1
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Coscia SM, Moore AS, Wong YC, Holzbaur ELF. Mitochondrially-associated actin waves maintain organelle homeostasis and equitable inheritance. Curr Opin Cell Biol 2024; 88:102364. [PMID: 38692079 PMCID: PMC11179979 DOI: 10.1016/j.ceb.2024.102364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Revised: 04/02/2024] [Accepted: 04/08/2024] [Indexed: 05/03/2024]
Abstract
First identified in dividing cells as revolving clusters of actin filaments, these are now understood as mitochondrially-associated actin waves that are active throughout the cell cycle. These waves are formed from the polymerization of actin onto a subset of mitochondria. Within minutes, this F-actin depolymerizes while newly formed actin filaments assemble onto neighboring mitochondria. In interphase, actin waves locally fragment the mitochondrial network, enhancing mitochondrial content mixing to maintain organelle homeostasis. In dividing cells actin waves spatially mix mitochondria in the mother cell to ensure equitable partitioning of these organelles between daughter cells. Progress has been made in understanding the consequences of actin cycling as well as the underlying molecular mechanisms, but many questions remain, and here we review these elements. Also, we draw parallels between mitochondrially-associated actin cycling and cortical actin waves. These dynamic systems highlight the remarkable plasticity of the actin cytoskeleton.
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Affiliation(s)
- Stephen M Coscia
- Department of Physiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA; Pennsylvania Muscle Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA; Cell and Molecular Biology Graduate Group, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA. https://twitter.com/StephenMCoscia
| | - Andrew S Moore
- Howard Hughes Medical Institute, Janelia Research Campus, Ashburn, VA, USA
| | - Yvette C Wong
- Department of Neurology, Northwestern University, Feinberg School of Medicine, Chicago, IL, USA
| | - Erika L F Holzbaur
- Department of Physiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA; Pennsylvania Muscle Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA; Cell and Molecular Biology Graduate Group, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA, USA.
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2
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Gallo G. The Axonal Actin Filament Cytoskeleton: Structure, Function, and Relevance to Injury and Degeneration. Mol Neurobiol 2024:10.1007/s12035-023-03879-7. [PMID: 38216856 DOI: 10.1007/s12035-023-03879-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Accepted: 12/13/2023] [Indexed: 01/14/2024]
Abstract
Early investigations of the neuronal actin filament cytoskeleton gave rise to the notion that, although growth cones exhibit high levels of actin filaments, the axon shaft exhibits low levels of actin filaments. With the development of new tools and imaging techniques, the axonal actin filament cytoskeleton has undergone a renaissance and is now an active field of research. This article reviews the current state of knowledge about the actin cytoskeleton of the axon shaft. The best understood forms of actin filament organization along axons are axonal actin patches and a submembranous system of rings that endow the axon with protrusive competency and structural integrity, respectively. Additional forms of actin filament organization along the axon have also been described and their roles are being elucidated. Extracellular signals regulate the axonal actin filament cytoskeleton and our understanding of the signaling mechanisms involved is being elaborated. Finally, recent years have seen advances in our perspective on how the axonal actin cytoskeleton is impacted by, and contributes to, axon injury and degeneration. The work to date has opened new venues and future research will undoubtedly continue to provide a richer understanding of the axonal actin filament cytoskeleton.
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Affiliation(s)
- Gianluca Gallo
- Department of Neural Sciences, Shriners Pediatric Research Center, Lewis Katz School of Medicine at Temple University, 3500 North Broad St, Philadelphia, PA, 19140, USA.
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3
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Riedl M, Sixt M. The excitable nature of polymerizing actin and the Belousov-Zhabotinsky reaction. Front Cell Dev Biol 2023; 11:1287420. [PMID: 38020899 PMCID: PMC10643615 DOI: 10.3389/fcell.2023.1287420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 10/16/2023] [Indexed: 12/01/2023] Open
Abstract
The intricate regulatory processes behind actin polymerization play a crucial role in cellular biology, including essential mechanisms such as cell migration or cell division. However, the self-organizing principles governing actin polymerization are still poorly understood. In this perspective article, we compare the Belousov-Zhabotinsky (BZ) reaction, a classic and well understood chemical oscillator known for its self-organizing spatiotemporal dynamics, with the excitable dynamics of polymerizing actin. While the BZ reaction originates from the domain of inorganic chemistry, it shares remarkable similarities with actin polymerization, including the characteristic propagating waves, which are influenced by geometry and external fields, and the emergent collective behavior. Starting with a general description of emerging patterns, we elaborate on single droplets or cell-level dynamics, the influence of geometric confinements and conclude with collective interactions. Comparing these two systems sheds light on the universal nature of self-organization principles in both living and inanimate systems.
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Affiliation(s)
- Michael Riedl
- Institute of Science and Technology Austria (ISTA), Klosterneuburg, Austria
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4
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Beta C, Edelstein-Keshet L, Gov N, Yochelis A. From actin waves to mechanism and back: How theory aids biological understanding. eLife 2023; 12:e87181. [PMID: 37428017 DOI: 10.7554/elife.87181] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Accepted: 06/01/2023] [Indexed: 07/11/2023] Open
Abstract
Actin dynamics in cell motility, division, and phagocytosis is regulated by complex factors with multiple feedback loops, often leading to emergent dynamic patterns in the form of propagating waves of actin polymerization activity that are poorly understood. Many in the actin wave community have attempted to discern the underlying mechanisms using experiments and/or mathematical models and theory. Here, we survey methods and hypotheses for actin waves based on signaling networks, mechano-chemical effects, and transport characteristics, with examples drawn from Dictyostelium discoideum, human neutrophils, Caenorhabditis elegans, and Xenopus laevis oocytes. While experimentalists focus on the details of molecular components, theorists pose a central question of universality: Are there generic, model-independent, underlying principles, or just boundless cell-specific details? We argue that mathematical methods are equally important for understanding the emergence, evolution, and persistence of actin waves and conclude with a few challenges for future studies.
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Affiliation(s)
- Carsten Beta
- Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany
| | | | - Nir Gov
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Arik Yochelis
- Swiss Institute for Dryland Environmental and Energy Research, Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, Midreshet Ben-Gurion, Israel
- Department of Physics, Ben-Gurion University of the Negev, Be'er Sheva, Israel
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5
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Villard C. Spatial confinement: A spur for axonal growth. Semin Cell Dev Biol 2023; 140:54-62. [PMID: 35927121 DOI: 10.1016/j.semcdb.2022.07.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Revised: 07/16/2022] [Accepted: 07/16/2022] [Indexed: 01/28/2023]
Abstract
The concept of spatial confinement is the basis of cell positioning and guidance in in vitro studies. In vivo, it reflects many situations faced during embryonic development. In vitro, spatial confinement of neurons is achieved using different technological approaches: adhesive patterning, topographical structuring, microfluidics and the use of hydrogels. The notion of chemical or physical frontiers is particularly central to the behaviors of growth cones and neuronal processes under confinement. They encompass phenomena of cell spreading, boundary crossing, and path finding on surfaces with different adhesive properties. However, the most universal phenomenon related to confinement, regardless of how it is implemented, is the acceleration of neuronal growth. Overall, a bi-directional causal link emerges between the shape of the growth cone and neuronal elongation dynamics, both in vivo and in vitro. The sensing of adhesion discontinuities by filopodia and the subsequent spatial redistribution and size adaptation of these actin-rich filaments seem critical for the growth rate in conditions in which adhesive contacts and actin-associated clutching forces dominate. On the other hand, the involvement of microtubules, specifically demonstrated in 3D hydrogel environments and leading to ameboid-like locomotion, could be relevant in a wider range of growth situations. This review brings together a literature collected in distinct scientific fields such as development, mechanobiology and bioengineering that highlight the consequences of confinement and raise new questions at different cellular scales. Its ambition is to stimulate new research that could lead to a better understanding of what gives neurons their ability to establish and regulate their exceptional size.
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Affiliation(s)
- Catherine Villard
- Laboratoire Interdisciplinaire des Energies de Demain (LIED), Université Paris Cité, UMR 8236 CNRS, F-75013 Paris, France.
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6
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Ghose A, Pullarkat P. The role of mechanics in axonal stability and development. Semin Cell Dev Biol 2023; 140:22-34. [PMID: 35786351 PMCID: PMC7615100 DOI: 10.1016/j.semcdb.2022.06.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Revised: 06/05/2022] [Accepted: 06/13/2022] [Indexed: 01/28/2023]
Abstract
Much of the focus of neuronal cell biology has been devoted to growth cone guidance, synaptogenesis, synaptic activity, plasticity, etc. The axonal shaft too has received much attention, mainly for its astounding ability to transmit action potentials and the transport of material over long distances. For these functions, the axonal cytoskeleton and membrane have been often assumed to play static structural roles. Recent experiments have changed this view by revealing an ultrastructure much richer in features than previously perceived and one that seems to be maintained at a dynamic steady state. The role of mechanics in this is only beginning to be broadly appreciated and appears to involve passive and active modes of coupling different biopolymer filaments, filament turnover dynamics and membrane biophysics. Axons, being unique cellular processes in terms of high aspect ratios and often extreme lengths, also exhibit unique passive mechanical properties that might have evolved to stabilize them under mechanical stress. In this review, we summarize the experiments that have exposed some of these features. It is our view that axonal mechanics deserves much more attention not only due to its significance in the development and maintenance of the nervous system but also due to the susceptibility of axons to injury and neurodegeneration.
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Affiliation(s)
- Aurnab Ghose
- Indian Institute of Science Education and Research, Pune 411 008, India.
| | - Pramod Pullarkat
- Raman Research Institute, C. V. Raman Avenue, Bengaluru 560 080, India.
