Jeong Su Oh

Centromeres play a vital role in ensuring accurate chromosome segregation during meiosis by serving as the foundation for kinetochore assembly and microtubule attachment. In oocytes, maintaining centromere integrity is particularly critical due to the extended arrest period prior to meiotic resumption. However, the molecular safeguards that preserve centromere structure and function throughout oocyte maturation remain poorly understood. Here, we identify ZSCAN4 as an essential regulator of centromere integrity during mouse oocyte meiosis. ZSCAN4 depletion leads to a marked reduction in key centromeric and kinetochore proteins, including CENP-A, accompanied by aberrant centromere stretching under spindle tension. Mechanistically, ZSCAN4 promotes pericentromeric H3K9me3 enrichment, facilitating proper chromatin compaction and chromosome alignment. Moreover, ZSCAN4 contributes to genomic stability by mediating the chromosomal recruitment of the CIP2A complex in response to DNA damage during meiotic progression. These findings establish ZSCAN4 as a critical factor in preserving centromere structure and function during oocyte meiosis, with potential implications for female reproductive health and developmental competence.

Double-strand breaks (DSBs) are a formidable threat to genome integrity, potentially leading to cancer and various genetic diseases. The prolonged lifespan of mammalian oocytes increases their susceptibility to DNA damage over time. While somatic cells suppress DSB repair during mitosis, oocytes exhibit a remarkable capacity to repair DSBs during meiotic maturation. However, the precise mechanisms underlying DSB repair in oocytes remain poorly understood. Here, we describe the pivotal role of the BRCA1–PLK1–CIP2A axis in safeguarding genomic integrity during meiotic maturation in oocytes. We found that inhibition of homologous recombination (HR) severely impaired chromosome integrity by generating chromosome fragments during meiotic maturation. Notably, HR inhibition impaired the recruitment of CIP2A to damaged chromosomes, and the depletion of CIP2A led to chromosome fragmentation following DSB induction. Moreover, BRCA1 depletion impaired chromosomal recruitment of CIP2A, but not vice versa. Importantly, the impaired chromosomal recruitment of CIP2A could be rescued by PLK1 inhibition. Consequently, our findings not only underscore the importance of the chromosomal recruitment of CIP2A in preventing chromosome fragmentation, but also demonstrate the regulatory role of the BRCA1–PLK1–CIP2A axis in this process during oocyte meiotic maturation.

DNA damage is a critical threat that poses significant challenges to all cells. To address this issue, cells have evolved a sophisticated molecular and cellular process known as the DNA damage response (DDR). Among the various cell types, mammalian oocytes, which remain dormant in the ovary for extended periods, are particularly susceptible to DNA damage. The occurrence of DNA damage in oocytes can result in genetic abnormalities, potentially leading to infertility, birth defects, and even abortion. Therefore, understanding how oocytes detect and repair DNA damage is of paramount importance in maintaining oocyte quality and preserving fertility. Although the fundamental concept of the DDR is conserved across various cell types, an emerging body of evidence reveals striking distinctions in the DDR between mammalian oocytes and somatic cells. In this review, we highlight the distinctive characteristics of the DDR in oocytes and discuss the clinical implications of DNA damage in oocytes.

The maintenance of spindle pole integrity is essential for spindle assembly and chromosome segregation during mitosis. However, the underlying mechanisms governing spindle pole integrity remain unclear. ENSA was inhibited by siRNA or MKI-2 treatment and its effect on cell cycle progression, chromosome alignment and microtubule alignment was observed by immunohistochemical staining and western blotting. PP2A-B55α knockdown by siRNA was performed to rescue the phenotype caused by ENSA inhibition. The interaction between ENSA and Aurora A was detected by in situ PLA. Furthermore, orthotopic implantation of 4Tl-luc cancer cells was conducted to confirm the consistency between the in vitro and in vivo relationship of the ENSA-Aurora A interaction. During mitosis, p-ENSA is localized at the spindle poles, and the inhibition of ENSA results in mitotic defects, such as misaligned chromosomes, multipolar spindles, asymmetric bipolar spindles, and centrosome defects, with a delay in mitotic progression. Although the mitotic delay caused by ENSA inhibition was rescued by PP2A-B55α depletion, spindle pole defects persisted. Notably, we observed a interaction between ENSA and Aurora A during mitosis, and inhibition of ENSA reduced Aurora A expression at the mitotic spindle poles. Injecting MKI-2-sensitized tumors led to increased chromosomal instability and downregulation of the MASTL-ENSA-Aurora A pathway in an orthotopic breast cancer mouse model. These findings provide novel insights into the regulation of spindle pole integrity by the MASTL-ENSA-Aurora A pathway during mitosis, highlighting the significance of ENSA in recruiting Aurora A to the spindle pole, independent of PP2A-B55α.

