Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A BMS 381 - Developmental neurobiology > Reprogramming > Flashcards

Reprogramming Flashcards

1
Q

What happens to axons when they reach intermediate targets?

A

They reprogramme

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

What happens to the neurons in the hindbrain when they cross the floor plate?

How is this different to in the spinal cord?

A

In the hindbrain: neurons continue straight on

In the spinal cord: neurons turn anteriorly

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

What happens to pre-crossing neurons if they are exposed to an ectopic floor plate?

A

They are attracted to the ectopic floor plate

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

What happens to post-crossing neurons if they are exposed to an ectopic floor plate?

A

They are not attracted to the ectopic floor plate

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

What happens to neuron sensitivity when they cross the floor plate?

A

Sensitivity changes:

  • No longer attracted to netrins in the floor plate
  • Now sensitive to repellants in the floor plate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How are semaphorins and slits expressed in the floor plate?

A

In 3 bands

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

Why do spinal cord axons turn after crossing the floor plate?

A

Repelled by slits and semaphorins in the floor plate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Why don’t the axons in the spinal cord go straight on once crossing the floor plate in the spinal cord? (like in the hindbrain)

A

Slits and semaphorins (repelllants in the floor plate) create a channel at which the axons grow

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

What is expressed in INSECT midline glial cells?

A
  • Diffusible attractants (netrins)

- Cell surface repellants (slits)

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

What occurs in the roundabout mutant? (NO ROBO)

A

Neurons lose sensitivity to repellants in the midline:

- Axons cross the midline many times

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

What occurs in the commissurless mutant? (NO COMM)

A

Neurons are permanently sensitive to repellants in the midline:
- Axons don’t cross the midline

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What happens when FORCE expression of comm?

What does this show?

A

Looks like robo mutant (no robo) - no longer sensitive to midline repellants

Shows that comm controls robo

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

Do all axons cross the midline?

A

NO some axons cross to form commissures that join with longitudinal pathways formed by axons that have not crossed the midline

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

What determines whether or not axons can cross the midline?

A

Levels of SLIT receptors at the cell surface

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

What type of molecule is comm?

Where is it found?

A

A membrane-associated protein

Found at the cell surface and on intracellular components

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How does comm control robo?

A

Controls the intracellular trafficking of robo to the cell surface

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

What is Robo?

A

A receptor for the inhibitory protein SLIT

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

Where is robo expression high/low?

A

High on neurons that DON’T cross (repelled by the midline)

High on C neurons AFTER they have crossed (prevent crossing again)

Low on C neurons BEFORE crossing (so they can be attracted to the midline)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Why do the axons continuously cross the midline in robo mutants?

A

No robo, no slit detected, not repelled from the midline

Can constantly be attracted to the midline by netrins

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

Which 2 places is comm expressed?

A

1) In the MIDLINE

2) In neurons that normally cross the midline

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

Why do the axons not cross the midline in comm mutants?

A

Robo upregulated, higher sensitivity to slits, extend axons longitudinally

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

What are the 2 possible models of how Comm controls Robo?

A

1) Sorting model

2) Clearance model

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

Describe the sorting model of how comm controls robo

A

Presence of Comm forces the sorting of newly synthesised Robo into late endosomes:

Pre-crossing/during crossing - Robo recycled and degraded

Post-crossing - Robo upregulated

In neurons that DON’T cross - no Comm, no robo degredation

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

Describe the clearance model of how comm controls robo

A
  • Robo goes down the axon with comm
  • Robo gets to the surface but is CLEARED from the surface (during crossing)
  • Following crossing, Robo is UPREGULATED
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How is robo cleared from the cell surface during the crossing of a commisural axon?

A

Due to the HOMOPHILLIC interactions between comm in the axon and comm in the midline

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

In the clearance model, how is robo upregulated in post-crossing axons?

A

No longer homophillic interactions between comm in the axon and comm in the midline

27
Q

What predictions distinguish between the clearance and the sorting model?

A

1) Only the clearance model requires comm expression in the midline
2) In the clearance model, robo is sent down the axon before the axon crosses, but in the sorting model, robo stays in the cell body before the axon crosses

28
Q

Why is the clearance model an attractive model for how comm controls robo?

A

Suggests a mechanism for up regulation of robo in crossed axon segments

29
Q

What 2 things are used to test if the clearance model or the sorting model is correct?

