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Developmental Neurobiology > Axon Guidance > Flashcards

Axon Guidance Flashcards

1
Q

what is the connectome

A

how nerve cells connect together

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2
Q

when does axon guidance occur

A

during development of the embryo and shortly after birth

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3
Q

why is identifying genes involved in nerve growth beneficial

A

aids nerve regrowth in spinal injury and nerve degeneration

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4
Q

limitations of axon guidance

A

-brain contains 10^11 neurons, each form single/multiple connections
-specificity of connections
-distance of connections
-lack of coding information (only 30-40,000 genes)

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5
Q

scale issues

A

axon distance is 250x cell body diameter

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6
Q

growth cone function

A

sensor and motor for growth

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7
Q

axons involved in initial outgrowth

A

pioneer axons - use a variety of cues to find their specific pathway

developing axons - use scaffold laid out by pioneers (follower axons) select pathways and join via selective fasciculations

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8
Q

guidepost cells/intermediate target cells

A

division of longer axon pathways into shorter trajectories

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9
Q

what occurs in guidepost cell ablation in grasshoppers

A

no directionality

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10
Q

what are cues provided by

A

substrate along they grow

secreted from targets

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11
Q

4 mechanisms to guide axonal outgrowth

A

contact mediated attraction
contact mediated repulsion/inhibition
chemoattraction
chemorepulsion

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12
Q

axon pathways at midline of SC

A

motor neurons (axons to periphery)
nerve cells (ipsilateral)
reach target then extend
commissure axons which turn

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13
Q

Unc-6 role and mutant

A

Grow towards and away from the midline
Dorsal and ventral axon projections impaired

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14
Q

Unc 5 role and mutants

A

Grow away from midline
Dorsal projections impaired

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15
Q

Unc40 role and mutant

A

Grow towards midline
Ventral projections impaired

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16
Q

Role of floor plate cells

A

Located at ventral SC
Attract commissural axons from distance of around 100um

17
Q

Which unc is netrin similar to in conservation

A

Unc6

18
Q

Netrin KO

A

Commissural axons fail to cross at the midline. Some still cross and orient towards midline

19
Q

Conservation of netrin receptors

A

DCC (vertebrates)
Unc-40 (C.elegans)
Frazzled (flies)

20
Q

What does unc5 bind to

A

Unc40 and netrin
Converts netrin signal to become a repellant

21
Q

What is the other attractant the floorplate produces

A

Shh

22
Q

what does the roofplate release

A

BMP7 (repellant)

23
Q

what is slit

A

repellant which prevents ipsilateral neurons moving towards the midline
ligand for roundabout
expressed in floorplate

24
Q

commissureless and roundabout mutants

A

commissureless mutant - no axons crossing midline
robo mutant - many axons cross and recross

25
Q

how many slit genes do mice have

A

3

26
Q

where is robo protein restricted to

A

longitudinal regions of commissural axons

all neurons have robo mRNA

27
Q

where is comm expressed

A

commissural region of commissural axons

negative regulator of robo

28
Q

robo and comm transport

A

robo and comm interact with DNedd4

move to endosome/proteasome

29
Q

what do robo vary in

A

cytoplasmic domain and function

30
Q

role of robo3/rig1

A

acts like commissureless to control midline crossing

31
Q

where do commissural axons extend after crossing the midline

A

anteriorly
via non diffusable cue

32
Q

what causes anterior extention

A

wnt4

33
Q

which molecule prevents posterior crossing

A

Shh

34
Q

Shh receptors

A

cyclopamine insensitive and no SMO receptor involved
alternative Shh receptor Hib used by commissural axons after crossing

35
Q

role of robo in flies

A

influences how far axons extend from midline

36
Q

role of robo in drosophila

A

robo 1 and 2 prevents axons crossing midline
axon tract positioning (fascicles)
overlapping expression patterns

37
Q

robo code

A

place axons a certain distance from midline where they choose which fascicle to join
re-use of fascicle marker

Developmental Neurobiology (19 decks)

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