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Distinct Microtubule Subsets Organize Around The Newly Forming Lumen During Epithelial Polarization

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Abstract

Epithelial tissues maintain body homeostasis by acting as a barrier to the outside environment and allowing for the vectorial transport of molecules and solutes. To establish this barrier, epithelial cells must form and maintain distinct apical and basolateral domains separated by tight junctions. This polarization process is triggered by signals initiated at cell-substratum and cell-cell adhesions and propagated by rho GTPases and multiple signaling complexes. Cytoskeletal reorganization accompanies polarization and both microtubules and kinesin-mediated transport are required for apical membrane maintenance. However, how microtubules respond to polarization cues and affect formation of the apical membrane is currently unknown. To address this, I characterized how microtubules reorganize during early events in epithelial polarization. I utilized both 2D and 3D cell culture to visualize microtubule subsets during early polarization events and examined the effects of perturbing microtubule dynamics on lumen formation. Two biochemically distinct subsets of microtubules reorganized around the vacuolar apical compartment (VAC), a transient organelle containing apical proteins, and again following exocytosis into the lumen. Dynamic microtubules arranged perpendicular to VACs and lumens, and post-translationally modified, stable microtubules arranged circumferentially around VACs and against the lumen face. Nocodazole-induced microtubule depolymerization and taxol-induced microtubule stabilization either delayed or halted lumen formation in both systems. Microtubule regrowth revealed that microtubules are nucleated near the VAC/lumen and at the cell periphery while live recordings of fluorescently tagged EB1 revealed that growing microtubule plus ends are oriented both towards and away from the nascent apical membrane. These findings show that microtubules are required for lumen formation and rearrange as the nascent apical membrane is transcytosed to form a lumen. Aspects of the microtubule array are indicative of how microtubules might respond to polarization cues and how kinesins might recognize distinct tracks for targeted transport. Since adherens junctions can induce microtubule stabilization and recruit dynein, it is likely that microtubules are stabilized and modified following cell-cell contact. Then dynein might provide a pulling force on stabilized MTs to reposition VACs prior to lumen formation. Finally, kinesins might use MT modifications to direct apical membrane exocytosis at the lateral membrane to form a lumen.

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2015

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Epithelia; Lumen; MDCK; Microtubule; Polarization

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Union Local

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Cell & Developmental Biology

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Doctor of Philosophy

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Government Document

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Attribution-NonCommercial-NoDerivatives 4.0 International

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dissertation or thesis

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