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Abstract
Transcription of eukaryotic genes by RNA polymerase II (Pol II) yields RNA precursors containing introns that must be spliced out and the flanking exons ligated together. Splicing is catalyzed by a dynamic ribonucleoprotein complex called the spliceosome. Recent evidence has shown that a large fraction of splicing occurs cotranscriptionally as the RNA chain is extruded from Pol II at speeds of up to 5 kb/minute. Splicing is more efficient when it is tethered to the transcription elongation complex, and this linkage permits functional coupling of splicing with transcription. We discuss recent progress that has uncovered a network of connections that link splicing to transcript elongation and other cotranscriptional RNA processing events.
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Affiliation(s)
- Hossein Shenasa
- Department of Biochemistry and Molecular Genetics, RNA Bioscience Initiative, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA
| | - David L Bentley
- Department of Biochemistry and Molecular Genetics, RNA Bioscience Initiative, University of Colorado School of Medicine, PO Box 6511, Aurora, CO 80045, USA.
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2
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Koh E, Shin D, Kim KS. Exon definitive regions for MPC1 microexon splicing and its usage for splicing modulation. Mol Ther Nucleic Acids 2023; 31:398-410. [PMID: 36817727 PMCID: PMC9929638 DOI: 10.1016/j.omtn.2023.01.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Accepted: 01/20/2023] [Indexed: 01/26/2023]
Abstract
Alternative splicing of microexons (3-30 base pairs [bp]) is involved in important biological processes in brain development and human cancers. However, understanding a splicing process of non-3x bp microexons is scarce. We showed that 4 bp microexon of mitochondrial pyruvate carrier1 (MPC1) is constitutively included in mRNA. Based on our studies with minigene and exon island constructs, we found the strong exon definition region in the proximal introns bordering MPC1 microexon. Ultimately, we defined a nucleotide fragment from the 3'ss 67 bp of MPC1 microexon to the 5'ss consensus sequence, as a core exon island, which can concatenate its microexon and neighboring exons by splicing. Furthermore, we showed that insertion of the core exon island into a target exon or intron induced skip the target exon or enhance the splicing of an adjacent exon, respectively. Collectively, we suggest that the exon island derived from MPC1 microexon modifies genuine splicing patterns depending on its position, thereby providing insights on strategies for splicing-mediated gene correction.
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Affiliation(s)
- Eunjin Koh
- Department of Biochemistry and Molecular Biology, Institute of Genetic Science, Yonsei University College of Medicine, Seoul 03722, Korea
| | - Daye Shin
- Department of Biochemistry and Molecular Biology, Institute of Genetic Science, Yonsei University College of Medicine, Seoul 03722, Korea
| | - Kyung-Sup Kim
- Department of Biochemistry and Molecular Biology, Institute of Genetic Science, Yonsei University College of Medicine, Seoul 03722, Korea,Corresponding author: Kyung-Sup Kim, Department of Biochemistry and Molecular Biology, Institute of Genetic Science, College of Medicine, Yonsei University, Seoul 03722, Korea.
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3
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Zeng Y, Fair BJ, Zeng H, Krishnamohan A, Hou Y, Hall JM, Ruthenburg AJ, Li YI, Staley JP. Profiling lariat intermediates reveals genetic determinants of early and late co-transcriptional splicing. Mol Cell 2022; 82:4681-4699.e8. [PMID: 36435176 PMCID: PMC10448999 DOI: 10.1016/j.molcel.2022.11.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Revised: 09/10/2022] [Accepted: 11/02/2022] [Indexed: 11/27/2022]
Abstract
Long introns with short exons in vertebrate genes are thought to require spliceosome assembly across exons (exon definition), rather than introns, thereby requiring transcription of an exon to splice an upstream intron. Here, we developed CoLa-seq (co-transcriptional lariat sequencing) to investigate the timing and determinants of co-transcriptional splicing genome wide. Unexpectedly, 90% of all introns, including long introns, can splice before transcription of a downstream exon, indicating that exon definition is not obligatory for most human introns. Still, splicing timing varies dramatically across introns, and various genetic elements determine this variation. Strong U2AF2 binding to the polypyrimidine tract predicts early splicing, explaining exon definition-independent splicing. Together, our findings question the essentiality of exon definition and reveal features beyond intron and exon length that are determinative for splicing timing.
