ScienceDaily reports on a new discovery in the biochemical regulation of stem cells: "After injury, even adult muscles can heal very well because they have a reserve supply of muscle stem cells, called satellite cells, which they can utilize for repair. Until now, it was unclear how this supply of satellite and muscle progenitor cells, out of which both muscle cells as well as satellite cells develop, keeps itself 'fresh'. ... 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." It doesn't look like the researchers have yet conclusively proven that this switch controls the age-related decline in the satellite cell population (and resulting loss of healing capacity), however. The root cause of this decline is likely an evolutionary adaptation to avoid cancer resulting from age-damaged stem cells - so even if manipulation of RBP-J can induce elderly muscles to vigor, you'd better have a good cancer therapy to hand.