Effect of colcemid on the centriole cycle in Chinese hamster ovary cells

The structural changes in the centrioles in Chinese hamster ovary cells were monitored by electron microscopy of whole mount preparations to investigate the effects of colcemid on the events in the centriole cycle. The population of mitotic cells increased with time of incubation with colcemid, but the arrest at mitosis by this drug was soon overcome, resulting in the formation of nuclei and a change in the shape of the cells again spreading over the substrate. The maximal mitotic index was reached every 25 h in the presence of either 0.10 or 0.91 micrograms/ml of colcemid. During this time, cells became multinucleated, increased greatly in size, and accumulated 8 to 10-nm filamentous bundles in the cytoplasm instead of microtubules, almost all of which had been depolymerized after exposure to colcemid. In the cells that were continuously treated with colcemid, a pair of centrioles became disoriented and each subsequently produced a daughter centriole. However, these daughter centrioles elongated to only half their full length; many unusual figures in the centriolar pairs resulted from their proceeding normally to the phases for disorientation and nucleation for centrioles in the next cycle. Although the rate of centriole elongation and the frequency of formation of the daughter centrioles were decreased by increasing the concentration of colcemid, the disorientation of the centrioles was not disturbed by this drug. The inhibitory effect of colcemid on centriolar nucleation and elongation was found to be totally reversible; the formation and elongation of new daughter centrioles occurred again just after removal of the drug. Prolonged treatment of cells with colcemid caused ultrastructural changes in the centrioles, such as the outgrowth of microtubules from the wall of centriolar triplets or the formation of unusual bundles of microtubules around the centrioles.