201
|
Physiological activation of synaptic Rac>PAK (p-21 activated kinase) signaling is defective in a mouse model of fragile X syndrome. J Neurosci 2010; 30:10977-84. [PMID: 20720104 DOI: 10.1523/jneurosci.1077-10.2010] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The abnormal spine morphology found in fragile X syndrome (FXS) is suggestive of an error in the signaling cascades that organize the actin cytoskeleton. We report here that physiological activation of the small GTPase Rac1 and its effector p-21 activated kinase (PAK), two enzymes critically involved in actin management and functional synaptic plasticity, is impaired at hippocampal synapses in the Fmr1-knock-out (KO) mouse model of FXS. Theta burst afferent stimulation (TBS) caused a marked increase in the number of synapses associated with phosphorylated PAK in adult hippocampal slices from wild-type, but not Fmr1-KO, mice. Stimulation-induced activation of synaptic Rac1 was also absent in the mutants. The polymerization of spine actin that occurs immediately after theta stimulation appeared normal in mutant slices but the newly formed polymers did not properly stabilize, as evidenced by a prolonged vulnerability to a toxin (latrunculin) that disrupts dynamic actin filaments. Latrunculin also reversed long-term potentiation when applied at 10 min post-TBS, a time point at which the potentiation effect is resistant to interference in wild-type slices. We propose that a Rac>PAK signaling pathway needed for rapid stabilization of activity-induced actin filaments, and thus for normal spine morphology and lasting synaptic changes, is defective in FXS.
Collapse
|
202
|
Yuen GS, McEwen BS, Akama KT. LIM kinase mediates estrogen action on the actin depolymerization factor Cofilin. Brain Res 2010; 1379:44-52. [PMID: 20696146 DOI: 10.1016/j.brainres.2010.07.067] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2010] [Revised: 07/15/2010] [Accepted: 07/18/2010] [Indexed: 12/24/2022]
Abstract
The ovarian hormone estrogen increases the axospinous synapse density in the hippocampal CA1 region of young female rats but fails to do so in aged rats. This estrogen-mediated alteration of spine synapse structures suggests the coincident requirement for the structural reorganization of the underlying actin cytoskeleton network. Actin reorganization is known to require the deactivation of Cofilin, an actin depolymerization factor. Cofilin is deactivated by LIM kinase (LIMK), and LIMK activity is modulated by the phosphorylation of specific residues. We have previously demonstrated that estrogen is able to increase phosphorylated LIMK (pLIMK) immunoreactivity (IR) in the hippocampus in vivo and that this estrogen-stimulated pLIMK-IR is decreased in the aged brain. Because Cofilin phosphorylation allows for actin filament elongation and spine synapse growth, we sought to determine if estrogen acts through Cofilin and if such estrogen action requires the observed LIMK activity. Using both hippocampal neurons and the NG108-15 neuroblastoma cell line, we demonstrate here that estrogen stimulates the phosphorylation of Cofilin in vitro. Furthermore, this estrogen action on Cofilin requires LIMK. Lastly, while initiating the phosphorylation of LIMK and Cofilin, estrogen can also stimulate the formation of filopodial extensions, an early step in the formation of nascent spines, demonstrating that estrogen can alter the actin-dependent neuronal morphology. This linkage of estrogen communication to Cofilin via LIMK provides the functionality to the age-sensitive pLIMK-IR that we have observed in vivo.
Collapse
Affiliation(s)
- Genevieve S Yuen
- Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, The Rockefeller University, New York, NY 10065-6399, USA
| | | | | |
Collapse
|
203
|
Smrt RD, Zhao X. Epigenetic regulation of neuronal dendrite and dendritic spine development. FRONTIERS IN BIOLOGY 2010; 5:304-323. [PMID: 25635180 PMCID: PMC4307848 DOI: 10.1007/s11515-010-0650-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Dendrites and the dendritic spines of neurons play key roles in the connectivity of the brain and have been recognized as the locus of long-term synaptic plasticity, which is correlated with learning and memory. The development of dendrites and spines in the mammalian central nervous system is a complex process that requires specific molecular events over a period of time. It has been shown that specific molecules are needed not only at the spine's point of contact, but also at a distance, providing signals that initiate a cascade of events leading to synapse formation. The specific molecules that act to signal neuronal differentiation, dendritic morphology, and synaptogenesis are tightly regulated by genetic and epigenetic programs. It has been shown that the dendritic spine structure and distribution are altered in many diseases, including many forms of mental retardation (MR), and can also be potentiated by neuronal activities and an enriched environment. Because dendritic spine pathologies are found in many types of MR, it has been proposed that an inability to form normal spines leads to the cognitive and motor deficits that are characteristic of MR. Epigenetic mechanisms, including DNA methylation, chromatin remodeling, and the noncoding RNA-mediated process, have profound regulatory roles in mammalian gene expression. The study of epigenetics focuses on cellular effects that result in a heritable pattern of gene expression without changes to genomic encoding. Despite extensive efforts to understand the molecular regulation of dendrite and spine development, epigenetic mechanisms have only recently been considered. In this review, we will focus on epigenetic mechanisms that regulate the development and maturation of dendrites and spines. We will discuss how epigenetic alterations could result in spine abnormalities that lead to MR, such as is seen in fragile X and Rett syndromes. We will also discuss both general methodology and recent technological advances in the study of neuronal dendrites and spines.
Collapse
Affiliation(s)
- Richard D. Smrt
- Department of Neuroscience, University of New Mexico School of Medicine, Albuquerque, New Mexico 87131, USA
| | - Xinyu Zhao
- Department of Neuroscience, University of New Mexico School of Medicine, Albuquerque, New Mexico 87131, USA
| |
Collapse
|
204
|
Abstract
Calcium-dependent secretion of neurotransmitters and hormones is essential for brain function and neuroendocrine-signaling. Prior to exocytosis, neurotransmitter-containing vesicles dock to the target membrane. In electron micrographs of neurons and neuroendocrine cells, like chromaffin cells many synaptic vesicles (SVs) and large dense-core vesicles (LDCVs) are docked. For many years the molecular identity of the morphologically docked state was unknown. Recently, we resolved the minimal docking machinery in adrenal medullary chromaffin cells using embryonic mouse model systems together with electron-microscopic analyses and also found that docking is controlled by the sub-membrane filamentous (F-)actin. Currently it is unclear if the same docking machinery operates in synapses. Here, I will review our docking assay that led to the identification of the LDCV docking machinery in chromaffin cells and also discuss whether identical docking proteins are required for SV docking in synapses.
Collapse
|
205
|
Abstract
Synaptic plasticity, the ability of neurons to change the number and strength of their synapses, has long been considered the sole province of the neuron. Yet neurons do not function in isolation; they are a part of elaborate glial networks where they are intimately associated with astrocytes. Astrocytes make extensive contacts with synaptic sites where they release soluble factors that can increase synapse number, provide synaptic insulation restricting the spread of neurotransmitter to neighboring synapses, and release neuroactive compounds, gliotransmitters, that can directly influence synaptic transmission. During periods of synaptogenesis, astrocyte processes are highly mobile and may contribute to the stabilization of new synapses. As our understanding of the extent of their influence at the synapse unfolds, it is clear that astrocytes are well poised to modulate multiple aspects of synaptic plasticity.
Collapse
Affiliation(s)
- Alison J Barker
- Department of Ophthalmology, University of California, San Francisco, California, USA
| | | |
Collapse
|
206
|
Transcriptomic responses in mouse brain exposed to chronic excess of the neurotransmitter glutamate. BMC Genomics 2010; 11:360. [PMID: 20529287 PMCID: PMC2896956 DOI: 10.1186/1471-2164-11-360] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2010] [Accepted: 06/07/2010] [Indexed: 12/11/2022] Open
Abstract
Background Increases during aging in extracellular levels of glutamate (Glu), the major excitatory neurotransmitter in the brain, may be linked to chronic neurodegenerative diseases. Little is known about the molecular responses of neurons to chronic, moderate increases in Glu levels. Genome-wide gene expression in brain hippocampus was examined in a unique transgenic (Tg) mouse model that exhibits moderate Glu hyperactivity throughout the lifespan, the neuronal Glutamate dehydrogenase (Glud1) mouse, and littermate 9 month-old wild type mice. Results Integrated bioinformatic analyses on transcriptomic data were used to identify bio-functions, pathways and gene networks underlying neuronal responses to increased Glu synaptic release. Bio-functions and pathways up-regulated in Tg mice were those associated with oxidative stress, cell injury, inflammation, nervous system development, neuronal growth, and synaptic transmission. Increased gene expression in these functions and pathways indicated apparent compensatory responses offering protection against stress, promoting growth of neuronal processes (neurites) and re-establishment of synapses. The transcription of a key gene in the neurite growth network, the kinase Ptk2b, was significantly up-regulated in Tg mice as was the activated (phosphorylated) form of the protein. In addition to genes related to neurite growth and synaptic development, those associated with neuronal vesicle trafficking in the Huntington's disease signalling pathway, were also up-regulated. Conclusions This is the first study attempting to define neuronal gene expression patterns in response to chronic, endogenous Glu hyperactivity at brain synapses. The patterns observed were characterized by a combination of responses to stress and stimulation of nerve growth, intracellular transport and recovery.
