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Ares M, Igel H, Katzman S, Donohue JP. Intron lariat spliceosomes convert lariats to true circles: implications for intron transposition. Genes Dev 2024; 38:322-335. [PMID: 38724209 PMCID: PMC11146597 DOI: 10.1101/gad.351764.124] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2024] [Accepted: 04/24/2024] [Indexed: 05/21/2024]
Abstract
Rare, full-length circular intron RNAs distinct from lariats have been reported in several species, but their biogenesis is not understood. We envisioned and tested a hypothesis for their formation using Saccharomyces cerevisiae, documenting full-length and novel processed circular RNAs from multiple introns. Evidence implicates a previously undescribed catalytic activity of the intron lariat spliceosome (ILS) in which the 3'-OH of the lariat tail (with optional trimming and adenylation by the nuclear 3' processing machinery) attacks the branch, joining the intron 3' end to the 5' splice site in a 3'-5' linked circle. Human U2 and U12 spliceosomes produce analogous full-length and processed circles. Postsplicing catalytic activity of the spliceosome may promote intron transposition during eukaryotic genome evolution.
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Affiliation(s)
- Manuel Ares
- Center for Molecular Biology of RNA, University of California, Santa Cruz, Santa Cruz, California 95064, USA;
- Genomics Institute, University of California, Santa Cruz, Santa Cruz, California 95064, USA
| | - Haller Igel
- Center for Molecular Biology of RNA, University of California, Santa Cruz, Santa Cruz, California 95064, USA
| | - Sol Katzman
- Center for Molecular Biology of RNA, University of California, Santa Cruz, Santa Cruz, California 95064, USA
- Genomics Institute, University of California, Santa Cruz, Santa Cruz, California 95064, USA
| | - John P Donohue
- Center for Molecular Biology of RNA, University of California, Santa Cruz, Santa Cruz, California 95064, USA
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2
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Ares M, Igel H, Katzman S, Donohue JP. Intron-lariat spliceosomes convert lariats to true circles: implications for intron transposition. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.26.586863. [PMID: 38585890 PMCID: PMC10996645 DOI: 10.1101/2024.03.26.586863] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/09/2024]
Abstract
Rare, full length circular intron RNAs distinct from lariats have been reported in several species, but their biogenesis is not understood. We envision and test a hypothesis for their formation using Saccharomyces cerevisiae, documenting full length and novel processed circular RNAs from multiple introns. Evidence implicates a previously undescribed catalytic activity of the intron-lariat spliceosome (ILS) in which the 3'-OH of the lariat tail (with optional trimming and adenylation by the nuclear 3' processing machinery) attacks the branch, joining the intron 3' end to the 5' splice site in a 3'-5' linked circle. Human U2 and U12 spliceosomes produce analogous full length and processed circles. Post-splicing catalytic activity of the spliceosome may promote intron transposition during eukaryotic genome evolution.
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Affiliation(s)
- Manuel Ares
- Center for Molecular Biology of RNA, University of California, Santa Cruz
- Genomics Institute, Santa Cruz, CA 95064 USA
| | - Haller Igel
- Center for Molecular Biology of RNA, University of California, Santa Cruz
| | - Sol Katzman
- Center for Molecular Biology of RNA, University of California, Santa Cruz
- Genomics Institute, Santa Cruz, CA 95064 USA
| | - John P. Donohue
- Center for Molecular Biology of RNA, University of California, Santa Cruz
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3
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Nagasawa CK, Garcia-Blanco MA. Early Splicing Complexes and Human Disease. Int J Mol Sci 2023; 24:11412. [PMID: 37511171 PMCID: PMC10379813 DOI: 10.3390/ijms241411412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2023] [Revised: 07/07/2023] [Accepted: 07/10/2023] [Indexed: 07/30/2023] Open
Abstract
Over the last decade, our understanding of spliceosome structure and function has significantly improved, refining the study of the impact of dysregulated splicing on human disease. As a result, targeted splicing therapeutics have been developed, treating various diseases including spinal muscular atrophy and Duchenne muscular dystrophy. These advancements are very promising and emphasize the critical role of proper splicing in maintaining human health. Herein, we provide an overview of the current information on the composition and assembly of early splicing complexes-commitment complex and pre-spliceosome-and their association with human disease.
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Affiliation(s)
- Chloe K. Nagasawa
- Human Pathophysiology and Translational Medicine Program, Institute for Translational Sciences, University of Texas Medical Branch, Galveston, TX 77555-5302, USA;
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77555-5302, USA
- Department of Microbiology, Immunology and Cancer Biology, University of Virginia, Charlottesville, VA 22903-2628, USA
| | - Mariano A. Garcia-Blanco
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77555-5302, USA
- Department of Microbiology, Immunology and Cancer Biology, University of Virginia, Charlottesville, VA 22903-2628, USA
- Institute of Human Infections and Immunity, University of Texas Medical Branch, Galveston, TX 77555-5302, USA
- Department of Internal Medicine, University of Texas Medical Branch, Galveston, TX 77555-5302, USA
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4
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Calumenin knockdown, by intronic artificial microRNA, to improve expression efficiency of the recombinant human coagulation factor IX. Biotechnol Lett 2022; 44:713-728. [PMID: 35412165 DOI: 10.1007/s10529-022-03249-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Accepted: 03/25/2022] [Indexed: 11/02/2022]
Abstract
OBJECTIVES To improve the expression efficiency of recombinant hFIX, by enhancing its γ-carboxylation, which is inhibited by Calumenin (CALU), we used intronic artificial microRNAs (amiRNAs) for the CALU downregulation. METHODS Two human CALU (hCALU)-specific amiRNAs were designed, validated and inserted within a truncated form of the hFIX intron 1, in either 3'- or 5'-untranslated regions of the hFIX cDNA, in an expression vector. After transfections of a human cell line with the recombinant constructs, processing of the miRNAs confirmed by RT-PCR, using stem-loop primers. The hFIX and hCALU expression assessments were done based on RT-PCR results. The Gamma(γ)-carboxylation of the expressed hFIX was examined by a barium citrate precipitation method, followed by Enzyme-Linked Immunosorbent Assay. RESULTS Efficient CALU down regulations, with more than 30-fold decrease, occurred in the cells carrying either of the two examined the 3'-located amiRNAs. The CALU downregulation in the same cells doubled the FIX γ-carboxylation, although the transcription of the FIX decreased significantly. On the other hand, while the expression of the amiRNAs from the 5'-located intron had no decreasing effect on the expression level of CALU, the level of hFIX transcription in these cells increased almost twofold compared to the construct without amiRNA. CONCLUSION The CALU downregulation, consistent with efficient hFIX γ-carboxylation, occurred in the cells carrying either of the two amiRNAs containing constructs, although it was affected by the locations of the amiRNA carrying introns, suggesting a possible need to optimize the conditions for the amiRNAs expression.
