Cytoskeleton

12 Key excerpts on "Cytoskeleton"

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  eBook - ePub

  Embryogenesis Explained

  • Natalie K Gordon retired, Richard Gordon(Authors)
  • 2016(Publication Date)
  • WSPC

    (Publisher)

  Chapter 5

  The Cytoskeleton

  If one consults any of the standard developmental biology textbooks, the Cytoskeleton will be briefly presented as the support structure of the cell and about as interesting to most biologists as the floor struts in a ballet school would be to an artistic director seeking the next prima ballerina. However, to think of Cytoskeleton only as the structure on which cells do their remarkable things, leaves out a good part of the story of how cells work.

  We prefer to think of the Cytoskeleton as a troupe of acrobats. They run about in the cell, come together, stack to form some remarkable structure and then as rapidly as it appears, the structure falls apart and/or moves and the acrobats appear elsewhere on the stage. These acrobats are the individual proteins that make up the Cytoskeleton, and the many proteins that bind to Cytoskeleton, transiently hold it together, or move along it. The surface area available on the Cytoskeleton filaments for molecules to electrostatically and chemically bind is huge, far exceeding that of all cell membranes in an organism1 . Ignoring the Cytoskeleton while doing molecular biology would be like trying to choreograph a classical ballet while sharing the same stage with a troupe from Cirque de Soleil

  2 ,3

  .

  This unfortunate attitude towards the Cytoskeleton is beginning to change. For example, several of the pharmaceutical scientific supply companies have begun manufacturing kits designed specifically to detect the phenomenon of “cytoskeletal rearrangements” because all kinds of interesting other stuff seems to happen precisely when these rearrangements occur and therefore the rearrangements can be used to time such events

  4 ,5

  . We find it ironic that only a few people seem to actually think this is more than a convenient coincidence.

  The Cytoskeleton is, as the name implies, the skeleton of the cell giving it shape and form. The concept goes back to Nikolai K. Koltsov in 19036 . Koltsov formulated the idea that the deviation of the shape of a cell from the simple ball, that one would expect if it were a liquid drop, is caused by a stiff but elastic Cytoskeleton within the cell7 . Cytoskeleton is nowadays more precisely defined as the various structures that are filamentous polymers of a single class of protein. These filamentous polymers have long-range order within the cell8

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  Case Studies in Cell Biology

  • Merri Lynn Casem(Author)
  • 2016(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 6

  Cytoskeleton and Intracellular Motility

  Summary

  A cell’s Cytoskeleton provides the structural support necessary to maintain cell shape or anchor the cell to the extracellular matrix. At the same time, the Cytoskeleton creates a dynamic scaffold for the movement of organelles, chromosomes, and the cell itself. The potential for integration between the different distinct cytoskeletal filament systems is investigated in the case study, “Plakins: Keeping the Cytoskeleton Safe,” (Yang Y, Bauer C, Strasser G, Wollman R, Julien J-P, Fuchs E. Integrators of the Cytoskeleton that stabilize microtubules. Cell 1999;98:229–238). The discovery of the microtubule motor protein kinesin (Vale RD, Schnapp BJ, Reese TS, Sheetz MP. Organelle, bead and microtubule translocations promoted by soluble factors from the squid giant axon. Cell 1985;40:559–569) sets the stage for the case study, “The Moving Story of a Microtubule Motor Protein.” The case studies, ”The WASP and the Barbed End” (Co C, Wong DT, Gierke S, Chang V, Taunton J. Mechanism of actin network attachment to moving membranes: barbed end capture by N-WASP WH2 domains. Cell 2007;128: 901–913) and “Cilia Grow Where Vesicles Go” (Wood CR, Rosenbaum JL. Proteins of the ciliary axoneme are found on cytoplasmic membrane vesicles during growth of cilia. Curr Biol 2014; 24: 1114–1120.) investigate different aspects of the dynamic nature of the Cytoskeleton.

