Mammalian ovaries might retain their capacity to generate new eggs during adulthood, suggests a study published online this week in Nature Cell Biology. The finding may have important implications in regenerative and reproductive medicine.

It is currently accepted that, in most mammalian species, the production of eggs, known as 'oocytes', terminates before birth. Despite recent evidence indicating that ovaries exhibit regenerative activity in juvenile and adult mice, the existence of female germline stem cells (FGSCs) in postnatal mammalian ovaries remained controversial.

Ji Wu and colleagues report the isolation of functional FGSCs from the ovaries of 5-day-old and adult mice. Upon isolation, FGSC lines were generated, which were able to maintain their proliferative potential even after long-term culture. When transplanted into the ovaries of infertile mice, FGSCs gave rise to new oocytes and reversed chemically-induced infertility, as demonstrated by the production of offspring. These young mice had no abnormalities and were fertile.