AN ONCOGENIC FORM OF HUMAN RAF CAN SPECIFY TERMINAL BODY PATTERN IN DROSOPHILA

Terminal portions of the Drosophila body pattern are specified by an e xtracellular ligand generated at each end of the early syn-cytial embr yo. This ligand triggers the localized transcription of two gap segmen tation genes, tailless (tll) and huckebein (hkb) through a signal tran sduction cascade involving the receptor tyrosine kinase torso (tor) an d homologues of ras, raf, and mek (map kinae kinase). In contrast to t he ligand, these signal transducing components are expressed ubiquitou sly. Here, we show that a constitutively active form of human raf1 pro tein can trigger tll and hkb transcription in Drosophila embryos and s pecify elements of the terminal body pattern. This result indicates a strong functional conservation between Drosophila and mammalian raf pr oteins and argues that the localized activity of Drosophila raf (D-raf ) normally carries spatial information specifying the end portions of the body.