Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

BMS 249 - Developmental Neurobiology > Axon Guidance II > Flashcards

Axon Guidance II Flashcards

1
Q

What are filopodia?

A

Finger-like projections

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are lamellipodia?

A

Sheet-like cellular outgrowths

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are filopodia and lamellipodia important for?

A

Cell shape changes, migrating cells and growth cones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the 3 growth cone domains?

A
  • Central (palm)
  • Transitional
  • Peripheral
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the 2 filamentous proteins in the growth cone?

A

1) Microtubules (tubulin)

2) F-actin (filamentous actin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is different about the F-actin in filopodia and lamellipodia?

A

In lamella:
- Actin bundles are crosslinked into a net

In filopodia:
- Actin bundles are polarised to form larger bundles, with a linear array

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is ‘treadmilling’?

A
  • Single actin subunits are added to the tips of the of filaments (F-actin)
  • In the peripheral domain, F-actin flows back
  • In the transitional domain, the filaments break down into single actin subunits
  • In the
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Where does treadmilling occur?

A

In filopodia in a resting growth cone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What happens to the microtubules in the central domain during treadmilling?

A

They are dragged sporadically dragged into the filopodia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What happens to the movement of the microtubules in the central domain when the growth cone comes into contact with an attractive cue?

A

The microtubules are more dramatically dragged into the filopodia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What happens in the F-actin when the growth cone comes into contact with an attractive cue?

What does this cause?

A
  • F-actin tread-milling slows down and F-actin accumulates (increases in concentration)

The F-actin accumulation:

  • Stabilises the filopodium
  • Drags the microtubules into the back of the filopodium - stabilsing the microtubules
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

When a growth cue is encountered, where do F-actin and microtubules point towards?

How is this done?

A

Towards the growth cue

Reorganisation of the microtubules to completely establish and new growth direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

When a growth cue is encountered, what 2 key components lead to filopodial extension and reorientation of the microtubules, to point towards the growth cue?

A

1) MOLECULAR CLUTCH
- Cross-linking to the backwards flowing actin to arrest backwards flow
- Filopodia don’t shorten
- Results in forwards movement of the filopodia (get longer)

2) ACTIN-TUBULIN LINK
- Actin-myosin based link
- Pulls the microtubules into the wake of the extending filopodium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What was discovered when neurons of different types were mixed in culture?

What is this NOT due to?

A
  • Neurons fasciculated only with their OWN kind

- NOT due to attractive forces

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the ‘growth-cone collapse’?

A
  • F-actin is destabilised
  • High to low levels of actin
  • Causes the growth cone to retract
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

When does ‘growth-cone collapse’ occur?

A

When the growth cone of an axon comes into contact with the axon of another neuron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

When ‘growth-cone collapse’ occurs, what happens afterwards?

A

Growth cone moves in a different direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are semaphorins?

A
  • A family of inhibitory guidance cues which can be membrane bound or secretory (have a lipid anchor)
  • All have a strongly conserved semaphorin domain
  • Non-permissive contact repellants
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What happens when add semaphorins to a growth cone?

A

It moves away, due to dramatic collapse of F-actin (Growth cone collapse)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What does an axon require to allow it to grow?

A

Must be able to attach to the substrate it is growing on

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the relationship between strength of adhesion and the amount of axon growth on a substrate?

A

There is no simple relationship - substrate adhesion does not determine how fast an axon will grow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are permissive substrates and why are they important?

A

Substrates which ALLOW growth

Important because attachment alone is not enough for axon growth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Between collagen and laminin, which substance is the most adhesive?

A

Collagen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Between collagen and laminin, which substance is the most permissive?