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Li Z, Tang J, Bassham DC, Howell SH. Daily temperature cycles promote alternative splicing of RNAs encoding SR45a, a splicing regulator in maize. PLANT PHYSIOLOGY 2021; 186:1318-1335. [PMID: 33705553 PMCID: PMC8195531 DOI: 10.1093/plphys/kiab110] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Accepted: 02/18/2021] [Indexed: 05/04/2023]
Abstract
Elevated temperatures enhance alternative RNA splicing in maize (Zea mays) with the potential to expand the repertoire of plant responses to heat stress. Alternative RNA splicing generates multiple RNA isoforms for many maize genes, and here we observed changes in the pattern of RNA isoforms with temperature changes. Increases in maximum daily temperature elevated the frequency of the major modes of alternative splices (AS), in particular retained introns and skipped exons. The genes most frequently targeted by increased AS with temperature encode factors involved in RNA processing and plant development. Genes encoding regulators of alternative RNA splicing were themselves among the principal AS targets in maize. Under controlled environmental conditions, daily changes in temperature comparable to field conditions altered the abundance of different RNA isoforms, including the RNAs encoding the splicing regulator SR45a, a member of the SR45 gene family. We established an "in protoplast" RNA splicing assay to show that during the afternoon on simulated hot summer days, SR45a RNA isoforms were produced with the potential to encode proteins efficient in splicing model substrates. With the RNA splicing assay, we also defined the exonic splicing enhancers that the splicing-efficient SR45a forms utilize to aid in the splicing of model substrates. Hence, with rising temperatures on hot summer days, SR45a RNA isoforms in maize are produced with the capability to encode proteins with greater RNA splicing potential.
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Affiliation(s)
- Zhaoxia Li
- Plant Sciences Institute, Iowa State University, Ames, Iowa 50011, USA
| | - Jie Tang
- Genetics, Development and Cell Biology Department, Iowa State University, Ames, Iowa 50011, USA
| | - Diane C Bassham
- Genetics, Development and Cell Biology Department, Iowa State University, Ames, Iowa 50011, USA
| | - Stephen H. Howell
- Plant Sciences Institute, Iowa State University, Ames, Iowa 50011, USA
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6
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Jabre I, Chaudhary S, Guo W, Kalyna M, Reddy ASN, Chen W, Zhang R, Wilson C, Syed NH. Differential nucleosome occupancy modulates alternative splicing in Arabidopsis thaliana. THE NEW PHYTOLOGIST 2021; 229:1937-1945. [PMID: 33135169 DOI: 10.1111/nph.17062] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Accepted: 10/24/2020] [Indexed: 05/13/2023]
Abstract
Alternative splicing (AS) is a major gene regulatory mechanism in plants. Recent evidence supports co-transcriptional splicing in plants, hence the chromatin state can impact AS. However, how dynamic changes in the chromatin state such as nucleosome occupancy influence the cold-induced AS remains poorly understood. Here, we generated transcriptome (RNA-Seq) and nucleosome positioning (MNase-Seq) data for Arabidopsis thaliana to understand how nucleosome positioning modulates cold-induced AS. Our results show that characteristic nucleosome occupancy levels are strongly associated with the type and abundance of various AS events under normal and cold temperature conditions in Arabidopsis. Intriguingly, exitrons, alternatively spliced internal regions of protein-coding exons, exhibit distinctive nucleosome positioning pattern compared to other alternatively spliced regions. Likewise, nucleosome patterns differ between exitrons and retained introns, pointing to their distinct regulation. Collectively, our data show that characteristic changes in nucleosome positioning modulate AS in plants in response to cold.
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Affiliation(s)
- Ibtissam Jabre
- School of Human and Life Sciences, Canterbury Christ Church University, Canterbury, CT1 1QU, UK
- School of Biosciences and Medicine, University of Surrey, Guildford, GU2 7XH, UK
| | - Saurabh Chaudhary
- School of Human and Life Sciences, Canterbury Christ Church University, Canterbury, CT1 1QU, UK
- Cardiff School of Biosciences, Cardiff University, Cardiff, CF10 3AX, UK
| | - Wenbin Guo
- Computational Sciences, The James Hutton Institute, Dundee, DD2 5DA, UK
| | - Maria Kalyna
- Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences - BOKU, Muthgasse 18, 1190, Vienna, Austria
| | - Anireddy S N Reddy
- Department of Biology and Program in Cell and Molecular Biology, Colorado State University, Fort Collins, CO, 80523-1878, USA
| | - Weizhong Chen
- Department of Molecular Biology & Genetics, Cornell University, Ithaca, NY, 14853-2703, USA
| | - Runxuan Zhang
- Computational Sciences, The James Hutton Institute, Dundee, DD2 5DA, UK
| | - Cornelia Wilson
- School of Human and Life Sciences, Canterbury Christ Church University, Canterbury, CT1 1QU, UK
| | - Naeem H Syed
- School of Human and Life Sciences, Canterbury Christ Church University, Canterbury, CT1 1QU, UK
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7
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Splicing mutations in inherited retinal diseases. Prog Retin Eye Res 2021. [DOI: 10.1016/j.preteyeres.2020.100874
expr 921883647 + 833887994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/16/2023]
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8
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Wang T, Zhang X, Zheng B. Identification of Intronic Lariat-Derived Circular RNAs in Arabidopsis by RNA Deep Sequencing. Methods Mol Biol 2021; 2362:93-100. [PMID: 34195958 DOI: 10.1007/978-1-0716-1645-1_5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Lariat RNAs are well-known by-products of pre-mRNA splicing in eukaryotes, which are produced by the excised introns when the 5' splice site (5' ss) joins with the branchpoint (BP) during splicing. In general, most of lariat RNAs are usually linearized by RNA debranching enzyme 1 (DBR1), followed by degradation for intron turnover. However, with the high-throughput RNA sequencing technology and bioinformatics methods, increasing evidences have shown that many lariat RNAs can stably accumulate under physiological conditions in both animals and plants. Here, we describe a large-scale analysis to systematically identify the lariat RNAs (i.e., intronic circular RNAs) in Arabidopsis by utilizing the RNA-sequencing data.
