LoxP sites were inserted to flank exon 1. In addition, EGFP-FRT-flanked neomycin cassette was inserted 3' to exon 1. The floxed exon was removed by mating mutant animals to the cre deleter strain FVB/N-Tg(EIIa-cre)C5379Lmgd/J. Protein was undetectable by Western blot analysis of bladder proteins. The EGFP-neomycin cassette was not removed by Cre recombinase.