No evidence for new eggs in adulthood
Progress Educational Trust22 May 2007
Hopes aroused by a controversial study suggesting that women may be able to produce new egg cells have been seemingly dashed. The 2005 paper, published in the journal Cell by researchers at Massachusetts General Hospital, fleetingly gave hope to infertile women when it suggested that egg production may be restarted in sterile mice.
This work, however, was challenged last year in a Nature paper published by Harvard researchers, who could find no evidence of egg regeneration. And now a new study, published in the latest issue of the journal Developmental Biology, further entrenches this viewpoint.
Pioneering work by Solly Zuckerman in the 1950's showed that female mammals are born with all of their eggs, a viewpoint that remained unchallenged until reproductive endocrinologist Jonathan Tilly's work on mice 2004-5. His research seemed to provide evidence for 'ovarian stem cells' present in the mouse bone marrow, which had the ability to migrate and repopulate mice ovaries rendered infertile by chemotherapeutic agents, following a transplant.
The latest research, led by University of South Florida scientists Lin Liu and David Keefe looked at gene expression profiles (which reveal gene activity) in the ovaries of 12 women aged between 28 and 53. They found no evidence of any expression pattern signatures consistent with egg cell production and subsequent ovulation.
'Despite using the most sensitive methods available, we found no evidence of any egg stem cells in human ovaries, demonstrating that Dr Tilly's findings in mice do not apply to women', Dr Keefe said. 'Dr. Tilly likely was seeing non-egg cells which resemble eggs'.
Tilly countered in the most recent issue of Cell Cycle, 'It is disappointing to see arguments against the possibility of postnatal oogenesis [new egg cell production] in mammals still being drawn using solely an 'absence of evidence' approach'.
Some hope remains though, as the cells Tilly has visualised in mice may prove to be eggs, albeit immature non dividing ones, which could prove central to some form of future treatment.
Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.