(CBS/AP) Stem cells in young women's ovaries are capable of producing new eggs, according to a new study. The findings challenge 60 years of dogma that women are born with all the eggs they'll ever have.

PICTURES: Human eggs: 9 fascinating facts

For the study, published in the Feb. 26 issue of Nature Medicine and led by Jonathan Tilly of Massachusetts General Hospital, researchers examined healthy human ovaries donated by 20-something Japanese women who were undergoing a sex-change operation. The researchers fished out stem cells by searching for a protein found only on the surface of stem cells. The researchers then injected those stem cells into pieces of human ovary, transplanting the tissue under the skin of mice, to provide the tissue with a nourishing blood supply.

What happened? New egg cells formed within two weeks.

That's still a long way from showing they'll mature into usable, quality eggs, David Albertini, director of the University of Kansas' Center for Reproductive Sciences, cautioned.

Still, these findings could lead to better treatments for women left infertile because of disease - or simply because they're getting older.

"Our current views of ovarian aging are incomplete. There's much more to the story than simply the trickling away of a fixed pool of eggs," Tilly, who has long hunted these cells in a series of controversial studies, said.

Tilly's previous work has drawn skepticism, and independent experts urged caution about the latest findings, so the next step is to see whether other laboratories can verify the work. If the findings are confirmed, then it would take years of additional research to learn how to use the cells, Teresa Woodruff, fertility preservation chief at Northwestern University's Feinberg School of Medicine, said.

"This is experimental," Dr. Avner Hershlag, chief of the Center for Human Reproduction at North Shore-LIJ Health System in Manhasset, N.Y., told HealthDay. He said the study is "exciting" but emphasized the work is still very preliminary. "This is a beginning of perhaps something that could bring in new opportunities, but it's going to be a long time in my estimation until clinically we'll be able to actually have human eggs created from stem cells that make babies."

Still, even a leading critic said such research may help dispel some of the enduring mystery surrounding how human eggs are born and mature.

"This is going to spark renewed interest, and more than anything else it's giving us some new directions to work in," Albertini said. While he has plenty of questions about the latest work, "I'm less skeptical," he said.

Scientists have long taught that all female mammals are born with a finite supply of egg cells, called ooctyes, that runs out in middle age. Tilly, Mass General's reproductive biology director, first challenged that notion in 2004, reporting that the ovaries of adult mice harbor some egg-producing stem cells. Recently, Tilly noted, a lab in China and another in the U.S. also have reported finding those rare cells in mice.

More work is needed to tell exactly what these cells are, cautioned reproductive biologist Kyle Orwig of the University of Pittsburgh Medical Center, who has watched Tilly's work with great interest.

But if they're really competent stem cells, Orwig asked, then why would women undergo menopause? Indeed, something so rare wouldn't contribute much to a woman's natural reproductive capacity, added Northwestern's Woodruff.

Tilly argues that using stem cells to grow eggs in lab dishes might one day help preserve cancer patients' fertility. Today, Woodruff's lab and others freeze pieces of girls' ovaries before they undergo fertility-destroying chemotherapy or radiation. They're studying how to coax the immature eggs inside to mature so they could be used for in vitro fertilization years later when the girls are grown. If that eventually works, Tilly says stem cells might offer a better egg supply.

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Stem cells in ovaries may grow new eggs, study shows

Contrary to the belief that women are born with a finite number of eggs, there may in fact be a way to replenish the supply, a new study suggests.

Researchers have isolated stem cells from adult human ovaries that appear to be capable of producing eggs.

The new findings follow a number of recent studies that have suggested such stem cells exist in adult mice, and can give rise to healthy offspring in animals that have had their fertility destroyed by chemotherapy. However, these studies have been controversial, because they go against years of research suggesting otherwise, experts say.

In the new study, the researchers devised a more rigorous way to isolate these cells, and for the first time, suggested their existence in people.

If true, the findings could have  implications for women's fertility treatments. Currently, women who choose to undergo in vitro fertilization (IVF) for infertility must endure hormone injections so doctors can retrieve eggs for fertilization, said study researcher Jonathan Tilly, director of the Vincent Center for Reproductive Biology at Massachusetts General Hospital. But if researchers could isolate egg-producing stem cells from ovaries, it might be possible to conduct that whole process outside the body, Tilly said.

"That whole program of IVF… becomes a non-necessity," Tilly said.

The study is published online today (Feb. 26) in the journal Nature Medicine.

Egg stem cells

In the new study, Tilly and colleagues isolated egg-producing stem cells from human ovary tissue by targeting a protein found on the surface of only these cells. In dishes, the cells grew into cells that had properties of human eggs. For instance, they had half the genetic material of other cells in the body.

Next, to show the stem cells could produce eggs, the researchers placed a gene into the stem cells that made them glow green, placed the stem cells into human ovarian tissue (taken during a biopsy), and grafted this tissue into mice. One to two weeks later, this tissue contained egg cells glowing green, showing they had formed from the stem cells, the researchers said.

