Cell Crawling Driven by Spontaneous Actin Polymerization Waves

Abstract

Cell motility is a signature of life. Crawling of eukaryotic cells on solid substrates is, for example, used to feed, to evade unfavorable environments, or to heal wounds and to fight pathogens in organisms. This process is driven by the actin cytoskeleton and can occur in the absence of external cues. The crawling of some cells appears to be random on large time scales, whereas others move directionally with a high persistence. The latter is even observed for cell fragments not containing the nucleus or microtubules. How the actin cytoskeleton is orchestrated during spontaneous cell motility is largely unknown. In this context, spontaneous polymerization waves that have been observed in many cell types offer a promising concept. Here, we discuss theoretical approaches for studying cell motility driven by spontaneous actin waves. We start by reviewing experimental results. Then, we give an introduction into physical descriptions of actin dynamics and discuss possible mechanisms for wave generation. In the next step, we describe methods to theoretically study the coupling of the actin network to the cell membrane. Our analysis shows that spontaneous polymerization waves offer a unifying framework for explaining directional and erratic cell motility. We conclude by indicating possible directions of future studies.