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Updated: Apr 25, 2026
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Published on: September 15, 2021
Wnt-mediated repression via bipartite DNA recognition by TCF in the Drosophila hematopoietic system
Chen U Zhang1, Timothy A Blauwkamp1, Peter E Burby1
1Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America.
Abstract:
The Wnt/β-catenin signaling pathway plays many important roles in animal development, tissue homeostasis and human disease. Transcription factors of the TCF family mediate many Wnt transcriptional responses, promoting signal-dependent activation or repression of target gene expression. The mechanism of this specificity is poorly understood. Previously, we demonstrated that for activated targets in Drosophila, TCF/Pangolin (the fly TCF) recognizes regulatory DNA through two DNA binding domains, with the High Mobility Group (HMG) domain binding HMG sites and the adjacent C-clamp domain binding Helper sites. Here, we report that TCF/Pangolin utilizes a similar bipartite mechanism to recognize and regulate several Wnt-repressed targets, but through HMG and Helper sites whose sequences are distinct from those found in activated targets. The type of HMG and Helper sites is sufficient to direct activation or repression of Wnt regulated cis-regulatory modules, and protease digestion studies suggest that TCF/Pangolin adopts distinct conformations when bound to either HMG-Helper site pair. This repressive mechanism occurs in the fly lymph gland, the larval hematopoietic organ, where Wnt/β-catenin signaling controls prohemocytic differentiation. Our study provides a paradigm for direct repression of target gene expression by Wnt/β-catenin signaling and allosteric regulation of a transcription factor by DNA.
Insights
The Wnt/β-catenin pathway uses TCF transcription factors to control genes. This study reveals TCF/Pangolin uses distinct DNA sites and conformations to repress Wnt targets, impacting development.
Area of Science:
- Molecular Biology
- Developmental Biology
- Genetics
Background:
- The Wnt/β-catenin signaling pathway is crucial for development and disease.
- TCF transcription factors mediate Wnt responses, but their specificity is unclear.
- Previous work showed TCF/Pangolin uses bipartite DNA binding for activated targets.
Purpose of the Study:
- To investigate the mechanism by which TCF/Pangolin recognizes and regulates Wnt-repressed target genes.
- To determine if distinct DNA binding sites and conformations are involved in repression.
Main Methods:
- Analysis of Wnt-repressed target genes in Drosophila.
- Identification and characterization of HMG and Helper DNA binding sites.
- Protease digestion studies to assess protein conformation.
Main Results:
- TCF/Pangolin recognizes Wnt-repressed targets via distinct HMG and Helper DNA sites compared to activated targets.
- The specific HMG-Helper site combination dictates gene activation or repression.
- TCF/Pangolin adopts different conformations when bound to distinct HMG-Helper site pairs.
- This repressive mechanism is functional in the fly lymph gland during development.
Conclusions:
- TCF/Pangolin employs a bipartite DNA binding mechanism for both activation and repression of Wnt targets.
- Distinct DNA site sequences and TCF/Pangolin conformations mediate signal-dependent gene repression.
- This provides a model for direct Wnt-mediated gene repression and allosteric regulation of transcription factors by DNA.
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