Dynamic turnover and transport of actin filament network is essential for protrusive force generation and traction force development during cell migration. To elucidate the dynamic coupling between actin network flow and turnover. we focused on flow dynamics in the lamella of one of the simplest but elegant motility systems: crawling fragments derived from fish keratocytes. Interestingly, we show that actin network in the lamella of fragments is not stationary as earlier reported, but exhibits a flow dynamics that is strikingly similar to that reported for higher order cells, suggesting that network flow is an intrinsic property of the actin cytoskeleton that is fundamental to cell migration. We also demonstrate that whereas polymerization mediates network assembly at the front, surprisingly, network flow convergence modulates network disassembly toward the rear of the lamella, suggesting that flow and turnover are coupled during migration. These results obtained using simple motility systems are significant to the understanding of actin network dynamics in migrating cells, and they will be found useful for developing biophysical models for elucidating the fundamental mechanisms of cell migration. (C) 2009 Elsevier Inc. All rights reserved.