Dendrites In Vitro and In Vivo Contain Microtubules of Opposite Polarity and Axon Formation Correlates with Uniform Plus-End-Out Microtubule Orientation.
UNLABELLED
In cultured vertebrate neurons, axons have a uniform arrangement of microtubules with plus-ends distal to the cell body (plus-end-out), whereas dendrites contain mixed polarity orientations with both plus-end-out and minus-end-out oriented microtubules. Rather than non-uniform microtubules, uniparallel minus-end-out microtubules are the signature of dendrites in Drosophila and Caenorhabditis elegans neurons. To determine whether mixed microtubule organization is a conserved feature of vertebrate dendrites, we used live-cell imaging to systematically analyze microtubule plus-end orientations in primary cultures of rat hippocampal and cortical neurons, dentate granule cells in mouse organotypic slices, and layer 2/3 pyramidal neurons in the somatosensory cortex of living mice. In vitro and in vivo, all microtubules had a plus-end-out orientation in axons, whereas microtubules in dendrites had mixed orientations. When dendritic microtubules were severed by laser-based microsurgery, we detected equal numbers of plus- and minus-end-out microtubule orientations throughout the dendritic processes. In dendrites, the minus-end-out microtubules were generally more stable and comparable with plus-end-out microtubules in axons. Interestingly, at early stages of neuronal development in nonpolarized cells, newly formed neurites already contained microtubules of opposite polarity, suggesting that the establishment of uniform plus-end-out microtubules occurs during axon formation. We propose a model in which the selective formation of uniform plus-end-out microtubules in the axon is a critical process underlying neuronal polarization.


SIGNIFICANCE STATEMENT
Live-cell imaging was used to systematically analyze microtubule organization in primary cultures of rat hippocampal neurons, dentate granule cells in mouse organotypic slices, and layer 2/3 pyramidal neuron in somatosensory cortex of living mice. In vitro and in vivo, all microtubules have a plus-end-out orientation in axons, whereas microtubules in dendrites have mixed orientations. Interestingly, newly formed neurites of nonpolarized neurons already contain mixed microtubules, and the specific organization of uniform plus-end-out microtubules only occurs during axon formation. Based on these findings, the authors propose a model in which the selective formation of uniform plus-end-out microtubules in the axon is a critical process underlying neuronal polarization.
['Yau|Kah Wai|KW|', 'Schätzle|Philipp|P|http://orcid.org/0000-0001-5412-0006', 'Tortosa|Elena|E|', 'Pagès|Stéphane|S|http://orcid.org/0000-0003-0618-777X', 'Holtmaat|Anthony|A|', 'Kapitein|Lukas C|LC|', 'Hoogenraad|Casper C|CC|']
D000818:Animals D001369:Axons D016764:Cell Polarity D002478:Cells, Cultured D002502:Centrioles D002540:Cerebral Cortex D003712:Dendrites D049452:Green Fluorescent Proteins D006624:Hippocampus D006801:Humans D066298:In Vitro Techniques D051379:Mice D008822:Mice, Transgenic D008840:Microfilament Proteins D008869:Microtubule-Associated Proteins D008870:Microtubules D009474:Neurons D034741:RNA, Small Interfering D051381:Rats D013997:Time Factors D014404:Tubulin
dendrites polarity neuron development cytoskeleton microtubule dynamics