A cre/ERT2 sequence (cre recombinase fused to a G400V/M543A/L544A triple mutation ofthe human estrogen receptor ligand binding domain) and an FRT-flanked puromycin resistance cassette were knocked into exon 2 of the Axin2 gene. Transient flp expression in ES cells and crosses to flp-expressing strains were unsuccessful at excising the selection cassette, but its presence does not seem to have negative side effects. (J:74286, J:186834)