Assembling the myofibril: coordinating contractile cable construction with calcium

Over the last half century, major theoretical and experimental advances have been made in understanding the molecular architecture (e.g., sarcomeric organization) and biophysics (e.g., excitation-contraction coupling) of striated muscle. Studies of how the contractile apparatus is assembled have a shorter history, but our understanding has deepened considerably over the last decade. This review focuses on spontaneous intracellular calcium (Ca2+) signals and their role in skeletal muscle myofibrillogenesis. In embryonic skeletal muscle, several classes of spontaneous Ca2+ signal occur both in vivo and in culture, and blocking their production prevents de novo sarcomere assembly. This review includes a brief overview of myofibrillogenesis, discussion of spontaneous Ca2+ signals produced in embryonic skeletal muscle, the Xenopus model system, the role of Ca2+ signals in regulating assembly of the three major filament systems (actin, titin, and myosin), integration of physiological and biochemical approaches to the problem, and the clinical relevance of basic research in this area. Interspersed throughout are suggestions for future directions and citations for reviews in closely related areas not covered herein.