scholarly journals Axon Initial Segment Cytoskeleton: Architecture, Development, and Role in Neuron Polarity

2016 ◽  
Vol 2016 ◽  
pp. 1-19 ◽  
Author(s):  
Steven L. Jones ◽  
Tatyana M. Svitkina
Keyword(s):  
Actin Filaments ◽  
Initial Segment ◽  
Structural Features ◽  
Axon Initial Segment ◽  
Action Potential Firing ◽  
Potential Firing ◽  
Triangular Network ◽  
Specialized Structure ◽  
Architecture Development ◽  
Neuron Polarity

The axon initial segment (AIS) is a specialized structure in neurons that resides in between axonal and somatodendritic domains. The localization of the AIS in neurons is ideal for its two major functions: it serves as the site of action potential firing and helps to maintain neuron polarity. It has become increasingly clear that the AIS cytoskeleton is fundamental to AIS functions. In this review, we discuss current understanding of the AIS cytoskeleton with particular interest in its unique architecture and role in maintenance of neuron polarity. The AIS cytoskeleton is divided into two parts, submembrane and cytoplasmic, based on localization, function, and molecular composition. Recent studies using electron and subdiffraction fluorescence microscopy indicate that submembrane cytoskeletal components (ankyrin G,βIV-spectrin, and actin filaments) form a sophisticated network in the AIS that is conceptually similar to the polygonal/triangular network of erythrocytes, with some important differences. Components of the AIS cytoplasmic cytoskeleton (microtubules, actin filaments, and neurofilaments) reside deeper within the AIS shaft and display structural features distinct from other neuronal domains. We discuss how the AIS submembrane and cytoplasmic cytoskeletons contribute to different aspects of AIS polarity function and highlight recent advances in understanding their AIS cytoskeletal assembly and stability.

scholarly journals The Palmitoyl Acyltransferase ZDHHC14 Controls Kv1-Family Potassium Channel Clustering at the Axon Initial Segment

2020 ◽  
Author(s):  
Shaun S. Sanders ◽  
Luiselys M. Hernandez ◽  
Heun Soh ◽  
Santi Karnam ◽  
Randall S. Walikonis ◽  
...  
Keyword(s):  
Potassium Channels ◽  
Hippocampal Neurons ◽  
Initial Segment ◽  
Neuronal Excitability ◽  
Pdz Domain ◽  
Axon Initial Segment ◽  
Type I ◽  
Action Potential Firing ◽  
Potential Firing ◽  
Palmitoyl Acyltransferase

AbstractThe palmitoyl acyltransferase (PAT) ZDHHC14 is highly expressed in the hippocampus and is the only PAT predicted to bind Type I PDZ domain-containing proteins. However, ZDHHC14’s neuronal roles are unknown. Here, we identify the PDZ domain-containing Membrane-associated Guanylate Kinase (MaGUK) PSD93 as a direct ZDHHC14 interactor and substrate. PSD93, but not other MaGUKs, localizes to the Axon Initial Segment (AIS). Using lentiviral-mediated shRNA knockdown in rat hippocampal neurons, we find that ZDHHC14 controls palmitoylation and AIS clustering of PSD93 and also of Kv1 potassium channels, which directly bind PSD93. Neurodevelopmental expression of ZDHHC14 mirrors that of PSD93 and Kv1 channels and, consistent with ZDHHC14’s importance for Kv1 channel clustering, loss of ZDHHC14 decreases outward currents and increases action potential firing in hippocampal neurons. To our knowledge, these findings identify the first neuronal roles and substrates for ZDHHC14 and reveal a previously unappreciated role for palmitoylation in control of neuronal excitability.Impact StatementZDHHC14 controls palmitoylation and axon initial segment targeting of PSD93 and Kv1-family potassium channels, events that are essential for normal neuronal excitability.

scholarly journals The palmitoyl acyltransferase ZDHHC14 controls Kv1-family potassium channel clustering at the axon initial segment

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Shaun S Sanders ◽  
Luiselys M Hernandez ◽  
Heun Soh ◽  
Santi Karnam ◽  
Randall S Walikonis ◽  
...  
Keyword(s):  
Hippocampal Neurons ◽  
Initial Segment ◽  
Neuronal Excitability ◽  
Pdz Domain ◽  
Axon Initial Segment ◽  
Type I ◽  
Action Potential Firing ◽  
Outward Currents ◽  
Potential Firing ◽  
Palmitoyl Acyltransferase

The palmitoyl acyltransferase (PAT) ZDHHC14 is highly expressed in the hippocampus and is the only PAT predicted to bind Type-I PDZ domain-containing proteins. However, ZDHHC14’s neuronal roles are unknown. Here, we identify the PDZ domain-containing Membrane-associated Guanylate Kinase (MaGUK) PSD93 as a direct ZDHHC14 interactor and substrate. PSD93, but not other MaGUKs, localizes to the axon initial segment (AIS). Using lentiviral-mediated shRNA knockdown in rat hippocampal neurons, we find that ZDHHC14 controls palmitoylation and AIS clustering of PSD93 and also of Kv1 potassium channels, which directly bind PSD93. Neurodevelopmental expression of ZDHHC14 mirrors that of PSD93 and Kv1 channels and, consistent with ZDHHC14’s importance for Kv1 channel clustering, loss of ZDHHC14 decreases outward currents and increases action potential firing in hippocampal neurons. To our knowledge, these findings identify the first neuronal roles and substrates for ZDHHC14 and reveal a previously unappreciated role for palmitoylation in control of neuronal excitability.

