Project description:Nonsense-mediated mRNA decay (NMD) controls gene expression by eliminating mRNAs with premature or aberrant translation termination. Degradation of NMD substrates is initiated by the central NMD factor UPF1, which recruits the endonuclease SMG6 and the deadenylation-promoting SMG5/7 complex. Here we map transcriptome-wide sites of SMG6-mediated endocleavage via 3′ fragment capture and degradome sequencing.
Project description:We have HA-tagged two nonsense-mediated decay proteins, UPF1 and UPF2, in the malaria parasite Plasmodium falciparum. We then performed co-immunoprecipitation experiments to determine the protein-protein interactions of these nonsense-mediated decay components.
Project description:Eukaryotic RNAs with premature termination codons (PTCs) are eliminated by nonsense-mediated decay (NMD). While human nonsense RNA degradation can be initiated either by an endonucleolytic cleavage event near the PTC or through decapping, the individual contribution of these activities on endogenous substrates has remained unresolved. Here we unambiguously establish that SMG6-catalyzed endonucleolysis is the primary initiating step in human nonsense RNA decay. We also show that both protein-coding and ‘non-coding’ genes hosting snoRNAs in their introns produce considerable amounts of NMD-sensitive splice variants, suggesting that these RNAs are merely by-products of a primary snoRNA production process. Finally, genes encoding multiple snoRNAs generally yield elevated numbers of alternative transcript isoforms, enabling the differential expression of individual snoRNAs. These findings demonstrate a hitherto unappreciated potential for decoupling of the individual expression levels of functional exon- and intron-encoded species from such composite genes. HEK293 Flp-In T-Rex cells were subjected to siRNA-mediated depletion of XRN1 and co-depletion of XRN1 with either SMG6 or UPF1. All the treated samples together with the controls were subjected to both RNA-seq and 5'-end-seq. RNA-seq was used for detecting NMD isoforms and their expression levels. 5'-end-seq was used for finding NMD decay intermediates (decapped and endocleaved molecules). CAGE was used to distinguish decapped from endocleaved RNA fragments.
Project description:Eukaryotic RNAs with premature termination codons (PTCs) are eliminated by nonsense-mediated decay (NMD). While human nonsense RNA degradation can be initiated either by an endonucleolytic cleavage event near the PTC or through decapping, the individual contribution of these activities on endogenous substrates has remained unresolved. Here we unambiguously establish that SMG6-catalyzed endonucleolysis is the primary initiating step in human nonsense RNA decay. We also show that both protein-coding and ‘non-coding’ genes hosting snoRNAs in their introns produce considerable amounts of NMD-sensitive splice variants, suggesting that these RNAs are merely by-products of a primary snoRNA production process. Finally, genes encoding multiple snoRNAs generally yield elevated numbers of alternative transcript isoforms, enabling the differential expression of individual snoRNAs. These findings demonstrate a hitherto unappreciated potential for decoupling of the individual expression levels of functional exon- and intron-encoded species from such composite genes. ------------------------------------------------------------------------------------- This article was corrected in http://genesdev.cshlp.org/content/30/9/1128.short Completely mapped 5'p-end sequencing data from the corrigendum have been updated in corresponding samples.
Project description:Purpose: We present a genome-wide investigation to distinguish mRNA substrates directly regulated by nonsense-mediated mRNA decay (NMD) from indirect secondary effects using true NMD null alleles Methods: mRNA profiles of wild type (N2), smg-1(r910), and smg-1(r910) smg-2(r915) animals were generated by deep sequencing, in triplicate, using Illumina HiSeq2000. We further performed deep sequencing in triplicate on RNAs that co-immunoprecipitate with the central effector of NMD, SMG-2, in both smg-1(r910) and smg-1(r910) smg-2(r915) mutant animals. The sequence reads that passed quality filters were analyzed at both the gene level and the intron level using Tophat2 and edgeR. qRT-PCR validation was performed using SYBR Green assays. Results: Using an optimized data analysis workflow, we mapped about 30 million sequence reads per sample to the mouse genome (build mm9) and identified 16,014 transcripts in the retinas of WT and Nrl−/− mice with BWA workflow and 34,115 transcripts with TopHat workflow. RNA-seq data confirmed stable expression of 25 known housekeeping genes, and 12 of these were validated with qRT–PCR. RNA-seq data had a linear relationship with qRT–PCR for more than four orders of magnitude and a goodness of fit (R2) of 0.8798. Approximately 10% of the transcripts showed differential expression between the WT and Nrl−/− retina, with a fold change ≥1.5 and p value <0.05. Altered expression of 25 genes was confirmed with qRT–PCR, demonstrating the high degree of sensitivity of the RNA-seq method. Hierarchical clustering of differentially expressed genes uncovered several as yet uncharacterized genes that may contribute to retinal function. Data analysis with BWA and TopHat workflows revealed a significant overlap yet provided complementary insights in transcriptome profiling. Conclusions: We found that a significant portion of genes with increased expression in an NMD-deficient background are direct substrates of SMG-2. Among the list of direct targets, we find many mRNAs from pseudogenes, alternative splice isoforms harboring PTCs, mRNAs encoding RNA processing factors, and two recently expanded gene families are directly regulated by the NMD pathway.
Project description:Analysis of cellular NMD (Nonsense-mediated mRNA decay) substrates that regulated by Upf1, SMG5, SMG7 and/or PNRC2 in HeLa cell. The hypothesis tested in the present study was that endogenous NMD substrates may co-regulated by Upf1, SMG5, SMG7 and PNRC2.
Project description:Nonsense-mediated mRNA decay (NMD) is a translation-dependent RNA quality-control pathway targeting transcripts such as messenger RNAs harboring premature stop-codons or short upstream open reading frame (uORFs). Our transcription start sites (TSSs) analysis of Saccharomyces cerevisiae cells deficient for RNA degradation pathways revealed that about half of the pervasive transcripts are degraded by NMD, which provides a fail-safe mechanism to remove spurious transcripts that escaped degradation in the nucleus. Moreover, we found that the low specificity of RNA polymerase II TSSs selection generates, for 47% of the expressed genes, NMD-sensitive transcript isoforms carrying uORFs or starting downstream of the ATG START codon. Despite the low abundance of this last category of isoforms, their presence seems to constrain genomic sequences, as suggested by the significant bias against in-frame ATGs specifically found at the beginning of the corresponding genes and reflected by a depletion of methionines in the N-terminus of the encoded proteins. 5'-end profile of WT and NMD deficient yeast cells
Project description:To exmine the role of nonsense-mediated mRNA decay process in the longevity regulation of daf-2 mutants, we sequenced transcriptomes from day 1 adult Caenorhabditis elegans: Bristol N2 (wild-type), and smg-2(qd101), daf-2(e1370) and smg-2(qd101); daf-2(e1370) mutants.
Project description:Nonsense-mediated mRNA decay (NMD) pathway promotes the degradation of several mRNA species, including transcripts containing a premature termination codon. Here,we measured global mRNA half-lives in NMD deficient and wild-type (WT) embryonic stem cells (ESCs). This allowed us to discriminate which transcripts are affected by NMD. Several transcripts had an impaired half-life in Smg5 and Smg6 KO ESCs compared to WT. They belong to different pathways and cellular processing indicating that NMD regulates multiple processes in the cells. Finally, majority of the transcripts had an impairment on the half-life in both Smg5 and Smg6 KO ESCs indicating that endo- and exonucleolityc branches of the NMD pathway target the same mRNAs.