CDK1 facilitates RAD51-mediated DNA repair to protect dictyate stage arrested oocytes from genotoxic stress

Abstract Oocytes arrested at the dictyate stage of meiosis I must maintain genomic integrity for prolonged periods to preserve female fertility. During this extended arrest, DNA lesions arising from endogenous and exogenous sources threaten oocyte survival, yet the molecular mechanisms coordinating DNA repair in dormant oocytes remain poorly understood. Here, we identify cyclin-dependent kinase 1 (CDK1) as a critical regulator of the oocyte DNA damage response and homologous recombination (HR) repair under genotoxic stress. Using cisplatin-induced DNA damage models in fetal goat ovaries and neonatal mouse ovaries, we investigated repair mechanisms operating within the ovarian reserve. Label-free proteomic profiling revealed significant enrichment of DNA damage response pathways following cisplatin exposure, with CDK1 emerging as one of the most prominently upregulated kinases. Pharmacological inhibition of CDK1 had little effect on follicle survival under physiological conditions but aggravated oocyte and follicle loss following DNA damage, indicating a stress-dependent role for CDK1 in preserving ovarian follicle pool integrity. Mechanistically, DNA damage activated a Chk2-dependent signaling pathway that promoted p63 phosphorylation and altered the WEE1–CDK1 regulatory axis, resulting in reduced inhibitory CDK1 phosphorylation (Thr14/Tyr15) and increased activating phosphorylation (Thr161). Activated CDK1 was associated with enhanced RAD51 phosphorylation and accumulation at DNA damage foci, supporting homologous recombination (HR)-mediated repair in dictyate-arrested oocytes. In contrast, CDK1 inhibition reduced phospho-RAD51 levels, impaired RAD51 localization, increased persistent γH2AX accumulation, and elevated oocyte apoptosis. Notably, suppression of CDK1 was accompanied by increased expression of the non-homologous end joining (NHEJ) marker Ku80 and the nucleotide excision repair (NER) factor XPA, suggesting increased engagement of alternative DNA repair pathways. Furthermore, inhibition of Chk2 abolished the DNA damage-associated CDK1 activation signature and restored WEE1 expression, supporting a model in which CDK1 functions downstream of Chk2 signaling during the oocyte DNA damage response. Collectively, our findings identify a previously unrecognized Chk2–CDK1–RAD51 signaling axis that coordinates homologous recombination repair in dormant oocytes and safeguards ovarian follicular pool integrity under genotoxic stress. These findings provide new mechanistic insight into how dictyate-arrested oocytes maintain genome stability during prolonged meiotic arrest.