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Affiliation(s)
- Taiyun Wang
- State Key Laboratory of Genetic Engineering, Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Collaborative Innovation Center of Genetics and Development, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China
| | - Xiaotuo Zhang
- State Key Laboratory of Genetic Engineering, Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Collaborative Innovation Center of Genetics and Development, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China
| | - Binglian Zheng
- State Key Laboratory of Genetic Engineering, Ministry of Education Key Laboratory of Biodiversity Sciences and Ecological Engineering, Collaborative Innovation Center of Genetics and Development, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, China.
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9
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Splicing mutations in inherited retinal diseases. Prog Retin Eye Res 2020; 80:100874. [PMID: 32553897 DOI: 10.1016/j.preteyeres.2020.100874] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Revised: 05/30/2020] [Accepted: 05/31/2020] [Indexed: 12/15/2022]
Abstract
Mutations which induce aberrant transcript splicing represent a distinct class of disease-causing genetic variants in retinal disease genes. Such mutations may either weaken or erase regular splice sites or create novel splice sites which alter exon recognition. While mutations affecting the canonical GU-AG dinucleotides at the splice donor and splice acceptor site are highly predictive to cause a splicing defect, other variants in the vicinity of the canonical splice sites or those affecting additional cis-acting regulatory sequences within exons or introns are much more difficult to assess or even to recognize and require additional experimental validation. Splicing mutations are unique in that the actual outcome for the transcript (e.g. exon skipping, pseudoexon inclusion, intron retention) and the encoded protein can be quite different depending on the individual mutation. In this article, we present an overview on the current knowledge about and impact of splicing mutations in inherited retinal diseases. We introduce the most common sub-classes of splicing mutations including examples from our own work and others and discuss current strategies for the identification and validation of splicing mutations, as well as therapeutic approaches, open questions, and future perspectives in this field of research.
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10
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A Silent Exonic Mutation in a Rice Integrin-α FG-GAP Repeat-Containing Gene Causes Male-Sterility by Affecting mRNA Splicing. Int J Mol Sci 2020; 21:ijms21062018. [PMID: 32188023 PMCID: PMC7139555 DOI: 10.3390/ijms21062018] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Revised: 03/12/2020] [Accepted: 03/14/2020] [Indexed: 12/11/2022] Open
Abstract
Pollen development plays crucial roles in the life cycle of higher plants. Here we characterized a rice mutant with complete male-sterile phenotype, pollen-less 1 (pl1). pl1 exhibited smaller anthers with arrested pollen development, absent Ubisch bodies, necrosis-like tapetal hypertrophy, and smooth anther cuticular surface. Molecular mapping revealed a synonymous mutation in the fourth exon of PL1 co-segregated with the mutant phenotype. This mutation disrupts the exon-intron splice junction in PL1, generating aberrant mRNA species and truncated proteins. PL1 is highly expressed in the tapetal cells of developing anther, and its protein is co-localized with plasma membrane (PM) and endoplasmic reticulum (ER) signal. PL1 encodes an integrin-α FG-GAP repeat-containing protein, which has seven β-sheets and putative Ca2+-binding motifs and is broadly conserved in terrestrial plants. Our findings therefore provide insights into both the role of integrin-α FG-GAP repeat-containing protein in rice male fertility and the influence of exonic mutation on intronic splice donor site selection.
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11
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Neil CR, Fairbrother WG. Intronic RNA: Ad'junk' mediator of post-transcriptional gene regulation. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2019; 1862:194439. [PMID: 31682938 DOI: 10.1016/j.bbagrm.2019.194439] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Accepted: 09/30/2019] [Indexed: 01/23/2023]
Abstract
RNA splicing, the process through which intervening segments of noncoding RNA (introns) are excised from pre-mRNAs to allow for the formation of a mature mRNA product, has long been appreciated for its capacity to add complexity to eukaryotic proteomes. However, evidence suggests that the utility of this process extends beyond protein output and provides cells with a dynamic tool for gene regulation. In this review, we aim to highlight the role that intronic RNA plays in mediating specific splicing outcomes in pre-mRNA processing, as well as explore an emerging class of stable intronic sequences that have been observed to act in gene expression control. Building from underlying flexibility in both sequence and structure, intronic RNA provides mechanisms for post-transcriptional gene regulation that are amenable to the tissue and condition specific needs of eukaryotic cells. This article is part of a Special Issue entitled: RNA structure and splicing regulation edited by Francisco Baralle, Ravindra Singh and Stefan Stamm.
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Affiliation(s)
- Christopher R Neil
- Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI, United States of America
| | - William G Fairbrother
- Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI, United States of America; Center for Computational Molecular Biology, Brown University, Providence, RI, United States of America.
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12
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Zhang Q, Fan X, Wang Y, Sun MA, Shao J, Guo D. BPP: a sequence-based algorithm for branch point prediction. Bioinformatics 2018. [PMID: 28633445 DOI: 10.1093/bioinformatics/btx401] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Motivation Although high-throughput sequencing methods have been proposed to identify splicing branch points in the human genome, these methods can only detect a small fraction of the branch points subject to the sequencing depth, experimental cost and the expression level of the mRNA. An accurate computational model for branch point prediction is therefore an ongoing objective in human genome research. Results We here propose a novel branch point prediction algorithm that utilizes information on the branch point sequence and the polypyrimidine tract. Using experimentally validated data, we demonstrate that our proposed method outperforms existing methods. Availability and implementation: https://github.com/zhqingit/BPP. Contact djguo@cuhk.edu.hk. Supplementary information Supplementary data are available at Bioinformatics online.
