CDC25B is required for the metaphase I-metaphase II transition in mouse oocytes

SETD2 regulates oocytes in vitro maturation through histone methylation and maternal mRNA degradation in yak

In vitro maturation (IVM) of oocytes is a vital aspect of assisted reproductive technology (ART), and its proper application can enhance reproductive efficiency. However, owing to the scarcity of research on the IVM of yak oocytes, its application in yak breeding remains underexplored. Therefore, in this study, we conducted high-throughput mRNA sequencing of immature and mature yak oocytes, which revealed transcriptomic changes during the IVM process in this unique high-altitude domesticated animal. Transcriptomic analysis also identified the histone methyltransferase SET domain-containing 2 (SETD2) as a key factor associated with post-translational modifications during oocyte maturation. To determine the role of SETD2 in oocytes, we employed the SETD2 inhibitor EZM0414 during oocyte maturation. Inhibition of SETD2 resulted in a significant reduction in histone methylation levels, lower oocyte maturation rate in vitro, and suppression of maternal mRNAs degradation suppression (P < 0.05). These findings indicated that SETD2 modulates oocyte maturation by regulating histone methylation and maternal mRNAs degradation. Furthermore, suppression of SETD2 markedly reduced the expression of oocyte secretion-related proteins (TSG6 and GDF9) and cumulus expansion-related protein (PTGS2), demonstrating that oocyte secretion and cumulus expansion were positively correlated with SETD2. Overall, our findings establish SETD2 as an essential regulator of yak oocyte maturation via histone methylation and maternal mRNAs degradation.

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.

Protein-targeting reverse genetic approaches: the future of oocyte and preimplantation embryo research

Reverse genetic approaches are the standard in molecular biology to determine a protein's function. Traditionally, nucleic acid targeting via gene knockout (DNA) and knockdown (RNA) has been the method of choice to remove proteins-of-interest. However, the nature of mammalian oocyte maturation and preimplantation embryo development can make nucleic acid-targeting approaches difficult. Gene knockout allows time for compensatory mechanisms and secondary phenotypes to develop which can make interpretation of a protein's function difficult. Furthermore, genes can be essential for animal and/or oocyte survival, and therefore, gene knockout is not always a viable approach to investigate oocyte maturation and preimplantation embryo development. Conversely, RNA-targeting approaches, i.e. RNA interference (RNAi) and morpholinos, rely on protein half-life and therefore are unable to knockdown every protein-of-interest. An increasing number of reverse genetic approaches that directly target proteins have been developed to overcome the limitations of nucleic acid-based approaches, including Trim-Away and auxin-inducible degradation. These protein-targeting approaches give researchers exquisite and fast control of protein loss. This review will discuss how Trim-Away and auxin-inducible degradation can overcome many of the challenges of nucleic acid-based reverse genetic approaches. Furthermore, it highlights the unique research opportunities these approaches afford, such as targeting post-translationally modified proteins.

Functional validation to explore the protective role of miR-223 in Staphylococcus aureus-induced bovine mastitis

BACKGROUND

Mastitis caused by Staphylococcus aureus (S. aureus) is one of the most intractable problems for the dairy industry, causing significantly reduced milk yields and early slaughter of cows worldwide. MicroRNAs (miRNAs) can post-transcriptionally regulate gene expression and studies in recent years have shown the importance of miRNA-associated gene regulation in S. aureus-induced mastitis.

RESULTS

In this study, to investigate the role of miR-223 in mastitis, we performed experiments to overexpress and suppress miR-223 in an immortalized bovine mammary epithelial cell line (MAC-T) infected with S. aureus. Overexpression of miR-223 in MAC-T cells repressed cell apoptosis and necrosis induced by S. aureus infection, whereas suppression of miR-223 had the opposite effect. Transcriptome expression profiling with weighted gene co-expression network analysis (WGCNA) and gene set variation analysis (GSVA) showed that miR-223 affects apoptosis and inflammation-related pathways. Furthermore, differentially expressed (DE) genes were evaluated, and genes exhibiting contrasting expression trends in the miR-223 overexpressed and suppressed groups were assessed as potential target genes of miR-223. Potential target genes, including CDC25B, PTPRF, DCTN1, and DPP9, were observed to be associated with apoptosis and necroptosis. Finally, through integrative analysis of genome-wide association study (GWAS) data and the animal quantitative trait loci (QTL) database, we determined that target genes of miR-223 were significantly enriched in single-nucleotide polymorphisms (SNP) and QTLs related to somatic cell count (SCC) and mastitis.

CONCLUSION

In summary, miR-223 has an inhibitory effect on S. aureus-induced cell apoptosis and necrosis by regulating PTPRF, DCTN1, and DPP9. These genes were significantly enriched in QTL regions associated with bovine mastitis resistance, underscoring their relevance in genetic regulation of disease resilience. Our findings provide critical genetic markers for enhancing mastitis resistance, particularly S. aureus-induced mastitis, through selective breeding. This work offers valuable insights for developing cattle with improved resistance to mastitis via targeted genetic selection.

