U.S. researchers said they have cloned mice using stem cells obtained from the rodents' skin, a new technique that could help researchers sidestep the ethical debates over embryonic stem-cell use.

Stem cells have the unique ability to develop into any type of cell, and while scientists have known about adult stem cells, embryonic stem cells have always been considered more versatile.

In human medical research, embryonic stem cells are seen as a powerful tool to fight diseases and replace diseased organs, but the use of embryonic stem cells has been controversial.

What's unique about the stem cells uncovered in the skin of the mice is their potential to be cultivated into embryonic stem cells.

"This work opens the door for generating embryonic stem cells (easier than cloning mice) from adult skin stem cells," said Elaine Fuchs, co-senior author of the paper, and head of the Laboratory of Mammalian Cell Biology and Development at Rockefeller University in New York City.

"If researchers overcome the current technical hurdles of making human embryonic stem cells by nuclear cloning, it may one day be possible to generate tailor-made embryonic stem cells from a patient's skin stem cells," she said.

The researchers, from Rockefeller University and the Howard Hughes Medical Institute, published their findings in Monday's online edition of Proceedings of the National Academy of Sciences.

The key to the cloning technique is cells called keratinocyte stem cells found in hair follicles underneath the skin that are involved in both hair growth and repairing skin wounds.

Team creates mouse embryos

The researchers were able to create mouse embryos by removing the nucleus from an unfertilized egg cell and replacing it with the nucleus of the adult skin cell. These early-stage embryos, called blastocysts, were put in the wombs of adult mice.

The success rate was 5.4 per cent for skin obtained from male mice and 1.6 per cent using cells from females, suggesting that female cells undergo more complex changes. Typically, only one to two per cent of transferred mouse blastocysts result in a live birth.

While the public often hears about the success stories in cloning — Dolly the sheep, for example — the study's other senior author, Peter Mombaerts, said the practice is usually "very inefficient."

Mombaerts, head of Rockefeller University's Laboratory of Development and Neurogenetics, said the results weren't as good as with embryonic stem cells, but better than other attempts using adult stem cells. The hope, he said, is to achieve a 20 to 30 per cent success rate.

With files from the Canadian Press