ABSTRACT: Small RNAs have been implicated in numerous cellular processes, including effects on chromatin structure and the repression of transposons. We describe the generation of a small RNA response at DNA ends in Drosophila that is analogous to the recently reported DSB-induced RNAs (diRNAs) or Dicer and Drosha dependent small RNAs (ddRNAs) in Arabidopsis and vertebrates. Active transcription in the vicinity of the break amplifies this small RNA response, demonstrating that the normal mRNA contributes to the endo-siRNA precursor. The double-stranded RNA precursor forms with an antisense transcript that initiates at the DNA break. Breaks are thus sites of transcription initiation, a novel aspect of the cellular DSB response. This response is specific to a double-strand break since nicked DNA structures do not trigger small RNA production. The small RNAs are generated independently of the exact end structure (blunt, 3'- or 5'-overhang), can repress homologous sequences in trans and may therefore - in addition to putative roles in repair - exert a quality control function by clearing potentially truncated messages from genes in the vicinity of the break.
Project description:Small RNAs have been implicated in numerous cellular processes, including effects on chromatin structure and the repression of transposons. We describe the generation of a small RNA response at DNA ends in Drosophila that is analogous to the recently reported DSB-induced RNAs (diRNAs) or Dicer and Drosha dependent small RNAs (ddRNAs) in Arabidopsis and vertebrates. Active transcription in the vicinity of the break amplifies this small RNA response, demonstrating that the normal mRNA contributes to the endo-siRNA precursor. The double-stranded RNA precursor forms with an antisense transcript that initiates at the DNA break. Breaks are thus sites of transcription initiation, a novel aspect of the cellular DSB response. This response is specific to a double-strand break since nicked DNA structures do not trigger small RNA production. The small RNAs are generated independently of the exact end structure (blunt, 3'- or 5'-overhang), can repress homologous sequences in trans and may therefore - in addition to putative roles in repair - exert a quality control function by clearing potentially truncated messages from genes in the vicinity of the break. Drosophila melanogaster S2 cells were cultured and transfected with reporter gene plasmids that were either circular or modified by restriction digest prior to transfection. Following transfection, total RNA was isolated from the cells and gel-purified for size selection (~18-30 nt). Digested plasmid samples were compared to those of circular plasmids and a nontransfected control.
Project description:Here we identify a novel class of small RNAs that are ~21-nucleotide in length and are produced from the sequences in the vicinity of DNA double strand break (DSB) sites in Arabidopsis and humans. We named them diRNAs for DSB-induced small RNAs. In Arabidopsis, the biogenesis of diRNAs requires the PI3 kinase ATR, RNA polymerase IV (Pol IV), and Dicer-like proteins. Mutations in these proteins as well as in Pol V cause significant reduction in DSB repair efficiency. diRNAs are recruited by Argonaute 2 (AGO2) to mediate DSB repair. In humans, knocking down Dicer or Ago2 causes a significant reduction in DSB repair. Our findings reveal a novel biological function for small RNAs in the DSB repair pathway. We propose that diRNAs may function as guide molecules for chromatin modifications or recruitment of repair complexes at DSB sites to facilitate repair. 28 samples from Arabidopsis thaliana in various genetic backgrounds and 5 samples from the human cells, small RNA sequencing
Project description:Here we identify a novel class of small RNAs that are ~21-nucleotide in length and are produced from the sequences in the vicinity of DNA double strand break (DSB) sites in Arabidopsis and humans. We named them diRNAs for DSB-induced small RNAs. In Arabidopsis, the biogenesis of diRNAs requires the PI3 kinase ATR, RNA polymerase IV (Pol IV), and Dicer-like proteins. Mutations in these proteins as well as in Pol V cause significant reduction in DSB repair efficiency. diRNAs are recruited by Argonaute 2 (AGO2) to mediate DSB repair. In humans, knocking down Dicer or Ago2 causes a significant reduction in DSB repair. Our findings reveal a novel biological function for small RNAs in the DSB repair pathway. We propose that diRNAs may function as guide molecules for chromatin modifications or recruitment of repair complexes at DSB sites to facilitate repair.
