Blood and bone marrow stem cells may contain stem cells which can develop into eggs, says an article in the latest issue of the journal Cell. The controversial findings by scientists at Massachusetts General Hospital could rewrite textbooks on the female reproductive system and eventually extend women’s reproductive life. Jonathan Tilly and Joshua Johnson say that mouse ovaries destroyed by chemotherapy were replenished after the mice received bone marrow transplants from female donors. And oocytes began to grow in mice which were genetically infertile after transplants.

These results could explain why some women who receive cancer treatment later bear children even though doctors predicted that they would be infertile. Bone marrow transplants might have stimulated the growth of healthy oocytes.

The research is exciting but inconclusive. The scientists have not actually proved that these cells can trigger ovulation or give rise to new offspring. “Until the authors have shown that the putative oocytes are functional, we should be cautious,” says Margaret Goodell, of Baylor College of Medicine in Houston. However, Tilly says that if he is right, the implications are “mind-boggling”. He believes that the stem cells could be harvested when a woman is young as an insurance policy against infertility or to prevent, delay or reverse menopause.