Department of Biology
Department of Mathematics, CIMS
New York University
May 3, 2016
Design principles of actin treadmill: lessons from the fragment
Actin treadmill is the central driver of cell migration. Though biochemical players enabling the actin treadmill are known, its quantitative understanding is lacking. We focused on lamellipodial fragments form fish keratocytes lacking cell body but retaining the ability to migrate. The geometric simplicity and steady crawling of fragments allowed us to characterize quantitatively the spatial actin organization in motile fragments. We used fluorescent microscopy, mathematical modeling and FRAP to understand the organization of the actin turnover and treadmill. We found that more than half of actin is not part of the rapidly turning over F-actin network but is a diffusing fraction of oligomers and monomers, most of which is not available for polymerization. Scaling and perturbation theory uncovers that key turnover and transport processes occur on multiple hierarchical time scales and suggest that such organization of the actin treadmill enables diffusion to recycle actin effectively and makes cell migration steady, yet prepared for rapid focused acceleration.