Fig. 4. Cyclic behavior of cells corresponds with specific patterns of bead movement. (a) A representative time course of the gained area of a migrating wild-type cell. Two successive contours of a cell were superimposed, and the gained area was calculated by subtraction of the retraction area from the extension area. Note that extension and retraction phases alternated. The average time of a cycle was 70.4±28.3 seconds (n=22). Two patterns of bead movement (pattern 1, circled number 1; pattern 2, circled number 2) were well correlated with the extension and the retraction phases, respectively. The vertical lines are drawn on the basis of the transition points of the two patterns. (b) The displacement of the anterior (squares) and posterior (triangles) edges of the cell was plotted over time. The definition of the anterior and the posterior edges is described in Materials and Methods. When the speed of the advance of the posterior edge reached its maximum value, the bead movement switched from pattern 1 to pattern 2 (arrows in b). Note that the anterior edge advanced significantly after the peak of the forward movement of the posterior edge (arrowheads in b).