A targeting vector was designed to insert a single loxP site, followed by a frt-flanked neomycin resistance (neo) cassette, upstream of exon 2 of the gene. A 3X Flag sequence and a second loxP site were inserted into exon 2, upstream of the Nkx2-5 stop codon. FLP mediated recombination removed the FRT-flanked neo cassette. (J:101977)