Immunocytochemical localization of desmin in human fetal skeletal muscle

The distribution of desmin filaments in the skeletal and cardiac muscles of experimental animals and cultured cells have been extensively studied. The purpose of this report is to identify the distribution of desmin filaments in vivo in human fetal skeletal muscle. Using 10nm gold-particle-labeling immunoelectron microscopy, desmin intermediate filaments were localized in skeletal muscles of 12, 20 and 29-week-old human fetuses. A number of desmin filaments were closely associated with the nascent nonstriated myofibrils. Nascent myofibrils were distributed in the subsarcolemmal space at all three developmental stages. Desmin, accompanying the nascent myofibrils, was most abundant after 12 weeks of gestation. An irregular network of desmin filaments was conspicuous in the subsarcolemmal space after 20 weeks of gestation. Desmin filaments penetrated the myofibrils and the Z-discs after 29 weeks of gestation. The developmental change in fine structural localization of desmin between 12, 20 and 29 weeks of gestation in human fetuses indicated that desmin filaments were involved in myofibril assembly in the subsarcolemmal space, and also in myofibrillogenesis in the inner space of the myofibrils.