyses for imprinting defects have been reported. Here, we present the genome-wide methylation profiles of both spontaneous androgenetic and biparental NLRP7 defective molar tissues. We observe total paternalization of all ubiquitous and placenta-specific differentially methylated regions (DMRs) in four androgenetic moles; namely gain of methylation at paternally methylated loci and absence of methylation at maternally methylated regions. The methylation defects observed in five RHM biopsies from NLRP7 defective patients are restricted to lack-of-methylation at maternal DMRs. Surprisingly RHMs from two sisters with the same missense mutations, as well as consecutive RHMs from one affected female show subtle allelic methylation differences, suggesting inter-RHM variation. These epigenotypes are consistent with NLRP7 being a maternal-effect gene and involved in imprint acquisition in the oocyte. In addition, bioinformatic screening of the resulting methylation datasets identified over sixty loci with methylation profiles consistent with imprinting in the placenta, of which we confirm 22 as novel maternally methylated loci. These observations strongly suggest that the molar phenotypes are due to defective placenta-specific imprinting and over-expression of paternally expressed transcripts, highlighting that maternal-effect mutations of NLRP7 are associated with the most severe form of multi-locus imprinting defects in humans.

[Complete hydatidiform mole]

"The battle of the sexes begins in the zygote" W. Reik and J. Walter. Complete hydatidiform mole (CHM) is a pathology of the placenta with androgenetic diploid origin (chromosomes only from paternal origin). Placental villi present an abnormal hyperproliferation and hydropic degeneration associated with the absence of embryo. Three mechanisms can be envisaged at its origin: (1) destruction/expulsion of the female pronucleus at the time of fertilization by one or two spermatozoa, the former being followed by an endoreplication of the male pronucleus (homozygous mole), (2) a triploid zygote (fertilization by two spermatozoa) leading to a haploid and a diploid clones. The diploid clone may produce a normal fetus while the haploid clone, after endoreplication, generates a complete hydatidiform mole, (3) a nutritional defect during the differentiation of the oocytes of the female embryo that will affect the integrity and maturity of her oocytes during her adult life and lead to hydatidiform mole. In countries with a poor medical health care system, moles can be invasive or, in rare cases, lead to gestational choriocarcinomas.

The hydatidiform mole

The hydatidiform mole (HM) is a placental pathology of androgenetic origin. Placental villi have an abnormal hyperproliferation event and hydropic degeneration. Three situations can be envisaged at its origin: 1. The destruction/expulsion of the female pronucleus at the time of fertilization by 1 or 2 spermatozoa with the former being followed by an endoreplication of the male pronucleus leading to a complete hydatidiform mole (CHM) 2. A triploid zygote (fertilization by 2 spermatozoa) leading to a partial hydatidiform mole (PHM) but can also lead to haploid and diploid clones. The diploid clone may produce a normal fetus while the haploid clone after endoreplication generates a CHM 3. A nutritional defect during the differentiation of the oocytes or the deterioration of the limited oxygen pressure during the first trimester of gestation may lead to the formation of a HM. In countries with poor medical health care system, moles (mainly the CHM) can become invasive or, in rare cases, lead to gestational choriocarcinomas.

Germline-derived DNA methylation and early embryo epigenetic reprogramming: The selected survival of imprints

DNA methylation is an essential epigenetic mechanism involved in many essential cellular processes. During development epigenetic reprograming takes place during gametogenesis and then again in the pre-implantation embryo. These two reprograming windows ensure genome-wide removal of methylation in the primordial germ cells so that sex-specific signatures can be acquired in the sperm and oocyte. Following fertilization the majority of this epigenetic information is erased to give the developing embryo an epigenetic profile coherent with pluripotency. It is estimated that ∼65% of the genome is differentially methylated between the gametes, however following embryonic reprogramming only parent-of-origin methylation at known imprinted loci remains. This suggests that trans-acting factors such as Zfp57 can discriminate imprinted differentially methylated regions (DMRs) from the thousands of CpG rich regions that are differentially marked in the gametes. Recently transient imprinted DMRs have been identified suggesting that these loci are also protected from pre-implantation reprograming but succumb to de novo remethylation at the implantation stage. This highlights that "ubiquitous" imprinted loci are also resilient to gaining methylation by protecting their unmethylated alleles. In this review I examine the processes involved in epigenetic reprograming and the mechanisms that ensure allelic methylation at imprinted loci is retained throughout the life of the organism, discussing the critical differences between mouse and humans. This article is part of a Directed Issue entitled: Epigenetics Dynamics in development and disease.