Ultrastructure of the actin cytoskeleton.

The actin cytoskeleton is the primary force-generating machinery in the cell, which can produce pushing (protrusive) forces using energy of actin polymerization and pulling (contractile) forces via sliding of bipolar filaments of myosin II along actin filaments, as well as perform other key functions. These functions are essential for whole cell migration, cell interaction with the environment, mechanical properties of the cell surface and other key aspects of cell physiology. The actin cytoskeleton is a highly complex and dynamic system of actin filaments organized into various superstructures by multiple accessory proteins. High resolution architecture of functionally distinct actin arrays provides key clues for understanding actin cytoskeleton functions. This review summarizes recent advance in our understanding of the actin cytoskeleton ultrastructure.