Isolation, purification, and culture of oogonial stem cells from adult human and bovine ovarian cortex

Background The longstanding belief that women are born with a finite ovarian reserve has been debated for almost a decade, ever since the discovery, and subsequent isolation, of purported oogonial stem cells (OSCs). These cells, described in both mice and man, seemingly have the ability to generate oocytes when cultured in vitro under specific conditions, resulting in live offspring in the case of mice. The aims of this study were to verify independently the existence of OSCs in human ovarian tissue and to determine whether they could be isolated from bovine tissue. Methods We isolated OSCs from disaggregated bovine and human ovarian cortex using a fluorescence-activated cell sorting (FACS)-based technique, with cells being sorted for the presence of VASA, a germ-cell-specific protein. The cells were subsequently cultured in vitro without the need for a feeder layer, and mRNA expression of germline-specific markers was analysed with RT-PCR. The cells were transduced to express green fluorescent protein (GFP) by use of a lentivirus for the purposes of tracking. Findings A rare population of mitotically active VASA-positive cells was isolated from both bovine and human tissue and they have been grown in vitro for several months. Up to November, 2013, cells were retrieved from three human samples, but isolation has been replicated on five separate occasions in bovine ovary samples. RT-PCR demonstrated consistent expression of several germline markers, including IFITM3, DPPA3, PRDM1, POU5F1 , and KIT . It has been possible to cryopreserve the cells with successful re-initiation of growth on thawing, and stable expression of GFP was achieved after lentivirus transduction. Interpretation The expression of germline markers indicates that these cells have characteristics of germline (oogonial) stem cells. To our knowledge, this is the first report of such cells being isolated from bovine ovarian cortex and corroborates a previous report showing the isolation of OSCs from human ovary. These cells provide a novel model for investigating germ-cell development; future experiments will involve injection of OSCs into ovarian cortex to assess whether they have the capability to undergo follicle formation and oocyte development in an in-vitro environment. If their potential can be harnessed, OSCs might have a future role in clinical applications—eg, in fertility preservation. Funding UK Medical Research Council.