EGF receptor/Rolled MAP kinase signalling protects cells against activatedArmadillo in the Drosophila eye

beta -catenin/Armadillo are transcriptional co-activators that mediate Wnt signalling in normal development. Activated forms of beta -catenin are onco genic. We have constructed mutant forms of Drosophila Armadillo which corre spond to common human oncogenic mutations, and find them to activate Armadi llo constitutively. When expressed in the Drosophila eye, these eventually induce apoptosis in all cell types. Intriguingly, cells in the eye are resi stant to the effects of activated Armadillo for a long period prior to the onset of cell death at the mid-pupal stage. This latency is conferred by EG F receptor (EGFR)/MAP kinase signalling, which prevents activated Armadillo from inducing apoptosis; when EGFR signalling naturally ceases, the cells rapidly die. Nemo, the Drosophila homologue of NLK in mice and LIT-1 in Cae norhabditis elegans, does not antagonize activated Armadillo, suggesting th at the Nemo-like MAP kinases may not generally interact with Armadillo/beta -catenin Thus, our results show that activated Armadillo is subject to a s pecific negative control by EGFR/Rolled MAP kinase signalling.