  Keywords

  microtubules microfilaments intermediate filaments microtubule binding assay

  in vitro motility assay

  kinesin actin comet tails flagellar regeneration primary cilia video microscopy immunoelectron microscopy

  Subchapter 6.1

  Plakins: Keeping the Cytoskeleton Safe [1]

  Introduction

  The Cytoskeleton of a cell is made up of three types of protein filaments: actin microfilaments (MF ), intermediate filaments (IF ), and microtubules (MT

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  Biomedical Applications

  • Malgorzata Lekka, Daniel Navajas, Manfred Radmacher, Alessandro Podestà, Malgorzata Lekka, Daniel Navajas, Manfred Radmacher, Alessandro Podestà(Authors)
  • 2023(Publication Date)
  • De Gruyter

    (Publisher)

  All intracellular organelles are embedded in the cytoplasm filling the cell interior. The cytoplasm contains two elements, that is, the cytosol (a liquid fraction) and the Cytoskeleton (a network of protein filaments).

  The cytosol is the intracellular fluid comprised of water, dissolved ions, large water-soluble molecules, smaller molecules, and proteins. Within it, multiple levels of organization can be found. These include concentration gradients of small molecules such as calcium, large complexes of enzymes that act together to carry out metabolic pathways, and protein complexes such as proteasomes that enclose and separate parts of the cytosol.

  The Cytoskeleton is a mesh-like structure composed of various filamentous proteins. Apart from its structural functions related to maintaining cellular shape and providing the tool for organelles’ arrangements, the Cytoskeleton participates in various processes through interactions with other proteins, such as muscle contraction, cell division, migration, adhesion, and intracellular transport. The Cytoskeleton helps establish regularity within the cytoplasm and, together with the plasma membrane, determines the mechanical stability of the cell. The Cytoskeleton comprises three main elements – actin, intermediate filaments, and microtubules. A mesh-like structure composed of actin filaments is located beneath the cell membrane. Intermediate filaments form a ring around the cell nucleus and span over the whole cell volume. Microtubules have one end located at the microtubule-organizing center (a centrosome) close to the cell nucleus and the other in the cell membrane.

  In the following chapters, detailed descriptions of cell structural components are presented.

  Reference

  Lodish, H., A. Berk, P. Matsudaira, C. A. Kaiser, M. Krieger, M. P. Scott, L. Zipursky and J. Darnell (2004). “Molecular Cell Biology.” →

  4.2  The Cytoskeleton

  Wolfgang H. Goldmann

  Biophysics Group, Friedrich-Alexander-University Erlangen-Nuremberg , Department of Physics , Germany

  Acknowledgment:

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  Ultimate Computing

  Biomolecular Consciousness and NanoTechnology

  • S.R. Hameroff(Author)
  • 2014(Publication Date)
  • North Holland

    (Publisher)

  101 Chapter 5 Cytoskeleton/Cytocomputer Living organisms are collective assemblies of cells which contain collective assemblies of organized material called protoplasm. In turn, protoplasm con-sists of membranes, organelles, nuclei and the bulk interior medium of living cells: cytoplasm. Dynamic rearrangements of cytoplasm within eukaryotic cells account for their changing shape, repositioning of internal organelles, and in many cases, movement from one place to another. We now know that the Cytoskeleton, a dynamic network of filamentous proteins, is responsible for cytoplasmic organization (Figures 5.1 thru 5.3). 5.1 The Nature of Cytoplasm The nature of cytoplasm has been scientifically studied for at least a cen-tury and a half. That history was described by Beth Burnside (1974) in a landmark meeting devoted to the Cytoskeleton at the New York Academy of Sciences. An early French observer of cellular material, Felix DuJardin proposed in 1835 that all cells were composed of a motile material called sarcode that had both structural and contractile properties. In 1861, Austrian E. Brucke linked the mechanical and physiological properties of cells to a fundamen-tal organization or architecture of cytoplasm as distinguished from purely chemical or physical properties. Early Dutch microscopist van Leeuwenhoek observed that red blood cells became deformed passing through capillaries and then sprang back into shape, demonstrating the elasticity of cytoplasm. The variety of elaborate forms that cells assume and maintain also require some cytoplasmic rigidity, properties which led nineteenth century biologists 102 CHAPTER 5. Cytoskeleton/CYTOCOMPUTER Figure 5.1: Cytoskeletal network in a rat kangaroo kidney cell (ptK2) il-lustrated by tubulin antibody and light microscopy. Microtubules emanate from a dense MTOC region near the nucleus (N).