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Affiliation(s)
- Yi Zeng
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA
| | - Benjamin J Fair
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA
| | - Huilin Zeng
- 855 Jefferson Ave. Redwood City, CA 94063, USA
| | - Aiswarya Krishnamohan
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA
| | - Yichen Hou
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA
| | - Johnathon M Hall
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA
| | - Alexander J Ruthenburg
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA; Department of Biochemistry & Molecular Biology, University of Chicago, Chicago, IL 60637, USA
| | - Yang I Li
- Department of Medicine, University of Chicago, Chicago, IL 60637, USA; Department of Human Genetics, University of Chicago, Chicago, IL 60637, USA.
| | - Jonathan P Staley
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
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Liu L, Das U, Ogunsola S, Xie J. Transcriptome-Wide Detection of Intron/Exon Definition in the Endogenous Pre-mRNA Transcripts of Mammalian Cells and Its Regulation by Depolarization. Int J Mol Sci 2022; 23:10157. [PMID: 36077555 DOI: 10.3390/ijms231710157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Revised: 08/31/2022] [Accepted: 09/01/2022] [Indexed: 11/23/2022] Open
Abstract
Pairing of splice sites across an intron or exon is the central point of intron or exon definition in pre-mRNA splicing with the latter mode proposed for most mammalian exons. However, transcriptome-wide pairing within endogenous transcripts has not been examined for the prevalence of each mode in mammalian cells. Here we report such pairings in rat GH3 pituitary cells by measuring the relative abundance of nuclear RNA-Seq reads at the intron start or end (RISE). Interestingly, RISE indexes are positively correlated between 5′ and 3′ splice sites specifically across introns or exons but inversely correlated with the usage of adjacent exons. Moreover, the ratios between the paired indexes were globally modulated by depolarization, which was disruptible by 5-aza-Cytidine. The nucleotide matrices of the RISE-positive splice sites deviate significantly from the rat consensus, and short introns or exons are enriched with the cross-intron or -exon RISE pairs, respectively. Functionally, the RISE-positive genes cluster for basic cellular processes including RNA binding/splicing, or more specifically, hormone production if regulated by depolarization. Together, the RISE analysis identified the transcriptome-wide regulation of either intron or exon definition between weak splice sites of short introns/exons in mammalian cells. The analysis also provides a way to further track the splicing intermediates and intron/exon definition during the dynamic regulation of alternative splicing by extracellular factors.
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Tammer L, Hameiri O, Keydar I, Roy VR, Ashkenazy-Titelman A, Custódio N, Sason I, Shayevitch R, Rodríguez-Vaello V, Rino J, Lev Maor G, Leader Y, Khair D, Aiden EL, Elkon R, Irimia M, Sharan R, Shav-Tal Y, Carmo-Fonseca M, Ast G. Gene architecture directs splicing outcome in separate nuclear spatial regions. Mol Cell 2022; 82:1021-1034.e8. [PMID: 35182478 DOI: 10.1016/j.molcel.2022.02.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Revised: 01/31/2022] [Accepted: 01/31/2022] [Indexed: 12/13/2022]
Abstract
How the splicing machinery defines exons or introns as the spliced unit has remained a puzzle for 30 years. Here, we demonstrate that peripheral and central regions of the nucleus harbor genes with two distinct exon-intron GC content architectures that differ in the splicing outcome. Genes with low GC content exons, flanked by long introns with lower GC content, are localized in the periphery, and the exons are defined as the spliced unit. Alternative splicing of these genes results in exon skipping. In contrast, the nuclear center contains genes with a high GC content in the exons and short flanking introns. Most splicing of these genes occurs via intron definition, and aberrant splicing leads to intron retention. We demonstrate that the nuclear periphery and center generate different environments for the regulation of alternative splicing and that two sets of splicing factors form discrete regulatory subnetworks for the two gene architectures. Our study connects 3D genome organization and splicing, thus demonstrating that exon and intron definition modes of splicing occur in different nuclear regions.
