Feedback-Driven Assembly of the Axon Initial Segment

Neuron. 2019 Oct 23;104(2):305-321.e8. doi: 10.1016/j.neuron.2019.07.029. Epub 2019 Aug 29.


The axon initial segment (AIS) is a unique neuronal compartment that plays a crucial role in the generation of action potential and neuronal polarity. The assembly of the AIS requires membrane, scaffolding, and cytoskeletal proteins, including Ankyrin-G and TRIM46. How these components cooperate in AIS formation is currently poorly understood. Here, we show that Ankyrin-G acts as a scaffold interacting with End-Binding (EB) proteins and membrane proteins such as Neurofascin-186 to recruit TRIM46-positive microtubules to the plasma membrane. Using in vitro reconstitution and cellular assays, we demonstrate that TRIM46 forms parallel microtubule bundles and stabilizes them by acting as a rescue factor. TRIM46-labeled microtubules drive retrograde transport of Neurofascin-186 to the proximal axon, where Ankyrin-G prevents its endocytosis, resulting in stable accumulation of Neurofascin-186 at the AIS. Neurofascin-186 enrichment in turn reinforces membrane anchoring of Ankyrin-G and subsequent recruitment of TRIM46-decorated microtubules. Our study reveals feedback-based mechanisms driving AIS assembly.

Keywords: axon initial segment; axonal transport; endocytosis; microtubules.

Publication types

  • Research Support, Non-U.S. Gov't
  • Video-Audio Media

MeSH terms

  • Animals
  • Ankyrins / metabolism*
  • Axon Initial Segment / metabolism*
  • Axon Initial Segment / ultrastructure
  • Axonal Transport
  • COS Cells
  • Cell Adhesion Molecules / metabolism*
  • Cell Line, Tumor
  • Chlorocebus aethiops
  • Cytoskeleton
  • Endocytosis
  • Feedback, Physiological
  • HEK293 Cells
  • Hippocampus / cytology
  • Humans
  • Microtubule-Associated Proteins / metabolism*
  • Microtubules / metabolism*
  • Microtubules / ultrastructure
  • Nerve Growth Factors / metabolism*
  • Neurons / metabolism*
  • Neurons / ultrastructure
  • Rats
  • Tripartite Motif Proteins / metabolism


  • Ank3 protein, rat
  • Ankyrins
  • Cell Adhesion Molecules
  • Microtubule-Associated Proteins
  • Nerve Growth Factors
  • Nfasc protein, rat
  • Trim46 protein, rat
  • Tripartite Motif Proteins