NEW YORK — Scientists have turned mouse skin cells into eggs that produced baby mice — a technique that, if successfully applied to humans, could someday allow women to stop worrying about the ticking of their biological clocks.
For technical as well as ethical reasons, nobody expects doctors will be making eggs from women's skin cells any time soon. But some see possibilities.
Some experts say that someday it could help millions of women who don't have working eggs of their own.
"It could mean the reproductive clock doesn't tick for women anymore," said Hank Greely, a Stanford University law professor who studies the implications of biomedical technologies.
"I think it's a pretty large advance in the next generation of reproductive technologies for women," said Amander Clark, who studies egg development at the University of California at Los Angeles.
The mice experiments were reported online Thursday in the journal Science by scientists at Kyoto University in Japan.
They began with genetically reprogrammed skin cells from female fetal mice. The reprogramming technique, discovered several years ago, makes an ordinary cell revert to a kind of blank slate, so it can be chemically prodded to develop into any kind of cell.
The Japanese researchers turned these cells into an early-stage version of eggs. Then they mixed them with mouse ovarian cells and implanted them into mice. Four weeks later they collected immature eggs, matured and fertilized them in the laboratory and placed them into surrogate mother mice. The result: three baby mice, which grew into fertile adults.
That procedure is too cumbersome to be adapted directly for human use, experts said, and study co-author Katsuhiko Hayashi said in an email that it is also too inefficient. What's more, he and others said, biological differences between mice and humans would have to be overcome.
The obstacles are so big that some experts are skeptical about ever using the approach in humans. "I don't think there's a lot of clinical potential here," said David Albertini, who has studied the development of eggs at the University of Kansas.
A human therapy is in "the quite far future," Hayashi said. Clark said it would take at least a decade.
Greely, the Stanford law professor, speculated that in 20 to 40 years, the technique might make couples more likely to go through test-tube fertilization just so they could choose characteristics of their babies. That is because donating skin cells to make eggs would be easier than going through the medical and surgical procedure of having one's own eggs harvested.
The technique raises a host of medical and ethical concerns.
The new work moves scientists closer to the possibility of tinkering with genes that would affect not only one person but also be inherited by future generations, said Dr. George Daley of the Harvard Stem Cell Institute. And basic research with such eggs could mean making and destroying human embryos in the lab, which many people oppose.
More controversy could arise over using the method for women who are infertile simply because of their age.
"Society is not clear about how it feels about older women having children," said Josephine Johnston of the Hastings Center, a bioethics research institute in Garrison, N.Y. She said there has been no sustained public discussion of "how old is too old, and what does that even mean?"