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BISC 407 > Chapter 54 - Axon Growth and Guidance > Flashcards

Chapter 54 - Axon Growth and Guidance Flashcards

1
Q

when do differences in axons vs. dendrites emerge?

A

-early in development

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2
Q

what is a growth cone? (2 functions)

A
  1. sensory transducer

2. molecular motor

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3
Q

what does differentiation of axons and dendrites establish?

A

-neuronal polarity

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4
Q

how is neuronal polarity established?

A

-differentiation of axons and dendrites

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5
Q

what is stage one of axon/dendrite differentiation?

A

-lamellipodia formation

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6
Q

what is stage 2 of axon/dendrite differentiation?

A

-neurite formation

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7
Q

what happens after neurite formation?

A

one neurite becomes an axon

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8
Q

what happens to the other neurites that do not become an axon?

A

-they become dendrites

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9
Q

what happens if an axon is removed in vitro?

A

an existing dendrite is converted into an axon

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10
Q

what does the promotion of axon suppress?

A

axon formation in neighboring dendrites

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11
Q

what seems to promote axon specification?

A

-destabilization of actin filaments

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12
Q

what is required for neuronal polarization?

A

SAD kinases

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13
Q

what is a SAD kinase?

A
  • par family gene

- involved in polarity

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14
Q

what factors determine whether a process becomes an axon or dendrite in vivo?

A

-extracellular factors

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15
Q

what is a common ECM protein?

A

-laminin

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16
Q

what happens to neurons grown on laminin?

A

-acquire polarity

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17
Q

do axons like laminin? does the cell body + dendrites?

A
  • yes, the axon stays on the entire line and never leaves

- cell body + dendrites don’t show preference to be on the laminin

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18
Q

what do semporaphins do?

A

-provide axon guidance and tell dendrites where to go

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19
Q

what do semphorins attract?

A

-growing dendrites

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20
Q

what is Sema 3a?

A
  • secreted by cells near the surface

- attracts growing dendrites

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21
Q

what happens in a Sema 3a mutant mouse?

A

neuronal polarity is disrupted

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22
Q

what are the 5 stages of dendritic branching?

A
  1. initiation
  2. outgrowth
  3. branching
  4. spine formation
  5. stopping/pruning
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23
Q

what happens to the morphologies of neurons in a dissociated cell culture? what does this mean?

A
  • the morphologies are preserved

- neurons must have intrinsic information about their shape

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24
Q

what does the pyramidal cell in the brain vs. in culture reveal?

A

-suggests intrinsic transcription factor programs play key role in determining dendritic arborization + complexity

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25
Q

how are dendrites patterned?

A

-by intrinsic and extrinsic factors

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26
Q

what is dendritic tiling in Drosophila?

A

-dendrites of neighboring neurons provide cues to ensure non-overlap + coverage of a particular field

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27
Q

what is the normal expression of neurons in a drosophila dscam?

A
  • normally, dendrites of two different neurons express distinct dscam splice variants
  • allowing them to cross + cover overlapping receptive fields
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28
Q

what happens when both neurons are forced to express the same dscam isoform?

A
  • they avoid each other

- fail to cover total field

29
Q

what controls tiling?

A
  • self-recognition of dendritic branches by others of same cells
  • drives repulsion
30
Q

what are 3 main domains in a growth cone?

A
  1. filopodia (sense chemical signals)
  2. lamellipodia (membrane movement)
  3. central core (rich in organelles/mitochondria)
31
Q

where is actin concentrated?

A

-in filopodia/lamellipodia

32
Q

where are tubulin/microtubules concentrated?

A

-in central core

33
Q

what are filopodia/lamellipodia made of?

A

-actin

34
Q

what is the central core made of?

A

-tubulin/microtubules

35
Q

where does the growth cone receive directional cues from?

A

the environment

36
Q

what drives elongation?

A

the growth cone

37
Q

how is the growth cone directional?