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7
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Gu X, Jia C, Wang J. Advances in Understanding the Molecular Mechanisms of Neuronal Polarity. Mol Neurobiol 2023; 60:2851-2870. [PMID: 36738353 DOI: 10.1007/s12035-023-03242-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 01/22/2023] [Indexed: 02/05/2023]
Abstract
The establishment and maintenance of neuronal polarity are important for neural development and function. Abnormal neuronal polarity establishment commonly leads to a variety of neurodevelopmental disorders. Over the past three decades, with the continuous development and improvement of biological research methods and techniques, we have made tremendous progress in the understanding of the molecular mechanisms of neuronal polarity establishment. The activity of positive and negative feedback signals and actin waves are both essential in this process. They drive the directional transport and aggregation of key molecules of neuronal polarity, promote the spatiotemporal regulation of ordered and coordinated interactions of actin filaments and microtubules, stimulate the specialization and growth of axons, and inhibit the formation of multiple axons. In this review, we focus on recent advances in these areas, in particular the important findings about neuronal polarity in two classical models, in vitro primary hippocampal/cortical neurons and in vivo cortical pyramidal neurons, and discuss our current understanding of neuronal polarity..
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Affiliation(s)
- Xi Gu
- Fujian Key Laboratory for Translational Research in Cancer and Neurodegenerative Diseases, Institute for Translational Medicine, School of Basic Medical Sciences, Fujian Medical University, Fuzhou, China.
| | - Chunhong Jia
- Department of Pediatrics, The Third Affiliated Hospital of Guangzhou Medical University, Guangzhou, China.
| | - Junhao Wang
- Fujian Key Laboratory for Translational Research in Cancer and Neurodegenerative Diseases, Institute for Translational Medicine, School of Basic Medical Sciences, Fujian Medical University, Fuzhou, China
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8
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Bamburg JR, Minamide LS, Wiggan O, Tahtamouni LH, Kuhn TB. Cofilin and Actin Dynamics: Multiple Modes of Regulation and Their Impacts in Neuronal Development and Degeneration. Cells 2021; 10:cells10102726. [PMID: 34685706 PMCID: PMC8534876 DOI: 10.3390/cells10102726] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Revised: 10/06/2021] [Accepted: 10/07/2021] [Indexed: 02/06/2023] Open
Abstract
Proteins of the actin depolymerizing factor (ADF)/cofilin family are ubiquitous among eukaryotes and are essential regulators of actin dynamics and function. Mammalian neurons express cofilin-1 as the major isoform, but ADF and cofilin-2 are also expressed. All isoforms bind preferentially and cooperatively along ADP-subunits in F-actin, affecting the filament helical rotation, and when either alone or when enhanced by other proteins, promotes filament severing and subunit turnover. Although self-regulating cofilin-mediated actin dynamics can drive motility without post-translational regulation, cells utilize many mechanisms to locally control cofilin, including cooperation/competition with other proteins. Newly identified post-translational modifications function with or are independent from the well-established phosphorylation of serine 3 and provide unexplored avenues for isoform specific regulation. Cofilin modulates actin transport and function in the nucleus as well as actin organization associated with mitochondrial fission and mitophagy. Under neuronal stress conditions, cofilin-saturated F-actin fragments can undergo oxidative cross-linking and bundle together to form cofilin-actin rods. Rods form in abundance within neurons around brain ischemic lesions and can be rapidly induced in neurites of most hippocampal and cortical neurons through energy depletion or glutamate-induced excitotoxicity. In ~20% of rodent hippocampal neurons, rods form more slowly in a receptor-mediated process triggered by factors intimately connected to disease-related dementias, e.g., amyloid-β in Alzheimer’s disease. This rod-inducing pathway requires a cellular prion protein, NADPH oxidase, and G-protein coupled receptors, e.g., CXCR4 and CCR5. Here, we will review many aspects of cofilin regulation and its contribution to synaptic loss and pathology of neurodegenerative diseases.
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Affiliation(s)
- James R. Bamburg
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523, USA; (L.S.M.); (O.W.); (L.H.T.); (T.B.K.)
- Correspondence: ; Tel.: +1-970-988-9120; Fax: +1-970-491-0494
| | - Laurie S. Minamide
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523, USA; (L.S.M.); (O.W.); (L.H.T.); (T.B.K.)
| | - O’Neil Wiggan
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523, USA; (L.S.M.); (O.W.); (L.H.T.); (T.B.K.)
| | - Lubna H. Tahtamouni
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523, USA; (L.S.M.); (O.W.); (L.H.T.); (T.B.K.)
- Department of Biology and Biotechnology, The Hashemite University, Zarqa 13115, Jordan
| | - Thomas B. Kuhn
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523, USA; (L.S.M.); (O.W.); (L.H.T.); (T.B.K.)
- Department of Chemistry and Biochemistry, University of Alaska, Fairbanks, AK 99775, USA
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9
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Weaver CJ, Poulain FE. From whole organism to ultrastructure: progress in axonal imaging for decoding circuit development. Development 2021; 148:271122. [PMID: 34328171 DOI: 10.1242/dev.199717] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Since the pioneering work of Ramón y Cajal, scientists have sought to unravel the complexities of axon development underlying neural circuit formation. Micrometer-scale axonal growth cones navigate to targets that are often centimeters away. To reach their targets, growth cones react to dynamic environmental cues that change in the order of seconds to days. Proper axon growth and guidance are essential to circuit formation, and progress in imaging has been integral to studying these processes. In particular, advances in high- and super-resolution microscopy provide the spatial and temporal resolution required for studying developing axons. In this Review, we describe how improved microscopy has revolutionized our understanding of axonal development. We discuss how novel technologies, specifically light-sheet and super-resolution microscopy, led to new discoveries at the cellular scale by imaging axon outgrowth and circuit wiring with extreme precision. We next examine how advanced microscopy broadened our understanding of the subcellular dynamics driving axon growth and guidance. We finally assess the current challenges that the field of axonal biology still faces for imaging axons, and examine how future technology could meet these needs.
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Affiliation(s)
- Cory J Weaver
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Fabienne E Poulain
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
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10
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Braïni C, Bugnicourt G, Villard C. Neuronal growth from a volume perspective. Phys Biol 2021; 18:016007. [PMID: 33147573 DOI: 10.1088/1478-3975/abc79c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Microfluidic-based fluorescent exclusion method allows to tackle the issue of neuronal growth from a volume perspective. Based on this technology, we studied the two main actin-rich structures accompanying the early stages of neuron development, i.e. growth cones, located at the tip of growing neuronal processes, and propagative actin waves. Our work reveals that growth cones tend to loose volume during their forward motion, as do actin waves during their journey from the cell body to the tip of neuronal processes, before the total transfer of their remaining volume to the growth cone. Actin waves seem thus to supply material to increasingly distant growth cones as neurons develop. In addition, our work may suggest the existence of a membrane recycling phenomena associated to actin waves as a pulsatile anterograde source of material and by a continuous retrograde transport.
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Affiliation(s)
- Céline Braïni
- Physico-Chimie Curie, CNRS UMR 168, Université PSL, Sorbonne Université, Paris, France
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11
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Abstract
While the organization of inanimate systems such as gases or liquids is predominantly thermodynamically driven—a mixture of two gases will tend to mix until they reach equilibrium—biological systems frequently exhibit organization that is far from a well-mixed equilibrium. The anisotropies displayed by cells are evident in some of the dynamic processes that constitute life including cell development, movement, and division. These anisotropies operate at different length-scales, from the meso- to the nanoscale, and are proposed to reflect self-organization, a characteristic of living systems that is becoming accessible to reconstitution from purified components, and thus a more thorough understanding. Here, some examples of self-organization underlying cellular anisotropies at the cellular level are reviewed, with an emphasis on Rho-family GTPases operating at the plasma membrane. Given the technical challenges of studying these dynamic proteins, some of the successful approaches that are being employed to study their self-organization will also be considered.
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Affiliation(s)
- Derek McCusker
- Dynamics of Cell Growth and Division, European Institute of Chemistry and Biology, F-33607 Bordeaux, France; Institute of Biochemistry and Cellular Genetics, UMR 5095, University of Bordeaux and Centre National de la Recherche Scientifique, F-33000 Bordeaux, France
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12
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Beta C, Gov NS, Yochelis A. Why a Large-Scale Mode Can Be Essential for Understanding Intracellular Actin Waves. Cells 2020; 9:cells9061533. [PMID: 32585983 PMCID: PMC7349605 DOI: 10.3390/cells9061533] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 06/16/2020] [Accepted: 06/18/2020] [Indexed: 01/18/2023] Open
Abstract
During the last decade, intracellular actin waves have attracted much attention due to their essential role in various cellular functions, ranging from motility to cytokinesis. Experimental methods have advanced significantly and can capture the dynamics of actin waves over a large range of spatio-temporal scales. However, the corresponding coarse-grained theory mostly avoids the full complexity of this multi-scale phenomenon. In this perspective, we focus on a minimal continuum model of activator-inhibitor type and highlight the qualitative role of mass conservation, which is typically overlooked. Specifically, our interest is to connect between the mathematical mechanisms of pattern formation in the presence of a large-scale mode, due to mass conservation, and distinct behaviors of actin waves.
