The Viability of Frozen-Thawed Mouse Blastocysts

The successful preservation of mouse embryos at sub-zero temperatures has been accomplished with suitably slow rates of cooling and thawing and in the presence of the cryoprotective agent, dimethylsulphoxide (DMSO). In the first report, full-term fetuses and live young were obtained from one-cell, two-cell and eight-cell embryos stored at −196°C for up to 8 days (Whittingham, Leibo & Mazur, 1972) and more recently eight-cell embryos were stored for 8 months at −196°C without any deterioration in viability (Whittingham & Whitten, 1974). The viability of frozen-thawed mouse blastocysts has only been demonstrated by their subsequent expansion during 24 hr in culture. When DMSO was added to the blastocysts at 0°C before freezing and diluted out at 0°C on thawing, the percentage surviving (18%) was low (Whittingham et al., 1972) but higher survival rates (up to 86%) were obtained when DMSO was added and diluted in several increments at 20°C (Wilmut, 1972).