Sarcomere formation in dystrophic skeletal muscle.

Early aspects of in vivo sarcomere organization were studied using normal and dystrophic New Hampshire chick embryos. Brachial somites 17-22 were removed from stages 16 through 28 embryos, processed for electron microscopy, and analyzed. Comparisons of normal and dystrophic material disclosed that thick filaments appeared later in dystrophic myotomal cells. This was correlated with a similar delay in the appearance of long polyribosomes. By stage 28, normal myotomal cells contained well-defined sarcomeres, whereas dystrophic sarcomeres were frequently unorganized, with myofilaments in poor longitudinal alignment. Periodic tubules were poorly developed or lacking.