Consider the relationship between an air traffic controller and a pilot. The pilot gets the passengers to their destination, but the air traffic controller decides when the plane can take off and when it must wait. The same relationship plays out at the cellular level in animals, including humans. A region of an animal’s genome – the controller – directs when a particular gene – the pilot – can perform its prescribed function. A new study by cell and systems biologists at the University of Toronto (U of T) investigating stem cells in mice shows, for the first time, an instance of such a relationship between the Sox2 gene which is critical for early development, and a region elsewhere on the genome that effectively regulates its activity. The discovery could mean a significant advance in the emerging field of human regenerative medicine, as the Sox2 gene is essential for maintaining embryonic stem cells that can develop into any cell type of a mature animal.