The morphological development of chick embryo skeletal muscle grown in tissue culture as studied by electron microscopy

Abstract

The understanding of events in normal myogenesis is essential before the examination of disordered muscle development can begin. In this study observations on the development of muscle explants from chick embryo muscle grown in tissue culture have been made. The growth of muscle in vitro appears to coincide with or at least is very similar to that of myogenesis in the embryo although the rate of development is accelerated in the culture environment. Actin filaments appear to be the first component of the myofibril that is synthesized and they appear randomly oriented in the sarcoplasm until the myosin filaments are formed. The larger filaments are almost always seen in a myofibrillary pattern with ribosomes often occurring along their length. At 4 days, 2–4 electron-dense masses appeared in the middle of the I-band and later these coalesced to form the Z-band. The M-band could also be identified for the first time in cells from the 4-day cultures and as this band evolved, the A-band achieved a mature appearance. The problems imposed by attempting to interpret sequential events by studying a series of electron micrographs made it difficult to follow the formation of the sarco-tubular systems, mitochondria and other cellular organelles. In these instances supplementary information accumulated from studies reported by many investigators was utilized and integrated with our own findings.