Growth Cone Advance is Inversely Proportional to Retrograde F-actin Flow

In a previous study, F-actin appeared to play a key role in guiding microtubules during growth cone-target interactions. Here, F-actin flow patterns were assessed to investigate the relationship among F-actin flow, microtubule/organelle protrusion, and rates of outgrowth. We first demonstrated conditions in which surface markers (beads) moved at the same rate as underlying F-actin. These beads were then positioned, using laser tweezers, to assess F-actin movements during target interactions. We found retrograde F-actin flow was attenuated specifically along the target interaction axis in direct proportion to the rate of growth cone advance. Retrograde actin flow adjacent to the interaction axis was unperturbed. Our results suggest that growth cones transduce retrograde F-actin flux into forward movement by modulating F-actin-substrate coupling efficiency.