Mirimus specializes in the generation of RNAi tools for effective gene silencing to induce up to 95% gene silencing with only a single-copy integration into the genome. Thus, a near-knockout phenotype can be achieved with only one copy of the transgene. Hypomorphic phenotypes may also be achieved using less potent shRNAs. We have previously generated RNAi mouse models in which a tet-inducible promoter (TRE) was used drive expression of a miRE-based shRNA targeting a gene of interest (GOI), in the presence of a reverse tet-transactivator (rtTA3). Using a recombination mediated approach, a tet-inducible GFP-coupled shRNA is inserted at the “safe-harbor” Col1a1 locus via mouse embryonic stem cell targeting. This insertion does not affect the expression of the Col1a1 gene but does confer wide-spread expression of the shRNA cassette. Our pre-engineered ESCs also contain either a CAG-rtTA3 or Rosa26-M2rtTA cassette for ubiquitous shRNA expression. Please note that the rtTA3 cassette is not linked to the shRNA cassette, thus mice can be crossed to additional tet-transactivator strains.