A Positive Regulatory Feedback Loop Between 1 EKLF/ KLF1 and TAL1/SCL2 Sustaining the Erythropoiesis

The erythroid Kruppel-like factor EKLF/KLF1 is a hematopoietic transcription factor binding to CACCC DNA motif and participating in the regulation of erythroid differentiation. With combined use of microarray-based gene expression profiling and promoter-based ChIP-chip assay of E14.5 fetal liver cells from wild type (WT) and EKLF-knockout (Eklf-/-) mouse embryos, we have identified the pathways and direct target genes activated or repressed by EKLF. This genome-wide study together with molecular/cellular analysis of mouse erythroleukemic cells (MEL) indicate that among the downstream direct target genes of EKLF is Tal1/Scl. Tal1/Scl encodes another DNA-binding hematopoietic transcription factor TAL1/SCL known to be an Eklf activator and essential for definitive erythroid differentiation. Further identification of the authentic Tall gene promoter in combination with in vivo genomic footprinting approach and DNA reporter assay demonstrate that EKLF activates Tall gene through binding to a specific CACCC motif located in its promoter. These data establish the existence of a previously unknow positive regulatory feedback loop between two DNA-binding hematopoietic transcription factors that sustains the mammalian erythropoiesis.