Description of facility

The MCCA Transgenic facility provides the typical services related to the generation and cryopreservation of mutant mouse strains, such as construct design, Embryonic Stem Cell (ESC) culture, micro-injection and sperm cryopreservation. On top of that we have developed a new pipeline for the fast and easy modification of existing Genetically Engineered Mouse Models (GEMMs), called the GEMM-ESC strategy (Huijbers et al., Nature Protocols 2015). This approach is based on the re-derivation of ESCs from existing mouse strains. The re-derived ESCs, referred to as GEMM-ESCs, contain all the modified alleles present in the original strain and can be used for further genetic engineering, either by classic targeting, genome editing or recombinase-mediated transgene integration (Addgene vectors 63575, 63576). Once the newly introduced modifications have been validated, the GEMM-ESCs are micro-injected into either morula or blastocysts to generate chimeric animals. Provided the chimeras are of high quality, they can be directly used in an experimental cohort, omitting any breeding. This is particularly relevant for mouse models of human cancer. The chimeras can also be mated with the original GEMM from which they were derived to establish a stable line.

The GEMM-ESCs strategy has many benefits

1) Fast modification of complex models; by re-deriving ESCs from existing GEMMs all the energy that has been invested in the original model, for instance in phenotyping and backcrossing, is captured and used as the basis for further manipulations.
2) Shift from large breeding colonies to more focused experimental cohorts. The GEMM-ESCs strategy is ideally suited for the generation of allelic series, allowing for side-by-side comparison of phenotypes in chimeric animals.
3) Suitable for all mouse strains. Our ESC culture is performed in 2i medium, which allows us to derived ESCs from all strain backgrounds, including C57Bl6 and FVB.
4) Easy distribution; a bank of GEMM-ESCs will be established at the MCCA and distributed via the European Mouse Mutant Archive (EMMA, via www.infrafrontier.eu) to make models accessible to the scientific community.

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