Axonal Transport, Polarity, and Local Translation
Spatial organization in large neurons
Why transport matters
Because neurons can extend over long distances, they depend on microtubule-based transport to deliver vesicles, organelles, RNA, and proteins to precise subcellular domains. Kinesins and dyneins move cargo with adaptor proteins that regulate direction, cargo specificity, and processivity.
Local control
Local translation allows axons and dendrites to respond to stimuli without waiting for somatic protein synthesis.
Polarity and trafficking
Neuronal polarity is maintained by differential cytoskeletal organization, membrane sorting signals, and targeted vesicular trafficking. Local translation in dendrites and axons is regulated by RNA-binding proteins, microRNAs, and translational repressors.
Which cytoskeletal track is primarily used for long-range axonal transport?
Microtubules are the major tracks for fast axonal transport.
Correct answer: Microtubules
Name the motor protein typically associated with anterograde axonal transport.
Kinesins generally move cargo toward the microtubule plus end, supporting anterograde transport.
Correct answer: Kinesin
Transport strategies
Somatic synthesis
- High output capacity
- Slower response to local demand
Local translation
- Rapid spatially restricted response
- Requires local mRNA and translational control
Key transport factors
What is one major advantage of local translation in dendrites?
Local translation lets synapses remodel rapidly and specifically.
Correct answer: It permits spatially restricted protein synthesis near active synapses
Tracking axonal cargo experimentally
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Step 1: Label cargo or organelles with a fluorescent marker.
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Step 2: Acquire time-lapse imaging along axons.
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Step 3: Quantify velocity, directionality, and run length.
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Step 4: Perturb motors or adaptors genetically.
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Step 5: Relate transport defects to cellular pathology.