Figure 1.

Actin networks organize in distinct architectures and modules in cells. (a) Actin organization in a U2OS cell, visualized by fluorescent actin. The actin cytoskeleton organizes into diverse superstructures in cells, including branched networks in the lamellipodium at the cell front, contractile transverse arcs in the lamella behind the lamellipodium, cross-linked and contractile meshworks in the cortex, and stress fibers stretching toward the cell rear. Scale bar represents 10 μm. Panel adapted from Reference 9. (b) Actin is a living polymer that utilizes energy from ATP-hydrolysis to assemble monomers at the barbed end and to disassemble them from the pointed end. By associating with specific binding partners, actin can assemble the diverse architectures seen in panel a.(c) Flow of information toward actin. Extracellular cues are integrated by membrane receptors to activate signaling pathways, including those that regulate the assembly of actin structures. As an example, here we show the Rho pathway that synchronizes the assembly of the actomyosin system through formin-mediated actin polymerization and myosin II–driven contractility.