Microtubules during germinal vesicle breakdown (GVBD) of Xenopus oocytes: effect of Ca2+ ionophore A-23187 and taxol.

During the first meiotic cell division of the Xenopus oocyte, a transient microtubule network appears at the basal part of the disintegrating nucleus. In order to know if this structure plays a role in the formation of the first meiotic spindle, we have studied the actions of Ca2+ ions and taxol during the whole maturation process. We now report that when the free cytosolic Ca2+ concentration is raised by ionophore A 23187, the perinuclear microtubule array is disrupted and the spindle formation is inhibited. When taxol is microinjected into maturing oocytes, the perinuclear microtubules become anarchically distributed and the normal organization of the metaphase spindle is blocked. MPF (Maturation promoting factor) activity is maintained in these experimental conditions (Germinal vesicle breakdown is induced). These results indicate that polymerization/depolymerization of perinuclear microtubules are involved in the nuclear envelope breakdown and the subsequent assembly of the first meiotic spindle.