Described as secreting a mouse monoclonal antibody (IgG1) reacting with human and rat embryonic fibers in immunofluorescence and with human and rat embryonic myosin heavy chains (MHCs) in Western blotting; this antibody reacts more weakly also with adult rat 2B fibers in immunofluorescence and adult rat 2B MHCs in Western blotting; moreover, it stains muscle cells in the conduction tissue of newborn rat heart; this cell line was produced by fusing NSO myeloma cells with spleen cells from a BALB/c mouse immunized with purified myosin from bovine fetal muscles