Mll-AF9 induced changes in gene expression in various hematopoietic cells

The pathways by which oncogenes, such as MLL-AF9, initiate transformation and leukemia in humans and mice are incompletely defined. In a study of target cells and oncogene dosage, we found that Mll-AF9, when under endogenous regulatory control, efficiently transformed LSK (Lin- Sca1+ c-kit+) stem cells while committed granulocyte-monocyte progenitors (GMPs) were transformation-resistant and did not cause leukemia. Mll-AF9 was expressed at higher levels in hematopoietic stem (HSC) than GMP cells. Mll- AF9 gene dosage effects were directly shown in experiments where GMPs were efficiently transformed by the high dosage of Mll-AF9 resulting from retroviral transduction. Mll-AF9 up-regulated expression of 196 genes in both LSK and progenitor cells, but to higher levels in LSKs than in committed myeloid progenitors. Keywords: mutant hematopoietic cells Comparison of gene expression profiles among four types of hematopoietic cells (GMP, CMP, CLP and HSC), FACS sorted from wild type and Mll-AF9 knock-in mice. The goal was to identify genes differentially expressed in each Mll-AF9 cell type compared to the corresponding wild type cells.