Oocyte Differentiation is Genetically Dissociable from the Meiotic Program in Mice

Oogenesis is a developmental program by which a gametogenesis-competent germ cell becomes a fertilization-competent egg. During oogenesis, growth and differentiation of oocytes are closely coordinated with initiation and progression through meiosis. In mammals, the timing of meiotic initiation is sexually dimorphic, with only ovarian and not testicular germ cells initiating meiosis during fetal development. Consequentially, fetal meiotic initiation is thought to be prerequisite to subsequent growth and differentiation of the ovarian germ cell into a fully grown oocyte. Here I present evidence that meiotic initiation and prophase I are genetically separable from oocyte growth and differentiation, thereby, demonstrating that oogenesis consists of two independent processes under separate regulation. This represents a novel view of the oogenesis program and revises the current model of germ cell commitment to oogenesis in mice. The proposed revised model accounts for independent commitment of a germ cell to meiosis and differentiation. This model may provide insights into previously unexplained cases of female infertility and has practical implications for in vitro oogenesis strategies.