301
|
Action potential generation requires a high sodium channel density in the axon initial segment. Nat Neurosci 2008; 11:178-86. [PMID: 18204443 DOI: 10.1038/nn2040] [Citation(s) in RCA: 457] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2007] [Accepted: 12/17/2007] [Indexed: 02/08/2023]
Abstract
The axon initial segment (AIS) is a specialized region in neurons where action potentials are initiated. It is commonly assumed that this process requires a high density of voltage-gated sodium (Na(+)) channels. Paradoxically, the results of patch-clamp studies suggest that the Na(+) channel density at the AIS is similar to that at the soma and proximal dendrites. Here we provide data obtained by antibody staining, whole-cell voltage-clamp and Na(+) imaging, together with modeling, which indicate that the Na(+) channel density at the AIS of cortical pyramidal neurons is approximately 50 times that in the proximal dendrites. Anchoring of Na(+) channels to the cytoskeleton can explain this discrepancy, as disruption of the actin cytoskeleton increased the Na(+) current measured in patches from the AIS. Computational models required a high Na(+) channel density (approximately 2,500 pS microm(-2)) at the AIS to account for observations on action potential generation and backpropagation. In conclusion, action potential generation requires a high Na(+) channel density at the AIS, which is maintained by tight anchoring to the actin cytoskeleton.
Collapse
|
302
|
The axon-dendrite targeting of Kv3 (Shaw) channels is determined by a targeting motif that associates with the T1 domain and ankyrin G. J Neurosci 2008; 27:14158-70. [PMID: 18094255 DOI: 10.1523/jneurosci.3675-07.2007] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Kv3 (Shaw) channels regulate rapid spiking, transmitter release and dendritic integration of many central neurons. Crucial to functional diversity are the complex targeting patterns of channel proteins. However, the targeting mechanisms are not known. Here we report that the axon-dendrite targeting of Kv3.1 is controlled by a conditional interaction of a C-terminal axonal targeting motif (ATM) with the N-terminal T1 domain and adaptor protein ankyrin G. In cultured hippocampal neurons, although the two splice variants of Kv3.1, Kv3.1a and Kv3.1b, are differentially targeted to the somatodendritic and axonal membrane, respectively, the lysine-rich ATM is surprisingly common for both splice variants. The ATM not only directly binds to the T1 domain in a Zn2+-dependent manner, but also associates with the ankyrin-repeat domain of ankyrin G. However, the full-length channel proteins of Kv3.1b display stronger association to ankyrin G than those of Kv3.1a, suggesting that the unique splice domain at Kv3.1b C terminus influences ATM binding to T1 and ankyrin G. Because ankyrin G mainly resides at the axon initial segment, we propose that it may function as a barrier for axon-dendrite targeting of Kv3.1 channels. In support of this idea, disrupting ankyrin G function either by over-expressing a dominant-negative mutant or by siRNA knockdown decreases polarized axon-dendrite targeting of both Kv3.1a and Kv3.1b. We conclude that the conditional ATM masked by the T1 domain in Kv3.1a is exposed by the splice domain in Kv3.1b, and is subsequently recognized by ankyrin G to target Kv3.1b into the axon.
