Project description:The LSM2-8 complex specifically targets nuclear RNAs generated from loci bearing histone H3K27me3 for degradation through the exonuclease XRN-2 In fission yeast and plants RNA-processing pathways including co-transcriptional degradation of nuclear mRNAs contributes to heterochromatic gene silencing additionally to the well-known transcriptional repression, but it was not knownunclear if this extra level of regulation also to occur in metazoans. Here we report the discovery of a related pathway in somatic cells of the flatworm C. elegans. The highly conserved, RNA binding LSM2-8 complex is shown to silence selectively heterochromatic reporters and endogenous genes bearing the Polycomb mark H2K27me3. LSM2-8-mediated silencing is independent of H3K9me2/me3 but depends on mes-2, the Polycomb-like histone methyl transferase. LSM2-8-mediated silencing is detectable from early embryonic stages through adulthood. The LSM2-8 complex works cooperatively with XRN-2, a 5’-3’ exonuclease, and disruption of the pathway leads to stabilized targeted mRNAs. Developmental defects and premature death were observed in worms lacking LSM-8, and levels of H3K27me3 dropped slightly at Pc-targeted loci. LSM2-8-mediated silencing of H3K27me3-bound regions defines a new mechanism of selective heterochromatin gene silencing not previously shown for higher eukaryotes.
Project description:The LSM2-8 complex specifically targets nuclear RNAs generated from loci bearing histone H3K27me3 for degradation through the exonuclease XRN-2 In fission yeast and plants RNA-processing pathways including co-transcriptional degradation of nuclear mRNAs contributes to heterochromatic gene silencing additionally to the well-known transcriptional repression, but it was not knownunclear if this extra level of regulation also to occur in metazoans. Here we report the discovery of a related pathway in somatic cells of the flatworm C. elegans. The highly conserved, RNA binding LSM2-8 complex is shown to silence selectively heterochromatic reporters and endogenous genes bearing the Polycomb mark H2K27me3. LSM2-8-mediated silencing is independent of H3K9me2/me3 but depends on mes-2, the Polycomb-like histone methyl transferase. LSM2-8-mediated silencing is detectable from early embryonic stages through adulthood. The LSM2-8 complex works cooperatively with XRN-2, a 5’-3’ exonuclease, and disruption of the pathway leads to stabilized targeted mRNAs. Developmental defects and premature death were observed in worms lacking LSM-8, and levels of H3K27me3 dropped slightly at Pc-targeted loci. LSM2-8-mediated silencing of H3K27me3-bound regions defines a new mechanism of selective heterochromatin gene silencing not previously shown for higher eukaryotes.
Project description:The LSM2-8 complex specifically targets nuclear RNAs generated from loci bearing histone H3K27me3 for degradation through the exonuclease XRN-2 In fission yeast and plants RNA-processing pathways including co-transcriptional degradation of nuclear mRNAs contributes to heterochromatic gene silencing additionally to the well-known transcriptional repression, but it was not knownunclear if this extra level of regulation also to occur in metazoans. Here we report the discovery of a related pathway in somatic cells of the flatworm C. elegans. The highly conserved, RNA binding LSM2-8 complex is shown to silence selectively heterochromatic reporters and endogenous genes bearing the Polycomb mark H2K27me3. LSM2-8-mediated silencing is independent of H3K9me2/me3 but depends on mes-2, the Polycomb-like histone methyl transferase. LSM2-8-mediated silencing is detectable from early embryonic stages through adulthood. The LSM2-8 complex works cooperatively with XRN-2, a 5’-3’ exonuclease, and disruption of the pathway leads to stabilized targeted mRNAs. Developmental defects and premature death were observed in worms lacking LSM-8, and levels of H3K27me3 dropped slightly at Pc-targeted loci. LSM2-8-mediated silencing of H3K27me3-bound regions defines a new mechanism of selective heterochromatin gene silencing not previously shown for higher eukaryotes.
Project description:XRN2 is a conserved 5â??-->3â?? exoribonuclease that complexes with XTB-domain containing proteins. Thus, in Caenorhabditis elegans (C. elegans), the XTBD-protein PAXT-1 stabilizes XRN2 to retain its activity. XRN2 activity is also promoted by 3'(2'),5'-bisphosphate nucleotidase 1 (BPNT1) through its hydrolysis of 3â??-phosphoadenosine-5'-bisphosphate (PAP), an endogenous XRN inhibitor. Here, we find through unbiased screening that loss of bpnt-1 function suppresses lethality caused by paxt-1 deletion. This unexpected finding is explained by XRN2 autoregulation, which occurs through repression of a cryptic promoter activity and destabilization of the xrn-2 transcript. Autoregulation appears to be triggered at different thresholds of XRN2 inactivation, such that more robust XRN2 perturbation, by elimination of both PAXT-1 and BPNT1, is less detrimental to worm viability than absence of PAXT-1 alone. Like more than 15% of C. elegans genes, xrn-2 occurs in an operon, and we identify additional operons under its control, consistent with a broader function of XRN2 in polycistronic gene regulation. Regulation occurs through intercistronic regions that link genes in an operon, but similar mechanisms may allow XRN2 to operate on monocistronic genes in organisms lacking operons. Wild-type C. elegans worms were subjected to mock or xrn-2 RNAi from L1 to L4 stage at 20°C. Total RNA was extracted from the worms, and polyadenylated RNA was analyzed.
Project description:XRN2 is a conserved 5’-->3’ exoribonuclease that complexes with XTB-domain containing proteins. Thus, in Caenorhabditis elegans (C. elegans), the XTBD-protein PAXT-1 stabilizes XRN2 to retain its activity. XRN2 activity is also promoted by 3'(2'),5'-bisphosphate nucleotidase 1 (BPNT1) through its hydrolysis of 3’-phosphoadenosine-5'-bisphosphate (PAP), an endogenous XRN inhibitor. Here, we find through unbiased screening that loss of bpnt-1 function suppresses lethality caused by paxt-1 deletion. This unexpected finding is explained by XRN2 autoregulation, which occurs through repression of a cryptic promoter activity and destabilization of the xrn-2 transcript. Autoregulation appears to be triggered at different thresholds of XRN2 inactivation, such that more robust XRN2 perturbation, by elimination of both PAXT-1 and BPNT1, is less detrimental to worm viability than absence of PAXT-1 alone. Like more than 15% of C. elegans genes, xrn-2 occurs in an operon, and we identify additional operons under its control, consistent with a broader function of XRN2 in polycistronic gene regulation. Regulation occurs through intercistronic regions that link genes in an operon, but similar mechanisms may allow XRN2 to operate on monocistronic genes in organisms lacking operons.