SRF and myopathy: MicroRNAs (miRNAs) are critical for SMC growth, differentiation and survival within the gastrointestinal (GI) track.9 Furthermore, several hundred miRNAs that determine cellular fate and phenotype, including SMC-specific miR-143 and miR-145, are expressed in SMCs.10 Depletion of Dicer, a RNase III that generates mature miRNAs, in mouse SMCs results in the degeneration of smooth muscle and severe myopathy within the GI tract,9 and a similar phenotype results with Srf ablation in mouse SMCs.11, 12 The cellular mechanism of SMC loss in the Srf KO mice, however, remains poorly understood.