FULL ACTIVATION OF THE RAT OOCYTE BY PROTEIN-SYNTHESIS INHIBITION REQUIRES PROTEIN PHOSPHATASE-ACTIVITY

The rat oocyte provides an interesting system in which to dissect the control mechanisms involved in the transition between a meiotic M phas e and a mitotic interphase. In this study, we show that in rat oocytes activated parthenogenetically by puromycin, okadaic acid (a potent in hibitor of protein phosphatases 1 and 2A) induced an increase in histo ne Hl kinase activity suggesting that MPF was reactivated. However, th e inhibition of phosphatases 1 and 2A shortly after second polar body extrusion did not allow the formation of a metaphase-like spindle, alt hough microtubule polymerization was not inhibited. Instead, the chrom atin remained condensed as a single mass and a large aster formed arou nd it.