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Affiliation(s)
- Qing Zhang
- School of Life Sciences and the State Key Laboratory of Agrobiotechnology
| | - Xiaodan Fan
- Department of Statistics, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China
| | - Yejun Wang
- Department of Cell Biology and Genetics, Shenzhen University Health Science Center, Shenzhen 518060, China
| | - Ming-An Sun
- School of Life Sciences and the State Key Laboratory of Agrobiotechnology
| | - Jianlin Shao
- First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China
| | - Dianjing Guo
- School of Life Sciences and the State Key Laboratory of Agrobiotechnology
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13
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Wen J, Wang J, Zhang Q, Guo D. A heuristic model for computational prediction of human branch point sequence. BMC Bioinformatics 2017; 18:459. [PMID: 29065858 PMCID: PMC5655975 DOI: 10.1186/s12859-017-1864-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Accepted: 10/09/2017] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Pre-mRNA splicing is the removal of introns from precursor mRNAs (pre-mRNAs) and the concurrent ligation of the flanking exons to generate mature mRNA. This process is catalyzed by the spliceosome, where the splicing factor 1 (SF1) specifically recognizes the seven-nucleotide branch point sequence (BPS) and the U2 snRNP later displaces the SF1 and binds to the BPS. In mammals, the degeneracy of BPS motifs together with the lack of a large set of experimentally verified BPSs complicates the task of BPS prediction in silico. RESULTS In this paper, we develop a simple and yet efficient heuristic model for human BPS prediction based on a novel scoring scheme, which quantifies the splicing strength of putative BPSs. The candidate BPS is restricted exclusively within a defined BPS search region to avoid the influences of other elements in the intron and therefore the prediction accuracy is improved. Moreover, using two types of relative frequencies for human BPS prediction, we demonstrate our model outperformed other current implementations on experimentally verified human introns. CONCLUSION We propose that the binding energy contributes to the molecular recognition involved in human pre-mRNA splicing. In addition, a genome-wide human BPS prediction is carried out. The characteristics of predicted BPSs are in accordance with experimentally verified human BPSs, and branch site positions relative to the 3'ss and the 5'end of the shortened AGEZ are consistent with the results of published papers. Meanwhile, a webserver for BPS predictor is freely available at http://biocomputer.bio.cuhk.edu.hk/BPS .
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Affiliation(s)
- Jia Wen
- School of Life Science, State Key Laboratory of Agrobiotechnology and ShenZhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China
| | - Jue Wang
- School of Life Science, State Key Laboratory of Agrobiotechnology and ShenZhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China
| | - Qing Zhang
- School of Life Science, State Key Laboratory of Agrobiotechnology and ShenZhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China
| | - Dianjing Guo
- School of Life Science, State Key Laboratory of Agrobiotechnology and ShenZhen Research Institute, The Chinese University of Hong Kong, Hong Kong, China
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14
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Herzel L, Ottoz DSM, Alpert T, Neugebauer KM. Splicing and transcription touch base: co-transcriptional spliceosome assembly and function. Nat Rev Mol Cell Biol 2017; 18:637-650. [PMID: 28792005 DOI: 10.1038/nrm.2017.63] [Citation(s) in RCA: 225] [Impact Index Per Article: 32.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Several macromolecular machines collaborate to produce eukaryotic messenger RNA. RNA polymerase II (Pol II) translocates along genes that are up to millions of base pairs in length and generates a flexible RNA copy of the DNA template. This nascent RNA harbours introns that are removed by the spliceosome, which is a megadalton ribonucleoprotein complex that positions the distant ends of the intron into its catalytic centre. Emerging evidence that the catalytic spliceosome is physically close to Pol II in vivo implies that transcription and splicing occur on similar timescales and that the transcription and splicing machineries may be spatially constrained. In this Review, we discuss aspects of spliceosome assembly, transcription elongation and other co-transcriptional events that allow the temporal coordination of co-transcriptional splicing.
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Affiliation(s)
- Lydia Herzel
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA.,Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Diana S M Ottoz
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA
| | - Tara Alpert
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA
| | - Karla M Neugebauer
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA
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15
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Gallego-Paez LM, Bordone MC, Leote AC, Saraiva-Agostinho N, Ascensão-Ferreira M, Barbosa-Morais NL. Alternative splicing: the pledge, the turn, and the prestige : The key role of alternative splicing in human biological systems. Hum Genet 2017; 136:1015-1042. [PMID: 28374191 PMCID: PMC5602094 DOI: 10.1007/s00439-017-1790-y] [Citation(s) in RCA: 85] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Accepted: 03/25/2017] [Indexed: 02/06/2023]
Abstract
Alternative pre-mRNA splicing is a tightly controlled process conducted by the spliceosome, with the assistance of several regulators, resulting in the expression of different transcript isoforms from the same gene and increasing both transcriptome and proteome complexity. The differences between alternative isoforms may be subtle but enough to change the function or localization of the translated proteins. A fine control of the isoform balance is, therefore, needed throughout developmental stages and adult tissues or physiological conditions and it does not come as a surprise that several diseases are caused by its deregulation. In this review, we aim to bring the splicing machinery on stage and raise the curtain on its mechanisms and regulation throughout several systems and tissues of the human body, from neurodevelopment to the interactions with the human microbiome. We discuss, on one hand, the essential role of alternative splicing in assuring tissue function, diversity, and swiftness of response in these systems or tissues, and on the other hand, what goes wrong when its regulatory mechanisms fail. We also focus on the possibilities that splicing modulation therapies open for the future of personalized medicine, along with the leading techniques in this field. The final act of the spliceosome, however, is yet to be fully revealed, as more knowledge is needed regarding the complex regulatory network that coordinates alternative splicing and how its dysfunction leads to disease.
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Affiliation(s)
- L M Gallego-Paez
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal
| | - M C Bordone
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal
| | - A C Leote
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal
| | - N Saraiva-Agostinho
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal
| | - M Ascensão-Ferreira
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal
| | - N L Barbosa-Morais
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal.
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16
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Unmasking a novel disease gene NEO1 associated with autism spectrum disorders by a hemizygous deletion on chromosome 15 and a functional polymorphism. Behav Brain Res 2016; 300:135-42. [DOI: 10.1016/j.bbr.2015.10.041] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Revised: 10/14/2015] [Accepted: 10/21/2015] [Indexed: 11/20/2022]
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17
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Identification and Functional Characterization of Two Intronic NIPBL Mutations in Two Patients with Cornelia de Lange Syndrome. BIOMED RESEARCH INTERNATIONAL 2016; 2016:8742939. [PMID: 26925417 PMCID: PMC4746300 DOI: 10.1155/2016/8742939] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/03/2015] [Accepted: 11/16/2015] [Indexed: 12/03/2022]
Abstract
Cornelia de Lange syndrome (CdLS) is a rare genetically heterogeneous disorder with a high phenotypic variability including mental retardation, developmental delay, and limb malformations. The genetic causes in about 30% of patients with CdLS are still unknown. We report on the functional characterization of two intronic NIPBL mutations in two patients with CdLS that do not affect a conserved splice-donor or acceptor site. Interestingly, mRNA analyses showed aberrantly spliced transcripts missing exon 28 or 37, suggesting the loss of the branch site by the c.5329-15A>G transition and a disruption of the polypyrimidine by the c.6344del(-13)_(-8) deletion. While the loss of exon 28 retains the reading frame of the NIBPL transcript resulting in a shortened protein, the loss of exon 37 shifts the reading frame with the consequence of a premature stop of translation. Subsequent quantitative PCR analysis demonstrated a 30% decrease of the total NIPBL mRNA levels associated with the frameshift transcript. Consistent with our results, this patient shows a more severe phenotype compared to the patient with the aberrant transcript that retains its reading frame. Thus, intronic variants identified by sequencing analysis in CdLS diagnostics should carefully be examined before excluding them as nonrelevant to disease.
