Axon guidance Flashcards
what prevents growth cone collapse?
ligands for receptors on the regrowth cone
ere can axon guidance cues be found?
- on the ECM or diffuse from the target
what are the 4 families of axon cues?
- slits and their receptors
- ephrins and EPH receptors
- semaphorins (neuropilin and plexin)
- VEGF-A and its receptor
what do ROBO receptors bind to?
SLIT ligands
what so SLIT ligands bind to?
the robo receptors
what do EPH receptors bind to?
ephrins
what do ephrins bind to?
EPH receptors
what do semaphorins bind to?
neuropilin and an A-type plexi
what so neurpilin and A-type plexus bind to?
Semaphorins
what does the fact that both the EPH and the ephrins have intracellular domain mean?
there can be bidirectional signalling
what is so special about SEMA3E?
it can bind the A type plexin (plexinD1) without the neuropillin
what does the fact there are many combinations of the 3 semaphoring and 4 neuroplexins and 2 neuropillins mean?
many combinations can result for- when you have limited genes you can have lots of outcomes
what can neurpillin bind that isn’t semaphorin?
- VEGF164
when these bind what do they normally activate?
the PI3K pathways because this is involved in cytoskeletal
what is an in vivo approach to axon guidance studies?
- in situ hybridisation to monitor the expression of the candidate gene
- antibody labelling to visualise axons relative to their axon guidance cue
- axon tracing by lipophilic dye diffusion in axonal membranes
what is an ex vivo approach to looking at axon guidance cues?
- explant assays of neural tissues
- neurons differentiated from proliferative progenitor cell lines
what is an example of an ex vivo approach?
explant spinal cord tissue and explant a source of signal and see if the axons will grow towards it
what is a growth cone turning assay?
you can putt he axons in culture and then puff your guidance into the culture medium and then look at the turning towards the pipette and then can add an antibody and see if you get the same result or not
what is the dye used to retrogradely label the neurons?
DiI
what was an explant culture used to identify the correceptor of SEMA3A?
They placed sensory neurones from dorsal root ganglion and use COS cells that had been transfected with sema3a and you put them next to each other and if there nothing in the cells then there is no repulsion and the axons grow all the way around, but if you put SEMA3A in then the axons are repelled.
- then had a backer
- then they used DRGs from KO mice and they looked at different plexins KO
- they used a Plexina4 KO and there were partial repuslions
- then they sis plexina3 and there are some repulsion too but not completely
- but then they did a double KO and the axons were completley blind tot he SEMA3 so this showed that both of these are required int he cell for a repulsive affect
once they had done the explant culture and shown that plxn3A and plexin4A was needed in conjunction with neuropillin to bind semaphorin3A, how did they show that this was the case ex vivo?
they use embryonic KO mice and they strained for neurofilaments and they showed that normally the axons dont grow along the ridge of the arm but without plexin3A and the plexin4A there are axons growing on the ridge. They also looked at the neural tube and they found that normally there are no axons but there were in the double mutants
what are the two models that are used to look at the commissural axon guidance?
the drosophila and the mouse
how were the molecules involved in the formation of the commissural axons in the dorosphila nerve cord found, what were found and what were the phenotypes?
they did a screen and stained the commissary neurons and they found slit mutant which has no organisation of the axons and they were all bunched up like a slit (SLIT) and they also found the opposing phenotype where there were only commissural neurons going round and round in circles like a roundabout (ROBO)
what do the midline glial express at the commissures of the ventral nerve cord?
SLIT