Figure 2.

Geometry of the force generation. (A) Three principal forces on a single MT (green line) of length r in the cell with radius R: length-dependent force f_dyn by outward-pulling dyneins, flow- and length-dependent force f_act generated by the centripetal actin drag, and inward pushing force f_push. CS (blue) is displaced from the cell center by x. O, C, P, B, d, s, and θ are the geometric variables characterizing MT position and orientation used for force calculations in the Supplemental Material. (B) Perturbation (i): When dynein is inhibited and only actin drag and dynamic MT forces are present, centering is destabilized and the CS moves away from the center. (C) Perturbation (ii): When myosin is inhibited, the actin flow stops and only dynein and dynamic MT forces are present; the CS is stabilized at the center. (D) Perturbation (iv): When both dynein is inhibited and MTs are stabilized by Taxol, the actin flow stabilizes the CS at the center. (E) Perturbation (v): After the local application of nocodazole (modeled by eliminating MTs from the wedge of the cell), the CS shifts toward this wedge. (F) Perturbation (vi): After the local application of nocodazole and inhibition of myosin, the CS shifts away from the wedge. Green arrows, the CS is stabilized and moves toward the center; red arrows, the CS is destabilized and moves away from the center; blue arrows, pulling dynein forces; white arrows, actin–myosin drag forces; and black arrows, decentering forces associated with dynamic MTs. Dynamic MTs are shown in green, and Taxol-treated stable MTs are shown in black.