Mechanisms of Oocyte Maturation and Related Epigenetic Regulation

Single-cell proteomics analysis of human oocytes during GV-to-MI transition

STUDY QUESTION

Which proteins are involved in the transition of human oocytes from the germinal vesicle (GV) to metaphase I (MI) phase?

SUMMARY ANSWER

A total of 2369 proteins were identified, including 149 with significantly differential expression, 79 with upregulated expression in MI oocytes and 70 with downregulated expression.

WHAT IS KNOWN ALREADY

During oocyte maturation, maternal proteins and RNA are stored to support early embryo development. However, GV oocytes matured in vitro have a lower chance of developing into blastocysts than MI oocytes. Therefore, identifying key differentially expressed proteins between the GV and MI stages can provide a better understanding of human oocyte development and maturation mechanisms and improve the utilization of oocytes.

STUDY DESIGN, SIZE, DURATION

In total, 16 oocytes at the GV and MI stages were collected from female patients who underwent ovulation induction due to male factor infertility requiring embryo retrieval for ICSI. Differential proteins were identified in 16 oocytes using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, and the expression of several differential proteins was verified by immunofluorescence (IF). RNA interference was employed to identify the functions of specific proteins during oocyte maturation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

16 immature human oocytes discarded during ICSI cycles (eight GV oocytes and eight MI oocytes) were collected from 10 female patients. Two cohorts of oocytes underwent zona pellucida removal, lysis, and enzymatic digestion prior to peptide detection using LC-MS/MS methodology. Peptide detection outcomes were subjected to differential protein screening and functional annotation employing distinct analytical algorithms and datasets. To corroborate the sequencing findings, proteins exhibiting notable differential expression were authenticated via IF. Concerning protein functionality, siRNA was introduced during the GV phase, and oocyte maturation was evaluated through observation of polar body extrusion, alongside assessment of siRNA interference efficacy via IF analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 2369 proteins were identified, including 149 with significantly differential expression, 79 with upregulated expression in MI oocytes and 70 with downregulated expression. Gene ontology functional annotation and functional analysis revealed that these differentially expressed proteins are involved mainly in organic matter and cell metabolism, biological regulation, primary metabolism, nitrogen compound metabolism, and other biological processes. Kyoto Encyclopedia of Genes and Genomes analysis revealed that the differentially expressed genes were involved mainly in the following pathways: transport and catabolism, signal transduction, protein folding, and energy and amino acid metabolism. The differentially expressed proteins included actin-related protein 2 (ACTR2), NADH: Ubiquinone Oxidoreductase Core Subunit S1 (NDUFS1), Tubulin Gamma Complex Component 3 (TUBGCP3), Heat Shock Protein Family B (Small) Member 1 (HSPB1), and Eukaryotic Translation Initiation Factor 3 Subunit B, which are involved mainly in mitochondrial function, cell division, and signal transduction. ACTR2, HSPB1, NDUFS1, and TUBGCP3 were selected for IF staining, and the difference in fluorescence intensity between GV and MI oocytes was consistent with the sequencing results. Three pairs of primers were designed for each gene corresponding to the top 10 differentially upregulated and downregulated proteins (with siRNAs successfully designed for eight upregulated and seven downregulated proteins) to study their function, and the results revealed that the protein expression of TUBGCP3 was downregulated after RNA interference.

LARGE SCALE DATA

See supplementary tables.

LIMITATIONS, REASONS FOR CAUTION

Although we have identified some differentially expressed proteins during the transition from human oocyte GV to MI stage, their crucial roles in oocyte maturation remain elusive. To elucidate the functions of these proteins in oocyte maturation, we have generated conditional knockout mice targeting selected proteins.

WIDER IMPLICATIONS OF THE FINDINGS

We conducted single-cell level analysis to identify differentially expressed proteins between the human oocyte GV and MI stages. Our objective is to ascertain the potential of supplementing these proteins in the in vitro maturation culture medium to augment both oocyte maturation rates and quality.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by the National Natural Science Foundation of China (82171599 and 82471657, B.X., 82301871, L.L.); China Postdoctoral Science Foundation (2024M763169, S.B.); and the National Key Research and Development Project of China (2029YFA0802600, B.X.). None of the authors has any conflict of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Non-Redundant Essential Roles of Proteasomal Ubiquitin Receptors Rpn10 and Rpn13 in Germ Cell Formation and Fertility

Primordial germ cells (PGCs) undergo proliferation, migration, and sexual differentiation to produce gonocytes, which eventually generate germ cells. The proteasome, which degrades most cellular proteins, is a protein complex with dozens of subunits. The proteasomal ubiquitin receptors Rpn10 and Rpn13 have been shown to play partially overlapping roles in binding ubiquitin chains in vitro and in liver function in vivo. However, the specific role of Rpn10 and Rpn13 in germ cell production remains unclear. We show here that Rpn10 and Rpn13 are each essential for germ cell production and fertility. The conditional deletion of either Rpn10 or Rpn13 in PGCs results in infertility in both male and female mice. Germ cells in testes and ovaries all decreased dramatically in the Rpn13 conditional knockout (cKO) mice. Specifically, the deletion of Rpn13 in PGCs disrupts the assembly of the 26S proteasome, reduces the number of PGCs, and blocks the meiosis of spermatocytes at the zygotene stage during prophase I; on the other hand, the deletion of Rpn10 in PGCs sharply reduces PGC migration. These results are important for understanding the roles of Rpn10 and Rpn13 in germ cell development and related reproductive diseases.

Transcriptional insights on the incomplete cytoplasmic maturation and developmental potential of oocytes cultured without granulosa cells in mice

BACKGROUND

Oocyte maturation is crucial for female fertility and embryonic development, encompassing nuclear and cytoplasmic maturation. Supportive cells of follicles, such as granulosa cells, are essential for oocyte growth and maturation. Oocytes can achieve nuclear maturation without granulosa cells during in vitro maturation (IVM). However, there is still a higher chance of incomplete cytoplasmic maturation for these oocytes with mature nuclei compared with oocytes cultured with granulosa cells. Oocytes with incomplete cytoplasmic maturation have lower fertilization rates and developmental potential than mature ones, although underlying mechanisms are poorly understood. Identifying key genes and signaling pathways associated with oocyte cytoplasmic maturation can help further elucidate the maturing process of oocytes and understand the impact of immature oocytes on embryonic development, throwing insights into the strategy to improve the success rate of assisted reproductive technologies.

RESULTS

Our study investigated murine oocytes maturing with and without granulosa cells. IVM without granulosa cells yielded oocytes with lower nuclear maturation rates than IVM with granulosa cells and in vivo maturation (IVO). Even though oocytes could achieve nuclear maturation without granulosa cells, they showed incomplete cytoplasmic maturation featuring higher levels of reactive oxygen species, lower mitochondrial density, and higher proportions of cells with abnormal distributions of cortical granules. Of note, oocytes with immature and mature cytoplasm had distinct transcriptional profiles. In the immature oocytes, we observed a deficient mRNA restoration of genes in crucial regulatory pathways of cellular growth and division, potentially affecting embryonic development. Differentially expressed genes (DEGs) between immature and mature oocytes were identified to be highly expressed in different pre-implantation stages, such as the MII oocyte, the 8-cell stage, and the ICM stage. Identified DEGs were enriched in key regulatory pathways of fertilization and embryonic development, such as energy and metabolic pathways. These observations indicated that the impeded development potential of oocytes with immature cytoplasm might be the result of abnormal gene expressions during oocyte maturation.

CONCLUSIONS

We show that granulosa cells are important for both nuclear and cytoplasmic maturation of oocytes. Abnormal gene expression in oocytes with incomplete cytoplasmic maturation may be associated with potential defects in fertilization and embryonic development.

Bioinformatics-Driven Investigations of Signature Biomarkers for Triple-Negative Breast Cancer

Breast cancer is a highly heterogeneous disorder characterized by dysregulated expression of number of genes and their cascades. It is one of the most common types of cancer in women posing serious health concerns globally. Recent developments and discovery of specific prognostic biomarkers have enabled its application toward developing personalized therapies. The basic premise of this study was to investigate key signature genes and signaling pathways involved in triple-negative breast cancer using bioinformatics approach. Microarray data set GSE65194 from the National Center for Biotechnology Information (NCBI) Gene Expression Omnibus was used for identification of differentially expressed genes (DEGs) using R software. Gene ontology and Kyoto Encyclopedia of Genes and Genome (KEGG) pathway enrichment analyses were carried out using the ClueGO plugin in Cytoscape software. The up-regulated DEGs were primarily engaged in the regulation of cell cycle, overexpression of spindle assembly checkpoint, and so on, whereas down-regulated DEGs were employed in alteration to major signaling pathways and metabolic reprogramming. The hub genes were identified using cytoHubba from protein-protein interaction (PPI) network for top up-regulated and down-regulated DEG's plugin in Cytoscape software. The hub genes were validated as potential signature biomarkers by evaluating the overall survival percentage in breast cancer patients.

