Individual stage selector element mutations lead to reciprocal changes in β- Vs. eε-globin gene transcription: Genetic confirmation of promoter competition during globin gene switching

Abstract

Biochemical and genetic analysis of the embryonic to adult β-like globin gene switch in chickens has led to the hypothesis that competition between the promoters of the cis-linked ε- and β-globin genes for interaction with a shared enhancer mediates the developmental changes in expression of β-globin protein isotypes. To test specific predictions of this promoter competition model, a sensitive RNA/polymerase chain reaction assay has been used to investigate the effects of individual β-globin promoter mutations on expression of the two linked genes in transiently transfected erythroid cells. Mutations that attenuated adult β-globin transcription resulted concomitantly in a proportional increase in expression of the embryonic ε-globin gene. Consistent with the model, mutations disrupting the binding sites for either of two adult stage-specific transcription factors (NF-E4 and βCTF) indicate that these sites are essential both for induction of β-globin gene expression and for indirect suppression (through promoter competition) of ε-globin transcription in definitive (adult) erythroid cells. These results provide direct evidence that stage-specific transcription factors affect the equilibrium existing between multiple interacting globin cis-regulatory elements. We conclude that promoter competition is an important mechanism through which developmental regulation of chicken β-globin gene switching is achieved and that such competitive interactions may prove to be generally applicable to the regulation of a variety of other temporally or spatially restricted gene expression patterns.