HOME

TheInfoList



OR:

Guidepost cells are cells which assist in the subcellular organization of both neural
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
growth and migration. They act as intermediate targets for long and complex axonal growths by creating short and easy pathways, leading axon
growth cone A growth cone is a large actin-supported extension of a developing or regenerating neurite seeking its synaptic target. It is the growth cone that drives axon growth. Their existence was originally proposed by Spanish histologist Santiago Ram� ...
s towards their target area.


Identification

In 1976, guideposts cells were identified in both grasshopper embryos and ''
Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species ...
''. 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. However, guidepost cells can also act as a group. There is a band of
epithelial cells Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
, called floor-plate cells, present in the
neural tube In the developing chordate (including vertebrates), the neural tube is the embryonic precursor to the central nervous system, which is made up of the brain and spinal cord. The neural groove gradually deepens as the neural fold become elevated, ...
of Drosophila available for the binding of growing axons. 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. Guidepost cells are typically immature
glial cells Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form mye ...
and neuron cells, that have yet to grown an axon.Colón-Ramos DA, Shen K, 200
Cellular Conductors: Glial Cells as Guideposts during Neural Circuit Development.
PLoS Biol 6(4): e112.
They can either be labeled as short range cells or axon dependent cells. To qualify as a guidepost cell,
neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
s hypothesized to be influenced by a guidance cell are examined during development. To test the guidance cell in question, neural axon growth and migration is first examined in the presence of the guidance cell. Then, the guidance cell is destroyed to further examine neural axon growth and migration in the absence of the guidance cell. 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. Ti1
pioneer neuron A pioneer neuron is a cell that is a derivative of the preplate in the early stages of corticogenesis of the brain. Pioneer neurons settle in the marginal zone of the cortex and project to sub-cortical levels. In the rat, pioneer neurons are onl ...
s is a common example neurons that require guidepost cells to reach its final destination. They have to come in contact with three guidepost neurons to reach the CNS: Fe1, Tr1, and Cx1. When Cx1 is destroyed, the Ti1 pioneer is unable to reach the CNS.


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. In this migrational pathway, olfactory neurons move from the nasal cavities to the
mitral cells Mitral cells are neurons that are part of the olfactory system. They are located in the olfactory bulb in the mammalian central nervous system. They receive information from the axons of olfactory receptor neurons, forming synapses in neuropils ca ...
in the
olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OF ...
. The mitral primary axons extend and form a bundle of axons, called the LOT, towards higher olfactory centers:
anterior olfactory nucleus The anterior olfactory nucleus (AON; also called the anterior olfactory cortex) is a portion of the forebrain of vertebrates. It is involved in olfaction and has supposedly strong influence on other olfactory areas like the olfactory bulb and the ...
,
olfactory tubercle The olfactory tubercle (OT), also known as the tuberculum olfactorium, is a multi-sensory processing center that is contained within the olfactory cortex and ventral striatum and plays a role in reward cognition. The OT has also been shown to ...
,
piriform cortex The piriform cortex, or pyriform cortex, is a region in the brain, part of the rhinencephalon situated in the cerebrum. The function of the piriform cortex relates to the sense of smell. Structure The piriform cortex is part of the rhinencephalo ...
r,
entorhinal cortex The entorhinal cortex (EC) is an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time.Integrating time from experience in the ...
, and cortical nuclei of the
amygdala The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verte ...
. "Lot cells", the first neurons to appear in the
telencephalon The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In ...
, are considered to be guideposts because they have cellular substrates to attract LOX axons. To test their role in guidance, scientists ablated lot cells with a toxin called 6-OHDA. As a result, LOT axons were stalled in the areas where lot cells were destroyed, which confirmed lot cells as guidepost cells.


Entorhinal projections

Cajal-Retzius cells are the first cells to cover the cortical sheet and hippocampal primordium, and regulate cortical lamination by
Reelin Reelin, encoded by the ''RELN'' gene, is a large secreted extracellular matrix glycoprotein that helps regulate processes of neuronal migration and positioning in the developing brain by controlling cell–cell interactions. Besides this import ...
. In order to make connections with GABAergic neurons in different regions of the
hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
( stratum oriens,
stratum radiatum In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...
, and inner molecular layer), pioneer entorhinal neurons make synaptic contacts with Cajal-Retzius cells. To test their role in guidance, scientists (Del Rio and colleagues) ablated Cajal-Retzius cells with 6-OHDA. As a result, entorhinal axons did not grow in the hippocampus and ruled Cajal-Retzius cells as guidepost cells.


