Individual stage selector element mutations lead to reciprocal changes in beta- vs. epsilon-globin gene transcription: genetic confirmation of promoter competition during globin gene switching.
Biochemical and genetic analysis of the embryonic to adult beta-like globin gene switch in chickens has led to the hypothesis that competition between the promoters of the cis-linked epsilon- and beta-globin genes for interaction with a shared enhancer mediates the developmental changes in expression of beta-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 beta-globin promoter mutations on expression of the two linked genes in transiently transfected erythroid cells. Mutations that attenuated adult beta-globin transcription resulted concomitantly in a proportional increase in expression of the embryonic epsilon-globin gene. Consistent with the model, mutations disrupting the binding sites for either of two adult stage-specific transcription factors (NF-E4 and beta CTF) indicate that these sites are essential both for induction of beta-globin gene expression and for indirect suppression (through promoter competition) of epsilon-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 beta-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.
Foley
K P
KP
Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, Illinois 60208-3500.
Engel
J D
JD
D000818:Animals; D001483:Base Sequence; D002461:Cell Line, Transformed; D002642:Chick Embryo; D004252:DNA Mutational Analysis; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005786:Gene Expression Regulation / Q000235:genetics*; D005812:Genes, Switch; D005914:Globins / Q000235:genetics*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics
D014157:Transcription Factors; D005914:Globins