Drosophila DNA double-strand break induced siRNAs

It has been well established that small interfering RNAs (siRNAs), a class of small RNAs, act as line of defense against harmful transcripts stemming from exogenous (e.g. viral) or endogenous (e.g. transposons) sources. Recent publications describe the DNA double-strand break (DSB) induced production of small RNAs in Neurospora crassa, Arabidopsis thaliana, Drosophila melanogaster and human cell lines, which suggests a conserved function. A current hypothesis is that break-induced small RNAs ensure efficient homologous recombination (HR). However, biogenesis of siRNAs is often intertwined with other small RNA species, such as microRNAs (miRNAs), which complicates interpretation of experimental results. In Drosophila, siRNAs are produced by Dcr-2 while miRNAs are processed by Dcr-1. Thus, it is possible to examine siRNA function without indirect effects due to miRNA deregulation. We now report that Drosophila DSB repair in cultured cells and flies is independent of siRNAs. Our assays comprised in vivo cleavable reporters, genome editing via HR and camptothecin treatment. Since break induced siRNAs depend on local transcription in Drosophila, any function during DNA repair would also have a limited scope within the genome. Instead, they might function in an mRNA quality control pathway that is triggered by perturbed transcription due to DNA breaks.