The researchers don't yet know if these egg cells could be fertilized to produce children. The United States does not allow human eggs to be fertilized for research purposes. The researchers also don't know whether these egg-producing stem cells are active throughout a woman's life, or only when they receive a particular signal, Tilly said, although the researchers have a follow-up study planned to address this question.

The number of egg-producing stem cells appear to be quite minute. In mice, they make up about 0.014 percent of all cells in the ovary, Tilly said.

Still a controversy

"It's very novel and it's very exciting," said Dr. Sandra Carson, professor of obstetrics and gynecology, at Brown University's Women & Infants Hospital, who was not involved in the study.

"It certainly makes sense that there would be those stem cells still there," said Carson, noting men have stem cells that produce sperm throughout life.

However, other researchers say the new paper does not resolve the controversy of whether egg-producing cells exist in adult ovaries.

"I would like to see better characterization of this very small pool of cells that may be present in the ovary," said Dr. Marco Conti, professor and director of the Center for Reproductive Sciences at the University of California, San Francisco. Conti noted that some properties of the egg-producing cells described in this study do not match descriptions from previous studies.

And the paper still does not address whether these cells have any role in adult humans.

"There is no real functional evidence that this pool of cells indeed contributes to [egg formation] in the adult," Conti said.

But if these cells do in fact work in the way the researchers suspect, it might be possible to grow and mature them in an environment that resembles an ovary, Carson said.

In addition, unlike human eggs, these stem cells can be frozen without damage, Tilly said, so it may be possible to store them for future use.

Tilly is a co-founder of OvaScience, Inc, which has licensed the commercial potential of these findings for development of new fertility-enhancing procedures.

Pass it on:  Women's ovaries may contain stem cells that are capable of producing eggs after birth.

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Read more from the original source:
Stem Cells in Women's Ovaries May Produce New Eggs, Study Finds

Contrary to the belief that women are born with a finite number of eggs, there may in fact be a way to replenish the supply, a new study suggests.

Researchers have isolated stem cells from adult human ovaries that appear to be capable of producing eggs.

ANALYSIS: Old Genes Making Hulking Ants

The new findings follow a number of recent studies that have suggested such stem cells exist in adult mice, and can give rise to healthy offspring in animals that have had their fertility destroyed by chemotherapy. However, these studies have been controversial, because they go against years of research suggesting otherwise, experts say.

In the new study, the researchers devised a more rigorous way to isolate these cells, and for the first time, suggested their existence in people.

If true, the findings could have implications for women's fertility treatments. Currently, women who choose to undergo in vitro fertilization (IVF) for infertility must endure hormone injections so doctors can retrieve eggs for fertilization, said study researcher Jonathan Tilly, director of the Vincent Center for Reproductive Biology at Massachusetts General Hospital. But if researchers could isolate egg-producing stem cells from ovaries, it might be possible to conduct that whole process outside the body, Tilly said.

"That whole program of IVF… becomes a non-necessity," Tilly said.

The study is published online Feb. 26 in the journal Nature Medicine.

Egg Stem Cells

In the new study, Tilly and colleagues isolated egg-producing stem cells from human ovary tissue by targeting a protein found on the surface of only these cells. In dishes, the cells grew into cells that had properties of human eggs. For instance, they had half the genetic material of other cells in the body.

Next, to show the stem cells could produce eggs, the researchers placed a gene into the stem cells that made them glow green, placed the stem cells into human ovarian tissue (taken during a biopsy), and grafted this tissue into mice. One to two weeks later, this tissue contained egg cells glowing green, showing they had formed from the stem cells, the researchers said.

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The researchers don't yet know if these egg cells could be fertilized to produce children. The United States does not allow human eggs to be fertilized for research purposes. The researchers also don't know whether these egg-producing stem cells are active throughout a woman's life, or only when they receive a particular signal, Tilly said, although the researchers have a follow-up study planned to address this question.

The number of egg-producing stem cells appear to be quite minute. In mice, they make up about 0.014 percent of all cells in the ovary, Tilly said.

Still a Controversy

"It's very novel and it's very exciting," said Dr. Sandra Carson, professor of obstetrics and gynecology, at Brown University's Women & Infants Hospital, who was not involved in the study.

"It certainly makes sense that there would be those stem cells still there," said Carson, noting men have stem cells that produce sperm throughout life.

However, other researchers say the new paper does not resolve the controversy of whether egg-producing cells exist in adult ovaries.

"I would like to see better characterization of this very small pool of cells that may be present in the ovary," said Dr. Marco Conti, professor and director of the Center for Reproductive Sciences at the University of California, San Francisco. Conti noted that some properties of the egg-producing cells described in this study do not match descriptions from previous studies.

And the paper still does not address whether these cells have any role in adult humans.

"There is no real functional evidence that this pool of cells indeed contributes to [egg formation] in the adult," Conti said.

But if these cells do in fact work in the way the researchers suspect, it might be possible to grow and mature them in an environment that resembles an ovary, Carson said.

In addition, unlike human eggs, these stem cells can be frozen without damage, Tilly said, so it may be possible to store them for future use.

Tilly is a co-founder of OvaScience, Inc, which has licensed the commercial potential of these findings for development of new fertility-enhancing procedures.

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