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.