ZAR1/2‐Regulated Epigenetic Modifications are Essential for Age‐Associated Oocyte Quality Maintenance and Zygotic Activation

Abstract The developmental competence and epigenetic progression of oocytes gradually become dysregulated with increasing maternal age. However, the mechanisms underlying age‐related epigenetic regulation in oocytes remain poorly understood. Zygote arrest proteins 1 and 2 (ZAR1/2) are two maternal factors with partially redundant roles in maintaining oocyte quality, mainly known by regulating mRNA stability. In addition to this known function, it is found that ZAR1/2 is required for oocyte epigenetic maturation and zygotic reprogramming. Zar1/2 ‐deleted oocytes exhibited reduced levels of multiple histone modifications and of the expression of corresponding histone modifiers, along with over‐condensed chromatin, leading to compromised minor zygotic genome activation and deficient embryo development following fertilization. Cytoplasmic ZAR1/2 participated in intranuclear epigenetic maturation by binding the transcripts encoding histone modifiers and regulating their stability and translational activity. Moreover, oocytes from aged mice exhibited similar histone‐modification deficiencies as the Zar1/2 ‐deleted oocytes. ZAR1/2 mRNA and protein levels are downregulated in oocytes from mice and women with advanced ages, suggesting ZAR1/2 as regulators of epigenetic changes with reproductive aging. This study presents a new nucleo‐cytoplasmic interaction mechanism that is involved in preventing oocyte epigenetic aging. Further, ZAR1/2 represents potential gene targets for diagnosis and clinical interventions in age‐associated deficiencies in oocyte and embryo development.