Study confirms mammals don't produce new oocytes after birth

For decades, researchers have believed that no new oocytes are produced after birth in mammals. However, a 2004 study by Johnson et al. challenged the conventional concept, reporting the presence of germ cells on the ovary's surface that could potentially form new oocytes. Subsequent studies further supported this idea by isolating female germline stem cells (FGSCs) from mouse and human ovaries. However, controversy remained, as these cells might have been induced to differentiate due to abnormal stimuli during isolation.

To clarify this debate, a research team from Fudan University and Shanghai University of Traditional Chinese Medicine used various models, including mice of different ages, an ovarian mouse model with mechanical injury, and a rat model of endometriosis, to explore the presence of FGSCs in rodents. They used markers such as mouse VASA homolog (MVH) and ubiquitin carboxy-terminal hydrolase L1 (UCHL1) to label germ cells with proliferative activity in the ovary.

The study found that FGSCs were not detectable in any of the models tested, across all conditions. In addition to the in vivo models, the researchers also investigated the feasibility of inducing FGSCs in vitro using cultured ovarian tissues. They treated the tissues with various factors, including estrogen (E2), follicle-stimulating hormone (FSH), epidermal growth factor (EGF), and fibroblast growth factor (FGF). Despite significant proliferation of ovarian surface epithelial cells, still no FGSC formation was observed.

"Strategies relying on the presence of FGSCs in postnatal ovaries may need to be reconsidered," noted Dr. Sun Zhaogui, the corresponding author. The study also highlights the importance of careful experimental design and the need for rigorous validation of findings. The research result is published in Reproductive and Developmental Medicine.