A

-integrates positive/negative signals that regulate the cytoskeleton to guide pathfinding

38
Q

how are growth cones extended?

A
  • adhesion drives actin filament nucleation

- membrane exocytosis -> drives movement

39
Q

what are the 4 steps to growth cone extension?

A
  1. filopodium contacts an adhesive cue -> pulls growth cone forward
  2. actin filaments assemble at leading edge, disassemble at trailing edge
  3. actin polymerization -> filopodium forward
  4. force generated by retrograde flow -> filopdium forward
40
Q

where do actin filaments assemble? where do they disassemble?

A
  • assemble at leading edge of filopodia

- disassemble at trailing edge of filopodia

41
Q

what do actin filaments interact with along the way?

A

-myosin

42
Q

actin provides ____ while microtubules provide ____

A

actin -> direction

microtubules -> force

43
Q

what is actin depleted space filled by?

A

-advance of microtubules from the central core

44
Q

what is the actin depleted space filled with?

A

-filled by the advance of microtubules from central core

45
Q

how does the growth cone advance?

A

-under control of cellular motors

46
Q

what must happen for the creation of a new segment of the axonal shaft?

A
  • individual microtubules condense -> form thick bundle

- cytoplasm collapses

47
Q

what pushes filopodium forward?

A

actin polymerization

48
Q

what guide axons to their targets?

A

-molecular cues

49
Q

how is adhesion converted into directional cues in the growth cone?

A

-changes in level of intracellular reg. proteins determine whether same extrinsic cue attracts or repels the growth cone

50
Q

what happens when PKA activity and intracellular cAMP levels are low?

A

-growth cone is repelled by Netrin

51
Q

what happens when PKA is high?

A

-increased cAMP -> growth cones attracted to local Netrin sources

52
Q

do chemical or mechanical cues guide axons to targets?

A

-chemical cues guide axons to target

53
Q

what experiment demonstrated chemical cues?

A

-you can cut axons and they will grow back in frogs

54
Q

what is the organization of the frog visual system?

A
  • lens projects inverted visual image onto retina

- optic nerve transfers image with more inversion to optic tectum

55
Q

in a frog, where do anterior and posterior neurons project?

A

anterior -> posterior tectum

posterior -> anterior tectum

56
Q

what happened in the frog experiment?

A
  • retinal axons were cut

- eye inverted 180 degrees

57
Q

what was the result of the frog experiment?

A

-visual information + wiring the same
-behavior is opposite
(molecular not activity defined)

58
Q

what are 6 major types of extracellular cues that guide growth cones?

A
  1. extracellular matrix adhesion
  2. adhesion to other neurons
  3. adhere to other “pioneer” axons
  4. soluble chemical signals induce attraction
  5. cell surface repellent cues
  6. soluble chemical cues -> repulsion
59
Q

how do various molecular families control growth + guidance of developing axons?

A
  • extracellular domains that interact with ligands

- modulate cytoskeleton to promote assembly or disassembly

60
Q

what are examples of diverse molecular families that control growth/guidance of axons?

A

-immunoglobins, ephrins, laminins, semphorins

61
Q

what are commissural neuron?

A
  • convey sensory info from spinal cord to brain

- at ventral midline of the spinal cord across the floor plate

62
Q

what happens to commisural neurons after crossing?

A

-axons turn abruptly toward the brain

63
Q

_____ direct developing commissural axons to cross the midline

A

netrins

64
Q

what do netrins do?

A

mediate chemo-attraction or repulsion

65
Q

where do netrins attract spinal commissural axons?

A

to the floor plate

66
Q

how has the expression/activity of netrins been conserved through evolution?

A

-netrin is secreted by ventral midline cells in worms, flies etc.

67
Q

what do netrins interact with?

A

-netrins interact with receptors on cells/axons that migrate or extend along the dorsoventral axis

68
Q

what factors pattern the midline?

A

-chemo-attractant and chemo-repellent factors

BISC 407 (3 decks)

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