Transcription factor control of cell-specific downstream targets can be significantly altered when the controlling factor is mutated. We show that the semi-dominant neonatal anemia (Nan) mutation in the EKLF/ KLF1 transcription factor leads to ectopic expression of proteins that are not normally expressed in the red blood cell, leading to systemic effects that exacerbate the intrinsic anemia in the adult and alter correct development in the early embryo. Even when expressed as a heterozygote, the Nan-EKLF protein accomplishes this by direct binding and aberrant activation of genes encoding secreted factors that exert a negative effect on erythropoiesis and iron use. Our data form the basis for a novel mechanism of physiological deficiency that is relevant to human dyserythropoietic anemia and likely other disease states.

Erythroblastic islands are a specialized niche that contain a central macrophage surrounded by erythroid cells at various stages of maturation. However, identifying the precise genetic and transcriptional control mechanisms in the island macrophage remains difficult due to macrophage heterogeneity. Using unbiased global sequencing and directed genetic approaches focused on early mammalian development, we find that fetal liver macrophage exhibit a unique expression signature that differentiates them from erythroid and adult macrophage cells. The importance of EKLF/KLF1 in this identity is shown by expression analyses in EKLF-/- and in EKLF-marked macrophage cells. Single cell sequence analysis simplifies heterogeneity and identifies clusters of genes important for EKLF-dependent macrophage function and novel cell surface biomarkers. Remarkably, this singular set of macrophage island cells appears transiently during embryogenesis. Together these studies provide a detailed perspective on the importance of EKLF in establishment of the dynamic gene expression network within erythroblastic islands in the developing embryo and provide the means for their efficient isolation.

e Understanding how transcriptional regulators are themselves controlled is important in attaining a complete picture of the intracellular effects that follow signaling cascades during early development and cell-restricted differentiation. We have addressed this issue by focusing on the regulation of EKLF/KLF1, a zinc finger transcription factor that plays a necessary role in the global regulation of erythroid gene expression. Using biochemical affinity purification, we have identified the DEK oncoprotein as a critical factor that interacts with an essential upstream enhancer element of the EKLF promoter and exerts a positive effect on EKLF levels. This element also binds a core set of erythroid transcription factors, suggesting that DEK is part of a tissue-restricted enhanceosome that contains BMP4-dependent and -independent components. Together with local enrichment of properly coded histones and an open chromatin domain, optimal transcriptional activation of the EKLF locus can be established. Studies of the erythroid lineage have led to the successful characterization of intracellular regulators that act as transcription factors to generate red-cell-specific expression (1). However, in many cases it remains unresolved how these factors are themselves regulated. Based on this notion, we have been studying the regulation of erythroid Krüppel-like factor (EKLF or KLF1 [2]), a zinc finger hematopoietic transcription factor that plays a global role in activation of genes critical for genetic control within the erythroid lineage (3-5). It performs this function by binding to its cognate DNA 5=CCMCRCCCN3= element and recruiting chromatin-remodeling proteins and histone modifiers.Regulation of EKLF itself is of interest because of a number of functional properties and expression characteristics. EKLF expression remains tissue specific throughout early development and in the adult. Its onset in the yolk sac is strictly limited to the mesodermal, primitive erythroid cells that populate the blood islands at the early headfold stage (embryonic day 7.5 [E7.5]), switching by E9.5 to definitive cells within the hepatic primordia and then to the red pulp of the adult spleen and the bone marrow (6). During definitive hematopoietic differentiation, EKLF is expressed at low levels in multipotent progenitors (MPP) and retains an expression pattern restricted to the common myeloid progenitor (CMP) and megakaryocyte erythroid progenitor (MEP) prior to eventual segregation to erythroid progeny (7-9).We have demonstrated that a 950-bp region adjacent to the EKLF start site of transcription, encompassing two critical erythroid hypersensitive sites (EHS1 and -2) and the proximal promoter (10), contains all the information needed for developmentally regulated, blood-cell-specific expression of a linked reporter in vivo in mice (11). The tissue specificity and enhancer properties of hypersensitive sites in this region are also seen in human erythroid cells (12). The EHS1 enhancer element contains a very highly conserved (7 species) clus...

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Background: EKLF is a transcription factor that is critical for red cell proliferation and differentiation. Results: EKLF interactions with the PIAS family of proteins repress or superactivate expression of its target genes. Conclusion: PIAS3 interaction modulates EKLF activity in a promoter-dependent and SUMO-independent manner. Significance: Our studies reveal a novel group of coregulators that affect differentiation of red blood cells.