Developmental biologists Professor Carmen Birchmeier, Dr. Elena Vasyutina, and Diana Lenhard of the Max Delbrück Center for Molecular Medicine (MDC) Berlin-Buch, Germany, have now demonstrated that a molecular switch, abbreviated RBP-J, regulates this “fountain of youth”. If the switch is absent, the satellite cells generate muscle cells in an uncontrolled way, resulting in the depletion of the satellite cell reserves. As a consequence, too few muscles form during the developmental phase of a living organism and the fetus can no longer build up a reserve supply of satellite cells. The MDC scientists’ research report, which could be of significance for the future development of stem cell therapies, has just been published in the online edition of the Proceedings of the National Academy of Sciences