Shedding light on Toll signaling through live imaging

The Toll receptor propagates the ventralizing signal designating dorsal/ventral cell fate in the Drosophila embryo. The application of live-imaging approaches to this classical developmental signaling pathway is yielding some surprising new insights into Toll receptor signaling. In addition to its previously known plasma membrane localization, Toll is present in Rab5+ early endosomes. Dominant, constitutively active forms of Toll preferentially partition into endosomes. Blocking endocytosis locally prevents Toll from signaling suggesting that endocytosis is required for Toll to signal. Augmenting endocytosis increases Toll signaling. Both interventions alter the shape of the Dorsal gradient globally indicating an important role of endocytosis in fixing spatial information for the Dorsal gradient.