17.2 Dynamics of Actin Filaments

The actin cytoskeleton is not a static, unchanging structure consisting of bundles and networks of actin filaments. Both the assembly and disassembly of microfilaments is exquisitely regulated. As a consequence, microfilaments are stable for hours in some structures, whereas in others they are highly dynamic, growing or shrinking in length over a period of seconds. These changes in the organization of actin filaments can generate forces that cause large changes in the shape of a cell or drive intracellular movements. In this section, we consider how the actin protein itself polymerizes and depolymerizes, which is responsible for the dynamic nature of filaments in cells. We will see that several actin-binding proteins make important contributions to the stability and disassembly of filaments. In the subsequent section, we turn to the mechanisms that cells use to assemble filaments and how the location of assembly is regulated by signaling pathways.