Mouse Strain Rederivation (MSR) and Import

Frozen Embryo Import (FEI) is a rapid and cost-effective way of introducing new mouse strains into the facility. Current cryopreservation protocols such as slow freezing or vitrification generally ensure good cryo-recovery rates and our transfer and quarantine SOPs allow the import and rederivation of embryos originating from hygienically compromised mouse colonies.

The CTM will implant the embryos provided by the researcher into microbiologically defined recipient females. The resulting offspring will be turned over to the researcher once the hygiene status of the new colony has been confirmed by an independent testing laboratory.

In order to carry out successful rederivation; the CTM must receive sufficient numbers of embryos. Generally we require at least 60 viable embryos distributed in 2-3 cryopreservation samples (cryotubes or straws). The embryos should be shipped directly of the CTM by the means of dry LN2 shipper.

Frozen sperm import allows the researcher to rederive the strain from cryopreserved sperm samples by means of in vitro fertilization (IVF). In general FSI is more problematic then LSI or FEI as the success of IVF is frequently strain dependent.

The CTM will use the sperm to fertilize oocytes isolated from wild-type females and the viable embryos will be surgically implanted into microbiologically defined recipient females. Any resulting offspring will be turned over to the researcher once the hygiene status of the new colony has been confirmed by an independent testing laboratory.

In order to carry out successful rederivation; the CTM must receive sufficient numbers of samples. Generally we require at least in 2-3 cryopreservation sperm samples (cryotubes or straws). The materials must be shipped in liquid nitrogen (or dry ice) directly to the CTM.

Live Strain Import (LSI) is a common means of distributing mouse strains. The main advantage of this approach is that live mice can be bred to ensure sufficient supply of embryos for rederivation thus minimizing the risk of losing valuable lines.

The CTM will use the mice imported / provided by the researcher to generate embryos which will subsequently be implanted into microbiologically defined recipient females. The resulting offspring will be turned over to the researcher once the hygiene status of the new colony has been confirmed by an independent testing laboratory.

In order to carry out successful rederivation; the CTM must receive sufficient numbers of starting mice. The preferred option is to use transgenic males which are mated to wild-type C57Bl/6 females. In this case 3-5 fertile males are usually sufficient as they can be mated repeatedly with multiple females. In the case of strains with complex genotypes where the rederivation has to be carried out using both transgenic male and females, the CTM requires 3-5 fertile males and 6-10 young (4-12 weeks) females.