Changes in the activity of type 2A protein phosphatases during meiotic maturation and the first mitotic cell cycle in mouse oocytes

We have established an assay to measure protein phosphatase activity in mou se oocytes using [P-32]-radiolabeled phosphorylase a as the substrate. Remo val of the radiolabel from the substrate in vitro was linear with time and could be inhibited totally by the addition of okadaic acid (inhibitor of ty pe 1 and type 2 protein phosphatases), or partially by protein inhibitor 2 (inhibitor of type 1 protein phosphatases). We performed a detailed study o f the activity of type 2A protein phosphatases in mouse oocytes undergoing meiotic maturation and after parthenogenetic activation of mature oocytes a rrested in metaphase II. Significant changes in the activity of type 2A pro tein phosphatases were observed during the first meiotic and the first mito tic cell cycles. These alterations in type 2A protein phosphatase activity occurred in the absence of changes in the quantity of the catalytic subunit and can be correlated with changes in the activity of protein kinases and rearrangement of the cellular cytoskeleton. Our observations support a role for type 2A protein phosphatases in cell cycle regulation and demonstrate that, like the protein kinases, the type 2A phosphatases also undergo chang es in their activity during early mammalian development. (C) Elsevier, Pari s.