EXPRESSION OF V-SRC ALTERS THE EXPRESSION OF MYOGENIC REGULATORY FACTOR GENES

Inactivation of v-src in transformed chicken myoblasts induced changes in expression of the myogenic regulatory factors (MRF's), MyoD, myoge nin and Myf5. Both MyoD and Myf5 were expressed in the transformed cel ls. The inactivation of v-src by a temperature up-shift resulted in th e loss of Myf5 expression, a transient increase in MyoD, followed by a rise in myogenin mRNA levels. The increase in transcripts for the lat er muscle proteins, myosin heavy and light chains, alpha-actin and tro ponin T followed the sequence of changes in MRF expression suggesting that their induction was the result of altered MRF expression. Thus, v -src appears to operate through effects on MRF's and not directly on t he expression of the late muscle-specific proteins. When v-src was rea ctivated in mature myotubes by a temperature down-shift, the pattern o f expression was quite different, the late muscle-specific transcripts decreased before the loss of myogenin transcripts and before the rise of Myf5 transcripts.