Part of the Drosophila dorsalventral signalling pathway. For simplicity, not all the downstream targets of dorsal are shown. Toll is a transmembrane receptor, homologous to the mammalian interleukin-1 receptor in its intra cellular domain.
Tube is a novel protein with no known homologues.
Pelle is a protein kinase homologous to the IRAK kinase in the mammalian Rel pathway. Cactus, the homologue of IkB's, has several ankyrin repeats. It binds dorsal, a rel- transcription factor homologue, and sequesters it in the nucleus. The activation of this pathway to the degradation of cactus, and the nuclear localization of dorsal. Since this pathway is only activated in the ventral area, a dorsalventral nuclear gradient forms in the embryo.