Array ( [0] => {{short description|Network of filamentous proteins that forms the internal framework of cells}} [1] => {{Organelle diagram}} [2] => [[Image:0317 Cytoskeletal Components.jpg|thumb|right|300px|The cytoskeleton consists of (a) microtubules, (b) microfilaments, and (c) intermediate filaments.{{CC-notice|cc=by4|url=https://openstax.org/books/anatomy-and-physiology/pages/3-2-the-cytoplasm-and-cellular-organelles}} {{cite book|last1=Betts|first1=J Gordon|last2=Desaix|first2=Peter|last3=Johnson|first3=Eddie|last4=Johnson|first4=Jody E|last5=Korol|first5=Oksana|last6=Kruse|first6=Dean|last7=Poe|first7=Brandon|last8=Wise|first8=James|last9=Womble|first9=Mark D|last10=Young|first10=Kelly A|title=Anatomy & Physiology|location=Houston|publisher=OpenStax CNX|isbn=978-1-947172-04-3|date=June 8, 2023|at=3.2 The cytoplasm and cellular organelles}}]] [3] => [4] => The '''cytoskeleton''' is a complex, dynamic network of interlinking [[protein filament]]s present in the [[cytoplasm]] of all [[Cell (biology)|cells]], including those of [[bacteria]] and [[archaea]].{{cite book|title=Becker's World of the Cell|last1=Hardin|first1=Jeff|last2=Bertoni|first2=Gregory|last3=Kleinsmith|first3=Lewis J.|date=2015|publisher=Pearson|isbn=978013399939-6|edition=8th|location=New York|pages=422–446|name-list-style=vanc}} In [[eukaryote]]s, it extends from the [[cell nucleus]] to the [[cell membrane]] and is composed of similar proteins in the various organisms. It is composed of three main components: [[microfilaments]], [[intermediate filaments]], and [[microtubules]], and these are all capable of rapid growth or disassembly depending on the cell's requirements.{{Cite book|title = Human Anatomy|edition = 4th|last1 = McKinley|first1 = Michael|publisher = McGraw Hill Education|year = 2015|isbn = 978-0-07-352573-0|location = New York|page = 29|last2 = Dean O'Loughlin|first2 = Valerie|last3 = Pennefather-O'Brien|first3 = Elizabeth|last4 = Harris|first4 = Ronald}} [5] => [6] => A multitude of functions can be performed by the cytoskeleton. Its primary function is to give the cell its shape and mechanical resistance to deformation, and through association with extracellular [[connective tissue]] and other cells it stabilizes entire tissues.{{cite book|title=Molecular Biology of the Cell|last1=Alberts|first1=Bruce|date=2008|publisher=Garland Science|isbn=978-0-8153-4105-5|edition=5th|location=New York|name-list-style=vanc|display-authors=etal}} The cytoskeleton can also contract, thereby deforming the cell and the cell's environment and allowing [[Cellular migration|cells to migrate]].{{cite journal|vauthors=Fletcher DA, Mullins RD|date=January 2010|title=Cell mechanics and the cytoskeleton|journal=Nature|volume=463|issue=7280|pages=485–92|bibcode=2010Natur.463..485F|doi=10.1038/nature08908|pmc=2851742|pmid=20110992}} Moreover, it is involved in many [[cell signaling]] pathways and in the uptake of extracellular material ([[endocytosis]]),{{cite journal | vauthors = Geli MI, Riezman H | title = Endocytic internalization in yeast and animal cells: similar and different | journal = Journal of Cell Science | volume = 111 ( Pt 8) | issue = 8 | pages = 1031–7 | date = April 1998 | doi = 10.1242/jcs.111.8.1031 | pmid = 9512499 }} the segregation of [[chromosome]]s during [[Cell division|cellular division]], the [[cytokinesis]] stage of cell division,{{cite journal|vauthors=Wickstead B, Gull K|date=August 2011|title=The evolution of the cytoskeleton|journal=The Journal of Cell Biology|volume=194|issue=4|pages=513–25|doi=10.1083/jcb.201102065|pmc=3160578|pmid=21859859}} as scaffolding to organize the contents of the cell in space and in [[intracellular transport]] (for example, the movement of [[vesicle (biology)|vesicles]] and [[organelle]]s within the cell) and can be a template for the construction of a [[cell wall]]. Furthermore, it can form specialized structures, such as [[flagellum|flagella]], [[cilium|cilia]], [[lamellipodia]] and [[podosomes]]. The structure, function and dynamic behavior of the cytoskeleton can be very different, depending on organism and cell type.{{cite journal |last1=Fuchs |first1=E. |last2=Karakesisoglou |first2=I. |date=2001 |title=Bridging cytoskeletal intersections |journal=Genes & Development |volume=15 |issue=1 |pages=1–14 | pmid=11156599 | doi=10.1101/gad.861501| doi-access=free}} Even within one cell, the cytoskeleton can change through association with other proteins and the previous history of the network. [7] => [8] => A large-scale example of an action performed by the cytoskeleton is [[muscle contraction]]. This is carried out by groups of highly specialized cells working together. A main component in the cytoskeleton that helps show the true function of this muscle contraction is the [[microfilament]]. Microfilaments are composed of the most abundant cellular protein known as actin. During contraction of a [[muscle]], within each muscle cell, [[myosin]] molecular motors collectively exert forces on parallel [[actin]] filaments. Muscle contraction starts from nerve impulses which then causes increased amounts of calcium to be released from the [[sarcoplasmic reticulum]]. Increases in calcium in the cytosol allows muscle contraction to begin with the help of two proteins, [[tropomyosin]] and [[troponin]].{{Cite journal|last=Cooper|first=Geoffrey M.|date=2000|title=Actin, Myosin, and Cell Movement|url=https://www.ncbi.nlm.nih.gov/books/NBK9961/|journal=The Cell: A Molecular Approach. 2nd Edition|language=en|url-status=live|archive-url=https://web.archive.org/web/20180428005948/https://www.ncbi.nlm.nih.gov/books/NBK9961/|archive-date=2018-04-28}} Tropomyosin inhibits the interaction between actin and myosin, while troponin senses the increase in calcium and releases the inhibition.{{Cite journal|last1=Berg|first1=Jeremy M.|last2=Tymoczko|first2=John L.