Stage-specific mice ovarian somatic cell is involved in primordial folliculogenesis.

Although recent studies have shown that female germ cells can be produced from stem-cell lines in mice, whether these germ cells can interact with ovarian somatic cells (OSCs) to form primordial follicles (PFs) is still unclear. Here, we found after the PF pool is established, Irx3 and FoxL2 which were extensively expressed in the OSCs of the perinatal mouse decreased. Additionally, during primordial folliculogenesis, down-regulation of FoxL2 prevents OSCs invading germ cell cysts. Therefore, we investigated whether OSCs at different stages of folliculogenesis were able to reconstitute PFs with fetal ovarian germ cells in vitro. In this system, neither OSCs at the post-PF pool-establishment stage nor OSCs from normal or doxorubicin-treated adult mice were able to reconstitute PFs. Mice eliminated most of pre-existing PFs failed to exhibit any spontaneous regeneration of PFs. Our results suggest that OSCs can only support physiological primordial folliculogenesis during the prenatal period. OSCs lose the ability to form PFs after the establishment of the PF pool may be another reason why the PF pool is non-renewable in most adult mammals.