CtBP represses Dpp signaling as a dimer.

C-terminal binding protein (CtBP) is a highly conserved transcriptional co-repressor in animal development and human diseases. In Drosophila, CtBP is critical for fly development and is thought to exert its repressive roles in many signaling pathways including Dpp/BMP pathway. Here we provide evidence that although wild type CtBP negatively and dominantly influences Dpp signaling in fly presumptive wings, mutant CtBP unable to form dimer does not, indicating that dimerization is required for the repression role of CtBP in Dpp signaling in vivo.