An attempt of cryopreservation of mouse embryos at the ACTREC laboratory animal facility in India

Hollow fiber vitrification allows cryopreservation of embryos with compromised cryotolerance

PURPOSE

This study aims to demonstrate vitrification methods that provide reliable cryopreservation for embryos with compromised cryotolerance.

METHODS

Two-cell stage mouse embryos and in vitro produced porcine embryos were vitrified using the hollow fiber vitrification (HFV) and Cryotop (CT) methods. The performance of these two methods was compared by the viability of the vitrified-rewarmed embryos.

RESULTS

Regardless of the method used, 100% of the mouse 2-cell embryos developed successfully after vitrification-rewarming into the blastocyst stage, whereas vitrification tests using porcine morulae with the HFV method produced significantly better results. The developmental rates of vitrified porcine morula into the blastocyst stage, as well as blastocyst cell number, were 90.3% and 112.3 ± 6.9 in the HFV group compared with 63.4% and 89.5 ± 8.1 in the CT group (P < .05). Vitrification tests using 4- to 8-cell porcine embryos resulted in development into the blastocyst stage (45.5%) in the HFV group alone, demonstrating its better efficacy. The HFV method did not impair embryo viability, even after spontaneous rewarming at room temperature for vitrified embryos, which is generally considered a contraindication.

CONCLUSION

Vitrification test using embryos with compromised cryotolerance allows for more precise determining of effective cryopreservation methods and devices.

Strain preservation of experimental animals: vitrification of two-cell stage embryos for multiple mouse strains

Strain preservation of experimental animals is crucial for experimental reproducibility. Maintaining complete animal strains, however, is costly and there is a risk for genetic mutations as well as complete loss due to disasters or illness. Therefore, the development of effective vitrification techniques for cryopreservation of multiple experimental animal strains is important. We examined whether a vitrification method using cryoprotectant solutions, P10 and PEPeS, is suitable for preservation of multiple inbred and outbred mouse strains. First, we investigated whether our vitrification method using cryoprotectant solutions was suitable for two-cell stage mouse embryos. In vitro development of embryos exposed to the cryoprotectant solutions was similar to that of fresh controls. Further, the survival rate of the vitrified embryos was extremely high (98.1%). Next, we collected and vitrified two-cell stage embryos of 14 mouse strains. The average number of embryos obtained from one female was 7.3-33.3. The survival rate of vitrified embryos ranged from 92.8% to 99.1%, with no significant differences among mouse strains. In vivo development did not differ significantly between fresh controls and vitrified embryos of each strain. For strain preservation using cryopreserved embryos, two offspring for inbred lines and one offspring for outbred lines must be produced from two-cell stage embryos collected from one female. The expected number of surviving fetuses obtained from embryos collected from one female of either the inbred or outbred strains ranged from 2.9 to 19.5. The findings of the present study indicated that this vitrification method is suitable for strain preservation of multiple mouse strains.

Re-establishment of a breeding colony of immunocompromised mice through revival of cryopreserved embryos

Cryopreservation of embryos or germ cells is commonly used in animal facilities to archive strains of genetically modified mice, both to reduce facility space usage and to protect the strains from losses due to environmental disaster, genetic drift, disease outbreak or breeding failure. The authors' institution maintains a cryopreservation repository for various mouse strains, including immunocompromised mice. When the institution experienced a breeding failure with one strain of immunocompromised mice (NOD.CB17-Prkdc(scid)/NcrCrl), the authors successfully re-established a breeding colony of the mice by reviving frozen embryos from the institution's cryopreservation repository. They confirmed that the recovered progeny lacked T and B cells. The authors conclude that a breeding colony of immunocompromised mice can be successfully re-established from a minimal number of cryopreserved embryos.