Because DNA double-strand breaks (DSBs) greatly threaten genomic integrity, effective DNA damage sensing and repair are essential for cellular survival in all organisms. However, DSB repair mainly occurs during interphase and is repressed during mitosis. Here, we show that, unlike mitotic cells, oocytes can repair DSBs during meiosis I through microtubule-dependent chromosomal recruitment of the CIP2A–MDC1–TOPBP1 complex from spindle poles. After DSB induction, we observed spindle shrinkage and stabilization, as well as BRCA1 and 53BP1 recruitment to chromosomes and subsequent DSB repair during meiosis I. Moreover, p-MDC1 and p-TOPBP1 were recruited from spindle poles to chromosomes in a CIP2A-dependent manner. This pole-to-chromosome relocation of the CIP2A–MDC1–TOPBP1 complex was impaired not only by depolymerizing microtubules but also by depleting CENP-A or HEC1, indicating that the kinetochore/centromere serves as a structural hub for microtubule-dependent transport of the CIP2A–MDC1–TOPBP1 complex. Mechanistically, DSB-induced CIP2A–MDC1–TOPBP1 relocation is regulated by PLK1 but not by ATM activity. Our data provide new insights into the critical crosstalk between chromosomes and spindle microtubules in response to DNA damage to maintain genomic stability during oocyte meiosis.

DNA double‐strand breaks (DSBs) are highly toxic lesions that can cause genomic instability and can be repaired by non‐homologous end‐joining (NHEJ) and homologous recombination (HR) pathways. Despite extensive studies about DSB repair pathways, the roles of each pathway during meiotic maturation in oocytes are not well understood. Here we show that oocytes selectively utilize NHEJ and HR to repair DSBs during meiotic maturation. Inhibition of NHEJ impaired the meiotic maturation of oocytes with DNA damage by activating the spindle assembly checkpoint (SAC) with a concomitant increase in metaphase I (MI) arrest and DNA damage levels. In contrast, oocytes with DNA damage bypassed SAC‐mediated MI arrest despite the presence of fragmented DNA when HR was inhibited. Notably, this bypass of SAC arrest by HR inhibition was associated with a loss of centromere integrity and subsequent impairment of chromosome architecture. Our results demonstrate that, while NHEJ is critical for the meiotic maturation of oocytes with DNA damage, HR is essential to maintain centromere integrity against DNA damage during meiotic maturation, revealing distinct roles of NHEJ and HR during meiotic maturation in mouse oocytes.

Fungicides are a type of pesticide used to protect plants and crops from pathogenic fungi. Azoxystrobin (AZO), a natural methoxyacrylate derived from strobilurin, is one of the most widely used fungicides in agriculture. AZO exerts its fungicidal activity by inhibiting mitochondrial respiration, but its cytotoxicity to mammalian oocytes has not been studied. In this study, we investigated the effect of AZO exposure on mouse oocyte maturation to elucidate the underlying mechanisms of its possible reproductive toxicity. We found that AZO exposure disturbed meiotic maturation by impairing spindle formation and chromosome alignment, which was associated with decreased microtubule organizing center (MTOC) integrity. Moreover, AZO exposure induced abnormal mitochondrial distribution and increased oxidative stress. The AZO-induced toxicity to oocytes was relieved by melatonin supplementation during meiotic maturation. Therefore, our results suggest that AZO exposure impairs oocyte maturation not only by increasing oxidative stress and mitochondrial dysfunction, but also by decreasing MTOC integrity and subsequent spindle formation and chromosome alignment.

Because DNA double-strand breaks (DSBs) greatly threaten genomic integrity, effective DNA damage sensing and repair are essential for cellular survival in all organisms. However, DSB repair mainly occurs during the interphase and is repressed during mitosis. Here, we show that, unlike mitotic cells, oocytes can repair DSBs during meiosis through microtubule-dependent chromosomal recruitment of the CIP2A-MDC1-TOPBP1 complex from spindle poles. After DSB induction, we observed spindle shrinkage and stabilization, as well as BRCA1 and 53BP1 recruitment to chromosomes and subsequent DSB repair during meiosis I. Moreover, p-MDC1 and p-TOPBP1 were recruited from spindle poles to chromosomes in a CIP2A-dependent manner. This pole-to-chromosome relocation of the CIP2A-MDC1-TOPBP1 complex was impaired not only by depolymerizing microtubules but also by depleting CENP-A or HEC1, indicating that the kinetochore/centromere serves as a structural hub for microtubule-dependent transport of the CIP2A-MDC1-TOPBP1 complex. Mechanistically, DSB-induced CIP2A-MDC1-TOPBP1 relocation is regulated by PLK1 but not by ATM activity. Our data provide new insights into the critical crosstalk between chromosomes and spindle microtubules in response to DNA damage to maintain genomic stability during oocyte meiosis.