Centriole
7682
224529240
2008-07-09T07:29:19Z
Chris Capoccia
286058
not a stub
[[Image:Spindle centriole - embryonic brain mouse - TEM.jpg|thumb|A centriole, showing the nine triplets of [[microtubule]]s. [[Transmission electron microscope]] image.]]
[[Image:Centriole-schema.SVG|thumb|Schematic of centriole showing [[microtubule]] triplets]]
[[Image:Centriole3D.png|thumb|3-dimensional view of a centriole]]
A '''centriole''' is a barrel shaped [[organelle]]<ref name=edde>{{cite journal |author=Eddé B, Rossier J, Le Caer JP, Desbruyères E, Gros F, Denoulet P |title=Posttranslational glutamylation of alpha-tubulin |journal=[[Science (journal)|Science]] |volume=247 |issue=4938 |pages=83–5 |year=1990 |month=January |pmid=1967194 |doi=10.1126/science.1967194 |url=http://www.sciencemag.org/cgi/content/abstract/247/4938/83 |accessdate=2008-07-09}}</ref> found in most animal [[eukaryotic]] [[Cell (biology)|cell]]s, though absent in [[higher plant]]s and [[fungi]].<ref>{{cite journal |author=Quarmby LM, Parker JD |title=Cilia and the cell cycle? |journal=The Journal of Cell Biology |volume=169 |issue=5 |pages=707–710 |year=2005 |month=June |pmid=15928206 |pmc=2171619 |doi=10.1083/jcb.200503053 |url=http://www.jcb.org/cgi/pmidlookup?view=long&pmid=15928206 |accessdate=2008-07-08}}</ref> The walls of each centriole are usually composed of nine triplets of [[microtubule]]s (protein of the cytoskeleton). Deviations from this structure include ''[[Drosophila melanogaster]]'' embryos, with nine doublets, and ''[[Caenorhabditis elegans]]'' [[sperm]] cells and early embryos, with nine singlets.<ref>{{cite journal |author=Delattre M, Gönczy P |title=The arithmetic of centrosome biogenesis |journal=Journal of Cell Science |volume=117 |issue=Pt 9 |pages=1619–1630 |year=2004 |month=April |pmid=15075224 |doi=10.1242/10.1242/jcs.01128 |url=http://jcs.biologists.org/cgi/content/full/117/9/1619 |accessdate=2008-07-08 |doi_brokendate=2008-07-08}}</ref><ref>{{cite journal |author=Leidel S, Delattre M, Cerutti L, Baumer K, Gönczy P |title=SAS-6 defines a protein family required for centrosome duplication in C. elegans and in human cells |journal=Nature Cell Biology |volume=7 |issue=2 |pages=115–25 |year=2005 |month=February |pmid=15665853 |doi=10.1038/ncb1220 |url=http://www.nature.com/ncb/journal/v7/n2/abs/ncb1220.html |accessdate=2008-07-08}}</ref> An associated pair of centrioles, arranged [[perpendicular]]ly and surrounded by an [[amorphous]] mass of dense material (known as the Pericentriolar material) constitutes the compound structure known as the [[centrosome]].<ref name=edde/>
==Function==
===Cell division===
Centrioles are involved in the organization of the [[mitotic spindle]] and in the completion of [[cytokinesis]].<ref name="Salisbury">{{cite journal |author=Salisbury JL, Suino KM, Busby R, Springett M |title=Centrin-2 is required for centriole duplication in mammalian cells |journal=Current Biology |volume=12 |issue=15 |pages=1287–1292 |year=2002 |month=August |pmid=12176356 |url=http://www.current-biology.com/content/article/fulltext?uid=PIIS0960982202010199 |accessdate=2008-07-08 |doi=10.1016/S0960-9822(02)01019-9}}</ref> Centrioles were historically thought to be required for the formation of a mitotic spindle in animal cells. However, more recent experiments have demonstrated that cells whose centrioles have been removed via laser ablation can still undergo mitosis.<ref name="Terra">{{cite journal |author=La Terra S, English CN, Hergert P, McEwen BF, Sluder G, Khodjakov A |title=The de novo centriole assembly pathway in HeLa cells: cell cycle progression and centriole assembly/maturation |journal=The Journal of Cell Biology |volume=168 |issue=5 |pages=713–722 |year=2005 |month=February |pmid=15738265 |pmc=2171814 |doi=10.1083/jcb.200411126 |url=http://www.jcb.org/cgi/pmidlookup?view=long&pmid=15738265 |accessdate=2008-07-08}}</ref> Additionally, mutant flies lacking centrioles can develop almost normally, although the adult flies lack [[flagella]] and [[cilia]], a lack that underscores the requirement of centrioles for the formation of these organelles (see below).<ref name="Basto">{{cite journal |author=Basto R, Lau J, Vinogradova T, ''et al'' |title=Flies without centrioles |journal=[[Cell (journal)|Cell]] |volume=125 |issue=7 |pages=1375–1386 |year=2006 |month=June |pmid=16814722 |doi=10.1016/j.cell.2006.05.025 |url=http://linkinghub.elsevier.com/retrieve/pii/S0092-8674(06)00654-4 |accessdate=2008-07-08}}</ref> Cells whose centrioles have been removed (either via laser ablation, or genetic manipulation) lack aster microtubules. These cells often fail to undergo proper asymmetric cell division, as the aster microtubules help to position the spindle within the cell.
