Decrease in expression of maternal effect gene Mater is associated with maternal ageing in mice

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.

Oocyte aging: looking beyond chromosome segregation errors

The age-associated decline in female fertility is largely ascribable to a decrease in oocyte quality. This phenomenon is multifaceted and influenced by numerous interconnected maternal and environmental factors. An increase in the rate of meiotic errors is the major cause of the decline in oocyte developmental competence. However, abnormalities in the ooplasm accumulating with age - including altered metabolism, organelle dysfunction, and aberrant gene regulation - progressively undermine oocyte quality. Stockpiling of maternal macromolecules during folliculogenesis is crucial, as oocyte competence to achieve maturation, fertilization, and the earliest phases of embryo development occur in absence of transcription. At the same time, crucial remodeling of oocyte epigenetics during oogenesis is potentially exposed to interfering factors, such as assisted reproduction technologies (ARTs) or environmental changes, whose impact may be enhanced by reproductive aging. As the effects of maternal aging on molecular mechanisms governing the function of the human oocyte remain poorly understood, studies in animal models are essential to deepen current understanding, with translational implications for human ARTs. The present mini review aims at offering an updated and consistent view of cytoplasmic alterations occurring in oocytes during aging, focusing particularly on gene and epigenetic regulation. Appreciation of these mechanisms could inspire solutions to mitigate/control the phenomenon, and thus benefit modern ARTs.

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.

Integrative analysis of the 3D genome structure reveals that CTCF maintains the properties of mouse female germline stem cells

The three-dimensional configuration of the genome ensures cell type-specific gene expression profiles by placing genes and regulatory elements in close spatial proximity. Here, we used in situ high-throughput chromosome conformation (in situ Hi-C), RNA sequencing (RNA-seq) and chromatin immunoprecipitation sequencing (ChIP-seq) to characterize the high-order chromatin structure signature of female germline stem cells (FGSCs) and identify its regulating key factor based on the data-driven of multiple omics data. By comparison with pluripotent stem cells (PSCs), adult stem cells (ASCs), and somatic cells at three major levels of chromatin architecture, A/B compartments, topologically associating domains, and chromatin loops, the chromatin architecture of FGSCs was most similar to that of other ASCs and largely different from that of PSCs and somatic cells. After integrative analysis of the three-dimensional chromatin structure, active compartment-associating loops (aCALs) were identified as a signature of high-order chromatin organization in FGSCs, which revealed that CCCTC-binding factor was a major factor to maintain the properties of FGSCs through regulation of aCALs. We found FGSCs belong to ASCs at chromatin structure level and characterized aCALs as the high-order chromatin structure signature of FGSCs. Furthermore, CTCF was identified to play a key role in regulating aCALS to maintain the biological functions of FGSCs. These data provide a valuable resource for future studies of the features of chromatin organization in mammalian stem cells and further understanding of the fundamental characteristics of FGSCs.

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.

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.

Transcriptome Analysis of Testes and Uterus: Reproductive Dysfunction Induced by Toxoplasma gondii in Mice

Toxoplasma gondii (T. gondii) infection in female mammals during pregnancy can result in poor pregnancy. Similarly, it can result in male reproductive disorders in male mammals. Although the testes and uterus have very different biological makeup, they are still both attacked by T. gondii resulting in reproductive dysfunctions. We hypothesized that there are significant common genes in the testes and uterus that interact with T. gondii. Finding out and studying these genes is vital to understand the infection mechanism of T. gondii and the induced disease pathogenesis. To achieve this goal, we built a mice model of acute infection with T. gondii and the testes and uterus of the mice were sequenced by RNA-Seq. A total of 291 and 679 significantly differently expressed genes (DEGs) were obtained from the testes and the uterus, respectively. In the Gene Ontology (GO) analysis, part of the DEGs in the testes and uterus were related to 35 GO functions. When compared with the KEGG database, seven pathways affecting both the testes and uterus during the course of T. gondii infection were identified. In addition, Toxoplasmosis can significantly affect the expression of Nlrp5 and Insc leading to negative outcomes in the host. On the other hand, the host regulates Gbp7, Gbp2b, and Ifit3 to defend against T. gondii infection.

