The targeting vector was designed to have a loxP site upstream of exon 2, followed by an FRT-flanked neo cassette. An F3-flanked puromycin cassette followed by a second loxP site is located downstream of exon 6. Exons 2-6 were duplicated and inserted downstream of the second loxP site, and an L252P amino acid substitution (orthologous to the human L265P mutation) was introduced into duplicated exon 5. Flp-mediated recombination removed the neo and puromycin cassettes. (J:232098)