Coordinated Movement of Vesicles and Actin Bundles during Nerve Growth Revealed by Superresolution Microscopy

Summary: The growth cone is an essential structure for nerve growth. Although its membrane and cytoskeleton are likely to interact coordinately during nerve growth, the mechanisms are unknown due to their close proximity. Here, we used superresolution microscopy to simultaneously observe vesicles and F-actin in growth cones. We identified a novel vesicular generation mechanism that is independent of clathrin and dependent on endophilin-3- and dynamin-1 and that occurs proximal to the leading edge simultaneously with fascin-1-dependent F-actin bundling. In contrast to conventional clathrin-dependent endocytosis, which occurs distal from the leading edge at the basal surfaces of growth cones, this mechanism was distinctly observed at the apical surface using 3D imaging and was involved in mediating axon growth. Reduced endophilin or fascin inhibited this endocytic mechanism. These results suggest that, at the leading edge, vesicles are coordinately generated and transported with actin bundling during nerve growth. : Nozumi et al. simultaneously observe the movements of vesicles and F-actin in growth cones using SIM superresolution microscopy to characterize their coordinated trafficking at the leading edge. They find that endophilin-mediated endocytosis is linked to fascin-dependent F-actin bundling during nerve growth, while clathrin-mediated endocytosis is not. Keywords: filopodi