Collapse
|
207
|
Engerer P, Sigrist SJ. Relax? Don't do it!-Linking presynaptic vesicle clustering with mechanical tension. HFSP JOURNAL 2010; 3:367-72. [PMID: 20514128 DOI: 10.2976/1.3260842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2009] [Indexed: 11/19/2022]
Abstract
The release of transmitter-filled vesicles from presynaptic terminals is a key step of neurotransmission. Prior to release, synaptic vesicles get clustered at a specialized patch of the presynaptic membrane, here referred to as the active zone. So far, mainly biochemical regulations at the active zone were regarded as decisive for synaptic vesicle clustering and release. However, using biophysical approaches, a recent paper [Siechen, et al. (2009). Proc. Natl. Acad. Sci. U.S.A. 106, 12611-12616] indicated also that the micromechanical regulations within axon and terminal could be crucial for proper vesicle clustering. The authors demonstrated that the synaptic vesicle accumulations vanished after axotomy but were restored after the application of physical tension. Furthermore, axons seem to be under an intrinsic tension, which could be perceived and tuned by an axon-internal tension sensing mechanism. Therefore, mechanical force could steer vesicle clustering and consequently synapse function. Here, we review this interdisciplinary study of Siechen, et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 12611-12616 (2009)] and discuss the significance of cellular mechanics on synaptic function.
Collapse
Affiliation(s)
- Peter Engerer
- Institut für Biologie-Neurogenetik, Freie Universität Berlin, 14195 Berlin, Germany
| | | |
Collapse
|
208
|
Rust MB, Gurniak CB, Renner M, Vara H, Morando L, Görlich A, Sassoè-Pognetto M, Banchaabouchi MA, Giustetto M, Triller A, Choquet D, Witke W. Learning, AMPA receptor mobility and synaptic plasticity depend on n-cofilin-mediated actin dynamics. EMBO J 2010; 29:1889-902. [PMID: 20407421 DOI: 10.1038/emboj.2010.72] [Citation(s) in RCA: 166] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2009] [Accepted: 03/26/2010] [Indexed: 11/09/2022] Open
Abstract
Neuronal plasticity is an important process for learning, memory and complex behaviour. Rapid remodelling of the actin cytoskeleton in the postsynaptic compartment is thought to have an important function for synaptic plasticity. However, the actin-binding proteins involved and the molecular mechanisms that in vivo link actin dynamics to postsynaptic physiology are not well understood. Here, we show that the actin filament depolymerizing protein n-cofilin is controlling dendritic spine morphology and postsynaptic parameters such as late long-term potentiation and long-term depression. Loss of n-cofilin-mediated synaptic actin dynamics in the forebrain specifically leads to impairment of all types of associative learning, whereas exploratory learning is not affected. We provide evidence for a novel function of n-cofilin function in synaptic plasticity and in the control of extrasynaptic excitatory AMPA receptors diffusion. These results suggest a critical function of actin dynamics in associative learning and postsynaptic receptor availability.
Collapse
Affiliation(s)
- Marco B Rust
- Mouse Biology Unit, European Molecular Biology Laboratory, Monterotondo, Italy
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
209
|
Ceglia I, Kim Y, Nairn AC, Greengard P. Signaling pathways controlling the phosphorylation state of WAVE1, a regulator of actin polymerization. J Neurochem 2010; 114:182-90. [PMID: 20403076 DOI: 10.1111/j.1471-4159.2010.06743.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The Wiskott-Aldrich syndrome protein (WASP)-family verprolin homologous protein 1 (WAVE1) is a key regulator of Arp (actin-related protein) 2/3 complex-mediated actin polymerization. We have established previously that the state of phosphorylation of WAVE1 at three distinct residues controls its ability to regulate actin polymerization and spine morphology. Cyclin-dependent kinase 5 phosphorylates WAVE1 at Ser310, Ser397 and Ser441 to a high basal stoichiometry, resulting in inhibition of WAVE1 activity. Our previous and current studies show that WAVE1 can be dephosphorylated at all three sites and thereby activated upon stimulation of the D1 subclass of dopamine receptors and of the NMDA subclass of glutamate receptors, acting through cAMP and Ca(2+) signaling pathways, respectively. Specifically, we have identified protein phosphatase-2A and protein phosphatase-2B as the effectors for these second messengers. These phosphatases act on different sites to mediate receptor-induced signaling pathways, which would lead to activation of WAVE1.
Collapse
Affiliation(s)
- Ilaria Ceglia
- Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, New York 10065, USA
| | | | | | | |
Collapse
|
210
|
Li YC, Bai WZ, Zhou L, Sun LK, Hashikawa T. Nonhomogeneous distribution of filamentous actin in the presynaptic terminals on the spinal motoneurons. J Comp Neurol 2010; 518:3184-92. [DOI: 10.1002/cne.22374] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
211
|
Abstract
Docking, the stable association of secretory vesicles with the plasma membrane, is considered to be the necessary first step before vesicles gain fusion-competence, but it is unclear how vesicles dock. In adrenal medullary chromaffin cells, access of secretory vesicles to docking sites is controlled by dense F-actin (filamentous actin) beneath the plasma membrane. Recently, we found that, in the absence of Munc18-1, the number of docked vesicles and the thickness of cortical F-actin are affected. In the present paper, I discuss the possible mechanism by which Munc18-1 modulates cortical F-actin and how it orchestrates the docking machinery via an interaction with syntaxin-1. Finally, a comparison of Munc18's role in embryonic mouse and adult bovine chromaffin cell model systems will be made to clarify observed differences in cortical F-actin as well as docking phenotypes.
Collapse
|
212
|
Okamoto K, Bosch M, Hayashi Y. The roles of CaMKII and F-actin in the structural plasticity of dendritic spines: a potential molecular identity of a synaptic tag? Physiology (Bethesda) 2010; 24:357-66. [PMID: 19996366 DOI: 10.1152/physiol.00029.2009] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Ca2+/calmodulin-dependent protein kinase II (CaMKII) and actin are two crucial molecules involved in long-term potentiation (LTP). In addition to its signaling function, CaMKII plays a structural role via direct interaction with actin filaments, thus coupling functional and structural plasticity in dendritic spines. The status of F-actin, regulated by CaMKII, determines the postsynaptic protein binding capacity and thus may act as a synaptic tag that consolidates LTP.
Collapse
Affiliation(s)
- Kenichi Okamoto
- Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
| | | | | |
Collapse
|
213
|
Gopalakrishnan G, Thostrup P, Rouiller I, Lucido AL, Belkaïd W, Colman DR, Lennox RB. Lipid bilayer membrane-triggered presynaptic vesicle assembly. ACS Chem Neurosci 2010; 1:86-94. [PMID: 22778819 PMCID: PMC3368651 DOI: 10.1021/cn900011n] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2009] [Accepted: 10/01/2009] [Indexed: 11/30/2022] Open
Abstract
The formation of functional synapses on artificial substrates is a very important step in the development of engineered in vitro neural networks. Spherical supported bilayer lipid membranes (SS-BLMs) are used here as a novel substrate to demonstrate presynaptic vesicle accumulation at an in vitro synaptic junction. Confocal fluorescence microscopy, cryo-transmission electron microscopy (cryo-TEM), and fluorescence recovery after photobleaching (FRAP) experiments have been used to characterize the SS-BLMs. Conventional immunocytochemistry combined with confocal fluorescence microscopy was used to observe the formation of presynaptic vesicles at the neuron-SS-BLM contacts. These results indicate that lipid phases may play a role in the observed phenomenon, in addition to the chemical and electrostatic interactions between the neurons and SS-BLMs. The biocompatibility of lipid bilayers along with their membrane tunability makes the suggested approach a useful "toolkit" for many neuroengineering applications including artificial synapse formation and synaptogenesis in vivo.
