The targeting construct inserted into the locus a splice acceptor from pBigT, puromycin resistance gene, bovine growth hormone polyA sequence, CAGGS enhancer/promoter/intron/SA cassette, a floxed tpA (3 SV40 polyA sequences from pBigT), Axin1 with a Myc epitope tag, cassette containing IRES2-LacZ preceded by a nuclear localization signal and finally the pCAGGS polyA sequence. (J:306371)