ABSTRACT
The maintenance of eukaryotic genome stability is ensured by the interplay of transcriptional as well as post-transcriptional mechanisms that control recombination of repeat regions and the expression and mobility of transposable elements. We report here that mutations in two (cytosine-5) RNA methyltransferases, Dnmt2 and NSun2, impact the accumulation of mobile element-derived sequences and DNA repeat integrity in Drosophila. Loss of Dnmt2 function caused moderate effects under standard conditions, while heat shock exacerbated these effects. In contrast, NSun2 function affected mobile element expression and genome integrity in a heat shock-independent fashion. Reduced tRNA stability in both RCMT mutants indicated that tRNA-dependent processes affected mobile element expression and DNA repeat stability. Importantly, further experiments indicated that complex formation with RNA could also contribute to the impact of RCMT function on gene expression control. These results thus uncover a link between tRNA modification enzymes, the expression of repeat DNA, and genomic integrity.
Subject(s)
DNA (Cytosine-5-)-Methyltransferases/genetics , Drosophila Proteins/genetics , Drosophila melanogaster/enzymology , Drosophila melanogaster/genetics , Gene Expression Regulation , Genomic Instability , Interspersed Repetitive Sequences/genetics , Amino Acid Sequence , Animals , Base Sequence , Biocatalysis , DNA (Cytosine-5-)-Methyltransferases/chemistry , DNA (Cytosine-5-)-Methyltransferases/metabolism , DNA Methylation/genetics , DNA Transposable Elements/genetics , Drosophila Proteins/chemistry , Drosophila Proteins/metabolism , Female , Gene Silencing , Genetic Loci , Heat-Shock Response/genetics , Male , RNA Stability , RNA, Transfer/genetics , Transcriptome/genetics , Y Chromosome/geneticsABSTRACT
Transfer RNA (tRNA) fragmentation in response to stress conditions has been described in many organisms. tRNA fragments have been found in association with small interfering RNA (siRNA) components, but the biological role of these interactions remains unclear. We report here that the tRNA methyltransferase Dnmt2 is essential for efficient Dicer-2 (Dcr-2) function in Drosophila. Using small RNA (sRNA) sequencing, we confirmed that Dnmt2 limits the extent of tRNA fragmentation during the heat-shock response. tRNAs as well as tRNA fragments serve as Dcr-2 substrates, and Dcr-2 degrades tRNA-derived sequences, especially under heat-shock conditions. tRNA-derived RNAs are able to inhibit Dcr-2 activity on long double-stranded RNAs (dsRNAs). Consequently, heat-shocked Dnmt2 mutant animals accumulate dsRNAs, produce fewer siRNAs, and show misregulation of siRNA pathway-dependent genes. These results reveal the impact of tRNA fragmentation on siRNA pathways and implicate tRNA modifications in the regulation of sRNA homeostasis during the heat-shock response.
