Search

Drosophila melanogaster flies mount an impressive immune response to a variety of pathogens with an efficient system comprised of both humoral and cellular responses. The fat body is the main producer of the anti-microbial peptides (AMPs) with anti-pathogen activity. During bacterial infection, an array of secreted peptidases, proteases and other enzymes are involved in the dissolution of debris generated by pathogen clearance. Although pathogen destruction should result in the release a large amount of nucleic acids, the mechanisms for its removal are still not known. In this report, we present the characterization of a nuclease gene that is induced not only by bacterial infection but also by oxidative stress. Expression of the identified protein has revealed that it encodes a potent nuclease that has been named Stress Induced DNase (SID). SID belongs to a family of evolutionarily conserved cation-dependent nucleases that degrade both single and double-stranded nucleic acids. Down-regulation of sid expression via RNA interference leads to significant reduction of fly viability after bacterial infection and oxidative stress. Our results indicate that SID protects flies from the toxic effects of excess DNA/RNA released by pathogen destruction and from oxidative damage. [ABSTRACT FROM AUTHOR]

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. [Copyright &y& Elsevier]