Folliculogenesis: A Cellular Crosstalk Mechanism

In vitro embryo production has accelerated in the cattle industry in recent years. Because women are similar to cows, this represents an opportunity to improve women's reproductive protocols. This review focuses on crosstalk communication during folliculogenesis for an in-depth understanding of the events involved in developing the oocyte competence necessary to generate an embryo after fertilization. This knowledge can be used to improve oocytes in in vitro maturation cultures, which would allow us to obtain oocytes of high quality and competence, resulting in successful pregnancies in both women and cows. The first part of this review covers the concepts of cellular crosstalk before puberty in the primordial, primary, and secondary follicles. The next part involves cellular crosstalk after puberty, when gonadotropin hormones act on the ovary, promoting oocyte maturation. The final part comprises a perspective on using cow models to study human ovary physiology.

Role of epigenetic regulation in diminished ovarian reserve

Diminished ovarian reserve (DOR) is characterized by a decrease in the number and quality of oocytes, with its incidence increasing annually. Its pathogenesis remains unclear, making it one of the most challenging problems in the field of assisted reproduction. Epigenetic modification, a molecular mechanism affecting genomic activity and expression without altering the DNA sequence, has been widely studied in reproductive medicine and has attracted considerable attention regarding DOR. This review comprehensively examines the various epigenetic regulatory changes in ovarian granulosa cells (OGCs) and oocytes during DOR. DNA methylation plays a crucial role in regulating granulosa cell function, hormone production, and oocyte development, maturation, and senescence. Histone modifications are involved in regulating follicular activation, while non-coding RNAs, such as long noncoding RNAs (lncRNAs) and microRNAs (miRNAs), regulate granulosa cell function and oocyte development. N6-methyladenosine (m6A) modifications are associated with age-related oocyte senescence. Epigenetic clocks based on DNA methylation show potential in predicting ovarian reserve in DOR. Furthermore, it discusses the potential for utilizing epigenetic mechanisms to better diagnose and manage DOR.

p300 maintains primordial follicle activation by repressing VEGFA transcription

During the reproductive life, most primordial follicles (PFs) remain dormant for years or decades, while some are progressively activated for development. Misactivation of primordial follicles can cause ovarian diseases, for example, premature ovarian insufficiency (POI). Our results show that p300 expression increased with primordial follicle activation. Using a p300 inhibitor resulted in premature activation of primordial follicles in cultured mouse ovaries. Conversely, the ratio of primordial follicle activation was markedly decreased upon culturing with the p300 agonist. Furthermore, p300 regulated primordial follicle activation by inhibiting Vegfa transcription in granulosa cells. In addition, this study was extended to potential clinical applications, showing that short-term treatment with a p300 inhibitor in vitro significantly increased primordial follicle activation in newborn mouse ovaries after the renal subcapsular transplantation in female NSG mice. Our results revealed that p300 controls the activation of primordial follicles in mammalian ovaries.NEW & NOTEWORTHY In this study, our results show that p300 expression increases with primordial follicle activation. A p300 inhibitor results in premature activation of primordial follicles in cultured mouse ovaries. Conversely, the ratio of primordial follicle activation markedly decreases upon culturing with the p300 agonist. Furthermore, p300 regulates primordial follicle activation by inhibiting Vegfa transcription in granulosa cells.

N6-Methyladenosine Modification on the Function of Female Reproductive Development and Related Diseases

BACKGROUND

N6-methyladenosine (m6A) modification is a widespread and reversible epigenetic alteration in eukaryotic mRNA, playing a pivotal role in various biological functions. Its significance in female reproductive development and associated diseases has recently become a focal point of research.

OBJECTIVE

This review aims to consolidate current knowledge of the role of m6A modification in female reproductive tissues, emphasizing its regulatory dynamics, functional significance, and implications in reproductive health and disease.

METHODS

A comprehensive analysis of recent studies focusing on m6A modification in ovarian development, oocyte maturation, embryo development, and the pathogenesis of reproductive diseases.

RESULTS

m6A modification exhibits dynamic regulation in female reproductive tissues, influencing key developmental stages and processes. It plays critical roles in ovarian development, oocyte maturation, and embryo development, underpinning essential aspects of reproductive health. m6A modification is intricately involved in the pathogenesis of several reproductive diseases, including polycystic ovary syndrome (PCOS), premature ovarian failure (POF), and endometriosis, offering insights into potential molecular mechanisms and therapeutic targets.

CONCLUSION

The review highlights the crucial role of m6A modification in female reproductive development and related diseases. It underscores the need for further research to explore innovative diagnostic and therapeutic strategies for reproductive disorders, leveraging the insights gained from understanding m6A modification's impact on reproductive health.

Oocyte competence develops: nuclear maturation synchronously with cytoplasm maturation

Human oocyte maturation is a lengthy process that takes place over the course of which oocytes gain the inherent ability to support the next developmental stages in a progressive manner. This process includes intricate and distinct events related to nuclear and cytoplasmic maturation. Nuclear maturation includes mostly chromosome segregation, whereas rearrangement of organelles, storage of mRNAs and transcription factors occur during cytoplasmic maturation.Human oocyte maturation, both in vivo and in vitro, occurs through a process that is not yet fully understood. However, it is believed that the second messenger, cyclic adenosine monophosphate (cAMP), plays a pivotal role in the upkeep of the meiotic blocking of the human oocyte. Relatively high levels of cAMP in the human oocyte are required to maintain meiosis blocked, whereas lower levels of cAMP in the oocyte enable meiosis to resume. Oocyte cAMP concentration is controlled by a balance between adenylate cyclase and phosphodiesterases, the enzymes responsible for cAMP generation and breakdown.In addition to nuclear maturation, the female gamete requires a number of complicated structural and biochemical modifications in the cytoplasmic compartment to be able to fertilize normally. According to ultrastructural studies, during the transition from the germinal vesicle stage to metaphase II (MII), several organelles reorganize their positions. The cytoskeletal microfilaments and microtubules found in the cytoplasm facilitate these movements and regulate chromosomal segregation.The aim of this review is to focus on the nuclear and cytoplasmic maturation by investigating the changes that take place in the process of oocytes being competent for development.

The Role of N6-methyladenosine Modification in Gametogenesis and Embryogenesis: Impact on Fertility

The most common epigenetic modification of messenger RNAs (mRNAs) is N6-methyladenosine (m6A), which is mainly located near the 3' untranslated region of mRNAs, near the stop codons, and within internal exons. The biological effect of m6A is dynamically modulated by methyltransferases (writers), demethylases (erasers), and m6A-binding proteins (readers). By controlling post-transcriptional gene expression, m6A has a significant impact on numerous biological functions, including RNA transcription, translation, splicing, transport, and degradation. Hence, m6A influences various physiological and pathological processes, such as spermatogenesis, oogenesis, embryogenesis, placental function, and human reproductive system diseases. During gametogenesis and embryogenesis, genetic material undergoes significant changes, including epigenomic modifications such as m6A. From spermatogenesis and oogenesis to the formation of an oosperm and early embryogenesis, m6A changes occur at every step. m6A abnormalities can lead to gamete abnormalities, developmental delays, impaired fertilization, and maternal-to-zygotic transition blockage. Both mice and humans with abnormal m6A modifications exhibit impaired fertility. In this review, we discuss the dynamic biological effects of m6A and its regulators on gamete and embryonic development and review the possible mechanisms of infertility caused by m6A changes. We also discuss the drugs currently used to manipulate m6A and provide prospects for the prevention and treatment of infertility at the epigenetic level.

The antioxidant betulinic acid enhances porcine oocyte maturation through Nrf2/Keap1 signaling pathway modulation

During in vitro maturation, excess levels of reactive oxygen species (ROS) are a major cause of developmental defects in embryos. Betulinic acid (BA) is a naturally produced antioxidant in white birch bark. Recent studies have shown that BA exhibits antioxidant properties in various cells through the activation of antioxidant genes. Therefore, we investigated the effect of BA treatment on porcine oocytes and its underlying mechanism during oocyte maturation. Treatment with 0.1 μM BA significantly increased the proportion of MII oocytes compared with controls, and BA-treated oocytes had significantly higher development rates, trophectoderm cell numbers, and cell survival rates than controls. These results demonstrate that BA treatment improved the developmental competence of oocytes. Following BA treatment, oocytes exhibited reduced ROS levels and elevated glutathione (GSH) levels, accompanied by the enhanced expression of antioxidant genes, compared with control oocytes. To evaluate the antioxidant effects of BA, oocytes were exposed to H2O2, a potent ROS activator. Impaired nuclear maturation, ROS levels, and GSH levels induced in oocytes by H2O2 exposure was restored by BA treatment. As these antioxidant genes are regulated by the Nrf2/Keap1 signaling pathway, which is involved in antioxidant responses, we applied the Nrf2 inhibitor brusatol to investigate the effects of BA on this pathway. The negative effects of brusatol on meiotic maturation and oocyte quality, including levels of ROS, GSH, and antioxidant-related gene expression, were mitigated by BA treatment. Our results suggested that BA plays an effective role as an antioxidant in porcine oocyte maturation through adjusting the Nrf2/Keap1 signaling pathway. This finding provides valuable insights into the mechanisms governing oocyte maturation and embryonic development.

