Lecture 10

Question 1

Axon guidance

Answer 1

• Neuron migrates to final position to create neurites
• Neurites travel long distances to reach final targets, where each neurite has growth cone
• Have filopodia that interact with intermediate environment

Question 2

What does axonal transport provide

Answer 2

Supplies to growth cone

• Cell body site of protein synthesis
• Membrane components for growth cone extension made as vesicles transported in growing neurite
• Proteins for neuronal extension transported inside vesicles by anterograde axonal transport

Question 3

Actin and Tubulin

Answer 3

Movement of filopodia driven by actin filaments

As growth cone moves forward, backbone continually reinforced with microtubules

Growth cone adheres to adjacent cells/ECM

Question 4

What is axon growth influenced by

Answer 4

Cell adhesion molecules (CAMs)

Substrate adhesion molecules (SAMs)

Diffusible guidance molecules

Question 5

Structure of growth cone

Answer 5

Central domain - microtubules, organelles, vesicles etc

Transitional zone

Peripheral domain - actin, lamellipodia (flat regions of dense actin between filopodia), filopodia

Answer 6

Actin pushes the cell forward; myosin II pulls it back.

Clutch proteins anchor the actin to the surface.

Microtubules and organelles move forward.

Attractive cues boost movement; repulsive cues inhibit it.

Directional migration is controlled by cue balance.

Question 7

How does an axon know where to go?

Answer 7

• Growth cone highly motile
• Sensitive to attractive/repellent cues as guideposts
• CAMs/SAMs/diffusible chemotropic molecules give guidance

Question 8

N-CAM

Answer 8

On surface of neurons/glial cells

Homophilic adhesion via immunoglobulin domains

> 27 isoforms

N-CAM knockout mice shows axon migration defects

Question 9

N-cadherin

Answer 9

• 5 cadherin repeats
• B-sheet sandwich
• Homophilic calcium ion dependent adhesion
• Functional unit is a dimer
• Anti N-cadherin antibodies prevent outgrowth of Xenopus retinal axons