The cohesin stabilizer Sororin drives G2-M transition and spindle assembly in mammalian oocytes

Inhibition of ferroptosis counteracts the advanced maternal age-induced oocyte deterioration

Ferroptosis, a recently discovered form of programmed cell death triggered by the excessive accumulation of iron-dependent lipid peroxidation products, plays a critical role in the development of various diseases. However, whether it is involved in the age-related decline in oocyte quality remains unexplored. Here, we took advantage of nano-proteomics to uncover that reduced ferritin heavy chain (Fth1) level is a major cause leading to the occurrence of ferroptosis in aged oocytes. Specifically, induction of ferroptosis in young oocytes by its activators RSL3 and FAC, or knockdown of Fth1 all phenocopied the meiotic defects observed in aged oocytes, including failed oocyte meiotic maturation, aberrant cytoskeleton dynamics, as well as impaired mitochondrial function. Transcriptome analysis showed that knockdown of Fth1 affected meiosis-related and aging-related pathways in oocytes. Conversely, inhibition of ferroptosis by its inhibitors or expression of Fth1 improved the quality of aged oocytes. We also validated the effects of ferroptosis on the porcine oocyte quality in vitro. Altogether, we demonstrate the contribution of ferroptosis to the age-induced oocyte defects and evidence that inhibition of ferroptosis might be a feasible strategy to ameliorate the reproductive outcomes of female animals at an advanced age.

A Microtubule-Associated Protein Functions in Preventing Oocytes from Evading the Spindle Assembly Checkpoint

Aneuploidy eggs are a common cause of human infertility, spontaneous abortion, or trisomy syndromes. The spindle assembly checkpoint (SAC) plays a crucial role in preventing aneuploidy in oocytes, yet it is unclear if additional mechanisms exist to ensure oocyte adherence to this checkpoint. It is now revealed that the microtubule-associated protein NUSAP can prevent oocytes from evading the SAC and regulate the speed of the cell cycle. Mechanistically, the study identifies NUSAP as a novel stabilizer of the E3 ubiquitin ligase APC/CCDH1, protecting CDH1 from SCFBTRC-mediated degradation. Depletion of NUSAP reduces CDH1 protein level, leading to abnormal spindle assembly and chromosome alignment, and disrupting the balance of cell cycle proteins. This misregulated balance causes oocytes to evade the SAC. Consequently, these abnormal oocytes not only fail to arrest at metaphase but also accelerate the cell process, ultimately resulting in the production of aneuploid eggs. Together, the findings not only clarify the existence of mechanisms that ensure oocytes compliance with the spindle assembly checkpoint but also expand the new functions of NUSAP beyond its role as a microtubule- associated protein.

Microseparation of Lipophilic and Hydrophilic Metabolites for Single Oocyte Mass Spectrometry Analysis

Single-cell metabolic analysis has not yet achieved the coverage of bulk analysis due to the diversity of cellular metabolites and the ionization competition among species. Direct ionization methods without separation lead to the masking of low-intensity species. By designing a capillary column emitter and introducing reverse-phase chromatography principles, we achieved the microseparation of lipophilic and hydrophilic metabolites and lowered the limit of detection of hydrophilic metabolites to the level of a single oocyte. We identified 517 metabolite species in a single oocyte, achieving coverage and reproducibility comparable to those of bulk analysis. By comparing oocytes at different maturation stages, 76 metabolic features were identified with significant differences between the germinal vesicle and meiosis II stages. Metabolite level changes suggested the roles of lipid metabolism remodeling, increased amino acid synthesis, and a shift from pyrimidine metabolism to purine metabolism in the process of oocyte maturation. This microseparation mass spectrometry analysis is expected to promote single-cell metabolomics.

