A loxP site was inserted upstream of exon 12. An FRT- and loxP-flanked neomycin resistance cassette was inserted downstream of exon 12. Flp-mediated recombination removed the selection cassette and left exon 12 floxed. Cre-mediated recombination removed exon 12 and results in premature truncation in the C-terminus. Western blot analysis confirmed low expression levels of a truncated protein in bone marrow-derived macrophage.