ID - A DOMINANT-NEGATIVE REGULATOR OF SKELETAL-MUSCLE DIFFERENTIATION- IS NOT INVOLVED IN MATURATION OR DIFFERENTIATION OF VASCULAR SMOOTH-MUSCLE CELLS

Rat aortic vascular smooth muscle cells (VSMCs) expressing the MyoD ge ne formed myotubes at a low frequency in the presence of serum but at a high frequency in the absence of serum. Expression of an antisense I d gene increased myotube formation in the presence of serum indicating that a reduction in Id levels is a major mechanism by which serum wit hdrawal promotes myotube formation, The role of Id in the development of VSMCs was investigated by expressing an antisense Id gene in neonat al VSMCs. No evidence was found for the conversion of neonatal VSMCs t o adult VSMCs in the presence of the antisense Id gene. Similarly redu ction in Id by serum withdrawal also failed to cause conversion of the neonatal VSMCs to the adult phenotype. These data suggest that the ma turation of neonatal smooth muscle cells is not controlled by a VSMC h omologue of the skeletal muscle basic-helix-loop-helix proteins.