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Affiliation(s)
- Carsten Beta
- Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany;
| | - Nir S. Gov
- Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 76100, Israel;
| | - Arik Yochelis
- Department of Solar Energy and Environmental Physics, Blaustein Institutes for Desert Research (BIDR), Ben-Gurion University of the Negev, Sede Boqer Campus, Midreshet Ben-Gurion 8499000, Israel
- Department of Physics, Ben-Gurion University of the Negev, Be’er Sheva 8410501, Israel
- Correspondence:
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13
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Muñoz-Lasso DC, Mollá B, Calap-Quintana P, García-Giménez JL, Pallardo FV, Palau F, Gonzalez-Cabo P. Cofilin dysregulation alters actin turnover in frataxin-deficient neurons. Sci Rep 2020; 10:5207. [PMID: 32251310 PMCID: PMC7090085 DOI: 10.1038/s41598-020-62050-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 03/04/2020] [Indexed: 01/04/2023] Open
Abstract
Abnormalities in actin cytoskeleton have been linked to Friedreich's ataxia (FRDA), an inherited peripheral neuropathy characterised by an early loss of neurons in dorsal root ganglia (DRG) among other clinical symptoms. Despite all efforts to date, we still do not fully understand the molecular events that contribute to the lack of sensory neurons in FRDA. We studied the adult neuronal growth cone (GC) at the cellular and molecular level to decipher the connection between frataxin and actin cytoskeleton in DRG neurons of the well-characterised YG8R Friedreich's ataxia mouse model. Immunofluorescence studies in primary cultures of DRG from YG8R mice showed neurons with fewer and smaller GCs than controls, associated with an inhibition of neurite growth. In frataxin-deficient neurons, we also observed an increase in the filamentous (F)-actin/monomeric (G)-actin ratio (F/G-actin ratio) in axons and GCs linked to dysregulation of two crucial modulators of filamentous actin turnover, cofilin-1 and the actin-related protein (ARP) 2/3 complex. We show how the activation of cofilin is due to the increase in chronophin (CIN), a cofilin-activating phosphatase. Thus cofilin emerges, for the first time, as a link between frataxin deficiency and actin cytoskeleton alterations.
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Affiliation(s)
- Diana C Muñoz-Lasso
- CIBER de Enfermedades Raras (CIBERER), Valencia, Spain
- Department of Physiology, Faculty of Medicine and Dentistry. University of Valencia-INCLIVA, Valencia, 46010, Spain
- Associated Unit for Rare Diseases INCLIVA-CIPF, Valencia, Spain
| | - Belén Mollá
- CIBER de Enfermedades Raras (CIBERER), Valencia, Spain
- Instituto de Biomedicina de Valencia (IBV), CSIC, Valencia, 46010, Spain
| | - Pablo Calap-Quintana
- CIBER de Enfermedades Raras (CIBERER), Valencia, Spain
- Department of Physiology, Faculty of Medicine and Dentistry. University of Valencia-INCLIVA, Valencia, 46010, Spain
- Associated Unit for Rare Diseases INCLIVA-CIPF, Valencia, Spain
| | - José Luis García-Giménez
- CIBER de Enfermedades Raras (CIBERER), Valencia, Spain
- Department of Physiology, Faculty of Medicine and Dentistry. University of Valencia-INCLIVA, Valencia, 46010, Spain
- Associated Unit for Rare Diseases INCLIVA-CIPF, Valencia, Spain
| | - Federico V Pallardo
- CIBER de Enfermedades Raras (CIBERER), Valencia, Spain
- Department of Physiology, Faculty of Medicine and Dentistry. University of Valencia-INCLIVA, Valencia, 46010, Spain
- Associated Unit for Rare Diseases INCLIVA-CIPF, Valencia, Spain
| | - Francesc Palau
- CIBER de Enfermedades Raras (CIBERER), Valencia, Spain
- Institut de Recerca Sant Joan de Déu and Department of Genetic & Molecular Medicine and IPER, Hospital Sant Joan de Déu, Barcelona, 08950, Spain
- Hospital Clínic and Division of Pediatrics, University of Barcelona School of Medicine and Health Sciences, Barcelona, Spain
| | - Pilar Gonzalez-Cabo
- CIBER de Enfermedades Raras (CIBERER), Valencia, Spain.
- Department of Physiology, Faculty of Medicine and Dentistry. University of Valencia-INCLIVA, Valencia, 46010, Spain.
- Associated Unit for Rare Diseases INCLIVA-CIPF, Valencia, Spain.
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14
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Meka DP, Scharrenberg R, Calderon de Anda F. Emerging roles of the centrosome in neuronal development. Cytoskeleton (Hoboken) 2020; 77:84-96. [DOI: 10.1002/cm.21593] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Revised: 12/16/2019] [Accepted: 01/04/2020] [Indexed: 12/24/2022]
Affiliation(s)
- Durga Praveen Meka
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH)University Medical Center Hamburg‐Eppendorf Hamburg Germany
| | - Robin Scharrenberg
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH)University Medical Center Hamburg‐Eppendorf Hamburg Germany
| | - Froylan Calderon de Anda
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH)University Medical Center Hamburg‐Eppendorf Hamburg Germany
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15
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Venkatesh K, Mathew A, Koushika SP. Role of actin in organelle trafficking in neurons. Cytoskeleton (Hoboken) 2020; 77:97-109. [DOI: 10.1002/cm.21580] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Revised: 10/14/2019] [Accepted: 11/05/2019] [Indexed: 01/29/2023]
Affiliation(s)
- Keertana Venkatesh
- Department of Biological SciencesTata Institute of Fundamental Research Mumbai India
| | - Amal Mathew
- Department of Biological SciencesTata Institute of Fundamental Research Mumbai India
| | - Sandhya P. Koushika
- Department of Biological SciencesTata Institute of Fundamental Research Mumbai India
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16
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Much More Than a Scaffold: Cytoskeletal Proteins in Neurological Disorders. Cells 2020; 9:cells9020358. [PMID: 32033020 PMCID: PMC7072452 DOI: 10.3390/cells9020358] [Citation(s) in RCA: 63] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 01/27/2020] [Accepted: 01/29/2020] [Indexed: 02/08/2023] Open
Abstract
Recent observations related to the structure of the cytoskeleton in neurons and novel cytoskeletal abnormalities involved in the pathophysiology of some neurological diseases are changing our view on the function of the cytoskeletal proteins in the nervous system. These efforts allow a better understanding of the molecular mechanisms underlying neurological diseases and allow us to see beyond our current knowledge for the development of new treatments. The neuronal cytoskeleton can be described as an organelle formed by the three-dimensional lattice of the three main families of filaments: actin filaments, microtubules, and neurofilaments. This organelle organizes well-defined structures within neurons (cell bodies and axons), which allow their proper development and function through life. Here, we will provide an overview of both the basic and novel concepts related to those cytoskeletal proteins, which are emerging as potential targets in the study of the pathophysiological mechanisms underlying neurological disorders.
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17
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Locally Activating TrkB Receptor Generates Actin Waves and Specifies Axonal Fate. Cell Chem Biol 2019; 26:1652-1663.e4. [PMID: 31678045 DOI: 10.1016/j.chembiol.2019.10.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 08/26/2019] [Accepted: 10/10/2019] [Indexed: 01/15/2023]
Abstract
Actin waves are filamentous actin (F-actin)-rich structures that initiate in the somato-neuritic area and move toward neurite ends. The upstream cues that initiate actin waves are poorly understood. Here, using an optogenetic approach (Opto-cytTrkB), we found that local activation of the TrkB receptor around the neurite end initiates actin waves and triggers neurite elongation. During actin wave generation, locally activated TrkB signaling in the distal neurite was functionally connected with preferentially localized Rac1 and its signaling pathways in the proximal region. Moreover, TrkB activity changed the location of ankyrinG--the master organizer of the axonal initial segment-and initiated the stimulated neurite to acquire axonal characteristics. Taken together, these findings suggest that local Opto-cytTrkB activation switches the fate from minor to major axonal neurite during neuronal polarization by generating actin waves.
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18
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Meka DP, Scharrenberg R, Zhao B, Kobler O, König T, Schaefer I, Schwanke B, Klykov S, Richter M, Eggert D, Windhorst S, Dotti CG, Kreutz MR, Mikhaylova M, Calderon de Anda F. Radial somatic F-actin organization affects growth cone dynamics during early neuronal development. EMBO Rep 2019; 20:e47743. [PMID: 31650708 PMCID: PMC6893363 DOI: 10.15252/embr.201947743] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Revised: 09/06/2019] [Accepted: 09/27/2019] [Indexed: 11/16/2022] Open
Abstract
The centrosome is thought to be the major neuronal microtubule‐organizing center (MTOC) in early neuronal development, producing microtubules with a radial organization. In addition, albeit in vitro, recent work showed that isolated centrosomes could serve as an actin‐organizing center, raising the possibility that neuronal development may, in addition, require a centrosome‐based actin radial organization. Here, we report, using super‐resolution microscopy and live‐cell imaging of cultured rodent neurons, F‐actin organization around the centrosome with dynamic F‐actin aster‐like structures with F‐actin fibers extending and retracting actively. Photoactivation/photoconversion experiments and molecular manipulations of F‐actin stability reveal a robust flux of somatic F‐actin toward the cell periphery. Finally, we show that somatic F‐actin intermingles with centrosomal PCM‐1 (pericentriolar material 1 protein) satellites. Knockdown of PCM‐1 and disruption of centrosomal activity not only affect F‐actin dynamics near the centrosome but also in distal growth cones. Collectively, the data show a radial F‐actin organization during early neuronal development, which might be a cellular mechanism for providing peripheral regions with a fast and continuous source of actin polymers, hence sustaining initial neuronal development.
