Effect of CRF on actin polymerization in 4T1 cells. 4T1 cells were cultured on coverglass and stimulated with CRF for 2 or 4 h. After fixation, cells were permeabilized and stained for F-actin with rhodamine-conjugated phalloidin, as described in Materials and methods. CRF treatment resulted in a more intense actin staining compared to untreated control, especially after 4 h (A). Moreover, CRF treated 4T1 cells showed more pronounced actin stress fibers compared to untreated control (indicated by the arrow). Pictures are representatives of two independent experiments.