Scientists at the Whitehead Institute in Cambridge, Mass., have developed a technique for uncovering the interactions of transcription factors. These are the agents that switch genes on or off in the cell. By figuring out these interactions on a genomewide scale, they have reconstructed the top level of the controls that govern a human embryonic stem cell.

The discovery is a starting point for addressing the next question, that of how an embryonic stem cell commits itself to a specific fate, like becoming a cell of the brain or liver or pancreas gland.