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Nuclear cyclophilins affect spliceosome assembly and function in vitro. Biochem J 2015; 469:223-33. [PMID: 25967372 DOI: 10.1042/bj20150396] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Accepted: 05/13/2015] [Indexed: 11/17/2022]
Abstract
Cyclophilins are ubiquitously expressed proteins that bind to prolines and can catalyse cis/trans isomerization of proline residues. There are 17 annotated members of the cyclophilin family in humans, ubiquitously expressed and localized variously to the cytoplasm, nucleus or mitochondria. Surprisingly, all eight of the nuclear localized cyclophilins are found associated with spliceosomal complexes. However, their particular functions within this context are unknown. We have therefore adapted three established assays for in vitro pre-mRNA splicing to probe the functional roles of nuclear cyclophilins in the context of the human spliceosome. We find that four of the eight spliceosom-associated cyclophilins exert strong effects on splicing in vitro. These effects are dose-dependent and, remarkably, uniquely characteristic of each cyclophilin. Using both qualitative and quantitative means, we show that at least half of the nuclear cyclophilins can act as regulatory factors of spliceosome function in vitro. The present work provides the first quantifiable evidence that nuclear cyclophilins are splicing factors and provides a novel approach for future work into small molecule-based modulation of pre-mRNA splicing.
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Gao S, Ruan Q, Ma Y, Li M, Wang L, Zheng B, Qi Y, Ji Y, Sun Z, Huang Y. Validation of three splice donor and three splice acceptor sites for regulating four novel low-abundance spliced transcripts of human cytomegalovirus UL21.5 gene locus. Int J Mol Med 2014; 35:253-62. [PMID: 25370414 DOI: 10.3892/ijmm.2014.1987] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Accepted: 10/23/2014] [Indexed: 11/06/2022] Open
Abstract
In a previous study, one spliced transcript of human cytomegalovirus (HCMV), named UL21.5 was identified. UL21.5 has been found to be one of the viral transcripts packaged within HCMV particles. The UL21.5 mRNA is translated into a secreted glycoprotein, which is a viral chemokine decoy receptor specifically interacting with regulated upon activation normal T cell expressed and secreted (RANTES). In the present study, four novel low-abundance 3'-coterminal spliced transcripts were identified to be transcribed from the UL21.5 gene region of a low-passage HCMV strain during the late infection phase by cDNA library screening, northern blot hybridization, reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE)-PCR. Three splicing donor and three splicing acceptor sites found in the UL21.5 gene region were validated to be functional in an in vitro expression system. In addition, the determinant regulatory region that is necessary for the splice donor site at nucleotide (nt) 25533 was located in a 9-bp sequence around the site; the regulatory regions for the splice acceptor sites at nt 26597 and nt 26633 were located in a 20-bp sequence upstream of the site at nt 26597 and in a 10-bp sequence from nt 26641 to nt 26650 downstream of the site at nt 26633, respectively.
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Affiliation(s)
- Shuang Gao
- Virus Laboratory, Affiliated Shengjing Hospital, China Medical University, Shenyang, Liaoning 110004, P.R. China
| | - Qiang Ruan
- Virus Laboratory, Affiliated Shengjing Hospital, China Medical University, Shenyang, Liaoning 110004, P.R. China
| | - Yanping Ma
- Virus Laboratory, Affiliated Shengjing Hospital, China Medical University, Shenyang, Liaoning 110004, P.R. China
| | - Mali Li
- Virus Laboratory, Affiliated Shengjing Hospital, China Medical University, Shenyang, Liaoning 110004, P.R. China
| | - Lin Wang
- Virus Laboratory, Affiliated Shengjing Hospital, China Medical University, Shenyang, Liaoning 110004, P.R. China
| | - Bo Zheng
- Virus Laboratory, Affiliated Shengjing Hospital, China Medical University, Shenyang, Liaoning 110004, P.R. China
| | - Ying Qi
- Virus Laboratory, Affiliated Shengjing Hospital, China Medical University, Shenyang, Liaoning 110004, P.R. China
| | - Yaohua Ji
- Virus Laboratory, Affiliated Shengjing Hospital, China Medical University, Shenyang, Liaoning 110004, P.R. China
| | - Zhengrong Sun
- Virus Laboratory, Affiliated Shengjing Hospital, China Medical University, Shenyang, Liaoning 110004, P.R. China
| | - Yujing Huang
- Virus Laboratory, Affiliated Shengjing Hospital, China Medical University, Shenyang, Liaoning 110004, P.R. China
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Sumoylation is Required for the Cytoplasmic Accumulation of a Subset of mRNAs. Genes (Basel) 2014; 5:982-1000. [PMID: 25333844 PMCID: PMC4276922 DOI: 10.3390/genes5040982] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2014] [Revised: 09/26/2014] [Accepted: 10/04/2014] [Indexed: 12/17/2022] Open
Abstract
In order to discover novel proteins that promote the nuclear export of newly synthesized mRNAs in mammalian cells, we carried out a limited RNAi screen for proteins required for the proper cytoplasmic distribution of a model intronless mRNA. From this screen we obtained two hits, Ubc9 (SUMO-conjugating E2 enzyme) and GANP (germinal center-associated nuclear protein). Depletion of Ubc9 inhibited the proper cytoplasmic distribution of certain overexpressed intronless mRNAs, while depletion of GANP affected all tested mRNAs. Depletion of Sae1, which is also required for sumoylation, partially inhibited the cytoplasmic distribution of our model mRNA. Interestingly, the block in cytoplasmic accumulation in Ubc9-depleted cells could be overcome if an intron was incorporated into the mRNA. Surprisingly, Ubc9-depleted cells had normal nuclear export of newly synthesized intronless mRNAs, indicating that the observed accumulation of the model mRNA in the nuclei of transfected cells was likely due to some more general perturbation. Indeed, depletion of Ubc9, coupled with the overexpression of the intronless mRNAs, caused the redistribution of the nuclear speckle protein SC35 to cytoplasmic foci. Our results suggest that sumoylation may play a role in the proper assembly of mRNPs and/or the distribution of key RNA binding proteins, and may thus contribute to general protein expression patterns.
