Bo Xiong

Oocytes rely on a cohort of proteins whose sustained expression ensures normal meiotic progression and reproductive competence throughout an animal’s reproductive life. Age-related declines in these proteins are a major cause of reduced oocyte quality and female fertility during reproductive aging. Here, we report that the cohesin regulatory protein PDS5B, a dynamically maintained factor in oocytes, declines with age and plays a noncanonical role in the spindle pole formation independent of its cohesion function during oocyte meiotic maturation. Specifically, we found that PDS5B was expressed throughout the oocyte meiosis and localized at the spindle poles at metaphase stages, while its protein abundance was reduced in aged oocytes, concomitant with decreased messenger ribonucleic acid (mRNA) levels and translational efficiency. Knockdown or heterozygous knockout of PDS5B caused spindle assembly defects, meiotic arrest, and aneuploidy in oocytes, ultimately leading to female subfertility. Mechanistically, immunoprecipitation/mass spectrometry analyses revealed that PDS5B recruited deubiquitinating enzyme USP9X to spindle poles to stabilize nuclear mitotic apparatus and promote proper spindle assembly. Moreover, expression of exogenous PDS5B in aged oocytes partially alleviated meiotic defects associated with advanced maternal age. Altogether, our findings uncover a unique spindle pole-specific function of PDS5B in oocytes and suggest that maintaining PDS5B levels may be a potential strategy to improve the quality of aged oocytes.

The gut microbiota plays a vital role in maintaining the physiological function of host health and the pathogenesis of various diseases. However, its relationship with maternal age-associated decline in oocyte quality remains elusive. Here, we report that establishment of gut microbiota from young donors in aged mice by fecal microbiota transplantation (FMT) is an effective method to rejuvenate the quality of maternally aged oocytes. Specifically, young gut microbiota promoted the ovulation and maturation of aged oocytes, and inhibited occurrence of cytoplasm fragmentation and spindle/chromosome abnormalities, hence enhancing the oocyte quality and female fertility. By integrating metagenome and untargeted metabolome of intestinal digesta, as well as targeted metabolome of ovaries and micro-transcriptome of oocytes, we identified that Bacteroides_caecimuris -modulated glutamic acid levels mediated the restorative effects of young gut microbiota on the aged oocytes through strengthening the mitochondria function. In addition, we demonstrated that in vivo supplementation of glutamic acid also enhanced the quality of aged oocytes, and the improvement of oocyte quality by glutamic acid was conserved across species. Altogether, our findings highlight the importance of gut microbiota in the oocyte aging and provide potential improvement strategies for age-related decline in oocyte quality and female fertility.

Advanced maternal age is a key factor in female infertility, primarily due to declines in ovarian reserve and oocyte quality. However, the metabolic mechanisms underlying reproductive aging remain unclear. Here, we show that uridine levels in the plasma and ovaries of aged mice are significantly reduced compared with young controls. Building on this, we find that uridine supplementation significantly improves meiotic maturation, fertilization, and early embryonic development of aged oocytes, both in vivo and in vitro. Further microtranscriptomic analyses reveal that uridine enhances oocyte quality by inhibiting ferroptosis and enhancing mitochondrial function. Moreover, by integrating Limited Proteolysis-Small Molecule Mapping, western blotting and siRNA-based functional assays, we identify that uridine binds to poly(rC)-binding protein 1, thereby suppressing ferroptosis and preserving mitochondrial function. Collectively, these findings demonstrate that uridine supplementation improves fertility in aged female mice and provide mechanistic insight into ferroptosis in oocyte aging.

