Human beta-globin gene expression in transgenic mice is enhanced by a distant DNase I hypersensitive site.

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Abstract
Several lines of evidence suggest that erythroid-specific DNase I hypersensitive sites (HS) located far upstream of the human .beta.-globin gene are important in regulating .beta.-globin gene expression. We used the polymerase chain reaction technique to amplify and clone an 882-base-pair DNA fragment spanning one of these HS, designated HSII, which is located 54 kilobases upstream of the .beta.-globin gene. The cloned HSII fragment was linked to a human .beta.-globin gene in either the genomic (gHSH-.beta.) or antigenomic (aHSH-.beta.) orientation. These two constructs and a .beta.-globin gene alone (.beta.) were injected into fertilized mouse eggs, and expression was analyzed in liver and brain from day-16 transgenic fetuses. Five of 7 .beta.-transgenic fetuses expressed human .beta.-globin mRNA, but the level of expression per gene copy was low, ranging from 0.93 to 22.4% of mouse .alpha.-globin mRNA (average 9.9%). In contrast, 11 of 12 gHSII-.beta. transgenic fetuses expressed .beta.-globin mRNA at levels per gene copy ranging from 31.3 to 336.6% of mouse .alpha.-globin mRNA (average 139.5%). Only three fetuses containing intact copies of the aHSII-.beta. construct were produced. Two of three expressed human .beta.-globin mRNA at levels per gene copy of 179.2 and 387.1%. Expression of human .beta.-globin mRNA was tissue-specific in all three types of transgenic fetuses. These studies demonstrate that a small DNA fragment containing a single erythroid-specific HS can stimulate high-level human .beta.-globin gene expression in transgenic mice.