Collapse
Affiliation(s)
- Gopakumar Gopalakrishnan
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, H3A 2K6 Montreal, Canada
- Montreal Neurological Institute & Hospital, McGill University, 3801 University Street, H3A 2B4 Montreal, Canada
- McGill Program in Neuroengineering, McGill University, Montreal, Canada
- FQRNT Centre for Self-Assembled Chemical Structures (CSACS), McGill University, Montreal, Canada
| | - Peter Thostrup
- Department of Physics, McGill University, 3600 University Street, H3A 2T8 Montreal, Canada
- McGill Program in Neuroengineering, McGill University, Montreal, Canada
| | - Isabelle Rouiller
- Department of Anatomy & Cell Biology, McGill University, 3640 University Street, H3A 2B2 Montreal, Canada
| | - Anna Lisa Lucido
- Montreal Neurological Institute & Hospital, McGill University, 3801 University Street, H3A 2B4 Montreal, Canada
- McGill Program in Neuroengineering, McGill University, Montreal, Canada
| | - Wiam Belkaïd
- Montreal Neurological Institute & Hospital, McGill University, 3801 University Street, H3A 2B4 Montreal, Canada
- McGill Program in Neuroengineering, McGill University, Montreal, Canada
| | - David R. Colman
- Montreal Neurological Institute & Hospital, McGill University, 3801 University Street, H3A 2B4 Montreal, Canada
- McGill Program in Neuroengineering, McGill University, Montreal, Canada
| | - R. Bruce Lennox
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, H3A 2K6 Montreal, Canada
- McGill Program in Neuroengineering, McGill University, Montreal, Canada
- FQRNT Centre for Self-Assembled Chemical Structures (CSACS), McGill University, Montreal, Canada
| |
Collapse
|
214
|
Paris I, Perez-Pastene C, Cardenas S, Iturriaga-Vasquez P, Iturra P, Muñoz P, Couve E, Caviedes P, Segura-Aguilar J. Aminochrome induces disruption of actin, alpha-, and beta-tubulin cytoskeleton networks in substantia-nigra-derived cell line. Neurotox Res 2010; 18:82-92. [PMID: 20087799 DOI: 10.1007/s12640-009-9148-4] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2009] [Revised: 11/19/2009] [Accepted: 12/23/2009] [Indexed: 10/20/2022]
Abstract
In previous studies, we observed that cells treated with aminochrome obtained by oxidizing dopamine with oxidizing agents dramatically changed cell morphology, thus posing the question if such morphological changes were dependent on aminochrome or the oxidizing agents used to produce aminochrome. Therefore, to answer this question, we have now purified aminochrome on a CM-Sepharose 50-100 column and, using NMR studies, we have confirmed that the resulting aminochrome was pure and that it retained its structure. Fluorescence microscopy with calcein-AM and transmission electron microscopy showed that RCSN-3 cells presented an elongated shape that did not change when the cells were incubated with 50 muM aminochrome or 100 muM dicoumarol, an inhibitor of DT-diaphorase. However, the cell were reduced in size and the elongated shape become spherical when the cells where incubated with 50 muM aminochrome in the presence of 100 muM dicoumarol. Under these conditions, actin, alpha-, and beta-tubulin cytoskeleton filament networks became condensed around the cell membrane. Actin aggregates were also observed in cells processes that connected the cells in culture. These results suggest that aminochrome one-electron metabolism induces the disruption of the normal morphology of actin, alpha-, and beta-tubulin in the cytoskeleton, and that DT-diaphorase prevents these effects.
Collapse
Affiliation(s)
- Irmgard Paris
- Program of Molecular and Clinical Pharmacology, Faculty of Medicine, ICBM, Independencia1027, Casilla, Santiago, 70000, Chile
| | | | | | | | | | | | | | | | | |
Collapse
|
215
|
Bolduc FV, Bell K, Rosenfelt C, Cox H, Tully T. Fragile x mental retardation 1 and filamin a interact genetically in Drosophila long-term memory. Front Neural Circuits 2010; 3:22. [PMID: 20190856 PMCID: PMC2813723 DOI: 10.3389/neuro.04.022.2009] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2009] [Accepted: 12/03/2009] [Indexed: 11/13/2022] Open
Abstract
The last decade has witnessed the identification of single-gene defects associated with an impressive number of mental retardation syndromes. Fragile X syndrome, the most common cause of mental retardation for instance, results from disruption of the FMR1 gene. Similarly, Periventricular Nodular Heterotopia, which includes cerebral malformation, epilepsy and cognitive disabilities, derives from disruption of the Filamin A gene. While it remains unclear whether defects in common molecular pathways may underlie the cognitive dysfunction of these various syndromes, defects in cytoskeletal structure nonetheless appear to be common to several mental retardation syndromes. FMR1 is known to interact with Rac, profilin, PAK and Ras, which are associated with dendritic spine defects. In Drosophila, disruptions of the dFmr1 gene impair long-term memory (LTM), and the Filamin A homolog (cheerio) was identified in a behavioral screen for LTM mutants. Thus, we investigated the possible interaction between cheerio and dFmr1 during LTM formation in Drosophila. We show that LTM specifically is defective in dFmr1/cheerio double heterozygotes, while it is normal in single heterozygotes for either dFmr1 or cheerio. In dFmr1 mutants, Filamin (Cheerio) levels are lower than normal after spaced training. These observations support the notion that decreased actin cross-linking may underlie the persistence of long and thin dendritic spines in Fragile X patients and animal models. More generally, our results represent the first demonstration of a genetic interaction between mental retardation genes in an in vivo model system of memory formation.
Collapse
Affiliation(s)
- François V Bolduc
- Watson School of Biological Sciences, Cold Spring Harbor Laboratory, Cold Spring Harbor New York, NY, USA
| | | | | | | | | |
Collapse
|
216
|
Gutiérrez RC, Flynn R, Hung J, Kertesz AC, Sullivan A, Zamponi GW, El-Husseini A, Colicos MA. Activity-driven mobilization of post-synaptic proteins. Eur J Neurosci 2009; 30:2042-52. [PMID: 20128843 DOI: 10.1111/j.1460-9568.2009.07007.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Synapses established during central nervous system development can be modified through synapse elimination and formation. These processes are, in part, activity dependent and require regulated trafficking of post-synaptic components. Here, we investigate the activity-driven remodeling of cultured rat hippocampal neurons at 14 days in vitro, focusing on the post-synaptic proteins PSD-95, Shank, neuroligin (NL)1 and actin. Using live imaging and photoconductive stimulation, we found that high-frequency activity altered the trajectory, but not velocity, of PSD-95-GFP and Shank-YFP clusters, whereas it reduced the speed and increased the number of NL1 clusters. Actin-CFP reorganized into puncta following activity and approximately 50% of new puncta colocalized with NL1 clusters. Actin reorganization was enhanced by the overexpression of NL1 and decreased by the expression of an NL1 mutant, NL1-R473C. These results demonstrate activity-dependent changes that may result in the formation of new post-synaptic sites and suggest that NL1 modulates actin reorganization. The results also suggest that a common mechanism underlies both the developmental and activity-dependent remodeling of excitatory synapses.
Collapse
|
217
|
Abstract
CNS synapse assembly typically follows after stable contacts between "appropriate" axonal and dendritic membranes are made. We show that presynaptic boutons selectively form de novo following neuronal fiber adhesion to beads coated with poly-d-lysine (PDL), an artificial cationic polypeptide. As demonstrated by atomic force and live confocal microscopy, functional presynaptic boutons self-assemble as rapidly as 1 h after bead contact, and are found to contain a variety of proteins characteristic of presynaptic endings. Interestingly, presynaptic compartment assembly does not depend on the presence of a biological postsynaptic membrane surface. Rather, heparan sulfate proteoglycans, including syndecan-2, as well as others possibly adsorbed onto the bead matrix or expressed on the axon surface, are required for assembly to proceed by a mechanism dependent on the dynamic reorganization of F-actin. Our results indicate that certain (but not all) nonspecific cationic molecules like PDL, with presumably electrostatically mediated adhesive properties, can effectively bypass cognate and natural postsynaptic ligands to trigger presynaptic assembly in the absence of specific target recognition. In contrast, we find that postsynaptic compartment assembly depends on the prior presence of a mature presynaptic ending.
Collapse
|
218
|
Zulauf L, Coste O, Marian C, Möser C, Brenneis C, Niederberger E. Cofilin phosphorylation is involved in nitric oxide/cGMP-mediated nociception. Biochem Biophys Res Commun 2009; 390:1408-13. [PMID: 19896457 DOI: 10.1016/j.bbrc.2009.10.166] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2009] [Accepted: 10/31/2009] [Indexed: 12/21/2022]
Abstract
There is convincing evidence that nitric oxide (NO), cGMP and cGMP-dependent protein kinase I (PKG-I) are involved in the development of hyperalgesia in response to noxious stimuli. However, downstream target proteins contributing to nociception have not been completely identified so far. Several reports indicate a role of the NO/cGMP/PKG cascade in the regulation of neurite outgrowth which is suggested to be involved in specific mechanisms of nociception. Since neurite outgrowth is strongly dependent on modulation of cytoskeleton proteins we were interested in the impact of PKG-I activation on the actin cytoskeleton and its role in inflammatory hyperalgesia. Therefore we investigated the actin-destabilising protein cofilin and its NO-dependent effects in vitro in primary neuronal cultures as well as in vivo in the zymosan-induced paw inflammation model in rats. In primary neurons from rats, treatment with the PKG-I activator 8-Br-cGMP induced a time-dependent phosphorylation of cofilin and significantly increased neurite outgrowth. Further functional analysis revealed that the underlying signal transduction pathways involve activation of the Rho-GTPases RhoA, Rac1 and Cdc42 and their corresponding downstream targets Rho-kinase (ROCK) and p21-activated kinase (PAK). In vivo, treatment of rats with the NO-synthase inhibitor l-NAME and the ROCK-inhibitor Y-27632, respectively, led to a significant decrease of cofilin phosphorylation in the spinal cord and resulted in antinociceptive effects in a model of inflammatory hyperalgesia. Our results suggest that cofilin represents a downstream target of NO/cGMP/PKG signal transduction in neurons thus indicating that it is involved in NO-mediated nociception.
