Key mechanisms and in vitro reconstitution of fetal oocyte development in mammals.

During fetal oocyte development in mammals, germ cells progress through meiotic prophase I to form primordial follicles with pregranulosa cells. The primordial follicles remain dormant until oogenesis resumes during puberty. Studies in mice have elucidated mechanisms governing oogenesis, leading to the successful induction of functional oocytes from mouse pluripotent stem cells in vitro. Based on the in vivo/in vitro knowledge in mice and the histological and transcriptomic evidence for fetal oocyte development in humans and primates, human/primate oocyte-like cells corresponding to the early stage of oocytes in vivo have been successfully induced in vitro. Here, we discuss recent advances in our understanding of the mechanisms of fetal oocyte development in mammals, as well as in in vitro oogenesis.