Unfused C2C12 mouse skeletal muscle cells express neurofilament 140K protein

Expression of neurofilament 140K protein in C2C12 mouse skeletal muscle cells was studied. Immunofluorescence and immunoblot analyses revealed that NF140K was expressed at the proliferative stage and was colocalized with the muscle-specific intermediate protein desmin. As muscle cell differentiation proceeded, the number of NF140K-positive cells decreased whereas the number of cells expressing muscle-specific marker proteins such as sarcomeric myosin heavy chain and troponin-T increased. Down-regulation of NF140K and upregulation of a myogenic regulatory gene, the myogenin gene, started simultaneously. In differentiated muscle cell cultures, unfused cells residing between myotubes remained NF140K-positive. NF140K and desmin double-positive cells were also found in a primary culture of adult mouse skeletal muscle cells. The results suggest that NF140K may be a unique marker for uncommitted myoblasts.