a PREM views of axonal actin braids (magenta, arrowheads) labeled with fluorescent phalloidin and immunogold detection of the fluorophore (15 nm gold beads, pseudo-colored yellow). b PREM views of myosin S1-treated axonal actin braids (magenta, arrowheads). c Length of the actin braids measured on PREM views in unlabeled (unlab) and myosin S1-labeled (S1) axons (mean ± SEM, n = 45–76 braids from 2 to 5 independent experiments). d, e High-magnification views of individual unlabeled d and immunogold-labeled e actin braids showing Y bifurcations (asterisks). f Thickness of filaments measured on PREM views: axonal actin braids before (braid) and after (split) splitting (blue), dendritic single-actin filaments (purple) and axonal microtubules (gray) (mean ± SEM, n = 33–90 braids from 3 to 8 independent experiments). g PREM views of unroofed axons showing the mesh (yellow) connecting actin braids. h PREM views of unroofed axons immunogold-labeled (yellow) for β4-spectrin between actin braids (magenta, arrowheads). i PREM views of unroofed axons simultaneously immunogold-labeled (yellow) for α2/β2/β4-spectrin between actin braids (magenta, arrowheads). Scale bars 2 µm, 1, 0.5, 0.2 µm a–b, g–i, left to right), 0.1 µm d, e. Source data for graphs c and f are provided as a Source Data file.