Institute of Neurology, Queen Square, London, UK.
Monoclonal antibody 24.1D5 reacts specifically with an epitope expressed on the cell surface of mononucleate myoblasts in primary cultures of human skeletal muscle cells, but not with either multinucleate myotubes or fibroblasts. Polypeptides of 60 and 100 X 10(3) Mr were identified by immunoblotting with the McAb. Human muscle cDNAs encoding the 24.1D5 epitope were used to study further the structure and expression of 24.1D5 during skeletal muscle development. Two mRNA species of 3.0 and 2.5 kb were identified in primary cultures of human skeletal muscle and in mouse muscle cell lines. The levels of both transcripts decreased during myotube formation in vitro and were similarly decreased during myogenesis in the mouse embryo. 24.1D5 mRNAs were expressed by multipotential cells and myoblast derivatives of the mouse embryonic cell line C3H10T1/2, suggesting that 24.1D5 is expressed at an early stage during skeletal muscle development.