Project description:Repair of DNA double-strand break (DSB) is critical for the maintenance of genome integrity. We have previously shown that a class of DSB-induced small RNAs (diRNAs) facilitates homologous recombination (HR)-mediated DSB repair in Arabidopsis thaliana. Here we show that INVOLVED IN DE NOVO 2 (IDN2), a double-stranded RNA (dsRNA) binding protein involved in small RNA-directed DNA methylation, is required for DSB repair in Arabidopsis. We find that IDN2 interacts with the heterotrimeric replication protein A (RPA) complex. Depletion of IDN2 or the diRNA-binding ARGONAUTE 2 (AGO2) leads to increased accumulation of RPA at DSB sites and mislocalization of the recombination factor RAD51. These findings support a model in which IDN2 interacts with RPA and facilitates the release of RPA from ssDNA tails and subsequent recruitment of RAD51 at DSB sites to promote DSB repair.
Project description:The repair of DNA double strand breaks (DSBs) has recently been shown to depend not only on protein function but also on RNA. In particular, the processing of a long damage-induced RNA into small damage induced RNAs (diRNAs) has been a focus of interest. Given that the RNA exosome has been shown in Drosophila and human cells to participate in DSB repair, we investigated whether the catalytic components EXOSC10 and DIS3 have a function in diRNA biogenesis in human cells.
Project description:Recent studies suggest that the repair of DNA double-strand breaks (DSBs) is supported by damage-induced small RNAs (diRNAs) that are generated by Drosha and Dicer from transcripts that originate from the regions flanking the break. However, transcription and diRNA production at naturally occurring DSBs in mammalian genomes remain controversial. We have used the homing endonuclease I-PpoI to produce DSBs in human and mouse cells, and we have analyzed the biogenesis of diRNAs at I-PpoI induced breaks in the 28S rDNA and the Ryr2 gene. We provide direct evidence that RNA polymerase II transcribes the sequences that flank the DSBs. Our results also reveal that the resulting transcripts are processed into two types of diRNAs with characteristic length and terminal nucleotide signatures. Furthermore, diRNA production is independent of Drosha and DGCR8, and only a subset of diRNAs depends on Dicer, as shown by small RNA analyses of knock-out cells that lack specific RNA processing enzymes. Our findings are compatible with previous observations of a general transcription inhibition at DSBs and provide novel insights into the mechanisms of RNA synthesis and processing at DSBs.
Project description:Sex chromosomes in males of most mammalian species share only a small homologous segment, the pseudoautosomal region (PAR), wherein double-strand break (DSB) formation must occur for correct meiotic segregation. We find that multiple DSB-promoting factors hyperaccumulate in the PAR, including the ankyrin-repeat domain-containing protein ANKRD31. We used immunoprecipitation and mass spectrometry from extracts of juvenile mouse testes to identify potential ANKRD31-interacting proteins.
Project description:SPO11-promoted DNA double-strand breaks (DSBs) formation is a crucial step for meiotic recombination, and it is indispensable to detect the broken DNA ends accurately for dissecting the molecular mechanisms behind. Here, we report a novel technique, named DEtail-seq (DNA End tailing followed by sequencing), that can directly and quantitatively capture the meiotic DSB 3’ overhang hotspots at single-nucleotide resolution.
Project description:SPO11-promoted DNA double-strand breaks (DSBs) formation is a crucial step for meiotic recombination, and it is indispensable to detect the broken DNA ends accurately for dissecting the molecular mechanisms behind. Here, we report a novel technique, named DEtail-seq (DNA End tailing followed by sequencing), that can directly and quantitatively capture the meiotic DSB 3’ overhang hotspots at single-nucleotide resolution.