Protein Modifications During Early Embryo Development

BACKGROUND

Infertility is a global reproductive health burden. Assisted reproductive technologies (ARTs) have been widely used to help patients become pregnant. Few embryos develop to the blastocyst stage with ARTs, leading to relatively low live birth rates. Protein modifications play crucial roles in nearly every aspect of cell biology, including reproductive processes. The aim of this study was to explore the characteristics of protein modifications during embryonic development.

METHODS

Proteomic data from humans and mice were acquired from the integrated proteome resources (iProX) of ProteomeXchange (PXD024267) and a tandem mass tag (TMT)-mass spectrometry dataset. Gene ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were applied for functional annotation. Protein-protein interactions (PPIs) of the modification-related genes were revealed by the STRING database. Modified proteins during mouse embryogenesis were visualized through heatmaps of hierarchically clustering using k-means.

RESULTS

We identified modification-related proteins in human embryo development and characterized them through heatmaps, GO analysis, KEGG analysis, and PPI network analysis. We found that the 4-cell stage to the 8-cell stage might be the demarcation period for modification-related protein expression patterns during embryo development. Using quantitative mass spectrometry, we elucidated the methylation, acetylation, and ubiquitination events that occur during mouse embryogenesis to validate our findings in human embryonic development to some extent.

CONCLUSIONS

The results of our study suggest that the posttranslational modifications (PTMs) of human preimplantation embryos might exhibit the same trends as those in mice to exert synergistic and fine-tuned regulatory effects during embryonic development.

Age-Dependent Differences in Radiation-Induced DNA Damage Responses in Intestinal Stem Cells

Age at exposure is a critical modifier of the risk of radiation-induced cancer. However, the effects of age on radiation-induced carcinogenesis remain poorly understood. In this study, we focused on tissue stem cells using Lgr5-eGFP-ires-CreERT2 mice to compare radiation-induced DNA damage responses between Lgr5+ and Lgr5- intestinal stem cells. Three-dimensional immunostaining analyses demonstrated that radiation induced apoptosis and the mitotic index more efficiently in adult Lgr5- stem cells than in adult Lgr5+ stem cells but not in infants, regardless of Lgr5 expression. Supporting this evidence, rapid and transient p53 activation occurred after irradiation in adult intestinal crypts but not in infants. RNA sequencing revealed greater variability in gene expression in adult Lgr5+ stem cells than in infant Lgr5+ stem cells after irradiation. Notably, the cell cycle and DNA repair pathways were more enriched in adult stem cells than in infant stem cells after irradiation. Our findings suggest that radiation-induced DNA damage responses in mouse intestinal crypts differ between infants and adults, potentially contributing to the age-dependent susceptibility to radiation carcinogenesis.

An integrated analysis of multiple datasets reveals novel gene signatures in human granulosa cells

Granulosa cells (GCs) play crucial roles in oocyte maturation. Through gap junctions and extracellular vesicles, they mediate the exchange of molecules such as microRNAs and messenger RNAs. Different ovarian cell types exhibit unique gene expression profiles, reflecting their specialized functions and stages. By combining RNA-seq data from various cell types forming the follicle, we aimed at capturing a wide range of expression patterns, offering insights into the functional diversity and complexity of the transcriptome regulation across GCs. Herein, we performed an integrated bioinformatics analysis of RNA sequencing datasets present in public databases, with a unique and standardized workflow., By combining the data from different studies, we successfully increased the robustness and reliability of our findings and discovered novel genes, miRNAs, and signaling pathways associated with GCs function and oocyte maturation. Moreover, our results provide a valuable resource for further wet-lab research on GCs biology and their impact on oocyte development and competence.

G-Protein-Coupled Receptor Kinase 2 Inhibition Induces Meiotic Arrest by Disturbing Ca2+ Release in Porcine Oocytes

G-protein-coupled receptor kinase 2 (GRK2) interacts with Gβγ and Gαq, subunits of G-protein alpha, to regulate cell signalling. The second messenger inositol trisphosphate, produced by activated Gαq, promotes calcium release from the endoplasmic reticulum (ER) and regulates maturation-promoting factor (MPF) activity. This study aimed to investigate the role of GRK2 in MPF activity during the meiotic maturation of porcine oocytes. A specific inhibitor of GRK2 (βi) was used in this study. The present study showed that GRK2 inhibition increased the percentage of oocyte arrest at the metaphase I (MI) stage (control: 13.84 ± 0.95%; βi: 31.30 ± 4.18%), which resulted in the reduction of the maturation rate (control: 80.36 ± 1.94%; βi: 65.40 ± 1.14%). The level of phospho-GRK2 decreased in the treated group, suggesting that GRK2 activity was reduced upon GRK2 inhibition. Furthermore, the addition of βi decreased Ca2+ release from the ER. The protein levels of cyclin B and cyclin-dependent kinase 1 were higher in the treatment group than those in the control group, indicating that GRK2 inhibition prevented a decrease in MPF activity. Collectively, GRK2 inhibition induced meiotic arrest at the MI stage in porcine oocytes by preventing a decrease in MPF activity, suggesting that GRK2 is essential for oocyte meiotic maturation in pigs.

Calcium signaling in oocyte quality and functionality and its application

Calcium (Ca2+) is a second messenger for many signal pathways, and changes in intracellular Ca2+ concentration ([Ca2+]i) are an important signaling mechanism in the oocyte maturation, activation, fertilization, function regulation of granulosa and cumulus cells and offspring development. Ca2+ oscillations occur during oocyte maturation and fertilization, which are maintained by Ca2+ stores and extracellular Ca2+ ([Ca2+]e). Abnormalities in Ca2+ signaling can affect the release of the first polar body, the first meiotic division, and chromosome and spindle morphology. Well-studied aspects of Ca2+ signaling in the oocyte are oocyte activation and fertilization. Oocyte activation, driven by sperm-specific phospholipase PLCζ, is initiated by concerted intracellular patterns of Ca2+ release, termed Ca2+ oscillations. Ca2+ oscillations persist for a long time during fertilization and are coordinately engaged by a variety of Ca2+ channels, pumps, regulatory proteins and their partners. Calcium signaling also regulates granulosa and cumulus cells' function, which further affects oocyte maturation and fertilization outcome. Clinically, there are several physical and chemical options for treating fertilization failure through oocyte activation. Additionally, various exogenous compounds or drugs can cause ovarian dysfunction and female infertility by inducing abnormal Ca2+ signaling or Ca2+ dyshomeostasis in oocytes and granulosa cells. Therefore, the reproductive health risks caused by adverse stresses should arouse our attention. This review will systematically summarize the latest research progress on the aforementioned aspects and propose further research directions on calcium signaling in female reproduction.

Impact of Heat Stress on Oocyte Developmental Competence and Pre-Implantation Embryo Viability in Cattle

Rectal and vaginal temperatures are utilised in both in vivo and in vitro models to study the effects of heat stress on oocyte competence and embryo viability in cattle. However, uterine temperature increases by only 0.5 °C in heat-stressed cows, significantly lower than simulated increases in in vitro models. Temperature variations within oviducts and ovarian follicles during heat stress are poorly understood or unavailable, and evidence is lacking that oocytes and pre-implantation embryos experience mild (40 °C) or severe (41 °C) heat stress inside the ovarian follicle and the oviduct and uterus, respectively. Gathering detailed temperature data from the reproductive tract and follicles is crucial to accurately assess oocyte competence and embryo viability under realistic heat stress conditions. Potential harm from heat stress on oocytes and embryos may result from reduced nutrient availability (e.g., diminished blood flow to the reproductive tract) or other unidentified mechanisms affecting tissue function rather than direct thermal effects. Refining in vivo stress models in cattle is essential to accurately identify animals truly experiencing heat stress, rather than assuming heat stress exposure as done in most studies. This will improve model reliability and aid in the selection of heat-tolerant animals.

Novel PATL2 variants cause female infertility with oocyte maturation defect

PURPOSE

Oocyte maturation defect (OOMD) is a rare cause of in vitro fertilization failure characterized by the production of immature oocytes. Compound heterozygous or homozygous PATL2 mutations have been associated with oocyte arrest at the germinal vesicle (GV), metaphase I (MI), and metaphase II (MII) stages, as well as morphological changes.

METHODS

In this study, we recruited three OOMD cases and conducted a comprehensive multiplatform laboratory investigation.

RESULTS

Whole exome sequence (WES) revealed four diagnostic variants in PATL2, nonsense mutation c.709C > T (p.R237*) and frameshift mutation c.1486_1487delinsT (p.A496Sfs*4) were novel mutations that have not been reported previously. Furthermore, the pathogenicity of these variants was predicted using in silico analysis, which indicated detrimental effects. Molecular dynamic analysis suggested that the A496S variant disrupted the hydrophobic segment, leading to structural changes that affected the overall protein folding and stability. Additionally, biochemical and molecular experiments were conducted on cells transfected with wild-type (WT) or mutant PATL2 (p.R237* and p.A496Sfs*4) plasmid vectors.

