Women may one day be able to delay the menopause, following a study showing that it is possible to prolong the working life of ovaries by transplanting female stem cells that develop into mature eggs.
The findings also raise the prospect of treating some forms of female infertility where the ovaries do not produce eggs. The hope is that one day stem cell transplants could replenish the supply of fresh eggs in infertile women.
Until recently the accepted dogma in reproductive biology was that all female mammals are born with a finite lifetime store of about 2 million egg-producing follicles. In humans, this number has already fallen to about 400,000 by puberty, and at the menopause too few eggs remain to permit fertility.
But four years ago US scientists showed it was possible to obtain stem cells from the ovaries of adult women and grow them into mature egg cells.
Now scientists in China have shown that it is possible to isolate stem cells from both immature and mature ovaries of mice, store the cells in the laboratory, and then transplant them back into sterile females to enable them to give birth to healthy offspring.
Research by Professor Ji Wu and colleagues at the Shanghai Jiao Tong University, published in the journal Nature Cell Biology, overturned the accepted wisdom by finding that it is possible to separate special cells in mice ovaries that seem to function as stem cells for the female germ-line cells – the eggs.
These female germ-line stem cells have the potential to divide indefinitely, so under correct experimental circumstances they can be grown in large numbers in the laboratory, stored for months or years and transplanted.
The scientists isolated female germ-line stem cells of newborn mice and adult females. They cultured them for up to 15 months and six months respectively before transplanting them into the ovaries of sterile mice, which gave birth to healthy offspring.
Professor Azim Surani, of the Gurdon Institute at Cambridge University, said the results of the study have important implications for women who do not produce mature eggs. "Sperm are produced continuously in men but the number of eggs in women is fixed at birth," he said. "This study ... suggests there are also stem cells present in ovaries that can be cultured in a dish, which can develop into viable eggs."
It might be possible to isolate these stem cells from a woman earlier in life so that she could have children later.
Professor Robin Lovell-Badge, of the Medical Research Council's National Institute for Medical Research, said that if the results are confirmed, "it could provide a means to restore fertility to women who have few eggs or who have had to undergo cancer treatments, by isolating these cells, expanding their numbers ... and keeping them frozen until needed for IVF".
But he added the study in Nature Cell Biology has failed to answer important questions. "Extraordinary claims require extraordinary evidence ... to me this is a very incomplete piece of work..." he said. "This [study] will stimulate lots of activity in the scientific community. But what would be unfortunate is if this is hyped as a cure for female infertility."