In vitro transformation ofHox-deficient hematopoietic progenitors byMLL-GAS7. (A) HPTAs using various MSCV retroviruses encoding MLL-GAS7 (MG), E2A-HLF (HF), or vector alone were performed on progenitors harvested from wild-type, Hoxa7^-/-, Hoxa9^-/-, and Hoxa7^+/-Hoxa9^+/- mice. Bar charts represent the average number of colonies obtained in each round of methylcellulose plating in 3 different independent assays. Error bars indicate SD. (B) Blast-type morphology of colonies induced by MLL-GAS7 in progenitors derived from different Hox-deficient genetic backgrounds. (C) RT-PCR analysis of Hoxa7 and Hoxa9 expression in normal and transformed hematopoietic cells. (Top) Differential expression of Hox genes in highly purified populations of hematopoietic stem cells and progenitors. (Bottom) Appropriate expression of Hox and fusion transcripts in transformed cells. Transcripts are listed to the left; progenitor genotypes and transduced genes are indicated above the lanes.