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Last Updated: Thursday, 11 March, 2004, 13:05 GMT
Female fertility extension hope
The study could open new research into female fertility
Scientists say they may have got one of the basic rules of human biology wrong, raising hopes of new advances in fertility.

For decades, scientists thought every female was born with a set number of eggs and that those eggs ran out over time, leading to the menopause.

But tests on mice suggest that may not actually be the case. Researchers have found that female mice continue to produce eggs after they are born.

Writing in Nature, they said if the same happens in humans it could have "significant clinical implications".

Scientific dogma

The study threatens to turn one of the basic concepts of science on its head.

In 1921, scientists first proposed a "basic biological doctrine", which stated that every female is born with a set number of eggs and that they cannot produce any more during their life.

If you assume that the same process works in humans then this is a really big deal
Professor Chris Barratt,
University of Birmingham
By 1951, it had become a dogma after a paper appeared to refute all other possible theories.

Only a few species, such as the fruitfly, were believed to be exempt.

However, researchers at Harvard Medical School say scientists may have to re-think this basic rule of biology.

They treated pre-pubertal female mice with a chemical that kills egg cells. They found that they still produced viable eggs in adulthood, showing that they can generate fresh eggs to replace damaged ones.

The researchers said stem cells in the ovaries produced these replacement eggs.

They acknowledged that their findings fly in the face of what most scientists believe.

But they said: "Although this dogma has persisted for more than 50 years, the present study provides evidence that challenges the validity of this belief, which represents one of the most basic underpinnings of reproductive biology."

If the study is replicated in humans, it could open up a whole new avenue for scientists trying to find better ways to treat infertility and the menopause.

For instance, they could start looking at ways of extending the life-span of these stem cells and, therefore, female fertility.

'Important questions'

In an accompanying article, a leading expert from the United States welcomed the study.

"The finding raises many interesting and important questions," said Allan Spradling of the Carnegie Institution of Washington.

"The question on everyone's lips will be whether there are germline stem cells in the human ovary."

Chris Barratt, professor of reproductive medicine at the University of Birmingham, described the discovery as "fantastic".

"If you assume that the same process works in humans then this is a really big deal," he told BBC News Online.

"I think it is probably reasonable to assume that it might be the same. There is similar ovarian development in mice as in humans."

The findings come just days after doctors in the United States said they successfully transplanted ovarian tissue back into a 36-year-old woman.

The tissue had been removed from the woman six years previously, before she had chemotherapy for breast cancer.

Writing in The Lancet, they said the woman now had fully functional ovaries. They said the technique could one day help other women to become fertile again.

23 Sep 99  |  Medical notes
Male fertility gene found
22 May 03  |  Health

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