Collapse
Affiliation(s)
- Lars Zulauf
- Pharmazentrum frankfurt/ZAFES, Klinikum der Goethe-Universität, Frankfurt, Theodor Stern Kai 7, 60590 Frankfurt, Germany.
| | | | | | | | | | | |
Collapse
|
219
|
Ramachandran P, Barria R, Ashley J, Budnik V. A critical step for postsynaptic F-actin organization: regulation of Baz/Par-3 localization by aPKC and PTEN. Dev Neurobiol 2009; 69:583-602. [PMID: 19472188 DOI: 10.1002/dneu.20728] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Actin remodeling has emerged as a critical process during synapse development and plasticity. Thus, understanding the regulatory mechanisms controlling actin organization at synapses is exceedingly important. Here, we used the highly plastic Drosophila neuromuscular junction (NMJ) to understand mechanisms of actin remodeling at postsynaptic sites. Previous studies have suggested that the actin-binding proteins Spectrin and Coracle play a critical role in NMJ development and the anchoring of glutamate receptors most likely through actin regulation. Here, we show that an additional determinant of actin organization at the postsynaptic region is the PDZ protein Baz/Par-3. Decreasing Baz levels in postsynaptic muscles has dramatic consequences for the size of F-actin and spectrin domains at the postsynaptic region. In turn, proper localization of Baz at this site depends on both phosphorylation and dephosphorylation events. Baz phosphorylation by its binding partner, atypical protein kinase C (aPKC), is required for normal Baz targeting to the postsynaptic region. However, the retention of Baz at this site depends on its dephosphorylation mediated by the lipid and protein phosphatase PTEN. Misregulation of the phosphorylation state of Baz by genetic alterations in PTEN or aPKC activity has detrimental consequences for postsynaptic F-actin and spectrin localization, synaptic growth, and receptor localization. Our results provide a novel mechanism of postsynaptic actin regulation through Baz, governed by the antagonistic actions of aPKC and PTEN. Given the conservation of these proteins from worms to mammals, these results are likely to provide new insight into actin organization pathways. (c) 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009.
Collapse
Affiliation(s)
- Preethi Ramachandran
- Department of Neurobiology, University of Massachusetts Medical School, Worcester, Massachusetts, USA
| | | | | | | |
Collapse
|
220
|
Hoy JL, Constable JR, Vicini S, Fu Z, Washbourne P. SynCAM1 recruits NMDA receptors via protein 4.1B. Mol Cell Neurosci 2009; 42:466-83. [PMID: 19796685 DOI: 10.1016/j.mcn.2009.09.010] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2009] [Revised: 09/12/2009] [Accepted: 09/21/2009] [Indexed: 11/27/2022] Open
Abstract
Cell adhesion molecules have been implicated as key organizers of synaptic structures, but there is still a need to determine how these molecules facilitate neurotransmitter receptor recruitment to developing synapses. Here, we identify erythrocyte protein band 4.1-like 3 (protein 4.1B) as an intracellular effector molecule of Synaptic Cell Adhesion Molecule 1 (SynCAM1) that is sufficient to recruit NMDA-type receptors (NMDARs) to SynCAM1 adhesion sites in COS7 cells. Protein 4.1B in conjunction with SynCAM1 also increased the frequency of NMDAR-mediated mEPSCs and area of presynaptic contact in an HEK293 cell/ neuron co-culture assay. Studies in cultured hippocampal neurons reveal that manipulation of protein 4.1B expression levels specifically affects NMDAR-mediated activity and localization. Finally, further experimentation in COS7 cells show that SynCAM1 may also interact with protein 4.1N to specifically effect AMPA type receptor (AMPAR) recruitment. Thus, SynCAM1 may recruit both AMPARs and NMDARs by independent mechanisms during synapse formation.
Collapse
Affiliation(s)
- Jennifer L Hoy
- Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA
| | | | | | | | | |
Collapse
|
221
|
Dierssen M, Herault Y, Estivill X. Aneuploidy: from a physiological mechanism of variance to Down syndrome. Physiol Rev 2009; 89:887-920. [PMID: 19584316 DOI: 10.1152/physrev.00032.2007] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Quantitative differences in gene expression emerge as a significant source of variation in natural populations, representing an important substrate for evolution and accounting for a considerable fraction of phenotypic diversity. However, perturbation of gene expression is also the main factor in determining the molecular pathogenesis of numerous aneuploid disorders. In this review, we focus on Down syndrome (DS) as the prototype of "genomic disorder" induced by copy number change. The understanding of the pathogenicity of the extra genomic material in trisomy 21 has accelerated in the last years due to the recent advances in genome sequencing, comparative genome analysis, functional genome exploration, and the use of model organisms. We present recent data on the role of genome-altering processes in the generation of diversity in DS neural phenotypes focusing on the impact of trisomy on brain structure and mental retardation and on biological pathways and cell types in target brain regions (including prefrontal cortex, hippocampus, cerebellum, and basal ganglia). We also review the potential that genetically engineered mouse models of DS bring into the understanding of the molecular biology of human learning disorders.
Collapse
Affiliation(s)
- Mara Dierssen
- Genes and Disease Program, Genomic Regulation Center-CRG, Pompeu Fabra University, Barcelona Biomedical Research Park, Dr Aiguader 88, PRBB building E, Barcelona 08003, Catalonia, Spain.
| | | | | |
Collapse
|
222
|
SMN, profilin IIa and plastin 3: A link between the deregulation of actin dynamics and SMA pathogenesis. Mol Cell Neurosci 2009; 42:66-74. [DOI: 10.1016/j.mcn.2009.05.009] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2009] [Revised: 05/20/2009] [Accepted: 05/26/2009] [Indexed: 11/21/2022] Open
|
223
|
Knöll B, Nordheim A. Functional versatility of transcription factors in the nervous system: the SRF paradigm. Trends Neurosci 2009; 32:432-42. [PMID: 19643506 DOI: 10.1016/j.tins.2009.05.004] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2009] [Revised: 05/18/2009] [Accepted: 05/18/2009] [Indexed: 12/23/2022]
Abstract
Individual transcription factors in the brain frequently display broad functional versatility, thereby controlling multiple cellular outputs. In accordance, neuron-restricted mutagenesis of the murine Srf gene, encoding the transcription factor serum response factor (SRF), revealed numerous SRF functions in the nervous system. First, SRF controls immediate early gene (IEG) activation associated with perception of synaptic activity, learning and memory. Second, processes linked to actin cytoskeletal dynamics are mediated by SRF, such as developmental neuronal migration, outgrowth and pathfinding of neurites, as well as synaptic targeting. Therefore, SRF seems to be instrumental in converting synaptic activity into plasticity-associated structural changes in neuronal connectivities. This highlights the decisive role of SRF in integrating cytoskeletal actin dynamics and nuclear gene expression. Finally, we relate SRF to the multi-functional transcription factor CREB and point out overlapping, distinct and concerted functions of these two transcriptional regulators in the brain.
Collapse
Affiliation(s)
- Bernd Knöll
- Neuronal Gene Expression Laboratory, Eberhard-Karls-University Tübingen, Interfaculty Institute for Cell Biology, Department of Molecular Biology, Auf der Morgenstelle 15, 72076 Tübingen, Germany.
| | | |
Collapse
|
224
|
Mechanical tension contributes to clustering of neurotransmitter vesicles at presynaptic terminals. Proc Natl Acad Sci U S A 2009; 106:12611-6. [PMID: 19620718 DOI: 10.1073/pnas.0901867106] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Memory and learning in animals are mediated by neurotransmitters that are released from vesicles clustered at the synapse. As a synapse is used more frequently, its neurotransmission efficiency increases, partly because of increased vesicle clustering in the presynaptic neuron. Vesicle clustering has been believed to result primarily from biochemical signaling processes that require the connectivity of the presynaptic terminal with the cell body, the central nervous system, and the postsynaptic cell. Our in vivo experiments on the embryonic Drosophila nervous system show that vesicle clustering at the neuromuscular presynaptic terminal depends on mechanical tension within the axons. Vesicle clustering vanishes upon severing the axon from the cell body, but is restored when mechanical tension is applied to the severed end of the axon. Clustering increases when intact axons are stretched mechanically by pulling the postsynaptic muscle. Using micro mechanical force sensors, we find that embryonic axons that have formed neuromuscular junctions maintain a rest tension of approximately 1 nanonewton. If the rest tension is perturbed mechanically, axons restore the rest tension either by relaxing or by contracting over a period of approximately 15 min. Our results suggest that neuromuscular synapses employ mechanical tension as a signal to modulate vesicle accumulation and synaptic plasticity.
