Preparation of a monoclonal antibody and expression of its antigen associated with myogenic differentiation on spontaneous and artificial myotubes derived from avian myoblasts.

Quail myoblasts transformed with a temperature-sensitive mutant of Rous sarcoma virus (ts-RSV) proliferate and do not differentiate at 35.5 degrees C, the permissive temperature for the virus, whereas their myoblast differentiation proceeds at 41.0 degrees C, a non-permissive temperature. In this experimental system, myogenic differentiation is controlled by src gene products. Using QM-RSV cells as an antigen, a monoclonal antibody, Mb-N3, was prepared. Expression of Mb-N3 antigen was found to increase during differentiation. Therefore, in studies on the mechanism of myogenic differentiation, we examined the expression of Mb-N3 antigen on spontaneously forming myotubes formed at 41.0 degrees C and fused myoblasts with hemagglutinating virus of Japan (HVJ, Sendai virus) disregarding programmed processes for myogenic differentiation. When the myoblasts cultured at 35.5 degrees C were treated with HVJ, they fused with each other. These fused myoblasts were elongated and were morphologically similar to spontaneously forming myotubes. Thus, we called fused myoblasts with HVJ "artificial myotubes." During culture at 35.5 degrees C, the artificial myotubes did not show increased expression of Mb-N3 antigen and increase of creatine kinase activity, which are markers of normal biochemical differentiation. When artificial myotubes were cultured at 41.0 degrees C, expression of Mb-N3 antigen and creatine kinase activity increased. These results suggest that the expression of the antigen is regulated by kinase activity derived from src gene products even after compulsory cell fusion. Moreover, compulsory fusion does not cause myogenic differentiation and expression of Mb-N3 antigen. Thus it seems that the differentiation program must proceed in order for myogenic differentiation and expression of Mb-N3 antigen to take place.