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BMS381 Developmental Neurobiology > L2 - Growth Cone Mechanics and Signalling > Flashcards

L2 - Growth Cone Mechanics and Signalling Flashcards

1
Q

3 domains of the growth cone

A

Central
Transitional
Peripheral

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2
Q

What (2) is the growth cone made of

A

Lammelapodia and filopodia

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3
Q

Describe the lamella

A

Contain F-actin bundles that are cross linked into a net strucutre

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4
Q

Describe the filopodia

A

Actin bundles are polarised to form much larger bundles

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5
Q

Describe the treadmilling of the F-actin

A

Addition at the + end
Flows back to the soma
Is then severed and recycled back to the + end

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6
Q

What term describes the following ….

“In the resting growth cone tubulin is dragged sporadically into the filopodia”

A

Microtubule capture

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7
Q

Do growth cones turn?

A

NO they reorganised

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8
Q

Describe what happens when the growth cone comes into contact w/ an attractive cue

A

Treadmilling slows - F actin accumulates

This stabilises the filopodium and dargs the MT into the back of the filopodia - MICROTUBULE CAPTURE

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9
Q

What are the two components that lead to extension of the filopida

A

Molecular clutch

Actomyosin based actin tubulin link

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10
Q

How does the molecule clutch lead to extension of the filopida

A

Slows the rearward actin treadmilling results in the forwards movement of the filopodia

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11
Q

How does the actomyosin based actin tubulin link lead to extension of the filopida

A

Captures microtubules in the wake of the extending filopodia

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12
Q

What is the evidence for the existence of the molecular clutch

A

M.Garcia et al. Micropatterened glass with receptor to N-cad

On the dots where N-cad receptor present NO ACTIN TREADMILLING - in that area no clutch engaged

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13
Q

What other mechanism could there be for the control of the clutch

A

Actin cross linking

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14
Q

How could Actin cross linking control the clutch

A

Cue may activate a IC cross linking protein … branched and crosslinked F actin has the strength to pus forward thus less retrograde flow

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15
Q

What is the cross linkinig protein most likely to be

A

Myosin

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16
Q

What is the general mechanism for growth cone collapse

A

Destabilisation of F-acin

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17
Q

Collapsin 1 aka

A

SEMA3A

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18
Q

SEMA3A must be able to …________ they do this through ___________

A

Modulation of the actin cytoskeleton

Intracellular GTPases of the Rho family

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19
Q

GAP turns ____-

A

OFF

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20
Q

GEF tunrs ______

A

ON

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21
Q

How does a GAP turn off ….

A

Activating the GTPase
GTP hydrolysed
SO GDP bound as inactive

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22
Q

How does a GEF turn on

A

Causes exchange so GDP dissociates

GTP binds - active

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23
Q

How do we study the functions of GTPases

A

DN and CA studies

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24
Q

What does RhoA control

A

Stress fibre formation

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25
What does Rac control
Lammelapodia
26
What does Cdc42 control
Filopodia
27
Describe Rac, RhoA and Cdc42
Rac and Cdc42 --> Positive regulators | RhoA --> negativee regulators
28
CA RhoA -->
Neutrite retraction
29
DN RhoA
Collapse is blocked
30
DN Cdc42
Blocks formation of both axons and dendrites
31
DN Rac
Affects only axonal not dendrite growth --> blocks assembly and prevents growth
32
DN Rac
Blocks assembly ==> growth prevented
33
CA Rac
Block disassembly leaving all of the filopodia stabilised and so growth will also be blocked
34
If the Rho GTPases were instructive
Would expect the cues to switch them on/off directly
35
If the Rho GTPases were permissive
Cues would act downstream and have no direct effect on Rho or Rac
36
Evidence suggests that the Rho GTPases are _________
Instructive
37
Since the evidence suggests RhoGTPases are instructive, where would factors that collapse growth cones act?
Activation of Rho and downregulation of Rac
38
How do cues affect the RhoGTPases
May bind and modulate RhoGTPases directly or bind to GEFs and GAPs which regulate the RhoGTPases
39
What does the semaphorin receptor Plexin B bind to
Rac
40
What is a plexin
Semaphorin receptors
41
What is the result of changing the relative levels of PlexinB, Rac and RhoA
Changes the senstivitiy of motor axons to the Semas
42
Increase plexin =
More sensitive
43
Decrease rac
More sensitive
44
Increase Rac
Less sensitive
45
Decrease RhoA
Less sensitive
46
What does the model of plexin, RhoA and Rac interaction suggest about what is needed for growth cone extension
For growth cone extension need lots of free Rac ... when sema binds plexin binds Rac sequestering tipping the balance of free RhoA and Rac so more free RhoA causing GC collapse
47
What is bigger Rho family or the GAPS and GEFs that regulate them
GEF/GAPs
48
Describe how ephrin signalling occurs
Occurs via ephexin a GEF regulating RhoA, Rac and Cdc42
49
What is the effect of ephexin on Cdc42 rac and RhoA
Turns OFF Rac and Cdc42 | Turns ON RhoA
50
Localised ___- flux is capable of turning growth cones
Ca2+
51
Describe the experiments used to show that a Ca flux can turn a growth cone
Ca liberated from a light sensitive cage (EGTA/EDTA chelator) by a laser pulse Can Ca flux by fluo-3-dye Leads to the turning of a growthcone
52
What is ryanodine
Chemical capable of binding IC Ca
53
Describe the role of ryanodine in growth cones
Ryanodine-induce release of Ca from IC stores can attract growth cones
54
What is the effect of ryanodine on the Rho family GTPases
Activation of Rac and Cdc42 | Supression of RhoA
55
Filament disassembly activated by
Cofillin
56
Branching initiated by _____________ in response to activation by ________________
Arp2/3 | Wave/Wasp complex proteins
57
Termination of branch extension by
Capping proteins
58
Filament assembly regulated by
Profillin and thymosin
59
What research suggests a potential role for microtubules
Detailed analysis of timing of MT capture shows that the MT invade first before the cessation actin retrograde flow
60
What is the purpose of MT invasion
MT may bring important signal transduction elements/factors required for membrane protrusion into the area of contact with the cue
61
Example of the MT invasion being benificial
Some RhoGEFs known to associate with MT plus end tracking proteins (+TIPS_
62
What other 'goodies' may help promoted cytoskeletal restrucuturing
Importation of monomeric actin Collapsin response mediator protein (CRMP) WAVE proteins into the filopodia
63
What are the two critical elements of guidance factor singalling
Ca | Rac/Rho balance
64
Rac signalling is the most important in ______________
Polarity establishment
65
Sema3A affects polarity via
cGMP

BMS381 Developmental Neurobiology (16 decks)

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