Collapse
|
225
|
Sousa VL, Bellani S, Giannandrea M, Yousuf M, Valtorta F, Meldolesi J, Chieregatti E. {alpha}-synuclein and its A30P mutant affect actin cytoskeletal structure and dynamics. Mol Biol Cell 2009; 20:3725-39. [PMID: 19553474 DOI: 10.1091/mbc.e08-03-0302] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The function of alpha-synuclein, a soluble protein abundant in the brain and concentrated at presynaptic terminals, is still undefined. Yet, alpha-synuclein overexpression and the expression of its A30P mutant are associated with familial Parkinson's disease. Working in cell-free conditions, in two cell lines as well as in primary neurons we demonstrate that alpha-synuclein and its A30P mutant have different effects on actin polymerization. Wild-type alpha-synuclein binds actin, slows down its polymerization and accelerates its depolymerization, probably by monomer sequestration; A30P mutant alpha-synuclein increases the rate of actin polymerization and disrupts the cytoskeleton during reassembly of actin filaments. Consequently, in cells expressing mutant alpha-synuclein, cytoskeleton-dependent processes, such as cell migration, are inhibited, while exo- and endocytic traffic is altered. In hippocampal neurons from mice carrying a deletion of the alpha-synuclein gene, electroporation of wild-type alpha-synuclein increases actin instability during remodeling, with growth of lamellipodia-like structures and apparent cell enlargement, whereas A30P alpha-synuclein induces discrete actin-rich foci during cytoskeleton reassembly. In conclusion, alpha-synuclein appears to play a major role in actin cytoskeletal dynamics and various aspects of microfilament function. Actin cytoskeletal disruption induced by the A30P mutant might alter various cellular processes and thereby play a role in the pathogenesis of neurodegeneration.
Collapse
Affiliation(s)
- Vítor L Sousa
- Department of Neuroscience, San Raffaele Scientific Institute, Milan, Italy
| | | | | | | | | | | | | |
Collapse
|
226
|
Leamey CA, Van Wart A, Sur M. Intrinsic patterning and experience-dependent mechanisms that generate eye-specific projections and binocular circuits in the visual pathway. Curr Opin Neurobiol 2009; 19:181-7. [PMID: 19502049 DOI: 10.1016/j.conb.2009.05.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2009] [Revised: 05/14/2009] [Accepted: 05/15/2009] [Indexed: 01/10/2023]
Abstract
A defining feature of the mammalian nervous system is its complex yet precise circuitry. The mechanisms which underlie the generation of neural connectivity are the topic of intense study in developmental neuroscience. The mammalian visual pathway demonstrates precise retinotopic organization in subcortical and cortical pathways, together with the alignment and matching of eye-specific projections, and sophisticated cortical circuitry that enables the extraction of features underlying vision. New approaches employing molecular-genetic analyses, transgenic mice, novel recombinant probes, and high-resolution imaging are contributing to rapid progress and a new synthesis in the field. These approaches are revealing the ways in which intrinsic patterning mechanisms act in concert with experience-dependent mechanisms to shape visual projections and circuits.
Collapse
Affiliation(s)
- Catherine A Leamey
- Discipline of Physiology, School of Medical Sciences and Bosch Institute, University of Sydney, NSW 2006, Australia.
| | | | | |
Collapse
|
227
|
Haditsch U, Leone DP, Farinelli M, Chrostek-Grashoff A, Brakebusch C, Mansuy IM, McConnell SK, Palmer TD. A central role for the small GTPase Rac1 in hippocampal plasticity and spatial learning and memory. Mol Cell Neurosci 2009; 41:409-19. [PMID: 19394428 DOI: 10.1016/j.mcn.2009.04.005] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Revised: 04/17/2009] [Accepted: 04/17/2009] [Indexed: 10/20/2022] Open
Abstract
Rac1 is a member of the Rho family of small GTPases that are important for structural aspects of the mature neuronal synapse including basal spine density and shape, activity-dependent spine enlargement, and AMPA receptor clustering in vitro. Here we demonstrate that selective elimination of Rac1 in excitatory neurons in the forebrain in vivo not only affects spine structure, but also impairs synaptic plasticity in the hippocampus with consequent defects in hippocampus-dependent spatial learning. Furthermore, Rac1 mutants display deficits in working/episodic-like memory in the delayed matching-to-place (DMP) task suggesting that Rac1 is a central regulator of rapid encoding of novel spatial information in vivo.
Collapse
Affiliation(s)
- Ursula Haditsch
- Department of Neurosurgery, Stanford School of Medicine, 1201 Welch Rd, MSLS P304, Stanford, California 94305, USA.
| | | | | | | | | | | | | | | |
Collapse
|
228
|
Abstract
The physical properties of the postsynaptic membrane (PSM), including its viscosity, determine its capacity to regulate the net flux of synaptic membrane proteins such as neurotransmitter receptors. To address these properties, we studied the lateral diffusion of glycophosphatidylinositol-anchored green fluorescent protein and cholera toxin bound to the external leaflet of the plasma membrane. Relative to extrasynaptic regions, their mobility was reduced at synapses and even more at inhibitory than at excitatory ones. This indicates a higher density of obstacles and/or higher membrane viscosity at inhibitory contacts. Actin depolymerization reduced the confinement and accelerated a population of fast, mobile molecules. The compaction of obstacles thus depends on actin cytoskeleton integrity. Cholesterol depletion increased the mobility of the slow diffusing molecules, allowing them to diffuse more rapidly through the crowded PSM. Thus, the PSM has lipid-raft properties, and the density of obstacles to diffusion depends on filamentous actin. Therefore, lipid composition and actin-dependent protein compaction regulate viscosity of the PSM and, consequently, the molecular flow in and out of synapses.
Collapse
|
229
|
Abstract
The roles of nonmuscle myosin II and cortical actin filaments in chromaffin granule exocytosis were studied by confocal fluorescence microscopy, amperometry, and cell-attached capacitance measurements. Fluorescence imaging indicated decreased mobility of granules near the plasma membrane following inhibition of myosin II function with blebbistatin. Slower fusion pore expansion rates and longer fusion pore lifetimes were observed after inhibition of actin polymerization using cytochalasin D. Amperometric recordings revealed increased amperometric spike half-widths without change in quantal size after either myosin II inhibition or actin disruption. These results suggest that actin and myosin II facilitate release from individual chromaffin granules by accelerating dissociation of catecholamines from the intragranular matrix possibly through generation of mechanical forces.
Collapse
|
230
|
Kim SM, Choi KY, Cho IH, Rhy JH, Kim SH, Park CS, Kim E, Song WK. Regulation of dendritic spine morphology by SPIN90, a novel Shank binding partner. J Neurochem 2009; 109:1106-17. [PMID: 19302483 DOI: 10.1111/j.1471-4159.2009.06039.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Dendritic spines are highly specialized actin-rich structures on which the majority of excitatory synapses are formed in the mammalian CNS. SPIN90 is an actin-binding protein known to be highly enriched in postsynaptic densities (PSDs), though little is known about its function there. Here, we show that SPIN90 is a novel binding partner for Shank proteins in the PSD. SPIN90 and Shank co-immunoprecipitate from brain lysates and co-localize in postsynaptic dendrites and act synergistically to mediate spine maturation and spine head enlargement. At the same time, SPIN90 causes accumulation of Shank and PSD-95 within dendritic spines. In addition, we found that the protein composition of PSDs in SPIN90 knockout mice is altered as is the actin cytoskeleton of cultured hippocampal SPIN90 knockout neurons. Taken together, these findings demonstrate that SPIN90 is a Shank1b binding partner and a key contributor to the regulation of dendritic spine morphogenesis and brain function.
Collapse
Affiliation(s)
- Seon-Myung Kim
- Cell Dynamics Research Center and Bioimaging Center, Gwangju Institute of Science and Technology, Gwangju, Korea
| | | | | | | | | | | | | | | |
Collapse
|
231
|
Kang MG, Guo Y, Huganir RL. AMPA receptor and GEF-H1/Lfc complex regulates dendritic spine development through RhoA signaling cascade. Proc Natl Acad Sci U S A 2009; 106:3549-54. [PMID: 19208802 PMCID: PMC2638734 DOI: 10.1073/pnas.0812861106] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2008] [Indexed: 01/15/2023] Open
Abstract
AMPA receptors (AMPA-R) are major mediators of synaptic transmission and plasticity in the developing and adult central nervous system. Activity-dependent structural plasticity mediated by dynamic changes in the morphology of spines and dendrites is also essential for the formation and tuning of neuronal circuits. RhoA and Rac1 are known to play important roles in the regulation of spine and dendrite development in response to neuronal activity. These Rho GTPases are activated by guanine nucleotide exchange factors (GEFs). In this study, we identified GEF-H1/Lfc as a component of the AMPA-R complex in the brain. GEF-H1 is enriched in the postsynaptic density and is colocalized with GluR1 at spines. GEF-H1 activity negatively regulates spine density and length through a RhoA signaling cascade. In addition, AMPA-R-dependent changes in spine development are eliminated by down-regulation of GEF-H1. Altogether, these results strongly suggest that GEF-H1 is an important mediator of AMPA-R activity-dependent structural plasticity in neurons.
