Pattern of polypeptide synthesis in myoblast hybrids

We have examined cell hybrids derived from L6J1 rat myoblasts and A9 mouse fibroblastic cells for expression of the myogenic phenotype. Initial results showed that hybrid cells were no longer able to form myotubes and hence showed extinction of the myogenic phenotype. We then proceeded to characterize the pattern of protein synthesis in these cells using two-dimensional gel electrophoresis. Although we did detect extinction of synthesis of a small number of myoblast polypeptides in the hybrids these did not appear to be rat myoblast specific. Instead they correlated well with polypeptides lost upon viral transformation in another rat cell line. Analysis of the ability of parental cells and hybrids to grow in soft agar confirmed that both A9 cells and hybrids were more transformed than the parental L6J1 cells. The results are consistent with the interpretation that extinction of the ability to form myotubes is due to either transformation and/or a disrupted cell organization but is unlikely to be due to specific extinction of myoblast specific polypeptides, at least at the level detectable by 2D gel electrophoresis.