Editing Microtubule (section)

==Functions==

===Cell migration===
Microtubule plus ends are often localized to particular structures. In polarized [[interphase]] cells, microtubules are disproportionately oriented from the MTOC toward the site of polarity, such as the leading edge of migrating [[fibroblast]]s. This configuration is thought to help deliver microtubule-bound vesicles from the [[Golgi apparatus|Golgi]] to the site of polarity.

Dynamic instability of microtubules is also required for the migration of most mammalian cells that crawl.<ref name="MikhailovGundersen1998">{{Cite journal |vauthors=Mikhailov A, Gundersen GG |year=1998 |title=Relationship between microtubule dynamics and lamellipodium formation revealed by direct imaging of microtubules in cells treated with nocodazole or taxol |journal=Cell Motility and the Cytoskeleton |volume=41 |issue=4 |pages=325–40 |doi=10.1002/(SICI)1097-0169(1998)41:4<325::AID-CM5>3.0.CO;2-D |pmid=9858157}}</ref> Dynamic microtubules regulate the levels of key [[G-proteins]] such as [[RhoA]]<ref name="Ren1999">{{Cite journal |vauthors=Ren XD, Kiosses WB, Schwartz MA |date=February 1999 |title=Regulation of the small GTP-binding protein Rho by cell adhesion and the cytoskeleton |journal=The EMBO Journal |volume=18 |issue=3 |pages=578–85 |doi=10.1093/emboj/18.3.578 |pmc=1171150 |pmid=9927417}}</ref> and [[Rac1]],<ref name="Waterman-StorerWorthylake1999">{{Cite journal |vauthors=Waterman-Storer CM, Worthylake RA, Liu BP, Burridge K, Salmon ED |date=May 1999 |title=Microtubule growth activates Rac1 to promote lamellipodial protrusion in fibroblasts |journal=Nature Cell Biology |volume=1 |issue=1 |pages=45–50 |doi=10.1038/9018 |pmid=10559863 |s2cid=26321103}}</ref> which regulate cell contractility and cell spreading. Dynamic microtubules are also required to trigger [[focal adhesion]] disassembly, which is necessary for migration.<ref>{{Cite journal |vauthors=Ezratty EJ, Partridge MA, Gundersen GG |date=June 2005 |title=Microtubule-induced focal adhesion disassembly is mediated by dynamin and focal adhesion kinase |journal=Nature Cell Biology |volume=7 |issue=6 |pages=581–90 |doi=10.1038/ncb1262 |pmid=15895076 |s2cid=37153935}}</ref> It has been found that microtubules act as "struts" that counteract the contractile forces that are needed for trailing edge retraction during cell movement. When microtubules in the trailing edge of cell are dynamic, they are able to remodel to allow retraction. When dynamics are suppressed, microtubules cannot remodel and, therefore, oppose the contractile forces.<ref name=pmid20696757/> The morphology of cells with suppressed microtubule dynamics indicate that cells can extend the front edge (polarized in the direction of movement), but have difficulty retracting their trailing edge.<ref name="ReferenceA">{{Cite journal |vauthors=Ganguly A, Yang H, Sharma R, Patel KD, Cabral F |date=December 2012 |title=The role of microtubules and their dynamics in cell migration |journal=The Journal of Biological Chemistry |volume=287 |issue=52 |pages=43359–69 |doi=10.1074/jbc.M112.423905 |pmc=3527923 |pmid=23135278 |doi-access=free}}</ref> On the other hand, high drug concentrations, or microtubule mutations that depolymerize the microtubules, can restore cell migration but there is a loss of directionality. It can be concluded that microtubules act both to restrain cell movement and to establish directionality.