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Affiliation(s)
- Durga Praveen Meka
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Robin Scharrenberg
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Bing Zhao
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Oliver Kobler
- Combinatorial Neuroimaging Core Facility (CNI), Leibniz Institute for Neurobiology, Magdeburg, Germany
| | - Theresa König
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Irina Schaefer
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Birgit Schwanke
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Sergei Klykov
- Emmy-Noether Group "Neuronal Protein Transport", Center for Molecular Neurobiology (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Melanie Richter
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Dennis Eggert
- Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany.,Heinrich Pette Institute-Leibniz Institute for Experimental Virology, Hamburg, Germany
| | - Sabine Windhorst
- Department of Biochemistry and Signal Transduction, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Carlos G Dotti
- Centro de Biología Molecular "Severo Ochoa", CSIC-UAM, Madrid, Spain
| | - Michael R Kreutz
- RG Neuroplasticity, Leibniz Institute for Neurobiology, Magdeburg, Germany.,Leibniz Guest Group "Dendritic Organelles and Synaptic Function", Center for Molecular Neurobiology (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Marina Mikhaylova
- Emmy-Noether Group "Neuronal Protein Transport", Center for Molecular Neurobiology (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Froylan Calderon de Anda
- RG Neuronal Development, Center for Molecular Neurobiology Hamburg (ZMNH), University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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19
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Minegishi T, Uesugi Y, Kaneko N, Yoshida W, Sawamoto K, Inagaki N. Shootin1b Mediates a Mechanical Clutch to Produce Force for Neuronal Migration. Cell Rep 2018; 25:624-639.e6. [DOI: 10.1016/j.celrep.2018.09.068] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2018] [Revised: 08/31/2018] [Accepted: 09/21/2018] [Indexed: 11/26/2022] Open
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20
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Abstract
Pai and Moore preview work from Nithianandam and Chien describing new actin structures called blobs that prefigure dendrite branching. The mechanisms by which the actin cytoskeleton regulates dendritic branching are not fully understood. Nithianandam and Chien (2018. J. Cell Biol.https://doi.org/10.1083/jcb.201711136) discover actin blobs, new structures that mediate dynamic actin delivery within a growing dendrite arbor and that mark sites of future branch formation.
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Affiliation(s)
- Yun-Jin Pai
- Neurodiversity, RIKEN Center for Brain Science, Wako, Saitama, Japan
| | - Adrian W Moore
- Neurodiversity, RIKEN Center for Brain Science, Wako, Saitama, Japan
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21
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Nithianandam V, Chien CT. Actin blobs prefigure dendrite branching sites. J Cell Biol 2018; 217:3731-3746. [PMID: 30042190 PMCID: PMC6168249 DOI: 10.1083/jcb.201711136] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Revised: 03/28/2018] [Accepted: 07/09/2018] [Indexed: 02/08/2023] Open
Abstract
Nithianandam and Chien show via in vivo imaging that a dynamic population of F-actin termed actin blobs propagates bidirectionally in dendrites and stalls at future branching sites. The F-actin–severing protein Tsr/cofilin is a regulator of actin blob dynamics and dendrite branching. The actin cytoskeleton provides structural stability and adaptability to the cell. Neuronal dendrites frequently undergo morphological changes by emanating, elongating, and withdrawing branches. However, the knowledge about actin dynamics in dendrites during these processes is limited. By performing in vivo imaging of F-actin markers, we found that F-actin was highly dynamic and heterogeneously distributed in dendritic shafts with enrichment at terminal dendrites. A dynamic F-actin population that we named actin blobs propagated bidirectionally at an average velocity of 1 µm/min. Interestingly, these actin blobs stalled at sites where new dendrites would branch out in minutes. Overstabilization of F-actin by the G15S mutant abolished actin blobs and dendrite branching. We identified the F-actin–severing protein Tsr/cofilin as a regulator of dynamic actin blobs and branching activity. Hence, actin blob localization at future branching sites represents a dendrite-branching mechanism to account for highly diversified dendritic morphology.
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Affiliation(s)
- Vanitha Nithianandam
- Molecular and Cell Biology, Taiwan International Graduate Program, Academia Sinica and Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan.,Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Cheng-Ting Chien
- Molecular and Cell Biology, Taiwan International Graduate Program, Academia Sinica and Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan .,Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
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22
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Papandréou MJ, Leterrier C. The functional architecture of axonal actin. Mol Cell Neurosci 2018; 91:151-159. [PMID: 29758267 DOI: 10.1016/j.mcn.2018.05.003] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 05/10/2018] [Accepted: 05/11/2018] [Indexed: 11/17/2022] Open
Abstract
The cytoskeleton builds and supports the complex architecture of neurons. It orchestrates the specification, growth, and compartmentation of the axon: axon initial segment, axonal shaft, presynapses. The cytoskeleton must then maintain this intricate architecture for the whole life of its host, but also drive its adaptation to new network demands and changing physiological conditions. Microtubules are readily visible inside axon shafts by electron microscopy, whereas axonal actin study has long been focused on dynamic structures of the axon such as growth cones. Super-resolution microscopy and live-cell imaging have recently revealed new actin-based structures in mature axons: rings, hotspots and trails. This has caused renewed interest for axonal actin, with efforts underway to understand the precise organization and cellular functions of these assemblies. Actin is also present in presynapses, where its arrangement is still poorly defined, and its functions vigorously debated. Here we review the organization of axonal actin, focusing on recent advances and current questions in this rejuvenated field.
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23
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Inner Workings: Uncovering the neuron's internal skeleton. Proc Natl Acad Sci U S A 2018; 113:13931-13933. [PMID: 27930346 DOI: 10.1073/pnas.1617651113] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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24
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Iuliano O, Yoshimura A, Prospéri MT, Martin R, Knölker HJ, Coudrier E. Myosin 1b promotes axon formation by regulating actin wave propagation and growth cone dynamics. J Cell Biol 2018; 217:2033-2046. [PMID: 29588377 PMCID: PMC5987710 DOI: 10.1083/jcb.201703205] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Revised: 12/20/2017] [Accepted: 03/02/2018] [Indexed: 02/06/2023] Open
Abstract
Single-headed myosin 1 has been identified in neurons, but its function in these cells is still unclear. We demonstrate that depletion of myosin 1b (Myo1b), inhibition of its motor activity, or its binding to phosphoinositides impairs the formation of the axon, whereas overexpression of Myo1b increases the number of axon-like structures. Myo1b is associated with growth cones and actin waves, two major contributors to neuronal symmetry breaking. We show that Myo1b controls the dynamics of the growth cones and the anterograde propagation of the actin waves. By coupling the membrane to the actin cytoskeleton, Myo1b regulates the size of the actin network as well as the stability and size of filopodia in the growth cones. Our data provide the first evidence that a myosin 1 plays a major role in neuronal symmetry breaking and argue for a mechanical control of the actin cytoskeleton both in actin waves and in the growth cones by this myosin.
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Affiliation(s)
- Olga Iuliano
- Institut Curie, Paris Sciences et Lettres Research University, Centre National de la Recherche Scientifique, UMR 144, Paris, France
| | - Azumi Yoshimura
- Institut Curie, Paris Sciences et Lettres Research University, Centre National de la Recherche Scientifique, UMR 144, Paris, France
| | - Marie-Thérèse Prospéri
- Institut Curie, Paris Sciences et Lettres Research University, Centre National de la Recherche Scientifique, UMR 144, Paris, France
| | - René Martin
- Department of Chemistry, Technische Univesität Dresden, Dresden, Germany
| | | | - Evelyne Coudrier
- Institut Curie, Paris Sciences et Lettres Research University, Centre National de la Recherche Scientifique, UMR 144, Paris, France
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25
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Mortal S, Iseppon F, Perissinotto A, D'Este E, Cojoc D, Napolitano LMR, Torre V. Actin Waves Do Not Boost Neurite Outgrowth in the Early Stages of Neuron Maturation. Front Cell Neurosci 2017; 11:402. [PMID: 29326552 PMCID: PMC5741660 DOI: 10.3389/fncel.2017.00402] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Accepted: 12/01/2017] [Indexed: 11/27/2022] Open
Abstract
During neurite development, Actin Waves (AWs) emerge at the neurite base and move up to its tip, causing a transient retraction of the Growth Cone (GC). Many studies have shown that AWs are linked to outbursts of neurite growth and, therefore, contribute to the fast elongation of the nascent axon. Using long term live cell-imaging, we show that AWs do not boost neurite outgrowth and that neurites without AWs can elongate for several hundred microns. Inhibition of Myosin II abolishes the transient GC retraction and strongly modifies the AWs morphology. Super-resolution nanoscopy shows that Myosin IIB shapes the growth cone-like AWs structure and is differently distributed in AWs and GCs. Interestingly, depletion of membrane cholesterol and inhibition of Rho GTPases decrease AWs frequency and velocity. Our results indicate that Myosin IIB, membrane tension, and small Rho GTPases are important players in the regulation of the AW dynamics. Finally, we suggest a role for AWs in maintaining the GCs active during environmental exploration.
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Affiliation(s)
- Simone Mortal
- Neurobiology Department, International School for Advanced Studies, Trieste, Italy
| | - Federico Iseppon
- Neurobiology Department, International School for Advanced Studies, Trieste, Italy
| | - Andrea Perissinotto
- Neurobiology Department, International School for Advanced Studies, Trieste, Italy
| | - Elisa D'Este
- Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Dan Cojoc
- Optical Manipulation Lab, Istituto Officina dei Materiali (CNR), Trieste, Italy
| | - Luisa M R Napolitano
- Neurobiology Department, International School for Advanced Studies, Trieste, Italy
| | - Vincent Torre
- Neurobiology Department, International School for Advanced Studies, Trieste, Italy
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26
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27
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Actin Waves: Origin of Cell Polarization and Migration? Trends Cell Biol 2017; 27:515-526. [DOI: 10.1016/j.tcb.2017.02.003] [Citation(s) in RCA: 83] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Revised: 01/26/2017] [Accepted: 02/07/2017] [Indexed: 01/22/2023]
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28
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Tomba C, Braïni C, Bugnicourt G, Cohen F, Friedrich BM, Gov NS, Villard C. Geometrical Determinants of Neuronal Actin Waves. Front Cell Neurosci 2017; 11:86. [PMID: 28424590 PMCID: PMC5372798 DOI: 10.3389/fncel.2017.00086] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 03/13/2017] [Indexed: 11/19/2022] Open
Abstract
Hippocampal neurons produce in their early stages of growth propagative, actin-rich dynamical structures called actin waves. The directional motion of actin waves from the soma to the tip of neuronal extensions has been associated with net forward growth, and ultimately with the specification of neurites into axon and dendrites. Here, geometrical cues are used to control actin wave dynamics by constraining neurons on adhesive stripes of various widths. A key observable, the average time between the production of consecutive actin waves, or mean inter-wave interval (IWI), was identified. It scales with the neurite width, and more precisely with the width of the proximal segment close to the soma. In addition, the IWI is independent of the total number of neurites. These two results suggest a mechanistic model of actin wave production, by which the material conveyed by actin waves is assembled in the soma until it reaches the threshold leading to the initiation and propagation of a new actin wave. Based on these observations, we formulate a predictive theoretical description of actin wave-driven neuronal growth and polarization, which consistently accounts for different sets of experiments.
