Fig. 9. The transactivating function of MEF2 is up-regulated by electrical stimulation of the motor nerve. Gastrocnemius muscles were dissected from the hindlimbs of desMEF2-lacZ transgenic mice that were subjected to 5 days of motor nerve stimulation (see Materials and methods). Photomicrographs of muscle cross sections stained for β-galactosidase activity representing the unstimulated contralateral limb (A and C) and the stimulated limb (B and D) of a single animal are shown at two different magnifications (bar, 100 µm). Similar results were observed in each of three animals subject to this stimulation protocol.