Engineering Inducible Knock-In Mice to Model Oncogenic Brain Tumor Mutations from Endogenous Loci.

To maximize the physiological relevance of in vivo brain tumor mouse models designed to study the downstream effects of oncogenic mutations, it is important to express the mutated genes at appropriate levels, in relevant cell types, and in the proper developmental context. For recurrent mutations found in the heterozygous state in tumors, expression of the mutation from the endogenous locus is a more physiologically relevant recapitulation of the brain tumor genome. Here, we describe an approach to generate knock-in mice with an inducible mutation recombined into the endogenous locus. In these engineered mice, the mutated allele is designed for expression controlled by the endogenous promoter and regulatory elements after Cre recombinase-mediated deletion of a loxP-STOP-loxP cassette inserted upstream of the translational start site. To preserve the structure of the endogenous locus, mutations or additional elements may need to be inserted at a considerable distance from the loxP-STOP-loxP cassette. We used recombineering to build a construct with two selectable markers and multiple genetic alterations that can be introduced into the endogenous allele in cis with a single ES cell targeting.