The protein phosphatase inhibitor okadaic acid inhibits exit from metaphase II in parthenogenetically activated pig oocytes

Abstract

The exposure of in vitro matured pig oocytes to the calcium ionophore A 23187 (50 microM, 7 min) resulted in parthenogenetic activation in 67% of the oocytes. When the activated oocytes were cultured, they formed pronuclei. In these oocytes, tubulin labelling revealed a rearrangement of the microtubules into an interphase meshwork. The activated oocytes also lost their ability to form cytoplasmic asters after short-term taxol treatment. The activation rate of the oocytes was further increased when they were cultured with a protein synthesis inhibitor, cycloheximide, after ionophore treatment. A culture of ionophore-treated oocytes with okadaic acid, the inhibitor of protein phosphatases 1 and 2A, prevents the events characterizing oocyte activation. In oocytes cultured with okadaic acid, chromatin remained condensed, and cytoplasm retained its ability to respond to taxol treatment by the formation of cytoplasmic asters. This effect of okadaic acid was observed even in oocytes in which the activating stimulus was followed by a culture with cycloheximide. This data allows us to conclude that protein phosphatases 1 and 2A play an important role during the transition from metaphase II to interphase after activation of the pig oocyte.

Parthenogenetic Activation of Porcine Oocytes by Electric Pulse and/or Butyrolactone I Treatment

“…Treatments with protein kinase inhibitors such as 6-DMAP, H7, or staurosporine also trigger meiotic resumption in several species by their effect on the MPF levels and on the mitogen-activated protein (MAP) kinase activities Wang, et al, 1997). A sequential treatment inducing a Ca 21 transient followed by a protein synthesis or kinase inhibitor resulted in higher activation and developmental rates of oocytes in several species (Susko-Parrish, et al, 1994;Nussbaum and Prather, 1995;Cha, et al, 1997;Grocholova, et al, 1997;Liu, et al, 1998;Mitalipov, et al, 1999). This combination treatment results in a rapid and sustained inactivation of MPF and hence the activation of the oocyte.…”

Nicotine combined with okadaic acid or taxol adversely affects bovine oocyte maturation and subsequent embryo development

“…This process results in the synthesis and organization of an extensive extracellular matrix around the cumulus cells (22,27). The expansion process is necessary for fertilization and early embryo development (28,29).…”

“…Cytogenetic Analysis of Oocytes After Incubation in Reagents-Containing Medium Oocytes were exposed to OA at concentrations of 0.01 and 0.05 mmol/L and to taxol at 0.05 and 0.1 mmol/L, which were much lower than reported in other published data (OA, 1.0 to 2.5 mmol/L [13,22,23]; taxol, 4 to 10 mmol/L [15,16,24]). The concentrations of nicotine (10 and 50 mmol/L) used in this study were selected because nicotine at these doses did not affect bovine oocyte maturation and subsequent embryo development (2,3).…”