Guidepost cells
| Guidepost cells | |
|---|---|
| Anatomical terminology |
Guidepost cells are cells which assist in the subcellular organization of both neural axon growth and migration.[1] 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.[2][3]
Identification
[edit]
In 1976, guideposts cells were identified in both grasshopper embryos and Drosophila.[4][5][6][7] 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.[4][6] However, guidepost cells can also act as a group.[4] 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.[4] 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.[2]
Guidepost cells are typically immature glial cells and neuron cells, that have yet to grown an axon.[2][4][8] They can either be labeled as short range cells or axon dependent cells.[2]
To qualify as a guidepost cell, neurons hypothesized to be influenced by a guidance cell are examined during development.[9] To test the guidance cell in question, neural axon growth and migration is first examined in the presence of the guidance cell.[9] Then, the guidance cell is destroyed to further examine neural axon growth and migration in the absence of the guidance cell.[10][9] 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.[9] Ti1 pioneer neurons is a common example neurons that require guidepost cells to reach its final destination.[6][9] They have to come in contact with three guidepost neurons to reach the CNS: Fe1, Tr1, and Cx1.[6][9] When Cx1 is destroyed, the Ti1 pioneer is unable to reach the CNS.[6][9]
Roles in formation
[edit]Lateral olfactory tract
[edit]The lateral olfactory tract (LOT) is the first system where guideposts cells were proposed to play a role in axonal guidance.[2] In this migrational pathway, olfactory neurons move from the nasal cavities to the mitral cells in the olfactory bulb.[2] 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.[2] "Lot cells", the first neurons to appear in the telencephalon, are considered to be guideposts because they have cellular substrates to attract LOX axons.[2] To test their role in guidance, scientists ablated lot cells with a toxin called 6-OHDA.[2] As a result, LOT axons were stalled in the areas where lot cells were destroyed, which confirmed lot cells as guidepost cells.[2]
Entorhinal projections
[edit]Cajal-Retzius cells[11] are the first cells to cover the cortical sheet and hippocampal primordium, and regulate cortical lamination by Reelin.[2] 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.[2] To test their role in guidance, scientists (Del Rio and colleagues) ablated Cajal-Retzius cells with 6-OHDA.[2] As a result, entorhinal axons did not grow in the hippocampus and ruled Cajal-Retzius cells as guidepost cells.[2]
Thalamocortical connections
[edit]Perirecular cells (or internal capsule cells) are neuronal guidepost cells located along the path of creating the internal capsule.[2] They provide a scaffold for corticothalamic and thalamocortical axons (TCAs) to send messages to the thalamus.[2] 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.[2]
Corridor cells are another set of guidepost cells present for TCA guidance.[2] These GABAergic neurons migrate to form a "corridor" between proliferation zones of the medial ganglionic eminence and globus pallidus.[2] Corridor cells provide TCA growth through MGE-derived regions.[clarification needed] 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.[2]
Corpus callosum
[edit]There are subpopulations of glial cells that provide guidance cues for axonal growth.[2] 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.[2][7] The "glial sling" is a second set, located at the corticoseptal boundary, which provide cellular substrates for callosal axon migration across the dorsal midline.[2][7] 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.[2][7] The last set of glial cells, located in the induseum griseum, control the positioning of pioneer cingulate neurons in the corpus callosum region.[2]
See also
[edit]- Nerve fiber
- Nerve
- Neuron
- Dendrite
- Synapse
- Axon guidance
- Pioneer axon
- Electrophysiology
- Neural cell adhesion molecule
References
[edit]- ^ Palka, J; John Palka; Kathleen E. Whitlock; Marjorie A. Murray (February 1992). "Guidepost cells". Current Opinion in Neurobiology. 2 (1): 48–54. doi:10.1016/0959-4388(92)90161-D. PMID 1638135.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y Rubenstein, Rakic, John, Pasko (2013). Cellular Migration and Formation of Neuronal Connections : Comprehensive Developmental Neuroscience. Academic Press. pp. 457–472. ISBN 9780123972668.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ Goodman, Corey S.; Tessier-Lavigne, Marc (1998). "Molecular mechanisms of axon guidance and target recognition". Molecular and Cellular Approaches to Neural Development. pp. 108–178. doi:10.1093/acprof:oso/9780195111668.003.0004. ISBN 9780195111668.
- ^ a b c d e Gordon-Weeks, Phillip (2005). Neuronal Growth Cones. Cambridge University Press. p. 104. ISBN 0521018544.
- ^ Black, Ira (2013). Cellular and Molecular Biology of Neuronal Development. Springer Science & Business Media. pp. 70–71. ISBN 9781461327172.
- ^ a b c d e Breidbach, Kutsch, O, Wolfram (1995). The Nervous Systems of Invertebrates: An Evolutionary and Comparative Approach. Springer Science & Business Media. pp. 252–253. ISBN 9783764350765.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ a b c d Lemke, Greg (2010). Developmental Neurobiology. Academic Press. pp. 387–391. ISBN 9780123751676.
- ^ Colón-Ramos DA, Shen K, 2008 Cellular Conductors: Glial Cells as Guideposts during Neural Circuit Development. PLoS Biol 6(4): e112. doi:10.1371/journal.pbio.0060112
- ^ a b c d e f g Sanes, Dan (2011). Development of the Nervous System. Academic Press. p. 107. ISBN 978-0123745392.
- ^ Bentley, David; Michael Caudy (1983-07-07). "Pioneer axons lose directed growth after selective killing of guidepost cells". Nature. 304 (5921): 62–65. doi:10.1038/304062a0. PMID 6866090.
- ^ Chao, Daniel L.; Ma, Le; Shen, Kang (2009). "Transient cell–cell interactions in neural circuit formation". Nature Reviews Neuroscience. 10 (4): 262–271. doi:10.1038/nrn2594. PMC 3083859. PMID 19300445.