The PHD fingers of MLL inhibit MLL-AF9 mediated transformation of mouse bone marrow. (A) MLL-AF9 and MLL-PHD-AF9 fusion constructs were engineered into the MSCV retroviral vector and transduced into mouse bone marrow. The final amino acid number of MLL in each construct is indicated with a dotted line. *indicates the absence of amino acids 1407 to 1432. Domains are colored-coded according to panel B. Bar graph indicates numbers of colonies per 10 000 cells plated in tertiary colony assays of transduced cells. Error bars indicate SD from duplicate experiments. (B) Schematic representation of wild-type MLL with color-coded domain structure. (C) Colony assays are shown after tertiary plating. Dense colonies were visible after tertiary plating only in MLL-AF9 and MLL-PHD#1-AF9–transduced cells. Representative dense transformed colonies are shown in insets. Micrographs were obtained using Olympus IX50 microscope, 10×/0.30 UPlanF1 Ph1 objective lens, Olympus DP70 camera, Olympus DP70 acquisition software, and Olympus DP contoller software (all Olympus, Center Valley, PA). (D) Real-time PCR detected expression of MLL-AF9 fusion constructs from cDNA generated from cells collected after the first round of colony assays. Expression is shown relative to MLL-AF9. Error bars indicate SD of experiments performed in triplicate.