Muscle LIM protein (MLP) is a novel positive regulator of myogenesis.
Its expression and that of its Drosophila homolog DMLP1 are enriched i
n striated muscle and coincide with myogenic differentiation. in the a
bsence of MLP, induced C2 cells express myogenin but fail to exit from
the cell cycle and to differentiate. Overexpression of MLP in C2 myob
lasts potentiates myogenic differentiation and reduces its sensitivity
to TGF beta. Like MLP, single LIM domain deletion mutants of MLP and
nonmuscle LIM-only proteins promote myogenic differentiation. In 3T3 f
ibroblasts, the same LIM proteins prevent phorbol ester-induced inhibi
tion of DNA replication. These results establish MLP as an essential p
romoter of myogenesis and suggest that LIM-only proteins act via simil
ar mechanisms to regulate aspects of cell differentiation.