Molecular Morphogenesis of the Z-Disc in Muscle Cells

Abstract

Perhaps one of the most fascinating visual impressions of skeletal and cardiac muscle cells is their striated appearance. It has been long suspected that in these cells there is a cytoskeleton present responsible for holding the constituent myofibrils in place. The presence of structural elements transverse to a muscle fiber’s long axis is suggested by the tendency for the Z-discs, M lines and other sarcomeric units of neighboring myofibrils to be in axial register across the fiber, thereby giving rise to the striking cross-striated appearance of the muscle cell. In addition, the ability of the membranous organelles such as mitochondria, the transverse tubular system (T system) and the sarcoplasmic reticulum (SR) to maintain an invariant topology during the contraction-relaxation cycle of muscle cells also attests to the presence of a cytoskeletal system, independent of the sarcomeric actin and myosin filaments, which is responsible for integrating these organelles with the sarcomere.