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Axon guidance
n/a
37
Biology
Undergraduate 4
11/10/2013

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Term
guides axons
Definition
previously formed axon bundles, cues in the *local* environment (e.g. direction/polarity)[image]
Term
What happens if an axon with a growth cone is cut?
Definition
It's autonomous: it still finds its way to its location
Term
cytochalasin B
Definition
blocks growth cone motility; axons lose their way
Term
interaction of long range and short range signals
Definition
Term
flow of information from environment to growth cone behavior
Definition
[image]
Term
drosophila: fasciclin II
Definition
specific adhesion molecule marking previously formed axonal fascicles[image]
Term
specific pathways of axon migration marked by ___
Definition
adhesion molecules
Term
adhesion molecues are released by ___ and regulate ___
Definition
axons; sorting of axons to specific targets
Term
laminin
Definition
adhesive molecule with grid pattern, appropriate growth cones travel along grid lines
Term
trigeminal sensory axon trowth
Definition
axons go straight to maxillary (whisker) pad due to attack from pad's attractive molecules
Term
NGF
Definition
attracts DRG growth cones
Term
netrin
Definition
attracts retinal axonal growth cones
Term
when growth cones are placed near unrelated tissue
Definition
unrelated tissue releases repellant molecules to deter the growth cone
Term
semaphorin 3A
Definition
repellant in areas peripheral axons avoid, keep from developing too many extraneous processes
Term
ephrin-A2
Definition
repellant of retinal growth cone
Term
Sema3A
Definition
expressed by limb tissues, keeps axons laterally on track through the limb[image]
Term

LMCl

LMCm

MMC

Definition

motor neurons of:

  • dorsal limb muscle
  • ventral limb muscle
  • axial muscle
Term
motor axon guidance to ventral vs. dorsal limb
Definition

motor neurons express EphA/B receptors

limb mesenchyme expresses ephrinA/B ligand[image]

Term

netrin - floor plate

DCC

Definition

attracts and repels to guide target innervation, derived from muscle

netrin receptor

[image]

Term
netrin, slit
Definition

fly midline cells' attractant and repellant

netrin guides axons to floor plate

Term
robo
Definition
receptor for slit, a repellant in the midline
Term

robo expression

comm

 

Definition

in growth cones that never cross the midline, or in growth cones that did cross but only after they crossed

comm blocks robo until after crossing midline

[image]

Term
vertebrate robo/slit functioning (no comm)
Definition
[image]
Term
wnt4
Definition
guides axons that have crossed midline to proceed towards the brain (turn)
Term
microtubule directionality
Definition

normally straight

filopodia etc extend in all directions

when they find an attractive site, microtubules quickly turn towards it

Term
guidance cue steps to regulate growth cone behavior
Definition
[image]
Term
F-actin bundle adhesion
Definition

ABPs

[image]

Term
growth cone adhesion molecules on substrate
Definition

cadherins

CAMs

integrins

Term
catenin
Definition
cadherin-actin linkage helper
Term
clutch hypothesis of growth cone migration
Definition
  • leading edge: F-actin pushes out filopodia/lamellipodia
  • myosin II pulls actin back; disassembled
  • IF adhesion is made THEN clutch engaged --> links actin to adhesion site
  • THEN motor proteins bring MTs, membrane, etc to facilitate extending protrusion
Term
actin organization factors
Definition
  • localization
  • relative concentration
  • activity levels of actin regulatory proteins
Term
Rac/RhoA activation in growth cone
Definition
induce polymerization of actin (axon growth)/growth cone collapse (axon retraction)
Term
how to switch netrin attraction to repulsion
Definition
block cAMP effector PKA (inhibit PKA)
Term
how to switch semaphorin 3A repulsion to attraction
Definition
enhance cGMP signaling
Term
cytoplasmic [Ca++]
Definition
  • growth cone regulatory factor
  • cytoplasm protein switched on and off
  • can induce growth cone turning
  • regulates endo/exocytosis, which also plays a part in growth cone turning
Term
mRNA in growth cone
Definition
nucleus sends bound mRNA to growth cone, which has proteins that isolate and translate it
Term
CNS midline signals
Definition
can induce translation of local mRNA inthe growth cone that wasn't being translated before, inserts EphA receptors for ephrin ligands[image]
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