PAX7 and teratoma: Furthermore, Pax7−/− teratomas were characterized by lower expression of genes coding proteins necessary for proper formation of myofiber structure, i.e., Myh3, Myh7, Myh4, and Myh2. Such “immature” structure of Pax7−/− myofibers was not previously reported in studies on Pax7 role during skeletal muscle development.