We investigated the effect of activin A on the in vitro differentiatio
n of primary myogenic cells isolated from chick embryonic breast muscl
e. As judged by the morphology of the cells and accumulation of creati
ne kinase, activin A inhibited myogenesis in a dose-dependent manner.
The inhibitory activity was reversibly suppressed by folistatin. Activ
in A also inhibited the expression of MyoD1. Our data also suggest tha
t the inhibitory activity of activin A is exerted neither on prolifera
tion of myoblasts or the growth of myotubes, but rather an early phase
of differentiation following the withdrawal from cell cycle. A compar
ison of actions of activin A and TGF-beta suggests that points of acti
on is similar.