L12

Question 1

Steps of neuronal circuit generation?

Answer 1

Neurogenesis and migration (neural crest cells migrate out, muscle progenitors migrate to skeletal mesenchhyme) -> axon growth (axons migrate towards target using growth cone) -> functional NS

Question 2

Evidence for growth cones being site of axonal elongation?

Answer 2

If axon severed, end with growth cone still migrates towards target

Question 3

Evidence for axonal wiring being target based?

Answer 3

Neurons in each retina send axons to contralateral tectum
(In frog)- if optic nerve severed and eye rotated 180 degrees, old connections reestablished-> spatiovisual coordination 180 degrees out

Question 4

EphA3 gradients in retina…

Answer 4

Attract posterior-nasal connection, repel anterior-temporal connection (EphrinA2/5 in tectum)
Chemoaffinity hypothesis: (Roger Sperry) neurons make connections with their targets based on specific molecular markers

Question 5

Growth cones have lots of MTs and actin, display surface receptors….

Answer 5

Cytoskeleton mediates morphogenetic changes induced by signals; F-actin affects GC directionality (back flow), open up space for and mediate signalling to MTs; MTs- locally stabilised splayed MTs guide extension of axonal MT bundles

Question 6

GC turning

Answer 6

F-actin needed: Cytochalasin B (F-actin destabiliser) causes DRG GCs growing on permissive fibronectin to fail to turn at border with the repellant CPSG-> MTs can’t splay
Thus actin opens up navigational space for MTs and attracts/stabilises them in direction of advance

Question 7

MT stabilising

Answer 7

Nocodazol- inhibits, taxol- promotes, cyto D inhibits actin polymerisation
Combination of taxol and cyto D shows directional stability induces GC turning (only turns in taxol ONLY medium)

Question 8

Spatiotemporal patterns of pathfinding molecules:

Answer 8

Learn the MF table

Question 9

Slit-Robo signalling…

Answer 9

Guides motor neurons away from floor plate: Slit on floor plate repels Robo2+ve MNs but not commissural Ns; Slit repels motor axonal growth away from ventral horn explants in culture

Question 10

Sem3A in the limb bud…

Answer 10

Sem3A expression in the middle of the limb bud repels GCs, separating them into a ventral and dorsal pattern; MN GCs (the migrating neural crest cells) collapse on Sem3A exposure

Question 11

MN TF codes..

Answer 11

… translate into a an Eph/ephrin dorsovenral path finding code

Question 12

RhoGTPases…

Answer 12

Are shared signalling effectors and orchestrators of actin dynamics; activated by GEFs, inhibited by GAPs

Question 13

GC guidance…

Answer 13

…distinct signalling pathways converge on housekeeping machinery of cytoskeleton; ABPs are key effectors of Rho-GTPase downstream of signalling events; MTPBs can also be targeted

Question 14

apCAM signalling in Aplysia…

Answer 14

…induces GC steering (actin back flow translates to surface, arrests upon surface interaction)

Question 15

Src signalling in Aplysia…

Answer 15

…inhibits GC turning if inhibited (Src signals downstream of apCAM); Src promotes advance on a clutch principle (series of adhesion complexes)

Question 16

N-Cad in rat hippocampal neurons…

Answer 16

…similar to Src: coupling-> slipping -> stiffening -> extension

Question 17

Signal-2…

Answer 17

…adhesion factor cross-talk; inhibits myelin in axon region (myelin inhibitors- IN-1 antigen, NogoA/reticulum4, MAG, OMgp); MAG repels axons; Myelin dependant repellants work through inter gin internalisation; MAG requires asymmetric down regulation of integrity but not N-Cad to repel GCs; MAG triggers Pi3K induced Ca2+ upregulation leading to clattering induced endocytosis of integrins