Upstream Gℽ-Globin and Downstream β-Globin Sequences Required for Stage-Specific Expression in Transgenic Mice

Abstract

The human Gℽ-globin and β-globin genes are expressed in erythroid cells at different stages of human development, and previous studies have shown that the two cloned genes are also expressed in a differential stage-specific manner in transgenic mice. The Gℽ-globin gene is expressed only in murine embryonic erythroid cells, while the β-globin gene is active only at the fetal and adult stages. In this study, we analyzed transgenic mice carrying a series of hybrid genes in which different upstream, intragenic, or downstream sequences were contributed by the β-globin or Gℽ-globin gene. We found that hybrid 5′Gℽ/3′β globin genes containing Gℽ-globin sequences upstream from the initiation codon were expressed in embryonic erythroid cells at levels similar to those of an intact Gℽ-globin transgene. In contrast, β-globin upstream sequences were insufficient for expression of 5′β/3′Gℽ hybrid globin genes or a β-globin-metallothionein fusion gene in adult erythroid cells. However, β-globin downstream sequences, including 212 base pairs of exon III and 1,900 base pairs of 3′-flanking DNA, were able to activate a 5′Gℽ/3′β hybrid globin gene in fetal and adult erythroid cells. These experiments suggest that positive regulatory elements upstream from the Gℽ-globin and downstream from the β-globin gene are involved in the differential expression of the two genes during development.