Fig. 7. Traction stresses under retracting pseudopodia mediated by myosin II. (A) Simultaneous recording of GFP-myosin-II fluorescence and traction stresses using a combination of TIRF and force microscopy: the dynamics of myosin II filaments (upper images) and traction stresses (lower images) under a pseudopod of a migrating myosin-II-null cell are shown. The stress map was made from three migrating cells randomly selected from nine cells. The time elapsed is indicated in each GFP-myosin-II image. Myosin II filaments begin to accumulate in the pseudopod during elongation (0-40 seconds), followed by increased traction stress in the silicone substratum just under the pseudopod (40-80 seconds). Retraction began at the same time as the beginning of the increase in traction stress (40 seconds). Bar, 1 µm. (B) Time-courses of pseudopod area (blue) and fluorescence intensity of GFP-myosin-II (red). (C) Time-courses of fluorescence intensity of GFP-myosin-II (red) and average traction stress in the pseudopod (blue). The increase in pseudopod area was followed by accumulation of myosin II (B). Traction stress in the pseudopod subsequently reached a maximum during retraction (C).