DNase I Hypersensitivity and ϵ-Globin Transcriptional Enhancement Are Separable in Locus Control Region (LCR) HS1 Mutant Human β-Globin YAC Transgenic Mice

Abstract

Expression of the five β-like globin genes (ϵ, Gγ, Aγ, δ, β) in the human β-globin locus depends on enhancement by the locus control region, which consists of five DNase I hypersensitive sites (5′HS1 through 5′HS5). We report here a novel enhancer activity in 5′HS1 that appears to be potent in transfected K562 cells. Deletion analyses identified a core activating element that bound to GATA-1, and a two-nucleotide mutation that disrupted GATA-1 binding in vitro abrogated 5′HS1 enhancer activity in transfection experiments. To determine the in vivo role of this GATA site, we generated multiple lines of human β-globin YAC transgenic mice bearing the same two-nucleotide mutation. In the mutant mice, ϵ-, but not γ-globin, gene expression in primitive erythroid cells was severely attenuated, while adult β-globin gene expression in definitive erythroid cells was unaffected. Interestingly, DNaseI hypersensitivity near the 5′HS1 mutant sequence was eliminated in definitive erythroid cells, whereas it was only mildly affected in primitive erythroid cells. We therefore conclude that, although the GATA site in 5′HS1 is critical for efficient ϵ-globin gene expression, hypersensitive site formation per se is independent of 5′HS1 function, if any, in definitive erythroid cells.