Precocious induction of activation responses in amphibian oocytes by divalent ionophore A23187

Temporal relationships between maturational events and the onset of activation in response to divalent ionophore and to pricking were examined following in vitro exposure of Rana pipiens oocytes to desoxycorticosterone acetate (DOCA). Activation was evaluated on the basis of vitelline envelope elevation and cortical granule breakdown. Ionophore-induced activation was first observed after 18 hr of DOCA incubation, coincident with the time of separation of the vitelline envelope from the oocyte surface and 2–3 hr after breakdown of the germinal vesicle. Activation in response to pricking was not observed until 30 hr of DOCA incubation. Neither ionophore treatment nor pricking resulted in activation of oocytes that had not been incubated with DOCA. These results indicate that oocytes can be activated many hours earlier than previously demonstrated. The time of onset of the capacity for activation appears to be related to germinal vesicle breakdown and vitelline envelope separation.