Asymmetric Clathrin-Mediated Endocytosis Drives Repulsive Growth Cone Guidance

Asymmetric Ca2+ elevations across the axonal growth cone mediate its turning responses to attractive and repulsive guidance cues. Here we show that clathrin-mediated endocytosis acts downstream of Ca2+ signals as driving machinery for growth cone turning. In dorsal root ganglion neurons, the formation of clathrin-coated pits is facilitated asymmetrically across the growth cone by a directionally applied chemorepellent, semaphorin 3A, or by Ca2+ signals that mediate repulsive guidance. In contrast, coated pit formation remains symmetric in the presence of attractive Ca2+ signals. Inhibition of clathrin-mediated endocytosis abolishes growth cone repulsion, but not attraction, induced by Ca2+ or extracellular physiological cues. Furthermore, asymmetric perturbation of the balance of endocytosis and exocytosis in the growth cone is sufficient to initiate its turning toward the side with less endocytosis or more exocytosis. With our previous finding that growth cone attraction involves asymmetric exocytosis, we propose that the balance between membrane addition and removal dictates bidirectional axon guidance.