GAMMA-TUBULIN PARTICIPATES IN THE FORMATION OF THE MIDBODY DURING CYTOKINESIS IN MAMMALIAN-CELLS

Animal cells undergoing cytokinesis form an inter-cellular bridge cont aining two bundles of microtubules interdigitated at their plus ends, which constitute the midbody. Polyclonal antibodies raised against thr ee specific amino acid sequences of gamma-tubulin (EEFATEGGDRKDV, NIIQ GEADPTDVHKSL and EYHAATRPDYISWGTQEQ) specifically stained the centroso me in interphase, the spindle poles in all stages of mitosis, and the extremities of the midbody in mammalian cells (Potorous, human, Chines e hamster, mouse). This staining was prevented by the corresponding pe ptides, by Xenopus gamma-tubulin, but was not modified by purified alp habeta-tubulin heterodimer. An identical staining was obtained with af finity-purified antibodies against the carboxyl-terminal amino acid se quence of human gamma-tubuli''. No gamma-tubulin could be detected in the interzone during anaphase and early telophase. Material containing gamma-tubulin first appeared in the two daughter cells on each side o f the division plane in late telophase, and accumulated transiently at the minus ends of the two microtubule bundles constituting the midbod y for one hour after metaphase. Micro-injection of gamma-tubulin antib odies into anaphase cells prevented the subsequent formation of the mi crotubule bundles between the two daughter cells. In contrast with pre vious views, these observations suggest that the microtubules constitu ting the midbody may be nucleated on special microtubule organizing ce ntres, active during late telophase only, and assembled on each side o f the dividing plane between the daughter cells.