Parthenogenetic activation of mouse oocytes induced by inhibitors of protein synthesis

Recently ovulated mouse oocytes at the Metaphase II stage undergo parthenogenetic activation (as indicated by the formation of pronuclei) when incubated for 6 h in the presence of cycloheximide or puromycin; the activation response increases progressively with the concentration of inhibitor. Activation is induced with concentrations of cycloheximide that depress protein synthesis by more than 70%. Pronoculear formation occurs when protein synthesis is almost totally inhibited. Incubation of oocyte in Actinomycin D failed to initiate activation. The results show that the Metaphase II oocyte of the mouse synthesizes protein factor(s) which are necessary for the maintenance of the meiotic block. Other protein(s) having opposite effects and a different rate of turnover may also participate in activation since when the oocytes are treated with a high concentration of cycloheximide (10 microgram ml-1) for varying periods of time, or with varying concentrations for a short period of time (1 h), a more complex activation response curve is obtained. Oocytes activated with cycloheximide are capable of further development, following transfer to the oviducts of pseudopregnant recipients, in a proportion similar to that of oocytes activated in other ways.