The role of EKLF in human beta-globin gene competition.

Abstract

We have investigated the role of erythroid Kruppel-like factor (EKLF) in expression of the human 13-globin genes in compound EKLF knockout/human I~-locus transgenic mice. EKLF affects only the adult mouse 13-globin genes in homozygous knockout mice; heterozygous mice are unaffected. Here we show that EKLF knockout mice express the human e and 7-globin genes normally in embryonic red cells. However, fetal liver erythropoiesis, which is marked by a period of 7" and 13-gene competition in which the genes are alternately transcribed, exhibits an altered ratio of 7" to 13-gene transcription. EKLF heterozygous fetal livers display a decrease in the number of transcriptionally active 13 genes with a reciprocal increase in the number of transcriptionally active 7 genes. 13-gene transcription is absent in homozygous knockout fetuses with coincident changes in chromatin structure at the 13 promoter. There is a further increase in the number of transcriptionally active 7 genes and accompanying 7 gene promoter chromatin alterations. These results indicate that EKLF plays a major role in 7-and I~-gene competition and suggest that EKLF is important in stabilizing the interaction between the Locus Control Region and the 13-globin gene. In addition, these findings provide further evidence that developmental modulation of globin gene expression within individual cells is accomplished by altering the frequency and/or duration of transcriptional periods of a gene rather than changing the rate of transcription.

Joining the loops: β‐Globin gene regulation

“…EKLF is not required for the expression of the embryonal e-and fetal c-genes, but strongly affects the expression of the adult b-globin gene (30). In homozygous EKLF knockout mice containing a transgenic human b-globin locus, b-gene expression is absent and c-globin expression is increased.…”

“…In homozygous EKLF knockout mice containing a transgenic human b-globin locus, b-gene expression is absent and c-globin expression is increased. In heterozygous EKLF mice, b-gene expression is delayed during differentiation, accompanied by increased c-gene expression, but b-globin levels are unaffected in adult mice (30). The exact mechanism of EKLF action in globin gene regulation is unclear because of several contradictory reports, most likely originating from different experimental designs.…”

“…In mice, EKLF activates a human b-globin reporter construct containing HS3 of the LCR and is required for formation of this HS in the construct (31). Similarly, HS3 is not formed at the full transgenic human locus in EKLF knockout mice (30) (32).…”

Non-random subcellular distribution of variant EKLF in erythroid cells

“…EKLF mRNA is highly restricted in its expression pattern, limited to hematopoietic organs such as the yolk sac, fetal liver, adult bone marrow, and the red pulp of the spleen [8,9]. Molecular and genetic ablation studies demonstrate that EKLF is absolutely required for β-globin transcription and plays a prominent role in the final developmental switch to adult β-globin in definitive erythroid cells [10][11][12][13][14]. EKLF protein can interact with coactivators such as p300/CBP histone acetyltransferases as well as chromatin remodelers such as SWI/SNF to maximally transactivate the β-globin gene [15,16].…”

Identification, characterization, and expression pattern of the chicken EKLF gene

“…It was initially thought that EKLF is not required for primitive erythropoiesis in the yolk sac but is required only during fetal liver erythropoiesis, for maturation of definitive erythroid cells (Nuez et al, 1995;Perkins et al, 1995;Wijgerde et al, 1996). It was intriguing, therefore, that EKLF is expressed during mouse primitive erythropoiesis, starting early in embryonic development (Southwood et al, 1996).…”