While knockout of Tet1 expression shows only very minor effects on normal development including hematopoiesis21, our recent studies demonstrated that TET1 plays a critical oncogenic role in AML through promoting expression of oncogenic targets (e.g., HOXA9, MEIS1, PBX3, etc.)and repressing expression of tumor-suppressor targets (e.g., miR-22)18,19,46. This evidence concerns the gene HOXA9 and acute myeloid leukemia.