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

Terminal portions of the Drosophila body pattern are specified by an extracellular ligand generated at each end of the early syn-cytial embryo. This ligand triggers the localized transcription of two gap segmentation genes, tailless (tll) and huckebein (hkb) through a signal transduction cascade involving the receptor tyrosine kinase torso (tor) and homologues of ras, raf, and mek (map kinae kinase). In contrast to the ligand, these signal transducing components are expressed ubiquitously. Here, we show that a constitutively active form of human raf1 protein can trigger tll and hkb transcription in Drosophila embryos and specify elements of the terminal body pattern. This result indicates a strong functional conservation between Drosophila and mammalian raf proteins and argues that the localized activity of Drosophila raf (D-raf) normally carries spatial information specifying the end portions of the body.