Collapse
Affiliation(s)
- Myoung-Goo Kang
- Department of Neuroscience, The Howard Hughes Medical Institute, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205; and
| | - Yurong Guo
- Department of Medicine, The Johns Hopkins University, 5200 Eastern Avenue, Baltimore, MD 21234
| | - Richard L. Huganir
- Department of Neuroscience, The Howard Hughes Medical Institute, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205; and
| |
Collapse
|
232
|
Richard M, Sacquet J, Jany M, Schweitzer A, Jourdan F, Andrieux A, Pellier-Monnin V. STOP proteins contribute to the maturation of the olfactory system. Mol Cell Neurosci 2009; 41:120-34. [PMID: 19236915 DOI: 10.1016/j.mcn.2009.02.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2008] [Revised: 01/13/2009] [Accepted: 02/06/2009] [Indexed: 01/09/2023] Open
Abstract
Regulation of microtubule dynamics is crucial for axon growth and guidance as well as for the establishment of synaptic connections. STOPs (Stable Tubule Only Polypeptides) are microtubule-associated proteins that regulate microtubule stabilization but are also able to interact with actin or Golgi membranes. Here, we have investigated the involvement of STOPs during the development of the olfactory system. We first describe the spatio-temporal expression patterns of N- and E-STOP, the two neuronal-specific isoforms of STOP. E- and N-STOP are expressed in the axonal compartment of olfactory sensory neurons, but are differentially regulated during development. Interestingly, each neuronal isoform displays a specific gradient distribution within the olfactory nerve layer. Then, we have examined the development of the olfactory system in the absence of STOPs. Olfactory axons display a normal outgrowth and targeting in STOP-null mice, but maturation of the synapses in the glomerular neuropil is altered.
Collapse
Affiliation(s)
- Marion Richard
- Laboratoire Neurosciences Sensorielles, Comportement, Cognition, CNRS-UMR 5020, Université de Lyon, Lyon 1, F-69366, France.
| | | | | | | | | | | | | |
Collapse
|
233
|
Abstract
Transmitter release at high probability phasic synapses of crayfish neuromuscular junctions depresses by over 50% in 60 min when stimulated at 0.2 Hz. Inhibition of the protein phosphatase calcineurin by intracellular pre-synaptic injection of autoinhibitory peptide inhibited low-frequency depression (LFD) and resulted in facilitation of transmitter release. Since this inhibitor had no major effects when injected into the post-synaptic cell, only pre-synaptic calcineurin activity is necessary for LFD. To examine changes in phosphoproteins during LFD we performed a phosphoproteomic screen on proteins extracted from motor axons and nerve terminals after LFD induction or treatment with various drugs that affect kinase and phosphatase activity. Proteins separated by PAGE were stained with phospho-specific/total protein ratio stains (Pro-Q Diamond/SYPRO Ruby) to identify protein bands for analysis by mass spectrometry. Phosphorylation of actin and tubulin decreased during LFD, but increased when calcineurin was blocked. Tubulin and phosphoactin immunoreactivity in pre-synaptic terminals were also reduced after LFD. The actin depolymerizing drugs cytochalasin and latrunculin and the microtubule stabilizer taxol inhibited LFD. Therefore, dephosphorylation of pre-synaptic actin and tubulin and consequent changes in the cytoskeleton may regulate LFD. LFD is unlike long-term depression found in mammalian synapses because the latter requires in most instances post-synaptic calcineurin activity.Thus, this simpler invertebrate synapse discloses a novel pre-synaptic depression mechanism.
Collapse
|
234
|
Abstract
Actin filaments are thin polymers of the 42 kD protein actin. In mature axons a network of subaxolemmal actin filaments provide stability for membrane integrity and a substrate for short distance transport of cargos. In developing neurons dynamic regulation of actin polymerization and organization mediates axonal morphogenesis and axonal pathfinding to synaptic targets. Other changes in axonal shape, collateral branching, branch retraction, and axonal regeneration, also depend on actin filament dynamics. Actin filament organization is regulated by a diversity of actin-binding proteins (ABP). ABP are the focus of complex extrinsic and intrinsic signaling pathways, and many neurological pathologies and dysfunctions arise from defective regulation of ABP function.
Collapse
Affiliation(s)
- Paul C Letourneau
- Department of Neuroscience, 6-145 Jackson Hall, University of Minnesota, Minneapolis, MN 55455, USA.
| |
Collapse
|
235
|
Lin WH, Webb DJ. Actin and Actin-Binding Proteins: Masters of Dendritic Spine Formation, Morphology, and Function. THE OPEN NEUROSCIENCE JOURNAL 2009; 3:54-66. [PMID: 20717495 PMCID: PMC2921857 DOI: 10.2174/1874082000903020054] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Dendritic spines are actin-rich protrusions that comprise the postsynaptic sites of synapses and receive the majority of excitatory synaptic inputs in the central nervous system. These structures are central to cognitive processes, and alterations in their number, size, and morphology are associated with many neurological disorders. Although the actin cytoskeleton is thought to govern spine formation, morphology, and synaptic functions, we are only beginning to understand how modulation of actin reorganization by actin-binding proteins (ABPs) contributes to the function of dendritic spines and synapses. In this review, we discuss what is currently known about the role of ABPs in regulating the formation, morphology, motility, and plasticity of dendritic spines and synapses.
Collapse
Affiliation(s)
- Wan-Hsin Lin
- Department of Biological Sciences and Vanderbilt Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, Tennessee 37235, USA
| | - Donna J. Webb
- Department of Biological Sciences and Vanderbilt Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, Tennessee 37235, USA
- Department of Cancer Biology, Vanderbilt University, Nashville, Tennessee 37235, USA
| |
Collapse
|
236
|
Perez-Mansilla B, Nurrish S. A network of G-protein signaling pathways control neuronal activity in C. elegans. ADVANCES IN GENETICS 2009; 65:145-192. [PMID: 19615533 DOI: 10.1016/s0065-2660(09)65004-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The Caenorhabditis elegans neuromuscular junction (NMJ) is one of the best studied synapses in any organism. A variety of genetic screens have identified genes required both for the essential steps of neurotransmitter release from motorneurons as well as the signaling pathways that regulate rates of neurotransmitter release. A number of these regulatory genes encode proteins that converge to regulate neurotransmitter release. In other cases genes are known to regulate signaling at the NMJ but how they act remains unknown. Many of the proteins that regulate activity at the NMJ participate in a network of heterotrimeric G-protein signaling pathways controlling the release of synaptic vesicles and/or dense-core vesicles (DCVs). At least four heterotrimeric G-proteins (Galphaq, Galpha12, Galphao, and Galphas) act within the motorneurons to control the activity of the NMJ. The Galphaq, Galpha12, and Galphao pathways converge to control production and destruction of the lipid-bound second messenger diacylglycerol (DAG) at sites of neurotransmitter release. DAG acts via at least two effectors, MUNC13 and PKC, to control the release of both neurotransmitters and neuropeptides from motorneurons. The Galphas pathway converges with the other three heterotrimeric G-protein pathways downstream of DAG to regulate neuropeptide release. Released neurotransmitters and neuropeptides then act to control contraction of the body-wall muscles to control locomotion. The lipids and proteins involved in these networks are conserved between C. elegans and mammals. Thus, the C. elegans NMJ acts as a model synapse to understand how neuronal activity in the human brain is regulated.
Collapse
Affiliation(s)
- Borja Perez-Mansilla
- MRC Cell Biology Unit, MRC Laboratory for Molecular Cell Biology and Department of Neurobiology, Physiology and Pharmacology, University College London, London, United Kingdom
| | - Stephen Nurrish
- MRC Cell Biology Unit, MRC Laboratory for Molecular Cell Biology and Department of Neurobiology, Physiology and Pharmacology, University College London, London, United Kingdom
| |
Collapse
|
237
|
Abstract
Information processing in the nervous system relies on properly localized and organized synaptic structures at the correct locations. The formation of synapses is a long and intricate process involving multiple interrelated steps. Decades of research have identified a large number of molecular components of the presynaptic compartment. In addition to neurotransmitter-containing synaptic vesicles, presynaptic terminals are defined by cytoskeletal and membrane specializations that allow highly regulated exo- and endocytosis of synaptic vesicles and that maintain precise registration with postsynaptic targets. Functional studies at multiple levels have revealed complex interactions between the transport of vesicular intermediates, the presynaptic cytoskeleton, growth cone navigation, and synaptic targets. With the advent of finer anatomical, physiological, and molecular tools, great insights have been gained toward the mechanistic dissection of functionally redundant processes controlling the specificity and dynamics of synapses. This review highlights the recent findings pertaining to the cellular and molecular regulation of presynaptic differentiation.
