Integration of Elf-4 into Stem/Progenitor and Erythroid Regulatory Networks through Locus-Wide Chromatin Studies Coupled with In Vivo Functional Validation

The ETS transcription factor Elf-4 is an important regulator of hematopoietic stem cell (HSC) and T cell homeostasis. To gain insights into the transcriptional circuitry within whichElf-4 operates, we used comparative sequence analysis coupled with chromatin immunoprecipitation (ChIP) with microarray technology (ChIP-chip) assays for specific chromatin marks to identify three promoters and two enhancers active in hematopoietic and endothelial cell lines. Comprehensive functional validation of each of these regulatory regions in transgenic mouse embryos identified a tissue-specific enhancer (−10E) that displayed activity in fetal liver, dorsal aorta, vitelline vessels, yolk sac, and heart. Integration of a ChIP-sequencing (ChIP-Seq) data set for 10 key stem cell transcription factors showedPu.1 ,Fli-1 , andErg were bound to the −10E element, and mutation of three highly conserved ETS sites within the enhancer abolished its activity. Finally, the transcriptional repressorGfi1b was found to bind to and repress one of theElf-4 promoters (−30P), and we show that this repression ofElf-4 is important for the maturation of primary fetal liver erythroid cells. Taken together, our results provide a comprehensive overview of the transcriptional control ofElf-4 within the hematopoietic system and, thus, integrateElf-4 into the wider transcriptional regulatory networks that govern hematopoietic development.