Fig. 3.

Myoblast fusion in cultured muscle cells. (A) Myoblasts proliferate in vitro in medium containing growth factors. To induce myotube formation, growth factors are removed and the majority of myoblasts will terminally differentiate into myocytes, which migrate, adhere and fuse with one another to form small nascent myotubes with few nuclei. Subsequently, nascent myotubes fuse with myocytes and other myotubes to form large mature myotubes with many nuclei. Representative phase contrast photos of mouse muscle cells are shown for each stage. (B) Muscle cells from adult wild-type and mutant mice cultured for 40 hours in vitro and visualized by immunostaining for myosin heavy chain.