A Cre cDNA, a polyadenylation signal (pA) from the human granulocyte-colony stimulating factor gene, a phosphoglycerate kinase (PGK) promoter-driven neomycin resistance gene (neo)-pA cassette (PGK-neo-pA cassette) flanked by two frt sites were inserted into the translation initiation
site (in exon 2) of the mouse Slc6a5 gene by homologous recombination in ES cells. The PGK-neo-pA cassette was removed by crossing mice with FLP66 transgenic mice.