Lymphoid and myeloid differentiation programs are regulated by the common genomic locus encoding for EVL and MIR-342

Extrinsic and intrinsic factors control HSC regulation to adapt the production of blood cells to the organism’s need. As retroviral integration sites (IS) are clustered nearby active genes and may lead to their upregulation, we systematically analyzed the IS repertoire of ten Wiskott-Aldrich syndrome patients enrolled in clinical gene therapy to identify novel regulators of hematopoiesis. In order to detect overrepresentation of IS in proximity to the transcription start site of gene loci, we developed a screening pipeline. By using this strategy, we identified a significant clustering of IS close to the locus encoding for Evl and its intronic miR-342. Therefore, we selected both genes encoded by one single locus to study their yet uncharacterized role in hematopoiesis. Lentiviral overexpression (OE) of Evl in murine primary LSK (lin-Sca1+ckit+) cells led to a 7.5-fold increase of preB-cell colonies as compared to mock-transduced LSK cells. By contrast, miR-342 OE led to a 2.3-fold larger number of myeloid colonies in vitro and a 3.3-fold increased number of myeloid progenitor-derived CFU-S in vivo. In line with this, global gene expression profiling revealed a profound deregulation of canonical pathways essential for the development of B-cells upon Evl, and myeloid development upon miR-342 OE. Self-renewal and multilineage reconstitution following transgene OE were assessed in serial BM transplantation experiments. Interestingly, EVL+ LSK cells led to a significantly increased donor-derived B-cell frequency within the spleens of primary recipient mice, and a 4.3-fold higher frequency of B-cells in peripheral blood after secondary transplantation. As our results point to an essential role of the Evl/miRNA-342 gene locus in lymphoid or myeloid lineage determination, we assessed its deregulation in human hematopoietic malignancies. Strikingly, the publicly available gene expression dataset of 2096 leukemia samples embedded in the MILE study demonstrated a significantly increased Evl expression in all lymphoid leukemias compared to healthy BM or myeloid malignancies. In summary, our data show that one common gene locus regulates distinct hematopoietic differentiation programs depending on the gene product expressed. While the protein-coding gene Evl drives B-cell lymphopoiesis, its intronic miR-342 promotes myeloid differentiation.