GRG5/AES interacts with T-cell factor 4 (TCF4) and downregulates Wnt signaling in human cells and zebrafish embryos

Area of Science:

• Molecular Biology
• Developmental Biology
• Genetics

Background:

• TCF/LEF proteins regulate crucial developmental processes like cell fate and tissue architecture.
• TCF proteins act as transcriptional activators with β-catenin in Wnt signaling, and as repressors with Groucho-family proteins (GRGs) in its absence.
• TCF4 is vital in intestinal epithelium, with its dysregulation linked to tumorigenesis, but the roles of TCF4-GRG complexes are not fully understood.

Purpose of the Study:

• To characterize the interaction between TCF4 and GRG5/AES, a Groucho family member.
• To elucidate the mechanisms by which TCF4-GRG complexes repress transcription.
• To investigate the role of GRG5/AES in embryonic development.

Main Methods:

• Mapping the core GRG interaction region in TCF4.
• Analyzing GRG5/AES binding specificity to TCF4 using a specific amino acid motif.
• Assessing GRG5/AES's effect on Wnt-mediated transcription in human cells and zebrafish embryos.
• Investigating GRG5/AES function in zebrafish dorsal-ventral patterning.

Main Results:

• The core GRG interaction region in TCF4 was mapped to a 111-amino acid fragment.
• GRG5/AES binding to TCF4 depends on a specific 4-amino acid motif (LVPQ), found only in TCF3 and some TCF4 isoforms.
• GRG5/AES was shown to repress Wnt-mediated transcription in human cells and zebrafish embryos.
• GRG5/AES exhibits an inherent repressive function in dorsal-ventral patterning during early zebrafish embryogenesis.

Conclusions:

• This study clarifies TCF4-GRG5/AES interactions, identifying a unique binding motif.
• The findings provide insights into the mechanisms of transcriptional repression by TCF-GRG complexes.
• GRG5/AES plays a direct role in embryonic development, specifically in dorsal-ventral patterning.