Drosophila toll pathway: the new model.

In Drosophila, recognition of microbe-specific molecules (such as bacterial peptidoglycans) activates serine protease cascades that converge to activate the Toll pathway. Recent data show that the serine protease Grass, which is activated downstream of pattern recognition receptors and was initially thought to be a component only of the Gram-positive bacteria-induced signaling cascade, is also required for the induction of the Toll pathway after fungal infection. Persephone, a serine protease known to be specifically activated by fungal proteases, was also found to be required for sensing Gram-positive bacterial proteases. Thus, Persephone serves as a sensor for microbial activities from both fungi and Gram-positive bacteria. With these new discoveries, a new model has been proposed for activation of the Drosophila Toll pathway.