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The cilium, plural cilia is a membrane-bound organelle found on most types of cell, and certain microorganisms known as ciliates. 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. 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.
Primary ciliary dyskinesia (PCD) is a rare, autosomal recessive genetic ciliopathy, that causes defects in the action of cilia lining the upper and lower respiratory tract, sinuses, Eustachian tube, middle ear, Fallopian tube, and flagella of sperm cells. The alternative name of "immotile ciliary syndrome" is no longer favored as the cilia do have movement, but are merely inefficient or unsynchronized. When accompanied by situs inversus the condition is known as Kartagener syndrome.
The ciliary body is a part of the eye that includes the ciliary muscle, which controls the shape of the lens, and the ciliary epithelium, which produces the aqueous humor. The aqueous humor is produced in the non-pigmented portion of the ciliary body. The ciliary body is part of the uvea, the layer of tissue that delivers oxygen and nutrients to the eye tissues. The ciliary body joins the ora serrata of the choroid to the root of the iris.
The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscle in the eye's middle layer, uvea. It controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. It also changes the shape of the lens within the eye but not the size of the pupil which is carried out by the sphincter pupillae muscle and dilator pupillae.
An axoneme, also called an axial filament is the microtubule-based cytoskeletal structure that forms the core of a cilium or flagellum. Cilia and flagella are found on many cells, organisms, and microorganisms, to provide motility. The axoneme serves as the "skeleton" of these organelles, both giving support to the structure and, in some cases, the ability to bend. Though distinctions of function and length may be made between cilia and flagella, the internal structure of the axoneme is common to both.
Bardet–Biedl syndrome (BBS) is a ciliopathic human genetic disorder that produces many effects and affects many body systems. It is characterized by rod/cone dystrophy, polydactyly, central obesity, hypogonadism, and kidney dysfunction in some cases. Historically, slower mental processing has also been considered a principal symptom but is now not regarded as such.
Intraflagellar transport (IFT) is a bidirectional motility along axoneme microtubules that is essential for the formation (ciliogenesis) and maintenance of most eukaryotic cilia and flagella. It is thought to be required to build all cilia that assemble within a membrane projection from the cell surface. Plasmodium falciparum cilia and the sperm flagella of Drosophila are examples of cilia that assemble in the cytoplasm and do not require IFT. The process of IFT involves movement of large protein complexes called IFT particles or trains from the cell body to the ciliary tip and followed by their return to the cell body. The outward or anterograde movement is powered by kinesin-2 while the inward or retrograde movement is powered by cytoplasmic dynein 2/1b. The IFT particles are composed of about 20 proteins organized in two subcomplexes called complex A and B.
Ciliary neurotrophic factor is a protein that in humans is encoded by the CNTF gene.
Afadin- and alpha-actinin-binding protein is a protein that in humans is encoded by the SSX2IP gene. It has been shown that it functions together with WDR8 in centrosome maturation, ensuring proper spindle length and orientation. The SSX2IP-WDR8 complex additionally promotes ciliary vesicle docking during ciliogenesis.
Dynein heavy chain 9, axonemal is a protein that in humans is encoded by the DNAH9 gene.
Mitogen-activated protein kinase 15, also known as MAPK15, ERK7, or ERK8, is an enzyme that in humans is encoded by the MAPK15 gene.
Tetratricopeptide repeat domain 8 (TTC8) also known as Bardet–Biedl syndrome 8 is a protein that in humans is encoded by the TTC8 gene.
Transmembrane protein 216 is a protein in humans that is encoded by the TMEM216 gene.
Serine/threonine-protein kinase Nek8, also known as never in mitosis A-related kinase 8, is an enzyme that in humans is encoded by the NEK8 gene.
Kintoun, is a protein that is encoded by the DNAAF2 gene.
The BBSome is an octameric protein complex. It is a component of the basal body and is involved in trafficking cargos to the primary cilium. The BBSome is a complex of seven Bardet–Biedl syndrome (BBS) proteins: BBS1, BBS2, BBS4, BBS5, BBS7, BBS8 and BBS9. In addition the BBSome contains the BBIP10 protein. Mutation in each of this eight BBSome genes causes a severe multiorganic syndrome (BBS) presenting in most cases by retinal dystrophy, obesity, renal anomalies, post-axial polydactyly, and developmental delay.
Sensenbrenner syndrome is a rare multisystem disease first described by Judith A. Sensenbrenner in 1975. It is inherited in an autosomal recessive fashion, and a number of genes appear to be responsible. Three genes responsible have been identified: intraflagellar transport (IFT)122 (WDR10), IFT43—a subunit of the IFT complex A machinery of primary cilia, and WDR35
Forkhead box protein J1 is a protein that in humans is encoded by the FOXJ1 gene. It is a member of the Forkhead/winged helix (FOX) family of transcription factors that is involved in ciliogenesis. FOXJ1 is expressed in ciliated cells of the lung, choroid plexus, reproductive tract, embryonic kidney and pre-somite embryo stage.
Ciliogenesis is defined as the building of the cell's antenna or extracellular fluid mediation mechanism. It includes the assembly and disassembly of the cilia during the cell cycle. Cilia are important organelles of cells and are involved in numerous activities such as cell signaling, processing developmental signals, and directing the flow of fluids such as mucus over and around cells. Due to the importance of these cell processes, defects in ciliogenesis can lead to numerous human diseases related to non-functioning cilia. Ciliogenesis may also play a role in the development of left/right handedness in humans.
Cytosolic ciliogenesis, otherwise cytoplasmic ciliogenesis, is a type of ciliogenesis where the cilium axoneme is formed in the cytoplasm or becomes exposed to the cytoplasm.
References
- ↑ Avidor-Reiss, Tomer; Leroux, Michel R. (7 December 2015). "Shared and Distinct Mechanisms of Compartmentalized and Cytosolic Ciliogenesis". Current Biology. 25 (23): R1143–R1150. doi:10.1016/j.cub.2015.11.001. PMC 5857621 . PMID 26654377.