Cryopreservation by embryo freezing
The number of genetically altered lines developed and maintained for research in animal facilities continually increases. Laboratories often develop their own strains, genetically modified for specific purposes. The high value of these strains often results in their continued maintenance, even though they may not be utilised for long periods. Such maintenance may produce excess animals, and is also financially expensive.
Cryopreservation of valuable strains as frozen embryos provides a less expensive, more ethical and efficient means of maintaining them. Cryopreservation may also provide a ‘back-up’ for stocks and strains held within the animal facility and a source of animals free from microbiological and genetic contamination.
Embryos from a pregnant female are removed at the 8-cell stage of development and frozen in a cryoprotectant medium. They are then frozen for long term storage in liquid nitrogen. When required by the customer, the strain can be revitalized by thawing the embryos and re-implanting them into a pseudo-pregnant female. This is only carried out after the vitality and viability has been checked by in vitro culture.
Animals (heterozgotes or homozygotes) are received into our Quarantine area and mated to obtain embryos for freezing at the 8-cell stage. Between 200 and 300 embryos are frozen in cryotubes, each containing about 40 embryos. During the process, various tests are carried out to verify the quality of the freezing procedure. A number of the embryos are cultured in vitro at the following stages of the process: before addition of the cryoprotectant, before freezing and after one week of crypreservation in liquid nitrogen. Embryo culture progresses until the blastocyste stage.
The process of embryo freezing can be combined with rederivation.
The embryo-cryopreservation service is for the moment only available through the Harlan UK transgenic services plateform.