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BIO 317 > 16 - Signaling Mechanisms Underlying Axon Guidance II > Flashcards

16 - Signaling Mechanisms Underlying Axon Guidance II Flashcards

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1
Q

What is the common effector of the cAMP and PI3K pathway?

A

GSK-3b

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2
Q

What is the benefit of a feed forward mechanism?

A

It creates a very powerful and forceful signaling mechanism

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3
Q

Why is a feed forward mechanism needed for axonal development?

A

It is a prolonged task, which requires relentless signaling to achieve

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4
Q

How does the PI3K pathway interact with GSK-3b?

A

Akt can inhibit GSK-3b through phosphorylation

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5
Q

How does the cAMP pathway interact with GSK-3b?

A

PKA can inhibit GSK-3b through phosphorylation

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6
Q

For a western blot of phosphorylated GSK-3b, what is the blot with cAMP and why?

A

Heavy blot, because cAMP activates PKA, which phosphorylates GSK-3b

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7
Q

For a western blot of phosphorylated GSK-3b, what is the blot with cAMP and PKA inhibitor and why?

A

No blot, because PKA is not active to phosphorylate GSK-3b

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8
Q

For a western blot of phosphorylated GSK-3b, what is the blot with forskolin and why?

A

Heavy blot, because forskolin activates AC, which leads to cAMP and PKA being active, thus phosphorylating GSK-3b

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9
Q

For a western blot of phosphorylated GSK-3b, what is the blot with forskolin and PKA inhibitor and why?

A

No blot, because PKA is not active to phosphorylate GSK-3b

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10
Q

True or false: the PKA pathway and the PI3K pathway only converge at GSK-3b

A

False: these two pathways have many levels of integration

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11
Q

How does aPKC interact with GSK-3b?

A

aPKC can phosphorylate GSK-3b and inhibit it

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12
Q

How does LKB1 interact with the PI3K pathway?

A

LKB1 can associate with aPKC and lead to cross activation

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13
Q

True or false: LKB1 can phosphorylate GSK-3b

A

True: this has been seen in some studies

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14
Q

Besides the PI3K pathway, what pathway is Akt an upstream regulator for?

A

The mTOR pathway

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15
Q

What does the mTOR pathway do (in terms of axonal development)?

A

Promote translation of PAR-1

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16
Q

How does Akt interact with the cAMP pathway?

A

Through the mTOR pathway, it can activate translation of PAR-1 (the downstream regulator of LKB1)

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17
Q

What three things are needed for a coherent feed forward mechanism?

A
  1. One upstream activator
  2. Diverging branches with the same “message”
  3. Convergence on one downstream target
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18
Q

True or false: the cAMP and PI3K pathway can be activated by the same extracellular factor

A

True: they can both be activated by BDNF

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19
Q

True or false: the cAMP and PI3K pathway can be activated by different extracellular factors

A

True: these pathway can run parallel to one another with different extracellular cues

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20
Q

Which extracellular factor can activate both the cAMP and the PI3K pathways?

A

BDNF

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21
Q

What pathways does BDNF promote?

A

Both the cAMP and the PI3K pathways

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22
Q

What does BDNF stand for?

A

Brain derived neurotrophic factor

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23
Q

What family of proteins does BDNF belong to?

A

Neurotrophin family of growth factors

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24
Q

What is BDNF related to?

A

NGF

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25
Q

What does NGF stand for?

A

Nerve growth factor

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26
Q

What functions does BDNF mediate?

A

Survival, growth differentiation, and synaptic function of neurons

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27
Q

What is the receptor for BDNF?

A

TrkB

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28
Q

What is TrkB?

A

An RTK for BDNF

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29
Q

Where are neurotrophins found?

A

In the brain and in the peripheral nervous system

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30
Q

How does BDNF activate the PI3K pathway?

A

Through the phosphorylation of its RTK TrkB

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31
Q

How does BDNF activate the cAMP pathway?

A

Through the inhibition of PDE4 (increase cAMP levels)

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32
Q

What is needed for axons to respond to BDNF in vitro?

A

LKB1, PKA, and PI3K

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33
Q

How can we test that axon formation in response to BDNF depends on LKB1, PKA, and PI3K?

A

Through genetic and/or pharmacological manipulations

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34
Q

If TrkB is phosphorylated, what is the effect on the axon?

A

It will promote axon development

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35
Q

Where does most of the axonal development happen?

A

At the growth cones

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36
Q

What occupies the “palm like” structure of the growth cone?

A

The actin cytoskeleton

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37
Q

Which part of the axon responds to the extracellular environment?

A

The growth cone

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38
Q

What do most of the signaling pathways in axonal development converge on?

A

Regulation of the cytoskeleton

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39
Q

What does MAP stand for?

A

Microtubule associated protein

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40
Q

What are some examples of MAPs?

A

CRMP-2, Tau, and MAP2

41
Q

What do MAPs do?

A

Regulate the growth of the microtubule cytoskeleton

42
Q

What type of protein is the Tau protein?

A

A MAP

43
Q

What is the downstream target of PAR-1?

A

Tau protein

44
Q

What is the upstream regulator of Tau protein?

A

PAR-1

45
Q

What does Tau protein do?

