A targeting vector was designed to insert an IRES linked to cre recombinase, followed by a Frt-flanked kanamycin resistance gene downstream of the oxytocin (Oxt) stop codon. The construct was
electroporated into 129S6/SvEvTac-derived W4 embryonic stem (ES) cells. Correctly targeted ES cells were injected into blastocysts and resulting chimeric mice were bred to flp expressing mice to delete the kanamycin selection cassette.