Immunocytochemical demonstration of myosin heavy chain expression in human muscle.

Three new monoclonal antibodies are shown by immunocytochemical techniques to recognise the adult fast, slow and neonatal myosin heavy chain (MHC) isoforms in adult and fetal human muscle. In fetal muscle of 17-20 weeks of gestation, slow MHC was present only in primary myotubes. Secondary myotubes contained neonatal MHC with different levels of fast and some embryonic MHC. We confirmed the presence of tertiary myotubes in the fetal muscle (Draeger et al. (1987) J. Neurol. Sci., 81: 19-43) and show that these contained fast, neonatal and possibly some embryonic MHC. Fast MHC was therefore present in secondary and tertiary myotubes at least as early as 17 days of gestation.