The targeting construct contained Fgfr2 exons IIa, IIb, IIIc, and exon 10, which codes for the transmembrane domain, a floxed neo cassette, and an A to G transition resulting in the amino acid substitution of Y for C at position 394 (Y394C) in exon 10. This mutation is analogous to the Y375C substitution in humans. The neo cassette was removed via cre-mediated recombination.