Investigations of a Human Embryonic Globin Gene Silencing Element Using YAC Transgenic Mice

Abstract

A silencing element has been previously located upstream of the human ε-globin gene promoter using transient assays and transgenic mice carrying plasmid constructs in which the element has been deleted or its transcriptional motifs have been mutated. To investigate whether this element functions in the context of the whole β-globin locus, we analyzed ε-globin gene expression in transgenic mice carrying a deletion of the silencing element in the context of a 213-kilobase human β-globin yeast artificial chromosome (β-YAC). ε-Globin gene expression was measured during embryonic and fetal development and in adult mice. ε-mRNA levels in embryonic cells in Day 12 blood were as high as those measured in wild-type β-YAC controls, indicating that the deletion does not affect ε gene promoter function. ε-Globin gene expression was confined to the embryonic cells, indicating that deletion of this silencing element did not affect ε-globin developmental expression in the context of the β-YAC. These results suggest that in the context of the whole β-globin locus, other proximal and upstream ε gene promoter elements as well as competition by the downstream globin genes contribute to the silencing of the ε-globin gene in the cells of definitive erythropoiesis.