Collapse
|
303
|
Visceral afferents directly activate catecholamine neurons in the solitary tract nucleus. J Neurosci 2008; 27:13292-302. [PMID: 18045923 DOI: 10.1523/jneurosci.3502-07.2007] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Brainstem A2/C2 neurons are catecholamine (CA) neurons within the solitary tract nucleus (NTS) that influence many homeostatic functions, including cardiovascular reflexes, food intake, and stress. Because NTS is a major interface between sensory visceral afferents and the CNS, NTS CA neurons are ideally suited to coordinate complex responses by their projections to multiple brain regions. To test how NTS CA neurons process visceral afferent information carried by solitary tract (ST) afferents, we identified CA neurons using transgenic mice expressing TH-EGFP (enhanced green fluorescent protein under the control of the tyrosine hydroxylase promoter) and recorded synaptic responses to ST activation in horizontal slices. ST shocks evoked large-amplitude, short-latency, glutamatergic EPSCs (ST-EPSCs) in 90% of NTS CA neurons. Within neurons, ST-EPSCs had constant latency, rarely failed, and depressed substantially at high ST frequencies, indicating that NTS CA neurons receive direct monosynaptic connections from afferent terminals. NTS CA neurons received direct ST inputs from only one or two afferent fibers, with one-half also receiving smaller amplitude indirect inputs. Up to 90% of ST shocks evoked action potentials in NTS CA neurons. However, transmission of sensory afferent information through NTS CA neurons critically depended on the expression of an A-type potassium current (I(KA)), which when active attenuated ST-activated action potentials to a 37% success rate. The satiety peptide, cholecystokinin, presynaptically facilitated glutamate transmission in one-half of NTS CA neurons. Thus, NTS CA neurons are directly driven by visceral afferents with output being modulated by presynaptic peptide receptors and postsynaptic potassium channels.
Collapse
|
304
|
Smith AJ, Sivaprasadarao A. Investigation of K(ATP) channel endocytosis and cell surface density by Biotinylation and Western blotting. Methods Mol Biol 2008; 491:79-89. [PMID: 18998085 DOI: 10.1007/978-1-59745-526-8_6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Macroscopic ion channel currents (I) are a product of the channel open probability (P(o)), the single channel current (i) and the number of channels present on the cell surface (N) at any given time (I = P(o)iN). Endocytosis has been shown to be one of the key determinants of cell surface channel density and defects of this process have been linked to diseases relating to ion channel dysfunction. Biotinylation allows the selective labelling and isolation of surface exposed proteins which can then be identified by Western blotting.
Collapse
Affiliation(s)
- Andrew J Smith
- Institute of Membrane and Systems Biology, University of Leeds, UK
| | | |
Collapse
|
305
|
Lasiecka ZM, Yap CC, Vakulenko M, Winckler B. Chapter 7 Compartmentalizing the Neuronal Plasma Membrane. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 272:303-89. [DOI: 10.1016/s1937-6448(08)01607-9] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
|
306
|
Duffield A, Caplan MJ, Muth TR. Chapter 4 Protein Trafficking in Polarized Cells. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 270:145-79. [DOI: 10.1016/s1937-6448(08)01404-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
|
307
|
Cusdin FS, Clare JJ, Jackson AP. Trafficking and cellular distribution of voltage-gated sodium channels. Traffic 2007; 9:17-26. [PMID: 17988224 DOI: 10.1111/j.1600-0854.2007.00673.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Electrical excitability in cells such as neurons and myocytes depends not only upon the expression of voltage-gated sodium channels but also on their correct targeting within the plasma membrane. Placing sodium channels within a broader cell biological context is beginning to shed new light on a variety of important questions such as the integration of neuronal signaling. Mutations that affect sodium channel trafficking have been shown to underlie several life-threatening conditions including cardiac arrhythmias, revealing an important clinical context to these studies.
Collapse
Affiliation(s)
- Fiona S Cusdin
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | | | | |
Collapse
|
308
|
Petralia RS, Yao PJ. AP180 and CALM in the developing hippocampus: expression at the nascent synapse and localization to trafficking organelles. J Comp Neurol 2007; 504:314-27. [PMID: 17640037 DOI: 10.1002/cne.21454] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Genetic and biochemical evidence has established that clathrin assembly protein AP180 is required for the proper assembly of synaptic vesicles via clathrin-mediated endocytosis. The assembly protein CALM, the ubiquitously expressed homolog of AP180, also regulates the formation of clathrin-coated vesicles. In this study we found high expression levels of AP180 and CALM in hippocampal tissues as early as embryonic day 18, before the expression of synaptophysin. We also used immunoelectron microscopy to establish the distribution of AP180 and CALM in the developing hippocampal synapses. We found AP180 and CALM in synapses at all developmental stages and in nonsynaptic growing processes. In addition to localization on the plasma membrane and clathrin-coated vesicles that originated from the plasma membrane, we also report the presence of AP180 and CALM on other types of membrane structures. Our observations link AP180 and CALM to multiple vesicular organelles and raise the possibility that these proteins may play additional roles in developing neurons.
