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Repurposed nuclear speckle and mitosis components induce CTCF clustering to sustain the senescence splicing program [RNA-seq]

ABSTRACT: Senescence —the end-point of the replicative life span of normal cells— is characterized by a complex sequence of molecular and biochemical events. One of these is the dramatic reorganization of CTCF into large senescence-induced CTCF clusters (SICCs). However, the molecular determinants, genomic consequences, and functional purpose of SICCs remained unknown. Here, we combine super-resolution imaging, 3D genomics, and functional assays with computational modelling to address all aspects of SICC emergence. First, we used modelling and data from the overexpression of nuclear factors lost upon senescence entry to explain how changes in the nuclear environment allow for CTCF clustering. Second, we discovered that cells entering senescence repurpose SRRM2 —a key component of nuclear speckles— and BANF1 —a protein known to act as ‘molecular glue’ for chromosomes during mitosis— to cluster CTCF on the surface of speckles, while rewiring higher-order genome architecture. Last, we could show that SICCs are required for the faithful execution of the senescence splicing program as their disruption by SRRM2 or BANF1 depletion reverts splicing choices. Together, the senescence-specific clustering of CTCF on nuclear speckles is a new paradigm of a change in the biochemical environment of the nucleus being translated into its architectural reorganization to allow for the deployment of a splicing program driving homeostatic deregulation.

ORGANISM(S): Homo sapiens

PROVIDER: GSE269856 | GEO | 2024/06/17

REPOSITORIES: GEO

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Repurposed nuclear speckle and mitosis components induce CTCF clustering to sustain the senescence splicing program [ChIPmentation]

Project description:Senescence —the end-point of the replicative life span of normal cells— is characterized by a complex sequence of molecular and biochemical events. One of these is the dramatic reorganization of CTCF into large senescence-induced CTCF clusters (SICCs). However, the molecular determinants, genomic consequences, and functional purpose of SICCs remained unknown. Here, we combine super-resolution imaging, 3D genomics, and functional assays with computational modelling to address all aspects of SICC emergence. First, we used modelling and data from the overexpression of nuclear factors lost upon senescence entry to explain how changes in the nuclear environment allow for CTCF clustering. Second, we discovered that cells entering senescence repurpose SRRM2 —a key component of nuclear speckles— and BANF1 —a protein known to act as ‘molecular glue’ for chromosomes during mitosis— to cluster CTCF on the surface of speckles, while rewiring higher-order genome architecture. Last, we could show that SICCs are required for the faithful execution of the senescence splicing program as their disruption by SRRM2 or BANF1 depletion reverts splicing choices. Together, the senescence-specific clustering of CTCF on nuclear speckles is a new paradigm of a change in the biochemical environment of the nucleus being translated into its architectural reorganization to allow for the deployment of a splicing program driving homeostatic deregulation.

2024-06-17 | GSE269858 | GEO

Repurposed nuclear speckle and mitosis components induce CTCF clustering to sustain the senescence splicing program [eCLIP]

2024-06-17 | GSE269857 | GEO

Characterizing the interactome of human Arginyl-tRNA Synthethase

Project description:Prior work revealed nuclear-localized aminoacyl-tRNA synthetases (aaRSs) that checked newly synthesized tRNAs for charging before export to the cytoplasm. To reveal other functions, we sought to identify nuclear proteins that interact with arginyl-tRNA synthetase (ArgRS) in the nucleus. Serine/Arginine Repetitive Matrix Protein 2 (SRRM2), which is stored with RNA splicing apparatus components in nuclear speckle condensates, was found as a consistent interaction partner that co localized with SRRM2 ArgRS in nuclear speckles. Dynamic photo-bleaching experiments showed that, consistent with condensate properties, SRRM2 has a fluctuating appearance in speckles. Knock down of ArgRS impeded SRRM2 speckle trafficking and, coincidently, altered splicing processing of pre-mRNA transcripts. Among the altered spliced variants, those of tRNA synthetase family members were prominent. Thus, nuclear ArgRS shapes the dynamics of a protein in class of nuclear condensates. Also, the work expands the repertoire of nuclear tRNA synthetase roles to include regulation of RNA splicing, including of aaRS family member transcripts.

2023-04-14 | PXD015692 | Pride

TAF2 condensation in nuclear speckles links basal transcription factor TFIID to RNA splicing [CUT&RUN]

Project description:TFIID is an essential basal transcription factor, crucial for RNA polymerase II (pol II) promoter recognition and transcription initiation. The TFIID complex consists of the TATA-binding protein (TBP) and 13 TBP-associated factors (TAFs) that contain intrinsically disordered regions (IDRs) with currently unknown functions. Here, we show that a conserved IDR drives TAF2 condensation in nuclear speckles, independently of other TFIID subunits. Quantitative mass spectrometry analyses reveal that the TAF2 IDR specifically interacts with the nuclear speckle and spliceosome-associated protein SRRM2. Consequently, TAF2 recruits SRRM2 to TFIID to form non-canonical TFIID-SRRM2 complexes. Reduced SRRM2 recruitment elicits alternative splicing events in RNAs coding for proteins involved in transcription and transmembrane transport. Further, genome-wide binding analyses suggest TAF2 shuttling between nuclear speckles and pol II promoters. This study identifies an IDR of the basal transcription machinery as a molecular guide for protein partitioning into nuclear compartments, controlling protein complex composition and pre-mRNA splicing.

