A construct containing CMV-IE enhancer/chicken-actin/rabbit beta-globin hybrid promoter (CAG), FRT site, loxP-flanked STOP cassette (with stop codons in all three reading frames and a triple poly(A) signal), flag-Kcnj2-2A-tdTomato sequence, WPRE, polyA signal, attB/attP-flanked PGK-FRT-neomycin cassette, and polyA was inserted between exons 1 and 2 of the locus. (J:335141)