CONCLUSIONS

The results demonstrated that PATL2A496Sfs*4 and PATL2R237* had impacts on protein size and expression level. Interestingly, expression levels of specific genes involved in oocyte maturation and early embryonic development were found to be simultaneously deregulated. The findings in our study expand the variation spectrum of the PATL2 gene, provide solid evidence for counseling on future pregnancies in affected families, strongly support the application of in the diagnosis of OOMD, and contribute to the understanding of PATL2 function.

Effects of orange peel extract (Citrus sinensis) treatment on zebrafish oocytes (Danio rerio) exposed to heat stress

Background and Aim

Heat stress (HS) can negatively impact oocytes by disrupting mitochondrial activity, increasing the production of reactive oxygen species, and decreasing antioxidant levels. This study investigated the impact of orange peel (OP) exposure on zebrafish oocytes (ZOs) diameter, survival rate, and germinal vesicle breakdown (GVBD) during HS.

Material and Methods

We investigated the antioxidant effect of flavonoids (concentration = 328.58 ppm) derived from OP (Citrus sinensis) added to in vitro maturation (IVM) media of ZOs (Danio rerio) under non-heat stress (NHS) and HS conditions to mimic in vivo HS conditions due to the global warming phenomenon on females. ZO in stage 3 (n = 1080) was treated with 4 μL of OP extract (not treated/control) under HS: 32°C (Heat stress 32°C solution/Heat stress 32°C orange peel [HS32S/HS32O]) and 34°C (Heat stress 34°C solution/Heat stress 34°C orange peel [HS34S/HS34O]); and NHS: 28°C (Non-heat stress solution/Non-heat stress orange peel [NHSS/NHSO]), during maturation. After 24 h of maturation, we observed the oocyte diameter, survival rate, and GVBD rate. The data were analyzed with IBM Statistics 23 software using two-way analysis of variance and Kruskal-Wallis (p < 0.05).

Results

The highest oocyte diameter data were in NHS treated with OP extract (NHSO) group (0.759 ± 0.01; mean ± standard error) compared with HS group using and without OP extract (HS32S [0.583 ± 0.02]; HS32O [0.689 ± 0.02]; HS34S [0.554 ± 0.02]; and HS34O [0.604 ± 0.02]). The survival rate of OP treated group, namely, NHSO (93% ± 3%), HS32O (85% ± 2%), and HS34O (80% ± 2%) was higher than that of the group without treatment (NHSS [83% ± 3%], HS32S [71% ± 6%], and HS34S [63% ± 3%]). ZO treated with OP extract (NHSO [93% ± 3%], HS32O [85% ± 2%], and HS34O [80% ± 2%]) showed a higher GVBD rate than the group without treatment (NHSS [83% ± 3%], HS32S [71% ± 6%], and HS34S [63% ± 3%]).

Conclusion

It revealed that OP can enhance the oocyte diameter, survival rate, and GVBD rate of ZO under NHS and HS. Further investigation should be conducted to determine the effect of OP extract (C. sinensis) on in vivo conditions in females as an alternative treatment to face global warming.

Ex ovo omnia-why don't we know more about egg quality via imaging?

Determining egg quality is the foremost challenge in assisted reproductive technology (ART). Although extensive advances have been made in multiple areas of ART over the last 40 years, oocyte quality assessment tools have not much evolved beyond standard morphological observation. The oocyte not only delivers half of the nuclear genetic material and all of the mitochondrial DNA to an embryo but also provides complete developmental support during embryonic growth. Oocyte mitochondrial numbers far exceed those of any somatic cell, yet little work has been done to evaluate the mitochondrial bioenergetics of an oocyte. Current standard oocyte assessment in in vitro fertilization (IVF) centers include the observation of oocytes and their surrounding cell complex (cumulus cells) via stereomicroscope or inverted microscope, which is largely primitive. Additional oocyte assessments include polar body grading and polarized light meiotic spindle imaging. However, the evidence regarding the aforementioned methods of oocyte quality assessment and IVF outcomes is contradictory and non-reproducible. High-resolution microscopy techniques have also been implemented in animal and human models with promising outcomes. The current era of oocyte imaging continues to evolve with discoveries in artificial intelligence models of oocyte morphology selection albeit at a slow rate. In this review, the past, current, and future oocyte imaging techniques will be examined with the goal of drawing attention to the gap which limits our ability to assess oocytes in real time. The implications of improved oocyte imaging techniques on patients undergoing IVF will be discussed as well as the need to develop point of care oocyte assessment testing in IVF labs.

HDAC6-dependent deacetylation of NGF dictates its ubiquitination and maintains primordial follicle dormancy

Rationale: Primordial follicles are limited in number and cannot be regenerated, dormant primordial follicles cannot be reversed once they enter a growth state. Therefore, the length of the female reproductive lifespan depends on the orderly progression and selective activation of primordial follicles, the mechanism of which remains unclear. Methods: We used human ovarian cortical biopsy specimens, granulosa cells from diminished ovarian reserve (DOR) patients, Hdac6-overexpressing transgenic mouse model, and RNA sequencing to analyze the crucial roles of histone deacetylase 6 (HDAC6) in fertility preservation and primordial follicle activation. Results: In the present study, we found that HDAC6 was highly expressed in most dormant primordial follicles. The HDAC6 expression was reduced accompanying reproductive senescence in human and mouse ovaries. Overexpression of Hdac6 delayed the rate of primordial follicle activation, thereby prolonging the mouse reproductive lifespan. Short-term inhibition of HDAC6 promoted primordial follicle activation and follicular development in humans and mice. Mechanism studies revealed that HDAC6 directly interacted with NGF, reducing acetylation modification of NGF and thereby accelerating its ubiquitination degradation. Consequently, the reduced NGF protein level maintained the dormancy of primordial follicles. Conclusions: The physiological significance of the high expression of HDAC6 in most primordial follicles is to reduce NGF expression and prevent primordial follicle activation to maintain female fertility. Reduced HDAC6 expression increases NGF expression in primordial follicles, activating their development and contributing to reproduction. Our study provides a clinical reference value for fertility preservation.

Epigenetic-related transcriptional reprogramming elucidated by identification and validation of a novel reference gene combination for RT-qPCR studies in porcine oocytes of contrasting quality

BACKGROUND

Reliable RT-qPCR results are dependent on appropriate normalisation. Oocyte maturation studies can be challenging in this respect, as the stage of development can distinctively affect reference gene transcript abundance. The aim of this study was to validate the use of reference genes in oocyte in vitro maturation RT-qPCR studies, and thereafter, examine the abundance of transcripts supporting histone modification during oocyte and early embryo development in oocytes of contrasting quality.

METHODS AND RESULTS

Total RNA from oocytes from prepubertal gilts and sows was extracted either directly succeeding follicle aspiration or after 44 h in vitro maturation, followed by RT-qPCR. The stability of YWHAG, HPRT1, ACTB, GAPDH, HMBS and PFKP, was analysed by NormFinder and further cross-validated by assessing results generated following application of different combinations of potential reference genes for normalisation of the RT-qPCR data. Combining ACTB and PFKP generated high stability according to NormFinder and concordant results. Applying this normalisation, gilt derived oocytes displayed significantly higher abundance than oocytes from sows of almost all the epigenetic-related transcripts studied (HDAC2, SIRT1, SALL4, KDM1A, KDM1B, KDM5A), both before and after maturation.

CONCLUSIONS

This study identified the combined use of ACTB and PFKP as the optimal normalisation for porcine oocyte RT-qPCR data. In oocytes collected from prepubertal gilts, transcription did not appear to be silenced at the time of aspiration, and accumulation of transcripts supporting histone modification facilitating proper fertilization and further embryo development seemed delayed. The results imply the epigenetic-related transcripts may have potential as markers of oocyte quality.

Role and Mechanism of Epigenetic Regulation in the Aging of Germ Cells: Prospects for Targeted Interventions

In modern times, a notable trend toward delayed childbearing has been observed in most developed countries. As a result, sperm aging and quality loss, as well as premature ovarian failure (POF), have emerged as major causes of infertility. The pathogenesis of sperm aging and POF is complex and has not been clearly elucidated. However, evidence from some studies has linked germ cell aging to epigenetic modifications. Epigenetics refers to the heritable changes in gene expression that occur in the absence of any alterations to the gene's nucleotide sequence. This paper systematically reviewed and analyzed the relevant literature to describe the relationship of DNA methylation, non-coding RNA regulation, histone modifications, chromatin remodeling, and RNA modifications with sperm aging and POF. In addition, we analyzed how sperm aging and POF can be mitigated via epigenetic interventions. This review could provide new therapeutic insights and guide strategies for improving sperm quality and ovarian function.