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Affiliation(s)
- Luna Tammer
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Ofir Hameiri
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Ifat Keydar
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Vanessa Rachel Roy
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Asaf Ashkenazy-Titelman
- The Mina & Everard Goodman Faculty of Life Sciences and the Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 5290002, Israel
| | - Noélia Custódio
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, 1649-028 Lisboa, Portugal
| | - Itay Sason
- Blavatnik School of Computer Science, Tel Aviv University, Tel Aviv 69978, Israel
| | - Ronna Shayevitch
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Victoria Rodríguez-Vaello
- Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain. Universitat Pompeu Fabra (UPF), Barcelona, Spain, ICREA, Barcelona, Spain
| | - José Rino
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, 1649-028 Lisboa, Portugal
| | - Galit Lev Maor
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Yodfat Leader
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Doha Khair
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Erez Lieberman Aiden
- The Center for Genome Architecture, Baylor College of Medicine, Houston, TX 77030, USA
| | - Ran Elkon
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel
| | - Manuel Irimia
- Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain. Universitat Pompeu Fabra (UPF), Barcelona, Spain, ICREA, Barcelona, Spain
| | - Roded Sharan
- Blavatnik School of Computer Science, Tel Aviv University, Tel Aviv 69978, Israel
| | - Yaron Shav-Tal
- The Mina & Everard Goodman Faculty of Life Sciences and the Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 5290002, Israel
| | - Maria Carmo-Fonseca
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, 1649-028 Lisboa, Portugal
| | - Gil Ast
- Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel.
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Drexler HL, Choquet K, Churchman LS. Splicing Kinetics and Coordination Revealed by Direct Nascent RNA Sequencing through Nanopores. Mol Cell 2020; 77:985-998.e8. [PMID: 31839405 PMCID: PMC7060811 DOI: 10.1016/j.molcel.2019.11.017] [Citation(s) in RCA: 106] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 09/17/2019] [Accepted: 11/18/2019] [Indexed: 02/06/2023]
Abstract
Understanding how splicing events are coordinated across numerous introns in metazoan RNA transcripts requires quantitative analyses of transient RNA processing events in living cells. We developed nanopore analysis of co-transcriptional processing (nano-COP), in which nascent RNAs are directly sequenced through nanopores, exposing the dynamics and patterns of RNA splicing without biases introduced by amplification. Long nano-COP reads reveal that, in human and Drosophila cells, splicing occurs after RNA polymerase II transcribes several kilobases of pre-mRNA, suggesting that metazoan splicing transpires distally from the transcription machinery. Inhibition of the branch-site recognition complex SF3B rapidly diminished global co-transcriptional splicing. We found that splicing order does not strictly follow the order of transcription and is associated with cis-acting elements, alternative splicing, and RNA-binding factors. Further, neighboring introns in human cells tend to be spliced concurrently, implying that splicing of these introns occurs cooperatively. Thus, nano-COP unveils the organizational complexity of RNA processing.
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Affiliation(s)
- Heather L Drexler
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA 02115, USA
| | - Karine Choquet
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA 02115, USA
| | - L Stirling Churchman
- Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, MA 02115, USA.
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7
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Abstract
Introns occasionally remain in mature messenger RNAs (mRNAs) due to splicing errors and the translated, aberrant proteins that result represent a metabolic cost and may have other deleterious consequences. The nonsense-mediated decay (NMD) pathway degrades aberrant mRNAs, which it recognizes by the presence of an in-frame premature termination codon (PTC). We investigated whether selection has shaped the location of PTCs in introns to reduce waste and facilitate NMD. We found across seven model organisms, that in both first and last introns, PTCs occur earlier in introns than expected by chance, suggesting that selection favors earlier position. This pattern is more pronounced in species with larger effective population sizes. The pattern does not hold for last introns in the two mammal species, however, perhaps because in these species NMD is not initiated from 3'-terminal introns. We conclude that there is compelling evidence that the location of PTCs is shaped by selection for reduced waste and efficient degradation of aberrant mRNAs.
