Axon guidance

Question 1

Cell body in neuron role

Answer 1

Synthesis of cytoskeleton and membrane components

Question 2

Axon role in neuron

Answer 2

Transport of membrane and cytoskeleton components

Question 3

Growth cone role in neuron

Answer 3

Incorporation of membrane and cytoskeleton

Question 4

How do axons move?

Answer 4

Filopodia extend (Adhesion)
Microtubule extension (membrane addition)
Cytoplasm collapse (actin polymerisation)

Question 5

Adhesion 2 major roles

Answer 5

1- attachment to substrate (growth)

2- navigation (guidance)

Question 6

How is cytoskeleton of growth cone reorganised?

Answer 6

1- guidance and targeting signals act on receptors on a growth cone
2- Activates intracellular signalling machinery which causes cytoskeleton reorganisation

Question 7

Mutations lacking guidance molecules

Answer 7

Roundabout loss of function

Commissureless loss of function

Question 8

Explain axon navigation

Answer 8

1- Target A secretes attractant molecules such as netrins that are fed through ‘guide post’
2- Target B secretes inhibitory molecules also fed through guide posts
3- Also by guidance via repulsion

Question 9

Why do contralateral axons migrate towards the midline?

Answer 9

1- Attractive cues

Question 10

After being attracted, how do they cross?

Answer 10

Down regulate Robo signal through Comm
Slit mutants resemble Robo mutants

Commissureless downregulates Robo so when OFF it can cross the midline

Question 11

Slit, Netrin roles

Answer 11

Slit- binds to Robo and initiates repulsive response

Netrin- encodes attractant