Model of Hoxa9/Meis1/Trib1 interaction in leukemogenesis. Cooperation of Hoxa9 and Meis1 up-regulates Flt3, and as a result the hematopoietic cells are sensitive for cytokine signals. Trib1 enhances the downstream response and thus Mapk phosphorylation is promoted. While cooperations between Hoxa9 and Meis1 and between Trib1 and Hoxa9/Meis1 are specific, subsequent genetic events are less specific for Hoxa9/Meis1/Trib1 pathways.