Project description:Piwi Argonautes and Piwi-interacting RNAs (piRNAs) mediate genome defense by targeting transposons. However, many piRNA species lack obvious sequence complementarity to transposons or other loci. For example, only one C. elegans transposon is a known piRNA target. Here we show that, in mutants lacking the Piwi Argonaute PRG-1 and associated piRNAs (21U-RNAs), many silent loci in the germline exhibit increased levels of mRNA expression and depletion of an amplified RNAdependent RNA polymerase (RdRP)-derived species of small RNA termed 22G-RNAs. Sequences depleted of 22G-RNAs are enriched nearby potential target sites that base pair imperfectly but extensively to 21U-RNAs. We show that PRG-1 is required to initiate, but not to maintain, silencing of transgenes engineered to contain complementarity to endogenous 21U-RNAs. Our findings support a model in which C. elegans piRNAs utilize their enormous repertoire of targeting capacity to scan the germline transcriptome for foreign sequences, while endogenous germline-expressed genes are actively protected from piRNA-induced silencing. Examine small RNA population changes in prg-1 and rescued strains
Project description:piRNAs are required to maintain germline integrity and fertility but their mechanism of action is poorly understood. Here we demonstrate that C. elegans piRNAs silence transcripts in trans through imperfectly complementary sites. We find that target silencing is independent of Piwi endonuclease activity or “slicing”. Instead, we show that piRNAs initiate a localized secondary endogenous small interfering RNA (endo-siRNA) response. Endogenous protein-coding gene, pseudogene and transposon transcripts exhibit Piwi-dependent endo-siRNAs at sites complementary to piRNAs and are derepressed in Piwi mutants. Genomic loci of piRNA biogenesis are depleted of protein-coding genes but not pseudogenes or transposons. Our data suggest that nematode piRNA clusters are evolving to generate piRNAs against active mobile elements. Thus, piRNAs provide heritable, sequence-specific triggers for RNAi in C. elegans. Affymetrix mRNA expression data from wild-type and two independent prg-1;prg-2 double mutant C. elegans strains (mRNA)
Project description:Small RNA libraries from total RNA isolated from adult animals Small RNA libraries were derived from genetically identical strains carrying a 21Usensor transgene in single copy. In one strain the transgene has become permanently silent and is not reactivated by RNAi against prg-1 (RNAe). In the other the transgene reactivates upon RNAi against prg-1.
Project description:Argonaute-associated siRNAs and Piwi-associated piRNAs have overlapping roles in silencing mobile genetic elements in animals. In C. elegans, mutator-class (mut) genes mediate siRNA-guided repression of transposons as well as exogenous RNA-directed gene silencing (RNAi), but their roles in endogenous RNA silencing pathways are not well understood. To characterize the endogenous small RNAs dependent on mutator-class genes, small RNA populations from a null allele of mut-16, as well as a regulatory mut-16(mg461) allele that disables only somatic RNAi, were subjected to deep sequencing. Small RNA analysis in wild type and mut-16 mutant C. elegans strains
Project description:piRNAs are required to maintain germline integrity and fertility but their mechanism of action is poorly understood. Here we demonstrate that C. elegans piRNAs silence transcripts in trans through imperfectly complementary sites. We find that target silencing is independent of Piwi endonuclease activity or “slicing”. Instead, we show that piRNAs initiate a localized secondary endogenous small interfering RNA (endo-siRNA) response. Endogenous protein-coding gene, pseudogene and transposon transcripts exhibit Piwi-dependent endo-siRNAs at sites complementary to piRNAs and are derepressed in Piwi mutants. Genomic loci of piRNA biogenesis are depleted of protein-coding genes but not pseudogenes or transposons. Our data suggest that nematode piRNA clusters are evolving to generate piRNAs against active mobile elements. Thus, piRNAs provide heritable, sequence-specific triggers for RNAi in C. elegans.
Project description:Animal germ cells employ small RNA-based mechanisms to recognize and silence DNA that invades their genome. One of these pathways is named the Piwi:piRNA pathway. Biogenesis of piRNAs is poorly understood. In C. elegans, the piRNA (21U-RNA)-binding Argonaute protein PRG-1 is the only known player acting downstream of pre-cursor transcription. From a screen aimed at the isolation of M-bM-^@M-^XpiRNA-induced silencing defectiveM-bM-^@M-^Y mutations we identified, amongst known Piwi-pathway components like MUT-7, RDE-3 and HRDE-1, PID-1 as a novel player. PID-1 is essential for 21U RNA biogenesis and affects an early step in the processing or transport of 21U precursor transcripts. 12 small RNA samples were analyzed as singletons.
Project description:piRNAs are required to maintain germline integrity and fertility but their mechanism of action is poorly understood. Here we demonstrate that C. elegans piRNAs silence transcripts in trans through imperfectly complementary sites. We find that target silencing is independent of Piwi endonuclease activity or “slicing”. Instead, we show that piRNAs initiate a localized secondary endogenous small interfering RNA (endo-siRNA) response. Endogenous protein-coding gene, pseudogene and transposon transcripts exhibit Piwi-dependent endo-siRNAs at sites complementary to piRNAs and are derepressed in Piwi mutants. Genomic loci of piRNA biogenesis are depleted of protein-coding genes but not pseudogenes or transposons. Our data suggest that nematode piRNA clusters are evolving to generate piRNAs against active mobile elements. Thus, piRNAs provide heritable, sequence-specific triggers for RNAi in C. elegans. 7 small RNA libraries were sequenced as part of 25 flow cell lanes on the Illumina GA II platform. Samples were treated with tobacco acid pyrophosphatase to allow cloning of small RNAs with a 5'-triphosphate. Samples were labelled for multiplexing using 4-bp 5'-barcodes or barcodes included in Illumina TruSeq adapters. In most cases a single flow cell lane included several multiplexed libraries.
Project description:piRNAs are required to maintain germline integrity and fertility but their mechanism of action is poorly understood. Here we demonstrate that C. elegans piRNAs silence transcripts in trans through imperfectly complementary sites. We find that target silencing is independent of Piwi endonuclease activity or “slicing”. Instead, we show that piRNAs initiate a localized secondary endogenous small interfering RNA (endo-siRNA) response. Endogenous protein-coding gene, pseudogene and transposon transcripts exhibit Piwi-dependent endo-siRNAs at sites complementary to piRNAs and are derepressed in Piwi mutants. Genomic loci of piRNA biogenesis are depleted of protein-coding genes but not pseudogenes or transposons. Our data suggest that nematode piRNA clusters are evolving to generate piRNAs against active mobile elements. Thus, piRNAs provide heritable, sequence-specific triggers for RNAi in C. elegans.
Project description:Animal germ cells employ small RNA-based mechanisms to recognize and silence DNA that invades their genome. One of these pathways is named the Piwi:piRNA pathway. Biogenesis of piRNAs is poorly understood. In C. elegans, the piRNA (21U-RNA)-binding Argonaute protein PRG-1 is the only known player acting downstream of pre-cursor transcription. From a screen aimed at the isolation of ‘piRNA-induced silencing defective’ mutations we identified, amongst known Piwi-pathway components like MUT-7, RDE-3 and HRDE-1, PID-1 as a novel player. PID-1 is essential for 21U RNA biogenesis and affects an early step in the processing or transport of 21U precursor transcripts.