Lecture 3: Neuronal polarization and maintenance of polarity

Question 1

What does it mean that neurons are polarized cells?

Answer 1

Neuronal polarity refers to the asymmetrical distribution of cellular components within a
neuron. (they need to have two ends: dendrite and axon)

Question 2

What is synaptogenesis?

Answer 2

Synaptogenesis is the formation of synapses between neurons in the nervous system. Although it occurs throughout a healthy person’s lifespan, an explosion of synapse formation occurs during early brain development, known as exuberant synaptogenesis.

Question 3

What is the general morphology of different polarity markers?

Answer 3

number (axon is often unique)
* A neuron commonly has 1 axon and few dendrites
- length
- branching
- thickness
-Spines (dendrites)
* Often act as postsynaptic sites of most excitatory synapses
* They also serve as a storage site for synaptic strength and help transmit electrical
signals to the neuron’s cell body
-Electrical activity: AP generation and propagation in the axon
-Myelinated or not (in vivo)

Question 4

What is electrical activity?

Answer 4

: AP generation and propagation in the axon

Question 5

How are the Micro-tubule-associated proteins called?

Answer 5

• enriched in the dendrites: MAP2
• enriched in the axon: Tau

Question 6

What are the polarization steps?

Answer 6

1. Initial stage
2. Neurites outgrowth
   - Small extensions occur, it is
   unknown which outgrowth will
   develop into axons and which
   into dendrites
   - The continuation from stage 2
   to stage 3 is also known as
   “breaking the symmetry” due
   to disproportional formation
   developing in stage 3
3. Axonal differentiation and growth
   - Small growths continue to
   occur but 1 particularly long
   outgrow is forming→ axon
4. Dendrite outgrowth
5. Network Formation

Question 7

The steps of polarization define the stages of neuron development when cultured in vitro
- The greater the polarization, the greater the development of the neuron. Is this statement True or False

Answer 7

True

Question 8

How to break the symmetry?

Answer 8

• neurons grow and retract their neurites before one differentiates into the axon
• intrinsic signal to differentiate one neurite into an axon

Question 9

What is/are the signal(s) involved?
What do we look for?

Answer 9

By using an axon marker, we can differentiate between soma and dendrites in live imaging experiments. The axon marker will first occur at various neurites,
but as it polarizes, one neurite will develop in an axon

Question 10

What are the factor(s) breaking the symmetry?

Answer 10

• In stage 2 (unpolarized neuron), PAR stains can be seen in the soma and the tips of all
  neurites in an isolated neuron
• In stage 3 (polarized neuron), PAR stains are in the longest neurite which will most
  likely become the axon

Question 11

What is the role of Par-3 in axon formation?

Answer 11

• Disruption of Par-3 blocks the polarization of neurons (no growth and no
  accumulation of Tau in the axon but in all neurites)

Question 12

Furthermore, neuronal signalling involves the regulation of the following factors that are also associated with the breaking of the symmetry. What are the factors?

Answer 12

• Microtubules (MT)
• Transport
• Cell adhesion
• F-actin

Question 13

What is the neuronal cytoskeleton made of?

Answer 13

The term “cytoskeleton” is often used as if it described a single, unified structure, but the cytoskeleton of neurons and other eukaryotic cells comprises three distinct, interacting structural complexes that have very different properties: microtubules (MTs), neurofilaments (NFs) and microfilaments (MFs).

Question 14

What happens in microtubules?

Answer 14

Microtubules -> regulation via available
monomers, associated proteins, and modifying enzymes
- They’re dynamic but we can control
them by the factors that affect them

Question 15

What happens in Actin?

Answer 15

regulation via available monomers, associated proteins, and modifying enzymes