Figure 6.

(a) Transfection of SM-differentiating cells with SRF and SRFΔ5 expression vectors, empty vector, or nontransfected controls. Primary cultures of mouse lung embryonic mesenchymal cells were plated under conditions that allow cell spreading. The cells were transfected 1 hour after attachment was completed. In the experiments in which the cells were stretched, transfection and stretching were initiated concomitantly. The cells were lysed 18 hours after transfection. SRF overexpression stimulates and SRFΔ5 overexpression inhibits SM differentiation. The vector alone does not affect differentiation (compare with nontransfected control cells). (b) SRFΔ5 overexpression inhibits stretch-induced SM differentiation. Notice that, as expected, untransfected stretched cells synthesize higher levels of SRF than untransfected nonstretched ones (lane 1). These experiments were repeated four times with similar results.