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  Cell Chemistry and Physiology: Part IV

  • Edward Bittar(Author)
  • 1996(Publication Date)
  • Elsevier Science

    (Publisher)

  Chapter 1 The Cytoskeleton--Microtubules and Microfilaments: A Biological Perspective S.K. MALHOTRA and T.K. SHNITKA Introduction General Comments A Brief History of Cytoskeletal Studies Microtubules Structure and Composition of Microtubules Tubulin Gene Families in Vertebrates Assembly of Microtubules Reconstitution Experiments in Vitro Microtubule-Associated Proteins Functions of Microtubule-Organizing Centers Morphology and Functions of Special Microtubular Structures Axoneme Movement Is Produced by a Sliding Microtubule Mechanism Genetic Mutations Affecting Cilia and Flagella Role of Microtubules in Cytokinesis and in Plant Cell Wall Formation Axonal (Axoplasmic) Transport Microtubules Determine the Intracellular Location, Shapes, and Dynamics of Membrane-Bound Organelles Role of the Cytoskeleton in Cell Division: Formation of the Mitotic Spindle, Mitosis, and Cytokinesis Drug Effects on Microtubules Microfilaments: Actin Filaments Structure and Composition 2 2 2 4 4 4 5 5 6 8 8 10 11 14 15 17 18 21 21 21 Principles of Medical Biology, Volume 4 Cell Chemistry and Physiology: Part IV, pages 1--41. Copyright 9 1996 by JAI Press Inc. All rights of reproduction in any form reserved. ISBN: 1-55938-808-0 2 S.K. MALHOTRA and T.K. SHNITKA NonmuscleActin-BindingProteins 22 Drugs AffectingActin Polymerization 23 Patterns of Arrangementof Actin Filamentsin AnimalCells 25 Three-Dimensional Net~orks 25 The Microtrabeeular Lattice 34 Concluding Remarks on the Organization and Polyfunctionalit). of the C)loskeleton 34 INTRODUCTION General Comments The cytoplasm of all eukaryotic cells contains a cytoskeletal framework that serves a multitude of dynamic functions exemplified by the control of cell shape, the internal positioning and movement of organelles, and the capacity of the cell to move and undergo division. The major types of cytoskeletal filaments are 7-nm-thick microfilaments. 25- nm-thick microtubules, and 10-nm-thick intermediate filaments (IFs).

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  Cell Press Reviews: Core Concepts in Cell Biology

  • (Author)
  • 2013(Publication Date)
  • AP Cell

    (Publisher)

  We apologize to authors whose work on Cytoskeleton self-organization was instructive and influential but not cited here because the purpose was to focus on the specific role of SBCs. We thank all members of the Physics of the Cytoskeleton and Morphogenesis Laboratory for their experimental work and discussions. This work was supported by grants from the Human Frontier Science Programs (RGP0004/2011 to L.B. and RGY0088/2012 to M.T.) and Institut National du Cancer (PLBIO 2011-141 to M.T.).