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Downs LM, Mellersh CS. An Intronic SINE insertion in FAM161A that causes exon-skipping is associated with progressive retinal atrophy in Tibetan Spaniels and Tibetan Terriers. PLoS One 2014; 9:e93990. [PMID: 24705771 PMCID: PMC3976383 DOI: 10.1371/journal.pone.0093990] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 03/10/2014] [Indexed: 11/19/2022] Open
Abstract
Progressive retinal atrophy (PRA) in dogs is characterised by the degeneration of the photoreceptor cells of the retina, resulting in vision loss and eventually complete blindness. The condition affects more than 100 dog breeds and is known to be genetically heterogeneous between breeds. Around 19 mutations have now been identified that are associated with PRA in around 49 breeds, but for the majority of breeds the mutation(s) responsible have yet to be identified. Using genome-wide association with 22 Tibetan Spaniel PRA cases and 10 controls, we identified a novel PRA locus, PRA3, on CFA10 (praw = 2.01×10−5, pgenome = 0.014), where a 3.8 Mb region was homozygous within 12 cases. Using targeted next generation sequencing, a short interspersed nuclear element insertion was identified near a splice acceptor site in an intron of a provocative gene, FAM161A. Analysis of mRNA from an affected dog revealed that the SINE causes exon skipping, resulting in a frame shift, leading to a downstream premature termination codon and possibly a truncated protein product. This mutation segregates with the disease in 22 out of 35 cases tested (63%). Of the PRA controls, none are homozygous for the mutation, 15% carry the mutation and 85% are homozygous wildtype. This mutation was also identified in Tibetan Terriers, although our results indicate that PRA is genetically heterogeneous in both Tibetan Spaniels and Tibetan Terriers.
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Affiliation(s)
- Louise M. Downs
- Kennel Club Genetics Centre, Animal Health Trust, Newmarket, United Kingdom
| | - Cathryn S. Mellersh
- Kennel Club Genetics Centre, Animal Health Trust, Newmarket, United Kingdom
- * E-mail:
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Isolation of Sporothrix schenckii GDA1 and functional characterization of the encoded guanosine diphosphatase activity. Arch Microbiol 2013; 195:499-506. [PMID: 23715619 DOI: 10.1007/s00203-013-0901-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Revised: 03/01/2013] [Accepted: 05/17/2013] [Indexed: 12/23/2022]
Abstract
Sporothrix schenckii is a fungal pathogen of humans and the etiological agent of sporotrichosis. In fungi, proper protein glycosylation is usually required for normal composition of cell wall and virulence. Upon addition of precursor oligosaccharides to nascent proteins in the endoplasmic reticulum, glycans are further modified by Golgi-glycosyl transferases. In order to add sugar residues to precursor glycans, nucleotide diphosphate sugars are imported from the cytosol to the Golgi lumen, the sugar is transferred to glycans, and the resulting nucleoside diphosphate is dephosphorylated by the nucleoside diphosphatase Gda1 before returning to cytosol. Here, we isolated the open reading frame SsGDA1 from a S. schenckii genomic DNA library. In order to confirm the function of SsGda1, we performed complementation assays in a Saccharomyces cerevisiae gda1∆ null mutant. Our results indicated that SsGDA1 restored the nucleotide diphosphatase activity to wild-type levels and therefore is a functional ortholog of S. cerevisiae GDA1.
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Mahadevan K, Zhang H, Akef A, Cui XA, Gueroussov S, Cenik C, Roth FP, Palazzo AF. RanBP2/Nup358 potentiates the translation of a subset of mRNAs encoding secretory proteins. PLoS Biol 2013; 11:e1001545. [PMID: 23630457 PMCID: PMC3635865 DOI: 10.1371/journal.pbio.1001545] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Accepted: 03/07/2013] [Indexed: 12/14/2022] Open
Abstract
After nuclear export, mRNAs encoding secretory proteins interact with RanBP2/Nup358 on the cytoplasmic face of the nuclear pore, a step that is required for the efficient translation of these mRNAs. In higher eukaryotes, most mRNAs that encode secreted or membrane-bound proteins contain elements that promote an alternative mRNA nuclear export (ALREX) pathway. Here we report that ALREX-promoting elements also potentiate translation in the presence of upstream nuclear factors. These RNA elements interact directly with, and likely co-evolved with, the zinc finger repeats of RanBP2/Nup358, which is present on the cytoplasmic face of the nuclear pore. Finally we show that RanBP2/Nup358 is not only required for the stimulation of translation by ALREX-promoting elements, but is also required for the efficient global synthesis of proteins targeted to the endoplasmic reticulum (ER) and likely the mitochondria. Thus upon the completion of export, mRNAs containing ALREX-elements likely interact with RanBP2/Nup358, and this step is required for the efficient translation of these mRNAs in the cytoplasm. ALREX-elements thus act as nucleotide platforms to coordinate various steps of post-transcriptional regulation for the majority of mRNAs that encode secreted proteins. About one-fifth of the protein-coding genes in the human genome code for secreted and/or membrane-bound proteins. In the nucleus these genes are transcribed into messenger RNAs (mRNAs), which are then exported to the cytoplasm. These mRNAs are then transported to the surface of the endoplasmic reticulum where they are translated into proteins destined for the secretory pathway. Most of these mRNAs contain signal sequence coding regions (SSCRs), which code for short hydrophobic polypeptides that target the newly synthesized proteins for translocation across the endoplasmic reticulum membrane. Previously, we found that many SSCRs also act as RNA elements that promote the efficient nuclear export of mRNAs. Here we present evidence that upon the completion of nuclear export, SSCR-containing mRNAs interact with RanBP2/Nup358, a large protein found on the cytoplasmic face of the nuclear pore. This interaction is mediated by direct binding between the SSCR and zinc finger repeats found within RanBP2/Nup358, and is ultimately required for the efficient translation of SSCR-containing mRNAs into secretory and/or membrane-bound proteins. Our work demonstrates that SSCRs act as nucleotide platforms that recruit various factors to the mRNA throughout its life to regulate distinct events, such as nuclear export and translation.
