{{Short description|Cells that assist in the subcellular organization of both neural axon growth and migration}} {{Infobox anatomy | Name = Guidepost cells }}
'''Guidepost cells''' are cells which assist in the subcellular organization of both neural axon growth and migration.<ref>{{cite journal|date=February 1992|title=Guidepost cells|journal=Current Opinion in Neurobiology|volume=2|issue=1|pages=48–54|doi=10.1016/0959-4388(92)90161-D|pmid=1638135|last1=Palka|first1=J|author2=John Palka|author3=Kathleen E. Whitlock|author4=Marjorie A. Murray}}<!--| accessdate = 2010-11-27--></ref> They act as intermediate targets for long and complex axonal growths by creating short and easy pathways, leading axon growth cones towards their target area.<ref name=":1">{{Cite book|title=Cellular Migration and Formation of Neuronal Connections : Comprehensive Developmental Neuroscience|last=Rubenstein, Rakic|first=John, Pasko|publisher=Academic Press|year=2013|isbn=9780123972668|pages=457–472}}</ref><ref>{{Cite book|chapter=Molecular mechanisms of axon guidance and target recognition|last=Goodman|first=Corey S.|last2=Tessier-Lavigne|first2=Marc|pages=108–178|language=en|doi=10.1093/acprof:oso/9780195111668.003.0004|title=Molecular and Cellular Approaches to Neural Development|year=1998|isbn=9780195111668}}</ref>
==Identification== thumb|When a guidepost cell is destroyed, the primary growth cone loses its sense in direction and fails to reach its final destination. In 1976, guideposts cells were identified in both grasshopper embryos and ''Drosophila''.<ref name=":0">{{Cite book|title=Neuronal Growth Cones|last=Gordon-Weeks|first=Phillip|publisher=Cambridge University Press|year=2005|isbn=0521018544|pages=104}}</ref><ref>{{Cite book|title=Cellular and Molecular Biology of Neuronal Development|last=Black|first=Ira|publisher=Springer Science & Business Media|year=2013|isbn=9781461327172|pages=70–71}}</ref><ref name=":3">{{Cite book|title=The Nervous Systems of Invertebrates: An Evolutionary and Comparative Approach|last=Breidbach, Kutsch|first=O, Wolfram|publisher=Springer Science & Business Media|year=1995|isbn=9783764350765|pages=252–253}}</ref><ref name=":4">{{Cite book|title=Developmental Neurobiology|last=Lemke|first=Greg|publisher=Academic Press|year=2010|isbn=9780123751676|pages=387–391}}</ref> Single guidepost cells, acting like "stepping-stones" for the extension of Ti1 pioneer growth cones to the CNS, were first discovered in grasshopper limb bud.<ref name=":0" /><ref name=":3" /> However, guidepost cells can also act as a group.<ref name=":0" /> There is a band of epithelial cells, called floor-plate cells, present in the neural tube of Drosophila available for the binding of growing axons.<ref name=":0" /> These studies have defined guidepost cells as non-continuous landmarks located on future paths of growing axons by providing high-affinity substrates to bind to for navigation.<ref name=":1" />
Guidepost cells are typically immature glial cells or still axonless neurons.<ref name=":1" /><ref name=":0" /><ref name="multiple">Colón-Ramos DA, Shen K, 2008 [http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.0060112 Cellular Conductors: Glial Cells as Guideposts during Neural Circuit Development.] PLoS Biol 6(4): e112. {{doi|10.1371/journal.pbio.0060112|doi-access=free}}</ref> They can either be labeled as short range cells or axon dependent cells.<ref name=":1" />
To qualify as a guidepost cell, neurons hypothesized to be influenced by a guidance cell are examined during development.<ref name=":2">{{Cite book|title=Development of the Nervous System|last=Sanes|first=Dan|publisher=Academic Press|year=2011|isbn=978-0123745392|pages=107}}</ref> To test the guidance cell in question, neural axon growth and migration is first examined in the presence of the guidance cell.<ref name=":2" /> Then, the guidance cell is destroyed to further examine neural axon growth and migration in the absence of the guidance cell.<ref>{{cite journal|last=Bentley|first=David|date=1983-07-07|title=Pioneer axons lose directed growth after selective killing of guidepost cells|journal=Nature|volume=304|issue=5921|pages=62–65|doi=10.1038/304062a0|pmid=6866090|author2=Michael Caudy}}<!--| accessdate = 2010-11-27 --></ref><ref name=":2" /> If the neuronal axon extends towards the path in the presence of the guidance cell and loses its path in the absence of the guidance cell, it is qualified as a guidepost cell.<ref name=":2" /> Ti1 pioneer neurons are a common example of neurons that require guidepost cells in order to reach their final destination.<ref name=":3" /><ref name=":2" /> They have to come in contact with three guidepost neurons to reach the CNS: Fe1, Tr1, and Cx1.<ref name=":3" /><ref name=":2" /> When Cx1 is destroyed, the Ti1 pioneer is unable to reach the CNS.<ref name=":3" /><ref name=":2" />