  Trends in Cell Biology, Vol. 22, No. 12, December 2012 © 2012 Elsevier Inc. http://dx.doi.org/10.1016/j.tcb.2012.08.012

  Summary

  The Cytoskeleton architecture supports many cellular functions. Cytoskeleton networks form complex intracellular structures that vary during the cell cycle and between different cell types according to their physiological role. These structures do not emerge spontaneously. They result from the interplay between intrinsic self-organization properties and the conditions imposed by spatial boundaries. Along these boundaries, Cytoskeleton filaments are anchored, repulsed, aligned, or reoriented. Such local effects can propagate alterations throughout the network and guide Cytoskeleton assembly over relatively large distances. The experimental manipulation of spatial boundaries using microfabrication methods has revealed the underlying physical processes directing Cytoskeleton self-organization. Here we review, step-by-step, from molecules to tissues, how the rules that govern assembly have been identified. We describe how complementary approaches, all based on controlling geometric conditions, from in vitro reconstruction to in vivo observation, shed new light on these fundamental organizing principles.

  Setting Boundaries

  The reproducible shape and spatial organization of organs imply the existence of deterministic rules directing the assembly of complex biological structures. Organ shape depends on cell architecture, which is supported by Cytoskeleton networks. The formation of defined and geometrically controlled intracellular structures relies on the self-organization properties of the Cytoskeleton. The contribution of self-organization in cell biology is vast and now well documented [1]

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  Cytoskeleton

  Structure, Dynamics, Function and Disease

  • Jose C. Jimenez-Lopez(Author)
  • 2017(Publication Date)
  • IntechOpen

    (Publisher)

  This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. an end point of signaling pathways adapting cells to immediate or long‐lasting behaviors in healthy and sick organisms. Cytoskeleton of most animal cells is constituted by three interconnected filament subsystems: microfilaments (MFs), microtubules (MTs) and intermediate filaments (IFs). Compelling evidence from the last decades has brought convincing understanding for the highly regu ‐ lated and interconnected interactions between the cytoskeletal elements giving support to sculpting and maintaining cell shape and sustaining all kinds of morphological alterations or internal organization, as well as their implications for the behavior of animal cells. Figure 1 demonstrates the organization of the Cytoskeleton in neurons. A cohort of accessory proteins and signaling machinery regulates the dynamic turnover of the Cytoskeleton. Although each type of filament has specific cell distribution, molecular constitu ‐ ents and equilibrium, the coordinated intertwining among the different networks provides the force for a number of coherent processes in response to all kinds of intra‐ and extracellular stimuli leading responses so decisive as cell survival or death [1 ]. This chapter initiates with a brief introduction about the structure and function of IFs, empha ‐ sizing those from neural cells. However, the main purposes of the chapter are the experimen ‐ tal evidence of our laboratory that the roles of IFs are beyond protection from mechanical and nonmechanical stress. They might be the end point of misregulated‐signaling mechanisms in neurotoxic conditions adapting their dynamics, in concert with the other cytoskeletal fibers, to cell survival or death.

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  Cellular Organelles

  • Edward Bittar(Author)
  • 1995(Publication Date)
  • Elsevier Science

    (Publisher)

  Chapter 6 The Cytoskeleton DAVID S. ETTENSON and AVRUM i. GOTLIEB . . . . Introduction ActinuAn Ubiquitous Molecule Formation of Actin Microfilaments Actin Binding Proteins Microfilaments and Cell Adhesion Microfilaments in Cell Contraction Microfilaments and Cytokinesis Microfilaments in Response to Physical Forces Microfilaments and Cell Migration Microfilaments in the Epithelial Cell Villus Microfilaments and Secretion Microfilaments and Phagocytosis Microtubules Associated Proteins Microtubule Motors Microtubules and Cell Migration Microtubules and Cilia Microtubules and Mitosis Microtubules and Axon Growth Alzheimer's Disease Summary 122 122 124 125 127 129 130 130 131 132 132 132 133 135 137 138 139 141 141 143 144 Principles of Medical Biology, Volume 2 Cellular Organelles, pages 121-145 Copyright 9 1995 by JAI Press Inc. All rights of reproduction in any form reserved. ISBN:l-55938-803-X 121 122 DAVID S. ETTENSON and AVRUM I. GOTLIEB INTRODUCTION In this chapter, we will discuss the structure-function relationships of two important cytoskeletal systems in eukaryotic cells~actin microfil- aments and microtubules. The third component of the Cytoskeleton, intermediate filaments, will be discussed in Chapter 7. Many of the molecular concepts presented in this chapter are derived from in vitro biochemical studies of the various isolated proteins. Novel methods, however, are now allowing for cellular work to be done both in cell and organ culture systems and in vivo. Both the protein monomers actin and tubulin form long polymers by helical polymerization which are able to self-associate to form actin microfilaments and microtubules. The efficient methods of polymerization and depolymerization of these proteins make them well designed to provide mechanical support and integrate numerous cellular processes.

