Microtubule-organizing centres in mammalian cells in culture.

When microtubules in animal cells are dissociated and then allowed to recover, they re-grow from discrete points in the cytoplasm known as microtubule-organizing centres (MTOC). The microtubules may be dissociated by antimitotic drugs such as colcemid, vinblastine and griseofulvin, or by chilling the cells. Immunofluorescence studies show that the number of MTOC seen does not depend on the concentration of antimitotic drug used or the duration of exposure to the drug; the same results are obtained with vinblastine, griseofulvin and colcemid. However, after cold treatment, the proprotion of cells showing only a single MTOC is greater than that seen with the antimitotic drugs and may exceed 90%. Evidence is presented for the view that procedures involving the use of antimitotic drugs give artificially high values for the number of MTOC per cell.