Drosophila Toll is activated by Gram-positive bacteria through a circulating peptidoglycan recognition protein

Tatiana Michel, Jean-Marc Reichhart, Jules A. Hoffmann and Julien Royet ()
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Tatiana Michel: Institut de Biologie Moléculaire et Cellulaire, UPR 9022 du CNRS
Jean-Marc Reichhart: Institut de Biologie Moléculaire et Cellulaire, UPR 9022 du CNRS
Jules A. Hoffmann: Institut de Biologie Moléculaire et Cellulaire, UPR 9022 du CNRS
Julien Royet: Institut de Biologie Moléculaire et Cellulaire, UPR 9022 du CNRS

Nature, 2001, vol. 414, issue 6865, 756-759

Abstract: Abstract Microbial infection activates two distinct intracellular signalling cascades in the immune-responsive fat body of Drosophila1,2. Gram-positive bacteria and fungi predominantly induce the Toll signalling pathway, whereas Gram-negative bacteria activate the Imd pathway3,4. Loss-of-function mutants in either pathway reduce the resistance to corresponding infections4,5. Genetic screens have identified a range of genes involved in these intracellular signalling cascades6,7,8,9,10,11,12, but how they are activated by microbial infection is largely unknown. Activation of the transmembrane receptor Toll requires a proteolytically cleaved form of an extracellular cytokine-like polypeptide, Spätzle13, suggesting that Toll does not itself function as a bona fide recognition receptor of microbial patterns. This is in apparent contrast with the mammalian Toll-like receptors14 and raises the question of which host molecules actually recognize microbial patterns to activate Toll through Spätzle. Here we present a mutation that blocks Toll activation by Gram-positive bacteria and significantly decreases resistance to this type of infection. The mutation semmelweis (seml) inactivates the gene encoding a peptidoglycan recognition protein (PGRP-SA). Interestingly, seml does not affect Toll activation by fungal infection, indicating the existence of a distinct recognition system for fungi to activate the Toll pathway.

Date: 2001
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DOI: 10.1038/414756a

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