Temperature-Induced Sex Differentiation in River Prawn (Macrobrachium nipponense): Mechanisms and Effects

Macrobrachium nipponense is gonochoristic and sexually dimorphic. The male prawn grows faster and usually has a larger size than the female. Therefore, a higher male proportion in stock usually results in higher yield. To investigate the impact of temperature on sexual differentiation in M. nipponense, two temperature treatments (26 °C and 31 °C) were conducted. The results showed that compared to the 31 °C treatment (3.20 ± 0.12), the 26 °C treatment displayed a lower female/male ratio (2.20 ± 0.11), which implied that a lower temperature could induce masculinization in M. nipponense. The temperature-sensitive sex differentiation phase was 25-35 days post hatching (DPH) at 26 °C while 15-20 DPH at 31 °C. Transcriptome and qPCR analysis revealed that a lower temperature up-regulated the expression of genes related to androgen secretion, and down-regulated the expressions of genes related to oogonia differentiation. Thirty-one temperature-regulated sex-differentiation genes were identified and the molecular mechanism of temperature-regulated sex differentiation was suggested. The finding of this study indicates that temperature regulation can be proposed as an innovative strategy for improving the culture yield of M. nipponense.

Maturation and culture affect the metabolomic profile of oocytes and follicular cells in young and old mares

Introduction: Oocytes and follicular somatic cells within the ovarian follicle are altered during maturation and after exposure to culture in vitro. In the present study, we used a nontargeted metabolomics approach to assess changes in oocytes, cumulus cells, and granulosa cells from dominant, follicular-phase follicles in young and old mares. Methods: Samples were collected at three stages associated with oocyte maturation: (1) GV, germinal vesicle stage, prior to the induction of follicle/oocyte maturation in vivo; (2) MI, metaphase I, maturing, collected 24 h after induction of maturation in vivo; and (3) MIIC, metaphase II, mature with collection 24 h after induction of maturation in vivo plus 18 h of culture in vitro. Samples were analyzed using gas and liquid chromatography coupled to mass spectrometry only when all three stages of a specific cell type were obtained from the same mare. Results and Discussion: Significant differences in metabolite abundance were most often associated with MIIC, with some of the differences appearing to be linked to the final stage of maturation and others to exposure to culture medium. While differences occurred for many metabolite groups, some of the most notable were detected for energy and lipid metabolism and amino acid abundance. The study demonstrated that metabolomics has potential to aid in optimizing culture methods and evaluating cell culture additives to support differences in COCs associated with maternal factors.

Differential Gene Expression Analysis of Human Ovarian Follicular Cumulus and Mural Granulosa Cells Under the Influence of Insulin in IVF Ovulatory Women and Polycystic Ovary Syndrome Patients Through Network Analysis

BACKGROUND

Polycystic ovarian syndrome (PCOS) is a commonly occurring reproductive disorder among the reproductive-aged women. Its global occurrence varies based on diagnostic guidelines, ethnicities, and locations of concern. Insulin resistance (IR) is commonly observed around 65-70% of women diagnosed with PCOS, representing a prevalent association. Consequently, the study was designed with an objective of illustrating the effect of insulin on mural and cumulus granulosa cells (GCs) of PCOS patients in comparison to normal ovulating women.

METHODOLOGY

This study is a case-control design, wherein a total of 80 participants were recruited meeting criterion of inclusion and exclusion, divided into 8 groups with each group consisting of 10 samples. The process involves the isolation and culturing of mural granulosa cells (MGC) and cumulus granulosa cells (CGC) with and without exposure to insulin. The proteins released by untreated GCs and insulin-treated GCs were extracted, and complex protein mixtures were digested with trypsin, followed by tandem mass spectrometry analysis and data processing using bioinformatics.

RESULTS

We found 595 proteins in both control and PCOS samples, of which 310 were contributed by MGCs and 285 by CGCs. The PCOS MGCs expressed 20%, both the normal MGCs and CGCs have equal representation of 16% by each, whereas the PCOS CGCs proteins contributed 15% of the total of the proteomic expression. However, the poor expression observed with the Insulin exposure, the Insulin treated PCOS CGCs contributes 13%, PCOS MGCs contributes 8%. The normal MGCs upon the Insulin treatment give 8% then and there only 4% of proteins expressed by normal CGCs after Insulin treatment. The Venn analysis widened on their precise expression topographies. The examination of strings exhibited important protein-protein interaction pathways.

CONCLUSION

This is a pioneering investigation aimed to establish the link between hyperinsulinemia in localized follicular GCs and PCOS mechanisms by comparing them to control group. The examination of various attributes, mechanisms, and traits shown by genes and proteins in individuals with PCOS compared to control populations, alongside the investigation of the dynamics of these genes and proteins following exposure to insulin, holds promise for the formulation of novel hypotheses and strategies in the identification of new biomarkers.

SIRT7: the seventh key to unlocking the mystery of aging

Aging is a chronic yet natural physiological decline of the body. Throughout life, humans are continuously exposed to a variety of exogenous and endogenous stresses, which engender various counteractive responses at the cellular, tissue, organ, as well as organismal levels. The compromised cellular and tissue functions that occur because of genetic factors or prolonged stress (or even the stress response) may accelerate aging. Over the last two decades, the sirtuin (SIRT) family of lysine deacylases has emerged as a key regulator of longevity in a variety of organisms. SIRT7, the most recently identified member of the SIRTs, maintains physiological homeostasis and provides protection against aging by functioning as a watchdog of genomic integrity, a dynamic sensor and modulator of stresses. SIRT7 decline disrupts metabolic homeostasis, accelerates aging, and increases the risk of age-related pathologies including cardiovascular and neurodegenerative diseases, pulmonary and renal disorders, inflammatory diseases, and cancer, etc. Here, we present SIRT7 as the seventh key to unlock the mystery of aging, and its specific manipulation holds great potential to ensure healthiness and longevity.

Cumulus Cell and Oocyte Gene Expression in Prepubertal Gilts and Sows Identifies Cumulus Cells as a Prime Informative Parameter of Oocyte Quality

Cumulus cells (CCs) are pivotal during oocyte development. This study aimed to identify novel marker genes for porcine oocyte quality by examining the expression of selected genes in CCs and oocytes, employing the model of oocytes from prepubertal animals being of reduced quality compared to those from adult animals. Total RNA was extracted either directly after follicle aspiration or after in vitro maturation, followed by RT-qPCR. Immature gilt CCs accumulated BBOX1 transcripts, involved in L-carnitine biosynthesis, to a 14.8-fold higher level (p < 0.05) relative to sows, while for CPT2, participating in fatty acid oxidation, the level was 0.48 (p < 0.05). While showing no differences between gilt and sow CCs after maturation, CPT2 and BBOX1 levels in oocytes were higher in gilts at both time points. The apparent delayed lipid metabolism and reduced accumulation of ALDOA and G6PD transcripts in gilt CCs after maturation, implying downregulation of glycolysis and the pentose phosphate pathway, suggest gilt cumulus-oocyte complexes have inadequate ATP stores and oxidative stress balance compared to sows at the end of maturation. Reduced expression of BBOX1 and higher expression of CPT2 in CCs before maturation and higher expression of G6PD and ALDOA after maturation are new potential markers of oocyte quality.

Epigenetic aging of mammalian gametes

The process of aging refers to physiological changes that occur to an organism as time progresses and involves changes to DNA, proteins, metabolism, cells, and organs. Like the rest of the cells in the body, gametes age, and it is well established that there is a decline in reproductive capabilities in females and males with aging. One of the major pathways known to be involved in aging is epigenetic changes. The epigenome is the multitude of chemical modifications performed on DNA and chromatin that affect the ability of chromatin to be transcribed. In this review, we explore the effects of aging on female and male gametes with a focus on the epigenetic changes that occur in gametes throughout aging. Quality decline in oocytes occurs at a relatively early age. Epigenetic changes constitute an important part of oocyte aging. DNA methylation is reduced with age, along with reduced expression of DNA methyltransferases (DNMTs). Histone deacetylases (HDAC) expression is also reduced, and a loss of heterochromatin marks occurs with age. As a consequence of heterochromatin loss, retrotransposon expression is elevated, and aged oocytes suffer from DNA damage. In sperm, aging affects sperm number, motility and fecundity, and epigenetic changes may constitute a part of this process. 5 methyl-cytosine (5mC) methylation is elevated in sperm from aged men, but methylation on Long interspersed nuclear elements (LINE) elements is reduced. Di and trimethylation of histone 3 lysine 9 (H3K9me2/3) is reduced in sperm from aged men and trimethylation of histone 3 lysine 27 (H3K27me3) is elevated. The protamine makeup of sperm from aged men is also changed, with reduced protamine expression and a misbalanced ratio between protamine proteins protamine P1 and protamine P2. The study of epigenetic reproductive aging is recently gaining interest. The current status of the field suggests that many aspects of gamete epigenetic aging are still open for investigation. The clinical applications of these investigations have far-reaching consequences for fertility and sociological human behavior.

