Changes in the distribution of slow skeletal myosin heavy chain SM1 in developing avian muscle fibres.

The use of monoclonal antibodies against fast skeletal and slow skeletal myosin heavy chains (MHC) has shown the presence of significant amounts of slow skeletal type MHC in embryonic skeletal muscles of white leghorn chickens. The presence of this slow skeletal myosin heavy chain (SMHC) was not restricted to presumptive slow muscles only, as it was also observed in presumptive fast skeletal muscles. As was the case for embryonic MHC reactive with the antibody against fast skeletal myosin heavy chain (FMHC), the presence of SMHC could be detected at the earliest stages of myogenesis. It appeared to be present in most muscle cells during early embryonic development. The changes in its cellular distribution during subsequent embryonic and post-hatch period indicated its suppression in a certain proportion of the cells in both presumptive fast and slow skeletal muscles. Its time course of suppression, however, was much prolonged, not synchronized, and varied in fast and slow skeletal muscles during both embryonic and post-hatch development.