In transactivator mice, tTA is expressed in HSCs and progenitors under control of the SCL enhancer, whereas transresponder mice do not express the BCR-ABL transgene regulated by the tetracycline response element (TRE). In double-transgenic progeny, tTA is repressed in the presence of tetracycline (Tet) but can transactivate the BCR-ABL gene in HSCs upon withdrawal of antibiotic. For details, see the article by Koschmieder et al beginning on page .
