A targeting vector is used to insert a loxP site and an FRT-site flanked PGK-NEO cassette into intron 1 followed by a second loxP site downstream of exon 3. Flp-mediated recombination removed the FRT-flanked neo cassette leaving exons 2 and 3 floxed. Cre-mediated recombination removed the exons 2 and 3.