Collapse
Affiliation(s)
- Yishi Jin
- Division of Biological Sciences, Section of Neurobiology, Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093, USA.
| | | |
Collapse
|
238
|
Modulation of SK channel trafficking by beta adrenoceptors enhances excitatory synaptic transmission and plasticity in the amygdala. J Neurosci 2008; 28:10803-13. [PMID: 18945888 DOI: 10.1523/jneurosci.1796-08.2008] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Emotionally arousing events are particularly well remembered. This effect is known to result from the release of stress hormones and activation of beta adrenoceptors in the amygdala. However, the underlying cellular mechanisms are not understood. Small conductance calcium-activated potassium (SK) channels are present at glutamatergic synapses where they limit synaptic transmission and plasticity. Here, we show that beta adrenoceptor activation regulates synaptic SK channels in lateral amygdala pyramidal neurons, through activation of protein kinase A. We show that SK channels are constitutively recycled from the postsynaptic membrane and that activation of beta adrenoceptors removes SK channels from excitatory synapses. This results in enhanced synaptic transmission and plasticity. Our findings demonstrate a novel mechanism by which beta adrenoceptors control synaptic transmission and plasticity, through regulation of SK channel trafficking, and suggest that modulation of synaptic SK channels may contribute to beta adrenoceptor-mediated potentiation of emotional memories.
Collapse
|
239
|
Schnizler MK, Schnizler K, Zha XM, Hall DD, Wemmie JA, Hell JW, Welsh MJ. The cytoskeletal protein alpha-actinin regulates acid-sensing ion channel 1a through a C-terminal interaction. J Biol Chem 2008; 284:2697-2705. [PMID: 19028690 PMCID: PMC2631967 DOI: 10.1074/jbc.m805110200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The acid-sensing ion channel 1a (ASIC1a) is widely expressed in central and
peripheral neurons where it generates transient cation currents when
extracellular pH falls. ASIC1a confers pH-dependent modulation on postsynaptic
dendritic spines and has critical effects in neurological diseases associated
with a reduced pH. However, knowledge of the proteins that interact with
ASIC1a and influence its function is limited. Here, we show that
α-actinin, which links membrane proteins to the actin cytoskeleton,
associates with ASIC1a in brain and in cultured cells. The interaction
depended on an α-actinin-binding site in the ASIC1a C terminus that was
specific for ASIC1a versus other ASICs and for α-actinin-1 and
-4. Co-expressing α-actinin-4 altered ASIC1a current density, pH
sensitivity, desensitization rate, and recovery from desensitization.
Moreover, reducing α-actinin expression altered acid-activated currents
in hippocampal neurons. These findings suggest that α-actinins may link
ASIC1a to a macromolecular complex in the postsynaptic membrane where it
regulates ASIC1a activity.
Collapse
Affiliation(s)
- Mikael K Schnizler
- Howard Hughes Medical Institute, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242; Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Katrin Schnizler
- Department of Pharmacology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Xiang-Ming Zha
- Howard Hughes Medical Institute, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242; Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Duane D Hall
- Department of Pharmacology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - John A Wemmie
- Department of Psychiatry, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242; Department of Veterans Affairs Medical Center, Iowa City, Iowa 52242
| | - Johannes W Hell
- Department of Pharmacology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242
| | - Michael J Welsh
- Howard Hughes Medical Institute, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242; Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242; Departments of Molecular Physiology and Biophysics, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242.
| |
Collapse
|
240
|
Mantzur L, Joels G, Lamprecht R. Actin polymerization in lateral amygdala is essential for fear memory formation. Neurobiol Learn Mem 2008; 91:85-8. [PMID: 18812227 DOI: 10.1016/j.nlm.2008.09.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2008] [Revised: 08/28/2008] [Accepted: 09/04/2008] [Indexed: 11/18/2022]
Abstract
Actin polymerization is involved in key neuronal functions such as intracellular trafficking and morphogenesis. In this study, we examined the role of actin polymerization in lateral amygdala (LA) in fear conditioning memory formation. Microinfusion of cytochalasin D, an actin polymerization inhibitor, into rat LA immediately before fear conditioning training impaired the formation of long-term fear memory (LTM) but not short-term fear memory (STM). Microinfusion of cytochalasin D into rat LA immediately after fear conditioning impaired LTM. Cytochalasin D had no effect on fear conditioning memory retrieval when injected immediately before LTM test. These results show that actin cytoskeleton rearrangement is essential for fear memory consolidation.
Collapse
Affiliation(s)
- Lilach Mantzur
- Department of Neurobiology and Ethology, Faculty of Science and Science Education, University of Haifa, Haifa, Israel
| | | | | |
Collapse
|
241
|
The actin-binding protein Abp1 controls dendritic spine morphology and is important for spine head and synapse formation. J Neurosci 2008; 28:10031-44. [PMID: 18829961 DOI: 10.1523/jneurosci.0336-08.2008] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Polymerization and organization of actin into complex superstructures, including those found in dendritic spines, is indispensable for structure and function of neuronal networks. Here we show that the filamentous actin (F-actin)-binding protein 1 (Abp1), which controls Arp2/3 complex-mediated actin nucleation and binds to postsynaptic scaffold proteins of the ProSAP (proline-rich synapse-associated protein 1)/Shank family, has a profound impact on synaptic organization. Overexpression of the two Abp1 F-actin-binding domains increases the length of thin, filopodia-like and mushroom-type spines but dramatically reduces mushroom spine density, attributable to lack of the Abp1 Src homology 3 (SH3) domain. In contrast, overexpression of full-length Abp1 increases mushroom spine and synapse density. The SH3 domain alone has a dominant-negative effect on mushroom spines, whereas the density of filopodia and thin, immature spines remains unchanged. This suggests that both actin-binding and SH3 domain interactions are crucial for the role of Abp1 in spine maturation. Indeed, Abp1 knockdown significantly reduces mushroom spine and synapse density. Abp1 hereby works in close conjunction with ProSAP1/Shank2 and ProSAP2/Shank3, because Abp1 effects were suppressed by ProSAP2 RNA interference and the ProSAP/Shank-induced increase of spine head width is further promoted by Abp1 cooverexpression and reduced on Abp1 knockdown. Also, interfering with the formation of functional Abp1-ProSAP protein complexes prevents ProSAP-mediated spine head extension. Spine head extension furthermore depends on local Arp2/3 complex-mediated actin polymerization, which is controlled by Abp1 via the Arp2/3 complex activator N-WASP (neural Wiskott-Aldrich syndrome protein). Abp1 thus plays an important role in the formation and morphology control of synapses by making a required functional connection between postsynaptic density components and postsynaptic actin dynamics.
Collapse
|
242
|
Proteomic analysis reveals selective impediment of neuronal remodeling upon Borna disease virus infection. J Virol 2008; 82:12265-79. [PMID: 18829749 DOI: 10.1128/jvi.01615-08] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The neurotropic virus Borna disease virus (BDV) persists in the central nervous systems of a wide variety of vertebrates and causes behavioral disorders. BDV represents an intriguing example of a virus whose persistence in neurons leads to altered brain function in the absence of overt cytolysis and inflammation. The bases of BDV-induced behavioral impairment remain largely unknown. To better characterize the neuronal response to BDV infection, we compared the proteomes of primary cultures of cortical neurons with and without BDV infection. We used two-dimensional liquid chromatography fractionation, followed by protein identification by nanoliquid chromatography-tandem mass spectrometry. This analysis revealed distinct changes in proteins implicated in neurotransmission, neurogenesis, cytoskeleton dynamics, and the regulation of gene expression and chromatin remodeling. We also demonstrated the selective interference of BDV with processes related to the adaptative response of neurons, i.e., defects in proteins regulating synaptic function, global rigidification of the cytoskeleton network, and altered expression of transcriptional and translational repressors. Thus, this work provides a global view of the neuronal changes induced by BDV infection together with new clues to understand the mechanisms underlying the selective interference with neuronal plasticity and remodeling that characterizes BDV persistence.
Collapse
|
243
|
Zhou Z, Meng Y, Asrar S, Todorovski Z, Jia Z. A critical role of Rho-kinase ROCK2 in the regulation of spine and synaptic function. Neuropharmacology 2008; 56:81-9. [PMID: 18718479 DOI: 10.1016/j.neuropharm.2008.07.031] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Revised: 06/30/2008] [Accepted: 07/16/2008] [Indexed: 10/21/2022]
Abstract
The actin cytoskeleton is critically involved in the regulation of the dendritic spine and synaptic properties, but the molecular mechanisms underlying actin dynamics in neurons are poorly defined. We took genetic approaches to create and analyze knockout mice specifically lacking ROCK2, a protein kinase that directly interacts with and is activated by the Rho GTPases, the central mediator of actin reorganization. We demonstrated that while these knockout mice were normal in gross brain anatomy, they were impaired in both basal synaptic transmission and hippocampal long-term potentiation (LTP). Consistent with the electrophysiological deficits, the ROCK2 knockout neurons showed deficits in spine properties, synapse density, the actin cytoskeleton, and the actin-binding protein cofilin. These results indicate that ROCK2/cofilin signaling is critical in the regulation of neuronal actin, spine morphology and synaptic function.
