Cryopreservation is cost and time saving method enabling preservation of valuable transgenic lines that are not currently in use.

Freezing of sperm or embryos is always recommended, as they constitute a ‘back-up’ in case of disease outbreak, fertility problems, spontaneous phenotype loss, etc. A complete cycle of cryopreserving a strain and reconstituting it from frozen material involves the same biological steps whether one uses embryos or sperm. In both cases, the production of fertilized embryos is the most expensive step. With embryo cryo, the fertilization step takes place before freezing, whereas with sperm cryo it is done after thawing.


For embryo freezing the Investigator should provide 6-10 practiced stud males, 3-6 months of age. The core will cryopreserve at least 300 embryos/line (heterozygotes)  or 200 embryos/line (homozygotes) at the morula or blastocyst  stage. 

For sperm cryopreservation we will freeze the sperm isolated from 3-5 practiced males (3-6 month of age) per line.

Comparison of mouse sperm and embryo cryopreservation:





Cheaper to cryopreserve, requires 1 day of work, requires only 3-5 males/line

Embryos are frozen post fertilization, easier to recover the offspring


The only gemetes that are frozen are males, rerival through IVF (costly and labor extensive), must use WT females as egg donors (the offspring always heterozygous)

More animals required, males and young females, requires the hormonal induction of superovulation,

Number of animals needed

Minimum 3 males/line

3-5 males and  and 8-20 young females

Days of experiment

1 day

At least 4-6 weeks,

Additional cost-recovery

IVF + embryotransfer 



The Nencki Institute Bank of Cells, Semen and Embryos of Transgenic Animals was created as part of the RPMA.01.01.00-14-025 / 10 project.