Figure 12.

Behavior of microtubules during the different phases of the activity of the growth cone. (A) During the advance of the growth cone, dynein generates traction forces that allow microtubules to overcome retrograde flow and to invade the peripheral domain and filopodia. The cut-out of the labile portion of the microtubules (dark blue) regulates the length of that portion, while cutting the stable portion of microtubules (light blue) creates short and more motile ones. (B) When the growth cone pauses, the progress of microtubules results in a non-compartmentalized growth cone in central and peripheral domains, which is dominated by a bundle of curved microtubules. (C) When the axon restarts the growth, microtubules disperse rapidly and increase their cutting rate, causing shorter microtubules to be thrown away from the beam. (D) When the growth cone needs to turn, the forces generated by the motor proteins kinesin-5 and kinesin-12 become polarized towards the opposite side to the direction of rotation; in this way, the forces driven by dynein allow the invasion of microtubules only on the side of the growth cone that is going to turn. The small black arrows indicate the direction of the movement of short microtubules. The long red arrows indicate the retrograde flow of actin. Reprinted from: [225], with the permission of Elsevier.