Via ScienceDaily: researchers "have turned back the clock on mature muscle tissue, coaxing it back to an earlier stem cell stage to form new muscle. Moreover, they showed in mice that the newly reprogrammed muscle stem cells could be used to help repair damaged tissue. The achievement [opens] the door to the development of new treatments to combat the degeneration of muscle associated with muscular dystrophy or aging. ... Muscle formation has been seen as a one-way trip, going from stem cells to myoblasts to muscle fiber, but we were able to get a multi-nucleated muscle fiber to reverse course and separate into individual myoblasts. For many years now, people have wanted to do this, and we accomplished that by exposing the tissue to small molecule inhibitor chemicals rather than altering the cell's genome. ... These tiny chemicals go inside the cell and change the way the cell behaves without changing its genome. The inhibitors were only used for 48 hours, enough time for the fused myofibers to split into individual cells, and then they were washed away. The cells can proceed to live and die as normal, so there is no risk of them dividing uncontrollably to become tumors. ... rather than going back to a pluripotent stage, we focused on the progenitor cell stage, in which cells are already committed to forming skeletal muscle and can both divide and grow in culture. Progenitor cells also differentiate into muscle fibers in vitro and in vivo when injected into injured leg muscle. ... To test the viability of the newly regenerated myobasts, the researchers first cultured them in the lab to show that they could grow, multiply and fuse normally into new myofibers. The researchers then injected the de-differentiated myoblasts into live mice with damaged muscles. ... After two to three weeks, we checked the muscle and saw new muscle fibers that glowed green, proving that the progenitor cells we derived from mature muscle tissue contributed to muscle repair in vivo in mice."