Actin, Spectrin, and Associated Proteins Form a Periodic Cytoskeletal Structure in Axons

TLDR

Actin and spectrin are key neuronal proteins, yet their spatial arrangement in axons and dendrites is not well defined. The authors employed stochastic optical reconstruction microscopy to map actin, spectrin, and associated proteins in neurons. Actin forms ~180‑190 nm periodic rings around axons, with adducin colocalizing and spectrin alternating in a complementary lattice, while sodium channels align with this cytoskeletal scaffold; this periodic arrangement is absent in dendrites, which instead contain longitudinal actin filaments.

Abstract

Actin and spectrin play important roles in neurons, but their organization in axons and dendrites remains unclear. We used stochastic optical reconstruction microscopy to study the organization of actin, spectrin, and associated proteins in neurons. Actin formed ringlike structures that wrapped around the circumference of axons and were evenly spaced along axonal shafts with a periodicity of ~180 to 190 nanometers. This periodic structure was not observed in dendrites, which instead contained long actin filaments running along dendritic shafts. Adducin, an actin-capping protein, colocalized with the actin rings. Spectrin exhibited periodic structures alternating with those of actin and adducin, and the distance between adjacent actin-adducin rings was comparable to the length of a spectrin tetramer. Sodium channels in axons were distributed in a periodic pattern coordinated with the underlying actin-spectrin-based cytoskeleton.