The Quiet Stem Cells of Aging Muscles
In the barracks of an aging body, muscle stem cells behave like reservists who have taken off their uniforms but never left the base. It used to seem that their numbers dwindled with age: a roll call by ID tags showed a decline. But when scientists tagged every single cell with a permanent yellow mark for life, it turned out that the soldiers are all still there. They simply stopped answering to the old call signs.