No abstract

Summary ― Total inhibition of germinal vesicle breakdown (GVBD) was observed in growing pig oocytes (internal diameter 80, 90 and 100 11m) when they were cultured in a medium conditioned by cumulus oocyte complexes (COCs) of fully grown oocytes. In denuded growing oocytes, only partial inhibition was observed. The inhibitory effect was fully reversible. The addition of heparin (300 IU/ml) could overcome the effect of the conditioned medium. Transient exposure (6 h) of oocytes to dibutyryl cyclic adenosine monophosphate (dbcAMP) (1 mg/mi) could also partly reverse the effect of factor (s) produced by cumulus cells of fully grown oocytes. Follicle-stimulating hormone (5 I1g/ml) was able to increase the percentage of maturing oocytes. The addition of luteinizing hormone (5 I1g/ml) had no effect on GVBD inhibition by cumulus-conditioned medium.growing oocyte / maturation / cumulus cells / pig Résumé ― Inhibitition de la maturation méiotique dans les ovocytes en croissance par des facteurs des cellules du cumulus. La rupture de la vésicule germinative est inhibée dans des ovocytes en croissance de porc (diamètre interne: 80, 90 et 100 ¡lM) cultivés dans un milieu conditionné avec des complexes cumuluslovocytes après croissance. Dans les ovocytes en croissance dénudés, c'est seulement une inhibition partielle qui se produit. L'inhibition est complètement réversible : l'addition d'héparine (300 UIlml) peut renverser l'effet du milieu conditionné. Une exposition transitoire (6 h) des ovocytes à 1 mglml de dibutyryl AMPc (dibutyryl cyclic adénosine monophosphate) est aussi capable de renverser partiellement l'effet des facteurs produits par les cellules du cumulus d'ovocytes après croissance. L'hormone folliculo-stimulante (5 wglml) augmente le taux de maturation des ovocytes. L'addition d'hormone lutéinisante (5¡ l g/ml) n'a pas d'effet sur l'inhibition de la rupture de la vésicule germinative par le milieu conditionné.

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The exposure of in vitro matured pig oocytes to the calcium ionophore A 23187 (50 μM, 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. J. Exp. Zool. 277:49–56, 1997. © 1997 Wiley‐Liss, Inc.

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.