12-Axon_growth_and_guidance

12-Axon_growth_and_guidance - Axon Growth & Guidance...

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The essential first step to build network connections
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Axon Growth in Vivo Increasing complexity of axon fibers in developing zebrafish brain just within 20 hrs period
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Axon Navigation Axon path finding is guided by local cues, which can be both attractive or repellant Unlike humans, most axons make long journeys for the first, and only, time without errors!!
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Axon Growth Follows Local Cues Anterior Posterior Rotate 180 o This hindbrain rotating experiment demonstrates that axon growth is guided by external cues, not intrinsic factors.
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Guidepost Cells For Axon Growth Grasshopper Guidepost cells (stepping stone cells) direct the Ti1 axon in developing leg to find a pathway leading to the brain. Ablating Cx1 guidepost cell, Ti1 axon loses direction, and retract back.
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Axon Growth Cone Is The Leading Engine Growing axons will move forward, make turns, avoid obstacles, and stop when reaching their target. These functions are mostly carried out by axon growth cones. Cutting off the growth cone from retinal ganglion cell body, the growth cone can still detect local cues and move toward its target, the optic tectum. This suggests that the genes in the cell body are not critical for retinal axon guidance. Xenopus
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Structure of Growth Cone Cell adhesion molecule and receptors Lamellipodia Actin tends to be in the edge or submembrane area of growth cones. Filopodia Filopodia have mostly actins, with little microtubules. Microtubule, consisted of tubulin, usually in the center of axon fibers.
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Growth Cone Movement Filopodium not only senses local cues, but also help growth cone advancement
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Actin in the Growth Cone Actin: green Filamentous actin: F-actin, polymerized actin from globular actin monomers Actin function is mainly carried out by F-actin Red: Ena/Vasp, anticapping agent, promoting actin elongation
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Growth Cone Shape Reaching target region, exploring environment, complex pattern of filopodia and lamellipodia. Ready to form synaptic connections. Moves very slowly. When in fascicles, not many filopodia. Moves fast. At choice point, extend filopodia and lamellipodia to detect environment
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actin on one side of a growth cone causes it to turn the other way. A. Local stabilization of microtubules on one side of a growth cone causes it to turn toward that side. A. Destabilization of microtubules on one side causes it to turn the other way. Actin and Microtubules
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12-Axon_growth_and_guidance - Axon Growth & Guidance...

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