===Cilia and flagella===
Microtubules have a major structural role in eukaryotic [[Cilium|cilia]] and [[Flagellum|flagella]]. Cilia and flagella always extend directly from a MTOC, in this case termed the basal body. The action of the dynein motor proteins on the various microtubule strands that run along a cilium or flagellum allows the organelle to bend and generate force for swimming, moving extracellular material, and other roles.  [[Prokaryote]]s possess tubulin-like proteins including [[FtsZ]]. However, prokaryotic flagella are entirely different in structure from eukaryotic flagella and do not contain microtubule-based structures.

===Development===
The cytoskeleton formed by microtubules is essential to the [[morphogenesis|morphogenetic process]] of an organism's [[Developmental biology|development]]. For example, a network of polarized microtubules is required within the [[oocyte]] of ''[[Drosophila melanogaster]]'' during its [[Drosophila embryogenesis|embryogenesis]] in order to establish the axis of the egg. Signals sent between the follicular cells and the oocyte (such as factors similar to [[epidermal growth factor]]) cause the reorganization of the microtubules so that their (-) ends are located in the lower part of the oocyte, polarizing the structure and leading to the appearance of an anterior-posterior axis.<ref name="Van1999">{{Cite journal |vauthors=van Eeden F, St Johnston D |date=August 1999 |title=The polarisation of the anterior-posterior and dorsal-ventral axes during Drosophila oogenesis |journal=Current Opinion in Genetics & Development |volume=9 |issue=4 |pages=396–404 |doi=10.1016/S0959-437X(99)80060-4 |pmid=10449356}}</ref> This involvement in the body's architecture is also seen in [[mammal]]s.<ref name="Beddington1999">{{Cite journal |vauthors=Beddington RS, Robertson EJ |date=January 1999 |title=Axis development and early asymmetry in mammals |journal=Cell |volume=96 |issue=2 |pages=195–209 |doi=10.1016/S0092-8674(00)80560-7 |pmid=9988215 |s2cid=16264083 |doi-access=free}}</ref>

Another area where microtubules are essential is the [[development of the nervous system]] in higher [[vertebrate]]s, where tubulin's dynamics and those of the associated proteins (such as the microtubule-associated proteins) are finely controlled during the development of the [[nervous system]].<ref name="Tucker1990">{{Cite journal |vauthors=Tucker RP |year=1990 |title=The roles of microtubule-associated proteins in brain morphogenesis: a review |journal=Brain Research. Brain Research Reviews |volume=15 |issue=2 |pages=101–20 |doi=10.1016/0165-0173(90)90013-E |pmid=2282447 |s2cid=12641708}}</ref>

===Gene regulation===
The cellular cytoskeleton is a dynamic system that functions on many different levels: In addition to giving the cell a particular form and supporting the transport of vesicles and organelles, it can also influence [[gene expression]]. The [[signal transduction]] mechanisms involved in this communication are little understood. However, the relationship between the drug-mediated depolymerization of microtubules, and the specific expression of [[transcription factors]] has been described, which has provided information on the differential expression of the genes depending on the presence of these factors.<ref name="Rosette1995">{{Cite journal |vauthors=Rosette C, Karin M |date=March 1995 |title=Cytoskeletal control of gene expression: depolymerization of microtubules activates NF-kappa B |journal=The Journal of Cell Biology |volume=128 |issue=6 |pages=1111–9 |doi=10.1083/jcb.128.6.1111 |pmc=2120413 |pmid=7896875}}</ref> This communication between the cytoskeleton and the regulation of the cellular response is also related to the action of [[growth factor]]s: for example, this relation exists for [[CTGF|connective tissue growth factor]].<ref name="Ott2003">{{Cite journal |vauthors=Ott C, Iwanciw D, Graness A, Giehl K, Goppelt-Struebe M |date=November 2003 |title=Modulation of the expression of connective tissue growth factor by alterations of the cytoskeleton |journal=The Journal of Biological Chemistry |volume=278 |issue=45 |pages=44305–11 |doi=10.1074/jbc.M309140200 |pmid=12951326 |doi-access=free}}</ref>