Axonal Transport and the Neuronal Cytoskeleton


The neuronal cytoskeleton is a system of highly organized polymers that provide architectural support for axons and dendrites, and also provide railways for the transport of various classes of cytoplasmic constituents. Molecular motor proteins use the energy derived from adenosine triphosphate hydrolysis for the transport of organelles along the cytoskeletal polymers and for the transport of the polymers themselves. Axons can traverse exceeding long distances in the body, and hence require sophisticated mechanisms of axonal transport in both the anterograde and the retrograde direction.

Keywords: axon; dendrite; neuron; axonal transport; microtubule; microfilament; motor protein

Figure 1.

Structure of cytoskeletal polymers and molecular motors. One example of each member of the motor families is shown. Other family members vary in their structure.

Figure 2.

Current theories on the mechanisms of organelle transport along microtubules and microfilaments within axons. Organelles that engage cytoplasmic dynein are transported towards minus ends of microtubules in retrograde fashion (from the distal end of axon towards the cell body), while organelles that engage most kinesins are transported towards plus ends of microtubules in anterograde fashion (from the cell body towards the distal end of the axon). Organelles that engage myosins are transported towards plus ends of microfilaments. In general, microtubules act as longer range ‘highways’ for organelle transport, while microfilaments act as shorter ‘streets’.

Figure 3.

Current theories on the mechanisms of cytoskeletal polymer transport within the axon. Microtubules are nucleated by gamma tubulin and released from the centrosome by katanin within the cell body of the neuron, and are then transported by cytoplasmic dynein into the axons with the plus end of the microtubule leading. Most of the microtubule transport occurs in anterograde fashion. There is also evidence that some microtubule transport occurs in retrograde fashion. Kinesin‐related motors may contribute to the transport microtubules in one direction or both. Neurofilaments are conveyed either by their association with microtubules or along the microtubules in a similar fashion to membranous organelles. Microfilaments are transported by myosins, and generate forces by pushing against cortical structures associated with sites where the axon adheres to the extracellular matrix.



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Further Reading

Brady S, Coleman DR and Brophy P (2002) Subcellular organization of the nervous system: organelles and their function. In: Zigmond MJ, Bloom FE, Landis SC, Roberts JL and Squire LR (eds) Fundamental Neuroscience, pp. 79–115. London: Academic Press

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Baas, PW, and Karabay, A(Sep 2005) Axonal Transport and the Neuronal Cytoskeleton. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0004050]