A tumorigenic culprit in ES cells

In the debate over whether ES cells or somatic stem cells have better prospects for stem cell therapies, ES cell proponents admit that their pluripotent cells carry an increased risk: ES cells can form teratomas. But now Kazutoshi Takahashi, Kaoru Mitsui, and Shinya Yamanaka (Nara Institute of Science and Technology, Nara, Japan) have found that a newly discovered Ras gene may be at the heart of this problem.

ERas, previously thought to be a pseudogene, was found by the group as being expressed specifically in ES cells. The other genes in this expression class are also expressed in early embryonic tissues such as the inner cell mass and epiblast, but no expression of ERas is evident in the embryo. The lack of phenotype of ERas knockout mice adds to the mystery.

Yamanaka suggests that ERas may be...