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Affiliation(s)
- Kohila Mahadevan
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - Hui Zhang
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - Abdalla Akef
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - Xianying A. Cui
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - Serge Gueroussov
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - Can Cenik
- Department of Biological Chemistry & Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, United States of America
- Howard Hughes Medical Institute, Department of Biochemistry and Molecular Pharmacology University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
| | - Frederick P. Roth
- Department of Biological Chemistry & Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, United States of America
- Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario, Canada
- Samuel Lunenfeld Research Institute, Mt. Sinai Hospital, Toronto, Ontario, Canada
| | - Alexander F. Palazzo
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
- * E-mail:
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Ajiro M, Jia R, Zhang L, Liu X, Zheng ZM. Intron definition and a branch site adenosine at nt 385 control RNA splicing of HPV16 E6*I and E7 expression. PLoS One 2012; 7:e46412. [PMID: 23056301 PMCID: PMC3464268 DOI: 10.1371/journal.pone.0046412] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Accepted: 08/29/2012] [Indexed: 11/19/2022] Open
Abstract
HPV16 E6 and E7, two viral oncogenes, are expressed from a single bicistronic pre-mRNA. In this report, we provide the evidence that the bicistronic pre-mRNA intron 1 contains three 5' splice sites (5' ss) and three 3' splice sites (3' ss) normally used in HPV16(+) cervical cancer and its derived cell lines. The choice of two novel alternative 5' ss (nt 221 5' ss and nt 191 5' ss) produces two novel isoforms of E6E7 mRNAs (E6*V and E6*VI). The nt 226 5' ss and nt 409 3' ss is preferentially selected over the other splice sites crossing over the intron to excise a minimal length of the intron in RNA splicing. We identified AACAAAC as the preferred branch point sequence (BPS) and an adenosine at nt 385 (underlined) in the BPS as a branch site to dictate the selection of the nt 409 3' ss for E6*I splicing and E7 expression. Introduction of point mutations into the mapped BPS led to reduced U2 binding to the BPS and thereby inhibition of the second step of E6E7 splicing at the nt 409 3' ss. Importantly, the E6E7 bicistronic RNA with a mutant BPS and inefficient splicing makes little or no E7 and the resulted E6 with mutations of (91)QYNK(94) to (91)PSFW(94) displays attenuate activity on p53 degradation. Together, our data provide structural basis of the E6E7 intron 1 for better understanding of how viral E6 and E7 expression is regulated by alternative RNA splicing. This study elucidates for the first time a mapped branch point in HPV16 genome involved in viral oncogene expression.
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Affiliation(s)
- Masahiko Ajiro
- Tumor Virus RNA Biology Section, HIV and AIDS Malignancy Branch, Center for Cancer Research, NCI, NIH, Bethesda, Maryland, United States of America
| | - Rong Jia
- Tumor Virus RNA Biology Section, HIV and AIDS Malignancy Branch, Center for Cancer Research, NCI, NIH, Bethesda, Maryland, United States of America
| | - Lifang Zhang
- Tumor Virus RNA Biology Section, HIV and AIDS Malignancy Branch, Center for Cancer Research, NCI, NIH, Bethesda, Maryland, United States of America
| | - Xuefeng Liu
- Tumor Virus RNA Biology Section, HIV and AIDS Malignancy Branch, Center for Cancer Research, NCI, NIH, Bethesda, Maryland, United States of America
| | - Zhi-Ming Zheng
- Tumor Virus RNA Biology Section, HIV and AIDS Malignancy Branch, Center for Cancer Research, NCI, NIH, Bethesda, Maryland, United States of America
- * E-mail:
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Hernández-Cervantes A, Mora-Montes HM, Álvarez-Vargas A, Jiménez DFD, Robledo-Ortiz CI, Flores-Carreón A. Isolation of Sporothrix schenckii MNT1 and the biochemical and functional characterization of the encoded α1,2-mannosyltransferase activity. Microbiology (Reading) 2012; 158:2419-2427. [DOI: 10.1099/mic.0.060392-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Affiliation(s)
- Arturo Hernández-Cervantes
- Departamento de Biología, División de Ciencias Naturales y Exactas, Campus Guanajuato, Universidad de Guanajuato, Noria Alta s/n, Col. Noria Alta, C.P. 36050, Guanajuato, Gto., Mexico
| | - Héctor M. Mora-Montes
- Departamento de Biología, División de Ciencias Naturales y Exactas, Campus Guanajuato, Universidad de Guanajuato, Noria Alta s/n, Col. Noria Alta, C.P. 36050, Guanajuato, Gto., Mexico
| | - Aurelio Álvarez-Vargas
- Departamento de Biología, División de Ciencias Naturales y Exactas, Campus Guanajuato, Universidad de Guanajuato, Noria Alta s/n, Col. Noria Alta, C.P. 36050, Guanajuato, Gto., Mexico
| | - Diana F. Díaz Jiménez
- Departamento de Biología, División de Ciencias Naturales y Exactas, Campus Guanajuato, Universidad de Guanajuato, Noria Alta s/n, Col. Noria Alta, C.P. 36050, Guanajuato, Gto., Mexico
| | - Claudia I. Robledo-Ortiz
- Departamento de Biología, División de Ciencias Naturales y Exactas, Campus Guanajuato, Universidad de Guanajuato, Noria Alta s/n, Col. Noria Alta, C.P. 36050, Guanajuato, Gto., Mexico
| | - Arturo Flores-Carreón
- Departamento de Biología, División de Ciencias Naturales y Exactas, Campus Guanajuato, Universidad de Guanajuato, Noria Alta s/n, Col. Noria Alta, C.P. 36050, Guanajuato, Gto., Mexico
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Cui XA, Zhang H, Palazzo AF. p180 promotes the ribosome-independent localization of a subset of mRNA to the endoplasmic reticulum. PLoS Biol 2012; 10:e1001336. [PMID: 22679391 PMCID: PMC3362647 DOI: 10.1371/journal.pbio.1001336] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Accepted: 04/12/2012] [Indexed: 12/21/2022] Open
Abstract
