Microtubule rearrangement during in vitro maturation of pig oocytes. Effect of cycloheximide.

In freshly isolated fully grown pig oocytes at the germinal vesicle (GV) stage, the cytoplasmic microtubules are arranged in a meshwork. This microtubule arrangement is also maintained during the initial phases of meiotic maturation in vitro. A perinuclear array of microtubules is formed immediately before germinal vesicle breakdown (GVBD). Short-term treatment of oocytes with taxol when oocytes are at metaphase I stage induced formation of cytoplasmic asters. The oocyte cytoplasm is unable to respond to the taxol treatment at the earlier stages of meiotic maturation. In oocytes cultured with the proteosynthesis inhibitor cycloheximide, meiotic maturation is blocked. Condensation of chromatin occurs but the nuclear envelope is preserved and the microtubule arrangement is unchanged. A perinuclear array of microtubules does not appear and oocyte cytoplasm does not respond to short-term taxol treatment by the formation of cytoplasmic asters. We can conclude that the microtubule rearrangement and the acquisition of competence for tubulin assembly are blocked by cycloheximide and are thus dependent on de novo proteosynthesis.