Mapping of traction force and velocity onto the cell surface.

<p>A) and B) DIC images of FN-beads deposited at various positions onto the surface of MEF cells. The cell surface is classified into three areas with area I referring to cellular protrusion, area II to the leading edge and area III to the cell body. A) For force measurements beads were positioned onto the cell surface and optical traps were operated with a predefined trap stiffness of 0.160 pN/nm for a time course of 5 minutes. Black arrows denote the direction and magnitude of cellular traction forces. B) For measurements of retrograde transport velocities, beads were positioned by optical traps onto the cell surface, traps were switched off after 5 seconds, and bead movements were recorded in a time lapse movie. Red arrows denote the direction and velocity of retrograde transport. C) Example trajectory of an individual bead positioned in area I (a pseudocolored overlay was added to highlight the outline of the cells and the nucleus was traced by a red line; scale bar = 10 µm). D and E) Forces and retrograde transport velocities are position-dependent and correlate with each other (N = 5).