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Affiliation(s)
- Caterina Tomba
- Université Grenoble Alpes, Centre National de la Recherche Scientifique (CNRS), Institut NéelGrenoble, France.,Université Grenoble Alpes, Centre National de la Recherche Scientifique (CNRS), Laboratoire des Technologies de la Microélectronique, CEA-LETIGrenoble, France
| | - Céline Braïni
- Université Grenoble Alpes, Centre National de la Recherche Scientifique (CNRS), Institut NéelGrenoble, France.,Laboratoire PhysicoChimie Curie, Institut Curie, Pierre-Gilles de Gennes Institute for Microfluidics, CNRS, PSL Research UniversityParis, France
| | - Ghislain Bugnicourt
- Université Grenoble Alpes, Centre National de la Recherche Scientifique (CNRS), Institut NéelGrenoble, France
| | - Floriane Cohen
- Laboratoire PhysicoChimie Curie, Institut Curie, Pierre-Gilles de Gennes Institute for Microfluidics, CNRS, PSL Research UniversityParis, France
| | - Benjamin M Friedrich
- Biological Algorithms Group, Center for Advancing Electronics Dresden, Technische Universität DresdenDresden, Germany
| | - Nir S Gov
- Department of Chemical Physics, Weizmann Institute of ScienceRehovot, Israel
| | - Catherine Villard
- Université Grenoble Alpes, Centre National de la Recherche Scientifique (CNRS), Institut NéelGrenoble, France.,Laboratoire PhysicoChimie Curie, Institut Curie, Pierre-Gilles de Gennes Institute for Microfluidics, CNRS, PSL Research UniversityParis, France
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29
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Pacheco A, Gallo G. Actin filament-microtubule interactions in axon initiation and branching. Brain Res Bull 2016; 126:300-310. [PMID: 27491623 DOI: 10.1016/j.brainresbull.2016.07.013] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 07/28/2016] [Accepted: 07/30/2016] [Indexed: 10/21/2022]
Abstract
Neurons begin life as spherical cells. A major hallmark of neuronal development is the formation of elongating processes from the cell body which subsequently differentiate into dendrites and the axon. The formation and later development of neuronal processes is achieved through the concerted organization of actin filaments and microtubules. Here, we review the literature regarding recent advances in the understanding of cytoskeletal interactions in neurons focusing on the initiation of processes from neuronal cell bodies and the collateral branching of axons. The complex crosstalk between cytoskeletal elements is mediated by a cohort of proteins that either bind both cytoskeletal systems or allow one to regulate the other. Recent studies have highlighted the importance of microtubule plus-tip proteins in the regulation of the dynamics and organization of actin filaments, while also providing a mechanism for the subcellular capture and guidance of microtubule tips by actin filaments. Although the understanding of cytoskeletal crosstalk and interactions in neuronal morphogenesis has advanced significantly in recent years the appreciation of the neuron as an integrated cytoskeletal system remains a frontier.
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Affiliation(s)
- Almudena Pacheco
- Temple University, Lewis Kats School of Medicine, Shriners Hospitals Pediatric Research Center, Department of Anatomy and Cell Biology, 3500 North Broad Street, Philadelphia, PA 19140, United States
| | - Gianluca Gallo
- Temple University, Lewis Kats School of Medicine, Shriners Hospitals Pediatric Research Center, Department of Anatomy and Cell Biology, 3500 North Broad Street, Philadelphia, PA 19140, United States.
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30
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Winans AM, Collins SR, Meyer T. Waves of actin and microtubule polymerization drive microtubule-based transport and neurite growth before single axon formation. eLife 2016; 5:e12387. [PMID: 26836307 PMCID: PMC4805541 DOI: 10.7554/elife.12387] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2015] [Accepted: 01/31/2016] [Indexed: 12/16/2022] Open
Abstract
Many developing neurons transition through a multi-polar state with many competing neurites before assuming a unipolar state with one axon and multiple dendrites. Hallmarks of the multi-polar state are large fluctuations in microtubule-based transport into and outgrowth of different neurites, although what drives these fluctuations remains elusive. We show that actin waves, which stochastically migrate from the cell body towards neurite tips, direct microtubule-based transport during the multi-polar state. Our data argue for a mechanical control system whereby actin waves transiently widen the neurite shaft to allow increased microtubule polymerization to direct Kinesin-based transport and create bursts of neurite extension. Actin waves also require microtubule polymerization, arguing that positive feedback links these two components. We propose that actin waves create large stochastic fluctuations in microtubule-based transport and neurite outgrowth, promoting competition between neurites as they explore the environment until sufficient external cues can direct one to become the axon. DOI:http://dx.doi.org/10.7554/eLife.12387.001 Nerve cells (also known as neurons) connect with each other to form complex networks through which signals are carried around the body. Signals are received by branch-like projections called dendrites, pass through the cell body and then pass along a long projection called the axon before being transmitted to the dendrites of neighboring neurons. In animal embryos, immature neurons in part of the brain called the hippocampus – which is crucial for learning and forming memories – develop into mature neurons through a series of steps. In the early stages of development, an immature neuron sends out multiple projections that extend out in all directions from its cell body. These projections randomly retract and lengthen for a while before a single projection grows into an axon and the others become dendrites. It is believed that signal proteins inside the neuron that promote the formation of an axon selectively accumulate in a projection as it grows into an axon. These axon-promoting proteins are carried to the axons by a motor protein called kinesin, which moves along fibers called microtubules. In immature neurons, kinesin motors randomly move in and out of different projections, before settling in the projection that will grow into the axon. However, it is not clear what drives these fluctuations. To address this question, Winans et al. used microscopy to study the transport of axon-promoting proteins in hippocampal neurons. The experiments show that a protein called actin forms a mesh of filaments in a wave-like manner, starting in the cell body and moving outwards into the projections. When a wave of actin reaches a projection, the projection grows for a while and then stops until the next actin wave arrives. Furthermore, the actin waves promote the formation of more microtubule filaments. This work shows that actin waves make the projections wider to create space for more microtubules to form, which increases the transport of axon-promoting proteins to the projections. Winans et al.’s findings suggest that actin waves direct axon-promoting proteins to axons and promote competition between the projections early on by generating random fluctuations that allow all the projections to grow and retract. This would allow each projection to explore its environment in the search for signals that promote axon growth. The next challenge is to understand how different signals select the “winning axon”. DOI:http://dx.doi.org/10.7554/eLife.12387.002
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Affiliation(s)
- Amy M Winans
- Biophysics Program, Stanford University, Stanford, United States.,Department of Chemical and Systems Biology, Stanford University, Stanford, United States.,Center for Systems Biology, Stanford University, Stanford, United States
| | - Sean R Collins
- Department of Chemical and Systems Biology, Stanford University, Stanford, United States.,Center for Systems Biology, Stanford University, Stanford, United States
| | - Tobias Meyer
- Department of Chemical and Systems Biology, Stanford University, Stanford, United States.,Center for Systems Biology, Stanford University, Stanford, United States
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31
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Miyagi T, Tanaka S, Hide I, Shirafuji T, Sakai N. The Subcellular Dynamics of the Gs-Linked Receptor GPR3 Contribute to the Local Activation of PKA in Cerebellar Granular Neurons. PLoS One 2016; 11:e0147466. [PMID: 26800526 PMCID: PMC4723318 DOI: 10.1371/journal.pone.0147466] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 01/03/2016] [Indexed: 12/12/2022] Open
Abstract
G-protein-coupled receptor (GPR) 3 is a member of the GPR family that constitutively activates adenylate cyclase. We have reported that the expression of GPR3 in cerebellar granular neurons (CGNs) contributes to neurite outgrowth and modulates neuronal proliferation and survival. To further identify its role, we have analyzed the precise distribution and local functions of GPR3 in neurons. The fluorescently tagged GPR3 protein was distributed in the plasma membrane, the Golgi body, and the endosomes. In addition, we have revealed that the plasma membrane expression of GPR3 functionally up-regulated the levels of PKA, as measured by a PKA FRET indicator. Next, we asked if the PKA activity was modulated by the expression of GPR3 in CGNs. PKA activity was highly modulated at the neurite tips compared to the soma. In addition, the PKA activity at the neurite tips was up-regulated when GPR3 was transfected into the cells. However, local PKA activity was decreased when endogenous GPR3 was suppressed by a GPR3 siRNA. Finally, we determined the local dynamics of GPR3 in CGNs using time-lapse analysis. Surprisingly, the fluorescent GPR3 puncta were transported along the neurite in both directions over time. In addition, the anterograde movements of the GPR3 puncta in the neurite were significantly inhibited by actin or microtubule polymerization inhibitors and were also disturbed by the Myosin II inhibitor blebbistatin. Moreover, the PKA activity at the tips of the neurites was decreased when blebbistatin was administered. These results suggested that GPR3 was transported along the neurite and contributed to the local activation of PKA in CGN development. The local dynamics of GPR3 in CGNs may affect local neuronal functions, including neuronal differentiation and maturation.