The subcortical maternal complex modulates the cell cycle during early mammalian embryogenesis via 14-3-3

The subcortical maternal complex (SCMC) is essential for safeguarding female fertility in mammals. Assembled in oocytes, the SCMC maintains the cleavage of early embryos, but the underlying mechanism remains unclear. Here, we report that 14-3-3, a multifunctional protein, is a component of the SCMC. By resolving the structure of the 14-3-3-containing SCMC, we discover that phosphorylation of TLE6 contributes to the recruitment of 14-3-3. Mechanistically, during maternal-to-embryo transition, the SCMC stabilizes 14-3-3 protein and contributes to the proper control of CDC25B, thus ensuring the activation of the maturation-promoting factor and mitotic entry in mouse zygotes. Notably, the SCMC establishes a conserved molecular link with 14-3-3 and CDC25B in human oocytes/embryos. This study discloses the molecular mechanism through which the SCMC regulates the cell cycle in early embryos and elucidates the function of the SCMC in mammalian early embryogenesis.

Spatio-temporal requirements of Aurora kinase A in mouse oocyte meiotic spindle building

Meiotic spindles are critical to ensure chromosome segregation during gamete formation. Oocytes lack centrosomes and use alternative microtubule-nucleation mechanisms for spindle building. How these mechanisms are regulated is still unknown. Aurora kinase A (AURKA) is essential for mouse oocyte meiosis because in pro-metaphase I it triggers microtubule organizing-center fragmentation and its expression compensates for the loss of the two other Aurora kinases (AURKB/AURKC). Although knockout mouse models were useful for foundational studies, AURK spatial and temporal functions are not yet resolved. We provide high-resolution analyses of AURKA/AURKC requirements during meiotic spindle-building and identify the subcellular populations that carry out these functions: 1) AURKA is required in early spindle assembly and later for spindle stability, whereas 2) AURKC is required in late pro-metaphase, and 3) Targeted AURKA constructs expressed in triple AURK knockout oocytes reveal that spindle pole-localized AURKA is the most important population controlling spindle building and stability mechanisms.

Fangchinoline inhibits mouse oocyte meiosis by disturbing MPF activity

Fangchinoline (FA) is an alkaloid derived from the traditional Chinese medicine Fangji. Numerous studies have shown that FA has a toxic effect on various cancer cells, but little is known about its toxic effects on germ cells, especially oocytes. In this study, we investigated the effects of FA on mouse oocyte maturation and its potential mechanisms. Our results showed that FA did not affect meiosis resumption but inhibited the first polar body extrusion. This inhibition is not due to abnormalities at the organelle level, such as chromosomes and mitochondrial, which was proved by detection of DNA damage and reactive oxygen species. Further studies revealed that FA arrested the oocyte at the metaphase I stage, and this arrest was not caused by abnormal kinetochore-microtubule attachment or spindle assembly checkpoint activation. Instead, FA inhibits the activity of anaphase-promoting complexes (APC/C), as evidenced by the inhibition of CCNB1 degeneration. The decreased activity of APC/C may be due to a reduction in CDC25B activity as indicated by the high phosphorylation level of CDC25B (Ser323). This may further enhance Maturation-Promoting Factor (MPF) activity, which plays a critical role in meiosis. In conclusion, our study suggests that the metaphase I arrest caused by FA may be due to abnormalities in MPF and APC/C activity.

Methylation analysis by targeted bisulfite sequencing in large for gestational age (LGA) newborns: the LARGAN cohort

BACKGROUND

In 1990, David Barker proposed that prenatal nutrition is directly linked to adult cardiovascular disease. Since then, the relationship between adult cardiovascular risk, metabolic syndrome and birth weight has been widely documented. Here, we used the TruSeq Methyl Capture EPIC platform to compare the methylation patterns in cord blood from large for gestational age (LGA) vs adequate for gestational age (AGA) newborns from the LARGAN cohort.

RESULTS

We found 1672 differentially methylated CpGs (DMCs) with a nominal p < 0.05 and 48 differentially methylated regions (DMRs) with a corrected p < 0.05 between the LGA and AGA groups. A systems biology approach identified several biological processes significantly enriched with genes in association with DMCs with FDR < 0.05, including regulation of transcription, regulation of epinephrine secretion, norepinephrine biosynthesis, receptor transactivation, forebrain regionalization and several terms related to kidney and cardiovascular development. Gene ontology analysis of the genes in association with the 48 DMRs identified several significantly enriched biological processes related to kidney development, including mesonephric duct development and nephron tubule development. Furthermore, our dataset identified several DNA methylation markers enriched in gene networks involved in biological pathways and rare diseases of the cardiovascular system, kidneys, and metabolism.

CONCLUSIONS

Our study identified several DMCs/DMRs in association with fetal overgrowth. The use of cord blood as a material for the identification of DNA methylation biomarkers gives us the possibility to perform follow-up studies on the same patients as they grow. These studies will not only help us understand how the methylome responds to continuum postnatal growth but also link early alterations of the DNA methylome with later clinical markers of growth and metabolic fitness.

CHK1-CDC25A-CDK1 regulate cell cycle progression and protect genome integrity in early mouse embryos

After fertilization, remodeling of the oocyte and sperm genomes is essential to convert these highly differentiated and transcriptionally quiescent cells into early cleavage-stage blastomeres that are transcriptionally active and totipotent. This developmental transition is accompanied by cell cycle adaptation, such as lengthening or shortening of the gap phases G1 and G2. However, regulation of these cell cycle changes is poorly understood, especially in mammals. Checkpoint kinase 1 (CHK1) is a protein kinase that regulates cell cycle progression in somatic cells. Here, we show that CHK1 regulates cell cycle progression in early mouse embryos by restraining CDK1 kinase activity due to CDC25A phosphatase degradation. CHK1 kinase also ensures the long G2 phase needed for genome activation and reprogramming gene expression in two-cell stage mouse embryos. Finally, Chk1 depletion leads to DNA damage and chromosome segregation errors that result in aneuploidy and infertility.