Fig. 4. Tracks of spots photobleached in the plasma membrane of moving cells. Spots were photobleached on the underside of cells expressing cAR1-GFP, and tracked until they faded. They were made either in the area where a pseudopod appeared (left and middle panels), or at the posterior of the cell (right panel `posterior'). The positions of the cells at various times is shown in the diagrams below. Graphs quantify displacement of the spot centre from the starting position in parallel with the leading edge (pseudopods) or the uropod (posterior) are shown at the bottom. Ax2 cells transformed with cAR1-GFP were made aggregation-competent and induced to migrate under a thin layer of agarose to constrain movement in the z-axis. Photobleaching was for 0.16, 0.79 or 1.32 seconds, giving spots of initial diameter 2.5 µm (pseudopods) or 2.0 µm (uropod); the frame rate was 1 frame per 0.8, 0.6 or 0.5 seconds; times are given in seconds; bar, 10 µm. See Movie 8 in supplementary material.