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 which Elf-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 showed Pu.1, Fli-1, and Erg were bound to the -10E element, and mutation of three highly conserved ETS sites within the enhancer abolished its activity. Finally, the transcriptional repressor Gfi1b was found to bind to and repress one of the Elf-4 promoters (-30P), and we show that this repression of Elf-4 is important for the maturation of primary fetal liver erythroid cells. Taken together, our results provide a comprehensive overview of the transcriptional control of Elf-4 within the hematopoietic system and, thus, integrate Elf-4 into the wider transcriptional regulatory networks that govern hematopoietic development.