Neuronal migration is the method by which neurons travel from their origin or birthplace to their final position in the brain. There are several ways they can do this, e.g. by radial migration or tangential migration.
Neuronal precursor cells proliferate in the ventricular zone of the developing neocortex. The first postmitotic cells to migrate from the preplate which are destined to become Cajal-Retzius cells and subplate neurons. These cells do so by somal translocation. Neurons migrating with this mode of locomotion are bipolar and attach the leading edge of the process to the pia. The soma is then transported to the pial surface by nucleokenisis, a process by which a microtubule “cage” around the nucleus elongates and contracts in association with the centrosome to guide the nucleus to its final destination . Radial fibres (also known as radial glia) can translocate to the cortical plate and differentiate either into astrocytes or neurons . Somal translocation can occur at any time during development .
Subsequent waves of neurons split the preplate by migrating along radial glial fibres to form the cortical plate. Each wave of migrating cells travel past their predecessors forming layers in an inside-out manner, meaning that the youngest neurons are the closest to the surface [4, 5]. It is estimated that glial guided migration represents 80-90% of migrating neurons.
Many neurons migrating along the anterior-posterior axis of the body use existing axon tracts to migrate along; this is called axophilic migration. An example of this mode of migration is in GnRH-expressing neurons, which make a long journey from their birthplace in the nose, through the forebrain, and into the hypothalamus . Many of the mechanisms of this migration have been worked out, starting with the extracellular guidance cues that trigger intracellular signalling . These intracellular signals, such as calcium signaling, lead to actin and microtubule cytoskeletal dynamics, which produce cellular forces that interact with the extracellular environment through cell adhesion proteins to cause the movement of these cells [8, 9, 10].
Most interneurons migrate tangentially through multiple modes of migration to reach their appropriate location in the cortex. An example of tangential migration is the movement of Cajal-Retzius cells from the cortical hem to the superfitial part of cortical neuroepithelium.
Corticogenesis: younger neurons migrate past older ones using radial glia as a scaffolding. Cajal-Retzius cells (red) release reelin (orange).orticogenesis_in_a_wild-type_mouse
This article uses material from the Wikipedia article Development of the nervous system in humans, which is released under the Creative Commons Attribution-Share-Alike License 3.0
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