Metabolic incorporation of electron-rich ribonucleosides enhances APEX-seq for profiling spatially restricted nascent transcriptome
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ABSTRACT: We present MERR APEX-seq, a method for newly transcribed RNAs subcellular profiling combined metabolic incorporation of electron-rich ribonucleosides, 6-thioguanosine and 4-thiouridine, with the peroxidase-mediated RNA labeling method, APEX-seq. MERR APEX-seq offers both high spatial specificity and high coverage in the mitochondrial matrix and at the endoplasmic reticulum membrane. Application of MERR APEX-seq at nuclear lamina of human cells reveals that the mRNA components tend to encode for transcripts processing related proteins. MERR APEX-seq with high spatial specificity and high coverage could be widely used to expand our knowledge of RNA localization and function at subcellular compartments.
Project description:We introduce APEX-seq, a method for RNA sequencing based on direct proximity labeling of RNA using the peroxidase enzyme APEX2. APEX-seq in nine distinct subcellular locales produced a nanometer-resolution spatial map of the human transcriptome as a resource, revealing extensive patterns of localization for diverse RNA classes and transcript isoforms. We uncover a radial organization of the nuclear transcriptome, which is gated at the inner surface of the nuclear pore for cytoplasmic export of processed transcripts. We identify two distinct pathways of messenger RNA localization to mitochondria, each associated with specific sets of transcripts for building complementary macromolecular machines within the organelle. APEX-seq should be widely applicable to many systems, enabling comprehensive investigations of the spatial transcriptome.
Project description:To address specificity of ALaP-seq for PMLwt, we performed genome-wide profiling of genomic regions associated with NLS-APEX or PMLca-APEX. Cells were treated with H2O2 to trigger labeling of chromatin with biotin (H2O2+). Experimental negative control for PMLca (H2O2-), where the H2O2 treatment was omitted, was also analyzed.
Project description:The spatial organization of RNA within cells is a crucial factor influencing a wide range of biological functions throughout all kingdoms of life. However, a general understanding of RNA localization has been hindered by a lack of simple, high-throughput methods for mapping the transcriptomes of subcellular compartments. Here, we develop such a method, termed APEX-RIP, which combines peroxidase-catalyzed, spatially restricted in situ protein biotinylation with RNA-protein chemical crosslinking. We demonstrate that, using a single protocol, APEX-RIP can isolate RNAs from a variety of subcellular compartments, including the mitochondrial matrix, nucleus, bulk cytosol, and endoplasmic reticulum (ER), with specificity and sensitivity that rival or exceed those of conventional approaches. We further identify candidate RNAs localized to mitochondria-ER junctions and nuclear lamina, two compartments that are recalcitrant to classical biochemical purification. Since APEX-RIP is simple, versatile, and does not require special instrumentation, we envision its broad application in a variety of biological contexts.
Project description:In addition to nucleic acids, a variety of biomolecules have been found on the plasma membrane. Whereas, researchers have realized that RNA has the ability to bind to membrane vesicles in vitro and connect to the plasma membrane of the cell. Hence, the combination of high-throughput sequencing and in suit labelling methods provides approaches for large-scale identification of subcellular RNAs. Here, we applied the recently published method APEX-seq, and identified 75 plasma membrane-associated RNAs, of which lncRNA PMAR72 is located around the membrane. In addition, we observed that PMAR72 was concentrated into foci in specific membrane areas. Our findings will provide some new evidence to elaborate the relationship between RNA and the plasma membrane of mammalian cells.
Project description:Stress granules are dynamic non-membrane bound organelles made up of untranslating messenger ribonucleoproteins (mRNPs) that form when cells integrate stressful environmental cues resulting in stalled translation initiation complexes. Although stress granules dramatically alter mRNA and protein localization, understanding these complexes has proven to be challenging through conventional imaging, purification, and crosslinking approaches. We therefore developed an RNA proximity labeling technique, APEX-Seq, which uses the ascorbate peroxidase APEX2 to probe the spatial organization of the transcriptome. We show that APEX-Seq can resolve the localization of RNAs within the cell and determine their enrichment or depletion near key RNA-binding proteins. Matching both the spatial transcriptome using APEX-seq, and the spatial proteome using APEX-mass spectrometry (APEX-MS) provide new insights into the organization of translation initiation complexes on active mRNAs, as well as revealing unanticipated complexity in stress granule contents, and provides a powerful approach to explore the spatial environment of macromolecules.
Project description:An integrating APEX proximity labeling and chemical cross-linking coupled with mass spectrometry (CXMS) platform named APEX-CXMS for spatially resolved subcellular interactome profiling in a high-throughput ma
Project description:Obtaining complete protein inventories for subcellular regions is a challenge that often limits our understanding of cellular function, especially for regions that are impossible to purify and are therefore inaccessible to traditional proteomic analysis. We recently developed a method to map proteomes in living cells with an engineered peroxidase (APEX) that bypasses the need for organellar purification when applied to membrane-bound compartments; however, it was insufficiently specific when applied to unbounded regions that allow APEX-generated radicals to escape. Here, we combine APEX technology with a SILAC-based ratiometric tagging strategy to substantially reduce unwanted background and achieve nanometer spatial resolution. This is applied to map the proteome of the mitochondrial intermembrane space (IMS), which can freely exchange small molecules with the cytosol. Our IMS proteome of 127 proteins has >94% specificity and includes nine newly discovered mitochondrial proteins. This approach will enable scientists to map proteomes of cellular regions that were previously inaccessible.
Project description:Although stress granules (SGs) are composed of a stable core structure, they are surrounded by a dynamic shell with assembly, disassembly, and transitions of proteins and RNA between the core and shell. Different SGs have distinct proteins and RNA constituents, which raises the possibility that different SGs might perform different biological functions. The RNA compositions of DDX3X- or DDX3Y-positive SGs are not known, nor is it known what differential effects DDX3X or DDX3Y may exert on these RNA components. To understand the biological function and the compositional differences between DDX3X- or DDX3Y-positive SGs, we first determined the RNA constituents in these SGs using an adapted Ascorbate-peroxidase (APEX)-based proximity labeling method. APEX converts exogenously supplied biotin-phenol (BP) to biotin-phenoxyl radicals, which in turn covalently labels protein and RNA in nanometers. APEX-mediated biotinylation has been widely used in studies of protein-protein interactions and recently in studying protein-RNA interactions. Here, we applied the APEX-mediated biotinylation in DDX3X and DDX3Y SGs to dissect their different RNA composition.