A loxP site was inserted into intron 3 and an FRT site flanked neomycin resistance gene cassette and a second loxP site into intron 4. The neo cassette was removed through subsequent flp-mediated recombination. Exon 4 was deleted through subsequent cre-mediated recombination. Western blot analysis showed an absent of expression in mouse embryonic fibroblasts, liver, and epididymal adipose tissues.