Wingless signaling leads to an asymmetric response to decapentaplegic-dependent signaling during sense organ patterning on the notum of Drosophila melanogaster

Wnt and Decapentaplegic cell signaling pathways act synergistically in thei r contribution to macrochaete (sense organ) patterning on the notum of Dros ophila melanogaster. The Wingless-signaling pathway was ectopically activat ed by removing Shaggy activity (the homologue of vertebrate glycogen syntha se kinase 3) in mosaics, Proneural activity is asymmetric within the Shaggy -deficient clone of cells and shows a fixed "polarity" with respect to body axis, independent of the precise location of the clone. This asymmetric re sponse indicates the existence in the epithelium of a second signal, which we suggest is Decapentaplegic. Ectopic expression of Decapentaplegic induce s extra macrochaetes only in cells which also receive the Wingless signal. Activation of Hedgehog signaling generates a long-range signal which can pr omote macrochaete formation in the Wingless activity domain. This signal de pends upon decapentaplegic function. Autonomous activation of the Wingless signal response in cells causes them to attenuate or sequester this signal. Our results suggest a novel patterning mechanism which determines sense or gan positioning in Drosophila. (C) 1999 Academic Press.