DNase II deficiency impairs innate immune function in Drosophila

Abstract

DNase II enzymes are highly conserved proteins that are required for the degradation of DNA within phagolysosomes. Engulfment of apoptotic cells and/or bacteria by phagocytic cells requires the function of DNase II to completely destroy ingested DNA. Mutation of the dnase II gene results in an increase of undegraded apoptotic DNA within phagocytic cells in mice and nematodes. Additionally, reduction of DNase II enzymatic activity in Drosophila melanogaster has been shown to lead to increased accumulation of DNA in the ovaries. Due to the importance of DNA clearance during infection, we hypothesized that a severe reduction of DNase II activity would result in diminished immune function and viability. To test this hypothesis, we knocked down DNase II activity in flies using RNAi. As expected, expression of a dnase II-RNAi construct in flies resulted in a dramatic reduction of DNase II activity and a significant decrease in total hemocyte numbers. Furthermore, infection of dnase II-RNAi flies with Gram negative or positive bacteria resulted in a severe reduction in fly viability. These results confirm that DNase II and the ability to clear macromolecular DNA is essential for maintaining proper immune function in Drosophila.

Persephone/Spätzle Pathogen Sensors Mediate the Activation of Toll Receptor Signaling in Response to Endogenous Danger Signals in Apoptosis-deficient Drosophila

“…The present study using Drosophila third instar larvae supports the scenario that Toll signaling is a key mechanism in the host defense system that responds to endogenous inflammatory factors, consistent with the dedicated role of Toll-like receptors in vertebrate "danger" sensing (1,47,48). A number of previous studies that focused on nonmicrobial signal-activated host defense in Drosophila showed that the Imd/Relish cascade is activated by endogenous inflammatory agents, such as undigested DNA (49,50) and the neuro-peptide bursicon (51), as well as undefined humoral factors released from the intestine after tissue damage (52). The observation of different signaling pathways that are activated in response to various forms of stress, and in the dronc mutant, indicate that specific detection mechanisms are used to discriminate among various forms of threat.…”

A Novel Pathway of Cell Death in Response to Cytosolic DNA in <b><i>Drosophila</i></b> Cells

“…A role for STING has not been investigated in the DNase II mutant fly, but we showed that it is unlikely to play a role in DNA-induced cell death. However, given the likely escape of undigested DNA into the cytosol of DNase II mutant cells, the cell death pathway we have described is consistent with the documented low level of haemocytes in the DNase II mutant flies [33]. …”

“…DNA within apoptotic cells is cut into nucleosomal units by caspase-activated DNase, and further DNase II-dependent degradation occurs following uptake into a macrophage phagolysosome [30,31]. A mutation in the Drosophila DNase II orthologue that leads to diminished enzyme activity results in accumulation of DNA in apoptotic cells in the ovary, increased susceptibility to bacterial infections, a reduced number of haemocytes, and elevated levels of the antimicrobial peptides diptericin and attacin A [32,33]. The induction of antimicrobial peptides was further increased in DNase II mutant flies without functional Drosophila caspase-activated DNase [32].…”

Journey to the grave: signaling events regulating removal of apoptotic cells

“…Studies in the nematode support this hypothesis: mutations in NUC-1 mimic mutations in the engulfment machinery, resulting in increased cell survival (Wu et al, 2000). Interestingly, Drosophila lacking DNase II also show decreased ability to phagocytose bacteria, providing further support for the idea that signaling from the lysosome to the phagosome is important for efficient phagocytosis (Seong et al, 2006).…”