A loxP site and a frt-flanked neomycin resistance cassette were inserted between exons 3 and 4, and a second loxP site was inserted between exons 11 and 12. Founder mice were crossed to a transgenic strain expressing Flp recombinase (Tg(ACTFLPe)9205Dym mice) to remove the neomycin cassette and leave exons 4 through 11 flanked by loxP sites. Southern blot and PCR analyses on genomic DNA confirmed that the correct targeting and recombinase events occurred.