A loxP site was inserted upstream of exon 1b. An FRT- and loxP-flanked hygromycin resistance cassette was inserted downstream of exon 2. Cre-mediated recombination removed exon 1b, exon 2 and the hygromycin resistance cassette. Western blot analysis confirmed the absence of protein expression in the uterus, rectum, colon, placenta and spleen.