A neomycin resistance cassette flanked by FRT sites and with a 5' loxP site was inserted in intron 1. An additional loxP site was also inserted in intron 2. The neomycin cassette was subsequently excised by crossing with flpe-deleter mice. Exon 2 was then removed by crossing with Tg(CMV-cre)1Cgn mice. (J:108628)