Collapse
Affiliation(s)
- Ronald S Petralia
- Laboratory of Neurochemistry, NIDCD/NIH, Bethesda, Maryland 20892, USA
| | | |
Collapse
|
309
|
Huang ZJ, Di Cristo G, Ango F. Development of GABA innervation in the cerebral and cerebellar cortices. Nat Rev Neurosci 2007; 8:673-86. [PMID: 17704810 DOI: 10.1038/nrn2188] [Citation(s) in RCA: 206] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In many areas of the vertebrate brain, such as the cerebral and cerebellar cortices, neural circuits rely on inhibition mediated by GABA (gamma-aminobutyric acid) to shape the spatiotemporal patterns of electrical signalling. The richness and subtlety of inhibition are achieved by diverse classes of interneurons that are endowed with distinct physiological properties. In addition, the axons of interneurons display highly characteristic and class-specific geometry and innervation patterns, and thereby distribute their output to discrete spatial domains, cell types and subcellular compartments in neural networks. The cellular and molecular mechanisms that specify and modify inhibitory innervation patterns are only just beginning to be understood.
Collapse
Affiliation(s)
- Z J Huang
- Cold Spring Harbour Laboratory, One Bungtown Road, Cold Spring Harbor, New York 11724, USA.
| | | | | |
Collapse
|
310
|
Shin M, Chetkovich DM. Activity-dependent regulation of h channel distribution in hippocampal CA1 pyramidal neurons. J Biol Chem 2007; 282:33168-80. [PMID: 17848552 PMCID: PMC2685032 DOI: 10.1074/jbc.m703736200] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The hyperpolarization-activated cation current, I(h), plays an important role in regulating intrinsic neuronal excitability in the brain. In hippocampal pyramidal neurons, I(h) is mediated by h channels comprised primarily of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel subunits, HCN1 and HCN2. Pyramidal neuron h channels within hippocampal area CA1 are remarkably enriched in distal apical dendrites, and this unique distribution pattern is critical for regulating dendritic excitability. We utilized biochemical and immunohistochemical approaches in organotypic slice cultures to explore factors that control h channel localization in dendrites. We found that distal dendritic enrichment of HCN1 is first detectable at postnatal day 13, reaching maximal enrichment by the 3rd postnatal week. Interestingly we found that an intact entorhinal cortex, which projects to distal dendrites of CA1 but not area CA3, is critical for the establishment and maintenance of distal dendritic enrichment of HCN1. Moreover blockade of excitatory neurotransmission using tetrodotoxin, 6-cyano-7-nitroquinoxaline-2,3-dione, or 2-aminophosphonovalerate redistributed HCN1 evenly throughout the dendrite without significant changes in protein expression levels. Inhibition of calcium/calmodulin-dependent protein kinase II activity, but not p38 MAPK, also redistributed HCN1 in CA1 pyramidal neurons. We conclude that activation of ionotropic glutamate receptors by excitatory temporoammonic pathway projections from the entorhinal cortex establishes and maintains the distribution pattern of HCN1 in CA1 pyramidal neuron dendrites by activating calcium/calmodulin-dependent protein kinase II-mediated downstream signals.
