Mature muscle cells contain highly organized myofibrils, which consist of well aligned sarcomeres. During embryonic development, sarcomere assembly starts as randomly distributed contractile units, which gradually turn into an organized array of myofibrils. To study this process, fluorescently labeled alpha-actinin was microinjected into developing chick myotubes to label the Z-lines (where actin filaments are anchored) and their precursors. |