Cortical and Cytoskeletal Structural Network regulates the Three-Dimensional Traction Forces Exerted by Migrating Amoeboid Cells

Abstract

Cells exert traction forces, which are necessary to perform their migration. There is still a lack of information regarding the mechanical aspects of cell migration and in particular the quantification of the three-dimensional traction forces exerted during migration and invasion.We use a novel traction force cytometry method to measure the three-dimensional traction forces exerted by Dictyostelium cells chemotaxing over flat elastic substrates. Our measurements of the 3-D traction forces show that there are two independent mechanisms in their generation, one that relies on the cytoskeletal crosslinking and contractility, and another based on the cortical stiffness. In particular, we examine the roles that specific cortical and cytoskeletal crosslinking proteins and those liking the cell's cortex and the cytoskeletal F-actin play in the development of the spatial and temporal distribution of three-dimensional traction forces during migration. We investigate mutants with cortical integrity defects, such as cells lacking the protein cortexillin to study the cortical function. We use mutants with cytoskeletal crosslinking defects, such as cells lacking the proteins Myosin II and Abp120 to quantify the function of the cytoskeletal crosslinking. In addition we examine the proteins Myosin IA and B, regarding their role liking the cell's cortex and the cytoskeletal F-actin network.The effects on the magnitude and distribution of the tangential and perpendicular components of the traction forces to the substrate are shown to be different depending on the specific cytoskeletal and cortical mutations. Our 3-D traction measurements indicate that the vertical and horizontal traction forces are regulated by the cortical and cytoskeletal crosslinking. These two mechanisms are interconnected since the time evolution of the vertical and horizontal forces is well correlated.