A loxP site was inserted 3' of exon 12 of the Vmp1 gene and 5' of the Mir21 sequence. Mir21 was then followed by an FRT flanked PGK-puro/deltaTK selection cassette and a second loxP site. Mir21 and the selection cassette were then excised by crossing properly targeted mice to Tg(EIIa-cre)C5379Lmgd mice. Northern blot and PCR analysis confirmed the absence of MIR21. (J:179235)