What is Rederivation?
The procedure by which an early, pre-implantation stage embryo is isolated from the reproductive tract of a donor female and transferred to the reproductive tract of a clean recipient pseudopregnant female.
To reduce or prevent the potential for transmission of pathogens from a mouse that is being placed inside a barrier facility.
Early embryo rederivation is a much safer procedure than late embryo caesarean section in avoiding pathogen transfer. Caesarean section is useful for removing bacterial pathogens, endoparasites and ectoparasites but it is limited in its ability to clear up viral infections.
Will my lines require rederivation?
In most cases, yes. Rederivation from early stage embryos provides us with the best possibility of keeping the facility SOPF (Specific Opportunistic Pathogen free). We only accept mice to establish colonies from selected high-health status facilities (e.g. Charles River, Margate, UK and Jackson Labs, Bar Harbor, Maine, USA) and only after a rigrous pathogen screening process. See the Import section for more details.
Does rederivation take more time than standard import for establishing colonies?
Yes, typically it can take up to 6 months (two breeding cycles) to expand colonies to the level required for experimental work to commence. Once embryos have been isolated, they are transferred into pseudopregnant recipients and the pups born can be transferred into the facility once pathogen screening results confirm their clean status. Breeding can then commence in the facility.
For lines rederived as heterozygotes or hemizygotes:
- Investigator will provide at least 5 males (7-25 weeks old) heterozygous, hemizygous or homozygous for the mutation;
- We will provide wild type females from the appropriate background, typically C57BL/6J is requested.
- Note that your rederived offspring will all be heterozygotes (or a mixture of heterozygotes and wild type if the founder males were heterozygotes). The rederived animals will need to be intercrossed by us to generate new homozygous animals.
For lines rederived as homozygotes:
Note: we will only rederive lines as homozygotes if they cannot be rederived as heterozygotes and intercrossed to obtain homozygotes. In the vast majority of cases, homozygous rederivation will not be performed.
- Investigator will provide at least 5 males (7-25 weeks old) homozygous for the mutation;
- Investigator will provide at least 10 homozygous females (21- to 28-day-old if possible though females up to 6 weeks can be used).
- Females are superovulated and embryos collected, pooled, and stringently washed in M2 medium to reduce the risk of pathogen transfer.
- The embryos are surgically transferred, using aseptic technique, into the reproductive tract of pseudopregnant recipient females.
- After weaning, one of the parent females is sent off for detailed health screening.
- Once the health status is ascertained to be clean, the animals can move into the main facility.
- Investigator to complete a rederivation request form through E-mus;
- Provide contact details so the Import Manger can assess health status of the incoming mice (see Import Section);
- Provide males of the appropriate age and genotype;
- All movement of mice into our facility must be coordinated through the Import Manager. See Import Section;
- Females (generally wild type supplied from our facility) will be superovulated, mated to the supplied males and embryos isolated;
- ALTERNATIVELY: We will isolate sperm from these animals, cryopreserve the sperm and use a frozen sample for an IVF with eggs from superovulated females. This service has the advantage that your line is cryopreserved at the same time as being rederived;
- Embryos will be transferred into SOPF pseudopregnant recipients;
- After litters have been weaned, one or more female parents will be sent off for pathogen screening. Faecal pellets from the weaned mice are also screened;
- The Rederivation Core will return to the investigator at least one breeding pair of SOPF health status. The procedure can be customized to accommodate larger numbers;
- Once a clear pathogen screening test result is received, the animals will be moved into the main facility;
- Once genotyping by the investigator confirms the animals have the appropriate genetic status, the original imported males will be culled.
The Rederivation Core cannot guarantee success though experience indicates rederivation is mostly successful as long as the animals used for import are fecund.
The procedure typically takes around 12 weeks though can be as short as 8 weeks.
Further information of importing lines and rederivation can be found in our FAQs.