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Affiliation(s)
- Megan G Behringer
- Department of Genetics, University of Georgia, Athens, Georgia 30602
| | - David W Hall
- Department of Genetics, University of Georgia, Athens, Georgia 30602
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Hayashi R, Handler D, Ish-Horowicz D, Brennecke J. The exon junction complex is required for definition and excision of neighboring introns in Drosophila. Genes Dev 2014; 28:1772-85. [PMID: 25081352 DOI: 10.1101/gad.245738.114] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The exon junction complex (EJC) plays a central role in controlling RNA fate and aids faithful splicing of pre-mRNAs containing large introns via an unknown mechanism. Brennecke and colleagues show that the core EJC plus the accessory factors RnpS1 and Acinus aid in the definition and efficient splicing of neighboring introns. Interestingly, the most highly affected intron belongs to the piwi locus, which explains the reported transposon desilencing in EJC-depleted Drosophila ovaries. Based on transcriptome-wide analysis, the authors propose that the dependency of splicing on the EJC is exploited to control the temporal order of splicing events. Splicing of pre-mRNAs results in the deposition of the exon junction complex (EJC) upstream of exon–exon boundaries. The EJC plays crucial post-splicing roles in export, translation, localization, and nonsense-mediated decay of mRNAs. It also aids faithful splicing of pre-mRNAs containing large introns, albeit via an unknown mechanism. Here, we show that the core EJC plus the accessory factors RnpS1 and Acinus aid in definition and efficient splicing of neighboring introns. This requires prior deposition of the EJC in close proximity to either an upstream or downstream splicing event. If present in isolation, EJC-dependent introns are splicing-defective also in wild-type cells. Interestingly, the most affected intron belongs to the piwi locus, which explains the reported transposon desilencing in EJC-depleted Drosophila ovaries. Based on a transcriptome-wide analysis, we propose that the dependency of splicing on the EJC is exploited as a means to control the temporal order of splicing events.
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Howe KJ, Kane CM, Ares M. Perturbation of transcription elongation influences the fidelity of internal exon inclusion in Saccharomyces cerevisiae. RNA 2003; 9:993-1006. [PMID: 12869710 PMCID: PMC1370465 DOI: 10.1261/rna.5390803] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2003] [Accepted: 05/13/2003] [Indexed: 05/17/2023]
Abstract
Unknown mechanisms exist to ensure that exons are not skipped during biogenesis of mRNA. Studies have connected transcription elongation with regulated alternative exon inclusion. To determine whether the relative rates of transcription elongation and spliceosome assembly might play a general role in enforcing constitutive exon inclusion, we measured exon skipping for a natural two-intron gene in which the internal exon is constitutively included in the mRNA. Mutations in this gene that subtly reduce recognition of the intron 1 branchpoint cause exon skipping, indicating that rapid recognition of the first intron is important for enforcing exon inclusion. To test the role of transcription elongation, we treated cells to increase or decrease the rate of transcription elongation. Consistent with the "first come, first served" model, we found that exon skipping in vivo is inhibited when transcription is slowed by RNAP II mutants or when cells are treated with inhibitors of elongation. Expression of the elongation factor TFIIS stimulates exon skipping, and this effect is eliminated when lac repressor is targeted to DNA encoding the second intron. A mutation in U2 snRNA promotes exon skipping, presumably because a delay in recognition of the first intron allows elongating RNA polymerase to transcribe the downstream intron. This indicates that the relative rates of elongation and splicing are tuned so that the fidelity of exon inclusion is enhanced. These findings support a general role for kinetic coordination of transcription elongation and splicing during the transcription-dependent control of splicing.
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Affiliation(s)
- Kenneth James Howe
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720, USA
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