CALCIUM SIGNALLING DURING STARFISH OOCYTE MATURATION: ROLE OF ACTIN CYTOSKELETON

Maturation induced by 1-MA in prophase arrested oocytes is indicated by the breakdown of the nuclear envelope and by the increased sensitivity of the Ca2+ stores to InsP3 starting at the animal hemisphere. We have investigated whether activated MPF was involved in the increased sensitivity of the Ca2+ response to InsP3 and found that its development was blocked in oocytes treated with the MPF inhibitor roscovitine. That the nuclear MPF activation is indeed required was shown by enucleating or by dissecting oocytes into vegetal and animal halves prior to 1-MA treatment. MPF activity after maturation was much lower in the enucleated oocyte and in the vegetal half, which did not contain the nucleus. The increased sensitivity to InsP3 correlated with the changes in actin cytoskeleton induced by MPF.