Activation of mammalian oocytes by intracellular injection of calcium

OOCYTES of many species undergo parthenogenetic activation after exposure to the calcium ionophore, A23187, even in the absence of external Ca2+ (refs 1 and 2), whereas those of mouse, rat and hamster will activate simply on exposure to Ca2+ free medium3,4. This suggests that Ca2+ is involved in parthenogenetic activation. Direct evidence of a transient increase in intracellular free Ca2+ at the time of fertilisation or activation of fish5 and sea urchin eggs6 has been obtained using the photoprotein aequorin. We report here that parthenogenetic activation and subsequent normal development can be induced in mouse oocytes by injecting them with Ca2+.