Cryopreservation of activated mouse oocytes and zygote reconstitution after thaw

A new approach to cryopreservation of unfertilized oocytes is proposed using techniques of artificial egg activation combined with nuclear transplantation. Matured mouse oocytes were released from metaphase II arrest by brief exposure to alcohol, allowed to progress to the pronuclear stage and then frozen according to a standard freezing protocol in propandiol. After thaw the female pronuclei were enucleated and fused with a male karyoplasts that were divided from in-vivo fertilized zygotes. Reconstituted zygotes, fresh and cryopreserved culture control zygotes were cultured to the blastocyst stage and transferred to pseudopregnant recipients. The rate of blastocyst formation was 75.8, 91.6 and 44.1% respectively. A total of 110, 215 and 70 blastocysts were transferred to pseudopregnant females respectively. The implantation rates were 36.4, 72.0 and 75.7% while the rates of fetal viability at mid-gestation were 15.5 (P < 0.0001), 51.1 and 37.1% respectively.