Research by scientists in China has suggested that the ovaries of female mice contain stem cells capable of growing into eggs that can be fertilised to produce healthy offspring.

The report in Nature Cell Biology states that female germline stem cells were isolated from mouse ovaries and grown in culture. Eggs in the ovaries of adult mice were killed, replaced with the cultured stem cells and tagged with green fluorescent protein (GFP) to allow their identification. The sterilised mice produced new eggs which were fertilised and gave rise to offspring, some of which carried GFP.

There have been suggestions that researchers failed to prove that the eggs used to produce offspring were grown from stem cells; it is possible that some of the endogenous eggs remained following sterilisation or that the GFP plasmid could have transfected these remaining eggs causing them to express GFP, resulting in its presence in some of the offspring. At present it is unknown whether such stem cells are present in human ovaries. Their discovery would be highly significant and challenge the long-held principle of reproductive biology that women are born with their full complement of eggs. Moreover, isolation and culture of such cells would raise the possibility of prolonging female fertility and restoring it following the menopause.

The reported findings are, however, controversial and much more work will be required to understand the nature of these cells and to verify the researchers' claims. (timesonline.co.uk 2009; 13 April)