Induction of nuclear breakdown and meiosis in Spisula solidissima oocytes by calcium ionophore.

Induction of germinal vesicle breakdown and reinitiation of the meiotic process resulted following exposure of immature Spisula solidissima oocytes to divalent ionophore A23187. Meiosis continued to completion in the presence of the ionophore; however, parthenogenetic development of the gametes did not occur. Incubation of oocytes in calcium deficient media (Ca++ free or Ca++Mg++ free seawater) but not Mg++ free seawater inhibited ionophore induced maturation. Effects of calcium deficiency were reversible. The results suggest that nuclear disintegration and the meiotic process induced by sperm are mediated by ionic stimuli and that the establishment of meiotic arrest is linked to the availability of calcium within the oocyte.