Why did we fund this project?
This award aims to refine the production of genetically modified (GM) mouse models by using sterile hybrid male mice generated by breeding two wild-type mouse strains.
Breeding programmes for GM animals require modified embryos to be transferred into recipient female mice. Prior to implantation, recipient mice must be mated with sterile males to create a pseudopregnancy in preparation for receiving the embryo. Male mice therefore either undergo surgical vasectomy under anaesthesia or require extensive breeding programmes to generate sterility. Dr Ben Davies has established a new method of generating naturally sterile mice by mating two wild-type strains of mice. Mating mice in this way results in all males being naturally sterile compared to the 12.5% in breeding programmes reducing the number of mice required.
Ben will collaborate with MRC Harwell and the University of Manchester to validate the pseudopregnancy rate of females mates with the hybrid sterile males in comparison to historical data from all three facilities. They will also determine whether the female mice produced are able to act as recipients for embryos to enable all animals from the breeding programme to be used. Hybrid embryos will be cryopreserved to enable uptake by other researchers.
To produce and distribute genetically modified (GM) mouse models, pseudopregnant embryo transfer recipients are required. For their preparation, vasectomized mice are commonly used, generated by surgical procedures associated with pain and discomfort. Sterile GM strains provide a non-surgical replacement. However, maintenance of GM strains requires extensive breeding and genotyping, which are regulated procedures and their breeding leads to a large wastage of animals, as mice of incorrect genotype are discarded. In contrast, certain wild-type hybrid males, generated by the simple intercrossing of two different wild-type strains, are sterile. We have been exploring the use of these sterile hybrids as alternatives for producing pseudopregnant embryo transfer recipients and find their behaviour to be indistinguishable from those generated by vasectomized males.
The method provides two substantial 3R impacts
- refinement, when comparing the use of these naturally sterile hybrids with vasectomized males, as clearly no surgical procedures are necessary
- reduction, when comparing the use of these naturally sterile hybrids with sterile GM mice, as the breeding is substantially more efficient, with all males born from production crosses being suitable for use.
The value of a 3Rs initiative is only as good as the uptake in the community. We thus plan to select a naturally sterile hybrid, which can be generated from strains which are common and easily sourced: the F1 hybrid between Mus spretus and C57BL/6 is a good candidate and we have confirmed the sterility of this strain and its good husbandry characteristics.
We seek funding from the NC3Rs to validate the use of this hybrid as a replacement for surgical vasectomized or sterile GM males. Importantly, we plan to achieve this comparison within three different research environments and thus validate its dissemination to achieve a maximal 3Rs impact.