We extended the study by evaluating age effects on the fertility and oocytes in adult mice deficient in Tet1. We find that Tet1 deficient mice at reproductive middle-age already are completely infertile, consistent with POF or primary ovarian insufficiency (POI), which is characterized by the premature depletion of ovarian follicles and infertility at mid-reproductive age (Shah and Nagarajan, 2014; Delcour et al., 2019). This evidence concerns the gene TET1 and primary ovarian failure.