An FRT-flanked neomycin resistance cassette with a 5' loxP site was inserted upstream of exon 1. An additional loxP site was inserted downsteam of exon 3. Flp-mediated recombination removed the selection cassette. Cre-mediated recombination removed exons 1 through 3 floxed. Western blot analysis confirmed the absence of protein expression in embryos.