| Abstract: | PtKl cells were examined by surface scanning and transmission electron microscopy to determine the mechanism responsible for the ability of these cells to remain flat during mitosis. Bundles of tightly packed 80–100 Å filaments were seen to radiate from synthesis-and-organizing centers, and to terminate in desmosomes at the plasma membrane. In the presence of Colcemid or colchicine, cells beginning mitosis rounded up and the synthesis-and-organizing centers could no longer be found. In contrast, the occurrence of these structures in interphase cells treated with Colcemid or colchicine was increased. A cytoskeletal role for the 80–100 Å filaments is proposed. |
