Figure 1.

(a) Cell shape in a confluent monolayer sheet. (b) Dirichlet description of cells. r_i is the position of the ith cell and r_j denotes the positions of neighboring cells surrounding the ith cell. l_j is the interface between the ith cell and its neighboring cell j. (c) Passive and active forces both drive collective cell migration. F_p is the passive force, which arises from cell volume elasticity and cell-cell adhesion; this force is cell-shape-dependent. F_a is the active force, which arises from cell protrusions and contractions in the polarization direction. F_R is the random force, which describes fluctuations in the polarization direction. To see this figure in color, go online.