"Meiosis arrester" C-natriuretic peptide directly stimulates oocyte mtDNA accumulation and is implicated in aging-associated oocyte mtDNA loss

C-natriuretic peptide (CNP) is the central regulator of oocyte meiosis progression, thus coordinating synchronization of oocyte nuclear-cytoplasmic maturation. However, whether CNP can independently regulate cytoplasmic maturation has been long overlooked. Mitochondrial DNA (mtDNA) accumulation is the hallmark event of cytoplasmic maturation, but the mechanism underlying oocyte mtDNA replication remains largely elusive. Herein, we report that CNP can directly stimulate oocyte mtDNA replication at GV stage, and deficiency of follicular CNP may contribute largely to lower mtDNA copy number in in vitro matured oocytes. The mechanistic study showed that cAMP-PKA-CREB1 signaling cascade underlies the regulatory role of CNP in stimulating mtDNA replication and upregulating related genes. Of interest, we also report that CNP-NPR2 signaling is inhibited in aging follicles, and this inhibition is implicated in lower mtDNA copy number in oocytes from aging females. Together, our study provides the first direct functional link between follicular CNP and oocyte mtDNA replication, and identifies its involvement in aging-associated mtDNA loss in oocytes. These findings, not only update the current knowledge of the functions of CNP in coordinating oocyte maturation but also present a promising strategy for improving in vitro fertilization outcomes of aging females.

Decreased HAT1 expression in granulosa cells disturbs oocyte meiosis during mouse ovarian aging

BACKGROUND

With advanced maternal age, abnormalities during oocyte meiosis increase significantly. Aneuploidy is an important reason for the reduction in the quality of aged oocytes. However, the molecular mechanism of aneuploidy in aged oocytes is far from understood. Histone acetyltransferase 1 (HAT1) has been reported to be essential for mammalian development and genome stability, and involved in multiple organ aging. Whether HAT1 is involved in ovarian aging and the detailed mechanisms remain to be elucidated.

METHODS

The level of HAT1 in aged mice ovaries was detected by immunohistochemical and immunoblotting. To explore the function of HAT1 in the process of mouse oocyte maturation, we used Anacardic Acid (AA) and small interfering RNAs (siRNA) to culture cumulus-oocyte complexes (COCs) from ICR female mice in vitro and gathered statistics of germinal vesicle breakdown (GVBD), the first polar body extrusion (PBE), meiotic defects, aneuploidy, 2-cell embryos formation, and blastocyst formation rate. Moreover, the human granulosa cell (GC)-like line KGN cells were used to investigate the mechanisms of HAT1 in this progress.

RESULTS

HAT1 was highly expressed in ovarian granulosa cells (GCs) from young mice and the expression of HAT1 was significantly decreased in aged GCs. AA and siRNAs mediated inhibition of HAT1 in GCs decreased the PBE rate, and increased meiotic defects and aneuploidy in oocytes. Further studies showed that HAT1 could acetylate Forkhead box transcription factor O1 (FoxO1), leading to the translocation of FoxO1 into the nucleus. Resultantly, the translocation of acetylated FoxO1 increased the expression of amphiregulin (AREG) in GCs, which plays a significant role in oocyte meiosis.

CONCLUSION

The present study suggests that decreased expression of HAT1 in GCs is a potential reason corresponding to oocyte age-related meiotic defects and provides a potential therapeutic target for clinical intervention to reduce aneuploid oocytes.

Human TIMP1 Is a Growth Factor That Improves Oocyte Developmental Competence

Oocyte developmental competence is the ability of a mature oocyte to be fertilized and subsequently support embryonic development. Such competence is gained during folliculogenesis and is facilitated by the bidirectional communication into a compacted cumulus-oocyte complex (COC). Human tissue inhibitor of metalloproteinases-1 (TIMP1) participates in biological processes, including cell growth, differentiation, and apoptosis. This study aimed to evaluate the influence of TIMP1 as a growth factor on the in vitro maturation (IVM) culture of bovine COCs to improve oocyte developmental competence. All TIMP1 treatments (50, 100, and 150 ng/mL) favored the COCs' compaction structure (p < 0.05). TIMP1 at 150 ng/mL produced more oocytes in metaphase II compared to the other treatments (p < 0.05). The 150 ng/mL TIMP1 generated oocytes with the most (p < 0.05) cortical granules below the plasma membrane (pattern I). In a parthenogenesis assay, oocyte IVM in 50 ng/mL of TIMP1 produced the most blastocyst compared to the other treatments (p < 0.05). The Principal Component Analysis (PCA) showed that 50 ng/mL of TIMP1 was the best condition to develop oocyte competence because it was associated with the COC compact and cortical granule pattern I. TIMP1 influences the development of oocyte competence when added to the IVM culture medium of COCs.

Potential Involvement of DNA Methylation in Hybrid Sterility in Hermaphroditic Argopecten Scallops

DNA methylation is an important epigenetic modification factor in regulating fertility. Corresponding process remains poorly investigated in hermaphroditic scallops. The interspecific F1 hybrids between the hermaphroditic bay scallops (Argopecten irradians) and Peruvian scallops (Argopecten purpuratus) exhibited significant heterosis in yield, but sterility in hybrids obstructs the utilization of the genetic resources. However, the determination mechanism of hybrid sterility in the hermaphroditic Argopecten scallops is still unclear. In this study, the effect of DNA methylation in the hybrid sterility of hermaphroditic Argopecten scallops was explored. The results showed that the mean methylation level was higher in sterile hybrids than fertile hybrids, especially on chromosome 11 of the paternal parent. A total of 61,062 differentially methylated regions (DMRs) were identified, containing 3619 differentially methylated genes (DMGs) and 1165 differentially methylated promoters that are located in the DMRs of CG sequence context. The hyper-methylated genes were enriched into five KEGG pathways, including ubiquitin-mediated proteolysis, ECM-receptor interaction, non-homologous end-joining, notch signaling, and the mismatch repair pathways. The DMGs might induce hybrid sterility by inhibition of oogenesis and egg maturation, induction of apoptosis, increased ROS, and insufficient ATP supply. Our results would enrich the determination mechanism of hybrid sterility and provide new insights into the utilization of the genetic resources of the interspecific hybrids.

Factors Influencing the Maturation and Developmental Competence of Yak (Bos grunniens) Oocytes In Vitro

The yak (Bos grunniens) is a unique breed living on the Qinghai-Tibet Plateau and its surrounding areas, providing locals with a variety of vital means of living and production. However, the yak has poor sexual maturity and low fertility. High-quality mature oocytes are the basis of animal breeding technology. Recently, in vitro culturing of oocytes and embryo engineering technology have been applied to yak breeding. However, compared to those observed in vivo, the maturation rate and developmental capacity of in vitro oocytes are still low, which severely limits the application of in vitro fertilization and embryo production in yaks. This review summarizes the endogenous and exogenous factors affecting the in vitro maturation (IVM) and developmental ability of yak oocytes reported in recent years and provides a theoretical basis for obtaining high-quality oocytes for in vitro fertilization and embryo production in yaks.

Histone acetyltransferases and histone deacetyl transferases play crucial role during oogenesis and early embryo development

Dynamic epigenetic regulation is critical for proper oogenesis and early embryo development. During oogenesis, fully grown germinal vesicle oocytes develop to mature Metaphase II oocytes which are ready for fertilization. Fertilized oocyte proliferates mitotically until blastocyst formation and the process is called early embryo development. Throughout oogenesis and early embryo development, spatio-temporal gene expression takes place, and this dynamic gene expression is controlled with the aid of epigenetics. Epigenetic means that gene expression can be altered without changing DNA itself. Epigenome is regulated through DNA methylation and histone modifications. While DNA methylation generally ends up with repression of gene expression, histone modifications can result in expression or repression depending on type of modification, type of histone protein and its specific residue. One of the modifications is histone acetylation which generally ends up with gene expression. Histone acetylation occurs through the addition of acetyl group onto amino terminal of the core histone proteins by histone acetyltransferases (HATs). Contrarily, histone deacetylation is associated with repression of gene expression, and it is catalyzed by histone deacetylases (HDACs). This review article focuses on what is known about alterations in the expression of HATs and HDACs and emphasizes importance of HATs and HDACs during oogenesis and early embryo development.

