Ultrastructural differentiation during embryonic Drosophila myogenesis in vitro

Summary Cultures of embryonicDrosophila melanogaster cells were examined by electron microscopy and events in myogenesis were recorded. Thick and thin myofilaments, T-tubules and sarcoplasmic reticulum all appeared at about the same time, 10.5 hr. This was about 5 hr after the final division of myoblasts and about the time that muscle cells were elongating, aligning and fusing. Sarcoplasm typical of insect muscle was detected by 18.5 hr, as were myotendonal and tendocuticular junctions. Two populations of myocytes were detected, the cytoplasm of one more electron-dense than the other. The only previous report of myofibrilogenesis in invertebrate embryos had described novel mechanisms. InDrosophila embryonic material, however, the sequence of myofibrilogenesis resembled that in post-embryonic insect or vertebrate material. Mrs. Pilar Toribio-Fiorio provided excellent technical assistance, and Patricia Minter, the secretarial expertise. This investigation was supported, in part, by NIH Grant NS9330 and the James Douglas Research Fund to Robert L. Seecof and NIH Grant No. 1 RO1 CA17223-01 to Raymond L. Teplitz.