A loxP site was inserted upstream of exon 2. An FRT-flanked neomycin resistance cassette with a 5' loxP site was inserted upstream of exon 3. Flp-mediated recombination removed the selection cassette. Cre-mediated recombination removed exon 2. Western blot analysis confirmed the absence of protein expression in the heart, lungs, brain and kidney at P0. (J:228948)