2024-02-06 | GSE254080 | GEO

TAF2 condensation in nuclear speckles links basal transcription factor TFIID to RNA splicing [RNA-Seq]

2024-02-06 | GSE254060 | GEO

SRRM2 Phase Separation Drives Assembly of Nuclear Speckle Subcompartments

Project description:Nuclear speckles (NSs) are nuclear biomolecular condensates that are postulated to arise through liquid-liquid phase separation (LLPS), although the detailed underlying forces driving NS formation remain elusive. SRRM2 and SON are 2 non-redundant scaffold proteins for NSs. How each individual protein governs assembly of NS protein network and the functional relationship between SRRM2 and SON are largely unknown. Here, we uncover immiscible multiphase of SRRM2 and SON within NSs. SRRM2 and SON are functionally independent, specifically regulating alternative splicing of subsets of mRNA targets, respectively. We further uncover that SRRM2 forms multicomponent liquid phase in cells to drive NS subcompartmentalization, which is reliant on homotypic interaction and heterotypic non-selective protein-RNA complex coacervation-driven multicomponent LLPS. SRRM2 RS domains form high-order oligomers, and can be replaced by oligomerizable synthetic modules, the serine residues within the RS domains, however, play an irreplaceable role in fine-tuning the liquidity of NSs.

2024-01-31 | GSE242898 | GEO

TAF2 condensation in nuclear speckles links basal transcription factor TFIID to RNA splicing

Project description:TFIID is an essential eukaryotic transcription factor, which is required for RNA polymerase II promoter recognition and activation. As a multiprotein complex, TFIID contains several intrinsically disordered regions (IDRs), but the functions of these IDRs are unknown. Here, we show that a conserved IDR drives the TFIID subunit TAF2 to nuclear speckles, where it forms biomolecular condensates, separate from the TFIID complex. Quantitative mass spectrometry analyses reveal that the TAF2 IDR is required for the interaction with the nuclear speckle and spliceosome-associated protein SRRM2, which is thereby recruited to TFIID. The formation of SRRM2-free TFIID complexes elicits a set of unique alternative splicing events. These include events in RNAs coding for proteins involved in transcription and transmembrane transport. Together, these data identify an IDR of the basal transcription machinery as a molecular switch between nuclear compartments to control protein complex composition and pre-mRNA splicing.

2024-04-26 | PXD049117 | Pride

Genome organization around nuclear speckles drives mRNA splicing efficiency

Project description:The nucleus is highly organized such that factors involved in transcription and processing of distinct classes of RNA are organized within specific nuclear bodies. One example is the nuclear speckle, which is defined by high concentrations of protein and non-coding RNA regulators of pre-mRNA splicing. What functional role, if any, speckles might play in the process of mRNA splicing remains unknown. Here we show that genes localized near nuclear speckles display higher spliceosome concentrations, increased spliceosome binding to their pre-mRNAs, and higher co-transcriptional splicing levels relative to genes that are located farther from nuclear speckles. We show that directed recruitment of a pre-mRNA to nuclear speckles is sufficient to increase mRNA splicing levels. Finally, we show that gene organization around nuclear speckles is highly dynamic with differential localization between cell types corresponding to differences in splicing efficiency. Together, our results integrate the longstanding observations of nuclear speckles with the biochemistry of mRNA splicing and demonstrate a critical role for dynamic 3D spatial organization of genomic DNA in driving spliceosome concentrations and controlling the efficiency of mRNA splicing.

2024-03-22 | GSE247833 | GEO

Effect of CLK2 expression in the regulation of intron retention during heat shock [RNA-seq]

Project description:Intron retention (IR) constitutes a less explored form of alternative splicing, wherein introns are retained within mature mRNA transcripts. Our investigation demonstrates that the CDC-like kinase 2 (CLK2) undergoes liquid-liquid phase separation (LLPS) within nuclear speckles in response to heat shock (HS). The formation of CLK2 condensates depends on the intrinsically disordered region (IDR) located within the N-terminal amino acids 1-148. Phosphorylation at residue T343 sustains CLK2 kinase activity and facilitates autophosphorylation, thus inhibiting the LLPS activity of the IDR. These CLK2 condensates initiate the reorganization of nuclear speckles, transforming them into larger, rounded structures. Moreover, these condensates facilitate the recruitment of splicing factors into these compartments, potentially restricting their access to mRNA for intron splicing. Consequently, the formation of CLK2 condensates promotes the IR.

2024-07-15 | GSE271918 | GEO

Dynamics of RNA localization to nuclear speckles are connected to splicing efficiency [RNA-Seq]

Project description:Nuclear speckles, a type of membraneless nuclear organelle in higher eukaryotic cells, play a vital role in gene expression regulation. Using the reverse transcription-based RBP binding sites sequencing (ARTR-seq) method, we study human transcripts associated with nuclear speckles. We identify three gene groups whose transcripts demonstrate different speckle localization properties and dynamics – stably enriched in nuclear speckle post-transcriptionally, transiently enriched in speckles at the pre-mRNA stage co-transcriptionally, and not enriched in speckles. We show that nuclear speckles specifically facilitate splicing of speckle-enriched transcripts. We further reveal RNA sequence features contributing to transcript speckle localization, underscoring a tight interplay between genome organization, RNA cis-elements, and transcript speckle enrichment, and connecting transcript speckle localization with splicing logic. Finally, we show that speckles can act as hubs for the regulated retention of introns during cellular stress. Collectively, our data highlight a role of nuclear speckles in both co- and post-transcriptional splicing regulation.

2024-09-05 | GSE255207 | GEO

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