INTERMEDIATE-SIZED FILAMENTS IN RAT KANGAROO PTK2 CELLS .1. MORPHOLOGY IN SITU

  • 1 January 1978
    • journal article
    • research article
    • Vol. 17  (2) , 365-391
Abstract
The system of the intermediate-sized filaments (IF) of rat kangaroo PtK2 kidney cells, which can be specifically demonstrated by immunofluorescence microscopy using certain rabbit autoantibodies and guinea pig antibodies against bovine hoof prekeratin was studied by EM. The characteristic ornamental, curved arrays of this system were shown after fixation in situ in both thin sections and whole cell preparations to represent bundles of 6-11 nm thick filaments extending through the whole cytoplasm. In some cells, however, they appear to be enriched in the perinuclear region. While many individual IF were recognized in the cytoplasm, the tendency of such filaments to aggregate laterally into bundles was one of their prominent features. Among such bundle formations one especially conspicuous form consists of tightly packed IF cemented together in a dense osmiophilic matrix. The appearance and arrangement of the IF was not significantly altered in cells treated with colcemid and/or cytochalasin B. Spatial relationships of IF with microfilament-containing cables and microtubules and with membranous structures were also described. IF were heterogeneous in width and revealed an unstained, apparently hollow core, indicative of a tubular organization. Many IF showed small, sometimes periodically arranged lateral projections apparently involved in IF cross-linking. Associations with polyribosomes were common. The changes in the IF system during mitosis were also examined. The structural details of the IF and their possible role as cytoskeletal elements involved in the control of cell cytoplasmic architecture were discussed in relation to data on various intermediate-sized filaments from other cell types. The close similarity of the IF of PtK2 cells to aggregates of prekeratin filaments was emphasized. PtK2 cells represent an epithelial cell line growing in a state of balanced semi-keratinization.