Egg cells derived from bone marrow in mice
Stem cells from bone marrow may serve as a source of egg cells, at least in mice, and may lead to new fertility treatments if the same proves true in people, scientists reported Thursday.
Their study, published in the journal Cell, challenges long-held scientific belief that mammals including mice and humans generate egg cells only when they are fetuses—and are born with all the eggs they will ever have.
“Here we show that adult mouse ovaries can produce hundreds of new oocytes within 24 hours,” the researchers wrote.
They also found evidence that these egg-generating stem cells also exist in human bone marrow.
“We may be ushering in a new era in the clinical management of female infertility and menopause,” said Jonathan Tilly, director of the Vincent Center for Reproductive Biology at Massachusetts General Hospital and Harvard Medical School, who led the study.
“This could lead to new treatment approaches based not on drugs but on regenerative medicine through adult stem cells,” he said in a statement.
Cancer patients whose ovaries have been destroyed by chemotherapy or radiation, or women whose ovaries have been surgically removed, might some day be helped by the finding—although this is a long way off.
Tilly also believes adult stem cells found in bone marrow might turn out to be a source of eggs for therapeutic cloning—a way to generate the more powerful and malleable embryonic stem cells that many researchers want to work with.
One limitation on human embryonic stem cell research is the need for female donors to undergo surgery to provide eggs for the process. Another is a law severely restricting federal funding of such work—which Congress has so far failed to either overturn or strengthen.
The same team of researchers had earlier been puzzled to report that female mice sterilized with chemotherapy spontaneously regenerated their ovaries and egg cells. They looked in the ovaries but could not find any evidence of oocyte stem cells - immature “master” cells that might be able to give rise to ovary tissue and oocytes.
Then they looked in the bone marrow, a rich source of adult stem cells that have matured somewhat, but not as much as fully developed tissue.
They found markers—protein signatures—of germ cells—the kind of stem cells that give rise to eggs and sperm.
“Everyone had missed finding female germline stem cells because they are not in the ovaries, where everyone would have looked for them,” Tilly said.
So they gave bone marrow transplants to some sterilized mice.
Just 24 hours later, the sterilized mice had new egg cells and follicles, which hold and nurture the eggs.
Two months later the researchers could hardly tell the sterilized mice from unsterilized mice.
They have yet to show that the mice can produce offspring with their new egg cells—but they have checked human bone marrow and found similar “markers” for germ cells.
The findings may explain the occasional report of a woman past menopause who become pregnant, Tilly said. Menopause begins when a woman’s eggs run out, precipitating hormonal changes.
Now his team is looking to see if the ovary sends a molecular signal to the bone marrow to “call” for the stem cells and if so, what it is. It might be possible to use this molecular signal to generate new egg cells.
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