Development 2

Question 1

4 main stages of development

Answer 1

neural tube + crest formation
AND generation of neurones

neurone migration

projection of axons to targets

synapse formation + excess neurone death

Question 2

2 groups of molecule involved in axon guidance + synapse formation

Answer 2

adhesion molecules

guidance cues

Question 3

synapse formation

• when?
• what does this allow?
• what happens if a neurone doesn’t connect with target?

Answer 3

when axons reach their targets

neurone survival

apoptosis of neurone

Question 4

synapse formation

- in muscle cells

Answer 4

= neuromuscular junctions

even after junctions are made, some are eliminated until each muscle fibre is innervated by only 1 motor neurone

Question 5

selection of correct connections

Answer 5

apoptosis eliminates inappropriate connections

growth factors secreted by target cells keep the neurone alive
- excess neurones die

target cells also die
- could be neurones with target dependency competing for GFs

Question 6

topographic projections

- what is it?

Answer 6

within each target there’s faded innveration for finer control or to provide more info

Question 7

topographic projections

- examples

Answer 7

mapping of medial-lateral axis of neurones from spinal cord to single muscle across dorsal-ventral axis e.g. gluteal muscle

mapping of retinal axis across axis of target nucleus in brain (tectum in birds)
= allows speck use of vision

Question 8

switch in dependence

Answer 8

axons most reach target and form connection before neurones become dependent on target cells

Question 9

factors in pathway to target cells

Answer 9

secreted from glia or other cells in pathway :
adhesion molecules
guidance cues

Question 10

target switching in brain development

Answer 10

some neurones must innervate a secondary target before reaching primary target

so transitory dependence on a secondary target

• > innervation of primary target
• > pruning/complete loss of innervation of secondary target

Question 11

haptotaxis

- define

Answer 11

= directional outgrowth of cells due to adhesive gradients

Question 12

CAMs

cell adhesion molecules

Answer 12

expressed by growth cones
-> modulate adhesion to ECM + other cells

recognise same molecules (homodimers) or different types of AM

can be adhesive or prevent growth

Question 13

adhesive molecules

- examples

Answer 13

CAMs
= recognise basal lamina proteins

laminin
= direct axonal tracts
(even if only transiently)

glycosaminoglycans
= impeded neural outgrowths

Question 14

CAMs

- examples with location + role

Answer 14

Ig-Cam + NCAM
- around cell membrane + bind molecules in membranes of neighbouring cells

Integrins
- sit in cell membrane + bind molecules in ECM

Cadherins
- localised to specific junctions + bind proteins in similar junctions on neighbours

Question 15

cadherins

- features

Answer 15

links to actin cytoskeleton via catenins

Ca2+ dependent

transmembrane

homophilic

Question 16

Ig-CAMs
(immunoglobulin- CAMs)
- features

Answer 16

links to actin cytoskeleton

Ca2+ independent

IgG domains bind to similar domains on other cells

transmembrane or surface-bound

Question 17

integrins

- features

Answer 17

links to actin cytoskeleton

Ca2+ dependent

transmembrane

binds to glycoproteins in ECM

Question 18

axonal fasciculation

- define

Answer 18

growing axon adhering to another

forms axon bundle groups

example of contact attraction

Question 19

axonal fasciculation

- maintained by

Answer 19

cell adhesion keep axon groups together

Question 20

nerve branching

• define
• why does this occur?

Answer 20

axons divergence when following different guidance cues

molecules in environment that affect cell adhesion

• > NCAM polysialylation
• > regulates homophilic interactions

Question 21

which molecule group is involved in axon pathfinding?

Answer 21

guidance cues

Question 22

axonal growth cone

- mediation of movement

Answer 22

mediated by cytoskeleton lacttice containing actin + myosin

Question 23

axonal growth cone movement

- filopodia

Answer 23

made of actin + detects environment

polymerisation extends filopodia towards guidance molecule

de-polymerisation of actin when guidance cue repels

Question 24

axonal growth cone

- structure

Answer 24

lamellipodia + filopodia

has CAMs + receptors for guidance cues

Question 25

axonal growth cone movement

- neurite

Answer 25

neurite extends behind moving growth cone

-> microtubule backbone of neurone constructed from tubular molecules

Question 26

growth cones respond when they bind guidance cues

- features of guidance cues

Answer 26

contact-mediated and chemotropic

attractive or repulsive

act over short or long range

can differentially affect different neurones

Question 27

how does the growth cone move through tissues?

Answer 27

secretes proteases

-> break down ECM of cells

Question 28

GAP-43

Answer 28

allows us to identify growth cones

unknown function

Question 29

2 agents that inhibit normal growth cone activity

Answer 29

cytochalasin

• binds to monomeric actin
• > block it from polymerisation

phalloidin

• binds to polymeric actin
• > blocks actin breakdown

Question 30

using phalloidin + cytochalasin in an experiment

Answer 30

have 2 growth cones

apply potential guidance cue

apply phalloidin to one

if nothing happens
-> sign of repulsion

(cytochalasin -> sign of attraction)