3.2 - neuronal migration

neuroepithelial cell

multipotent (multiple fates) neuronal stem cells at VZ that can give rise to CNS neurons + glia during development

leading edge

part of neuronal cytoplasm that extends first toward direction of migration

3 stages of migration

1. extension of leading edge towards migration direction

2. movement of nucleus toward direction of migration

3. dissociation of trailing process from its anchoring guidance molecules

nucleokinesis

movement of nucleus toward direction fo migration during neuronal migration

• mediated by microtubules

neuronal precursor

cell type that is fated to become a neuron

radial migration

migration path is perpendicular to brain ventricles

• forms 6 cortical laters

somal translocation characteristics

• mediates short-distance

• during early corticogenesis

• after radial migration

• fast + constant

somal translocation process

1. precursor from VT extends + attaches leading edge to pial surface

2. leading edge pulls rest of the cell to pial surface

glial-guided locomotion characteristics

• needs radial glia

• creates inside-out brain layers

• long range

glial-guided locomotion process

1. precursors migrate upward away from VZ by climbing along radial glia cells

2. climb by interacting w/ guidance molecules on radial cell surface

tangential migration

path is parallel to brain ventricles

• moves neurons from formation site → far away regions

• increases cell diversity

• guided by attractive + repulsive guidance molecules

multipolar migration (also regarded as type of radial migration)

neuron begins journey via radial migration until it reaches IZ

• in IZ multipolar → bipolar

• later resumes radial migration

why is the cortex considered to have inside-stratification?

1. 6 layers

2. new layers on top, old layers deeper

ventricular zone

transient layer of cells linin brain ventricles at center of the brain

• contains neuronal stem cells that give rise to neurons + glia

intermediate zone

transient layer btw the ventricular zone and cortical zone where cortical layers are formed

• where multipolar migration stops

long-range guidance molecule

• synthesized by far away cells from migrating neurons

• usually diffusible soluble factors

• guide general direction of migration

short-range guidance molecule

• synthesized by cells @ vicinity of migrating neurons

• usually plasma membrane or extracellular matrix protein

  • can bind to neuronal PM receptors + influence migration path of nearby neuron or neuronal extension

attractive guidance molecule

can bind to neuronal PM to mediate migration of neuronal cell body or neuronal extension toward cell that produces guidance molecule

repulsive guidance molecule

can bidn to neuronal PM to mediate migration of neuronal cell body or neuronal extension away from cell that produces guidance molecule

gyrification

formation of gyri or wrinkkles at surface of cortex

gyri

peak ridge

sulci

valley or depression

neuronal heterotropia

mislocalization of neurons

• cause = defective migration or guide

• consequences = clusters of ectopic neurons along path

  • little → dramatic changes in brain

• symptoms = epilepsy + infantile spasm

lissencephaly

smooth brain due to undermigration

• causes = defective radial migration → cortex has < 6 layers

• consequences = no gyri or deceased gyri

• symptoms = cary + may include seizures, retardation + many die

polymicrogyria

defect in overmigration

• causes = perturbation in stop signal molecules

  • migration through mirgational zone

• consequences = excessive + small gyri on cortical surface

  • brain affected locally or globally

• symptoms = vary depending on defect extend

  • range from retardation → motor problems