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Nanoscopic compartmentalization of membrane protein motion at the axon initial segment.

ABSTRACT: The axon initial segment (AIS) is enriched in specific adaptor, cytoskeletal, and transmembrane molecules. During AIS establishment, a membrane diffusion barrier is formed between the axonal and somatodendritic domains. Recently, an axonal periodic pattern of actin, spectrin, and ankyrin forming 190-nm-spaced, ring-like structures has been discovered. However, whether this structure is related to the diffusion barrier function is unclear. Here, we performed single-particle tracking time-course experiments on hippocampal neurons during AIS development. We analyzed the mobility of lipid-anchored molecules by high-speed single-particle tracking and correlated positions of membrane molecules with the nanoscopic organization of the AIS cytoskeleton. We observe a strong reduction in mobility early in AIS development. Membrane protein motion in the AIS plasma membrane is confined to a repetitive pattern of ?190-nm-spaced segments along the AIS axis as early as day in vitro 4, and this pattern alternates with actin rings. Mathematical modeling shows that diffusion barriers between the segments significantly reduce lateral diffusion along the axon.

SUBMITTER: Albrecht D

PROVIDER: S-EPMC5057285 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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Nanoscopic compartmentalization of membrane protein motion at the axon initial segment.

Albrecht David D Winterflood Christian M CM Sadeghi Mohsen M Tschager Thomas T Noé Frank F Ewers Helge H

The Journal of cell biology 20161003 1

The axon initial segment (AIS) is enriched in specific adaptor, cytoskeletal, and transmembrane molecules. During AIS establishment, a membrane diffusion barrier is formed between the axonal and somatodendritic domains. Recently, an axonal periodic pattern of actin, spectrin, and ankyrin forming 190-nm-spaced, ring-like structures has been discovered. However, whether this structure is related to the diffusion barrier function is unclear. Here, we performed single-particle tracking time-course e ...[more]

PMID: 27697928

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Project description:Selective cargo transport into axons and dendrites over the microtubule network is essential for neuron polarization. The axon initial segment (AIS) separates the axon from the somatodendritic compartment and controls the microtubule-dependent transport into the axon. Interestingly, the AIS has a characteristic microtubule organization; it contains bundles of closely spaced microtubules with electron dense cross-bridges, referred to as microtubule fascicles. The microtubule binding protein TRIM46 localizes to the AIS and when overexpressed in non-neuronal cells forms microtubule arrays that closely resemble AIS fascicles in neurons. However, the precise role of TRIM46 in microtubule fasciculation in neurons has not been studied. Here we developed a novel correlative light and electron microscopy approach to study AIS microtubule organization. We show that in cultured rat hippocampal neurons of both sexes, TRIM46 levels steadily increase at the AIS during early neuronal differentiation and at the same time closely spaced microtubules form, whereas the fasciculated microtubules appear at later developmental stages. Moreover, we localized TRIM46 to the electron dense cross-bridges and show that depletion of TRIM46 causes loss of cross-bridges and increased microtubule spacing. These data indicate that TRIM46 has an essential role in organizing microtubule fascicles in the AIS.SIGNIFICANCE STATEMENT The axon initial segment (AIS) is a specialized region at the proximal axon where the action potential is initiated. In addition the AIS separates the axon from the somatodendritic compartment, where it controls protein transport to establish and maintain neuron polarity. Cargo vesicles destined for the axon recognize specialized microtubule tracks that enter the AIS. Interestingly the microtubules entering the AIS form crosslinked bundles, called microtubule fascicules. Recently we found that the microtubule-binding protein TRIM46 localizes to the AIS, where it may organize the AIS microtubules. In the present study we developed a novel correlative light and electron microscopy approach to study the AIS microtubules during neuron development and identified an essential role for TRIM46 in microtubule fasciculation.

Dataset Information

Nanoscopic compartmentalization of membrane protein motion at the axon initial segment.

Publications

Nanoscopic compartmentalization of membrane protein motion at the axon initial segment.

Similar Datasets

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