A targeting vector containing, from 3' to 5': a single residual FRT site, an Engrailed 2 (En2) intron and H2B/Venus fusion cassette, a Rox-flanked beta-actin-NEO-pA cassette, and a loxP site was inserted upstream of exon 2. A second loxP site was inserted downstream of exon 2. Exon 2 contains the ATG start codon. (J:101977, J:264612)