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Blood, 15 December 2007, Vol. 110, No. 13, pp. 4188-4197. Prepublished online as a Blood First Edition Paper on September 6, 2007; DOI 10.1182/blood-2007-07-100883.
HEMATOPOIESIS Runx1-mediated hematopoietic stem-cell emergence is controlled by a Gata/Ets/SCL-regulated enhancer1 Medical Research Council (MRC) Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, United Kingdom; 2 Genomics Division, Lawrence Berkeley National Laboratory, Berkeley, CA; 3 United States Department of Energy Joint Genome Institute, Walnut Creek, CA; and 4 Department of Cell Biology, Erasmus Medical Center, Rotterdam, The Netherlands The transcription factor Runx1/AML1 is an important regulator of hematopoiesis and is critically required for the generation of the first definitive hematopoietic stem cells (HSCs) in the major vasculature of the mouse embryo. As a pivotal factor in HSC ontogeny, its transcriptional regulation is of high interest but is largely undefined. In this study, we used a combination of comparative genomics and chromatin analysis to identify a highly conserved 531-bp enhancer located at position + 23.5 in the first intron of the 224-kb mouse Runx1 gene. We show that this enhancer contributes to the early hematopoietic expression of Runx1. Transcription factor binding in vivo and analysis of the mutated enhancer in transient transgenic mouse embryos implicate Gata2 and Ets proteins as critical factors for its function. We also show that the SCL/Lmo2/Ldb-1 complex is recruited to the enhancer in vivo. Importantly, transplantation experiments demonstrate that the intronic Runx1 enhancer targets all definitive HSCs in the mouse embryo, suggesting that it functions as a crucial cis-regulatory element that integrates the Gata, Ets, and SCL transcriptional networks to initiate HSC generation.
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