Dual recombinases-mediated genetic tracing reveals no postnatal neo-oogenesis in mice.

The existence of postnatal neo-oogenesis in mammals has been debated since the initial reports of ovarian germline stem cells. To address this question, we employed a dual-recombinase-mediated genetic tracing system (Cre-loxP and Dre-rox). Pre-existing germ cells present after birth were labeled with ZsGreen via Stra8-Cre, whereas other ovarian cells were marked with tdTomato through tamoxifen-inducible Dre expression. Under physiological conditions, tdTomato+ cells labeled in young adult (8-week old), pubertal (3-week old), and newborn mice were traced for periods ranging from one to ten months. Regardless of the tracing duration, no tdTomato+ growing oocytes or metaphase II (MII) eggs were detected. Similarly, following busulfan-induced ovarian injury, no tdTomato+ growing oocytes or MII eggs were regenerated. Taken together, these findings provide compelling evidence against the occurrence of in vivo neo-oogenesis in mice, with implications for human reproductive biology.