Target selection

Question 1

target selection

Answer 1

1. de-fasciculation (turn towards target)
2. growthcone slows down, searches by branching, repellant edges (guard rails)
3. synaptogenesis
4. synapse refinement

Question 2

beat-1a mutant

Answer 2

motor axons fail to de-fasciculate
-continue on straight
-normally axon will bend to find target

Question 3

post-translational modifications of CAMs

Answer 3

polysialic acid addition (sugars) make CAMs less adhesive->promoting de-fasiculation

Question 4

concentration of FGF near growthcone

Answer 4

-high [FGF] promotes rapid cone growth
-low[FGF] when growth cone enters target zone, causing them to slow down->signal that growthcone is near target
-artificially add FGF near target: growth cone goes right past it

Question 5

containment barriers of repellants

Answer 5

DRG+collapsin KO: neurons migrate into inappropriate locations
-collapsin=repellant for DRG neurons

Question 6

functional molding

Answer 6

connections from retina to target are random initially, but then ‘higher centers’ in brain cause connections to rearrange so that ‘functionally appropriate’ connections are made

Question 7

draw frog optic nerve

Question 8

neuronal specificity theory

Answer 8

axon of each retinal ganglion cell is able to recognize its proper site in the tectum bc of some molecular recognition system

Question 9

topographic mapping and size disparity exps (relative matching)

Answer 9

remove 1/2 of retina
-tectum cells expand, form synapses where they have never been before

remove 1/2 of tectum
-tectum cells are compressed, form synapse w/ someone other than target

Question 10

draw gradients of ephrin