Figure 4.

Onset of migration for an initially suspended, nonpolar cell coming into contact with a substrate. Shown here are the cytoplasm in violet, lamellipodium in green, and nucleus in yellow in three different views. Shown top to bottom are items as follows: the top view of the (x,y) plane, oblique three-dimensional rendering (z axis has the shortest length), and lateral sectional view of the (z,y) plane. (A) shows the initial symmetrical nonmotile cell with no lamellipodium; (B) shows a nonmotile cell with symmetrical lamellipodium; (C) shows that competition between incipient leading edges leads to the symmetry breaking; (D) shows that the selection of a dominant leading edge leads to persistent cell motion in the direction from the nucleus to the center of mass of the leading edge. The cell cycles intermittently between states (C and D), changing direction with each cycle. The viewpoints are as follows: (A), (B), (C), and (D) show the top view; (A′), (B′), (C′), and (D′) show the three-quarters view; (A″), (B″), (C″), and (D″) show the sagittal section. To see this figure in color, go online.