Collapse
Affiliation(s)
- Minyoung Shin
- Davee Department of Neurology and Clinical Neurosciences, Feinberg School of Medicine, Northwestern University Medical School, Chicago, Illinois 60611
| | - Dane M. Chetkovich
- Davee Department of Neurology and Clinical Neurosciences, Feinberg School of Medicine, Northwestern University Medical School, Chicago, Illinois 60611
- Department of Physiology, Feinberg School of Medicine, Northwestern University Medical School, Chicago, Illinois 60611
- To whom correspondence should be addressed: Davee Dept. of Neurology and Clinical Neuroscience, Northwestern University Medical School, 303 East Chicago Ave., Ward 10-201, Chicago, IL 60611-3008. Tel.: 312-503-4362; Fax: 312-503-0872; E-mail:
| |
Collapse
|
311
|
Viviani B, Gardoni F, Marinovich M. Cytokines and neuronal ion channels in health and disease. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2007; 82:247-63. [PMID: 17678965 DOI: 10.1016/s0074-7742(07)82013-7] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The biophysical properties and the spatial distribution of ion channels define the signaling characteristics of individual neurons. Function, number localization, and ratio of receptor and ion channels are dynamically modulated in response to diverse stimuli and undergo dynamic changes in both physiological and pathological conditions. Increasing evidence indicates that cytokines may specifically interact with receptor and ion channels regulating neuronal excitability, synaptic plasticity, and injury. Interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha, two proinflammatory cytokines implicated in various pathophysiological conditions of the CNS, have been particularly studied. Literature data indicate that these cytokines (1) directly and promptly modulate ion channel activity, (2) exert different (and often opposite) effects on the same channels, and (3) act on ion channels both at physiological and pathological concentrations. Consequently, cytokines are now regarded as novel neuromodulators, opening important perspectives in the current view of brain behavior.
Collapse
Affiliation(s)
- Barbara Viviani
- Laboratory of Toxicology, Department of Pharmacological Sciences, University of Milan, Italy
| | | | | |
Collapse
|
312
|
Dzhashiashvili Y, Zhang Y, Galinska J, Lam I, Grumet M, Salzer JL. Nodes of Ranvier and axon initial segments are ankyrin G-dependent domains that assemble by distinct mechanisms. ACTA ACUST UNITED AC 2007; 177:857-70. [PMID: 17548513 PMCID: PMC2064285 DOI: 10.1083/jcb.200612012] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Axon initial segments (AISs) and nodes of Ranvier are sites of action potential generation and propagation, respectively. Both domains are enriched in sodium channels complexed with adhesion molecules (neurofascin [NF] 186 and NrCAM) and cytoskeletal proteins (ankyrin G and βIV spectrin). We show that the AIS and peripheral nervous system (PNS) nodes both require ankyrin G but assemble by distinct mechanisms. The AIS is intrinsically specified; it forms independent of NF186, which is targeted to this site via intracellular interactions that require ankyrin G. In contrast, NF186 is targeted to the node, and independently cleared from the internode, by interactions of its ectodomain with myelinating Schwann cells. NF186 is critical for and initiates PNS node assembly by recruiting ankyrin G, which is required for the localization of sodium channels and the entire nodal complex. Thus, initial segments assemble from the inside out driven by the intrinsic accumulation of ankyrin G, whereas PNS nodes assemble from the outside in, specified by Schwann cells, which direct the NF186-dependent recruitment of ankyrin G.
