An FRT-flanked neomycin resistance cassette with a 5' loxP site was inserted upstream of exon 2. An additional loxP site was inserted downstream of exon 2. Flp-mediated recombination removed the neomycin resistance cassette and left exon 2 floxed. Cre-mediated recombination removed exon 2. Western blot analysis confirmed the absence of protein expression.