Project description:Nearly every step of RNA regulation is mediated by binding proteins (RBPs). The most common method to identify specific RBP target transcripts in vivo is by crosslinking (“CLIP” and its variants), which rely on protein-RNA crosslinking and specific antibodies. Another recently introduced method exploits RNA editing, with the hyperactive mutant catalytic domain of ADAR covalently attached to a specific RBP (“HyperTRIBE”). Both CLIP and TRIBE approaches suffer from difficulties in distinguishing real RNA targets from false negative and especially false positive signals. To critically evaluate this problem, we used fibroblasts from a mouse where every endogenous β-actin mRNA molecule was tagged with the bacteriophage MS2 RNA stem loops in the β-actin 3’ UTR; hence there is only a single bona fide target mRNA for the MS2 capsid protein (MCP). CLIP and HyperTRIBE (hereafter referred to as TRIBE) could both detect the single RNA target, albeit with some false positives (transcripts lacking the MS2 stem loops). Consistent false positive CLIP signals could be attributed to nonspecific antibody interactions. However, to our surprise the putative false positive TRIBE targets correlated with the location of genes spatially proximal to the β-actin gene. This result indicates that MCP-ADAR bound to β-actin mRNA contacted and edited nearby nascent transcripts, as evidenced by frequent intronic editing. Importantly, nascent transcripts on nearby chromosomes were also edited, agreeing with the interchromosomal contacts observed in chromosome paint and Hi-C. These results were repeated in human osteosarcoma cells with a randomly integrated and inducible MS2 reporter and indicated that MS2-TRIBE can be applied to a broad array of cells and transcripts. The identification of nascent RNA-RNA contacts imply that RNA-regulatory proteins such as splicing factors can associate with multiple nascent transcripts and thereby form domains of post-transcriptional activity, which increase their local concentrations. These results indicate that TRIBE combined with the MS2 system, MS2-TRIBE, is a new tool to study nuclear RNA organization and regulation.
Project description:Most current methods to identify cell-specific RNA binding protein (RBP) targets require analyzing an extract, a strategy that is problematic with small amounts of material. We previously addressed this issue by developing TRIBE, a method that expresses an RBP of interest fused to the catalytic domain (cd) of the RNA editing enzyme ADAR. TRIBE performs Adenosine-to-Inosine editing on candidate RNA targets of the RBP. However, target identification is limited by the efficiency of the ADARcd. Here we describe HyperTRIBE, which carries a previously characterized hyperactive mutation (E488Q) of the ADARcd. HyperTRIBE identifies dramatically more editing sites than TRIBE, many of which are also edited by TRIBE but at a much lower editing frequency. The data have mechanistic implications for the enhanced editing activity of the HyperADARcd as part of a RBP fusion protein and also indicate that HyperTRIBE more faithfully recapitulates the known binding specificity of its RBP than TRIBE.
Project description:RNA transcripts are bound and regulated by RNA-binding proteins (RBPs). Current methods for identifying in vivo targets of a RBP are imperfect and not amenable to examining small numbers of cells. To address these issues, we developed TRIBE (Targets of RNA-binding proteins Identified By Editing), a technique that couples an RBP to the catalytic domain of the Drosophila RNA editing enzyme ADAR and expresses the fusion protein in vivo. RBP targets are marked with novel RNA editing events and identified by sequencing RNA. We have used TRIBE to identify the targets of three RBPs (Hrp48, dFMR1 and NonA). TRIBE compares favorably to other methods, including CLIP, and we have identified RBP targets from as little as 150 specific fly neurons. TRIBE can be performed without an antibody and in small numbers of specific cells.
Project description:C. elegans nuclear pore protein NPP-13 associates with small RNA genes transcribed by RNA Polymerase III. To test if the nuclear pore-chromatin interactions play a role in large-scale chromatin organization, we determined nuclear membrane-genome interactions and RNA Polymerase II localization in C. elegans embryos depleted for NPP-13. Genome-wide ChIP-seq and ChIP-chip for nuclear membrane protein LEM-2, RNA Polymerase II (AMA-1) and H3K4me3 were performed in mixed-stage C. elegans embryos depleted for NPP-13. As a control, ChIP was also performed in wild-type embryos treated with empty vector.
Project description:C. elegans nuclear pore protein NPP-13 associates with small RNA genes transcribed by RNA Polymerase III. To test if the nuclear pore-chromatin interactions play a role in large-scale chromatin organization, we determined nuclear membrane-genome interactions and RNA Polymerase II localization in C. elegans embryos depleted for NPP-13. Genome-wide ChIP-seq and ChIP-chip for nuclear membrane protein LEM-2, RNA Polymerase II (AMA-1) and H3K4me3 were performed in mixed-stage C. elegans embryos depleted for NPP-13. As a control, ChIP was also performed in wild-type embryos treated with empty vector.
Project description:C. elegans nuclear pore protein NPP-13 associates with small RNA genes transcribed by RNA Polymerase III. To test if the nuclear pore-chromatin interactions play a role in large-scale chromatin organization, we determined nuclear membrane-genome interactions and RNA Polymerase II localization in C. elegans embryos depleted for NPP-13.
Project description:C. elegans nuclear pore protein NPP-13 associates with small RNA genes transcribed by RNA Polymerase III. To test if the nuclear pore-chromatin interactions play a role in large-scale chromatin organization, we determined nuclear membrane-genome interactions and RNA Polymerase II localization in C. elegans embryos depleted for NPP-13.
Project description:It has been proposed that nucleome organization and genome function involve interplays between protein, RNA and chromatin architectures. However, how chromatin interactions are cooperatively mediated by nuclear proteins and RNAs have not been fully explored. Here, we report the multivalent interplays in Drosophila cells involving RNA Polymerase II (RNAPII), nuclear RNAs and chromatin interactions. Using a novel genomic approach (pRChIA-PET) for protein-RNA-chromatin interactions, we discovered that extensive combination of nuclear RNAs cooperatively act in trans and co-localize with RNAPII and associated protein cofactors at chromatin interaction loci of active promoters and enhancers. Nuclear perturbation by aliphatic alcohol and RNase-A revealed that chromatin associated nuclear RNAs (canRNAs) are likely integral components in phase-separation for transcriptional condensation, and may act to maintain open chromatin accessibility and long-range chromatin interactions. These findings suggest a significant architectural role for combinatorial canRNAs as potential scaffolding elements in 3D genome organization and transcriptional regulation.
Project description:RNA binding proteins (RBPs) perform a myriad of functions and are implicated in numerous neurological diseases. To identify the targets of RBPs in small numbers of cells, we developed TRIBE, in which the catalytic domain of the RNA editing enzyme ADAR (ADARcd) is fused to a RBP. In STAMP, the ADARcd is replaced by the RNA editing enzyme Apobec (REF). Here we compared the two enzymes fused to the RBP TDP43 in human cells. Although they both identified TDP43 target mRNAs, combining the two methods more successfully identified high confidence targets. We also assayed the two enzymes in Drosophila cells in which RBP-Apobec fusions generated only low numbers of editing sites comparable to the level of control editing. This was true for two different RBPs, Hrp48 and Thor (Drosophila EIF4E-BP), and contrasted with successful RBP-ADARcd fusions. The results indicate that TRIBE is the method of choice in Drosophila.