A loxP site was inserted into intron 1 and an FRT site flanked neomycin selection cassette and a second loxP site into intron 2. The neo cassette was removed via flp-mediated recombination and exon 2 was deleted via cre-mediated recombination in the germline. Western blot and qRT-PCR experiments confirmed the lack of peptide and transcript expression from this allele in liver and heart.