Cryopreservation of nuclear material as a potential method of fertility preservation

Objective: To establish a cryopreservation method for female nuclear materials with the aim of creating viable embryos or offspring by nuclear transfer. Design: A randomized controlled study. Setting: Clinical and academic research facility. Animal(s): B6D2F1 mice. Intervention(s): Female pronuclei (FPNs) and second polar bodies (2PBs) isolated from superovulated mouse zygotes were cryopreserved, thawed, and transferred into donor zygotes. Main Outcome Measure(s): Survival rates after freeze-thaw and blastocyst formation rates were evaluated. Result(s): Female pronuclei and 2PBs preserved with three tested methods resulted in survival rates ranging from 11.5% to 85% for FPNs vs. 46.9% to 95.0% for 2PBs and blastocyst formation rates ranging from 0% to 35.5% for FPNs vs. 9.1% to 47.4% for 2PBs. Live birth offspring also resulted from both FPNs and 2PBs preserved with vitrification. Conclusion(s): We have established a new system to effectively revive frozen nuclei into viable embryos by a combination of nuclei preservation, zygote reconstruction, and coculturing of reconstructed zygotes with mouse embryonic fibroblast cells. Our data suggest that the preserved female genomic DNA material can be potentially used for future nuclear transfer to preserve female fertility. (C) 2003 by American Society for Reproductive Medicine.