CRYOPRESERVED MOUSE EMBRYOS CAN SUCCESSFULLY SURVIVE BIOPSY AND REFREEZING

Objective: We examined whether cryopreserved mouse eight-cell embryos could be thawed, biopsied, refrozen, thawed, and grown in vitro and in vivo in two sets Of experiments. Method: In the in vitro studies, the blastulation rate of cryopreserved embryos which had been thawed --> biopsied --> refrozen --> thawed --> grown 48 hr in vitro were compared with that of sham-operated (zona dissected) and untreated control embryos (twice frozen only). For the in vivo studies, five control embryos were transferred to one horn and five experimental embryos were transferred to the contralateral horn of day 3 pseudopregnant recipient female mice. Recipient mice were sacrificed on day 18. Results: The day 2 blastulation rate was the same for the control, sham-operated, and biopsied embryos when examined in vitro. In the first set of in vivo studies, 42.7% of control and 39.7% of sham-operated embryos that had been transferred implanted, and most embryos progressed to day 18. In the second set, 45.6% (57/125) and 39.7% (49/125), respectively, of the transferred embryos progressed to day 18 fetuses. There were no significant differences in the rate of fetal development in the different groups. Conclusions: These studies demonstrate that cryopreserved mouse eight-cell embryos can successfully undergo thawing, biopsy, and refreezing. The results suggest that under certain conditions, it may be possible to utilize cryopreservation in strategies involving human genetic diagnosis in the preimplantation period.