BY MALCOLM RITTER

AP Science Writer

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 and perhaps even help couples create "designer babies."

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 and questions about its use.

Some experts say it could help millions of women who don't have working eggs of their own, whether because of a medical condition or cancer treatment, or because they are too old.

"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, Los Angeles. Discussion about policy and regulation "needs to begin now."

The mice experiments were reported online Thursday in the journal Science by scientists at Kyoto University in Japan.

In the new work, 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 e-mail that it is also too inefficient.