Microtubule minus-end anchorage at centrosomal and non-centrosomal sites: the role of ninein.
The novel concept of a centrosomal anchoring complex, which is distinct from the gamma-tubulin nucleating complex, has previously been proposed following studies on cochlear epithelial cells. In this investigation we present evidence from two different cell systems which suggests that the centrosomal protein ninein is a strong candidate for the proposed anchoring complex. Ninein has recently been observed in cultured fibroblast cells to localise primarily to the post-mitotic mother centriole, which is the focus for a classic radial microtubule array. We show here by immunoelectron microscopical analyses of centrosomes from mouse L929 cells that ninein concentrates at the appendages surrounding the mother centriole and at the microtubule minus-ends. We further show that localisation of ninein in the cochlear supporting epithelial cells, where the vast majority of the microtubule minus-ends are associated with apical non-centrosomal sites, suggests that it is not directly involved in microtubule nucleation. Ninein seems to play an important role in the positioning and anchorage of the microtubule minus-ends in these epithelial cells. Evidence is presented which suggests that ninein is released from the centrosome, translocated with the microtubules, and is responsible for the anchorage of microtubule minus-ends to the apical sites. We propose that ninein is a non-nucleating microtubule minus-end associated protein which may have a dual role as a minus-end capping and anchoring protein.
Department of Anatomy and Physiology, MSI/WTB complex, Dow Street, University of Dundee, Dundee, DD1 5EH, UK. m.m.mogensen@dundee.ac.uk
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Mogensen
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Malik
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Piel
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Bouckson-Castaing
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Bornens
D000818:Animals; D002135:Calcium-Binding Proteins / Q000032:analysis / Q000235:genetics; D002460:Cell Line; D018385:Centrosome / Q000378:metabolism* / Q000648:ultrastructure; D002868:Chromosomal Proteins, Non-Histone; D003598:Cytoskeletal Proteins; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D049452:Green Fluorescent Proteins; D066298:In Vitro Techniques; D007202:Indicators and Reagents / Q000494:pharmacology; D008164:Luminescent Proteins / Q000235:genetics / Q000494:pharmacology; D051379:Mice; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008954:Models, Biological; D015739:Nocodazole / Q000494:pharmacology; D009687:Nuclear Proteins; D009925:Organ of Corti / Q000166:cytology / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism
D002135:Calcium-Binding Proteins; D002868:Chromosomal Proteins, Non-Histone; D003598:Cytoskeletal Proteins; D007202:Indicators and Reagents; D008164:Luminescent Proteins; C099035:Nin protein, mouse; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; C056608:caltractin; D049452:Green Fluorescent Proteins; D019204:GTP-Binding Proteins; D015739:Nocodazole