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Developmental Neurobiology 🧠 > Exam 2: Chapter 5 > Flashcards

Exam 2: Chapter 5 Flashcards

1
Q

Axon growth occurs from the

A

growth cone

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2
Q

How do axons find targets?

A

Mechanical and chemical cues

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3
Q

Growth cones use ___ to changes shape

A

mobilization of cytoskeletal proteins

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4
Q

Short distance

A

interneurons

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5
Q

Long distance

A

projection neurons

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6
Q

Challenges faced by early axons

A

find their own path

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7
Q

Challenges faced by late axons

A

traverse complex environment

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8
Q

Zebrafish: look at axons, what happens

A

16-36 hr, nothing to a lot, real quick and efficiently

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9
Q

Grasshopper Ti Cells

A

axons use guidepost cells. If you ablate the guidepost cells, they lose their way

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10
Q

Hibbards Mauthner neurons

A

rotated salamander hindbrain 180 degrees
Normal: cross midline and go caudal
Rotate Soma 180: go rostral, but then hit the barrier and go back (little loop)

Significance: External cues too, not just intrinsic program

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11
Q

What happens if you cut through a frog tectum as it develops, cutting axon from soma?

A

still grows for a while, but won’t get to target

Significance: growth cone sufficient for environment response

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12
Q

What is faster: early or late axons?

A

Late, they have a path to follow

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13
Q

Growth cone shape depends on

A

filopodia

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14
Q

Growth cone speed (optic tract –> Tectum)

A

Slows down when it gets to the target (slows for tectum)

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15
Q

Growth cone at target

A

flattens and collapses

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16
Q

Pioneer (leader) axons

A

active filopodia
few lamellipodia
elaborate growth cones

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17
Q

Follower axons

A

simple, bullet shaped, few filopodia

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18
Q

Growth cones are complex at

A

midline

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19
Q

What happens at growth cone midline crossing?

A

Leaders become followers

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20
Q

Time lapse imaging

A

Method using GFP gene: make own floursecent protein, shows axons en route tectum. Watch growth in tissue

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21
Q

How do growth cones elongate?

A

Material added distally, Ca2+ dependent.

At actin/microtubules at axon tips

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22
Q

Experiment: FRAP fluorescence with bleach

A

bleach is still as growth cone advances, suggest distal assembly. If it had moved, then it would be soma.

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23
Q

Experiment: beads on axons, actin in axons

A

Beads: some interstitial growth, they move apart a little

Actin: at tips, goes back into the axon

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24
Q

P-zone

A

periphery, actin

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25
Q

C-zone

A

Central zone, microtubues

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26
Q

___ tethers actin/microtubules to use for transport

A

myosin

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27
Q

Growth Cone Guidence needs ___ and ___ interaction

A

filopodia and microtubules

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28
Q

Cytochalasin

A

inhibits filopodia formation

actin depolymerizing agent

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29
Q

Cytochalasin Experiment

A

Control: axon to tectum
Cytochalasin treated: can’t find tectum

Significance: actin filaments critical for growth cone navigation

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30
Q

How does 1 filopodia move growth cone?

A

Tension

Myosin pulls actin cables: clutch release mechanism
disconnected tubulin pulled forward
actin added at + end, disassembled at - end.

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31
Q

Axon turns in direction of polymerization and stabilization, as experimentally shown with

A

taxol

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32
Q

Axon turns away from depolymerization as experimentally shown with

A

cytochalasin and nocodazole

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33
Q

1) Mechanical Guidance

A

Physical Aspects of environment

Follows grooves/physical terrain

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34
Q

Mechanical Guidance experiment

A

cut corpus C.

Can guide around aspar region blocking
Artificial sling can get to other side

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35
Q

2) Adhesive Guidance (CAMS)

A

Filopodia adherence

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36
Q

Adhesive stuff

A

L1, polylysine

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37
Q

Non Adhesive stuff

A

cadherin, laminin, plain glass, plastic

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38
Q

Shape of growth cone on adhesive stuff

A

flat, slow growth cone

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39
Q

Shape/speed of growth cone on less adhesive stuff

A

fluffy and fast

40
Q

Is adhesion enough? Sometimes. What is the systems

A

Less adhesion: fast
Adhesion: where you wanna go, it’s a balance

test for it by blasting air, see if it will detact

41
Q

Homologous

A

Cadherin/Some CAM

42
Q

Heterologous

A

Some CAM/Integrins

43
Q

CAM heterophilic example

A

TAG-1 in interneurons binds to NrCAM in glial floorplate

44
Q

CAMs

A

big protein, membrane bound, gives neurons preferences

45
Q

Cadherins

A

Ca2+ dependent, need exact match

46
Q

Integrins

A

Alpha/Beta subunits

connect to other stuff like ECM, Fibronectin, and Laminin

47
Q

Vertebrate CNS adhesive path vs. PNS

A

CNS: laminin (retinal axons like it)
PNS: fibronectin

48
Q

Chemotaxis

A

Molecules attract and repulse

49
Q

Examples of chemoattraction

A

Nerve growth factor (NGF)

50
Q

Example of Chemorepulsion

A

Semaphorin

51
Q

Drosophilia Fas2

A

bundles axons together.
Fas2 in CAM, sticks together

KO Fas2- wandering axons
increase Fas2- stick too long

Significance: on and off selectively

52
Q

LAMP- CAM in limbic system

A

needed for limbic connections, if LAMP antibodies in mouse brain, abnormal fiber projection.

