Exam 4 Concepts

What is the growth cone responsible for?

Sensing environmental signals to guide the neuron

What does the growth cone use to probe its surroundings?

Filopodia

Lamellipodia

What are the different long-range cues?

Chemoattraction

Chemorepulsion

What is an example of a chemoattractant?

Netrin

What is an example of an chemorepelant?

Semaphorins

What are the different guidance mechanisms?

Long-range cues

Short-range (contact-dependent) cues

What are the different short-range cues?

Contact attraction

Contact repulsion

What is an example of a contact attractant?

Cadherin

What is an example of a contact repellent?

Eph ligands

What are the different conserved molecular families of directional guidance cues?

Netrins

Semaphorins

Slits

Ephrins

What are the different signal transduction and regulation cues for physical movement?

Rho Family Small GTPases

Differential interpretation

Gradients

How do the Rho Family Small GTPases mediate guidance?

They interact with the various signaling pathways to alter the cytoskeleton and cell morphology

What is differential interpretation?

The same receptor-ligand interaction can result in different outcomes depending on the cell type or the specific receptor complexes formed

What are the key genes that came from studies of unc mutants in C. elegans?

UNC-6

UNC-5

UNC-40

What genes are receptors for netrin?

UNC-5

UNC-40

What does the inhibition of UNC-6 result in?

Both neurons failing to migrate

What does the inhibition of UNC-5 result in?

The motor neuron failing to migrate

What does the inhibition of UNC-40 result in?

The sensory neuron failing to migrate

What does the mutation of the unc genes affect?

Axonogenesis and outgrowth

The ability of axons to form fascicles (bundles)

Directionality of outgrowth

What is the netrin gradient in the nerve cord?

Dorsal (none) to Ventral (high)

What is netrin similar to?

Lamin

Describe commissure neurons

Connect to the other side of the body

Always cross the midline

What is the purpose of both netrins and Slits?

Neuronal and mesodermal cell migrations

What is the purpose of semaphorin?

Neuronal cell migrations

Bone and heart morphogenesis

What is the purpose of ephrins?

Neuronal and neural crest cell migrations

Angiogenesis

What do special nerves go to?

Cadherins

What is not attracted by netrin?

Dorsal trochlear axons

What happens when only UNC-40 is expressed?

Neurons are attracted to Netrin

What happens when both UNC-5 and UNC-40 are expressed?

Neurons have a repulsive signal

What is the function of Slit?

Acts as a repellent to block neurons from crossing or to ensure they keep moving once they have crossed

What happens during the midline crossing?

Axons use Netrin as a chemoattractant and Slit (using Robo receptors) as a repellent to block neurons from crossing or to ensure they keep moving once they have crossed

What happens in Robo mutants?

Neurons try to cross but fail to leave the midline, staying stuck there

In amphibians, what happens if the optic nerve is severed and the eye is rotated 180 degrees?

The regenerating axons, instead of adapting to the new orientation, they re-establish their original connections, leading to inverted visual behavior where the animal attacks in the opposite direction of its target

How is the choice of target by retinal axons mediated?

By repulsion

What is the relationship between high concentrations of EphA3 receptors on temporal axons and Ephrin A2 ligands in the posterior tectum?

A repellent one, so when they interact, the axon’s growth cone collapses and it is forced to find its correct target somewhere else

What is the function of Sonic the Hedgehog (Shh) as a morphogen?

Ventral inducer (secreted by the notochord)

Establishes neural tube polarity

Stimulates the formation of neural folds

Induces myoD expression in the paraxial mesoderm (future somites)

What cells are nicknames the “fourth germ layer”?

Neural crest cells

Where do neural crest cells originate from?

Originate from the apical part of the developing neural tube

How is the fate of neural crest cells determined?

Determined by their position along the embryo

What does receptor heterodimerization entail?

The same guidance cue can induce opposite behaviors depending on the receptors present

What is the physical process for the formation of the neural crest

1. Neural fold formation (stimulated by Shh signaling)

2. Invagination (folds move toward each other)

3. Fusion (forms neural tube)

4. Delamination and migration

What are the different derivatives of the “fourth germ layer”?

Melanocytes

Glial Cells

Nervous system components (different neurons)

Endocrine cells

Skeletal structures (cartilage)