Stem cells have been the subject of worldwide scrutiny for years, yet they remain a puzzle. Although they carry the same DNA as regular body cells, they have a uniquely flexible identity that lets them develop into a wide variety of different tissues.
A team led by Joseph Ecker of the Salk Institute for Biological Studies in California recently made significant progress in discerning how stem cells keep their options open. He compared embryonic stem cells with cells from the lung called fibroblasts by analyzing their epigenetics—chemical changes that affect how genes behave without altering their DNA code. One major difference was in methylation, the way in which chemical structures called methyl groups cling to the rungs of DNA…