Cytoskeletal waves in the absence of molecular motors

Waves are a ubiquitous phenomenon in the cytoskeleton of cells crawling or spreading on a substrate. In theoretical analysis, cytoskeletal waves have been attributed to the action of molecular motors that actively cross-link cytoskeletal filaments. Motivated by recent observations of cytoskeletal waves in human neutrophils, we develop a description of treadmilling filaments in the presence of nucleating proteins that are active when bound to the membrane adjacent to the substrate. If these proteins bind cooperatively to the membrane, we find traveling waves even in the absence of molecular motors. In a confined domain the system can organize into a pair of counter-rotating spirals that emit planar waves.