Polarity and nucleation of microtubules in polarized epithelial cells.
Microtubules oriented in the apicobasal axis of columnar epithelial cells are arranged with a uniform polarity with minus ends toward the apical surface, suggesting that these cytoskeletal filaments might serve as a substrate for polarized movement of membrane vesicles within the cell. It is not known whether hepatocytes, a cuboidal epithelium in which transcellular transport is a requisite step in normal apical membrane biogenesis, contain microtubules arranged with a similar polarity. In the present study, we explore the question of microtubule polarity and possible mechanisms for nucleation in the epithelial cell lines WIF-B (hepatocyte), Caco-2 (intestine), and Madin-Darby canine kidney (MDCK). Caco-2 microtubules in the apicobasal axis had uniform polarity with minus ends nearest the apical surface. After cold and nocodazole-induced depolymerization, microtubule regrowth initiated in the apical region in all three cell types. The apex of WIF-B and Caco-2 cells contained two pools of gamma-tubulin: one associated with centrosomes and the other delocalized under the apical membrane. Non-centrosomal gamma-tubulin was present in complexes that sedimented between 10S and 29S; both forms could bind microtubules. The presence of both centrosomal and noncentrosomal gamma-tubulin in apical cytoplasm suggest multiple mechanisms by which microtubule nucleation might occur in epithelial cells.
Meads
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Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Schroer
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D000818:Animals; D018938:Caco-2 Cells / Q000737:chemistry / Q000166:cytology* / Q000648:ultrastructure; D006528:Carcinoma, Hepatocellular; D016764:Cell Polarity / Q000502:physiology*; D018385:Centrosome / Q000737:chemistry / Q000648:ultrastructure; D004285:Dogs; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D007686:Kidney Tubules, Distal / Q000166:cytology*; D008854:Microscopy, Electron; D008870:Microtubules / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D012995:Solubility; D014404:Tubulin / Q000032:analysis
D014404:Tubulin