Cours: Axon Growth and Survival

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Questions and Answers

Which of the following molecules are directly involved in regulating the dynamic steady-state of the cytoskeleton?

Microtubules

Profilin (correct)

Rho GTPases (correct)

Cofilin (correct)

What cytoskeletal element is responsible for the force exerted by filopodia?

Microfilaments

Intermediate filaments

Microtubules

Actin filaments (correct)

How do filopodia influence growth cone turning?

By directly interacting with guidance cues

By pulling on the growth cone membrane

By affecting the fluidity of the growth cone plasma membrane

By influencing the distribution and polymerization of microtubules (correct)

What happens when actin filaments are depolymerized in a growth cone?

The growth cone moves in the direction of the intact filaments (B) Signup and view all the answers

What happens when microtubules are stabilized in a growth cone?

The growth cone turns towards the stabilized microtubules (B) Signup and view all the answers

How is information about guidance cues transmitted to the cytoskeleton?

Through a complex signal transduction pathway (A) Signup and view all the answers

What is the role of the 'clutch mechanism' in axon growth?

It creates the force required for axon elongation (D) Signup and view all the answers

What is the significance of axon branching for neuronal connectivity?

It allows neurons to form connections with a wider range of target cells (C) Signup and view all the answers

What is the key role of neurotrophins in the context of neuronal survival?

They prevent the death of neurons by apoptosis. (C) Signup and view all the answers

What is the process by which axons grow in length?

Axons elongate by adding new microtubules at the distal end. (A) Signup and view all the answers

How does the size of the target tissue impact the number of surviving neurons?

Smaller target tissues lead to more competition for neurotrophins, resulting in fewer surviving neurons. (D) Signup and view all the answers

How does the growth cone's shape change during axon growth?

The growth cone's shape changes depending on the guidance cues provided by the environment. (A) Signup and view all the answers

What is the role of microtubules and actin filaments in axon growth?

They provide structural support and help in the transport of nutrients to the growing axon. (B) Signup and view all the answers

What is the significance of the 'treadmilling cycle' in axon growth?

It is a process of continuous addition and removal of actin monomers at the ends of actin filaments, aiding in growth cone motility. (B) Signup and view all the answers

What is the role of apoptosis in neuronal development?

Apoptosis is a process that eliminates unnecessary or damaged neurons during development, helping to shape the nervous system. (B) Signup and view all the answers

What is the key function of neurotrophins in the context of neuronal survival?

They prevent the death of neurons by apoptosis. (A) Signup and view all the answers

Which of the following is NOT a critical step in the process of axon guidance?

Formation of a myelin sheath (A) Signup and view all the answers

What is the relationship between the size of the target tissue and the number of surviving neurons?

Larger target tissues result in fewer surviving neurons due to increased competition for neurotrophins. (A) Signup and view all the answers

Study Notes

Axon Growth and Survival

Axons must survive, grow, find and reach their target cells, recognize their targets, and connect to them.
The complexity of axon tracts increases rapidly during early stages of development, as shown by diagrams of developing nervous system structures at various time points.
Neurons require trophic factors for survival. Dorsal root ganglion (DRG) neurons, without nerve growth factor (NGF), show reduced survival compared to those with NGF.
Viktor Hamburger (1900-2001) and Rita Levi-Montalcini (1909-2012) were pivotal in identifying the importance of growth factors and NGF in neuronal development. Montalcini's work won her a Nobel Prize in 1986.
Reducing the target area promotes cell death during neural development. Removal of a limb bud led to less survival of DRG and motor neurons.
The number of surviving neurons correlates with the size of the target tissue; adding a limb bud increased neuron survival, while removal reduced it.
NGF is the first identified neurotrophic factor (responsible for regulating growth and survival of neurons during development).
Apoptosis (programmed cell death) requires protein synthesis. Blocking protein synthesis interferes with apoptosis.
Neurotrophins (including NGF, BDNF, NT3, and NT4) support different sensory neuron subtypes via specific receptor engagement (trk receptors and p75).
Neurotrophins are released in a target-specific manner, influencing development of different types of nerve cells in different regions.
Neurotrophins (e.g., NGF) adapt innervation according to tissue size. Smaller or removed target tissues lead to less cell death in DRG neurons.
Neurotrophin signaling involves endocytosis and retrograde transport, influencing cell survival and growth.
Neurotrophins prevent apoptosis and support synaptogenesis (formation of synapses).
Axons extend long processes to connect to their targets.
Axons grow through adding new microtubules at the distal end, and by stretching.
Growth cones come in different shapes depending on their environment and phase of growth (fascicle, choice point, target region).
Growth cone speed varies depending on location.
Non-permissive substrates trigger growth cone turns at boundary areas.
In vertebrate growth cones, actin filaments and microtubules interact at the peripheral zone.
Actin and tubulin form the growth cone's cytoskeleton (filopodia, lamellipodia-like veil, etc.).
Filopodia exhibit force exertion and trigger growth cone turns.
The cytoskeleton directs growth cone movement through actin and microtubule depolymerization and stabilization.
Guidance cues (semaphores, netrin receptors) and molecules such as Eph ligands, Ig CAMs, cadherins, and ECM components influence axon interactions.
Actin filaments are essential for axon guidance and contribute to the clutch mechanism used to move the growth cone.
A pathway, involving Rho GTPases, transmits signals to the cytoskeleton to coordinate growth cone movement and shape.
Axon branching via growth cone bifurcation or collateral branching is vital for neuronal connectivity.
Branch formation requires actin filaments and microtubules in a set of well-regulated steps.
Molecules play a role as guidance cues, affecting how many and which axons follow a given pathway.

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Description

Explore the crucial processes involved in axon growth and survival in the nervous system. This quiz highlights the role of trophic factors like nerve growth factor (NGF) and the significant contributions of researchers such as Viktor Hamburger and Rita Levi-Montalcini. Test your knowledge of how target tissue influences neuronal survival.