Project description:Uncoupling X chromosome number from sex determination separates contribution of sex and X dose to sex-biased gene expression in C. elegans
Project description:During meiosis, gene expression is silenced in aberrantly unsynapsed chromatin and in heterogametic sex chromosomes. Initiation of sex chromosome silencing is disrupted in meiocytes with sex chromosome-autosome translocations. To determine whether this is due to aberrant synapsis or loss of continuity of sex chromosomes, we engineered Caenorhabditis elegans with non-translocated, bisected X chromosomes. In early meiocytes of mutant males and hermaphrodites, X segments were enriched with euchromatin assembly markers and active RNA polymerase II staining, indicating active transcription. Analysis of RNA-seq data showed that genes from the X chromosome were upregulated in gonads of mutant worms. Contrary to previous models, which predicted that any unsynapsed chromatin is silenced during meiosis, our data indicate that unsynapsed X segments are transcribed. Therefore, our results suggest that sex chromosome chromatin has a unique character that facilitates its meiotic expression when its continuity is lost, regardless of whether or not it is synapsed.
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: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: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.