scholarly journals Tropomyosin Tpm3.1 is required to maintain the structure and function of the axon initial segment

2019 ◽  
Author(s):  
Amr Abouelezz ◽  
Holly Stefen ◽  
Mikael Segerstråle ◽  
David Micinski ◽  
Rimante Minkeviciene ◽  
...  
Keyword(s):  
Actin Filaments ◽  
Hippocampal Neurons ◽  
Initial Segment ◽  
Actin Polymerization ◽  
Firing Frequency ◽  
Axon Initial Segment ◽  
Action Potential Initiation ◽  
Sodium Ion Channels ◽  
And Function ◽  
Filament Network

ABSTRACTThe axon initial segment (AIS) is the site of action potential initiation and serves as a vesicular filter and diffusion barrier that help maintain neuronal polarity. Recent studies have revealed details about a specialized structural complex in the AIS. While an intact actin cytoskeleton is required for AIS formation, pharmacological disruption of actin polymerization compromises the AIS vesicle filter but does not affect overall AIS structure. In this study, we found that the tropomyosin isoform Tpm3.1 decorates a population of relatively stable actin filaments in the AIS. Inhibiting Tpm3.1 in cultured hippocampal neurons led to the loss of AIS structure, the AIS vesicle filter, the clustering of sodium ion channels, and reduced firing frequency. We propose that Tpm3.1-decorated actin filaments form a stable actin filament network under the AIS membrane which provides a scaffold for membrane organization and AIS proteins.

scholarly journals Networks of Polarized Actin Filaments in the Axon Initial Segment Provide a Mechanism for Sorting Axonal and Dendritic Proteins

Cell Reports ◽  
2012 ◽  
Vol 2 (6) ◽  
pp. 1546-1553 ◽  
Author(s):  
Kaori Watanabe ◽  
Sarmad Al-Bassam ◽  
Yusuke Miyazaki ◽  
Thomas J. Wandless ◽  
Paul Webster ◽  
...  
Keyword(s):  
Actin Filaments ◽  
Initial Segment ◽  
Axon Initial Segment

scholarly journals COUP-TFI regulates diameter of the axon initial segment in the mammalian neocortex

2020 ◽  
Author(s):  
Xuanyuan Wu ◽  
Haixiang Li ◽  
Jiechang Huang ◽  
Cheng Xiao ◽  
Shuijin He
Keyword(s):  
Action Potential ◽  
Initial Segment ◽  
Neuronal Excitability ◽  
Developmental Stages ◽  
Pyramidal Cells ◽  
Axon Initial Segment ◽  
Action Potential Generation ◽  
Potential Generation ◽  
Cell Ablation ◽  
Specialized Structure

AbstractThe axon initial segment is a specialized structure that controls neuronal excitability by generating action potentials. Currently, AIS plasticity with regard to changes in length and location in response to neural activity has been extensively investigated, but how AIS diameter is regulated remains elusive. Here we report that COUP-TFI is an essential regulator of AIS diameter in both developing and adult mouse neocortex. Embryonic ablation of COUP-TFI prevented expansion of AIS diameter that occurs during postnatal development in layer II/III pyramidal cells of the mouse motor cortex, thereby leading to an impairment of action potential generation. Inactivation of COUP-TFI in adult neurons also led to reduced AIS diameter and impaired action potential generation. In contrast to different developmental stages, single-cell ablation and global ablation produced opposite effects on spontaneous network in COUP-TFI-deficient neurons. Further, mice exhibited less anxiety-like behaviors after postnatal inactivation of COUP-TFI induced by tamoxifen. Our results demonstrate that COUP-TFI is indispensable for both expansion and maintenance of AIS diameter and that a change in AIS diameter fine-tunes synaptic inputs through a metaplasticity mechanism in the adult neocortex.

scholarly journals Axon initial segment cytoskeleton comprises a multiprotein submembranous coat containing sparse actin filaments

2014 ◽  
Vol 205 (1) ◽  
pp. 67-81 ◽  
Author(s):  
Steven L. Jones ◽  
Farida Korobova ◽  
Tatyana Svitkina
Keyword(s):  
Actin Filaments ◽  
Hippocampal Neurons ◽  
Initial Segment ◽  
Neuronal Cell ◽  
Axon Initial Segment ◽  
Actin Dynamics ◽  
Neuronal Cell Adhesion Molecule ◽  
Voltage Gated Sodium Channels ◽  
Actin Structure ◽  
Action Potential Initiation

The axon initial segment (AIS) of differentiated neurons regulates action potential initiation and axon–dendritic polarity. The latter function depends on actin dynamics, but actin structure and functions at the AIS remain unclear. Using platinum replica electron microscopy (PREM), we have characterized the architecture of the AIS cytoskeleton in mature and developing hippocampal neurons. The AIS cytoskeleton assembly begins with bundling of microtubules and culminates in formation of a dense, fibrillar–globular coat over microtubule bundles. Immunogold PREM revealed that the coat contains a network of known AIS proteins, including ankyrin G, spectrin βIV, neurofascin, neuronal cell adhesion molecule, voltage-gated sodium channels, and actin filaments. Contrary to existing models, we find neither polarized actin arrays, nor dense actin meshworks in the AIS. Instead, the AIS contains two populations of sparse actin filaments: short, stable filaments and slightly longer dynamic filaments. We propose that stable actin filaments play a structural role for formation of the AIS diffusion barrier, whereas dynamic actin may promote AIS coat remodeling.

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