RMCE on KH2 cells inserted into the 3'UTR a RNU6 promoter driving expression of a single guide RNA targeting a nongenic region on mouse chromosome 8 followed by a tetracycline response element promoter driving inducible expression of a GFP report gene, IRES sequence, human codon optimized CRISPR-associated endonuclease cas9 (derived from Streptococcus pyogenes CRISPR associated protein 9 [SpCas9]) and polyadenylation sequence.