Researchers have long known about the amazing ability of muscles to repair themselves after injury.  For almost as long, researchers have debated about how this regeneration occurs.  A group of papers in a recent issue of the journal Development shine a spotlight on a small population of cells sandwiched within the muscle, and find that these cells are muscle stem cells.

It’s easy to take our skeletal muscles for granted as we eat, walk, and type our way through the day.  Once we’ve injured a muscle, though, we quickly appreciate how our muscles repair themselves.  Skeletal muscles are repaired by muscle stem cells, but the identity of these stem cells has been unclear.  A recent group of papers on muscle repair describes the requirement for satellite cells in muscle repair.  Satellite cells are found sandwiched in between the muscle fibers and the basement membrane, which lines the muscle to provide structural support.  Satellite cells are identified by the presence of a protein called Pax7.  Lepper and colleagues found and genetically removed Pax7-containing satellite cells in leg muscles in mice.  This removal of satellite cells prevented injured muscles from repairing themselves.  These results show that the Pax7-containing satellite cells are, in fact, muscle stem cells.  In the images above, damaged regions of muscle in control mice (left) were able to fully repair, as seen as the presence of an important muscle component called myosin (yellow).  When satellite cells were removed from the muscle (right), the tissue was unable to repair itself, as seen as the lack of myosin. 

For a more scientifically detailed description of this image, check out my post on The Node, the community forum for and by developmental biologists.