A CREB-binding site as a target for decapentaplegic signalling during Drosophila endoderm induction

Armadillo and dTCF: a marriage made in the nucleus

Within the past year, Armadillo and beta-catenin's role in transducing the Wingless/Wnt signal has been substantially clarified. It is now clear that Armadillo and beta-catenin bind directly to members of the T-cell factor/lymphoid enhancer factor subfamily of HMG box DNA-binding proteins, forming bipartite transcription factors that regulate Wingless/Wnt responsive genes in both Drosophila and vertebrates. These partners not only play key roles in a variety of cell fate decisions during normal development but, when inappropriately activated, contribute to both colon cancer and melanoma.

LEF-1, a nuclear factor coordinating signaling inputs from wingless and decapentaplegic

wingless and decapentaplegic signal during endoderm induction in Drosophila to regulate expression of the homeotic gene Ultrabithorax. Here, we define a minimal wingless response sequence in the midgut enhancer of Ultrabithorax. We show that this sequence is recognized by the murine transcription factor LEF-1 (lymphocyte enhancer binding factor 1) in a ternary complex with armadillo protein, the cytoplasmic target of the wingless signaling pathway. In stable transformants, transcriptional stimulation of the Ultrabithorax enhancer by LEF-1 depends on armadillo. Furthermore, overexpression of LEF-1 bypasses the need for wingless signaling and causes phenotypes in the midgut, notum, and wing that mimic wingless hyperstimulation. Finally, efficient transcriptional stimulation by LEF-1 in the midgut depends also on the decapentaplegic response sequence and is limited spatially by decapentaplegic signaling. Thus, LEF-1 coordinates inputs from multiple positional signals, consistent with its architectural role in regulating the assembly of multiprotein enhancer complexes.