| Cell motility is essential to embryogenesis, immune response, and the pathology of cancer metastasis. Many measurements have deepened our understanding of cell migration forces. Most of these forces have been measured previously in separate studies but analyzing all the forces together in one study to provide a complete picture has not been done. Using our newly established scanning force microscopy technique together with high resolution imaging and feature tracking we present complete and quantitative measurements of the cell migration forces and cytoskeletal flows within a fish keratocyte's lamellipodium. Furthermore, using various cytoskeletal drugs, we are able to show that protrusion of the leading edge is indeed predominantly driven by local actin polymerization. Moreover, we measure the retrograde and anterograde forces within the lamellum, providing the missing link to understand how forces are balanced and connected in motile cells. We find that protrusion and retrograde flow in the central lamellum are driven by actin polymerization and depolymerization forces, while retrograde flow in the lamellipodial wings depends on actin-myosin contractility. Combining our results leads to a consistent picture of keratocyte motility that unifies previously observed mechanisms and theoretical explanations which have been only observed in separate experiments. |
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