Collapse
Affiliation(s)
- Yulia Dzhashiashvili
- Department of Cell Biology, New York University School of Medicine, New York, NY 10016, USA
| | | | | | | | | | | |
Collapse
|
313
|
Torres YP, Morera FJ, Carvacho I, Latorre R. A Marriage of Convenience: β-Subunits and Voltage-dependent K+ Channels. J Biol Chem 2007; 282:24485-9. [PMID: 17606609 DOI: 10.1074/jbc.r700022200] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The movement of ions across cell membranes is essential for a wide variety of fundamental physiological processes, including secretion, muscle contraction, and neuronal excitation. This movement is possible because of the presence in the cell membrane of a class of integral membrane proteins dubbed ion channels. Ion channels, thanks to the presence of aqueous pores in their structure, catalyze the passage of ions across the otherwise ion-impermeable lipid bilayer. Ion conduction across ion channels is highly regulated, and in the case of voltage-dependent K(+) channels, the molecular foundations of the voltage-dependent conformational changes leading to the their open (conducting) configuration have provided most of the driving force for research in ion channel biophysics since the pioneering work of Hodgkin and Huxley (Hodgkin, A. L., and Huxley, A. F. (1952) J. Physiol. 117, 500-544). The voltage-dependent K(+) channels are the prototypical voltage-gated channels and govern the resting membrane potential. They are responsible for returning the membrane potential to its resting state at the termination of each action potential in excitable membranes. The pore-forming subunits (alpha) of many voltage-dependent K(+) channels and modulatory beta-subunits exist in the membrane as one component of macromolecular complexes, able to integrate a myriad of cellular signals that regulate ion channel behavior. In this review, we have focused on the modulatory effects of beta-subunits on the voltage-dependent K(+) (Kv) channel and on the large conductance Ca(2+)- and voltage-dependent (BK(Ca)) channel.
Collapse
Affiliation(s)
- Yolima P Torres
- Department of Biophysics and Molecular Physiology, Centro de Estudios Cientificos, Valdivia 5110246, Chile
| | | | | | | |
Collapse
|
314
|
Gardoni F, Mauceri D, Marcello E, Sala C, Di Luca M, Jeromin A. SAP97 directs the localization of Kv4.2 to spines in hippocampal neurons: regulation by CaMKII. J Biol Chem 2007; 282:28691-28699. [PMID: 17635915 DOI: 10.1074/jbc.m701899200] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The pore-forming alpha-subunit Kv4.2 is a key constituent of the A-type channel and critically involved in the regulation of dendritic excitability and plasticity. Here we show that Kv4.2 is enriched in the postsynaptic density (PSD) fraction and specifically interacts with synapse-associated protein 97 (SAP97). This interaction requires an intact C terminus of Kv4.2 and occurs via the PDZ domains of SAP97. Pharmacologically induced translocation of SAP97 to spines also drives Kv4.2 to the PSD, whereas SAP97 lentivirally based RNA interference reduces Kv4.2 in the PSD. In addition, calcium/calmodulin-dependent protein kinase II (CaMKII)-dependent SAP97 phosphorylation regulates the subcellular localization of Kv4.2. These results show that SAP97-CaMKII pathway plays an important role for the trafficking of Kv4.2 to dendrites and spines.
Collapse
Affiliation(s)
- Fabrizio Gardoni
- Department of Pharmacological Sciences and Center of Excellence on Neurodegenerative Diseases, University of Milan, via Balzaretti 9, 20133 Milan, Italy
| | - Daniela Mauceri
- Department of Pharmacological Sciences and Center of Excellence on Neurodegenerative Diseases, University of Milan, via Balzaretti 9, 20133 Milan, Italy
| | - Elena Marcello
- Department of Pharmacological Sciences and Center of Excellence on Neurodegenerative Diseases, University of Milan, via Balzaretti 9, 20133 Milan, Italy
| | - Carlo Sala
- Cellular and Molecular Pharmacology Section, Institute of Neuroscience, Consiglio Nazionale Ricerche, and Department of Pharmacology, University of Milan, 20129 Milan, Italy
| | - Monica Di Luca
- Department of Pharmacological Sciences and Center of Excellence on Neurodegenerative Diseases, University of Milan, via Balzaretti 9, 20133 Milan, Italy
| | - Andreas Jeromin
- Center for Learning and Memory, University of Texas, Austin, Texas 78712.
