Roles of fetal (G)γ-globin promoter elements and the adult β-globin 3' enhancer in the stage-specific expression of globin genes

The human fetal ^Gγ-globin and adult β-globin genes are expressed in a tissue- and developmental stage-specific pattern in transgenic mice: the ^Gγ gene in embryonic cells and the β gene in fetal and adult erythroid cells. Several of the cis-acting DNA sequences thought to be responsible for these patterns of expression are located 5′ to the ^Gγ-globin gene and 3′ to the β-globin gene. To further define the locations and functional roles of these elements, we examined the effects of 5′ truncations on the expression of the ^Gγ-globin gene, as well as the ability of ^Gγ-globin upstream sequences to alter the developmental regulation of a β-globin gene. We found that sequences between -201 and -136 are essential for expression of the ^Gγ-globin gene, whereas those upstream of -201 have little effect on the level or tissue or stage specificity of ^Gγ-globin expression. The ^Gγ-globin upstream sequences from -201 to -136 were, furthermore, capable of activating a linked β-globin gene in embryonic blood cells; however, a ^Gγ-globin fragment from -383 to -206 was similarly active in this assay, and the complete fragment from -383 to -136 was considerably more active than either of the smaller fragments, suggesting the presence of multiple cis-acting elements for embryonic blood cells. Our data also suggested the possibility of a negative regulatory element between -201 and -136. These results are discussed in relation to several DNA elements in the ^Gγ-globin upstream region, which have been shown to bind nuclear factors in erythroid cells. Finally, we observed that removal of the β-globin 3′-flanking sequences, including the 3′ enhancer, from the ^Gγ-globin upstream-β-globin hybrid gene resulted in a 25-fold reduction in expression in embryonic blood cells. This suggests that the β-globin 3′ enhancer is potentially active at the embryonic stage and thus cannot be solely responsible for the fetal or adult specificity of the β-globin gene.