title: Dendrites In Vitro and In Vivo Contain Microtubules of Opposite Polarity and Axon Formation Correlates with Uniform Plus-End-Out Microtubule Orientation.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Cell Biology, Faculty of Science, Utrecht University, 3584 CH, Utrecht, The Netherlands, and.
authors.forename: Kah Wai
authors.initials: KW
authors.lastname: Yau
authors.affiliation: Cell Biology, Faculty of Science, Utrecht University, 3584 CH, Utrecht, The Netherlands, and.
authors.forename: Philipp
authors.identifier: http://orcid.org/0000-0001-5412-0006
authors.initials: P
authors.lastname: Schätzle
authors.affiliation: Cell Biology, Faculty of Science, Utrecht University, 3584 CH, Utrecht, The Netherlands, and.
authors.forename: Elena
authors.initials: E
authors.lastname: Tortosa
authors.affiliation: Department of Basic Neurosciences, Faculty of Medicine and the Center for Neuroscience, University of Geneva, 1211 Geneva, Switzerland.
authors.forename: Stéphane
authors.identifier: http://orcid.org/0000-0003-0618-777X
authors.initials: S
authors.lastname: Pagès
authors.affiliation: Department of Basic Neurosciences, Faculty of Medicine and the Center for Neuroscience, University of Geneva, 1211 Geneva, Switzerland.
authors.forename: Anthony
authors.initials: A
authors.lastname: Holtmaat
authors.affiliation: Cell Biology, Faculty of Science, Utrecht University, 3584 CH, Utrecht, The Netherlands, and c.hoogenraad@uu.nl l.kapitein@uu.nl.
authors.forename: Lukas C
authors.initials: LC
authors.lastname: Kapitein
authors.affiliation: Cell Biology, Faculty of Science, Utrecht University, 3584 CH, Utrecht, The Netherlands, and c.hoogenraad@uu.nl l.kapitein@uu.nl.
authors.forename: Casper C
authors.initials: CC
authors.lastname: Hoogenraad
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology*; D002478:Cells, Cultured; D002502:Centrioles / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology; D003712:Dendrites / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008822:Mice, Transgenic; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D008870:Microtubules / Q000502:physiology*; D009474:Neurons / Q000166:cytology*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051381:Rats; D013997:Time Factors; D014404:Tubulin / Q000378:metabolism
chemical_list: C578014:Camsap2 protein, mouse; C095003:MACF1 protein, human; D008840:Microfilament Proteins; D008869:Microtubule-Associated Proteins; D034741:RNA, Small Interfering; D014404:Tubulin; C462941:beta3 tubulin, mouse; D049452:Green Fluorescent Proteins
keywords: cytoskeleton; dendrites; development; microtubule dynamics; neuron; polarity
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