Direct competition between Brinker and Drosophila Mad in Dpp target gene transcription.
Brinker is a nuclear protein that antagonizes Dpp signalling in Drosophila. Its expression is negatively regulated by Dpp. Here, we show that Brinker represses Ultrabithorax (Ubx) in the embryonic midgut, a HOX gene that activates, and responds to, the localized expression of Dpp during endoderm induction. We find that the functional target for Brinker repression coincides with the Dpp response sequence in the Ubx midgut enhancer, namely a tandem of binding sites for the Dpp effector Mad. We show that Brinker efficiently competes with Mad in vitro, preventing the latter from binding to these sites. Brinker also competes with activated Mad in vivo, blocking the stimulation of the Ubx enhancer in response to simultaneous Dpp signalling. These results indicate how Brinker acts as a dominant repressor of Dpp target genes, and explain why Brinker is a potent antagonist of Dpp.
Saller
E
E
MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH, UK.
Bienz
M
M
D000483:Alleles; D000818:Animals; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D002845:Chromatography; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004330:Drosophila; D029721:Drosophila Proteins; D004591:Electrophoresis, Polyacrylamide Gel; D004625:Embryo, Nonmammalian / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010641:Phenotype; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins; D012689:Sequence Homology, Nucleic Acid; D015398:Signal Transduction; D014157:Transcription Factors; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D019476:Insect Proteins; C112506:MAD protein, Drosophila; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C066177:Ubx protein, Drosophila; C118082:brk protein, Drosophila; C064196:dpp protein, Drosophila; D005982:Glutathione Transferase