As a major component of the cytoskeleton, intermediate filaments are generally considered to play a supporting role in mitotic cells. They also take part in the regulation of cell motility, proliferation, differentiation, and apoptosis. However, their specific functions during meiosis are largely unknown. Here, a unique role of an intermediate filament protein beaded filament structural protein 2 (BFSP2) is reported, which is predominantly expressed in lens fiber epithelial cells, as a spindle formation controller in oocyte meiosis. BFSP2 is constantly expressed during oocyte meiotic maturation, and specifically distributed on the spindle apparatus at metaphase I (MI) and metaphase II (MII) stages. Depletion of BFSP2 resulted in the meiotic arrest at MI stage due to the aberrant spindle assembly‐induced spindle assembly checkpoint activation. Depletion of BFSP2 also led to incorrect kinetochore‐microtubule attachments and the occurrence of aneuploidy in oocytes. Mechanistically, immunoprecipitation combined with mass spectrometry analysis identified clathrin heavy chain 1 (CLTC) as the downstream mediator of BFSP2 during meiotic spindle assembly. It is further determined that BFSP2 recruited the molecular chaperone heat shock cognate protein 70 (HSC70) to the spindle apparatus for stabilizing CLTC, and thus driving the spindle formation. In summary, these findings uncover a noncanonical function of the intermediate filament protein BFSP2 as a spindle assembly controller in oocyte meiosis.

The cytoskeleton is composed of microtubules, microfilaments, and intermediate filaments in cells. While the functions of microtubules and microfilaments have been well elucidated, the roles of intermediate filaments and associated proteins remain largely unknown, especially in meiosis. BFSP1 is an intermediate filament protein mainly expressed in the eye lens to play important roles in the development of congenital cataract. Here, we document that BFSP1 functions as a spindle regulator to drive the oocyte asymmetric division. Specifically, we found that BFSP1 distributed on the spindle apparatus during oocyte meiotic maturation. Depletion of BFSP1 resulted in symmetric division of oocytes, accompanied by the formation of elongated spindles at metaphase I and anaphase/telophase I stages. In addition, immunoprecipitation combined with mass spectrometry analysis identified MAP1B, a microtubule‐associated protein, as an interacting partner of BFSP1. Depletion or mutation of MAP1B phenocopied the meiotic defects observed in BFSP1‐depleted oocytes, and expression of exogenous MAP1B‐EGFP in BFSP1‐depleted oocytes recovered the spindle length and asymmetric division. We further determined that BFSP1 recruited molecular chaperone HSP90α on the spindle to stabilize MAP1B, thereby controlling the spindle length. To sum up, our findings reveal a unique meiotic role for BFSP1 in the regulation of spindle dynamics and oocyte asymmetric division.

Chromosome cohesion mediated by cohesin complex and its associated proteins is required for accurate chromosome segregation and genomic stability in mitosis. However, because of the distinct operation mechanisms, many proteins might exert different functions during meiosis in germ cells. Here, we document that cohesin-associated protein precocious dissociation of sisters 5A (Pds5A) plays a noncanonical role in the meiotic spindle assembly during oocyte maturation independent of its cohesion function. Pds5A distributes on the spindle fibers in oocytes at both metaphase I and metaphase II stages. Morpholino-based depletion or genetic ablation of Pds5A all lead to defects in spindle organization, chromosome euploidy and meiotic progression in oocytes and thus compromising the female fertility. Mechanistically, Pds5A recruits deubiquitinase ubiquitin-specific protease 14 to the spindle apparatus for stabilization of kinesin family member 5B, regulating the spindle elongation. Collectively, our findings unveil that cohesin-associated protein Pds5A can be used as a spindle regulator during oocyte meiosis.

PAK4 has been widely reported to function in somatic cells. However, its role and the underlying mechanisms in meiotic oocytes are largely unknown. Here, we show that PAK4 deficiency significantly disrupts maturational progression and meiotic apparatus in mouse oocytes. Furthermore, based on the kinase substrate binding preference and systematic functional screening, our mechanistic investigation demonstrated that PAK4 promotes cytoskeletal organization and oocyte maturation through phosphorylating serine 597 on DDX17. Of note, we identified a marked reduction of PAK4 protein in oocytes from diabetic mice. Importantly, ectopic expression of hyperphosphorylation-mimicking DDX17 mutant (DDX17-S597D) partly prevented the meiotic defects in these diabetic oocytes, indicating that the decreased phosphorylation of DDX17 due to PAK4 insufficiency is responsible for the impaired oocyte quality. In sum, these findings unveil the pivotal role of PAK4 in oocyte development and indicate a novel mechanism controlling meiotic progression and structure.