In female mammals, the size of the initially established primordial follicle pool within the ovaries determines the reproductive life span. Interestingly, the establishment of the primordial follicle pool is accompanied by a remarkable programmed oocyte loss for unclear reasons. Here, we identify a new role of ASH1-like histone lysine methyltransferase (ASH1L) in controlling the apoptosis of oocytes during meiotic prophase I in mice. Our results showed that overexpression of Ash1l led to a dramatic loss of fetal oocytes via apoptosis, which subsequently resulted in a reduced capacity of the primordial follicle pool. Overexpression of Ash1l also led to a deficiency in DNA double-strand break repair associated with premature upregulation of p63 and phosphorylated checkpoint kinase 2 (p-CHK2), the major genome guardian of the female germline, following Ash1l overexpression in fetal ovaries. In summary, ASH1L is one of the indispensable epigenetic molecules that acts as a guardian of the genome. It protects oocyte genome integrity and removes oocytes with serious DNA damage by regulating the expression of p63 and p-CHK2 during meiotic prophase I in mice. Our study provides a perspective on the physiological regulatory role of DNA damage checkpoint signaling in fetal oocyte guardianship and female fertility.
Keywords: ASH1L; DNA damage checkpoint; apoptosis; oocyte; primordial follicle.