===Cellular organization===
Centrioles are a very important part of centrosomes, which are involved in organizing [[microtubules]] in the [[cytoplasm]].<ref name="PLOS">{{cite journal |author=Feldman JL, Geimer S, Marshall WF |title=The mother centriole plays an instructive role in defining cell geometry |journal=[[PLoS Biology]] |volume=5 |issue=6 |pages=e149 |year=2007 |month=June |pmid=17518519 |pmc=1872036 |doi=10.1371/journal.pbio.0050149 |url=http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050149 |accessdate=2008-07-08}}</ref><ref>{{cite journal |author=Beisson J, Wright M |title=Basal body/centriole assembly and continuity |journal=Current Opinion in Cell Biology |volume=15 |issue=1 |pages=96–104 |year=2003 |month=February |pmid=12517710 |doi= |url=http://linkinghub.elsevier.com/retrieve/pii/S0955067402000170 |accessdate=2008-07-08}}</ref>The position of the centriole determines the position of the nucleus and plays a crucial role in the spatial arrangement of cell organelles.
===Ciliogenesis===
In organisms with [[flagella]] and [[cilia]], the position of these organelles is determined by the mother centriole, which becomes the [[basal body]]. An inability of cells to use centrioles to make functional cilia and flagella has been linked to a number of genetic and developmental diseases. In particular, the inability of centrioles to properly migrate prior to ciliary assembly has recently been linked to [[Meckel-Gruber syndrome]].
===Animal development===
Additionally, proper orientation of cilia via centriole positioning toward the posterior of embryonic node cells is critical for establishing left–right asymmetry during mammalian development.<ref name="PLOS"/>
==Structure of centrioles and mechanism of their duplication==
Cells in [[G0 phase|G0]] and [[G1 phase|G1]] usually contain two complete centrioles. The older of the two centrioles in a pair is termed the ''mother centriole'', whereas the younger is termed the ''daughter centriole''. During the [[Cell division|cell division cycle]], a new centriole grows from the side of each of the existing "mother" centrioles. After centriole duplication, the two pairs of centrioles remain attached to each other in an [[orthogonal]] configuration until [[mitosis]], when the mother and daughter centrioles separate in a manner dependent upon the [[enzyme]] [[separase]].<ref>{{cite journal |author=Tsou MF, Stearns T |title=Mechanism limiting centrosome duplication to once per cell cycle |journal=[[Nature (journal)|Nature]] |volume=442 |issue=7105 |pages=947–51 |year=2006 |month=August |pmid=16862117 |doi=10.1038/nature04985 |url=http://www.nature.com/nature/journal/v442/n7105/abs/nature04985.html |accessdate=2008-07-08}}</ref>
The two centrioles in the centrosome are connected to each other unidentified by proteins. The mother centriole has radiating appendages at the [[distal]] end of its long axis and is attached to the daughter centriole at the other [[proximal]] end. Each daughter cell formed after cell division will inherit one of these pairs (one older and one newer centriole). Duplication of centrioles starts at the time of the [[G1/S transition]] and ends before the onset of [[mitosis]].<ref name="Salisbury"/>
==References==
{{Reflist}}
{{organelles}}
[[Category:Organelles]]
[[ar:جسم مركزي]]
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