Development of Vertebrate Skeletal Muscle

An investigation of developing skeletal muscle necessitates the study of three categories; the derivation of muscle cells or fibers, myofilament synthesis and interactions, assembly of myofilaments into functional sarcomeres of striated myofibrils. With few exceptions, skeletal muscle cells are of mesodermal origin, and consist of rounded mononucleated cells which elongate and fuse with one another to become myotubes. Within the sarcoplasm, myofibrillar proteins are synthesized and grouped into interacting thick and thin filaments. Crude, non-striated myofibrils result from linear arrangements of thick and thin filaments which are horizontally aligned by the invaginating sarcotubular system. After Z-lines form, providing attachment sites for thin filaments, a typical banding pattern follows. The newly formed Z-lines pull apart, followed by the attached thin filaments, and repeating “relaxed” sarcomeres are the resulting striated myofibrillar pattern.