Wiring Eye to Brain

Question 1

3 main functions of growth cones

Answer 1

guidance
extension of neurite
form pre-synaptic element

Question 2

RGC and netrin

Answer 2

attracted and later repelled

Question 3

2 ways to study guidance mechanisms

Answer 3

expression analyses

culture approaches

Question 4

expression analyses

Answer 4

receptors expressed by neurons

ligands along path - present at right time?

Question 5

culture approaches

Answer 5

axon respond to signalling molecule? changes in rate and direction of growth

Question 6

why is optic projection ideal model for studying guidance mechanisms?

Answer 6

formed by axons of single neuronal type - RGC
accessible
navigated via intermediate targets

Question 7

3 important signalling molecules

Answer 7

robos/slits, ephs/ephrins and neuropilins/sema/vegf

Question 8

robos

Answer 8

receptors

1-4

Question 9

slits

Answer 9

ECM molecules
usually inhibit axon outgrowth
slit 1-3
little receptor specificty

Question 10

Ephs

Answer 10

receptor
tyrosine kinases
ephA bind ephrin A and EphB binds Ephrin B

Question 11

ephrins

Answer 11

cell surface associated molecules - inhibitory

Question 12

ephrins - reverse signalling

Answer 12

ephrins can be receptors and ephs as ligands

Question 13

neuropilin + flk1/flt1 co-receptors

Answer 13

VEGF

Question 14

neuropilin + plexins co-receptors

Answer 14

class 3 semaphorins

Question 15

growth into OFL

Answer 15

cells divide, cell bodies of RGC migrate up to RGC layer and extend into OFL

Question 16

attraction and repulsion - growth into OFL

Answer 16

attraction of OFL ECM

repulsion from outer retina

Question 17

Molecules help to repulse RGC from OFL

Answer 17

slit/robo

Question 18

Where are slits expressed and what to RGC express?

Answer 18

slit 1 and 2 in inner retina

RGC express robo 2

Question 19

mice lacking slit 1/2 - Where do RGC grow?

Answer 19

outer retina - not all but a subset of axons make mistakes - other important molecules

Question 20

growth to optic dis - robo/slit

Answer 20

KO slit 1/2 = axons grow disorganised
some grow peripherally then to optic disc
initial polarity lost

Question 21

What attracts neurons centrally to optic disc?

Answer 21

shh

Question 22

shh expression pattern in retina

Answer 22

low peripheral and high retina

Question 23

what is required for growth out of eye?

Answer 23

netrin/DD signal

Question 24

where is netrin expressed in optic disc?

Answer 24

by glia

Question 25

What axons express DCC

Answer 25

retinal axons

Question 26

no netrin

Answer 26

axons fail to exit eye | small optic nerves

Question 27

binocular disparity

Answer 27

image projected on each eye slightly differently

Question 28

what is size of ipsilateral projection related to?

Answer 28

degree of binocular overlap in visual field

Question 29

binocular overlap human vs mice

Answer 29

human 55:45 | mouse 97:3

Question 30

where do ipsilateral axons always arise from?

Answer 30

temporal retina

Question 31

albinism and guidance at optic chiasm

Answer 31

50% fewer ipsilateral axons | lack of melanin in RPE

Question 32

non-decussating retinal fugal fibre syndrome

Answer 32

no chiasm, very rare

Question 33

robos/slit path defining

Answer 33

expressed around RGC and absent from regions where they grow barrier function

Question 34

no slit 1,2 - optic chiasm

Answer 34

cross in wrong place, grow into other nerve, wander away from path

Question 35

what helps axons project contralaterally at chiasm?

Answer 35

NRP1-VEGFA

Question 36

marker of contralaterally projecting neurons?

Answer 36

NRP1

Question 37

mice lacking NRP1 - crossing at midline

Answer 37

many axons fail to cross the midline

Question 38

3 VEGF isoforms

Answer 38

VEGF 188, 164 and 120

Question 39

differences between VEGFA isoforms

Answer 39

exon 6 and 7

Question 40

importance of exon 6 and 7 in vegf a

Answer 40

influence neuropilin binding

Question 41

isoform VEGFa receptors

Answer 41

flt1,flk1 and NRP1/2

Question 42

what vegfa isoform has exon 6 and 7

Answer 42

188

Question 43

cant KO VEGFA in animal models - what is done?

Answer 43

use VEGF120 as no exon 7 for NRP1

Question 44

main NRP1 ligand in nervous system

Answer 44

sema3

Question 45

is sema3 required for axon crossing at chiasm?

Answer 45

no

Question 46

Mice lacking VEGFA/NRP1 - chiasm

Answer 46

many RGC axons fail to project contralaterally

Question 47

does VEGFA attract or repel growth cones?

Answer 47

attract

Question 48

Effect of KO NRP1 in RGC and epithelial cells

Answer 48

RGC - axons go ipsilaterally | no effect on epithelial cells

Question 49

What stops ipsilateral crossing?

Answer 49

lack NRP1 | ephrins/ephs

Question 50

xenopus - stage specific ephrin B at midline

Answer 50

lateral - eyes completely crossed projection, no ephrin B binocular vision - ephrin B at midline ephB in tadpole - precocious ipsilateral projection

Question 51

Is ephrin B necessary for ipsilateral growth?

Answer 51

yes - EphBs expressed by ipsis no ephb1 = fewer ipsis ephB2 expressed at chiasm no ephB2 = fewer ipsis

Question 52

what specifies ipsilateral RGCs?

Answer 52

zic2

Question 53

zic2 in fish/humans

Answer 53

none in fish - crossed | binocular species - zic2 in region that gives rise to ipsis

Question 54

in utero electroporation

Answer 54

tease embryo out of uterus inject DNA use small electric current to drive DNA into tissue of interest

Question 55

what happens when zic 2 electroporated?

Answer 55

drive cells ipsilaterally in optic chiasm

Question 56

what does zic2 do to ephb1?

Answer 56

induces expression

Question 57

which is expressed first - zic2 or ephb?

Answer 57

ephb

Question 58

electroporate zic2 into central retina in ephb1 KO mice

Answer 58

size of ectopic ipsilateral tract decreased substantially