A

1) Is comm required in the MIDLINE CELLS for correct crossing? (clearance models says should be)
2) Is robo PREVENTED from going to axons in the presence of comm? (sorting model says it should be)

30
Q

How to test if comm required in the MIDLINE CELLS for correct crossing?

A

Use neuron-specific promoter to drive axon marker in a subset of cells:

  • Use promoter to drive comm expression IN THE NEURONS in a comm mutant background
  • Comm is in the neurons but NOT the midline

–> rescues the phenotype, in favour of the SORTING model

31
Q

How to test if robo PREVENTED from going to axons in the presence of comm?

A

Use robo-GFP fusion protein in the fly:

Axon NOT expressing comm - robo moves down the axon

Axon expressing comm - robo remains in the CELL BODY

–> shows comm doesn’t ship robo down the axon, in favour of the SORTING model

32
Q

What model explains how comm controls robo?

What are the problems with this model?

A

Sorting model

Problems, don’t understand why:

1) Comm is expressed in the midline
2) What controls upregulation of robo on the contalateral side (after crossing the midline)

33
Q

What is the likely explanation of upregulation of robo after the midline?

A

Due to contact with the midline

34
Q

When is robo made in the axon?

What does this allow?

A

BEFORE axons cross

Allows robo to rapidly appear on the cell surface once the midline is crossed

35
Q

What type of molecules are TAG-1 and L1?

How are they expressed in commisural axons?

A

Cell adhesion molecules (on the cell surface) in MAMMALS

TAG-1:
High in axons pre-crossing, switched off post crossing

L1:
Up regulated in post-crossing axons

36
Q

What is the comm homologue in vertebrates?

A

There isn’t one, instead:

- Another Robo-like receptor is expressed in pre-crossing axons

37
Q

In vertebrates, what is the robo-like receptor expressed in pre-crossing axons?

A

Robo3/Rig1

- Also a receptor for slit

38
Q

What happens in mice if KO robo3?

Why is this surprising?

A

PREVENTS floorplate crossing (axons aren’t attracted to the FP)

Surprising because robo is a receptor slit, if KO - assume will cross the floor plate (less sensitive to slits)

39
Q

What are the 2 models of how Robo3 works?

A

1) Robo3 is a receptor for an ATTRACTANT not a repellant

2) Robo3 is an INHIBITOR of Robo

40
Q

What does model 1 of how Robo3 works suggest when KO robo3?

A

Neurons are prematurely sensitive to slit and are not attracted to the floorplate

41
Q

What happens in a mouse with Robo3KO AND blocked slit function?

What model is this consistent with?

A

Attraction to the floor plate is RESTORED

Consistent with model 2 (Robo3 is inhibitor of robo):
- NO inhibitor of Robo, robo can function and sense slits (doesn’t cross)

  • BUT, no slits, robo cannot sense slits (axons cross)
42
Q

How is slit function blocked?

A

Adding Robo1 ectodomain (part of receptor outside of the cell that usually binds to slit):

  • Binds to slits and stops slits binding to Robo in the neurons
43
Q

What experiments show that Robo3 function is to prevent premature slit sensitivity?

What does this show?

What is the control?

A

Take cells expressing slit in a bath with netrin:

  • WT pre-crossing C axons IGNORE slits in presence of netrin (axons grow into netrin)
  • Pre-crossing C axons LACKING Robo3 are REPELLED away from slit source (still grow into netrin, but away from slit)

Control: Not true for other inhibitory factors, only slit

44
Q

When can netrin override effect of slit?

A

In WT neurons

But ONLY when ROBO3 is present

45
Q

What prevents robo from functioning in the wrong part of the pathway?

A

Crosstalk between receptors

46
Q

What is the role of Robo3 and Comm?

A

Robo3 (in vertebrates) is ANALOGOUS to comm (in flies) (similar function, different protein):

  • Prevents Robo from signalling BEFORE the midline…
  • Allowing netrin to signal through its receptor
47
Q

What is the receptor of netrin?

A

Dcc

48
Q

How does Robo3 and Comm prevent robo signalling?

A

Robo3:
Robo GETS TO the surface but Robo3 prevents its signalling

Comm:
PREVENTS robo from getting to the surface

49
Q

How is the mechanism of how Robo3 works differnetly to comm?