A

Laminin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
In the eye, where is laminin localised? What does this allow?
Localised in the optic nerve, from the retina to the tectum Allows the growth of the retinal ganglion nerves to the tectum
26
Even though laminin is permissive, what information does it not provide?
Speed of growth Direction of growth (not instructive)
27
What does the blockage of receptors for laminin in the optic nerve cause?
Slows down the growth But doesn't change the direction of growth
28
What do gradients of laminin in vitro cause?
Nothing, they DO NOT direct axon growth
29
When is laminin permissive?
Within a specific concentration: | If the concentration is too high or low - there is NO axon growth
30
Where are permissive and non-permissive substrates found?
On axon surfaces
31
What are permissive and non-permissive substrates NOT involved in?
Attachment
32
When a growth cone collapses, what happens to the attachment on the surface, what does this imply?
Attachment remains - growth cone collapse doesn't imply lack of adhesion
33
What can non-permissive factors do? How is this done?
Channel axon growth 2 stripes of non-permissive factors can be expressed either side of the growing axon
34
How is semaphorin expressed in the grasshopper limb?
In stripes of Semaphorin I
35
What happens when a growth cone comes into contact with cells expressing semaphorin?
The growth turns (growth cone collapse)
36
How can semaphorins be inserted into them membrane of a cell and what are these molecules?
1) Membrane bound (contact attractants/repellants | 2) Lipid anchors (can be secreted - chemoattractants/repellants)
37
What happens if Sema I expression is disrupted in the grasshoppper limb?
Neurons stray into the wrong teritories
38
What semaporin is expressed in mice limbs?
Sem3A
39
What happens if Sem3A expression is disrupted in mice?
Neurons stray into the wrong territories
40
For axon growth, what must there be a balance between?
Permissive and non-permissive factors
41
What are ephrins?
Non-permissive ligands, which are all membrane bound (cell-surface molecules) CONTACT REPULSION FACTORS
42
What are the receptors for ephrins and what are they called?
Tyrosine kinases - Ephs
43
How are ephrins and ephs expressed in the embryo?
In reciprocal patterns (one is expressed where the other is not)
44
What are ephrins thought to be used for? (3 things)
- To compartmentalise the embryo into discrete domains (eg.rhombomeres) - And to keep axons out of specific areas of the embryo - Make topographic maps
45
What 2 things can non-permissive factors do to the paths taken by growth cones?
- Can work with permissive factors to channel the growth cone - Can keep the growth cone out of specific regions of the embryo
46
How do axons know which way to go?
Chemoattractants and chemorepellants, which act over long distances to direct axons in certain directions
47
What are permissive substrates also called?
Contact attractants
48
What are non-permissive substrates also called?
Contact repellants
49
How was it known that the roof plate and floor plate are organisers?
- Cut out the spinal cord and took the top half of it and lay it on its side - Commissural neurons grew ventrally, as they should do - If put an ectopic floor plate - axons turn towards the floor plate
50
How was it known that it was a SECRETED molecule coming from the floor plate which organises neurons?
If put floor plate out of direct contact of the axons, they still grow towards the floor plate
51
What do commisural axons do?
- Take information from the sensory afferents in the DRG and relay this information up to the thalamus - They find their way to the floor plate and cross underneath it
52
Where is the floor plate chemoattractant protein expressed?
Along the midline of the vertebrate nervous system
53
What is the chemoattractant protein in the floor plate and how was it discovered?
Netrin Discovered by biochemical purification and cloning
54
What molecule is netrin similar to and how?
Laminin - can associate with the ECM
55
How was it known that netrin attracts commisural axons?
Take cells artificially expressing netrin - axons are attracted
56
What repels commisural axons?
BMP (bone morphogenic protein), expressed by the roof plate
57
What is special about BMPs and Shh?
They are used in many stages of patterning the embyro. At early stages: - Pattern the DV axis and specify where neurons are BORN At later stages: - GUIDE axons, to their targets
58
What does purified BMP7 do?
Cause growth cone collapse
59
What happens in a netrin knockout?
- Commissural axons reach the floor plate | - BUT, they do not cross the floor plate
60
What 2 things are involved in guiding commissural axons to the floor plate?
BMP signalling from the roof plate | SHh signalling from the floor plate
61
Why can BMP alone not direct commissural axons to the floor plate?
They cannot reach the ventral part of the neural tube
62
What blocks shh signalling?
Cyclopamine
63
What is needed for Shh signalling?
Smo receptors
64
What does bacteriophage P1 encode and what does this allow the bacteriophage to do?
Cre recombinase Allows the bacteriophage to insert its DNA into the host genome
65
What does Cre do?
Binds to 2 loxP sites and joins them together
66
What can Cre recombinase be used to do and how?
Specifically delete DNA (knockout) - Flank a DNA sequence wishing to KO with 2 loxP sites - When exposed to Cre recombinase will cut and rejoin the 2 loxP sites together
67
What is flanking the gene with loxP sites called?
Floxing
68
How can smo be knocked out ONLY in the commisural axons in an organism?
1) Flox a smo allele 2) Cross into a mouse with Wnt 1 promoter which drives cre recombinase (Wnt 1 is normally expressed in the roof plate) 3) Offspring will have smo allele removed only in the commisural axons (as they are derived from the dorsal lip of the neural tube) and the DRG (derived from the neural crest)
69
Why is it important to only KO smo in commisural axons if wishing to study how it guides these axons?
Shh is important for development in the early embryo- if KO shh in the whole embryo the commisural axons will not form
70
Where are commissural axons derived from?
The dorsal lips of the neural tube
71
What is used to guide pioneer axons?
TF expressed in specific cells in specific domains in the environment which are set up by the early patterning information in the embyro (eg. BMPs Shh)
72
How are morphogenetic gradients re-used to guide axon paths?
BMP and Shh specify nerual fate BMPs and Shh co-operate with netrin to guide commissural axons
73
How do long-range and short-range cues work together in the grasshopper limb to guide axons to their targets?
Sema2 is secreted in a decreasing gradient towards the body and guides the Ti1 axons - long range cue Sema1 - short range cue
74
How is Sema2 secreted in the grasshopper limb?
In a decreasing gradient, towards the body
75
What does the blockage of Sema2 cause and what does this suggest?
Disruption of the initial guidance of the Ti1 axons towards the body Suggests that the gradient of secreted Sema2 directs the Ti1 growth cone towards the body
76
How are the four guidance cues used?
In combinations together, the guide axons at different stages in their pathway
77
How are complex neuron pathways built up?
In several stages
78
When axons reach their intermediate targets, what must they do?
Make navigational choices (these are choice points)
79
In the grasshopper limb, what is a short range cue?
Sema I
80
In the grasshopper limb, what is a long range cue?
Sema II
81
Which part of the growth cone is and isn't attached to the ECM?
Palm is attached Filopodia is not attached
82
How can sema1 function be blocked?
With antibodies
83
Why would you want to control when cre recombinase is turned on?
So can control WHEN a certain gene is knocked out
84
How big is the sequence of a loxP site?
34 base pairs
85
Where is Wnt1 normally expressed?
In the roof plate
86
What is lacZ? What does it do?
A reporter gene Marks the function or location of ANOTHER gene or function as its expression is easily monitored
87
When using a Wnt1 gene to drive cre recombinase to knock out smo, where is smo knocked out and why?
KO in commisural axons and DRG As Wnt1 is normally expressed in the roof plate Commisural axons are derived from the dorsal lips of the neural tube and the DRG are derived from the neural crest
88
Where do commisural axons derived from?
The dorsal lips of the neural tube
89
If knock out Shh or Smo what happens?
Early embryonic lethal

BMS 249 - Developmental Neurobiology (16 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions