On the other hand, an elegant model of MLL-AF9-induced AML showing the significance of the microenvironment in providing instructive signals for leukemic lineage fates, has suggested that the signaling through the small GTPase Rac1 pathway is critical to leukemia development within this particular lineage promiscuity scenario [86]. The gene discussed is KMT2A; the disease is acute myeloid leukemia.