Cilium

This article is about organelles. For fine hairs on insect wings, see Cilium (entomology).
Not to be confused with Cilium (computing).
Not to be confused with Psyllium.

Cilium
SEM micrograph of motile cilia projecting from respiratory epithelium in the trachea
Details
Identifiers
Latincilium
MeSHD002923
THH1.00.01.1.01014
FMA67181
Anatomical terms of microanatomy
Look up cilium in Wiktionary, the free dictionary.

The cilium (pl.: cilia; from Latin cilium 'eyelid'; in Medieval Latin and in anatomy, cilium) is a short hair-like membrane protrusion from many types of eukaryotic cell.[1][2] (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike projection that extends from the surface of the much larger cell body.[2] Eukaryotic flagella found on sperm cells and many protozoans have a similar structure to motile cilia that enables swimming through liquids; they are longer than cilia and have a different undulating motion.[3][4]

There are two major classes of cilia: motile and non-motile cilia, each with two subtypes, giving four types in all.[5] A cell will typically have one primary cilium or many motile cilia.[6] The structure of the cilium core, called the axoneme, determines the cilium class. Most motile cilia have a central pair of single microtubules surrounded by nine pairs of double microtubules called a 9+2 axoneme. Most non-motile cilia have a 9+0 axoneme that lacks the central pair of microtubules. Also lacking are the associated components that enable motility including the outer and inner dynein arms, and radial spokes.[7] Some motile cilia lack the central pair, and some non-motile cilia have the central pair, hence the four types.[5][7]

Most non-motile cilia, termed primary cilia or sensory cilia, serve solely as sensory organelles.[8][9] Most vertebrate cell types possess a single non-motile primary cilium, which functions as a cellular antenna.[10][11] Olfactory neurons possess a great many non-motile cilia. Non-motile cilia that have a central pair of microtubules are the kinocilia present on hair cells.[5]

Motile cilia are found in large numbers on respiratory epithelial cells – around 200 cilia per cell, where they function in mucociliary clearance, and also have mechanosensory and chemosensory functions.[12][13][14] Motile cilia on ependymal cells move the cerebrospinal fluid through the ventricular system of the brain. Motile cilia are also present in the oviducts (fallopian tubes) of female (therian) mammals, where they function in moving egg cells from the ovary to the uterus.[13][15] Motile cilia that lack the central pair of microtubules are found in the cells of the embryonic primitive node; termed nodal cells, these nodal cilia are responsible for the left-right asymmetry of bilaterians.[16]

  1. ^ "Definition of CILIUM". www.merriam-webster.com. Retrieved 15 April 2022.
  2. ^ a b Cite error: The named reference HHMIB2005 was invoked but never defined (see the help page).
  3. ^ Haimo LT, Rosenbaum JL (December 1981). "Cilia, flagella, and microtubules". The Journal of Cell Biology. 91 (3 Pt 2): 125s–130s. doi:10.1083/jcb.91.3.125s. PMC 2112827. PMID 6459327.
  4. ^ Alberts, Bruce (2015). Molecular biology of the cell (6 ed.). New York, NY. pp. 941–942. ISBN 9780815344643.{{cite book}}: CS1 maint: location missing publisher (link)
  5. ^ a b c Falk, N; Lösl, M; Schröder, N; Gießl, A (11 September 2015). "Specialized Cilia in Mammalian Sensory Systems". Cells. 4 (3): 500–19. doi:10.3390/cells4030500. PMC 4588048. PMID 26378583.
  6. ^ Wheatley, DN (September 2021). "Primary cilia: turning points in establishing their ubiquity, sensory role and the pathological consequences of dysfunction". Journal of Cell Communication and Signaling. 15 (3): 291–297. doi:10.1007/s12079-021-00615-5. PMC 8222448. PMID 33970456.
  7. ^ a b Fisch, C; Dupuis-Williams, P (June 2011). "Ultrastructure of cilia and flagella - back to the future!". Biology of the Cell. 103 (6): 249–70. doi:10.1042/BC20100139. PMID 21728999. S2CID 7636387.
  8. ^ Prevo, B; Scholey, JM; Peterman, EJG (September 2017). "Intraflagellar transport: mechanisms of motor action, cooperation, and cargo delivery". The FEBS Journal. 284 (18): 2905–2931. doi:10.1111/febs.14068. PMC 5603355. PMID 28342295.
  9. ^ Elliott, Kelsey H.; Brugmann, Samantha A. (1 March 2019). "Sending mixed signals: Cilia-dependent signaling during development and disease". Developmental Biology. 447 (1): 28–41. doi:10.1016/j.ydbio.2018.03.007. ISSN 1095-564X. PMC 6136992. PMID 29548942.
  10. ^ Singla, Veena; Reiter, Jeremy F. (4 August 2006). "The primary cilium as the cell's antenna: signaling at a sensory organelle". Science. 313 (5787): 629–633. Bibcode:2006Sci...313..629S. doi:10.1126/science.1124534. ISSN 1095-9203. PMID 16888132. S2CID 29885142.
  11. ^ Patel, MM; Tsiokas, L (1 November 2021). "Insights into the Regulation of Ciliary Disassembly". Cells. 10 (11): 2977. doi:10.3390/cells10112977. PMC 8616418. PMID 34831200.
  12. ^ Horani, A; Ferkol, T (May 2018). "Advances in the Genetics of Primary Ciliary Dyskinesia". Chest. 154 (3): 645–652. doi:10.1016/j.chest.2018.05.007. PMC 6130327. PMID 29800551.
  13. ^ a b Cite error: The named reference 2012-Enuka was invoked but never defined (see the help page).
  14. ^ Bloodgood, RA (15 February 2010). "Sensory reception is an attribute of both primary cilia and motile cilia". Journal of Cell Science. 123 (Pt 4): 505–9. doi:10.1242/jcs.066308. PMID 20144998. S2CID 207165576.
  15. ^ Cite error: The named reference Panelli was invoked but never defined (see the help page).
  16. ^ Desgrange, A; Le Garrec, JF; Meilhac, SM (22 November 2018). "Left-right asymmetry in heart development and disease: forming the right loop" (PDF). Development. 145 (22). doi:10.1242/dev.162776. PMID 30467108. S2CID 53719458. Archived (PDF) from the original on 9 October 2022.