CRISPR/cas9 meditated recombination inserted a cassette containing a modified human ACE2 cDNA, loxP site, woodchuck hepatitis virus post-transcriptional regulatory element, simian virus 40 polyA sequence, loxP site, and an FRT-flanked PGK-neo and loxP site directly after the ATG site in exon 2. The human ACE2 cDNA was modified to use the mouse Ace2 signal peptide and codon-optimized for a mouse. (J:315719)