Axon Guidance Flashcards
VEGF signalling in the visual system: Blood vessels & nerves (23 cards)
What are the 3 roles for VEGF in CNS
1.Promotes and maintains blood vessel growth
2. Can affect neural actiivty indirectly because of role in BV growth
3. VEGF-A can affect neural cells directly by signalling to neuronal VEGF-A receptors
Define axon guidance
Process of growth cone of neruons extends and retracts to migrate through CNS to correct target
Define chemo-attractant & give example
A chemoattractant is a chemical substance that induces movement in cells, towards the direction of its highest concentration- This process is known as chemotaxis.
Example VEGF is a chemoattractant
Describe the structure of VEGF
Secreated glycoprotein, anti-paralell homodimer
It has 8 cysteine residues -2 link to other monomer, 6 form a cysteine knot
What was difficult about studying VEGF role in axon guidance
Hetrozygote model was lethal if embryo lacked a single VEGFa allele
How do the splice variants of VEGF differ?
Different extracellular matrix affinity
Which VEGF isoform does not bind to the ECM?
120
Which 3 isoforms were used in study
164, 188, 120
How do you achieve BV branching
chemoattractive VEGF gradient
Why is the embryo hindbrain model used to study BV growth in CNS?
-simple multicellular environment, with fewer interacting cell types compared to more complex brain region
-hindbrain’s flat so readily visualizable architecture makes it ideal for observing vessel growth near the ventricular surface and neural progenitor proliferation in the ventricular zone.
What is the issue with VEGF KO mice models:
Vegf KO mice are heterozygous lethal- one copy loss of VEGF kills mice
Abnormal blood vessel development and lethality in embryos lacking a single Vegfa allele.
Heterozygous embryonic lethality induced by targeted inactivation of the Vegfa gene.
Phenotype: no endothelial cells > no blood vessels!*
how did they create mouse mutant that survives?
They knock out isoforms 188 & 164 because mouse does not need it to survive, so now you have a mouse that expresses a VEGF isoform 120.
-lack VEGF164 and VEGF188. Abnormal blood vessels, but viable to birth. We can use this mutant to study VEGF.
Why is the VEGF gradient important for BV growth?
Oxygen starved cells release VEGF and this gets the TIP endothelial cells to grow towards it and allow the VEGF receptors to contact the VEGF.
Tip ECs migrate towards growth-inducing cues, e.g., VEGF-A- high con near the oxygen starved cells
What part of endothelial cells do not require the VEGF gradient
Stalk ECs- these proliferate to form the lumen of BV
Why do BVs grow upwards toward nerual progenitors?- what study explored this
CreLoxP to delete VEGF-A from Neural progenitor cells.
Results- neural progenitors secrete VEGF-A to attract BV upwards
Conclusion: NPCs release VEGF-A to create BV
What is the marker for BV sprouting (angiogenesis)
PECAM-1
NPR1 is importtant for formation of…
Subventricular plexus
What does IB4 stain for
Marks neurons growing near vasaculture
What do number of somites tell you
time course
Why do they need a better animal model?
Cannot study long term after manipualting BV or NPC since mice dies
Results in NRP1-null mutants without subventricular BV
Normal lateral brain growth
Reduced brain growth
What do Mutant NRP1 models reveal about role
Role for NRP1 in blood vessel regulation of NPC behaviour
