A targeting vector was designed to insert an F3 site followed by an attB site and a loxP site upstream of exon 10. Inserted downstream of exon 10, from 5'to 3' are a second loxP site, an attP site, a FRT site, a neomycin resistance cassette, a second F3 site, and a mutated exon 10 with four aspartate residues mutated into alanine residues (D4A) followed by a second FRT site. (J:101977)