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  Introduction to Molecular Biophysics

  • Jack A. Tuszynski, Michal Kurzynski(Authors)
  • 2003(Publication Date)
  • CRC Press

    (Publisher)

  Tensegrity structures are mechanically stable because of the way the entire architecture distributes and balances mechanical stresses — not because of the strength of individual members. Since tension is continuously transmitted across all structural members, a global increase in tension is balanced by an increase in compression within members distributed throughout the structure. As described above, the interiors of living cells contain internal frameworks called Cytoskeletons composed of three types of molecular protein polymers, known as MFs, IFs and MTs.

  Cell shape is regulated by a complex balance of internal and external forces exerted by the extracellular matrices. This balance in terms of tensegrity was described by Ingber (1993, 1997). Cells acquire their shape from tensegrity arising from the three major types of Cytoskeleton filaments and also from the extracellular matrices — the anchoring scaffolding to which cells are naturally secured. A network of contractile microfilaments in the cell exerts tension and pulls the membrane and all its internal constituents toward the nucleus at the core. Opposing this inward pull are two main types of compressive elements, one outside the cell and the other inside. The component outside the cell is the extracellular matrix; the compressive “girders” inside the cell can be MTs or large bundles of cross-linked MFs within the Cytoskeleton. The third component of the Cytoskeleton, the intermediate filaments, interconnect MTs and contractile MFs to the surface membrane and the nucleus.

  Contractile actin bundles act as molecular cables. They exert tensile force on the cell membrane and the internal constituents, pulling them all toward the nucleus. MTs act as struts that resist the compressive force of the cables. In many cases, it is important to maintain cell shape to preserve its functionality. Chen et al. (1997) showed experimentally how cells switch between genetic programs when forced to grow into specific shapes. King and Wu revealed on theoretical grounds how cell geometry changes and the susceptibility of cells to electromagnetic fields.

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  Karp's Cell and Molecular Biology

  • Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  The cells of the neural plate elongate as microtubules become oriented with their 430 CHAPTER 9 The Cytoskeleton and Cell Motility long axes parallel to the axis of the cell (inset, Figure 9.71b). Following elongation, the cells of the neural epithelium become constricted at one end, causing them to become wedge-shaped and the entire layer of cells to curve inward (Figure 9.71c). This latter change in cell shape is brought about by the contraction of a band of microfilaments that assemble in the cortical region of the cells just beneath the apical cell membrane (inset, Figure 9.71c). Eventually, the curvature of the neural tube causes the outer edges to con- tact one another, forming a cylindrical, hollow tube (Figure 9.71d,e) that will give rise to the animal’s entire nervous system. Review 1. Describe the steps taken by a mammalian cell crawl- ing over a substratum. 2. Describe the role of actin filaments in the activities of the growth cone of a neuron. 9.13 The Bacterial Cytoskeleton For many years, it was widely held that the Cytoskeleton was strictly a eukaryotic innovation that was absent from pro- karyotic cells. Recent research has revealed that numerous prokaryotes contain tubulin-, actin- and intermediate fila- ment-like proteins. Many of these bacterial proteins have been found to be structurally and functionally related to eukaryotic cytoskeletal proteins, suggesting that actin, microtubules, and intermediate filaments have all evolved from prokaryotic structures (Figure 9.72). The bacterial Cytoskeleton must carry out many of the same tasks as the eukaryotic Cytoskeleton, albeit at a smaller scale. For example, the role of building the cytokinetic ring during cell division is carried out by actin in eukaryotes and by the protein FtsZ in prokaryotes. FtsZ polymerizes into numer- ous short rod-like filaments at the site of cell division, creating a force-generating contractile ring and pulling the membrane inward to carry out cell fission (Figure 9.72c).

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  Karp's Cell Biology

  • Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
  • 2018(Publication Date)
  • Wiley

    (Publisher)

  Legions of white blood cells patrol the tissues of the body searching for debris and microorganisms. Certain parts of cells can also be motile; broad projections of epithelial cells at the edge of a wound act as motile devices that pull the sheet of cells over the damaged area, sealing the wound. Similarly, the leading edge of a grow- ing axon sends out microscopic processes that survey the sub- stratum and guide the cell toward a synaptic target. All of these various examples of motility share at least one component: They all depend on actin, the third major type of cytoskeletal element. Actin is also involved in intracellular motile pro- cesses, such as the movement of vesicles, phagocytosis, and cytokinesis. In fact, plant cells rely primarily on actin, rather than microtubules, to serve as tracks for the long‐distance transport of cytoplasmic vesicles and organelles. This bias toward actin‐based motility reflects the rather restricted distri- bution of microtubules in many plant cells (see Figure 13.6). Actin also plays an important role in determining the shapes of cells and can provide structural support for various types of cellular projections (as in Figure 13.66). Microfilament Structure Actin filaments are approximately 8 nm in diameter and com- posed of globular subunits of the protein actin, which is the most abundant protein in most cells. In the presence of ATP, actin monomers polymerize to form a flexible, helical filament. As a result of its subunit organization (FIGURE 13.37a), an actin fila- ment is essentially a two‐stranded structure with two helical grooves running along its length (Figure 13.37b). The terms actin filament, F‐actin, and microfilament are basically synonyms for this type of filament. Depending on the type of cell and the activity in which it is engaged, actin filaments can be organized into ordered arrays, highly branched networks, or tightly anchored bundles.

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  Karp's Cell and Molecular Biology

  Concepts and Experiments

  • Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  9.17 The Bacterial Cytoskeleton For many years, it was widely held that the Cytoskeleton was strictly a eukaryotic innovation that was absent from prokaryotic cells. Recent research from the past decade has revealed that numerous prokaryotes contain tubulin‐, actin‐ and intermediate filament‐like proteins. Many of these bacterial proteins have been found to be structurally and functionally related to eukaryotic cytoskeletal pro- teins, suggesting that actin, microtubules and intermediate filaments have all evolved from prokaryotic structures (FIGURE 9.69). The bacterial Cytoskeleton must carry out many of the same tasks as the eukaryotic Cytoskeleton, albeit at a smaller scale. For example, the role of building the cytokinetic ring during cell division is carried out by actin in eukaryotes, and by the protein FtsZ in prokaryotes. FtsZ polymerizes into numerous short rod‐like fila- ments at the site of cell division, generating a force‐generating con- tractile ring and pulling the membrane inwards to carry out cell fission (Figure 9.69 c). Although it acts analogously to the actin Cytoskeleton during cytokinesis, FtsZ is actually a tubulin homolog that is found in nearly all prokaryotic cells. Another prokaryotic cytoskeletal protein, ParM, has been shown to play a role in plasmid segregation, analogous to the action of micro- tubules during mitosis (FIGURE 9.69 a, 9.70). During cell division, ParM filaments indirectly bind to specific centromere‐like regions of low‐copy number plasmids and push them to opposite poles of the cell through a bidirectional polymerization mechanism. The result is that each daughter cell receives a copy of the plasmid, an outcome that would be very unlikely without such a segregation system in place. Interestingly, biochemical studies of ParM have revealed that it under- goes cycles of rapid growth and disassembly, very much akin to the dynamic instability seen in microtubules.

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