The transgene construct contains an optimized reverse tetracycline-controlled transactivator, rtTAS*M2, or rtTA2S-M2, under the control of the mouse Axin2 expression cassette (which contains 2883 nucleotides upstream of exon 1, exon 1, intron 1 and part of exon 2). Founder line 7 was established. (J:119927)