Molecular integration of inductive and mesoderm-intrinsic inputs governs even-skipped enhancer activity in a subset of pericardial and dorsal muscle progenitors.
Individual somatic muscles and heart progenitors are specified at defined positions within the mesodermal layer of Drosophila. The expression of the homeobox gene even-skipped (eve) identifies one specific subset of cells in the dorsal mesoderm, which give rise to particular pericardial cells and dorsal body wall muscles. Genetic analysis has shown that the induction of eve in these cells involves the combined activities of genes encoding mesoderm-intrinsic factors, such as Tinman (Tin), and spatially restricted signaling activities that are largely derived from the ectoderm, particularly those encoded by wingless (wg) and decapentaplegic (dpp). Here we show that a Dpp-activated Smad protein, phosphorylated Mad, is colocalized in eve-expressing cells during an extended developmental period. We demonstrate further that a mesodermally active enhancer of eve contains several Smad and Tin binding sites that are essential for enhancer activity in vivo. This enhancer also contains a number of binding sites for the Wg-effector Pangolin (Pan/Lef-1), which are required for full levels of enhancer activity. However, we find that their main function is to prevent ectopic enhancer activity in the dorsal mesoderm. This suggests that, in the absence of Wg signaling, Pan binding serves to abrogate the synergistic activities of Smads and Tin in eve activation while, in cells that receive Wg signals, Pan is converted into a coactivator that promotes eve induction. Together, these data show that the eve enhancer integrates several regulatory pathways via the combinatorial binding of the mesoderm-intrinsic regulator Tin and the effectors of the Dpp and Wg signals.
Knirr
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Department of Biochemistry and Molecular Biology, Mount Sinai School of Medicine, New York, New York 10029, USA.
Frasch
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D000818:Animals; D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D003850:Deoxyribonuclease I / Q000378:metabolism; D004330:Drosophila / Q000196:embryology*; D029721:Drosophila Proteins / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D005982:Glutathione Transferase / Q000378:metabolism; D006321:Heart / Q000196:embryology; D018398:Homeodomain Proteins / Q000378:metabolism*; D019476:Insect Proteins / Q000378:metabolism; D008648:Mesoderm / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009132:Muscles / Q000378:metabolism*; D009154:Mutation; D009206:Myocardium / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D015398:Signal Transduction; D014018:Tissue Distribution; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D051155:Wnt1 Protein
D001426:Bacterial Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D019476:Insect Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D051155:Wnt1 Protein; C064196:dpp protein, Drosophila; C052837:eve protein, Drosophila; C115159:pan protein, Drosophila; C102933:tin protein, Drosophila; C074622:wg protein, Drosophila; D005982:Glutathione Transferase; D003850:Deoxyribonuclease I