ABSTRACT
Differentiation of skeletal muscle cells in vivo or in tissue culture proceeds through a precisely timed sequence of morphological and biochemical changes. These include the proliferation of myoblasts, their withdrawal from the cell cycle and fusion into multinucleated myotubes, followed by increased expression of musclespecific contractile, cytoplasmic and membrane proteins, including sarcoplasmic reticulum. The final phase of differentiation from embryonic myotubes to fully developed muscle fibers, with the distinctive isoenzyme composition, sarcoplasmic reticulum content, and morphological characteristic of the adult muscle, requires innervation and cannot be reproduced in pure muscle cell cultures.
