MICROTUBULE REARRANGEMENT DURING IN-VITRO MATURATION OF PIG OOCYTES -EFFECT OF CYCLOHEXIMIDE

In freshly isolated fully grown pig oocytes at the germinal vesicle (G V) stage, the cytoplasmic microtubules are arranged in a meshwork. Thi s microtubule arrangement is also maintained during the initial phases of meiotic maturation in vitro. A perinuclear array of microtubules i s formed immediately before germinal vesicle breakdown (GVBD). Short-t erm treatment of oocytes with taxol when oocytes are at metaphase I st age induced formation of cytoplasmic asters. The oocyte cytoplasm is u nable to respond to the taxol treatment at the earlier stages of meiot ic maturation. In oocytes cultured with the proteosynthesis inhibitor cycloheximide, meiotic maturation is blocked. Condensation of chromati n occurs but the nuclear envelope is preserved and the microtubule arr angement is unchanged. A perinuclear array of microtubules does not ap pear and oocyte cytoplasm does not respond to shortterm taxol treatmen t by the formation of cytoplasmic asters. We can conclude that the mic rotubule rearrangement and the acquisition of competence for tubulin a ssembly are blocked by cycloheximide and are thus dependent on de novo proteosynthesis.