Exon 2 was flanked by loxP sites and a positive-selection neomycin cassette flanked by FRT sites was inserted downstream of exon 2. The neomycin cassette was excised by FLP-mediated recombination. The floxed exon 2 from Mir22tm1.1Dzw was removed via Cre-mediated recombination leaving a single loxP in place of exon 2. Northern blot and quantitative real-time PCR analysis confirmed absence of expression. (J:213308)