Potential biomarkers to predict return to fertility after discontinuation of female contraceptives-looking to the future

Nowadays there are multiple types of contraceptive methods, from reversible to permanent, for those choosing to delay pregnancy. Misconceptions about contraception and infertility are a key factor for discontinuation or the uptake of family planning methods. Regaining fertility (the ability to conceive) after contraceptive discontinuation is therefore pivotal. Technical studies to date have evaluated return to fertility by assessing pregnancy as an outcome, with variable results, or return to ovulation as a surrogate measure by assessing hormone levels (such as progesterone, LH, FSH) with or without transvaginal ultrasound. In general, relying on time to pregnancy as an indicator of return to fertility following contraceptive method discontinuation can be problematic due to variable factors independent of contraceptive effects on fertility, hormone clearance, and fertility recovery. Since the ability to conceive after contraceptive method discontinuation is a critical factor influencing product uptake, it is important to have robust biomarkers that easily and accurately predict the timing of fertility return following contraception and isolate that recovery from extrinsic and circumstantial factors. The main aim of this review is to summarize the current approaches, existing knowledge, and gaps in methods of evaluating return-to-fertility as well as to provide insights into the potential of new biomarkers to more accurately predict fertility restoration after contraceptive discontinuation. Biomarker candidates proposed in this document include those associated with folliculogenesis, cumulus cell expansion, follicular rupture and ovulation, and endometrial transport and receptivity which have been selected and scored on predefined criteria meant to evaluate their probable viability for advancement. The review also describes limitations, regulatory requirements, and a potential path to clinically testing these selected biomarkers. It is important to understand fertility restoration after contraceptive method discontinuation to provide users and health providers with accurate evidence-based information. Predictive biomarkers, if easy and low-cost, have the potential to enable robust evaluation of RTF, and provide potential users the information they desire when selecting a contraceptive method. This could lead to expanded uptake and continuation of modern contraception and inform the development of new contraceptive methods to widen user's family planning choices.

β-hydroxybutyrate impairs bovine oocyte maturation via pyruvate dehydrogenase (PDH) associated energy metabolism abnormality

Background: Ketosis is one of the most frequent and costly metabolic disorders in high-producing dairy cows, and negatively associated with the health and reproductive performance of bovine. Ketosis is mainly caused by the accumulation of ketone body β-hydroxybutyric acid and its diagnosis is based on β-hydroxybutyrate (βHB) concentration in blood. Methods: In this study, we investigated the effects of βHB on bovine oocyte maturation in the concentration of subclinical (1.2 mM) βHB and clinical (3.6 mM). Results: The results showed βHB disrupted bovine oocyte maturation and development capacity. Further analysis showed that βHB induced oxidative stress and mitochondrial dysfunction, as indicated by the increased level of reactive oxygen species (ROS), disrupted mitochondrial structure and distribution, and depolarized membrane potential. Furthermore, oxidative stress triggered early apoptosis, as shown by the enhanced levels of Caspase-3 and Annexin-V. Moreover, 3.6 mM βHB induced the disruption of the pyruvate dehydrogenase (PDH) activity, showing with the decrease of the global acetylation modification and the increase of the abnormal spindle rate. Conclusion: Our study showed that βHB in subclinical/clinical concentration had toxic effects on mitochondrial function and PDH activity, which might affect energy metabolism and epigenetic modification of bovine oocytes and embryos.

Single-cell multi-omics profiling reveals key regulatory mechanisms that poise germinal vesicle oocytes for maturation in pigs

The molecular mechanisms controlling the transition from meiotic arrest to meiotic resumption in mammalian oocytes have not been fully elucidated. Single-cell omics technology provides a new opportunity to decipher the early molecular events of oocyte growth in mammals. Here we focused on analyzing oocytes that were collected from antral follicles in different diameters of porcine pubertal ovaries, and used single-cell M&T-seq technology to analyze the nuclear DNA methylome and cytoplasmic transcriptome in parallel for 62 oocytes. 10× Genomics single-cell transcriptomic analyses were also performed to explore the bi-directional cell-cell communications within antral follicles. A new pipeline, methyConcerto, was developed to specifically and comprehensively characterize the methylation profile and allele-specific methylation events for a single-cell methylome. We characterized the gene expressions and DNA methylations of individual oocyte in porcine antral follicle, and both active and inactive gene's bodies displayed high methylation levels, thereby enabled defining two distinct types of oocytes. Although the methylation levels of Type II were higher than that of Type I, Type II contained nearly two times more of cytoplasmic transcripts than Type I. Moreover, the imprinting methylation patterns of Type II were more dramatically divergent than Type I, and the gene expressions and DNA methylations of Type II were more similar with that of MII oocytes. The crosstalk between granulosa cells and Type II oocytes was active, and these observations revealed that Type II was more poised for maturation. We further confirmed Insulin Receptor Substrate-1 in insulin signaling pathway is a key regulator on maturation by in vitro maturation experiments. Our study provides new insights into the regulatory mechanisms between meiotic arrest and meiotic resumption in mammalian oocytes. We also provide a new analytical package for future single-cell methylomics study.

Chromatin Configuration in Diplotene Mouse and Human Oocytes during the Period of Transcriptional Activity Extinction

In the oocyte nucleus, called the germinal vesicle (GV) at the prolonged diplotene stage of the meiotic prophase, chromatin undergoes a global rearrangement, which is often accompanied by the cessation of its transcriptional activity. In many mammals, including mice and humans, chromatin condenses around a special nuclear organelle called the atypical nucleolus or formerly nucleolus-like body. Chromatin configuration is an important indicator of the quality of GV oocytes and largely predicts their ability to resume meiosis and successful embryonic development. In mice, GV oocytes are traditionally divided into the NSN (non-surrounded nucleolus) and SN (surrounded nucleolus) based on the specific chromatin configuration. The NSN-SN transition is a key event in mouse oogenesis and the main prerequisite for the normal development of the embryo. As for humans, there is no single nomenclature for the chromatin configuration at the GV stage. This often leads to discrepancies and misunderstandings, the overcoming of which should expand the scope of the application of mouse oocytes as a model for developing new methods for assessing and improving the quality of human oocytes. As a first approximation and with a certain proviso, the mouse NSN/SN classification can be used for the primary characterization of human GV oocytes. The task of this review is to analyze and discuss the existing classifications of chromatin configuration in mouse and human GV oocytes with an emphasis on transcriptional activity extinction at the end of oocyte growth.

The Implications of Insufficient Zinc on the Generation of Oxidative Stress Leading to Decreased Oocyte Quality

Zinc is a transition metal that displays wide physiological implications ranging from participation in hundreds of enzymes and proteins to normal growth and development. In the reproductive tract of both sexes, zinc maintains a functional role in spermatogenesis, ovulation, fertilization, normal pregnancy, fetal development, and parturition. In this work, we review evidence to date regarding the importance of zinc in oocyte maturation and development, with emphasis on the role of key zinc-binding proteins, as well as examine the effects of zinc and reactive oxygen species (ROS) on oocyte quality and female fertility. We summarize our current knowledge about the participation of zinc in the developing oocyte bound to zinc finger proteins as well as loosely bound zinc ion in the intracellular and extracellular environments. These include aspects related to (1) the impact of zinc deficiency and overwhelming production of ROS under inflammatory conditions on the offset of the physiological antioxidant machinery disturbing biomolecules, proteins, and cellular processes, and their role in contributing to further oxidative stress; (2) the role of ROS in modulating damage to proteins containing zinc, such as zinc finger proteins and nitric oxide synthases (NOS), and expelling the zinc resulting in loss of protein function; and (3) clarify the different role of oxidative stress and zinc deficiency in the pathophysiology of infertility diseases with special emphasis on endometriosis-associated infertility.

The spectrum of in vitro maturation in clinical practice: the current insight

In vitro oocyte maturation (IVM) has been used worldwide. Despite the long-term implementation, the uptake of this procedure to complement current in vitro fertilization (IVF) remains low. The main reason is likely due to the non-synchronization of protocol and definition criteria, leading to difficulty in collective proper outcome data worldwide and, thus, lack of understanding of the exact IVM procedure. The review aims to consolidate the current clinical practice of IVM by dissecting relevant publications to be tailored for a current spectrum of clinical practice. Nevertheless, the background theories of oocyte maturation were also explored to provide a comprehensive understanding of the basis of IVM theories. Additional discussion of other potential uses of IVM in the future, such as in ovarian tissue cryopreservation known as OTO-IVM for fertility preservation and among women with diminished ovarian reserve, was also explored. Otherwise, future collaboration among all IVM centers is paramount for better collection of clinical data to provide valid recommendations for IVM in clinical practice, especially in molecular integrity and possible DNA alteration if present for IVM offspring outcome safety purposes.

Developmental Hurdles That Can Compromise Pregnancy during the First Month of Gestation in Cattle

Several key developmental events are associated with early embryonic pregnancy losses in beef and dairy cows. These developmental problems are observed at a greater frequency in pregnancies generated from in-vitro-produced bovine embryos. This review describes critical problems that arise during oocyte maturation, fertilization, early embryonic development, compaction and blastulation, embryonic cell lineage specification, elongation, gastrulation, and placentation. Additionally, discussed are potential remediation strategies, but unfortunately, corrective actions are not available for several of the problems being discussed. Further research is needed to produce bovine embryos that have a greater likelihood of surviving to term.

