Mouse method turns skin cells to stem cells.

Scientists have reprogrammed mouse skin cells to mimic embryonic stem cells that can morph into any type of cell in the body.

Last year, Shinya Yamanaka and his team at Kyoto University in Japan found that they could insert into skin fibroblast cells active copies of four genes earlier identified as essential to a stem cell's pluripotency--the ability to turn into any cell. But the researchers had trouble isolating the less than 0.1 percent of skin cells that became fully reprogrammed by the added genes.

Yamanaka and his colleagues now describe online and in an upcoming Nature how they also inserted a novel marker gene that singled out the completely reprogrammed stem cells. The team implanted some of those selected cells into mouse embryos, where they acted as stem cells and grew into adult mice carrying DNA from the inserted genes. Two other research groups corroborated the results.

"It's one of the most exciting findings in recent years," says Marius Wernig of the Whitehead Institute of Biomedical Research in Cambridge, Mass., coauthor of one of the corroborating studies, which also appears in Nature. "It's really hard to believe that [cells] can be reprogrammed so easily."

However, scientists haven't yet shown that human cells can be reprogrammed in a similar way, Wernig cautions. Furthermore, 20 percent of Yamanaka's mice died of cancer brought on by two of the genes.-C.B.