Relief of gene repression by Torso RTK signaling: role of capicua in Drosophila terminal and dorsoventral patterning

Differentiation of the embryonic termini in Drosophila depends on signaling by the Tor RTK, which induces terminal gene expression by inactivating at the embryonic poles a uniformly distributed repressor activity that involve s the Gro corepressor. Here, we identify a new gene, cic, that acts as a re pressor of terminal genes regulated by the Tor pathway, cic also mediates r epression along the dorsoventral axis, a process that requires the Dorsal m orphogen and Gro, and which is also inhibited by Tor signaling at the termi ni. cic encodes an HMG-box transcription factor that interacts with Gro in vitro. We present evidence that Tor signaling regulates terminal patterning by inactivating Cic at the embryo poles. cic has been evolutionarily conse rved, suggesting that Cic-like proteins may act as repressors regulated by RTK signaling in other organisms.