Thalamocortical connections

Perirecular cells (or internal capsule cells) are neuronal guidepost cells located along the path of creating the
internal capsule The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the ...
. They provide a scaffold for corticothalamic and thalamocortical axons (TCAs) to send messages to the
thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...
. There are
transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fun ...
s 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. Corridor cells are another set of guidepost cells present for TCA guidance. These GABAergic neurons migrate to form a "corridor" between proliferation zones of the
medial ganglionic eminence The ganglionic eminence (GE) is a transitory structure in the development of the nervous system that guides cell and axon migration. It is present in the embryonic and fetal stages of neural development found between the thalamus and caudate nucl ...
and
globus pallidus The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a subcortical structure of the brain. It consists of two adjacent segments, one external, known in rodents simply as the globus pallidus, and one internal, known in rod ...
. Corridor cells provide TCA growth through MGE-derived regions. However, the Neurgulin1 signaling pathway needs to be activated, with the expression of
ErbB4 Receptor tyrosine-protein kinase erbB-4 is an enzyme that in humans is encoded by the ''ERBB4'' gene. Alternatively spliced variants that encode different protein isoforms have been described; however, not all variants have been fully characterized ...
receptors on the surface of TCAs, for the connection to occur between corridor cells and TCAs.


Corpus callosum

There are subpopulations of
glial cells Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form mye ...
that provide guidance cues for axonal growth. The first set of cells, called the "mid-line glial zipper", regulate the midline fusion and guidance of
pioneer axon Pioneer axon is the classification given to axons that are the first to grow in a particular region. They originate from pioneer neurons, and have the main function of laying down the initial growing path that subsequent growing axons, dubbed foll ...
s to the septum towards the contralateral hemisphere. The "glial sling" is a second set, located at the corticoseptal boundary, which provide cellular substrates for callosal axon migration across the dorsal midline. The "glial wedge" is made up of radial fibers, secreting repellent cues to prevent axons from entering the
septum In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatr ...
and positioning them towards the
corpus callosum The corpus callosum (Latin for "tough body"), also callosal commissure, is a wide, thick nerve tract, consisting of a flat bundle of commissural fibers, beneath the cerebral cortex in the brain. The corpus callosum is only found in placental ma ...
. The last set of glial cells, located in the induseum griseum, control the positioning of pioneer cingulate neurons in the
corpus callosum The corpus callosum (Latin for "tough body"), also callosal commissure, is a wide, thick nerve tract, consisting of a flat bundle of commissural fibers, beneath the cerebral cortex in the brain. The corpus callosum is only found in placental ma ...
region.


See also

*
Nerve fiber An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...
*
Nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...
*
Neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
*
Dendrite Dendrites (from Greek δένδρον ''déndron'', "tree"), also dendrons, are branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the n ...
*
Synapse In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...
*
Axon guidance Axon guidance (also called axon pathfinding) is a subfield of neural development concerning the process by which neurons send out axons to reach their correct targets. Axons often follow very precise paths in the nervous system, and how they mana ...
*
Pioneer axon Pioneer axon is the classification given to axons that are the first to grow in a particular region. They originate from pioneer neurons, and have the main function of laying down the initial growing path that subsequent growing axons, dubbed foll ...
*
Electrophysiology Electrophysiology (from Greek , ''ēlektron'', "amber" etymology of "electron"">Electron#Etymology">etymology of "electron" , ''physis'', "nature, origin"; and , ''-logia'') is the branch of physiology that studies the electrical properties of b ...
*
Neural cell adhesion molecule Neural cell adhesion molecule (NCAM), also called CD56, is a homophilic binding glycoprotein expressed on the surface of neurons, glia and skeletal muscle. Although CD56 is often considered a marker of neural lineage commitment due to its discover ...


References


External links


COPE entry on guidepost cells
{{DEFAULTSORT:Guidepost Cells Developmental neuroscience