Transfection of P311 into NIH-3T3 cells stimulates muscle-specific transcription factors. (a) RT-PCR showing mRNA for muscle-related transcription factors in cells transfected with empty vector or transfected with P311. Cells expressing P311 show higher levels of muscle transcription factors, whether related to striated or SM differentiation, except for Myf5, which was downregulated. (b) NIH 3T3 cells transiently transfected with P311 and double immunostained for P311 (immunoperoxidase, brown in the upper panel) and various myogenic transcription factors (green immunofluorescence in lower panel). Notice upregulation of muscle transcription factors in the nucleus of P311-transfected cells (white arrows). (c) Immunoprecipitation (P311) and immunoblots (others) demonstrating upregulation of muscle transcription factors by transfected P311 compared with control cells transfected with empty vector. The same membrane used for detection of SRF and reprobing for MEF2 was stained blue with Coomassie to show protein loading. Mgnin, myogenin.