Overexpression of HOXA9 enhances cell proliferation and emergence of myeloid progenitors in a DNA-binding–dependent manner. (A) Bone marrow cells isolated from 5-FU–treated Hoxa9^−/− mice were transduced with retroviral vectors expressing GFP alone (vector), or GFP together with either HOXA9 or the HOXA9NS DNA-binding mutant, and then placed in liquid suspension cultures. Viable cells were counted every 2 to 3 days for up to 10 days. The proliferation rate of cells transduced with wild-type HOXA9 was dramatically enhanced compared with cells transduced with the DNA-binding mutant or GFP alone. (B) After 8 days in culture, aliquots of the transduced cells described in panel A were plated in clonogenic assays to measure the number of committed myeloid progenitors. Wild-type HOXA9 effected a marked increase in colony numbers compared with the vector control and with the DNA-binding mutant (*P < .01). These experiments were repeated 3 times. Error bars indicate standard error.