Fig. 2. Cell polarization due to rearrangement of the actomyosin cytoskeleton. (A) An example of apical-basal cell polarity, such as that shown by epithelial cell layers in the intestines and skin. Myosin is concentrated at the apical side of the cell, where it might participate in assembly and disassembly of the apical junction complex (green rectangles), which tightly links cells, or in the process of apical constriction, which alters the shape of the cell and its tissue layer. (B) Diagram of cell migration and the establishment of front-to-back polarity. Extension of the lamellipodium at the front (right) of the migrating cell is due to addition of actin monomers to the branching actin network. The migrating cell attaches to and detaches from the surface via integrin clusters. Focal complexes form at the cell front and mature into focal adhesions owing to NMII contractility. Activation of NMII contributes to detachment of the rear (left) of the moving cell. Arrows indicate the direction of movement.