Enhances neurite outgrowth
3x IgG domains

53
Q

Neural Cell Adhesion Molecules (NCAM)

A

Some internal domains

Extracellular modified by carb residues, reduce adhesion

54
Q

Nonsialyated with sialic acid

A

Very adhesive (less is more)

55
Q

Sialyated

A

not adhesive

56
Q

Sialic acids controls

A

defasiculation of certain nerve pathways

Polysailaic acid = less sticky CAM

57
Q

Experiment: Endo-N, what does it do?

A

Digests sialic acid to make things more sticky

58
Q

Labelled Pathway in the Grasshopper: What happens if P axons ablated?

A

G can’t follow P anteriorly.
Need P-axons before G crosses midline.

Axons have specific molecules on surface, lay down pathways which help other neurons find their way

59
Q

Sometimes need to change CAM on surface

A 
CNS: longitudinal tract (Fas2 homolog)
Horizontal commissure (Fas1)
Allows midline crossing

Looks like a ladder. CAM tells where to cross

60
Q

Chemorepulsion: what does the semaphoring family do

A

Repulse DRG neurons to allow targeting

DRG neurons want dorsal

Collapsin is a semaphoring, shown to repulse growth cone

Semaphorin in ventral to keep DRG away

61
Q

Experiment: DRG and dorsal and ventral tissue

A

DRG goes dorsal

62
Q

Experiment: Olfactory and Septum

A

Olfactory grows away from septum

63
Q

Experiment: DRG and notochord and dermomytune

A

DRG grows in between them

64
Q

Vertebrates: KO Semaphorin

A

overgrowth in projections from both motor and sensory nerves –> peripheral targets

65
Q

What determines if a molecule is attractive/repulsive?

A

2nd messengers

66
Q

Local Cue test:

1) remove tectum
2) rotate epithelium square

A

1) still grow towards it
2) correct once they exit the rotated piece

Significance: local cues matter

67
Q

Ligand/Receptor: Neterin (unc-6)

A

Receptors:
DCC (Unc-40 in C. Elegans)
Attractive

68
Q

L/R: Slit

A

Receptors:

Robo = repulsive

69
Q

L/R: Wnt

A

Receptor:
Frazzeled = attractive
Ryk = repulsive

70
Q

Wnt is pro-

A

Anterior

71
Q

Experiment: add cos cells with wnt in wrong place

A

grow posteriorly instead of anteriorly

72
Q

Experiment: Ko Frazzeled receptors

A

not A or P after crossing

73
Q

If it’s anterior commissural interneurons, what wnt receptors?

A

Frazzeled

74
Q

If it’s posterior descending neuron, what wnt receptor?

A

Ryk

75
Q

Netrin location

A

Netrin/Unc-6: midline

Netrin-1: floorplate

76
Q

Experiment: Unc-6 mutant

A

growth defect

77
Q

Experiment: Unc-40 mutant

A

Can’t orient

78
Q

Experiment: Netrin-1 KO

A

Dorsal commissural interneurons can’t get to ventral midline

79
Q

In vertebrates, DCC gets axons to ____-

A

Floorplate

80
Q

Slit is a ligand found in

A

ventral midline

81
Q

Olfactory bulb and motor neurons have ___ receptor

A

Robo, repulsive

82
Q

Experiment: fuse robo and frazzeled

A

attracted to slit, repelled by netrin

intra Fraz + Extra Robo
Intracellular domain = attraction driver

83
Q

Experiment:

1) Commissurless mutant
2) Roundabout mutant

A

1) no Comm to destroy Robo before crossing, so it never crosses
2) only crosses, nothing to stop robo from crossing

Slit at midline.

84
Q

Drosophila Axon midline crossing

A

DCC-netrin gets axon to across

Once netrin leaves, slit sensitive, barrier up

85
Q

Vertebrate midline crossing:

Types of Robos

A

Rig 1 = Robo 3 = Comm
Robo 3A = against Robo
Robo1/Robo 3B - repulsive, regular Robo

86
Q

Vertebrate midline crossing: Before crossing

A

Robo 3A is high , so inhibits Robo1

Meanwhile, Netrin –> DCC, so attraction

87
Q

Vertebrate midline crossing: After crossing

A

Robo 3B is high

Slit binds to Robo 1, which inhibits DCC and causes repulsion

88
Q

If its in a vertebrate, and never meant to cross

A

no Robo3A

89
Q

KO misexpress Robo in vertebrates

A

Shifts intermediate to medial and vis versa

90
Q

Drosophila Experiment:

1) normal motor neuron (AVM) with Unc-40
2) Unc-40 and Unc-5
3) Unc-6 Mutant with any Unc-40/5 combo

A

1) Goes ventral
2) Goes dorsal
3) no preference

Why? unc-5 hates netrin even though unc-40 loves it.

Also: downstream signaling (cAMP levels)
Netrin + DCC = more cAMP, actin polymerizaition, attraction

Low cAMP = depolymerization, now repulsive

91
Q

Retina –> Tectum Pathway

A

1) Laminin: force axon in certain direction, low cAMP so repulsive, causes turn for netrin
2) Slit/Shh repulsive, but leaves chaism as pathway for dorsal/nasal axon to cross. Slit is guiding RGC.
3) Ephrin-B attracts to midline
4) Sema3A- repulses to tectum
5) decrease in FGF to show destination reached
6) Gradient of eph/ephrin/wnt = where to plug in

92
Q

Axons vs. Dendrites: Semaphorin

A

Axon- repelled (white matter)
Apical Dendrite: attracted

+cGMP = Sema attractive now

93
Q

If you cut axon process on developing neuron

A

another minor process will replace if done early enough

94
Q

Axon proteins

A

viral HA, HaemR1-distal, GAP43, Tau

95
Q

Dendrite Proteins

A

GluR1, HA with GLuR1 C-terminal Tag, HaemR1 and HaemR1-proximal, MAP2

Developmental Neurobiology 🧠 (11 decks)

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