Remodeling of myofibrils: subcellular distribution of myosin heavy chain mRNA and protein.

Myofibril remodeling occurs during the normal life, in growth and development, and in the special case when isoform switching occurs. In this review we concentrate on the ultrastructural aspects of how myosin is incorporated into the A-band. Anatomic methods of study are emphasized that include isotope and immunochemical labeling as well as in situ hybridization. We conclude that the mechanism of remodeling is one of continual orderly exchange between a monomeric myosin pool and the thick filament. Myosin mRNA distribution is intermyofibrillar and nonsarcomeric, which suggests that newly translated myosin is released before diffusion and insertion in the A-band of the myofibrillar lattice.