Time-dependent effects of α-amanitin on nuclear maturation and protein synthesis in mammalian oocytes

The addition of α-amanitin to extrafollicular, cumulus-enclosed ovine oocytes at explantation inhibits meiotic maturation and prevents many of the changes in protein synthesis that normally accompany maturation. By contrast, these inhibitory effects are considerably reduced by eitherdelaying the addition of the drug for 1–4 h or by denuding the oocytes of all associated cumulus cells at the onset of culture. The observations that the inhibitory effect of cordycepin onnuclear maturation is also time-dependent and cumulus-cell-dependent and that the oocyte is susceptible to cordycepin for longer than its sensitivity to α-amanitin are consistent with the differential effects of these drugs on RNA synthesis. It is concluded that a transcriptional event at the onset of maturation is essential for the initiation of those changes in protein synthesis required for the regulation of nuclear and cytoplasmic maturation. It is uncertain, however, whether this transcriptional event occurs within the cumulus cells or within the oocyte.