The targeting construct is designed to replace exon 2 with a human ACE2 cDNA inserted in-frame with the endogenous initiation codon. in addition, a loxP site is placed upstream of the ACE2 cDNA and a FRT-flanked neomycin resistance (neo) cassette and a second loxP site is placed downstream of the ACE2 cDNA. Flp-mediated recombination removed the FRT-flanked neo cassette. (J:296356)