Lecture 3 - Axonal Growth - Tropism Flashcards
(150 cards)
What is the first step in neuronal identity and the formation of connections?
Polarization (and is a primary property of all cells).
A neuron starts round with
no obvious processes (neurites).
Over time the neuron (neurite) begins to
extend multiple processes and becomes multipolar.
What defines the polarity of the neuron?
One of the multiple processes become the axon, which then defines the polarity of the neuron.
What is at the tip of the axons?
a specialized structure (or structures) called growth cones.
Where is the growth cone located?
specialized motile structure at the tip of extending axon
What does the growth cone do?
explores extracellular environment, determines direction of growth, and guides extension of axon; key decision-making structure in axon pathfinding morphological characteristics
lamellapodium –
fan-shaped sheet at tip of axon; contains actin filaments and microtubules
filopodia –
fine processes extending out from lamellapodium; contain actin filaments; form and disappear rapidly
How does the leading edge of filopodium respond to environmental cues?
Gobular actin (G-actin) can be incorporated into filamentous actin (F-actin)
A key to growth cone turning is
the binding of F-actin binding proteins to F-actin, which regulates retrograde flow.
In growth cone tuning what regulates retrograde flow?
The binding of F-actin binding proteins to F-actin
What happens when encountering an attractive cue?
assembly is increased and retrograde flow slowed causing turning towards the attractive cue (repulsion is the opposite)
What is the role of microtubules in growth cone tuning?
1) It makes the core of the cytoskeleton in the axon extremely stable and strong 2) Modulation of interactions with microtubules modulate stability and turning of the axons.
What are primarily responsible for axon elongation?
Microtubules
In growth cone signaling what dictates direction?
F-actin
How can discrete regions of the growth cones be detected?
by different types of actin and tubulin
F-actin is in
lamellipodium and filopodia
Tyrosinated microtubules are enriched in
lamellipodia
Acetylated microtubules are only in
the axons.
In axonal growth, what happens at decision points?
The growth cone shape changes
What are the axon guidance signals?
There are 4 types - non-diffusible (short-range) signals: 1) contact attraction 2) contact repulsion diffusible (long-range) signals: 3) chemoattraction 4) chemorepulsion
What is the function of the axon guidance signals?
all 4 types may act in concert to guide axon to appropriate target; ensures accurate guidance
What does the binding of axon guidance molecules to receptors do?
on growth cones binding activates signaling cascades that result in reorganization of the growth cone cytoskeleton which controls the direction and rate at which the growth cone moves.