Netrin
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2007-11-21T15:24:41Z
Richwil
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'''Netrin''' is a class of [[protein]] involved in [[axon guidance]]. It is named after the [[Sanskrit]] word "netr", which means "one who guides." Netrins are [[genetic conservation|genetically conserved]] across [[Caenorhabditis elegans|nematode worms]]<ref>Serafini T, Kennedy TE, Galko MJ, Mirzayan C, Jessell TM, Tessier-Lavigne M. (1994) The netrins define a family of axon outgrowth-promoting proteins homologous to
C. elegans UNC-6. Cell 78(3):409-24</ref>, [[Drosophila|fruitflies]], [[Xenopus laevis|frogs]], and [[Mus musculus|mice]]. Structurally, netrin resembles [[laminin]].
Netrins are [[chemotropism|chemotropic]]; a growing [[axon]] will either move towards or away from a higher concentration of netrin. Though the detailed mechanism of [[axon guidance]] is not fully understood, it is known that netrin attraction is mediated through [[UNC-40/DCC]] cell surface [[cell surface receptor|receptor]]s and repulsion is mediated through UNC-5 receptors. Netrins also act as [[growth factors]], encouraging cell growth activities in target cells. Mice deficient in netrin fail to form the [[hippocampal comissure]] or the [[corpus callosum]].
A proposed [[Scientific modelling|model]] for netrin activity in the [[spinal column]] of developing human [[embryos]] is that netrins are released by the [[floor plate]] and are picked up by receptor proteins embedded in the [[growth cones]] of axons belonging to neurons in the developing spinal column. The bodies of these neurons remain stationary while the axons follow a path defined by netrins, eventually connecting to neurons inside the embryonic brain by developing [[synapses]]. It seems that once a pathway has been traced by an axon, new axons tend to follow it rather than being guided by netrins or related chemotropic factors.<ref>Kennedy TE, Serafini T, de la Torre JR, Tessier-Lavigne M. (1994) Netrins are diffusible chemotropic factors for commissural axons in the
embryonic spinal cord. Cell 78(3):425-35</ref>
===Netrin-1===
'''Netrin-1''' is a typical member of the netrin family displaying both attractive and repulsive cues depending on context. [[Retinal ganglion cell]] (RGC) axons convey visual information from the [[retina]] to the [[brain]] via the [[optic nerve head]] (ONH) and the [[optic nerve]]. During [[morphogenesis|embryo development]], RGC axon growth follows a path to the ONH assisted by the attraction of netrin-1 expressed by ONH cells. It is thought that the axon is then guided through the ONH to the optic nerve by repulsion induced by the presence of [[laminin]] at the ONH. Evidence for this reversal in response to netrin-1 is provided by the finding that [[Xenopus]] RGC axons are repelled by netrin-1 in the presence of laminin.<ref>Oster SF, Deiner M, Birgbauer E, Sretavan DW. (2004) Ganglion cell axon pathfinding in the retina and optic nerve. Semin. Cell Dev. Biol. 15:125-36</ref>
==References==
<references/>
*[[Mendelian Inheritance in Man|OMIM]] [http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=601614 601614]
*''The Science Times Book of the Brain'' 1998. Nicholas Wade, editor. The Lyons Press.
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[[Category:Proteins]]
[[Category:Developmental neuroscience]]
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