|last3=Stryer|first3=Lubert | name-list-style = vanc |date=2002|title=Myosins Move Along Actin Filaments|url=https://www.ncbi.nlm.nih.gov/books/NBK22418/|journal=Biochemistry. 5th Edition|language=en|url-status=live|archive-url=https://web.archive.org/web/20180502014625/https://www.ncbi.nlm.nih.gov/books/NBK22418/|archive-date=2018-05-02}} This action contracts the muscle cell, and through the synchronous process in many muscle cells, the entire muscle. [9] => [10] => ==History== [11] => In 1903, [[Nikolai Koltsov|Nikolai K. Koltsov]] proposed that the shape of cells was determined by a network of tubules that he termed the cytoskeleton. The concept of a protein mosaic that dynamically coordinated cytoplasmic biochemistry was proposed by Rudolph Peters in 1929{{cite journal |author=Peters RA |title= The Harben Lectures, 1929. Reprinted in: Peters, R. A. (1963) Biochemical lesions and lethal synthesis, p. 216. Pergamon Press, Oxford. }} while the term (''cytosquelette'', in French) was first introduced by French embryologist [[Paul Wintrebert]] in 1931.{{cite journal | vauthors = Frixione E | s2cid = 16728876 | title = Recurring views on the structure and function of the cytoskeleton: a 300-year epic | journal = Cell Motility and the Cytoskeleton | volume = 46 | issue = 2 | pages = 73–94 | date = June 2000 | pmid = 10891854 | doi = 10.1002/1097-0169(200006)46:2<73::AID-CM1>3.0.CO;2-0 }} [12] => [13] => When the cytoskeleton was first introduced, it was thought to be an uninteresting gel-like substance that helped organelles stay in place.{{cite book|last1=Hardin|first1=Jeff| name-list-style = vanc |title=Becker's World of the Cell|publisher=Pearson|isbn=978-0-321-93492-5|pages=351|edition=9th|date=2015-12-03}} Much research took place to try to understand the purpose of the cytoskeleton and its components. [14] => [15] => Initially, it was thought that the cytoskeleton was exclusive to eukaryotes but in 1992 it was discovered to be present in prokaryotes as well. This discovery came after the realization that bacteria possess proteins that are homologous to tubulin and actin; the main components of the eukaryotic cytoskeleton.{{cite journal | vauthors = Wickstead B, Gull K | title = The evolution of the cytoskeleton | journal = The Journal of Cell Biology | volume = 194 | issue = 4 | pages = 513–25 | date = August 2011 | pmid = 21859859 | pmc = 3160578 | doi = 10.1083/jcb.201102065 }} [16] => [17] => ==Eukaryotic cytoskeleton== [18] => [19] => [[Eukaryotic]] cells contain three main kinds of cytoskeletal filaments: [[microfilaments]], [[microtubules]], and [[intermediate filaments]]. In [[neuron]]s the intermediate filaments are known as [[neurofilament]]s.{{cite journal |last1=Taran |first1=AS |last2=Shuvalova |first2=LD |last3=Lagarkova |first3=MA |last4=Alieva |first4=IB |title=Huntington's Disease-An Outlook on the Interplay of the HTT Protein, Microtubules and Actin Cytoskeletal Components. |journal=Cells |date=22 June 2020 |volume=9 |issue=6 |page=1514 |doi=10.3390/cells9061514 |pmid=32580314|pmc=7348758 |doi-access=free }} Each type is formed by the [[polymerization]] of a distinct type of [[protein subunit]] and has its own characteristic shape and [[intracellular]] distribution. Microfilaments are [[polymer]]s of the protein [[actin]] and are 7 nm in diameter. Microtubules are composed of [[tubulin]] and are 25 nm in diameter. Intermediate filaments are composed of various proteins, depending on the type of cell in which they are found; they are normally 8-12 nm in diameter. The cytoskeleton provides the cell with structure and shape, and by [[excluded volume|excluding]] [[macromolecules]] from some of the [[cytosol]], it adds to the level of [[macromolecular crowding]] in this compartment.{{cite journal | vauthors = Minton AP | title = Confinement as a determinant of macromolecular structure and reactivity | journal = Biophysical Journal | volume = 63 | issue = 4 | pages = 1090–100 | date = October 1992 | pmid = 1420928 | pmc = 1262248 | doi = 10.1016/S0006-3495(92)81663-6 | bibcode = 1992BpJ....63.1090M }} Cytoskeletal elements interact extensively and intimately with cellular membranes.{{cite journal | vauthors = Doherty GJ, McMahon HT | s2cid = 17352662 | title = Mediation, modulation, and consequences of membrane-cytoskeleton interactions | journal = Annual Review of Biophysics | volume = 37 | pages = 65–95 | year = 2008 | pmid = 18573073 | doi = 10.1146/annurev.biophys.37.032807.125912 }} [20] => [21] => Research into [[Neurodegeneration|neurodegenerative disorders]] such as [[Parkinson's disease]], [[Alzheimer's disease]], [[Huntington's disease]], and [[amyotrophic lateral sclerosis]] (ALS) indicate that the cytoskeleton is affected in these diseases.{{cite journal|last1=Pelucchi|first1=Silvia|last2=Stringhi|first2=Ramona|last3=Marcello|first3=Elena|title=Dendritic Spines in Alzheimer's Disease: How the Actin Cytoskeleton Contributes to Synaptic Failure|journal=International Journal of Molecular Sciences|volume=21|issue=3|year=2020|pages=908|issn=1422-0067|doi=10.3390/ijms21030908|pmid=32019166|pmc=7036943|doi-access=free}} Parkinson's disease is marked by the degradation of neurons, resulting in tremors, rigidity, and other non-motor symptoms. Research has shown that microtubule assembly and stability in the cytoskeleton is compromised causing the neurons to degrade over time.{{cite journal | vauthors = Pellegrini L, Wetzel A, Grannó S, Heaton G, Harvey K | title = Back to the tubule: microtubule dynamics in Parkinson's disease | journal = Cellular and Molecular Life Sciences | volume = 74 | issue = 3 | pages = 409–434 | date = February 2017 | pmid = 27600680 | pmc = 5241350 | doi = 10.1007/s00018-016-2351-6 }} In Alzheimer's disease, [[tau protein]]s which stabilize microtubules malfunction in the progression of the illness causing pathology of the cytoskeleton.