EFFECT OF WORTMANNIN, AN INHIBITOR OF PHOSPHATIDYLINOSITOL 3-KINASE, ON THE FIRST MITOTIC DIVISIONS OF THE FERTILIZED SEA-URCHIN EGG

We have reported earlier that the polyphosphoinositide messenger syste m may control mitosis in sea urchin eggs. Besides phospholipase C acti vation and its second messengers, phosphatidylinositol (PI) 3-kinase h as been proposed to affect a wide variety of cellular processes in oth er cellular systems. Therefore, we have investigated whether PI 3-kina se could play a role in regulating the sea urchin early embryonic deve lopment. Our data presented here suggest that PI 3-kinase is present i n sea urchin eggs. We found that wortmannin, an inhibitor of PI 3-kina se, led to arrest of the cell cycle. Chromosome condensation, nuclear envelope breakdown, microtubular aster polymerization, protein and DNA synthesis were not affect when fertilization was performed in the pre sence of the drug. However, maturation-promoting factor (MPF) activati on was inhibited and centrosome duplication was perturbed preventing t he formation of a bipolar mitotic spindle in wortmannin treated eggs, We discuss how PI 3-kinase might be involved in the cascade of events leading to the first mitotic divisions of the fertilized sea urchin eg g.