TRUNK-SPECIFIC MODULATION OF WINGLESS SIGNALING IN DROSOPHILA BY TEASHIRT BINDING TO ARMADILLO

Background: One function of the Wingless signal cascade is to determin e the 'naked' cuticle cell-fate choice instead of the denticled one in Drosophila larvae. Wingless stabilises cytoplasmic Armadillo, which m ay act in a transcriptional activator complex with the DNA-binding pro tein T-cell factor (also known as Pangolin). As these components are c ritical for all Wingless-dependent patterning events, the problem aris es as to how specific outputs are achieved. Results: The Teashirt zinc finger protein was found to be necessary for a subset of late Wingles s-dependent functions in the embryonic trunk segments where the teashi rt gene is expressed. Teashirt was found to be required for the mainte nance of the late Wingless signalling target gene wingless but not for an earlier one, engrailed. Armadillo and Teashirt proteins showed sim ilar Wingless-dependent modulation patterns in homologous parts of eac h trunk segment in embryos, with high levels of nuclear Teashirt and i ntracellular Armadillo within cells destined to form naked cuticle. We found that Teashirt associates with, and requires, Armadillo in a com plex for its function. Conclusions: Teashirt binds to, and requires, A rmadillo for the naked cell-fate choice in the larval trunk. Teashirt is required for trunk segment identity, suggesting that Teashirt provi des a region-specific output to Armadillo activity. Further modulation of Wingless is achieved in homologous parts of each trunk segment whe re Wingless and Teashirt are especially active. Our results provide a novel, cell-intrinsic mechanism to explain the modulation of the activ ity of the Wingless signalling pathway. (C) Current Biology Publicatio ns ISSN 0960-9822.