Immature frog eggs can rejuvenate adult human cells. Molecules in the amphibian nucleus coax mature human and mouse DNA back to an adaptable, stem-cell-like state1.

John Gurdon and his colleagues at Cambridge University, UK, hope to isolate the substances responsible and use them to reprogramme ordinary adult cells, from skin or blood, say. This would yield a limitless supply of donor-matched stem cells with which to repair tissue damaged in diseases such as Parkinson's and multiple sclerosis.