Conversion of female germline stem cells from neonatal and prepubertal mice into pluripotent stern cells

Pluripotent stem cells derived from neonatal or adult testes are a useful tool to examine the mechanisms of pluripotency and a resource for cell-based therapies. However, therapies usingthese cells will only benefit males but not females. Recently, female germline stem cells （FGSCs） were discovered in ovaries. Whether FGSCs can be converted into pluripotent stem cells, similar to spermatogonial stem cells, is unknown. Here, we demonstrate that female embryonic stem-like cells （fESLCs） can be generated within 1 month from the stably proliferating FGSCs cultured in embryonic stem cell （ESC） medium, fESLCs exhibit properties similar to those of ESCs in terms of marker expression and differentiation potential. Thus, our findings suggest that generation of patient-specific fESLCs is feasible and provides a foundation for personalized regenerative applications.

Production of transgenic mice by random recombination of targeted genes in female germline stem cells

Oocyte production in most mammalian species is believed to cease before birth.However,this idea has been challenged with the finding that postnatal mouse ovaries possess mitotically active germ cells.A recent study showed that female germline stem cells(FGSCs)from adult mice were isolated,cultured long term and produced oocytes and progeny after transplantation into infertile mice.Here,we demonstrate the successful generation of transgenic or gene knock-down mice using FGSCs.The FGSCs from ovaries of 5-day-old and adult mice were isolated and either infected with recombinant viruses carrying green fluorescent protein,Oocyte-G1 or the mouse dynein axonemal intermediate chain 2 gene,or transfected with the Oocyte-G1 specific shRNA expression vector(pRS shOocyte-G1 vector),and then transplanted into infertile mice.Transplanted cells in the ovaries underwent oogenesis and produced heterozygous offspring after mating with wild-type male mice.The offspring were genetically characterized and the biological functions of the transferred or knock-down genes were investigated.Efficiency of genetransfer or gene knock-down was 29%–37%and it took 2 months to produce transgenic offspring.Gene manipulation of FGSCs is a rapid and efficient method of animal transgenesis and may serve as a powerful tool for biomedical science and biotechnology.

Insights into female germ cell biology： from in vivo development to in vitro derivations

Understanding the mechanisms of human germ cell biology is important for developing infertility treatments. However, little is known about the mechanisms that regulate human gametogenesis due to the difficulties in collecting samples, especially germ cells during fetal development. In contrast to the mitotic arrest of spermatogonia stem cells in the fetal testis, female germ cells proceed into meiosis and began folliculogenesis in fetal ovaries. Regulations of these developmental events, including the initiation of meiosis and the endowment of primordial follicles, remain an enigma. Studying the molecular mechanisms of female germ cell biology in the human ovary has been mostly limited to spatiotemporal characterizations of genes or proteins. Recent efforts in utilizing in vitro differentiation system of stem cells to derive germ cells have allowed researchers to begin studying molecular mechanisms during human germ cell development. Meanwhile, the possibility of isolating female germline stem cells in adult ovaries also excites researchers and generates many debates. This review will mainly focus on presenting and discussing recent in vivo and in vitro studies on female germ cell biology in human. The topics will highlight the progress made in understanding the three main stages of germ cell developments： namely, primordial germ cell formation, meiotic initiation, and folliculogenesis.