Fig. 6. Correlation between bead displacement and phase transition of cell locomotory behavior. Solid squares on the line graphs represent the bead displacement around three regions, anterior (a,d), side (b,e) and posterior (c,f) of a wild-type (a-c) and a MHC-null (d-f) cell, respectively. The method for the measurement of bead displacements was described in Materials and Methods. Zero at the y axis indicates the original position of the beads before the cells were placed on the substrate. Negative values indicate displacement toward the cell, and positive values indicate displacement away from the cell. In wild-type cells, the bead displacement around the anterior region reversed and increased to positive values during the retraction phase (a), representing a pushing force in this region. The bead displacement around the side and the posterior regions reached zero during the retraction phase (b,c), suggesting that the adhesion of the cell body to the substrate in both regions was lost. Note that the bead displacement in MHC-null cells was not reversed but enhanced throughout the extension and the retraction phases. All graphs include results of several beads (multiple plotted lines).