== Roles in formation ==
=== Lateral olfactory tract === The lateral olfactory tract (LOT) is the first system where guideposts cells were proposed to play a role in axonal guidance.<ref name=":1" /> In this migrational pathway, olfactory neurons move from the nasal cavities to the mitral cells in the olfactory bulb.<ref name=":1" /> The mitral primary axons extend and form a bundle of axons, called the LOT, towards higher olfactory centers: anterior olfactory nucleus, olfactory tubercle, piriform cortexr, entorhinal cortex, and cortical nuclei of the amygdala.<ref name=":1" /> "LOT cells", the first neurons to appear in the telencephalon, are considered to be guideposts because they have cellular substrates to attract LOX axons.<ref name=":1" /> To test their role in guidance, scientists ablated LOT cells with a toxin called 6-OHDA.<ref name=":1" /> As a result, LOT axons were stalled in the areas where LOT cells were destroyed, which confirmed lot cells as guidepost cells.<ref name=":1" />
=== Entorhinal projections === Cajal-Retzius cells<ref>{{Cite journal|last=Chao|first=Daniel L.|last2=Ma|first2=Le|last3=Shen|first3=Kang|title=Transient cell–cell interactions in neural circuit formation|journal=Nature Reviews Neuroscience|volume=10|issue=4|pages=262–271|doi=10.1038/nrn2594|pmc=3083859|pmid=19300445|year=2009}}</ref> are the first cells to cover the cortical sheet and hippocampal primordium, and regulate cortical lamination by Reelin.<ref name=":1" /> In order to make connections with GABAergic neurons in different regions of the hippocampus (stratum oriens, stratum radiatum, and inner molecular layer), pioneer entorhinal neurons make synaptic contacts with Cajal-Retzius cells.<ref name=":1" /> To test their role in guidance, scientists (Del Rio and colleagues) ablated Cajal-Retzius cells with 6-OHDA.<ref name=":1" /> As a result, entorhinal axons did not grow in the hippocampus and ruled Cajal-Retzius cells as guidepost cells.<ref name=":1" />
=== Thalamocortical connections === Perirecular cells (or internal capsule cells) are neuronal guidepost cells located along the path of creating the internal capsule.<ref name=":1" /> They provide a scaffold for corticothalamic and thalamocortical axons (TCAs) to send messages to the thalamus.<ref name=":1" /> There are transcription factors associated with perirecular cells: ''Mash1'', ''Lhx2'', and ''Emx2''. When guidepost cells are mutated with knock out expressions of these factors, the guidance of TCAs are defected.<ref name=":1" />
Corridor cells are another set of guidepost cells present for TCA guidance.<ref name=":1" /> These GABAergic neurons migrate to form a "corridor" between proliferation zones of the medial ganglionic eminence and globus pallidus.<ref name=":1" /> Corridor cells provide TCA growth through MGE-derived regions.{{clarify|Jargon - makes no sense|date=October 2020}} However, the Neurgulin1 signaling pathway needs to be activated, with the expression of ErbB4 receptors on the surface of TCAs, for the connection to occur between corridor cells and TCAs.<ref name=":1" />
=== Corpus callosum === There are subpopulations of glial cells that provide guidance cues for axonal growth.<ref name=":1" /> The first set of cells, called the "mid-line glial zipper", regulate the midline fusion and guidance of pioneer axons to the septum towards the contralateral hemisphere.<ref name=":1" /><ref name=":4" /> The "glial sling" is a second set, located at the corticoseptal boundary, which provide cellular substrates for callosal axon migration across the dorsal midline.<ref name=":1" /><ref name=":4" /> The "glial wedge" is made up of radial fibers, secreting repellent cues to prevent axons from entering the septum and positioning them towards the corpus callosum.<ref name=":1" /><ref name=":4" /> The last set of glial cells, located in the induseum griseum, control the positioning of pioneer cingulate neurons in the corpus callosum region.<ref name=":1" />
== See also == *Nerve fiber *Nerve *Neuron *Dendrite *Synapse *Axon guidance *Pioneer axon *Electrophysiology *Neural cell adhesion molecule
== References == {{Reflist}}
== External links == * [http://www.copewithcytokines.de/cope.cgi?key=guidepost%20cells COPE entry on guidepost cells]
{{Nervous tissue}}
{{DEFAULTSORT:Guidepost Cells}} Category:Developmental neuroscience