Intrafollicular Retinoic Acid Signaling Is Important for Luteinizing Hormone-Induced Oocyte Meiotic Resumption

It has been clear that retinoic acid (RA), the most active vitamin A (VA) derivative, plays a central role in governing oocyte meiosis initiation. However, it has not been functionally determined if RA participates in luteinizing hormone (LH)-induced resumption from long-lasting oocyte meiotic arrest, which is essential for haploid oocyte formation. In the present study, using well-established in vivo and in vitro models, we identified that intrafollicular RA signaling is important for normal oocyte meiotic resumption. A mechanistic study indicated that mural granulosa cells (MGCs) are the indispensable follicular compartment for RA-prompted meiotic resumption. Moreover, retinoic acid receptor (RAR) is essential for mediating RA signaling to regulate meiotic resumption. Furthermore, we found zinc finger protein 36 (ZFP36) is the transcriptional target of RAR. Both RA signaling and epidermal growth factor (EGF) signaling were activated in MGCs in response to LH surge, and two intrafollicular signalings cooperate to induce rapid Zfp36 upregulation and Nppc mRNA decrease, which is critical to LH-induced meiotic resumption. These findings extend our understanding of the role of RA in oocyte meiosis: RA not only governs meiotic initiation but also regulates LH-induced meiotic resumption. We also emphasize the importance of LH-induced metabolic changes in MGCs in this process.

High-dose synthetic phenolic antioxidant propyl gallate impairs mouse oocyte meiotic maturation through inducing mitochondrial dysfunction and DNA damage

Propyl gallate (PG) is one of the most widely used antioxidants in food products, cosmetics and pharmaceutical industries. Increased research has suggested that exposure to PG influences reproductive health in humans and animals. However, until now, it has not yet been confirmed whether PG would impact oocyte quality. In this study, the hazardous effects of PG on oocyte meiotic maturation were investigated in mice. The findings showed that PG exposure compromises oocyte meiosis by inducing mitochondrial stress which activates apoptosis to trigger oocyte demise. Moreover, DNA damage was significantly induced in PG-treated oocytes, which might be another cause of oocyte developmental arrest and degeneration. Besides, the level of histone methylation (H3K27me2 and H3K27me3) in oocyte was also significantly increased by PG exposure. Furthermore, PG-induced oxidative stress was validated by the increased level of reactive oxygen species (ROS), which might be the underlying reason for these abnormities. In conclusion, the foregoing findings suggested that PG exposure impaired oocyte meiotic maturation by yielding mitochondrial stress to activate apoptosis, inducing DNA damage and oxidative stress, and altering histone methylation level.

cAMP controls the balance between dormancy and activation of primordial follicles in mouse ovaries

In mammalian ovaries, the balance between dormancy and activation of primordial follicles determines the female fecundity and endocrine homeostasis. Recently, several functional molecules and pathways have been reported to be involved in the activation of primordial follicles. However, the homeostasis regulatory mechanisms of primordial follicle activation are still scant. Our previous study has proved that a relatively higher concentration of cyclic AMP (cAMP) is required for primordial follicle formation. Here, we identified that cAMP also plays a vital role in the balance between dormancy and activation of primordial follicles. Our results showed that the concentration of cAMP remained stable in neonatal mouse ovaries, which is due to ADCY3, the synthetase of cAMP, and PDE3A, the hydrolytic enzyme of cAMP, were synchronously increased during the activation of primordial follicles in mouse ovaries. Once the concentration of cAMP in neonatal ovaries was either elevated or reduced in vitro, the activation of primordial follicles was either accelerated or decelerated accordingly. In addition, a higher concentration of cAMP in the ovaries of puberty mice improved primordial follicle activation in vivo. Finally, cAMP promoted primordial follicle activation via canonical mTORC1-PI3K signaling cascades and PKA signaling. In conclusion, our findings reveal that the concentration of cAMP acts as a key regulator in balancing the dormancy and activation of primordial follicles in the mouse ovary.

Autophagy-related gene and protein expressions during blastocyst development

PURPOSE

This study aims to examine the expression of autophagic genes and proteins during blastocyst development and differentiation.

METHODS

This is a prospective cohort study. Between March 2018 and November 2019, 30 females aged 30.13 ± 4.83 years underwent an intracytoplasmic sperm injection (ICSI) cycle at Madina Fertility Center. ICSI was used to develop and incubate 82 leftover embryos to day 5. Then, the embryos were divided into two groups based on their developmental structure: group D (n = 49) included embryos that developed into blastocysts, whereas group A (n = 33) included arrested embryos. These embryos were used to investigate the autophagic gene and protein expressions. The current study was approved by the Clinical Trial Ethical Committee of the Faculty of Medicine, Alexandria University, following the ethical standards of scientific research (Registration no. 0303721).

RESULTS

Embryos that developed into blastocysts on day 5 (group D) had significantly higher relative expression of the LC3 gene (1.11 ± 0.52) and beclin-1 gene (1.43 ± 0.34) and beclin-1 protein expression (3.8 ± 0.028) than those that did not develop into blastocysts on day 5 (group A) [0.72 ± 0.18 (P = 0.03), 0.35 ± 0.12 (P = 0.0001), and 3.14 ± 0.05, (P = 0.0001), respectively]. In contrast, mTOR and PIK3C3 protein expression was significantly higher in group A (arrested embryos) than those in group D (developed embryos) (P = 0.007 and P = 0.0001, respectively). Furthermore, the expression of the eIF4E gene was significantly lower in group D embryos (0.32 ± 0.07) than that in group A embryos (4.38 ± 1.16) (P = 0.0001).

CONCLUSIONS

This work identifies  autophagy as a well regulated process required to maintain cell allocation and differentiation during late preimplantation embryo developmental stages.

First Croatian Case of Double Aneuploidy: A Child With Klinefelter and Edwards Syndrome (48,XXY,+18) - Possible Causes and Contributing Factors

We report a case of double aneuploidy in a preterm male newborn with karyotype 48,XXY,+18 whose mother was of advanced age and infected with the SARS-CoV-2 virus during the early stages of her pregnancy. The clinical features observed in the newborn included intrauterine growth retardation, dysmorphic facial features, overlapping fingers on both hands, respiratory distress syndrome, ventricular septal defect, patent ductus arteriosus, persistent pulmonary hypertension, and bilateral clubfoot, a phenotype that mainly correlates with Edwards syndrome (trisomy 18). To our knowledge, this is the first reported case of double aneuploidy in Croatia. This paper provides a detailed description of the clinical presentation and treatment strategies used, with the aim of providing valuable data for future recognition and management of similar cases. Furthermore, we discuss the mechanisms of nondisjunction that might account for this rare form of aneuploidy.

Role of Obesity in Female Reproduction

Contemporary scientists need no "p value" and "relative risk" statistics to be exquisitely aware of the increasing prevalence of obesity and complications posed by obesity. It is now well recognized that obesity is strongly associated with type 2 diabetes, hypertension, vascular disease, tumors and reproductive disorders. Obese women show lower levels of gonadotropin hormones, reduced fecundity, higher miscarriage rates and poorer outcomes of in vitro fertilization, revealing that obesity affects female reproduction. In addition, adipose tissue contains special immune cells and obesity-induced inflammation is a chronic, low-grade inflammatory response. Herein, we mainly review detrimental influences of obesity in the complete process of female reproduction, including hypothalamic-pituitary-ovarian axis, oocyte maturation, embryo and fetal development. In the latter part, we view obesity-induced inflammation and discuss related epigenetic impact on female reproduction.

Cilostamide, a phosphodiesterase 3A inhibitor, sustains meiotic arrest of rat oocytes by modulating cyclic adenosine monophosphate level and the key regulators of maturation promoting factor

Cilostamide, a phosphodiesterase 3A (Pde3A) inhibitor, is known to increase intraoocyte cyclic adenosine monophosphate (cAMP) level which is involved in sustaining meiotic arrest of the oocytes. To explore the mechanisms involved in the cilostamide-mediated meiotic arrest of the oocytes, the present study describes the effects of cilostamide on cAMP level and related factors involved in maturation of the oocytes at its different meiotic stages; diplotene, metaphase I (MI) and metaphase II (MII). The oocytes from these three stages were collected from rat ovary and incubated with 10 µM cilostamide for 3 h in CO₂ incubator. The levels of cAMP, cyclic guanosine monophosphate (cGMP) and the key players of maintaining meiotic arrest during oocyte maturation; Emi2, Apc, Cyclin B1, and Cdk1, were analyzed in diplotene, MI and MII stages. Pde3A was found to be expressed at all three stages but with the lowest level in MI oocyte. As compared to the control sets, the cAMP concentration was found to be highest in MII whereas cGMP was highest in the diplotene stage of cilostamide-treated group. The treated group showed declined reactive oxygen species level as compared with the control counterparts. Relatively increased levels of the Emi2, Cyclin B1, and phosphorylated thr161 of Cdk1 versus declined levels of phosphorylated thr14/tyr15 of Cdk1 in diplotene and MII stage oocytes are known to be involved in maintaining meiotic arrest and all these factors were found to undergo similar pattern of change due to the treatment with cilostamide. The findings thus suggest that cilostamide treatment promotes meiotic arrest by Pde3A inhibition led increase of both cAMP and cGMP level vis-a-vis modulation of the related regulatory factors such as Emi2, CyclinB1, and phosphorylated status of Cdk1 in diplotene and MII stage oocytes. Such a mechanism of meiotic arrest could allow the oocyte to prepare itself for meiotic maturation and thereby to improve oocyte quality.