Cryopreservation and Assisted Reproduction Laboratory - Expertise
Embryo cryopreservation is particularly useful for maintaining the genotype of homozygous strains.
For most strains 500 8-cell embryos are collected and cryopreserved. However, some strain backgrounds
may not freeze well and some mutations may interfere with the cryopreservation process. For these it
is necessary to bank between 750 and 1,000 embryos. Quality control is performed on all strains once
they have been cryopreserved. Quality control consists of thawing one or two random vials of
cryopreserved embryos, transferring to pseudopregnant females and recovering liveborn pups.
Sperm cryopreservation is a cost-effective method of cryopreserving mouse strains if maintaining
homozygosity is not a concern. Caudae epididymides are removed from 5-8 males (3-8 months old) and
sperm samples are collected and cryopreserved in multiple vials. Quality control consists of
performing in vitro fertilization (IVF) with a randomly selected thawed sperm sample and hybrid
oocytes. Following transfer of the IVF embryos to pseudopregnant females, liveborn pups are
Ovary cryopreservation is a cost-effective method of cryopreserving strains. Ovaries are removed
from 4-5 females and cryopreserved. This method is recommended for strains in which sperm or embryo
cryopreservation is not efficient. The frozen and thawed half-ovaries are implanted in ovariectomized
female recipients, which after recovery from surgery will be mated with selected males, obtaining
pregnancies derived from the implanted ovary.
In vitro fertilization may be effectively used to rapidly expand a colony either for experimental
or breeding purposes. It is particularly effective for strains that are maintained by forced
heterozygosity in a continuous backcross to an inbred strain. In this case it is possible for a
single male to produce 500 or more offspring in a single IVF.