Unit 3: Neurodevelopment Flashcards
What is the ganglionic eminence?
A section of the developing cortex that produces inhibitory interneurons that migrate tangentially to radial glial cell progeny.
Which are the last nervous system cells to be developed?
Glia.
Where are oligodendrocytes born?
The ganglionic eminence.
Where are adult new neurons born from?
Stem cells lining the lateral ventricle and sub-ventricular zone.
What are somites?
Blocks of mesoderm that line the neural tube.
They determine the migratory path of neural crest cells and the axons of spinal nerve cells.
What are neural crest cells repulsed by?
Ephrin B on the caudal side of somites.
What do neural crest cells develop into?
Eye, sympathetic ganglion, parasympathetic ganglia, Schwann cells, melanocytes, Schwann cells for all cranial nerve ganglia, aortic arches, dorsal root ganglia, adrenal medulla, and enteric ganglia.
How do neural crest cells develop in different locations?
Their fate depends on local signals. They can change their differentiation if placed in a different environment.
What are some local factors that change neural crest cell fate?
BMP, Glial growth factor, and TGF-𝛽.
What is induction?
The process by which a tissue is instructed to adopt a particular fate.
What is determination?
When the cell commits to adopting a particular fate.
What is differentiation?
The process by which a neuron or glial cell attains all the mature properties of the fate to which it has committed. It has become that fate in morphology, gene expression, physiology, and synaptic connectivity.
What are progenitor cells?
Dividing cells gives rise to many early cells. Typically pluripotent or multipotent.
What are post-mitotic cells?
Progenitor cells offspring that induce expression of transcription factors that direct different differentiation programs.
How can differentiation be induced in cells?
Localization of different factors to separate sides of the cell. Ex: Numb and notch.
Expression of different transcription factors.
What is the difference between pan-neuronal factors and subtype-specific factors?
Pan-neuronal factors only specify a generalized neuronal phenotype.
Subtype-specific factors send neurons down a specific pathway.
What is Fezf2?
A transcription factor that is specific for layer V neurons. It leads to the expression of Ephb1 which promotes specific axonal guidance.
What are MAPs?
Microtubule-associated proteins.
What is the major MAP in the axon and in the dendrite?
Tau is the major MAP in the axon.
MAP-2 is the major MAP in the dendrite.
How is it decided which neurite becomes the axon?
It depends on which one enters a new substrate first.
How do axons get to where they need to go?
Axons are attracted to/repulsed by different factors/local guidance factors. Unique combinations of these lead to axons getting to their targets.
What are the 4 major cytoskeletal systems?
Microtubule
Neurofilament
Microfilament
Actin
Are microtubules polarized?
Yes.
Where are polymerization and depolarization faster in the microtubule?
In the + end.
How do microtubules become stable?
If they have a high molecular weight.
If they are linked to other cytoskeletal elements.
If they have a tubulin-binding end.
Why are neurofilaments cross-linked?
To provide strength and stiffness.
Where are neurofilaments used the most?
In the axon.
What are the crossbridges in axons?
Neurofilament projections.
What are the crossbridges in dendrites?
Microtubules.
How do motor MAPs work?
They move along MAPs using ATP-carrying vesicles.
Kinesins move toward the + end.
Dyneins move toward the - end.
How are microtubules oriented in axons?
The + ends are distal and away from the cell body.
How are microtubules oriented in dendrites?
They are randomly oriented.
What is transported in fast anterograde axonal transport?
Organelles and vesicles that are transported via kinesin.
What is transported in fast retrograde axonal transport?
Vesicles carrying signaling molecules from axon terminals → cell body.
Transported via dynein.
What is transported in slow axonal transport?
Actin, and soluble metabolic enzymes that are used for glycolysis and neurotransmitter synthesis.
What is transported in the slowest axonal transport?
Microtubules and neurofilaments.
Is kinesin in all neurites?
Initially yes, but they move to the axon during its specification.
Does microtubule stabilization promote axon specification?
Yes.
What are the domains of the growth cone?
Peripheral (P) domain
Central (C) domain
Transition (T) domain
What is the peripheral (P) domain of the growth cone?
A network of actin filaments (F-actin) that form the filopodia.
What is the central (C) domain of the growth cone?
The area that encloses stable microtubules that enter the growth cone from the axon shaft.
What is the transition (T) zone of the growth cone?
The area between the P and C domains that forms an actomyosin contractile arc.
How do growth cones grow?
Growth cones grow by adding material to the leading edge of the growth cone.
What happens to microtubules when they enter the growth cone?
Microtubules are organized into bundles by microtubule-associated proteins (MAPs). Once they center the C domain, they defasciculate. They go through the T zone and then enter the P domain where they become aligned with the F-actin bundle.
What happens to F-actin as the growth cone grows?
The terminal of F-actin is in the T domain where it is severed into short filaments. The broken actin parts are then added to the filopodia tip end.
What is Filamentous (F)-actin treadmilling?
F-actin is polymerized at the leading edge and severed at the T zone. Subunits are then recycled back to the leading edge.
What is F-actin retrograde flow?
Continuous movement of F-actin from the leading edge towards the center of the growth cone, leading to idle growth.
What happens with F-actin retrograde is slow?
Propulsion occurs.
This leads to microtubules no longer being cleared from the P domain. The microtubules can now serve as a track for lamellipodal engorgement which enables axon growth and growth cone turning.
What is defasciculation?
Axons leave a nerve bundle and enter a target area.
This is the first step of target selection.
What happens to microtubules when an attractant is found?
There are exploratory microtubules that act as a scaffold for actin bundles. Once an attractant is found, more microtubules are recruited.
What are the stages of axon growth?
A substrate is encountered.
Protrusion = filopodia and lamellipodia-like veils extend forward.
Engorgement = C domain moves forward.
Consolidation = new axon shaft forms.
What are the 4 different types of axon-guidance cues?
Contact-mediated repulsion
Contact-mediated attraction
Diffusible chemorepellants
Diffusible chemoattractants
What molecules are usually attractants?
Cell-ECM contact
Cell-cell contact with cell adhesion molecules
Cell-cell contact with cadherins.
Netrin family
Netrin-DCC signaling attracts growth cones.
What molecules are usually repulsive?
Cell-cell contact with semaphorins
Slit family; Slit-Robo signaling is repulsive.
Cell-cell contact with ephrins
What do attractive cues do?
Promote actin filament elongation.
Engage the clutch to stop retrograde flow
Promote microtubule extension.
What do repellant cues do?
Dissolution of actin filaments.
Loss of dynamic microtubules.
What is the role of Rho GTPases in axon growth? Which ones are involved?
Rho GTPases couple guidance cues to the actin cytoskeleton.
Cdc42, Rac1, and RhoA.
What is the role of RhoA in axon growth?
Depolymerizes actin and induces endocytosis to the leading edge of the plasma membrane.
This leads to filopodia and lamellopodia disappearing.
What is the role of Rac in axon growth?
Recruited by chemoattractant receptors to polymerize actin and facilitate filopodia and lamellopodia formation.
What is the role of Cdc42 in axon growth?
Recruited by chemoattractant receptors to polymerize actin and facilitate filopodia and lamellopodia formation.