Fig. 3. Tropomyosin is not associated with the free barbed ends of growing actin filaments at the leading edge in resting and EGF-stimulated MTLn3 cells. Cells were either unstimulated (A-E), or stimulated with EGF for 50 seconds (F-J) or 3 minutes (K-T). Cells were double-labeled for barbed ends (A,F,K,P) and tropomyosin (f9d,B,G,L; CG3, Q). Double-labeling overlays are shown (C,H,M,R; red, tropomyosin; green, barbed ends), as well as phase-contrast images (E,J,O,T). The white square in the overlay images (C,H,M,R) indicates an area that is shown at higher magnification directly below (D,I,N,S); from left to right: double labeling, barbed ends, tropomyosin. The size of the square is 7.5 µm by 7.5 µm. Bar, 10 µm. Arrows indicate regions at the leading edge with barbed ends, demonstrating the absence of tropomyosin. Arrowheads indicate regions of overlap between tropomyosin and barbed ends within stress fibers.