Gap junctions in polycystic ovary syndrome: Implications for follicular arrest

Gap junctions are specialized intercellular conduits that provide a direct pathway between neighboring cells, which are involved in numerous physiological processes, such as cellular differentiation, cell growth, and metabolic coordination. The effect of gap junctional hemichannels in folliculogenesis is particularly obvious, and the down-regulation of connexins is related to abnormal follicle growth. Polycystic ovary syndrome (PCOS) is a ubiquitous endocrine disorder of the reproductive system, affecting the fertility of adult women due to anovulation. Exciting evidence shows that gap junction is involved in the pathological process related to PCOS and affects the development of follicles in women with PCOS. In this review, we examine the expression of connexins in follicular cells of PCOS and figure out whether such communication could have consequences for PCOS women. While along with results from clinical and related animal studies, we summarize the mechanism of connexins involved in the pathogenesis of PCOS.

Polyamine metabolite spermidine rejuvenates oocyte quality by enhancing mitophagy during female reproductive aging

Advanced age is a primary risk factor for female infertility due to reduced ovarian reserve and declining oocyte quality. However, as an important contributing factor, the role of metabolic regulation during reproductive aging is poorly understood. Here, we applied untargeted metabolomics to identify spermidine as a critical metabolite in ovaries to protect oocytes against aging. In particular, we found that the spermidine level was reduced in ovaries of aged mice and that supplementation with spermidine promoted follicle development, oocyte maturation, early embryonic development and female fertility of aged mice. By microtranscriptomic analysis, we further discovered that spermidine-induced recovery of oocyte quality was mediated by enhancement of mitophagy activity and mitochondrial function in aged mice, and this mechanism of action was conserved in porcine oocytes under oxidative stress. Altogether, our findings suggest that spermidine supplementation could represent a therapeutic strategy to ameliorate oocyte quality and reproductive outcome in cis-gender women and other persons trying to conceive at an advanced age. Future work is needed to test whether this approach can be safely and effectively translated to humans.

Mitotic spindle disassembly in human cells relies on CRIPT having hierarchical redox signals

Swift and complete spindle disassembly in late mitosis is essential for cell survival, yet how it happens is largely unknown in mammalian cells. Here we used real-time live cell microscopy and biochemical assays to show that the primordial dwarfism (PD)-related cysteine-rich protein CRIPT dictates the spindle disassembly in a redox-dependent manner in human cells. This previously reported cytoplasmic protein was found to have a confined nuclear localization with a nucleolar concentration during interphase but was distributed to spindles and underwent redox modifications to form disulfide bonds in CXXC pairs during mitosis. Then, it directly interacted with, and might transfer a redox response to, tubulin subunits via a putative redox exchange among cysteine residues to induce microtubule depolymerization. Expression of CRIPT proteins with mutations of these cysteine residues blocked spindle disassembly, generating two cell types with long-lasting metaphase spindles or spindle remnants. Live-cell recordings of a disease-relevant mutant (CRIPTC3Y) revealed that microtubule depolymerization at spindle ends during anaphase and the entire spindle dissolution during telophase might share a common CRIPT-bearing redox-controlled mechanism.

The Role of m6A on Female Reproduction and Fertility: From Gonad Development to Ovarian Aging

The growth and maturation of oocyte is accompanied by the accumulation of abundant RNAs and posttranscriptional regulation. N6-methyladenosine (m⁶A) is the most prevalent epigenetic modification in mRNA, and precisely regulates the RNA metabolism as well as gene expression in diverse physiological processes. Recent studies showed that m⁶A modification and regulators were essential for the process of ovarian development and its aberrant manifestation could result in ovarian aging. Moreover, the specific deficiency of m⁶A regulators caused oocyte maturation disorder and female infertility with defective meiotic initiation, subsequently the oocyte failed to undergo germinal vesicle breakdown and consequently lost the ability to resume meiosis by disrupting spindle organization as well as chromosome alignment. Accumulating evidence showed that dysregulated m⁶A modification contributed to ovarian diseases including polycystic ovarian syndrome (PCOS), primary ovarian insufficiency (POI), ovarian aging and other ovarian function disorders. However, the complex and subtle mechanism of m⁶A modification involved in female reproduction and fertility is still unknown. In this review, we have summarized the current findings of the RNA m⁶A modification and its regulators in ovarian life cycle and female ovarian diseases. And we also discussed the role and potential clinical application of the RNA m⁶A modification in promoting oocyte maturation and delaying the reproduction aging.