Two LoxP sites were placed flanking exon 7 of the gene. A cassette containing SAIREStdTomato and an inverted PGKNeo (neomycin phosphotransferase gene) were flanked by two FRT (FLP recombinase target) sites and inserted between the first LoxP site and exon 7. A WPRE (woodchuck hepatitis post-transcriptional regulatory element) sequence was placed immediately downstream of tdTomato to enhance its expression. (J:217675)