A Global Role for EKLF in Definitive and Primitive Erythropoiesis.

Erythroid Kruppel-like factor (EKLF or Klf1) is an erythroid specific C₂H₂ zinc-finger transcription factor which is essential for definitive erythropoiesis and β-globin gene expression. The absence of EKLF results in fatal anaemia but correction of globin chain imbalance does result in rescue, suggesting the existence of additional EKLF target genes. The aim of this study was to search for such genes by expression profiling. We performed profiling on fetal livers from wild-type versus EKLF null litter mates, and also EKLF null erythroid cell lines containing an inducible EKLF-ER^TM fusion construct. Hybridisations were performed on microarray slides printed with a 23K oligo library from Compugen. Target gene validation was performed by real-time RT-PCR, chromatin immuno-precipitation (ChIP) and promoter-reporter assays. A large number of genes were down regulated in the absence of EKLF but few were up regulated, suggesting EKLF acts primarily as a transcriptional activator in vivo. One hundred genes were EKLF dependent in both systems. These include heme synthesis enzymes, red cell surface proteins including Rh and the transferrin receptor, and erythroid transcription factors. Two interesting highly EKLF-dependent genes are α-haemoglobin stabilising protein (AHSP), a key chaperone for free a-globin chains, and dematin (band 4.9) which links the cytoskeleton to the red cell membrane. A search for EKLF binding sites within the dematin and AHSP genes demonstrated a number of phylogenetically conserved CACC sites, and ChIP demonstrated in vivo EKLF occupancy at some but not all of these. Promoter-reporter assays showed EKLF directly activates dematin gene transcription through two promoters containing these sites. Lastly, investigation of EKLF target genes in the yolk sac lead to the discovery of unexpected defects in the embryonic red cell membrane and cytoskeleton. In conclusion, EKLF regulates global erythroid gene expression which is critical for development of primitive as well as definitive red cells.