EXPRESSION OF NEUROFILAMENT PROTEINS IN PROLIFERATING C2C12 MOUSE SKELETAL-MUSCLE CELLS

Expression of neurofilament proteins, NF140K, NF68K, and NF200K, in C2 C12 mouse skeletal muscle cells was studied. Immunofluorescence and im munoblot analyses revealed that NF140K was expressed in proliferating C2C12 cells and its localization was similar to desmin, a muscle-speci fic intermediate filament protein. NF140K became undetectable in C2C12 cells as muscle cell differentiation proceeded. Reverse transcription -polymerase chain reaction (RT-PCR) and Northern blot analyses confirm ed the expression of NF140K, NF68K, and NF200K in proliferating C2C12 cells. Sequences of the RT-PCR products of NF140K and NF68K were ident ical to that of authentic mouse NF140K and NF68K respectively. The NF1 40K and NF68K mRNA were down-regulated during myogenesis in contrast t o the up-regulation of mRNA encoding troponin-T. Furthermore, subclone d C2C12 cells, which express NF140K at a higher level, exhibited retar ded myogenesis, i.e., delayed onset of myosin heavy chain synthesis an d myoblast fusion. These results suggest that neurofilament proteins m ay play an inhibitory role in commitment of muscle cell differentiatio n. The presence of neurofilament proteins in skeletal muscle cells ind icates that desmin, vimentin, and neurofilament proteins can be expres sed in a single muscle cell. (C) Academic Press, Inc.