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.

Fam70A binds Wnt5a to regulate meiosis and quality of mouse oocytes

OBJECTIVES

Little is known about the roles of integral membrane proteins beyond channels, carriers or receptors in meiotic oocytes. The transmembrane protein Fam70A was previously identified as a likely "female fertility factor" in Fox3a-knockout mouse ovaries where almost all follicles underwent synchronous activation and the mice became infertile very early. However, whether Fam70A functions in oocyte meiosis remains unknown. Therefore, the present study aimed to address this question.

MATERIALS AND METHODS

Co-immunoprecipitation, immunogold labelling-electron microscopy, co-localization and yeast two-hybrid assays were used to verify the interaction. Antibody or small interfering RNA transfection was used to deplete the proteins. Immunofluorescence, immunohistochemistry and live tracker staining were used to examine the localization or characterize phenotypes. Western blot was used to examine the protein level.

RESULTS

Fam70A was enriched in oocyte membranes important for normal meiosis. Fam70A depletion remarkably disrupted spindle assembly, chromosome congression and first polar body extrusion, which subsequently increased aneuploidy and abnormal fertilization. Moreover, Fam70A directly bound Wnt5a, the most abundant Wnt member within oocytes. Depletion of either Fam70A or Wnt5a remarkably increased adenomatous polyposis coli (APC), which stabilizes active β-catenin and microtubules. Consequently, depletion of either Fam70A or Wnt5a remarkably increased p-β-catenin (inactive form) and acetylated tubulin, while APC knockdown remarkably decreased these two. Furthermore, Fam70A depletion remarkably reduced Akt phosphorylation.

CONCLUSIONS

Fam70A regulates meiosis and quality of mouse oocytes through both canonical and non-canonical Wnt5a signalling pathways.

Genomic imprinting disorders: lessons on how genome, epigenome and environment interact

Genomic imprinting, the monoallelic and parent-of-origin-dependent expression of a subset of genes, is required for normal development, and its disruption leads to human disease. Imprinting defects can involve isolated or multilocus epigenetic changes that may have no evident genetic cause, or imprinting disruption can be traced back to alterations of cis-acting elements or trans-acting factors that control the establishment, maintenance and erasure of germline epigenetic imprints. Recent insights into the dynamics of the epigenome, including the effect of environmental factors, suggest that the developmental outcomes and heritability of imprinting disorders are influenced by interactions between the genome, the epigenome and the environment in germ cells and early embryos.

Preovulatory Aging In Vivo and In Vitro Affects Maturation Rates, Abundance of Selected Proteins, Histone Methylation Pattern and Spindle Integrity in Murine Oocytes

Delayed ovulation and delayed fertilization can lead to reduced developmental competence of the oocyte. In contrast to the consequences of postovulatory aging of the oocyte, hardly anything is known about the molecular processes occurring during oocyte maturation if ovulation is delayed (preovulatory aging). We investigated several aspects of oocyte maturation in two models of preovulatory aging: an in vitro follicle culture and an in vivo mouse model in which ovulation was postponed using the GnRH antagonist cetrorelix. Both models showed significantly reduced oocyte maturation rates after aging. Furthermore, in vitro preovulatory aging deregulated the protein abundance of the maternal effect genes Smarca4 and Nlrp5, decreased the levels of histone H3K9 trimethylation and caused major deterioration of chromosome alignment and spindle conformation. Protein abundance of YBX2, an important regulator of mRNA stability, storage and recruitment in the oocyte, was not affected by in vitro aging. In contrast, in vivo preovulatory aging led to reduction in Ybx2 transcript and YBX2 protein abundance. Taken together, preovulatory aging seems to affect various processes in the oocyte, which could explain the low maturation rates and the previously described failures in fertilization and embryonic development.

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.