A Selective Filter for Cytoplasmic Transport at the Axon Initial Segment

Song, Aihong; Wang, Dong; Chen, Gang; Li, Yuju; Luo, Jianhong; Duan, Shumin; Poo, Mu‐ming

doi:10.1016/j.cell.2009.01.016

Cited by 304 publications

(410 citation statements)

References 40 publications

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“…At the molecular level, the extension of ankG (0.5-1 μm) (28) could allow ankG to link physically MT bundles (via EB proteins) and submembrane actin (via βIV-spectrin). This organization suggests a structural basis for the ankG-dependent diffusion and trafficking filter that assembles at the AIS during neuronal maturation (10). Furthermore, the connection between MTs and actin via EB protein/ankG/βIV-spectrin highlights the importance of ankG as a multifunctional scaffold that assembles and maintains the AIS structure.…”

Section: Discussionmentioning

confidence: 86%

“…However, the molecular role of ankG in the intracellular AIS organization is still unknown. The dependence of the AIS intracellular filter on ankG (10) and the disorganization of MT bundles in the AIS of Purkinje cells from ankG-deficient mice (12) suggest an unknown link between ankG and MTs in the AIS.…”

mentioning

confidence: 99%

“…The AIS maintains neuronal polarity by forming a diffusion barrier for membrane constituents at the cell surface (4,8,9) and also by dampening intracellular diffusion and vesicular transport through the AIS (10). Both phenomena depend on ankG, because depletion of ankG results in the disappearance of AIS and the acquisition of dendritic identity by the proximal axon (11,12).…”

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confidence: 99%

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End-binding proteins EB3 and EB1 link microtubules to ankyrin G in the axon initial segment

Leterrier

Vacher

Fache

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

148

152

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The axon initial segment (AIS) plays a key role in maintaining the molecular and functional polarity of the neuron. The relationship between the AIS architecture and the microtubules (MTs) supporting axonal transport is unknown. Here we provide evidence that the MT plus-end-binding (EB) proteins EB1 and EB3 have a role in the AIS in addition to their MT plus-end tracking protein behavior in other neuronal compartments. In mature neurons, EB3 is concentrated and stabilized in the AIS. We identified a direct interaction between EB3/EB1 and the AIS scaffold protein ankyrin G (ankG). In addition, EB3 and EB1 participate in AIS maintenance, and AIS disassembly through ankG knockdown leads to cell-wide up-regulation of EB3 and EB1 comets. Thus, EB3 and EB1 coordinate a molecular and functional interplay between ankG and the AIS MTs that supports the central role of ankG in the maintenance of neuronal polarity. N eurons are highly polarized cells that rely on microtubules (MTs) for maintenance of their architecture and long-range polarized trafficking (1). MTs supporting axonal transport travel through the axon initial segment (AIS), a compartment that is essential for the generation of action potentials (2) and the maintenance of neuronal polarity (3). Generation of action potentials depends on the concentration of voltage-gated sodium (Nav) and potassium channels at the AIS, which are tethered at the plasma membrane via their interaction with ankyrin G (ankG (4-7). ankG, in turn, is linked to the actin cytoskeleton via βIV-spectrin and organizes AIS formation by recruiting membrane proteins and βIV-spectrin to the nascent AIS (3).The AIS maintains neuronal polarity by forming a diffusion barrier for membrane constituents at the cell surface (4,8,9) and also by dampening intracellular diffusion and vesicular transport through the AIS (10). Both phenomena depend on ankG, because depletion of ankG results in the disappearance of AIS and the acquisition of dendritic identity by the proximal axon (11,12). However, the molecular role of ankG in the intracellular AIS organization is still unknown. The dependence of the AIS intracellular filter on ankG (10) and the disorganization of MT bundles in the AIS of Purkinje cells from ankG-deficient mice (12) suggest an unknown link between ankG and MTs in the AIS.The end-binding (EB) proteins family, composed of three members (EB1-3), has been described as plus-end-tracking proteins (+TIPs) that coordinate a network of dynamic proteins on the growing MT plus-ends (13). In neurons, EB1 has been implicated in axonal transport (14, 15), whereas EB3 has been characterized as a molecular link between MTs and the actin cytoskeleton (16, 17). We hypothesized that EB proteins could have a role in the AIS via interaction with the ankG/βIV-spectrin scaffold. We first found that EB3 is accumulated and stabilized in the AIS of mature neurons. Both EB3 and EB1 bind to ankG and participate in the maintenance of the AIS scaffold. Reciprocally, altering neuronal polarity through ankG knockdown in...

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Section: Discussionmentioning

confidence: 86%

mentioning

confidence: 99%

mentioning

confidence: 99%

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End-binding proteins EB3 and EB1 link microtubules to ankyrin G in the axon initial segment

Leterrier

Vacher

Fache

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

148

152

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“…3). Lysosomes are relatively large (50-500 nm) and are predicted to be affected by the diffusion limit of the proposed cytoplasmic "filter" (43). However, anterograde and retrograde transport rates of the lysosomal protein LAMP-1 were identical in the AIS (first 50 μm of the axon) compared with the distal axon (distal 100 μm) in dissociated hippocampal cultures (Fig.…”

Section: Resultsmentioning

confidence: 93%

Giant ankyrin-G: A critical innovation in vertebrate evolution of fast and integrated neuronal signaling

