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The transport properties of axonal microtubules establish their polarity orientation
Journal article   Open access   Peer reviewed

The transport properties of axonal microtubules establish their polarity orientation

P W Baas and F J Ahmad
The Journal of cell biology, v 120(6), pp 1427-1437
Mar 1993
DOI: https://doi.org/10.1083/jcb.120.6.1427
PMID: 8449987
Featured in Collection :   UN Sustainable Development Goals @ Drexel
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https://doi.org/10.1083/jcb.120.6.1427View
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Abstract

Animals, Newborn Cells, Cultured Microtubules - physiology Axons - drug effects Ganglia, Sympathetic - physiology Rats Axons - physiology Microscopy, Electron Animals Neurons - ultrastructure Biological Transport Microtubules - drug effects Axons - ultrastructure Microtubules - ultrastructure Neurons - physiology Vinblastine - pharmacology Neurons - drug effects
It is well established that axonal microtubules (MTs) are uniformly oriented with their plus ends distal to the neuronal cell body (Heidemann, S. R., J. M. Landers, and M. A. Hamborg. 1981. J. Cell Biol. 91:661-665). However, the mechanisms by which these MTs achieve their uniform polarity orientation are unknown. Current models for axon growth differ with regard to the contributions of MT assembly and transport to the organization and elaboration of the axonal MT array. Do the transport properties or assembly properties of axonal MTs determine their polarity orientation? To distinguish between these possibilities, we wished to study the initiation and outgrowth of axons under conditions that would arrest MT assembly while maintaining substantial levels of preexisting polymer in the cell body that could still be transported into the axon. We found that we could accomplish this by culturing rat sympathetic neurons in the presence of nanomolar levels of vinblastine. In concentrations of the drug up to and including 100 nM, the neurons actively extend axons. The vinblastine-axons are shorter than control axons, but clearly contain MTs. To quantify the effects of the drug on MT mass, we compared the levels of polymer throughout the cell bodies and axons of neurons cultured overnight in the presence of 0, 16, and 50 nM vinblastine with the levels of MT polymer in freshly plated neurons before axon outgrowth. Without drug, the total levels of polymer increase by roughly twofold. At 16 nM vinblastine, the levels of polymer are roughly equal to the levels in freshly plated neurons, while at 50 nM, the levels of polymer are reduced by about half this amount. Thus, 16 nM vinblastine acts as a "kinetic stabilizer" of MTs, while 50 nM results in some net MT disassembly. At both drug concentrations, there is a progressive increase in the levels of MT polymer in the axons as they grow, and a corresponding depletion of polymer from the cell body. These results indicate that highly efficient mechanisms exist in the neuron to transport preassembled MTs from the cell body into the axon. These mechanisms are active even at the expense of the cell body, and even under conditions that promote some MT disassembly in the neuron. MT polarity analyses indicate that the MTs within the vinblastine-axons, like those in control axons, are uniformly plus-end-distal.

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Cell Biology
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