Collapse
Affiliation(s)
- Zikai Zhou
- Neurosciences and Mental Health, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8
| | | | | | | | | |
Collapse
|
244
|
Asrar S, Meng Y, Zhou Z, Todorovski Z, Huang WW, Jia Z. Regulation of hippocampal long-term potentiation by p21-activated protein kinase 1 (PAK1). Neuropharmacology 2008; 56:73-80. [PMID: 18644395 DOI: 10.1016/j.neuropharm.2008.06.055] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Revised: 06/19/2008] [Accepted: 06/20/2008] [Indexed: 11/27/2022]
Abstract
The Rho family small GTPases are critically involved in the regulation of spine and synaptic properties, but the underlying mechanisms are poorly defined. We took genetic approaches to create and analyze knockout mice deficient in the expression of the protein kinase PAK1 that is directly associated with and activated by the Rho GTPases. We demonstrated that while these knockout mice were normal in both basal and presynaptic function, they were selectively impaired in long-term potentiation (LTP) at hippocampal CA1 synapses. Consistent with the electrophysiological deficits, the PAK1 knockout mice showed changes in the actin cytoskeleton and the actin binding protein cofilin. These results indicate that PAK1 is critical in hippocampal synaptic plasticity via regulating cofilin activity and the actin cytoskeleton.
Collapse
Affiliation(s)
- Suhail Asrar
- Neurosciences and Mental Health, The Hospital for Sick Children, 555 University Avenue, Toronto, ON M5G 1X8, Canada
| | | | | | | | | | | |
Collapse
|
245
|
O'Connor-Giles KM, Ho LL, Ganetzky B. Nervous wreck interacts with thickveins and the endocytic machinery to attenuate retrograde BMP signaling during synaptic growth. Neuron 2008; 58:507-18. [PMID: 18498733 DOI: 10.1016/j.neuron.2008.03.007] [Citation(s) in RCA: 123] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2007] [Revised: 01/28/2008] [Accepted: 03/10/2008] [Indexed: 11/17/2022]
Abstract
Regulation of synaptic growth is fundamental to the formation and plasticity of neural circuits. Here, we demonstrate that Nervous wreck (Nwk), a negative regulator of synaptic growth at Drosophila NMJs, interacts functionally and physically with components of the endocytic machinery, including dynamin and Dap160/intersectin, and negatively regulates retrograde BMP growth signaling through a direct interaction with the BMP receptor, thickveins. Synaptic overgrowth in nwk is sensitive to BMP signaling levels, and loss of Nwk facilitates BMP-induced overgrowth. Conversely, Nwk overexpression suppresses BMP-induced synaptic overgrowth. We observe analogous genetic interactions between dap160 and the BMP pathway, confirming that endocytosis regulates BMP signaling at NMJs. Finally, we demonstrate a correlation between synaptic growth and pMAD levels and show that Nwk regulates these levels. We propose that Nwk functions at the interface of endocytosis and BMP signaling to ensure proper synaptic growth by negatively regulating Tkv to set limits on this positive growth signal.
Collapse
|
246
|
Pražnikar ZJ, Kovačič L, Rowan EG, Romih R, Rusmini P, Poletti A, Križaj I, Pungerčar J. A presynaptically toxic secreted phospholipase A2 is internalized into motoneuron-like cells where it is rapidly translocated into the cytosol. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1783:1129-39. [DOI: 10.1016/j.bbamcr.2008.01.011] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2007] [Revised: 01/07/2008] [Accepted: 01/08/2008] [Indexed: 10/22/2022]
|
247
|
Koch I, Schwarz H, Beuchle D, Goellner B, Langegger M, Aberle H. Drosophila ankyrin 2 is required for synaptic stability. Neuron 2008; 58:210-22. [PMID: 18439406 DOI: 10.1016/j.neuron.2008.03.019] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2007] [Revised: 12/10/2007] [Accepted: 03/20/2008] [Indexed: 10/22/2022]
Abstract
Synaptic connections are stabilized through transsynaptic adhesion complexes that are anchored in the underlying cytoskeleton. The Drosophila neuromuscular junction (NMJs) serves as a model system to unravel genes required for the structural remodeling of synapses. In a mutagenesis screen for regulators of synaptic stability, we recovered mutations in Drosophila ankyrin 2 (ank2) affecting two giant Ank2 isoforms that are specifically expressed in the nervous system and associate with the presynaptic membrane cytoskeleton. ank2 mutant larvae show severe deficits in the stability of NMJs, resulting in a reduction in overall terminal size, withdrawal of synaptic boutons, and disassembly of presynaptic active zones. In addition, lack of Ank2 leads to disintegration of the synaptic microtubule cytoskeleton. Microtubules and microtubule-associated proteins fail to extend into distant boutons. Interestingly, Ank2 functions downstream of spectrin in the anchorage of synaptic microtubules, providing the cytoskeletal scaffold that is essential for synaptic stability.
Collapse
Affiliation(s)
- Iris Koch
- Max-Planck-Institute for Developmental Biology, Department III/Genetics, Spemannstrasse 35, 72076 Tübingen, Germany
| | | | | | | | | | | |
Collapse
|
248
|
Cingolani LA, Goda Y. Actin in action: the interplay between the actin cytoskeleton and synaptic efficacy. Nat Rev Neurosci 2008; 9:344-56. [PMID: 18425089 DOI: 10.1038/nrn2373] [Citation(s) in RCA: 586] [Impact Index Per Article: 36.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Synapse regulation exploits the capacity of actin to function as a stable structural component or as a dynamic filament. Beyond its well-appreciated role in eliciting visible morphological changes at the synapse, the emerging picture points to an active contribution of actin to the modulation of the efficacy of pre- and postsynaptic terminals. Moreover, by engaging distinct pools of actin and divergent signalling pathways, actin-dependent morphological plasticity could be uncoupled from modulation of synaptic strength. The aim of this Review is to highlight some of the recent progress in elucidating the role of the actin cytoskeleton in synaptic function.
Collapse
Affiliation(s)
- Lorenzo A Cingolani
- MRC Laboratory for Molecular Cell Biology and MRC Cell Biology Unit, University College London, Gower Street, London, WC1E 6BT, UK
| | | |
Collapse
|
249
|
Perturbation of syndapin/PACSIN impairs synaptic vesicle recycling evoked by intense stimulation. J Neurosci 2008; 28:3925-33. [PMID: 18400891 DOI: 10.1523/jneurosci.1754-07.2008] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synaptic vesicle recycling has been proposed to depend on proteins which coordinate membrane and cytoskeletal dynamics. Here, we examine the role of the dynamin- and N-WASP (neural Wiskott-Aldrich syndrome protein)-binding protein syndapin/PACSIN at the lamprey reticulospinal synapse. We find that presynaptic microinjection of syndapin antibodies inhibits vesicle recycling evoked by intense (5 Hz or more), but not by light (0.2 Hz) stimulation. This contrasts with the inhibition at light stimulation induced by perturbation of amphiphysin (Shupliakov et al., 1997). Inhibition by syndapin antibodies was associated with massive accumulation of membranous cisternae and invaginations around release sites, but not of coated pits at the plasma membrane. Cisternae contained vesicle membrane, as shown by vesicle-associated membrane protein 2 (VAMP2)/synaptobrevin 2 immunolabeling. Similar effects were observed when syndapin was perturbed before onset of massive endocytosis induced by preceding intense stimulation. Selective perturbation of the Src homology 3 domain interactions of syndapin was sufficient to induce vesicle depletion and accumulation of cisternae. Our data show an involvement of syndapin in synaptic vesicle recycling evoked by intense stimulation. We propose that syndapin is required to stabilize the plasma membrane and/or facilitate bulk endocytosis at high release rates.
Collapse
|
250
|
Saneyoshi T, Wayman G, Fortin D, Davare M, Hoshi N, Nozaki N, Natsume T, Soderling TR. Activity-dependent synaptogenesis: regulation by a CaM-kinase kinase/CaM-kinase I/betaPIX signaling complex. Neuron 2008; 57:94-107. [PMID: 18184567 DOI: 10.1016/j.neuron.2007.11.016] [Citation(s) in RCA: 182] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2007] [Revised: 08/17/2007] [Accepted: 11/21/2007] [Indexed: 01/04/2023]
Abstract
Neuronal activity augments maturation of mushroom-shaped spines to form excitatory synapses, thereby strengthening synaptic transmission. We have delineated a Ca(2+)-signaling pathway downstream of the NMDA receptor that stimulates calmodulin-dependent kinase kinase (CaMKK) and CaMKI to promote formation of spines and synapses in hippocampal neurons. CaMKK and CaMKI form a multiprotein signaling complex with the guanine nucleotide exchange factor (GEF) betaPIX and GIT1 that is localized in spines. CaMKI-mediated phosphorylation of Ser516 in betaPIX enhances its GEF activity, resulting in activation of Rac1, an established enhancer of spinogenesis. Suppression of CaMKK or CaMKI by pharmacological inhibitors, dominant-negative (dn) constructs and siRNAs, as well as expression of the betaPIX Ser516Ala mutant, decreases spine formation and mEPSC frequency. Constitutively-active Pak1, a downstream effector of Rac1, rescues spine inhibition by dnCaMKI or betaPIX S516A. This activity-dependent signaling pathway can promote synapse formation during neuronal development and in structural plasticity.
Collapse
Affiliation(s)
- Takeo Saneyoshi
- Vollum Institute, Oregon Health and Sciences University, Portland, OR 97239, USA
| | | | | | | | | | | | | | | |
Collapse
|