A

Stabilize the assembly of the axon microtubule filaments

46
Q

When is Tau protein activated?

A

When it is phosphorylated by PAR-1

47
Q

What protein is similar to Tau protein?

A

CRMP-2

48
Q

What protein is similar to CRMP-2?

A

Tau protein

49
Q

What happens when Tau protein is phosphorylated?

A

It can associate with the tubulin monomers and regulate the microtubules

50
Q

True or false: MAPs are only axonal specific

A

False: there can also be dendritic specific MAPs

51
Q

What is an example of an axonal specific MAP protein?

A

CRMP-2, Tau protein

52
Q

What is an example of a dendritic specific MAP protein?

A

MAP2

53
Q

What is MAP2?

A

A dendrite specific MAP

54
Q

What does MAP2 do?

A

Mediate microtubule assembly, stabilization, and bundling

55
Q

How do the microtubules interact with the actin cytoskeleton in the growth cone?

A

They stabilize and penetrate the actin network

56
Q

What needs to happen for axons to experience “bursts of growth”?

A

Microtubules must penetrate the actin network

57
Q

What is needed to allow the microtubules to invade the actin cytoskeleton in the growth cone?

A

Actin destabilization (depolymerization)

58
Q

In terms of the cytoskeleton, what is needed to allow for the growth of the growth cones?

A

Actin instability, and microtubule stability

59
Q

Why is actin instability needed for the growth cones to grow?

A

Allow for microtubule invasion

60
Q

Why is microtubule stability needed for the growth cones to grow?

A

Allow for structure to move forward

61
Q

What does colchicine do?

A

Causes microtubule instability

62
Q

What does taxol do?

A

Causes microtubule stability

63
Q

What does cytochalasin do?

A

Causes actin filament instability

64
Q

What does phalloidin do?

A

Causes actin filament stability

65
Q

Which drug causes microtubule instability?

A

Colchicine

66
Q

Which drug causes microtubule stability?

A

Taxol

67
Q

Which drug causes actin filament instability?

A

Cytochalasin

68
Q

Which drug causes actin filament stability?

A

Phalloidin

69
Q

Which drugs (that target the cytoskeleton) would promote axon formation?

A

Taxol and cytochalasin

70
Q

Which drugs (that target the cytoskeleton) would not promote axon formation?

A

Colchicine and phalloidin

71
Q

If taxol or cytochalasin is presented to the whole cell, what happens?

A

It will develop multiple axons

72
Q

If taxol or cytochalasin is presented to a specific neurite, what happens?

A

That neurite will become the axon

73
Q

True or false: taxol could potentially rescue the function of LKB1

A

True: taxol stabilizes the microtubule cytoskeleton, which is a very downstream regulator

74
Q

What is a good target for the downstream regulation of axonal development?

A

The cytoskeleton

75
Q

Why is the cytoskeleton a good target for axonal development?

A

It is one of the most downstream targets that mediates axonal formation

76
Q

What is axonal guidance (or path finding)?

A

How the axon grows to a specific target

77
Q

True or false: axonal guidance is random

A

False: it is highly specific

78
Q

True or false: axonal guidance can only create straight lines

A

False: sharp turns can also be created through axonal guidance

79
Q

What is the purpose of axonal guidance?

A

Have the axon reach its innervation target (synpase)

80
Q

What happens when an axon reaches its innervation target?

A

It creates a synapse

81
Q

How does axonal guidance work?

A

It goes through intermediate proteins until it reaches its innervation target

82
Q

What is needed to choose a route to go from A to B?

A

A map

83
Q

What information does a map provide?

A

Where to go (positive cues) and where not to go (negative cues)

84
Q

What “map” is present in axonal guidance?

A

Molecular cues

85
Q

What do the intermediate proteins do in axonal guidance?

A

They secrete positive and negative cues to guide the axon

86
Q

In axonal guidance, what do positive cues do?

A

Signal for the axon to grow towards it

87
Q

In axonal guidance, what do negative cues do?

A

Signal for the axon to grow away from it

88
Q

How do negative cues cause the axon to grow away from it?

A

It causes cytoskeleton collapse

89
Q

What cues does the innervation target secrete?

A

Positive cues

90
Q

What mediates the turns in the growth cone?

A

The microtubule cytoskeleton

91
Q

What does a positive cue do to the microtubule cytoskeleton?

A

It causes the filaments to grow in that direction

92
Q

What does a negative cue do to the microtubule cytoskeleton?

A

It causes the filaments to collapse (depolymerization)

93
Q

What is the net result of a positive and negative cue being presented together in axonal guidance?

A

A turn is produced

94
Q

What happens to arrays of microtubules in axonal guidance?

A

Some microtubules can collapse, while others can grow (based on the spatial arrangement of these positive and negative cues)

95
Q

What are the positive cues in axonal guidance?

A

Chemoattractants

96
Q

What are the negative cues in axonal guidance?

A

Chemoretractants

97
Q

How does the growth cones detect the chemoattractants and chemoretractants?

A

Through specific cell surface receptors

98
Q

What is the affect of the chemoattractants and the chemoretractants on the cell (in axonal guidance)?

A

Activation or inhibition (respectively) of the microtubule cytoskeleton

BIO 317 (27 decks)

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