{{cite journal | vauthors = Bamburg JR, Bloom GS | title = Cytoskeletal pathologies of Alzheimer's Disease | journal = Cell Motility and the Cytoskeleton | volume = 66 | issue = 8 | pages = 635–49 | date = August 2009 | pmid = 19479823 | pmc = 2754410 | doi = 10.1002/cm.20388 }} Excess glutamine in the Huntington protein involved with linking vesicles onto the cytoskeleton is also proposed to be a factor in the development of Huntington's Disease.{{cite journal | vauthors = Caviston JP, Holzbaur EL | title = Huntingtin protein is an essential integrator of intracellular vesicular trafficking | journal = Trends in Cell Biology | volume = 19 | issue = 4 | pages = 147–55 | date = April 2009 | pmid = 19269181 | pmc = 2930405 | doi = 10.1016/j.tcb.2009.01.005 }} Amyotrophic lateral sclerosis results in a loss of movement caused by the degradation of motor neurons, and also involves defects of the cytoskeleton.{{cite book | vauthors = Julien JP, Millecamps S, Kriz J | chapter = Cytoskeletal Defects in Amyotrophic Lateral Sclerosis (Motor Neuron Disease) | title = Nuclear Organization in Development and Disease | journal = Novartis Foundation Symposium | series = Novartis Foundation Symposia | volume = 264 | pages = 183–92; discussion 192–6, 227–30 | date = 2005 | doi = 10.1002/0470093765.ch12 | pmid = 15773754 | isbn = 978-0-470-09373-3 }} [22] => [23] => [[Stuart Hameroff]] and [[Roger Penrose]] suggest a role of microtubule vibrations in [[neurons]] in the origin of [[consciousness]].{{Cite web|url=https://www.elsevier.com/about/press-releases/research-and-journals/discovery-of-quantum-vibrations-in-microtubules-inside-brain-neurons-corroborates-controversial-20-year-old-theory-of-consciousness|title=Discovery of Quantum Vibrations in "Microtubules" Inside Brain Neurons Corroborates Controversial 20-Year-Old Theory of Consciousness|last=Elsevier|website=www.elsevier.com|language=en|access-date=2017-11-20|url-status=live|archive-url=https://web.archive.org/web/20161107154319/https://www.elsevier.com/about/press-releases/research-and-journals/discovery-of-quantum-vibrations-in-microtubules-inside-brain-neurons-corroborates-controversial-20-year-old-theory-of-consciousness|archive-date=2016-11-07}}{{cite journal |last1=Hameroff |first1=Stuart |last2=Penrose |first2=Roger |title=Consciousness in the universe |journal=Physics of Life Reviews |date=March 2014 |volume=11 |issue=1 |pages=39–78 |doi=10.1016/j.plrev.2013.08.002|pmid=24070914 |doi-access=free }} [24] => [25] => Accessory proteins including [[motor protein]]s regulate and link the filaments to other cell compounds and each other and are essential for controlled assembly of cytoskeletal filaments in particular locations.{{Cite book|title=Molecular Biology of the Cell|last=Alberts|first=Bruce|publisher=Garland Science|year=2015|isbn=978-0-8153-4464-3|pages=889}} [26] => [27] => A number of small-molecule [[cytoskeletal drugs]] have been discovered that interact with actin and microtubules. These compounds have proven useful in studying the cytoskeleton, and several have clinical applications. [28] => [29] => ===Microfilaments=== [30] => {{main|Microfilament}} [31] => {{Multiple image [32] => | align = [33] => | direction = [34] => | total_width = 500 [35] => | image1 = Microfilament Structure.svg [36] => | caption1 = Structure of a [[microfilament]] [37] => | image2 = MEF microfilaments.jpg [38] => | caption2 = Actin cytoskeleton of [[mus musculus|mouse]] [[embryo]] [[fibroblast]]s, stained with [[phalloidin]] [39] => }} [40] => [41] => Microfilaments, also known as actin filaments, are composed of linear polymers of [[Actin#G-Actin|G-actin]] proteins, and generate force when the growing (plus) end of the filament pushes against a barrier, such as the cell membrane. They also act as tracks for the movement of [[myosin]] molecules that affix to the microfilament and "walk" along them. In general, the major component or protein of microfilaments are actin. The G-actin monomer combines to form a polymer which continues to form the microfilament (actin filament). These subunits then assemble into two chains that intertwine into what are called [[Actin#F-Actin|F-actin]] chains.{{Cite journal|last=Cooper|first=Geoffrey M.|date=2000|title=Structure and Organization of Actin Filaments|url=https://www.ncbi.nlm.nih.gov/books/NBK9908/|journal=The Cell: A Molecular Approach. 2nd Edition|language=en|url-status=live|archive-url=https://web.archive.org/web/20180502014625/https://www.ncbi.nlm.nih.gov/books/NBK9908/|archive-date=2018-05-02}} Myosin motoring along F-actin filaments generates contractile forces in so-called actomyosin fibers, both in muscle as well as most non-muscle cell types.{{cite journal | vauthors = Gunning PW, Ghoshdastider U, Whitaker S, Popp D, Robinson RC | title = The evolution of compositionally and functionally distinct actin filaments | journal = Journal of Cell Science | volume = 128 | issue = 11 | pages = 2009–19 | date = June 2015 | pmid = 25788699 | doi = 10.1242/jcs.165563 | doi-access = free }} Actin structures are controlled by the [[Rho family]] of small GTP-binding proteins such as Rho itself for contractile acto-myosin filaments ("stress fibers"), Rac for lamellipodia and Cdc42 for filopodia. [42] => [43] => Functions include: [44] => * [[Muscle contraction]] [45] => * Cell movement [46] => * Intracellular transport/trafficking [47] => * Maintenance of [[Eukaryote|eukaryotic]] cell shape [48] => * [[Cytokinesis]] [49] => * Cytoplasmic streaming [50] => [51] => ===Intermediate filaments=== [52] => {{main|Intermediate filament}} [53] => {{Multiple image [54] => | align = [55] => | direction = [56] => | total_width = 500 [57] => | image1 = Intermediate filaments.svg [58] => | caption1 = Structure of an [[intermediate filament]] [59] => | image2 = KeratinF9.png [60] => | caption2 = Microscopy of [[keratin]] filaments inside cells [61] => }} [62] => [63] => Intermediate filaments are a part of the cytoskeleton of many [[Eukaryote|eukaryotic]] cells. These filaments, averaging 10 nanometers in diameter, are more stable (strongly bound) than microfilaments, and heterogeneous constituents of the cytoskeleton. Like [[actin]] filaments, they function in the maintenance of cell-shape by bearing tension ([[microtubules]], by contrast, resist compression but can also bear tension during [[mitosis]] and during the positioning of the centrosome). Intermediate filaments organize the internal tridimensional structure of the cell, anchoring [[organelle]]s and serving as structural components of the [[nuclear lamina]]. They also participate in some cell-cell and cell-matrix junctions. [[Nuclear lamina]] exist in all animals and all tissues. Some animals like the [[drosophila melanogaster|fruit fly]] do not have any cytoplasmic intermediate filaments. In those animals that express cytoplasmic intermediate filaments, these are tissue specific.{{cite journal | vauthors = Herrmann H, Bär H, Kreplak L, Strelkov SV, Aebi U | title = Intermediate filaments: from cell architecture to nanomechanics | journal = Nature Reviews. Molecular Cell Biology | volume = 8 | issue = 7 | pages = 562–73 | date = July 2007 | pmid = 17551517 | doi = 10.1038/nrm2197 | s2cid = 27115011 }} Keratin intermediate filaments in [[epithelial]] cells provide protection for different mechanical stresses the skin may endure. They also provide protection for organs against metabolic, oxidative, and chemical stresses. Strengthening of epithelial cells with these intermediate filaments may prevent onset of [[apoptosis]], or cell death, by reducing the probability of stress.{{cite journal | vauthors = Pan X, Hobbs RP, Coulombe PA | title = The expanding significance of keratin intermediate filaments in normal and diseased epithelia | journal = Current Opinion in Cell Biology | volume = 25 | issue = 1 | pages = 47–56 | date = February 2013 | pmid = 23270662 | pmc = 3578078 | doi = 10.1016/j.ceb.2012.10.018 }} [64] => [65] => Intermediate filaments are most commonly known as the support system or "scaffolding" for the cell and nucleus while also playing a role in some cell functions. In combination with proteins and [[desmosome]]s, the intermediate filaments form cell-cell connections and anchor the cell-matrix junctions that are used in messaging between cells as well as vital functions of the cell. These connections allow the cell to communicate through the desmosome of multiple cells to adjust structures of the tissue based on signals from the cells environment. Mutations in the IF proteins have been shown to cause serious medical issues such as premature aging, desmin mutations compromising organs, [[Alexander disease|Alexander Disease]], and [[muscular dystrophy]]. [66] => [67] => Different intermediate filaments are: [68] => * made of [[vimentin]]s. Vimentin intermediate filaments are in general present in mesenchymal cells. [69] => * made of [[keratin]]. Keratin is present in general in epithelial cells. [70] => * [[neurofilament]]s of neural cells. [71] => * made of [[lamin]], giving structural support to the nuclear envelope. [72] => * made of [[desmin]], play an important role in structural and mechanical support of muscle cells.{{cite journal | vauthors = Paulin D, Li Z | title = Desmin: a major intermediate filament protein essential for the structural integrity and function of muscle | journal = Experimental Cell Research | volume = 301 | issue = 1 | pages = 1–7 | date = November 2004 | pmid = 15501438 | doi = 10.1016/j.yexcr.2004.08.004 }} [73] => [74] => ===Microtubules=== [75] => {{main|Microtubule}} [76] => {{Multiple image [77] => | align = [78] => | direction = [79] => | total_width = 500 [80] => | image1 = Microtubule Structure.svg [81] => | caption1 = Structure of a [[microtubule]] [82] => | image2 = Btub.jpg [83] => | caption2 = Microtubules in a gel-fixated cell [84] => }} [85] => [86] => Microtubules are hollow cylinders about 23 nm in diameter (lumen diameter of approximately 15 nm), most commonly comprising 13 [[Microtubule|protofilaments]] that, in turn, are polymers of alpha and beta [[tubulin]]. They have a very dynamic behavior, binding [[Guanosine triphosphate|GTP]] for polymerization. They are commonly organized by the [[centrosome]]. [87] => [88] => In nine triplet sets (star-shaped), they form the [[centrioles]], and in nine doublets oriented about two additional microtubules (wheel-shaped), they form cilia and flagella. The latter formation is commonly referred to as a "9+2" arrangement, wherein each doublet is connected to another by the protein [[dynein]]. As both flagella and cilia are structural components of the cell, and are maintained by microtubules, they can be considered part of the cytoskeleton. There are two types of cilia: motile and non-motile cilia. Cilia are short and more numerous than flagella. The motile cilia have a rhythmic waving or beating motion compared to the non-motile cilia which receive sensory information for the cell; processing signals from the other cells or the fluids surrounding it. Additionally, the microtubules control the beating (movement) of the cilia and flagella.{{cite journal |url=https://www.ncbi.nlm.nih.gov/books/NBK21698/| title=Cilia and Flagella: Structure and Movement |first1=Harvey |last1=Lodish |first2=Arnold |last2=Berk |first3=S. Lawrence |last3=Zipursky |first4=Paul |last4=Matsudaira |first5=David |last5=Baltimore |first6=James |last6=Darnell |date=2 May 2018 |access-date=2 May 2018|via=www.ncbi.nlm.nih.gov|url-status=live|archive-url= https://web.archive.org/web/20180502014625/https://www.ncbi.nlm.nih.gov/books/NBK21698/ |archive-date=2 May 2018}} Also, the dynein arms attached to the microtubules function as the molecular motors. The motion of the cilia and flagella is created by the microtubules sliding past one another, which requires ATP. [89] => They play key roles in: [90] => * intracellular transport (associated with dyneins and [[kinesin]]s, they transport [[organelles]] like [[mitochondria]] or [[vesicle (biology)|vesicles]]). [91] => * [[File:Bronchiolar area cilia cross-sections 2.jpg|thumb|Cross section diagram through the cilium, showing the “9 + 2” arrangement of microtubules]]the [[axoneme]] of [[cilium|cilia]] and [[flagellum|flagella]]. [92] => * the [[mitotic spindle]]. [93] => * synthesis of the cell wall in plants. [94] => [95] => In addition to the roles described above, Stuart Hameroff and Roger Penrose have proposed that microtubules function in consciousness.Hameroff, S. and Penrose, R. Physics of Life Reviews 2014, 11, 39-78 [96] => [97] => ===Comparison=== [98] => {| class=wikitable [99] => |- [100] => ! Cytoskeleton
typeUnless else specified in boxes, then ref is:{{cite book | first = Walter F. | last = Boron | name-list-style = vanc |title=Medical Physiology: A Cellular And Molecular Approaoch |publisher=Elsevier/Saunders |year=2003 |page=1300 |isbn=978-1-4160-2328-9 }} Page 25 [101] => ! Diameter
([[nanometre|nm]]){{cite journal | vauthors = Fuchs E, Cleveland DW | title = A structural scaffolding of intermediate filaments in health and disease | journal = Science | volume = 279 | issue = 5350 | pages = 514–9 | date = January 1998 | pmid = 9438837 | doi = 10.1126/science.279.5350.514 | bibcode = 1998Sci...279..514F }} [102] => ! Structure [103] => ! Subunit examples [104] => |- [105] => ! [[Microfilaments]] [106] => | 6 [107] => | [[Double helix]] [108] => | [[Actin]] [109] => |- [110] => ! [[Intermediate filament|Intermediate
filament]]s [111] => | 10 [112] => | Two anti-parallel [[helix|helices]]/dimers, forming tetramers [113] => | [114] => * [[Vimentin]] ([[mesenchyme]]) [115] => * [[Glial fibrillary acidic protein]] ([[glial cell]]s) [116] => * [[Neurofilament]] proteins (neuronal processes) [117] => * [[Keratin]]s ([[epithelial cell]]s) [118] => * [[Nuclear lamins]] [119] => |- [120] => ! [[Microtubule]]s [121] => | 23 [122] => | [[Protofilament]]s, in turn consisting of tubulin subunits in complex with [[Stathmin protein domain|stathmin]]{{cite journal | vauthors = Steinmetz MO | title = Structure and thermodynamics of the tubulin-stathmin interaction | journal = Journal of Structural Biology | volume = 158 | issue = 2 | pages = 137–47 | date = May 2007 | pmid = 17029844 | doi = 10.1016/j.jsb.2006.07.018 }} [123] => | [[α-bubulin|α-]] and [[β-tubulin|β-Tubulin]] [124] => |} [125] => [126] => ===Septins=== [127] => {{main|Septin}} [128] => [129] => Septins are a group of the highly conserved [[Guanosine triphosphate|GTP]] binding proteins found in [[eukaryotes]]. Different septins form [[protein complex]]es with each other. These can assemble to filaments and rings. Therefore, septins can be considered part of the cytoskeleton.{{cite journal | vauthors = Mostowy S, Cossart P | title = Septins: the fourth component of the cytoskeleton | journal = Nature Reviews. Molecular Cell Biology | volume = 13 | issue = 3 | pages = 183–94 | date = February 2012 | pmid = 22314400 | doi = 10.1038/nrm3284 | s2cid = 2418522 }} The function of septins in cells include serving as a localized attachment site for other [[protein]]s, and preventing the [[diffusion]] of certain molecules from one cell compartment to another. In yeast cells, they build scaffolding to provide structural support during cell division and compartmentalize parts of the cell. Recent research in human cells suggests that septins build cages around bacterial pathogens, immobilizing the harmful microbes and preventing them from invading other cells.{{cite journal | vauthors = Mascarelli A | title = Septin proteins take bacterial prisoners: A cellular defence against microbial pathogens holds therapeutic potential | journal = Nature |date=December 2011 | doi = 10.1038/nature.2011.9540 | s2cid = 85080734 }} [130] => [131] => ===Spectrin=== [132] => {{main|Spectrin}} [133] => [134] => Spectrin is a cytoskeletal [[protein]] that lines the intracellular side of the [[plasma membrane]] in eukaryotic cells. Spectrin forms pentagonal or hexagonal arrangements, forming a [[scaffolding]] and playing an important role in maintenance of [[plasma membrane]] integrity and cytoskeletal structure.{{cite journal | vauthors = Huh GY, Glantz SB, Je S, Morrow JS, Kim JH | title = Calpain proteolysis of alpha II-spectrin in the normal adult human brain | journal = Neuroscience Letters | volume = 316 | issue = 1 | pages = 41–4 | date = December 2001 | pmid = 11720774 | doi = 10.1016/S0304-3940(01)02371-0 | s2cid = 53270680 }} [135] => [136] => ===Yeast cytoskeleton=== [137] => {{see also | Yeast}} [138] => [139] => In budding [[yeast]] (an important [[model organism]]), [[actin]] forms cortical patches, actin cables, and a cytokinetic ring and the cap. Cortical patches are discrete actin bodies on the membrane and are vital for [[endocytosis]], especially the recycling of glucan synthase which is important for [[cell wall]] synthesis. Actin cables are bundles of [[actin filaments]] and are involved in the transport of [[vesicle (biology and chemistry)|vesicles]] towards the cap (which contains a number of different proteins to polarize cell growth) and in the positioning of mitochondria. The [[cytokinesis|cytokinetic]] ring forms and constricts around the site of [[cell division]].{{cite journal | vauthors = Pruyne D, Bretscher A | title = Polarization of cell growth in yeast | journal = Journal of Cell Science | volume = 113 ( Pt 4) | issue = 4 | pages = 571–85 | date = February 2000 | doi = 10.1242/jcs.113.4.571 | pmid = 10652251 | doi-access = free }} [140] => [141] => ==Prokaryotic cytoskeleton== [142] => {{main|Prokaryotic cytoskeleton}} [143] => Prior to the work of Jones et al., 2001, the cell wall was believed to be the deciding factor for many bacterial cell shapes, including rods and spirals. When studied, many misshapen bacteria were found to have mutations linked to development of a [[cell envelope]].{{Cite journal|last1=Jones|first1=Laura J. F.|last2=Carballido-López|first2=Rut|last3=Errington|first3=Jeffery|date=2001-03-23|title=Control of Cell Shape in Bacteria: Helical, Actin-like Filaments in Bacillus subtilis|journal=Cell|volume=104|issue=6|pages=913–922|doi=10.1016/S0092-8674(01)00287-2|pmid=11290328|s2cid=14207533|doi-access=free}} The cytoskeleton was once thought to be a feature only of [[eukaryote|eukaryotic]] cells, but [[homology (biology)|homologues]] to all the major proteins of the eukaryotic cytoskeleton have been found in [[prokaryote]]s.{{cite journal | vauthors = Shih YL, Rothfield L | title = The bacterial cytoskeleton | journal = Microbiology and Molecular Biology Reviews | volume = 70 | issue = 3 | pages = 729–54 | date = September 2006 | pmid = 16959967 | pmc = 1594594 | doi = 10.1128/MMBR.00017-06 }} Harold Erickson notes that before 1992, only eukaryotes were believed to have cytoskeleton components. However, research in the early '90s suggested that bacteria and archaea had homologues of actin and tubulin, and that these were the basis of eukaryotic microtubules and microfilaments.{{cite journal | vauthors = Erickson HP | title = The discovery of the prokaryotic cytoskeleton: 25th anniversary | journal = Molecular Biology of the Cell | volume = 28 | issue = 3 | pages = 357–358 | date = February 2017 | pmid = 28137947 | pmc = 5341718 | doi = 10.1091/mbc.E16-03-0183 }} Although the evolutionary relationships are so distant that they are not obvious from protein sequence comparisons alone, the similarity of their three-dimensional [[protein structure|structures]] and similar functions in maintaining cell shape and polarity provides strong evidence that the eukaryotic and prokaryotic cytoskeletons are truly homologous.{{cite journal | vauthors = Michie KA, Löwe J | title = Dynamic filaments of the bacterial cytoskeleton | journal = Annual Review of Biochemistry | volume = 75 | pages = 467–92 | year = 2006 | pmid = 16756499 | doi = 10.1146/annurev.biochem.75.103004.142452 | url = http://www2.mrc-lmb.cam.ac.uk/groups/JYL/PDF/annrev2006.pdf }} Three laboratories independently discovered that FtsZ, a protein already known as a key player in bacterial cytokinesis, had the "tubulin signature sequence" present in all α-, β-, and γ-tubulins. However, some structures in the bacterial cytoskeleton may not have been identified as of yet.{{cite journal | vauthors = Briegel A, Dias DP, Li Z, Jensen RB, Frangakis AS, Jensen GJ | title = Multiple large filament bundles observed in Caulobacter crescentus by electron cryotomography | journal = Molecular Microbiology | volume = 62 | issue = 1 | pages = 5–14 | date = October 2006 | pmid = 16987173 | doi = 10.1111/j.1365-2958.2006.05355.x | doi-access = free }} [144] => [145] => ===FtsZ=== [146] => [[FtsZ]] was the first protein of the prokaryotic cytoskeleton to be identified. Like tubulin, FtsZ forms filaments in the presence of [[guanosine triphosphate]] (GTP), but these filaments do not group into tubules. During [[cell division]], FtsZ is the first protein to move to the division site, and is essential for recruiting other proteins that synthesize the new [[cell wall]] between the dividing cells. [147] => [148] => ===MreB and ParM=== [149] => Prokaryotic actin-like proteins, such as [[MreB]], are involved in the maintenance of cell shape. All non-spherical bacteria have [[gene]]s encoding actin-like proteins, and these proteins form a helical network beneath the cell membrane that guides the proteins involved in cell wall [[biosynthesis]].{{cite journal | vauthors = Popp D, Narita A, Maeda K, Fujisawa T, Ghoshdastider U, Iwasa M, Maéda Y, Robinson RC | title = Filament structure, organization, and dynamics in MreB sheets | journal = The Journal of Biological Chemistry | volume = 285 | issue = 21 | pages = 15858–65 | date = May 2010 | pmid = 20223832 | pmc = 2871453 | doi = 10.1074/jbc.M109.095901 | doi-access = free }} [150] => [151] => Some [[plasmid]]s encode a separate system that involves an actin-like protein [[ParM]]. Filaments of ParM exhibit [[Microtubule#Dynamic instability|dynamic instability]], and may partition plasmid DNA into the dividing daughter cells by a mechanism [[Analogy (biology)|analogous]] to that used by microtubules during eukaryotic [[mitosis]].{{cite journal | vauthors = Popp D, Narita A, Lee LJ, Ghoshdastider U, Xue B, Srinivasan R, Balasubramanian MK, Tanaka T, Robinson RC | title = Novel actin-like filament structure from Clostridium tetani | journal = The Journal of Biological Chemistry | volume = 287 | issue = 25 | pages = 21121–9 | date = June 2012 | pmid = 22514279 | pmc = 3375535 | doi = 10.1074/jbc.M112.341016 | doi-access = free }} [152] => [153] => ===Crescentin=== [154] => The bacterium ''[[Caulobacter crescentus]]'' contains a third protein, [[crescentin]], that is related to the intermediate filaments of eukaryotic cells. Crescentin is also involved in maintaining cell shape, such as helical and [[vibrio]]id forms of bacteria, but the mechanism by which it does this is currently unclear.{{cite journal | vauthors = Ausmees N, Kuhn JR, Jacobs-Wagner C | title = The bacterial cytoskeleton: an intermediate filament-like function in cell shape | journal = Cell | volume = 115 | issue = 6 | pages = 705–13 | date = December 2003 | pmid = 14675535 | doi = 10.1016/S0092-8674(03)00935-8 | s2cid = 14459851 | doi-access = free }} Additionally, curvature could be described by the displacement of crescentic filaments, after the disruption of peptidoglycan synthesis.{{Cite journal|title=Dynamics of the Bacterial Intermediate Filament Crescentin In Vitro and In Vivo|last=Esue|first=Osigwe|date=January 2010|journal=PLOS ONE|volume=5|issue=1|pages=e8855|pmid=20140233|doi=10.1371/journal.pone.0008855|pmc=2816638|bibcode=2010PLoSO...5.8855E|doi-access=free}} [155] => [156] => == The cytoskeleton and cell mechanics == [157] => The cytoskeleton is a highly anisotropic and dynamic network, constantly remodeling itself in response to the changing cellular microenvironment. The network influences cell mechanics and dynamics by differentially polymerizing and depolymerizing its constituent filaments (primarily actin and myosin, but microtubules and intermediate filaments also play a role).{{Cite journal |last=Chen |first=Christopher S. |date=2008-10-15 |title=Mechanotransduction – a field pulling together? |url=https://journals.biologists.com/jcs/article/121/20/3285/35315/Mechanotransduction-a-field-pulling-together |journal=Journal of Cell Science |language=en |volume=121 |issue=20 |pages=3285–3292 |doi=10.1242/jcs.023507 |pmid=18843115 |s2cid=1287523 |issn=1477-9137}} This generates forces, which play an important role in informing the cell of its microenvironment. Specifically, forces such as tension, stiffness, and shear forces have all been shown to influence cell fate, differentiation, migration, and motility. Through a process called “mechanotransduction,” the cell remodels its cytoskeleton to sense and respond to these forces. [158] => [159] => [[Mechanotransduction]] relies heavily on [[focal adhesions]], which essentially connect the intracellular cytoskeleton with the [[extracellular matrix]] (ECM). Through focal adhesions, the cell is able to integrate extracellular forces into intracellular ones as the proteins present at focal adhesions undergo conformational changes to initiate signaling cascades. Proteins such as focal adhesion kinase (FAK) and Src have been shown to transduce force signals in response to cellular activities such as proliferation and differentiation, and are hypothesized to be key sensors in the mechanotransduction pathway.{{Cite journal |last1=Orr |first1=A. Wayne |last2=Helmke |first2=Brian P. |last3=Blackman |first3=Brett R. |last4=Schwartz |first4=Martin A. |date=January 2006 |title=Mechanisms of Mechanotransduction |journal=Developmental Cell |language=en |volume=10 |issue=1 |pages=11–20 |doi=10.1016/j.devcel.2005.12.006|pmid=16399074 |doi-access=free }} As a result of mechanotransduction, the cytoskeleton changes its composition and/or orientation to accommodate the force stimulus and ensure the cell responds accordingly. [160] => [161] => The cytoskeleton changes the mechanics of the cell in response to detected forces. For example, increasing tension within the plasma membrane makes it more likely that ion channels will open, which increases ion conductance and makes cellular change ion influx or efflux much more likely. Moreover, the mechanical properties of cells determine how far and where, directionally, a force will propagate throughout the cell and how it will change cell dynamics.{{Cite journal |last1=Janmey |first1=Paul A. |last2=McCulloch |first2=Christopher A. |date=2007-08-15 |title=Cell Mechanics: Integrating Cell Responses to Mechanical Stimuli |url=http://www.annualreviews.org/doi/10.1146/annurev.bioeng.9.060906.151927 |journal=Annual Review of Biomedical Engineering |language=en |volume=9 |issue=1 |pages=1–34 |doi=10.1146/annurev.bioeng.9.060906.151927 |pmid=17461730 |issn=1523-9829}} A membrane protein that is not closely coupled to the cytoskeleton, for instance, will not produce a significant effect on the cortical actin network if it is subjected to a specifically directed force. However, membrane proteins that are more closely associated with the cytoskeleton will induce a more significant response. In this way, the anisotropy of the cytoskeleton serves to more keenly direct cell responses to intra or extracellular signals. [162] => [163] => == Long-range order == [164] => The specific pathways and mechanisms by which the cytoskeleton senses and responds to forces are still under investigation. However, the [[long-range order]] generated by the cytoskeleton is known to contribute to mechanotransduction.{{Cite journal |last1=Fletcher |first1=Daniel A. |last2=Mullins |first2=R. Dyche |date=January 2010 |title=Cell mechanics and the cytoskeleton |journal=Nature |language=en |volume=463 |issue=7280 |pages=485–492 |doi=10.1038/nature08908 |issn=0028-0836 |pmc=2851742 |pmid=20110992 |bibcode=2010Natur.463..485F }} Cells, which are around 10–50 μm in diameter, are several thousand times larger than the molecules found within the cytoplasm that are essential to coordinate cellular activities. Because cells are so large in comparison to essential biomolecules, it is difficult, in the absence of an organizing network, for different parts of the cytoplasm to communicate.{{Cite journal |last=Mullins |first=R. D. |date=2010-01-01 |title=Cytoskeletal Mechanisms for Breaking Cellular Symmetry |journal=Cold Spring Harbor Perspectives in Biology |language=en |volume=2 |issue=1 |pages=a003392 |doi=10.1101/cshperspect.a003392 |issn=1943-0264 |pmc=2827899 |pmid=20182610}} Moreover, biomolecules must polymerize to lengths comparable to the length of the cell, but resulting polymers can be highly disorganized and unable to effectively transmit signals from one part of the cytoplasm to another. Thus, it is necessary to have the cytoskeleton to organize the polymers and ensure that they can effectively communicate across the entirety of the cell. [165] => [166] => ==Common features and differences between prokaryotes and eukaryotes== [167] => By definition, the cytoskeleton is composed of proteins that can form longitudinal arrays (fibres) in all organisms. These filament forming proteins have been classified into 4 classes. [[Tubulin]]-like, [[actin]]-like, Walker A cytoskeletal ATPases (WACA-proteins), and [[intermediate filaments]]. [168] => [169] => Tubulin-like proteins are [[tubulin]] in eukaryotes and [[FtsZ]], TubZ, RepX in prokaryotes. Actin-like proteins are [[actin]] in eukaryotes and [[MreB]], [[FtsA]] in prokaryotes. An example of a WACA-proteins, which are mostly found in prokaryotes, is [[MinD]]. Examples for intermediate filaments, which have almost exclusively been found in animals (i.e. eukaryotes) are the [[lamin]]s, [[keratin]]s, [[vimentin]], [[neurofilament]]s, and [[desmin]]. [170] => [171] => Although tubulin-like proteins share some [[amino acid sequence]] similarity, their equivalence in protein-fold and the similarity in the [[Guanosine triphosphate|GTP]] binding site is more striking. The same holds true for the actin-like proteins and their structure and [[Adenosine triphosphate|ATP]] binding domain. [172] => [173] => Cytoskeletal proteins are usually correlated with cell shape, DNA segregation and cell division in prokaryotes and eukaryotes. Which proteins fulfill which task is very different. For example, DNA segregation in all eukaryotes happens through use of tubulin, but in prokaryotes either WACA proteins, actin-like or tubulin-like proteins can be used. Cell division is mediated in eukaryotes by actin, but in prokaryotes usually by tubulin-like (often FtsZ-ring) proteins and sometimes ([[Thermoproteota]]) [[ESCRT#ESCRT-III|ESCRT-III]], which in eukaryotes still has a role in the last step of division. [174] => [175] => == Cytoplasmic streaming == [176] => [[File:Movement of organelles in Tradescantia stamen hair cells.webm|thumb|Movement of organelles in ''[[Tradescantia]]'' stamen hair cells]] [177] => [[Cytoplasmic streaming]], also known as cyclosis, is the active movement of a cell's contents along the components of the cytoskeleton. While mainly seen in plants, all cell types use this process for transportation of waste, nutrients, and organelles to other parts of the cell. {{cite journal | vauthors = Woodhouse FG, Goldstein RE | title = Cytoplasmic streaming in plant cells emerges naturally by microfilament self-organization | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 110 | issue = 35 | pages = 14132–7 | date = August 2013 | pmid = 23940314 | pmc = 3761564 | doi = 10.1073/pnas.1302736110 | bibcode = 2013PNAS..11014132W | arxiv = 1308.6422 | doi-access = free }} Plant and algae cells are generally larger than many other cells; so cytoplasmic streaming is important in these types of cells. This is because the cell's extra volume requires cytoplasmic streaming in order to move organelles throughout the entire cell.{{cite journal|vauthors = Goldstein RE, van de Meent JW | title = A physical perspective on cytoplasmic streaming|journal=Interface Focus|volume = 5|issue = 4|pages=20150030|date=August 2015|pmid=26464789|pmc=4590424 | doi = 10.1098/rsfs.2015.0030 }} Organelles move along [[microfilament]]s in the cytoskeleton driven by [[myosin]] motors binding and pushing along [[actin]] filament bundles.  [178] => [179] => == See also == [180] => {{Portal|Biology}} [181] => [182] => * {{annotated link|Nuclear matrix}} [183] => * {{annotated link|Cell cortex}} [184] => [185] => == References == [186] => {{Reflist|30em}} [187] => [188] => == External links == [189] => {{Commons category|Cytoskeleton}} [190] => * [http://www.cytoskeleton.com/blog Cytoskeleton Monthly News and Blog] [191] => * [http://www.mechanobio.info/topics/cytoskeleton-dynamics MBInfo - Cytoskeleton Dynamics] [192] => * [http://biochemweb.fenteany.com/cytoskeleton.shtml Cytoskeleton, Cell Motility and Motors - The Virtual Library of Biochemistry, Molecular Biology and Cell Biology] [193] => * [http://www.cytoskeletons.com/ Cytoskeleton database, clinical trials, recent literature, lab registry ...] [194] => * [http://aimediaserver.com/studiodaily/videoplayer/?src=harvard/harvard.swf&width=640&height=520 Animation of leukocyte adhesion] (Animation with some images of actin and microtubule assembly and dynamics.) [195] => * http://cellix.imba.oeaw.ac.at/ Cytoskeleton and cell motility including videos [196] => * [http://www.tandfonline.com/doi/full/10.1080/00018732.2013.771509 Open access review article] on the emergent complexity of the cytoskeleton (appeared in ''Advances in Physics'', 2013) [197] => [198] => {{Organelles}} [199] => {{Cytoskeletal Proteins}} [200] => [201] => {{Authority control}} [202] => [203] => [[Category:Cytoskeleton| ]] [204] => [[Category:Cell anatomy]] [] => )
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Cytoskeleton

The cytoskeleton is a complex network of protein filaments found in the cells of all organisms. It plays a crucial role in maintaining cell shape and structure, as well as enabling various cellular processes such as cell division, cell movement, and intracellular transport.

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It plays a crucial role in maintaining cell shape and structure, as well as enabling various cellular processes such as cell division, cell movement, and intracellular transport. The three types of filaments that make up the cytoskeleton are microfilaments, intermediate filaments, and microtubules. Each filaments type has distinct characteristics and functions. Microfilaments are involved in cell movement and support, intermediate filaments provide mechanical strength to cells, and microtubules serve as tracks for intracellular transport and are crucial for cell division. The cytoskeleton also acts as a scaffold for organizing organelles within the cell and plays a role in maintaining the overall integrity and functionality of the cell. Dysfunction of the cytoskeleton can lead to various human diseases, including cancer and neurodegenerative disorders. Thus, understanding the cytoskeleton is essential for comprehending cellular biology and human health.

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