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Affiliation(s)
- Tatsuhiro Miyagi
- Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan
| | - Shigeru Tanaka
- Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan
| | - Izumi Hide
- Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan
| | - Toshihiko Shirafuji
- Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan
| | - Norio Sakai
- Department of Molecular and Pharmacological Neuroscience, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan
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32
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Roy S. Waves, rings, and trails: The scenic landscape of axonal actin. J Cell Biol 2016; 212:131-4. [PMID: 26754647 PMCID: PMC4738387 DOI: 10.1083/jcb.201511016] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Accepted: 12/21/2015] [Indexed: 11/29/2022] Open
Abstract
The goal of this article is to provide the reader a snapshot of recent studies on axonal actin—largely emerging from superresolution and live-imaging experiments—and place this new information in context with earlier studies.
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Affiliation(s)
- Subhojit Roy
- Department of Pathology, University of California, San Diego, La Jolla, CA 92093 Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093
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33
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Chetta J, Love JM, Bober BG, Shah SB. Bidirectional actin transport is influenced by microtubule and actin stability. Cell Mol Life Sci 2015; 72:4205-20. [PMID: 26043972 PMCID: PMC11113749 DOI: 10.1007/s00018-015-1933-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Revised: 05/14/2015] [Accepted: 05/19/2015] [Indexed: 12/16/2022]
Abstract
Local and long-distance transport of cytoskeletal proteins is vital to neuronal maintenance and growth. Though recent progress has provided insight into the movement of microtubules and neurofilaments, mechanisms underlying the movement of actin remain elusive, in large part due to rapid transitions between its filament states and its diverse cellular localization and function. In this work, we integrated live imaging of rat sensory neurons, image processing, multiple regression analysis, and mathematical modeling to perform the first quantitative, high-resolution investigation of GFP-actin identity and movement in individual axons. Our data revealed that filamentous actin densities arise along the length of the axon and move short but significant distances bidirectionally, with a net anterograde bias. We directly tested the role of actin and microtubules in this movement. We also confirmed a role for actin densities in extension of axonal filopodia, and demonstrated intermittent correlation of actin and mitochondrial movement. Our results support a novel mechanism underlying slow component axonal transport, in which the stability of both microtubule and actin cytoskeletal components influence the mobility of filamentous actin.
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Affiliation(s)
- Joshua Chetta
- Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA
| | - James M Love
- Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA
| | - Brian G Bober
- Department of Bioengineering, University of California, San Diego, La Jolla, CA, USA
| | - Sameer B Shah
- Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA.
- Departments of Orthopaedic Surgery and Bioengineering, University of California, San Diego, 9500 Gilman Drive, MC 0863, La Jolla, CA, 92093, USA.
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Combinatorial influences of paclitaxel and strain on axonal transport. Exp Neurol 2015; 271:358-67. [DOI: 10.1016/j.expneurol.2015.06.023] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Revised: 05/18/2015] [Accepted: 06/24/2015] [Indexed: 11/21/2022]
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Ganguly A, Tang Y, Wang L, Ladt K, Loi J, Dargent B, Leterrier C, Roy S. A dynamic formin-dependent deep F-actin network in axons. J Cell Biol 2015. [PMID: 26216902 PMCID: PMC4523607 DOI: 10.1083/jcb.201506110] [Citation(s) in RCA: 120] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Although actin at neuronal growth cones is well-studied, much less is known about actin organization and dynamics along axon shafts and presynaptic boutons. Using probes that selectively label filamentous-actin (F-actin), we found focal "actin hotspots" along axons-spaced ∼3-4 µm apart-where actin undergoes continuous assembly/disassembly. These foci are a nidus for vigorous actin polymerization, generating long filaments spurting bidirectionally along axons-a phenomenon we call "actin trails." Super-resolution microscopy reveals intra-axonal deep actin filaments in addition to the subplasmalemmal "actin rings" described recently. F-actin hotspots colocalize with stationary axonal endosomes, and blocking vesicle transport diminishes the actin trails, suggesting mechanistic links between vesicles and F-actin kinetics. Actin trails are formin-but not Arp2/3-dependent and help enrich actin at presynaptic boutons. Finally, formin inhibition dramatically disrupts synaptic recycling. Collectively, available data suggest a two-tier F-actin organization in axons, with stable "actin rings" providing mechanical support to the plasma membrane and dynamic "actin trails" generating a flexible cytoskeletal network with putative physiological roles.
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Affiliation(s)
- Archan Ganguly
- Department of Pathology, University of California, San Diego, La Jolla, CA 92093
| | - Yong Tang
- Department of Pathology, University of California, San Diego, La Jolla, CA 92093
| | - Lina Wang
- Department of Pathology, University of California, San Diego, La Jolla, CA 92093
| | - Kelsey Ladt
- Department of Pathology, University of California, San Diego, La Jolla, CA 92093 Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093
| | - Jonathan Loi
- Department of Pathology, University of California, San Diego, La Jolla, CA 92093
| | - Bénédicte Dargent
- Aix Marseille Université, Centre National de la Recherche Scientifique, Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille (CRN2M) UMR7286, 13344 Marseille, France
| | - Christophe Leterrier
- Aix Marseille Université, Centre National de la Recherche Scientifique, Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille (CRN2M) UMR7286, 13344 Marseille, France
| | - Subhojit Roy
- Department of Pathology, University of California, San Diego, La Jolla, CA 92093 Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093
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Actin Migration Driven by Directional Assembly and Disassembly of Membrane-Anchored Actin Filaments. Cell Rep 2015; 12:648-60. [DOI: 10.1016/j.celrep.2015.06.048] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Revised: 05/18/2015] [Accepted: 06/11/2015] [Indexed: 11/24/2022] Open
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Tomba C, Braïni C, Wu B, Gov NS, Villard C. Tuning the adhesive geometry of neurons: length and polarity control. SOFT MATTER 2014; 10:2381-2387. [PMID: 24623029 DOI: 10.1039/c3sm52342j] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Neurons acquire their functional and morphological axo-dendritic polarity by extending, from competing minor processes (neurites), one long axon among numerous dendrites. We employed complementary sets of micropatterns built from 2 and 6 μm wide stripes of various lengths to constrain hippocampal neuron shapes. Using these geometries, we have (i) limited the number of neuronal extensions to obtain a minimal in vitro system of bipolar neurons and (ii) controlled the neurite width during growth by the generation of a progressive cell shape asymmetry on either side of the cellular body. From this geometrical approach, we gained a high level of control of each neurite length and of the localization of axonal specification. To analyze these results, we developed a model based on a width and polarization dependent neurite elongation rate and on the existence of a critical neurite length that sets the axonal fate. Our data on the four series of micro-patterns developed for this study are described by a single set of growth parameters, well supported by experiments. The control of neuronal shapes by adhesive micro-patterns thereby offers a novel paradigm to follow the dynamical process of neurite lengthening and competition through the process of axonal polarization.
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Affiliation(s)
- Caterina Tomba
- Univ. Grenoble Alpes, Inst NEEL and CRETA, F-38042 Grenoble, France
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Naoki H, Ishii S. Mathematical modeling of neuronal polarization during development. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 123:127-41. [PMID: 24560143 DOI: 10.1016/b978-0-12-397897-4.00003-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/24/2023]
Abstract
During development of the brain, morphogenesis of neurons is dynamically organized from a simple rounded shape to a highly polarized morphology consisting of soma, one axon, and dendrites, which is a basis for establishing the unidirectional transfer of electric signals between neurons. The mechanism of such polarization is thought to be "local activation-global inhibition"; however, globally diffusing inhibitor molecules have not been identified. In this chapter, we present a theoretical modeling approach of such neuronal development. We first summarize biological research on neuronal polarization and then develop a biophysical model. Through mathematical analysis, principles of local activation-global inhibition are illustrated based on active transport, protein degradation, and neurite growth, but not on globally diffusing inhibitor.
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Affiliation(s)
- Honda Naoki
- Imaging Platform for Spatio-Temporal Information, Graduate School of Medicine, Kyoto University, Kyoto, Kyoto, Japan
| | - Shin Ishii
- Graduate School of Informatics, Kyoto University, Uji, Kyoto, Japan
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Arnold DB, Gallo G. Structure meets function: actin filaments and myosin motors in the axon. J Neurochem 2013; 129:213-220. [PMID: 24147838 DOI: 10.1111/jnc.12503] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Revised: 10/16/2013] [Accepted: 10/17/2013] [Indexed: 12/14/2022]
Abstract
This review focuses on recent advances in the understanding of the organization and roles of actin filaments, and associated myosin motor proteins, in regulating the structure and function of the axon shaft. 'Patches' of actin filaments have emerged as a major type of actin filament organization in axons. In the distal axon, patches function as precursors to the formation of filopodia and branches. At the axon initial segment, patches locally capture membranous organelles and contribute to polarized trafficking. The trapping function of patches at the initial segment can be ascribed to interactions with myosin motors, and likely also applies to patches in the more distal axon. Finally, submembranous rings of actin filaments were recently described in axons, which form an actin-spectrin cytoskeleton, likely contributing to the maintenance of axon integrity. Continued investigation into the roles of axonal actin filaments and myosins will shed light on fundamental aspects of the development, adult function and the repair of axons in the nervous system.
