Mechanical Netrin-1-DCC Coupling Mediates Netrin-1-induced Axonal Haptotaxis

The growth cone, a motile structure located at the tip of growing axon, senses extracellular guidance cues and translates them into directional forces that drive axon outgrowth and guidance. Axon guidance directed by chemical cues on the extracellular adhesive substrate is termed haptotaxis. Recent studies reported that netrin-1 on the substrate functions as a haptotactic axon guidance cue. However, the mechanism mediating netrin-1-induced axonal haptotaxis remains unclear. Here, we demonstrate that substrate-bound netrin-1 induces axonal haptotaxis by facilitating physical interactions between the netrin-1 receptor, DCC, and the adhesive substrates. DCC serves as an adhesion receptor for netrin-1. The clutch molecule shootin1a interacted with DCC, linking it to actin filament retrograde flow at the growth cone. Speckle imaging analyses showed that DCC underwent either grip (stop) and retrograde slip on the adhesive substrate. The grip state was more prevalent on netrin-1-coated substrate compared to the control substrate polylysine, thereby transmitting larger traction force on the netrin-1-coated substrate. Furthermore, disruption of the linkage between actin flow and DCC by shootin1 knockout impaired netrin-1-induced axonal haptotaxis. These findings indicate that the directional force for netrin-1-induced haptotaxis is exerted on the substrates through the mechanical coupling between netrin-1 and DCC which occurs asymmetrically under the growth cone.