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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
Q

What does Rac control

A

Lammelapodia

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26
Q

What does Cdc42 control

A

Filopodia

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27
Q

Describe Rac, RhoA and Cdc42

A

Rac and Cdc42 –> Positive regulators

RhoA –> negativee regulators

28
Q

CA RhoA –>

A

Neutrite retraction

29
Q

DN RhoA

A

Collapse is blocked

30
Q

DN Cdc42

A

Blocks formation of both axons and dendrites

31
Q

DN Rac

A

Affects only axonal not dendrite growth –> blocks assembly and prevents growth

32
Q

DN Rac

A

Blocks assembly ==> growth prevented

33
Q

CA Rac

A

Block disassembly leaving all of the filopodia stabilised and so growth will also be blocked

34
Q

If the Rho GTPases were instructive

A

Would expect the cues to switch them on/off directly

35
Q

If the Rho GTPases were permissive

A

Cues would act downstream and have no direct effect on Rho or Rac

36
Q

Evidence suggests that the Rho GTPases are _________

A

Instructive

37
Q

Since the evidence suggests RhoGTPases are instructive, where would factors that collapse growth cones act?

A

Activation of Rho and downregulation of Rac

38
Q

How do cues affect the RhoGTPases

A

May bind and modulate RhoGTPases directly or bind to GEFs and GAPs which regulate the RhoGTPases

39
Q

What does the semaphorin receptor Plexin B bind to

A

Rac

40
Q

What is a plexin

A

Semaphorin receptors

41
Q

What is the result of changing the relative levels of PlexinB, Rac and RhoA

A

Changes the senstivitiy of motor axons to the Semas

42
Q

Increase plexin =

A

More sensitive

43
Q

Decrease rac

A

More sensitive

44
Q

Increase Rac

A

Less sensitive

45
Q

Decrease RhoA

A

Less sensitive

46
Q

What does the model of plexin, RhoA and Rac interaction suggest about what is needed for growth cone extension

A

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
Q

What is bigger Rho family or the GAPS and GEFs that regulate them

A

GEF/GAPs

48
Q

Describe how ephrin signalling occurs

A

Occurs via ephexin a GEF regulating RhoA, Rac and Cdc42

49
Q

What is the effect of ephexin on Cdc42 rac and RhoA

A

Turns OFF Rac and Cdc42

Turns ON RhoA

50
Q

Localised ___- flux is capable of turning growth cones

A

Ca2+

51
Q

Describe the experiments used to show that a Ca flux can turn a growth cone

A

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
Q

What is ryanodine

A

Chemical capable of binding IC Ca

53
Q

Describe the role of ryanodine in growth cones

A

Ryanodine-induce release of Ca from IC stores can attract growth cones

54
Q

What is the effect of ryanodine on the Rho family GTPases

A

Activation of Rac and Cdc42

Supression of RhoA

55
Q

Filament disassembly activated by

A

Cofillin

56
Q

Branching initiated by _____________ in response to activation by ________________

A

Arp2/3

Wave/Wasp complex proteins

57
Q

Termination of branch extension by

A

Capping proteins

58
Q

Filament assembly regulated by

A

Profillin and thymosin

59
Q

What research suggests a potential role for microtubules

A

Detailed analysis of timing of MT capture shows that the MT invade first before the cessation actin retrograde flow

60
Q

What is the purpose of MT invasion

A

MT may bring important signal transduction elements/factors required for membrane protrusion into the area of contact with the cue

61
Q

Example of the MT invasion being benificial

A

Some RhoGEFs known to associate with MT plus end tracking proteins (+TIPS_

62
Q

What other ‘goodies’ may help promoted cytoskeletal restrucuturing

A

Importation of monomeric actin
Collapsin response mediator protein (CRMP)
WAVE proteins into the filopodia

63
Q

What are the two critical elements of guidance factor singalling

A

Ca

Rac/Rho balance

64
Q

Rac signalling is the most important in ______________

A

Polarity establishment

65
Q

Sema3A affects polarity via

A

cGMP

BMS381 Developmental Neurobiology (16 decks)

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