| |
Collapse
|
315
|
Mert T. Roles of axonal voltage-dependent ion channels in damaged peripheral nerves. Eur J Pharmacol 2007; 568:25-30. [PMID: 17560568 DOI: 10.1016/j.ejphar.2007.05.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2007] [Revised: 04/30/2007] [Accepted: 05/03/2007] [Indexed: 12/19/2022]
Abstract
Ion channels are fundamental to the correct functioning of nerves. A high density of Na(v) channels at nodes of Ranvier is crucial for generating sufficient local current to initiate a self-regenerating action potential. K(v)7 (KCNQ) channels are also functional components of nodes of Ranvier and contribute to the repolarization of the action potential. Paranodes underlying the paranodal loops have no channels whereas K(v)1.1 and K(v)1.2 channels cluster at juxtaparanodes. The disruption of the normal balance of different channels causes the inappropriate nerve activity that underlies a variety of nervous system diseases. Axonal voltage-dependent channels, nodal Na(v) and juxtaparanodal K(v) channels disperse after the nerve injury and reorganize with regeneration.
Collapse
Affiliation(s)
- Tufan Mert
- University of Cukurova, Faculty of Medicine, Department of Biophysics, 01330 Balcali, Adana, Turkey.
| |
Collapse
|
316
|
Kim DY, Carey BW, Wang H, Ingano LAM, Binshtok AM, Wertz MH, Pettingell WH, He P, Lee VMY, Woolf CJ, Kovacs DM. BACE1 regulates voltage-gated sodium channels and neuronal activity. Nat Cell Biol 2007; 9:755-64. [PMID: 17576410 PMCID: PMC2747787 DOI: 10.1038/ncb1602] [Citation(s) in RCA: 244] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2007] [Accepted: 05/30/2007] [Indexed: 02/08/2023]
Abstract
BACE1 activity is significantly increased in the brains of Alzheimer's disease patients, potentially contributing to neurodegeneration. The voltage-gated sodium channel (Na(v)1) beta2-subunit (beta2), a type I membrane protein that covalently binds to Na(v)1 alpha-subunits, is a substrate for BACE1 and gamma-secretase. Here, we find that BACE1-gamma-secretase cleavages release the intracellular domain of beta2, which increases mRNA and protein levels of the pore-forming Na(v)1.1 alpha-subunit in neuroblastoma cells. Similarly, endogenous beta2 processing and Na(v)1.1 protein levels are elevated in brains of BACE1-transgenic mice and Alzheimer's disease patients with high BACE1 levels. However, Na(v)1.1 is retained inside the cells and cell surface expression of the Na(v)1 alpha-subunits and sodium current densities are markedly reduced in both neuroblastoma cells and adult hippocampal neurons from BACE1-transgenic mice. BACE1, by cleaving beta2, thus regulates Na(v)1 alpha-subunit levels and controls cell-surface sodium current densities. BACE1 inhibitors may normalize membrane excitability in Alzheimer's disease patients with elevated BACE1 activity.
Collapse
Affiliation(s)
- Doo Yeon Kim
- Neurobiology of Disease Laboratory, Genetics and Aging Research Unit, MassGeneral Institute for Neurodegenerative Disease, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
317
|
Grant SGN. Toward a molecular catalogue of synapses. ACTA ACUST UNITED AC 2007; 55:445-9. [PMID: 17572504 DOI: 10.1016/j.brainresrev.2007.05.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2006] [Revised: 04/30/2007] [Accepted: 05/07/2007] [Indexed: 11/30/2022]
Abstract
1906 was a landmark year in the history of the study of the nervous system, most notably for the first 'neuroscience' Nobel prize given to the anatomists Ramon Y Cajal and Camillo Golgi. 1906 is less well known for another event, also of great significance for neuroscience, namely the publication of Charles Sherrington's book 'The Integrative Action of the Nervous system'. It was Cajal and Golgi who debated the anatomical evidence for the synapse and it was Sherrington who laid its foundation in electrophysiological function. In tribute to these pioneers in synaptic biology, this article will address the issue of synapse diversity from the molecular point of view. In particular I will reflect upon efforts to obtain a complete molecular characterisation of the synapse and the unexpectedly high degree of molecular complexity found within it. A case will be made for developing approaches that can be used to generate a general catalogue of synapse types based on molecular markers, which should have wide application.
Collapse
Affiliation(s)
- Seth G N Grant
- Genes to Cognition Programme, The Wellcome Trust Sanger Institute, Hinxton, Cambridge, Cambridgeshire, UK.
| |
Collapse
|
318
|
Rolls MM, Satoh D, Clyne PJ, Henner AL, Uemura T, Doe CQ. Polarity and intracellular compartmentalization of Drosophila neurons. Neural Dev 2007; 2:7. [PMID: 17470283 PMCID: PMC1868948 DOI: 10.1186/1749-8104-2-7] [Citation(s) in RCA: 129] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2006] [Accepted: 04/30/2007] [Indexed: 11/16/2022] Open
Abstract
Background Proper neuronal function depends on forming three primary subcellular compartments: axons, dendrites, and soma. Each compartment has a specialized function (the axon to send information, dendrites to receive information, and the soma is where most cellular components are produced). In mammalian neurons, each primary compartment has distinctive molecular and morphological features, as well as smaller domains, such as the axon initial segment, that have more specialized functions. How neuronal subcellular compartments are established and maintained is not well understood. Genetic studies in Drosophila have provided insight into other areas of neurobiology, but it is not known whether flies are a good system in which to study neuronal polarity as a comprehensive analysis of Drosophila neuronal subcellular organization has not been performed. Results Here we use new and previously characterized markers to examine Drosophila neuronal compartments. We find that: axons and dendrites can accumulate different microtubule-binding proteins; protein synthesis machinery is concentrated in the cell body; pre- and post-synaptic sites localize to distinct regions of the neuron; and specializations similar to the initial segment are present. In addition, we track EB1-GFP dynamics and determine microtubules in axons and dendrites have opposite polarity. Conclusion We conclude that Drosophila will be a powerful system to study the establishment and maintenance of neuronal compartments.
Collapse
Affiliation(s)
- Melissa M Rolls
- Institutes of Neuroscience and Molecular Biology, Howard Hughes Medical Institute, University of Oregon, Eugene, USA
- Department of Biochemistry and Molecular Biology, Penn State, University Park, USA
| | - Daisuke Satoh
- Graduate School of Science, Kyoto University, Kyoto, Japan
| | - Peter J Clyne
- Department of Biochemistry and Biophysics, University of California, San Francisco, USA
| | - Astra L Henner
- Institutes of Neuroscience and Molecular Biology, Howard Hughes Medical Institute, University of Oregon, Eugene, USA
| | - Tadashi Uemura
- Graduate School of Biostudies, Kyoto University, Kyoto, Japan
| | - Chris Q Doe
- Institutes of Neuroscience and Molecular Biology, Howard Hughes Medical Institute, University of Oregon, Eugene, USA
| |
Collapse
|
319
|
Abstract
The regulation of ion channels involves more than just modulation of their synthesis and kinetics, as controls on their trafficking and localization are also important. Although the body of knowledge is fairly large, the entire trafficking pathway is not known for any one channel. This review summarizes current knowledge on the trafficking of potassium channels that are expressed in the heart. Our knowledge of channel assembly, trafficking through the Golgi apparatus and on to the surface is covered, as are controls on channel surface retention and endocytosis.
Collapse
Affiliation(s)
- David F Steele
- Department of Physiology, University of British Columbia, 2146 Health Sciences Mall, Vancouver, British Columbia, Canada V6T 1Z3
| | | | | |
Collapse
|
320
|
Avanzini G, Franceschetti S, Mantegazza M. Epileptogenic Channelopathies: Experimental Models of Human Pathologies. Epilepsia 2007; 48 Suppl 2:51-64. [PMID: 17571353 DOI: 10.1111/j.1528-1167.2007.01067.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The discovery of genetically determined epileptic syndromes associated with specific mutations of genes codifying for subunits of voltage or ligand-activated ion channels highlights the role of ion channels in epileptogenesis. In vitro and in vivo models of channel pathology have been used to define the functional consequence of the mutations identified in human epilepsies. The evaluation of gene-channel mutations based on molecular and physiological techniques have provided significant knowledge on the cellular mechanisms leading to inherited human epilepsies, and possibly to nongenetic human epilepsies due to "acquired" channel pathologies. We review some of the studies that have explored human epileptic disorders through experimental manipulations of these channels, highlighting some of the difficulties that have arisen using "in vitro" preparations or rodent models. These findings underscore the need for further studies to address the mechanisms involved in mutated-channel dysfunctions.
Collapse
Affiliation(s)
- Giuliano Avanzini
- Department ofNeurophysiopathology, Istituto Neurologico C. Besta, Milan, Italy.
| | | | | |
Collapse
|
321
|
Schubert V, Dotti CG. Transmitting on actin: synaptic control of dendritic architecture. J Cell Sci 2007; 120:205-12. [PMID: 17215449 DOI: 10.1242/jcs.03337] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Excitatory synaptic transmission in the central nervous system mainly takes place at dendritic spines, highly motile protrusions on the dendritic surface. Depending on the stimuli received, dendritic spines undergo rapid actin-based changes in their morphology. This plasticity appears to involve signaling through numerous proteins that control the organization of the actin cytoskeleton (actin regulators). At least in part, recruitment and activation of these depends on neurotransmitter receptors at the post-synapse, which directly link neurotransmission to changes in dendritic spine architecture. However, other, non-neurotransmitter-receptors present at dendritic spines also participate. It is likely that several receptor types can control the activity of a single actin-regulatory pathway and it is the complex integration of numerous signals that determines the overall architecture of a dendritic spine.
Collapse
Affiliation(s)
- Vanessa Schubert
- Cavalieri Ottolenghi Scientific Institute, Universita degli Studi di Torino, A.O. San Luigi Gonzaga, Regione Gonzole 10, 10043 Orbassano (Torino), Italy.
| | | |
Collapse
|
322
|
Matsuzaki M. Factors critical for the plasticity of dendritic spines and memory storage. Neurosci Res 2007; 57:1-9. [PMID: 17070951 DOI: 10.1016/j.neures.2006.09.017] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2006] [Revised: 09/16/2006] [Accepted: 09/25/2006] [Indexed: 11/17/2022]
Abstract
The structure of dendritic spines is highly plastic and responds to synaptic activity, including activity patterns that induce long-term potentiation (LTP) and depression (LTD). Induction of LTP causes enlargement of spine heads, while LTD causes spine head shrinkage. In addition, spine structure is well associated with synaptic weight and the extent of synaptic plasticity, such that structural changes of the spine may represent forms of memory storage. While the correlation between structural and functional plasticity appears to be simple, the underlying mechanisms of spine plasticity are intricate. Spine plasticity requires multiple molecular interactions, and is affected by the surrounding environment and by cellular metabolic state. Here, I synthesize the latest progress in this field by defining six determinants of spine plasticity, and discuss the role of each factor in memory storage.
Collapse
Affiliation(s)
- Masanori Matsuzaki
- Division of Biophysics, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
| |
Collapse
|
323
|
Affiliation(s)
- Bing Ye
- Departments of Physiology, Biochemistry, and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 94143
| | - Ye W. Zhang
- Departments of Physiology, Biochemistry, and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 94143
| | - Lily Yeh Jan
- Departments of Physiology, Biochemistry, and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 94143
| | - Yuh Nung Jan
- Departments of Physiology, Biochemistry, and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California 94143
| |
Collapse
|