A floxed hygro cassette was inserted upstream of exon 2 and a floxed neo cassette was inserted in the intron after exon 14. Successfully recombined ES cell clones were subjected to transient expression of Cre recombinase by transfection of pMC1-Cre. The resulting clone 18 with exons 2 to 14 floxed was used for the germline transmission. (J:245455)