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Affiliation(s)
- Don B Arnold
- University of Southern California Department of Biology 1050 Childs Way RRI 204b Los Angeles, CA 90089-2910 ph: 213-821-1266
| | - Gianluca Gallo
- Shriners Hospitals Pediatric Research Center, Temple University, Department of Anatomy and Cell Biology, 2500 North Broad St, Philadelphia, PA 19140, ph: 215-926-9362
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Lewis TL, Courchet J, Polleux F. Cell biology in neuroscience: Cellular and molecular mechanisms underlying axon formation, growth, and branching. ACTA ACUST UNITED AC 2013; 202:837-48. [PMID: 24043699 PMCID: PMC3776347 DOI: 10.1083/jcb.201305098] [Citation(s) in RCA: 114] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Proper brain wiring during development is pivotal for adult brain function. Neurons display a high degree of polarization both morphologically and functionally, and this polarization requires the segregation of mRNA, proteins, and lipids into the axonal or somatodendritic domains. Recent discoveries have provided insight into many aspects of the cell biology of axonal development including axon specification during neuronal polarization, axon growth, and terminal axon branching during synaptogenesis.
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Affiliation(s)
- Tommy L Lewis
- The Scripps Research Institute, Dorris Neuroscience Center, Department of Molecular and Cellular Neuroscience, La Jolla, CA 92037
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Gallo G. More than one ring to bind them all: recent insights into the structure of the axon. Dev Neurobiol 2013; 73:799-805. [PMID: 23784998 DOI: 10.1002/dneu.22100] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Revised: 06/06/2013] [Accepted: 06/06/2013] [Indexed: 01/12/2023]
Abstract
This brief review outlines recent developments in the understanding of the ultrastructural organization of the axonal and growth cone actin filament cytoskeleton. A novel form of structural organization has arisen as a regulator of the actin cytoskeleton: ring-like structures. Rings may represent a conserved functional theme exhibited by diverse molecular systems and have implications for the understanding of the axon in development, maturity, and disease.
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Affiliation(s)
- Gianluca Gallo
- Shriners Hospitals Pediatric Research Center, Department of Anatomy and Cell Biology, Temple University, School of Medicine Philadelphia, Pennsylvania, 19140
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Kakumoto T, Nakata T. Optogenetic control of PIP3: PIP3 is sufficient to induce the actin-based active part of growth cones and is regulated via endocytosis. PLoS One 2013; 8:e70861. [PMID: 23951027 PMCID: PMC3737352 DOI: 10.1371/journal.pone.0070861] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Accepted: 06/26/2013] [Indexed: 12/21/2022] Open
Abstract
Phosphatidylinositol-3,4,5-trisphosphate (PIP3) is highly regulated in a spatiotemporal manner and plays multiple roles in individual cells. However, the local dynamics and primary functions of PIP3 in developing neurons remain unclear because of a lack of techniques for manipulating PIP3 spatiotemporally. We addressed this issue by combining optogenetic control and observation of endogenous PIP3 signaling. Endogenous PIP3 was abundant in actin-rich structures such as growth cones and "waves", and PIP3-rich plasma membranes moved actively within growth cones. To study the role of PIP3 in developing neurons, we developed a PI3K photoswitch that can induce production of PIP3 at specific locations upon blue light exposure. We succeeded in producing PIP3 locally in mouse hippocampal neurons. Local PIP3 elevation at neurite tips did not induce neurite elongation, but it was sufficient to induce the formation of filopodia and lamellipodia. Interestingly, ectopic PIP3 elevation alone activated membranes to form actin-based structures whose behavior was similar to that of growth-cone-like "waves". We also found that endocytosis regulates effective PIP3 concentration at plasma membranes. These results revealed the local dynamics and primary functions of PIP3, providing fundamental information about PIP3 signaling in neurons.
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Affiliation(s)
- Toshiyuki Kakumoto
- Department of Cell Biology, Tokyo Medical and Dental University, Tokyo, Japan
- The Center for Brain Integration Research (CBIR), Tokyo Medical and Dental University, Tokyo, Japan
| | - Takao Nakata
- Department of Cell Biology, Tokyo Medical and Dental University, Tokyo, Japan
- The Center for Brain Integration Research (CBIR), Tokyo Medical and Dental University, Tokyo, Japan
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Yamamoto H, Demura T, Morita M, Banker GA, Tanii T, Nakamura S. Differential neurite outgrowth is required for axon specification by cultured hippocampal neurons. J Neurochem 2012; 123:904-10. [PMID: 22928776 DOI: 10.1111/jnc.12001] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2012] [Revised: 08/22/2012] [Accepted: 08/24/2012] [Indexed: 11/28/2022]
Abstract
Formation of an axon is the first morphological evidence of neuronal polarization, visible as a profound outgrowth of the axon compared with sibling neurites. One unsolved question on the mechanism of axon formation is the role of axon outgrowth in axon specification. This question was difficult to assess, because neurons freely extend their neurites in a conventional culture. Here, we leveraged surface nano/micro-modification techniques to fabricate a template substrate for constraining neurite lengths of cultured neurons. Using the template, we asked (i) Do neurons polarize even if all neurites cannot grow sufficiently long? (ii) Would the neurite be fated to become an axon if only one was allowed to grow long? A pattern with symmetrical short paths (20 μm) was used to address the former question, and an asymmetrical pattern with one path extended to 100 μm for the latter. Axon formation was evaluated by tau-1/MAP2 immunostaining and live-cell imaging of constitutively-active kinesin-1. We found that (1) neurons cannot polarize when extension of all neurites is restricted and that (2) when only a single neurite is permitted to grow long, neurons polarize and the longest neurite becomes the axon. These results provide clear evidence that axon outgrowth is required for its specification.
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Affiliation(s)
- Hideaki Yamamoto
- Department of Life Science and Biotechnology, Tokyo University of Agriculture and Technology, Tokyo, Japan.
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Kaech S, Huang CF, Banker G. General considerations for live imaging of developing hippocampal neurons in culture. Cold Spring Harb Protoc 2012; 2012:312-8. [PMID: 22383651 DOI: 10.1101/pdb.ip068221] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Dissociated cell cultures of the rodent hippocampus have become a standard model for studying many facets of neural development, including the development of polarity, axonal and dendritic growth, and synapse formation. The cultures are quite homogeneous--∼90% of the cells are pyramidal neurons--and it is relatively easy to express green fluorescent protein (GFP)-tagged proteins by transfection. This article describes the cultures and the key features of the system used to image them. It also includes suggestions on labeling cells with GFP-tagged proteins. It concludes with a discussion of the advantages and disadvantages of this culture system.
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Schevzov G, Curthoys NM, Gunning PW, Fath T. Functional diversity of actin cytoskeleton in neurons and its regulation by tropomyosin. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2012; 298:33-94. [PMID: 22878104 DOI: 10.1016/b978-0-12-394309-5.00002-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Neurons comprise functionally, molecularly, and spatially distinct subcellular compartments which include the soma, dendrites, axon, branches, dendritic spines, and growth cones. In this chapter, we detail the remarkable ability of the neuronal cytoskeleton to exquisitely regulate all these cytoplasmic distinct partitions, with particular emphasis on the microfilament system and its plethora of associated proteins. Importance will be given to the family of actin-associated proteins, tropomyosin, in defining distinct actin filament populations. The ability of tropomyosin isoforms to regulate the access of actin-binding proteins to the filaments is believed to define the structural diversity and dynamics of actin filaments and ultimately be responsible for the functional outcome of these filaments.
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Affiliation(s)
- Galina Schevzov
- Oncology Research Unit, Department of Pharmacology, School of Medical Sciences, University of New South Wales, Kensington, Australia
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Abstract
During development, axons are guided to their appropriate targets by a variety of guidance factors. On arriving at their synaptic targets, or while en route, axons form branches. Branches generated de novo from the main axon are termed collateral branches. The generation of axon collateral branches allows individual neurons to make contacts with multiple neurons within a target and with multiple targets. In the adult nervous system, the formation of axon collateral branches is associated with injury and disease states and may contribute to normally occurring plasticity. Collateral branches are initiated by actin filament– based axonal protrusions that subsequently become invaded by microtubules, thereby allowing the branch to mature and continue extending. This article reviews the current knowledge of the cellular mechanisms of the formation of axon collateral branches. The major conclusions of this review are (1) the mechanisms of axon extension and branching are not identical; (2) active suppression of protrusive activity along the axon negatively regulates branching; (3) the earliest steps in the formation of axon branches involve focal activation of signaling pathways within axons, which in turn drive the formation of actin-based protrusions; and (4) regulation of the microtubule array by microtubule-associated and severing proteins underlies the development of branches. Linking the activation of signaling pathways to specific proteins that directly regulate the axonal cytoskeleton underlying the formation of collateral branches remains a frontier in the field.
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Affiliation(s)
- Gianluca Gallo
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, Pennsylvania 19129, USA.
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Naoki H, Nakamuta S, Kaibuchi K, Ishii S. Flexible search for single-axon morphology during neuronal spontaneous polarization. PLoS One 2011; 6:e19034. [PMID: 21559492 PMCID: PMC3084731 DOI: 10.1371/journal.pone.0019034] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Accepted: 03/15/2011] [Indexed: 11/21/2022] Open
Abstract
Polarization, a disruption of symmetry in cellular morphology, occurs spontaneously, even in symmetrical extracellular conditions. This process is regulated by intracellular chemical reactions and the active transport of proteins and it is accompanied by cellular morphological changes. To elucidate the general principles underlying polarization, we focused on developing neurons. Neuronal polarity is stably established; a neuron initially has several neurites of similar length, but only one elongates and is selected to develop into an axon. Polarization is flexibly controlled; when multiple neurites are selected, the selection is eventually reduced to yield a single axon. What is the system by which morphological information is decoded differently based on the presence of a single or multiple axons? How are stability and flexibility achieved? To answer these questions, we constructed a biophysical model with the active transport of proteins that regulate neurite growth. Our mathematical analysis and computer simulation revealed that, as neurites elongate, transported factors accumulate in the growth cone but are degraded during retrograde diffusion to the soma. Such a system effectively works as local activation-global inhibition mechanism, resulting in both stability and flexibility. Our model shows good accordance with a number of experimental observations.