Jenkins

Kim²,

Jones

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

153

222

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Axon initial segments (AISs) and nodes of Ranvier are sites of clustering of voltage-gated sodium channels (VGSCs) in nervous systems of jawed vertebrates that facilitate fast long-distance electrical signaling. We demonstrate that proximal axonal polarity as well as assembly of the AIS and normal morphogenesis of nodes of Ranvier all require a heretofore uncharacterized alternatively spliced giant exon of ankyrin-G (AnkG). This exon has sequence similarity to I-connectin/Titin and was acquired after the first round of whole-genome duplication by the ancestral ANK2/ANK3 gene in early vertebrates before development of myelin. The giant exon resulted in a new nervous system-specific 480-kDa polypeptide combining previously known features of ANK repeats and β-spectrin-binding activity with a fibrous domain nearly 150 nm in length. We elucidate previously undescribed functions for giant AnkG, including recruitment of β4 spectrin to the AIS that likely is regulated by phosphorylation, and demonstrate that 480-kDa AnkG is a major component of the AIS membrane "undercoat' imaged by platinum replica electron microscopy. Surprisingly, giant AnkG-knockout neurons completely lacking known AIS components still retain distal axonal polarity and generate action potentials (APs), although with abnormal frequency. Giant AnkG-deficient mice live to weaning and provide a rationale for survival of humans with severe cognitive dysfunction bearing a truncating mutation in the giant exon. The giant exon of AnkG is required for assembly of the AIS and nodes of Ranvier and was a transformative innovation in evolution of the vertebrate nervous system that now is a potential target in neurodevelopmental disorders.neuropsychiatric disease | cognitive impairment disorder | axon initial segment | ankyrin-G | axonal polarity

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“…1 Axonogenesis can be regulated by many intracellular signals that involve cytoskeletal rearrangements, 2 local protein degradation, 3 as well as diffusional barriers. 4 Additionally, several extracellular neurotrophic factors and hormones have also been shown to have a role in axon guidance and synaptic formation in central neurons. 5,6 To date, the role of melatonin and its receptors in axonogenesis remains unclear.…”

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confidence: 99%

The MT2 receptor stimulates axonogenesis and enhances synaptic transmission by activating Akt signaling

Man

et al. 2014

Cell Death Differ

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The MT2 receptor is a principal type of G protein-coupled receptor that mainly mediates the effects of melatonin. Deficits of melatonin/MT2 signaling have been found in many neurological disorders, including Alzheimer's disease, the most common cause of dementia in the elderly, suggesting that preservation of the MT2 receptor may be beneficial to these neurological disorders. However, direct evidence linking the MT2 receptor to cognition-related synaptic plasticity remains to be established. Here, we report that the MT2 receptor, but not the MT1 receptor, is essential for axonogenesis both in vitro and in vivo. We find that axon formation is retarded in MT2 receptor knockout mice, MT2-shRNA electroporated brain slices or primary neurons treated with an MT2 receptor selective antagonist. Activation of the MT2 receptor promotes axonogenesis that is associated with an enhancement in excitatory synaptic transmission in central neurons. The signaling components downstream of the MT2 receptor consist of the Akt/GSK-3β/CRMP-2 cascade. The MT2 receptor C-terminal motif binds to Akt directly. Either inhibition of the MT2 receptor or disruption of MT2 receptor-Akt binding reduces axonogenesis and synaptic transmission. Our data suggest that the MT2 receptor activates Akt/GSK-3β/CRMP-2 signaling and is necessary and sufficient to mediate functional axonogenesis and synaptic formation in central neurons. Synaptic circuits are established at the sites of axon-dendritic, axon-somatic or axon-axonal contact, in which functional axonogenesis is a critical step. 1 Axonogenesis can be regulated by many intracellular signals that involve cytoskeletal rearrangements, 2 local protein degradation, 3 as well as diffusional barriers. 4 Additionally, several extracellular neurotrophic factors and hormones have also been shown to have a role in axon guidance and synaptic formation in central neurons. 5,6 To date, the role of melatonin and its receptors in axonogenesis remains unclear. Most of the biological functions of melatonin are mediated by its two receptors, MT1 and MT2 receptors, both of them belong to the G protein-coupled receptor (GPCR) subfamily and are widely expressed throughout the central nervous system (CNS). 7 Activation of the MT2 receptor in response to melatonin is critical for controlling circadian rhythms 7 and regulation of slow wave sleep. 8,9 Early studies have shown that activation of the MT2 receptor in the retina reduces the release of dopamine, while dopamine inhibits growth cone motility and neurite outgrowth during embryonic development, 10,11 suggesting the involvement of the MT2 receptor in functional axonogenesis. In mutant mice with deficient expression of the MT2 gene, the induction of long-term potentiation (LTP) of excitatory synaptic transmission is impaired, and this impairment is closely related to deficits in learning. 12 In the hippocampus, the MT2 receptor inhibits GABA A receptor-mediated current, 13 which is implicated in the synaptic transmission. In Alzheimer's disease, expression of the MT...

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A Selective Filter for Cytoplasmic Transport at the Axon Initial Segment

Cited by 304 publications

References 40 publications

End-binding proteins EB3 and EB1 link microtubules to ankyrin G in the axon initial segment

End-binding proteins EB3 and EB1 link microtubules to ankyrin G in the axon initial segment

Giant ankyrin-G: A critical innovation in vertebrate evolution of fast and integrated neuronal signaling

The MT2 receptor stimulates axonogenesis and enhances synaptic transmission by activating Akt signaling

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