AUTONOMOUS CONTROL OF EXPRESSION OF GENES FOR INSULIN-LIKE GROWTH-FACTORS DURING THE PROLIFERATION AND DIFFERENTIATION OF C2C12 MOUSE MYOBLASTS IN SERUM-FREE CULTURE

The proliferation and differentiation of skeletal muscle cells in cult ure are usually controlled by serum components, and the differentiatio n can be induced by a reduction in the serum concentration. Insulin-li ke growth factors (IGFs) play a critical role in stimulating myoblast differentiation, and the expression of their genes is controlled by se rum factors. We have found that C2Cl2 myoblasts are capable of prolife ration and differentiation even in serum-free medium that dose not con tain peptide mitogens. During these processes in serum-free medium, th e accumulation of mRNAs for IGFs in the cells was observed; and their levels increased with concomitant increases in creatine kinase activit y and myotube formation and a decrease in DNA synthesis. Thus, the pre sent results suggest that proliferation and differentiation of C2Cl2 c ells are autonomously controlled and that the increase in the expressi on of the IGFs may be independent of exogenous components.