RT Journal Article SR Electronic T1 Nanoscale architecture of the axon initial segment reveals an organized and robust scaffold JF bioRxiv FD Cold Spring Harbor Laboratory SP 022962 DO 10.1101/022962 A1 Christophe Leterrier A1 Jean Potier A1 Ghislaine Caillol A1 Fanny Rueda Boroni A1 Bénédicte Dargent YR 2015 UL http://biorxiv.org/content/early/2015/07/21/022962.abstract AB The Axon Initial Segment [AIS], located within the first 30 μm of the axon, has two essential roles: generating the action potential, and maintaining axonal identity. AIS assembly depends on an ankyrin G / βIV-spectrin scaffold, but its macromolecular arrangement is unknown, precluding the mechanistic understanding of its functions. We quantitatively determined the AIS nanoscale architecture using STochastic Optical Reconstruction Microscopy [STORM]. First, we directly demonstrated the existence of an AIS 190-nm periodic submembrane lattice composed of alternated actin rings and βIV-spectrin dimers. Next, we used antibodies against different domains of ankyrin G to map its 3D nanoscale positioning: multicolor STORM demonstrated that the two large isoforms of ankyrin G are radially oriented across the AIS, with a 30-nm radial extent. The robustness of the AIS nano-architecture features against cytoskeletal or pharmacological perturbations suggest their structural role in the overall stability of the compartment. This organized and robust nanoscale architecture likely underpins the AIS functions in physiological and pathological contexts.