Scientists have reprogrammed human skin cells to mimic the all-purpose embryonic stem cells from which the whole human body arises.

The feat, achieved by separate teams in the United States and Japan, is fueling hopes for regenerative medicine - the use of stem cells to regrow and repair tissues.

To reverse the developmental clock, four powerful genes were put in the DNA of skin cells, where they exerted control. Unlike ethically controversial methods for deriving embryonic stem cells, the new one requires no human eggs, no embryos - and no destruction of those embryos to extract the stem cells.

The method is relatively simple and faces no restrictions on federal funding, unlike research that destroys the embryos. Indeed, Wisconsin's James Thomson - leader of the breakthrough, as well as the first to isolate embryonic stem cells a decade ago - believes the political wrangling over embryonic stem cell research will soon be obsolete.

Big scientific obstacles remain to be overcome. Both the technique for inserting extra genes, and the inability to turn those genes off, pose risks of cancer.

But progress is accelerating. This month, researchers at the Whitehead Institute for Biomedical Research in Cambridge, Mass., treated sickle cell anemia in mice using skin cells that were reprogrammed into embryonic stem cells.

- Marie McCullough