THE MICROTUBULE SYSTEM AND THE REDUPLICATION OF MICROTUBULE ORGANIZING CENTERS IN DICTYOSTELIUM DISCOIDEUM

The microtubule system of normal and microtubule-poisoned amoebae of Dictyostelium discoideum has been investigated both by indirect immunofluorescence with antibodies to microtubule proteins and electron microscopy. Nocodazole, like some other microtubule poisons, destroys most of microtubules in both interphase and dividing cells resulting in an inhibition of nuclear and cell division. The microtubule organizing centres, however, continue to duplicate once or twice. The daughter organizing centres segregate, they seem to be connected with nuclear material, that splits partly, too, forming more or less extended nuclear clefts. This segregation, at least over short distances, takes place without intranuclear microtubules. Duplication of microtubule organizing centres is not strictly correlated with nuclear division and cytokinesis. Microtubule poisons are able to uncouple these events. Different levels of regulation should be responsible for microtubule organizing centre, nuclear, and cell division.