INVOLVEMENT OF THE CYTOSKELETON IN THE MOVEMENT OF CORTICAL GRANULES DURING OOCYTE MATURATION, AND CORTICAL GRANULE ANCHORING IN MOUSE EGGS

Exocytosis of cortical granules in mouse eggs is required to produce t he zona pellucida block to polyspermy. In this study, we examined the role of microfilaments and microtubules in the regulation of cortical granule movement toward the cortex during oocyte maturation and anchor ing of cortical granules in the cortex. Fluorescently labeled cortical granules, microfilaments, and microtubules were visualized using lase r-scanning confocal microscopy. It was observed that cortical granules migrate to the periphery of the oocyte during oocyte maturation. This movement is blocked by the treatment of oocytes with cytochalasin D, an inhibitor of microfilament polymerization, but not with nocodazole or colchicine, inhibitors of microtubule polymerization. Cortical gran ules, once anchored at the cortex, remained in the cortex following tr eatment of metaphase II-arrested eggs with each of these inhibitors; i .e., there was neither inward movement nor precocious exocytosis. Fina lly, the single cortical granule-free domain that normally becomes loc alized over the metaphase II spindle was not observed when the chromos omes become scattered following microtubule disruption with nocodazole or colchicine. In these instances a cortical granule-free domain was observed over each individual chromosome, suggesting that the chromoso me or chromosome-associated material, and not the spindle, dictates th e localization of the cortical granule-free domain. (C) 1998 Academic Press.