Axon Guidance 3 Flashcards
main target for RGC
mammals - LGN
tectum
what happens to xenopus eyes during metamorphosis
eyes positioned on head change
retinotectal projections in animals with non-overlapping visual fields
completely cross chiasm
overlapping vision results in what?
ipsilateral tract
first intermediate target?
ONH
first to differentiate from neuroepithelial pool
RGC
CSPG following RGC differentiation
differentiate just dorsal to ONH
CSPG regress from this point
nudge towards ONH
RGC permissive growth - neuroepithelial cell
NCAM and laminin
regression of CSPG
RGC cell adhesion molecules - examples and what they do
N-cadherin, NCAM, neurlin, DCC
interact with CAMS in other axons and glial endfeet - tramlining
what happens to axons if CAMS perturbated?
defasciculate
3 other factors which might drive RGC to ONH?
shh
slits
ephbs
what guides RGC out of eye?
netrins
where is netrin expressed in ONH?
retinal surface and throughout its depth
axons express netrin receptor needed for growth cone attraction
netrin deficient mice
axon mis-routing within RPE
optic nerve thinner
what does RGC attracted to netrin depend on?
cAMP
in the presence of what are growth cones repelled by netrin?
laminin
prevent cAMP stimulation
addition of laminin to eye - pathfinding
aberrant through the ONH
slit function at chiasm
expression suggest role in confining axon growth within appropriate pathway
2 types of cells at optic chiasm
radial glial cells
CD44 neurons
radial glial cell at chiasm
span the diencephalon throughout the chiasm
CD44 neurons
v shaped wedge express L1 and CD44 to promote or inhibit axon growth
CD44 neuron and first retinal axon
delimited trajectory
what happens if CD44 neurons ablated?
perturbs normal retinal axonal growth
what do the radial glial cells at midline express?
ephrins
difference between ephrin A and B
a = secreted b = membrane bound
what does early expression of ephrin B do to ipsilateral tract formation?
precocious formation
before metamorphosis ipsilateral tract forms
optic tract - retinal axons
first axons = deepest
later axons = more superficial
what happens if piece of neuroepitheium in optic tract rotated?
just prior to first axon growth, axon turns 90 degees too
Laminin in basement membrane at pial surface
retinal axons grow here - permissive role
tenascin - optic tract
one isoform in depper layers
confining axons to superficial pathway
possible role for tenascin-R at chiasm
help confine axons
what signalling is required for correct targeting to tectum?
FGF
block FGF - tectim
axons fail to grow into the tectum
axons bypass tectum or branch to avoid it
what also induces abnormal pathfinding at border with tectum?
disturbing formation of heparan sulphate (ECM)
main class of molecules for A?P difference in axon growth inhibition
ephrins
nasal/temporal retina and anterior/posterior tectum
nasal - posterior, less ephA
temporal - anterior
netrin - tectum
expressed in posterior tectum
repel axons
sema 3A - tectum
posterior tectum
retinal axons sensitive to sema3A as grow through optic tract
what ephrin in d/v mapping of retina?
Ephrin B