A
  • Doesn’t affect the trafficking, it blocks the receptor at the CELL SURFACE
  • Loss of Robo3 doesn’t lead to the upregulation of robo on pre-crossing axons, instead, allows robo to signal
50
Q

What happens to the level of slits as the FP is encountered?

A

Levels of slit increase

51
Q

How is robo stabilised in the membrane?

What does this cause?

A

When slit binds to robo as slit concentration increases

Causes:
- Amplification of the robo expression

  • When above certain threshold this slit-induced robo signalling OVERWHELMS robo3 inhibition
  • Through feedback, this TURNS OFF robo3 expression
  • -> Fully stabilising Robo and slit repulsion
52
Q

How do post-crossing axons respond to netrin in the presence of slit?

What does this show?

A

No longer respond to netrin (even though they do when slit is not present)

Shows that slits INHIBIT netrin

53
Q

What are the 2 proposed models that suggest how slit inhibits netrin?

A

1) Model 1: Ligand-ligand interaction
(Slit and netrin physically interact)

2) Model 2: receptor-mediated silencing
(Ligands BIND to the receptor but the EFFECT of SLIT binding to ROBO silences signalling from the netrin receptor DCC

54
Q

How can you test if it is ligand-ligand interaction or receptor-mediated silencing that blocks netrin signalling?

What were the results?

A

Create hybrid version of robo (intracellular domain - robo, extracellular domain Met) - test which part of the recpetor is important:

  • If ligand-ligand interaction: extracellular should be important
  • If receptor-mediated silencing: intracellular part should be important

Results:

  • HGF ligand binds to HGF receptor extracellularly
  • Turning response occurs
  • Since HGF doesn’t do this normally, shows it is the intracellular domain of robo that is important (silencing is due to receptor interactions)
55
Q

What causes the silencing of netrin once the floor plate is crossed?

A

Interactions between the cytoplasmic domains of DCC and Robo

56
Q

As well as loss of sensitivity of the commisural axons for netrin when the floor plate is crossed, what else occurs?

A

Sensitivity to repellants (slits) increase

57
Q

What are the 2 possibilites of the ‘switch’ in sensitivities as cross the floor plate?

Which model does the evidence suggest?

A

1) Contact with the floor plate as the trigger
2) Changes over TIME

Evidence for BOTH possibilities

58
Q

What are the 2 contact/proximity with the floor plate triggering the switch idea?

A

1) As get CLOSER to the floor plate - increase in concentration of SLIT that binds to ROBO on the cell surface:
- Concentration too high for robo3 to inhibit
- Feedback (shutdown of robo3 when there is slit signalling through its receptor)

2) Something on the surface of the FP - when come into contact with it it flips the switch
- NrCAM

59
Q

What is NrCAM and where is it present?

What does it interact with? What does this acheive?

A

Cell adhesion molecule ONLY expressed in the FP

Interacts with TAG1 on commisural axons to STABILISE robo on the commisural axons –> leads to increased sensitivity to sema –> repulsion

60
Q

What does shh do in the floor plate?

A

Attracts neurons to the floor plate by binding to receptor and then SWITCHES to repulsion as C axons cross the floor plate, due to a cell INTRINSIC change in the C axons

Changes how axons respond to repellants, switches response to netrin

Repulsion of axons by shh makes the neurons turn LEFT to travel anteriorly

61
Q

What happens if KO shh in the floor plate?

A

Confused neurons crossing of the floor plate and turning defects

62
Q

What is 14-3-3?

What is it involved in?

A

Par-5 homolog which INHIBITS PKA and stops it from responding to [cAMP] which controls the polarity of response

Mediating the sensitivity switch

63
Q

What revereses the response of C axons to shh?

A

Cell intrinsic levels of 14-3-3:
- Increases as C neurons get close to the floor plate

  • Change in expression causes C axons to be repelled by the floor plate (initially attracted)

(PKA is normally activated by smo, which is activated when shh binds)

(Inhibit PKA - stop responding to cAMP, which controls the attractant response to a cue)

64
Q

What makes post-crossing axons turn left and travel anteriorly

A

Repulsion by shh posteriorly

Attraction by wnt anteriorly (wnt4)

A BMS 381 - Developmental neurobiology (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions