Cytoskeletal assembly and organization in certain supporting cells in the mammalian organ of Corti
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This thesis deals with the assembly and composition of cytoskeletal components in the mammalian organ of Corti. It mainly concentrates on large cell surface-associated microtubule bundles in certain supporting cells called inner pillar cells. Two distinct microtubule arrays assemble in each cell. One of the arrays spans the entire length of a cell (transcellular array) whereas the other is confined to its lower portion (basal array). The basal array is situated more than 10mum from the apically situated centrosomal region. Serial cross- sectional analyses indicate that the transcellular array elongates from the cell apex to the cell base but that the basal array elongates towards the cell apex and is nucleated at the cell base. However, antibodies to centrosomal proteins reveal that each inner pillar cell probably contains only one microtubule nucleating site which is situated in the apical centrosomal region. Therefore, basal array microtubules do not appear to be nucleated at the cell base. Assessment of microtubule polarities support this hypothesis; they provide evidence that both arrays have their plus ends (elongating ends) directed towards the cell base. A sophisticated assembly sequence which involves the escape and capture of centrosomally nucleated microtubules is proposed to account for the assembly of the basal array. The microtubules in the supporting cells are post-translationally modified. However, the microtubules of the neighbouring sensory hair cells are not post-translationally modified. Two kinds of cytokeratins are deployed in a cell type-specific manner in the supporting cells and may help to link the ends of micro tubule bundles to cell junctions.
Thesis, PhD Doctor of Philosophy
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