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Affiliation(s)
- Honda Naoki
- Graduate School of Informatics, Kyoto University, Uji, Kyoto, Japan.
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Kurklinsky S, Chen J, McNiven MA. Growth cone morphology and spreading are regulated by a dynamin-cortactin complex at point contacts in hippocampal neurons. J Neurochem 2011; 117:48-60. [PMID: 21210813 DOI: 10.1111/j.1471-4159.2011.07169.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Neuronal growth cone (GC) migration and targeting are essential processes for the formation of a neural network during embryonic development. Currently, the mechanisms that support directed motility of GCs are not fully defined. The large GTPase dynamin and an interacting actin-binding protein, cortactin, have been localized to GCs, although the function performed by this complex is unclear. We have found that cortactin and the ubiquitous form of dynamin (Dyn) 2 exhibit a striking co-localization at the base of the transition zone of advancing GCs of embryonic hippocampal neurons. Confocal and total internal reflection fluorescence microscopies demonstrate that this basal localization represents point contacts. Exogenous expression of wild-type Dyn2 and cortactin leads to large, exceptionally flat, and static GCs, whereas disrupting this complex has no such effect. We find that excessive GC spreading is induced by Dyn2 and cortactin over-expression and substantial recruitment of the point contact-associated, actin-binding protein α-actinin1 to the ventral GC membrane. The distributions of other point contact proteins such as vinculin or paxillin appear unchanged. Immunoprecipitation experiments show that both Dyn2 and cortactin reside in a complex with α-actinin1. These findings provide new insights into the role of Dyn2 and the actin cytoskeleton in GC adhesion and motility.
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Affiliation(s)
- Svetlana Kurklinsky
- Mayo Graduate School, The Molecular Neuroscience Program, Rochester, Minnesota, USA
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Toriyama M, Sakumura Y, Shimada T, Ishii S, Inagaki N. A diffusion-based neurite length-sensing mechanism involved in neuronal symmetry breaking. Mol Syst Biol 2010; 6:394. [PMID: 20664640 PMCID: PMC2925530 DOI: 10.1038/msb.2010.51] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2010] [Accepted: 06/01/2010] [Indexed: 12/28/2022] Open
Abstract
Shootin1, one of the earliest markers of neuronal symmetry breaking, accumulates in the neurite tips of polarizing neurons in a neurite length-dependent manner. Thus, neurons sense their neurites' length and translate this spatial information into a molecular signal, shootin1 concentration. Quantitative live cell imaging of shootin1 dynamics combined with mathematical modeling analyses reveals that its anterograde transport and retrograde diffusion in neurite shafts account for the neurite length-dependent accumulation of shootin1. The neurite length-dependent shootin1 accumulation and shootin1-induced neurite outgrowth constitute a positive feedback loop that amplifies stochastic shootin1 signals in neurite tips. Quantitative mathematical modeling shows that the above positive feedback loop, together with shootin1 upregulation, constitutes a core mechanism for neuronal symmetry breaking.
Cell morphology and size must be properly controlled to ensure cellular function. Although there has been significant progress in understanding the molecular signals that change cell morphology, the manner in which cells monitor their size and length to regulate their morphology is poorly understood. Cultured hippocampal neurons polarize by forming a single long axon and multiple short dendrites (Craig and Banker, 1994; Arimura and Kaibuchi, 2007), and symmetry breaking is the initial step of this process. This symmetry-breaking step reproduces even when the neuronal axon is transected; the longest neurite usually grows rapidly to become an axon after transection, regardless of whether it is the axonal stump or another neurite (Goslin and Banker, 1989). Elongation of an immature neurite by mechanical tension also leads to its axonal specification (Lamoureux et al, 2002). These results suggest that cultured hippocampal neurons can sense neurite length, identify the longest one, and induce its subsequent axonogenesis for symmetry breaking. However, little is known about the mechanism for this process. Shootin1 is one of the earliest markers of neuronal symmetry breaking (Toriyama et al, 2006). During the symmetry-breaking step, it undergoes a stochastic accumulation in neurite tips, and eventually accumulates predominantly in a single neurite that subsequently grows to become an axon. In this study, we demonstrated that shootin1 accumulates in neurite tips in a neurite length-dependent manner, regardless of whether it is the axonal stump or another neurite (Figure 3A, C–F). Thus, morphological information (neurite length) is translated into a molecular signal (shootin1 concentration in neurite tips). We previously reported that shootin1 is transported from the cell body to neurite tips as discrete boluses and diffuses back to the cell body (Toriyama et al, 2006). The boluses containing variable amounts of shootin1 traveled repeatedly but irregularly along neurites, and their arrival caused large stochastic fluctuations in shootin1 concentration in the neurite tips. To understand the mechanism of length-dependent shootin1 accumulation, we performed quantitative live cell imaging of the anterograde transport and retrograde diffusion of shootin1 and fitted the obtained data into mathematical models of the anterograde transport and retrograde diffusion. The parameters of these two models were derived entirely from quantitative experimental data, without any adjustment. Shootin1 concentration at neurite tips, calculated by integrating the two models, was neurite length dependent (Figure 3B) and showed good agreement with the experimental data (Figure 3A). These results suggest that the neurite length-dependent accumulation of shootin1 is quantitatively explained by its anterograde transport and retrograde diffusion. This length-dependent shootin1 accumulation constitutes a positive feedback interaction with the previously reported shootin1-induced neurite outgrowth (Shimada et al, 2008). To analyze the functional role of this feedback loop, we quantified shootin1 upregulation (Toriyama et al, 2006) and shootin1-induced neurite outgrowth, and integrated them, together with the above model of length-dependent shootin1 accumulation, into a model neuron (Figure 7A). Furthermore, the parameters of the model components were chosen to give the best fit to the quantitative experimental data without any adjustment. Integrating the three components into a model neuron resulted in spontaneous symmetry breaking (Figure 7B and C). Furthermore, there are a total of 15 agreements between the model predictions and the experimental data, including the neurite length-dependent axon specification and regeneration (Goslin and Banker, 1989; Lamoureux et al, 2002). These data suggest that the three components in our model—namely, diffusion-based neurite length sensing system, shootin1-induced neurite outgrowth and shootin1 upregulation—are sufficient to induce neuronal symmetry breaking. Bolus-like transport of shootin1 caused large stochastic fluctuations in shootin1 concentration in neurite tips. Interestingly, the generation of continuous shootin1 transport in our model neuron impaired the symmetry-breaking process (Figure 7D). This is consistent with theoretical models in which feedback amplification of fluctuations in signaling can give rise to robust patterns (Turing, 1952; Meinhardt and Gierer, 2000; Kondo, 2002), and underscores the importance of the stochastic fluctuating signals in spontaneous neuronal symmetry breaking. The combination of quantitative experimentation and mathematical modeling is regarded as a powerful strategy for attaining a profound understanding of biological systems (Hodgkin and Huxley, 1952b; Lewis, 2008; Ferrell, 2009). By focusing on a simple system involving one of the earliest markers of neuronal symmetry breaking, shootin1, we were able to evaluate here the core components of neuronal symmetry breaking on the basis of quantitative experimental data. The present model may thus provide a core mechanism of neuronal symmetry breaking, to which other possible mechanisms can be added to increase the model's complexity in future studies. Although there has been significant progress in understanding the molecular signals that change cell morphology, mechanisms that cells use to monitor their size and length to regulate their morphology remain elusive. Previous studies suggest that polarizing cultured hippocampal neurons can sense neurite length, identify the longest neurite, and induce its subsequent outgrowth for axonogenesis. We observed that shootin1, a key regulator of axon outgrowth and neuronal polarization, accumulates in neurite tips in a neurite length-dependent manner; here, the property of cell length is translated into shootin1 signals. Quantitative live cell imaging combined with modeling analyses revealed that intraneuritic anterograde transport and retrograde diffusion of shootin1 account for its neurite length-dependent accumulation. Our quantitative model further explains that the length-dependent shootin1 accumulation, together with shootin1-dependent neurite outgrowth, constitutes a positive feedback loop that amplifies stochastic fluctuations of shootin1 signals, thereby generating an asymmetric signal for axon specification and neuronal symmetry breaking.
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Affiliation(s)
- Michinori Toriyama
- Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Japan
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Flynn KC, Pak CW, Shaw AE, Bradke F, Bamburg JR. Growth cone-like waves transport actin and promote axonogenesis and neurite branching. Dev Neurobiol 2009; 69:761-79. [PMID: 19513994 DOI: 10.1002/dneu.20734] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Axonogenesis involves a shift from uniform delivery of materials to all neurites to preferential delivery to the putative axon, supporting its more rapid extension. Waves, growth cone-like structures that propagate down the length of neurites, were shown previously to correlate with neurite growth in dissociated cultured hippocampal neurons. Waves are similar to growth cones in their structure, composition and dynamics. Here, we report that waves form in all undifferentiated neurites, but occur more frequently in the future axon during initial neuronal polarization. Moreover, wave frequency and their impact on neurite growth are altered in neurons treated with stimuli that enhance axonogenesis. Coincident with wave arrival, growth cones enlarge and undergo a marked increase in dynamics. Through their engorgement of filopodia along the neurite shaft, waves can induce de novo neurite branching. Actin in waves maintains much of its cohesiveness during transport whereas actin in nonwave regions of the neurite rapidly diffuses as measured by live cell imaging of photoactivated GFP-actin and photoconversion of Dendra-actin. Thus, waves represent an alternative axonal transport mechanism for actin. Waves also occur in neurons in organotypic hippocampal slices where they propagate along neurites in the dentate gyrus and the CA regions and induce branching. Taken together, our results indicate that waves are physiologically relevant and contribute to axon growth and branching via the transport of actin and by increasing growth cone dynamics.
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Affiliation(s)
- Kevin C Flynn
- Graduate Program in Cell and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523, USA
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