The localization of many secretory mRNAs to the endoplasmic reticulum does not require ribosomes or translation, but is instead promoted by p180, an abundant, membrane-bound protein that likely binds directly to mRNA. In metazoans, the majority of mRNAs coding for secreted and membrane-bound proteins are translated on the surface of the endoplasmic reticulum (ER). Although the targeting of these transcripts to the surface of the ER can be mediated by the translation of a signal sequence and their maintenance is mediated by interactions between the ribosome and the translocon, it is becoming increasingly clear that additional ER-localization pathways exist. Here we demonstrate that many of these mRNAs can be targeted to, and remain associated with, the ER independently of ribosomes and translation. Using a mass spectrometry analysis of proteins that associate with ER-bound polysomes, we identified putative mRNA receptors that may mediate this alternative mechanism, including p180, an abundant, positively charged membrane-bound protein. We demonstrate that p180 over-expression can enhance the association of generic mRNAs with the ER. We then show that p180 contains a lysine-rich region that can directly interact with RNA in vitro. Finally, we demonstrate that p180 is required for the efficient ER-anchoring of bulk poly(A) and of certain transcripts, such as placental alkaline phosphatase and calreticulin, to the ER. In summary, we provide, to our knowledge, the first mechanistic details for an alternative pathway to target and maintain mRNA at the ER. It is likely that this alternative pathway not only enhances the fidelity of protein sorting, but also localizes mRNAs to various subdomains of the ER and thus contributes to cellular organization. Messenger RNAs (mRNAs) that encode secreted or membrane-bound proteins must be delivered to, and then maintained on, the surface of the endoplasmic reticulum (ER). These mRNAs encode a short polypeptide that targets the mRNA/ribosome/nascent protein complexes to the ER surface during translation; however, recent studies support the existence of additional ER-localization signals that might be present within the mRNA molecules themselves. Here, we demonstrate that a fraction of these mRNAs, whose encoded proteins are destined for secretion, contain information that targets and anchors them to the ER independently of their encoded polypeptide or their association to ribosomes. We identify proteins on the ER that may serve as receptors for these mRNAs. We then show that one of these candidate membrane-bound receptors, p180, is required for the maintenance of certain mRNAs on the surface of the ER even after their translation into protein is disrupted. We also demonstrate that p180 contains a region that binds directly to RNA and likely mediates the anchoring of mRNA to the ER. Our study thus provides the first mechanistic details of an alternative pathway used to ensure that secretory mRNAs, and their encoded proteins, reach their proper destination in the ER.
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Affiliation(s)
| | | | - Alexander F. Palazzo
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
- * E-mail:
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Alternative splicing of RNA triplets is often regulated and accelerates proteome evolution. PLoS Biol 2012; 10:e1001229. [PMID: 22235189 PMCID: PMC3250501 DOI: 10.1371/journal.pbio.1001229] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2011] [Accepted: 11/18/2011] [Indexed: 11/19/2022] Open
Abstract
Thousands of human genes contain introns ending in NAGNAG (N any nucleotide), where both NAGs can function as 3' splice sites, yielding isoforms that differ by inclusion/exclusion of three bases. However, few models exist for how such splicing might be regulated, and some studies have concluded that NAGNAG splicing is purely stochastic and nonfunctional. Here, we used deep RNA-Seq data from 16 human and eight mouse tissues to analyze the regulation and evolution of NAGNAG splicing. Using both biological and technical replicates to estimate false discovery rates, we estimate that at least 25% of alternatively spliced NAGNAGs undergo tissue-specific regulation in mammals, and alternative splicing of strongly tissue-specific NAGNAGs was 10 times as likely to be conserved between species as was splicing of non-tissue-specific events, implying selective maintenance. Preferential use of the distal NAG was associated with distinct sequence features, including a more distal location of the branch point and presence of a pyrimidine immediately before the first NAG, and alteration of these features in a splicing reporter shifted splicing away from the distal site. Strikingly, alignments of orthologous exons revealed a ∼15-fold increase in the frequency of three base pair gaps at 3' splice sites relative to nearby exon positions in both mammals and in Drosophila. Alternative splicing of NAGNAGs in human was associated with dramatically increased frequency of exon length changes at orthologous exon boundaries in rodents, and a model involving point mutations that create, destroy, or alter NAGNAGs can explain both the increased frequency and biased codon composition of gained/lost sequence observed at the beginnings of exons. This study shows that NAGNAG alternative splicing generates widespread differences between the proteomes of mammalian tissues, and suggests that the evolutionary trajectories of mammalian proteins are strongly biased by the locations and phases of the introns that interrupt coding sequences.
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Tarnawsky SP, Palazzo AF. Positional requirements for the stimulation of mRNA nuclear export by ALREX-promoting elements. MOLECULAR BIOSYSTEMS 2012; 8:2527-30. [DOI: 10.1039/c2mb25016k] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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O'Driscoll KE, Pipe RA, Britton FC. Increased complexity of Tmem16a/Anoctamin 1 transcript alternative splicing. BMC Mol Biol 2011; 12:35. [PMID: 21824394 PMCID: PMC3170211 DOI: 10.1186/1471-2199-12-35] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Accepted: 08/08/2011] [Indexed: 01/09/2023] Open
Abstract
Background TMEM16A (Anoctamin 1; ANO1) is an eight transmembrane protein that functions as a calcium-activated chloride channel. TMEM16A in human exhibits alternatively spliced exons (6b, 13 and 15), which confer important roles in the regulation of channel function. Mouse Tmem16a is reported to consist of 25 exons that code for a 956 amino acid protein. In this study our aim was to provide details of mouse Tmem16a genomic structure and to investigate if Tmem16a transcript undergoes alternative splicing to generate channel diversity. Results We identified Tmem16a transcript variants consisting of alternative exons 6b, 10, 13, 14, 15 and 18. Our findings indicate that many of these exons are expressed in various combinations and that these splicing events are mostly conserved between mouse and human. In addition, we confirmed the expression of these exon variants in other mouse tissues. Additional splicing events were identified including a novel conserved exon 13b, tandem splice sites of exon 1 and 21 and two intron retention events. Conclusion Our results suggest that Tmem16a gene is significantly more complex than previously described. The complexity is especially evident in the region spanning exons 6 through 16 where a number of the alternative splicing events are thought to affect calcium sensitivity, voltage dependence and the kinetics of activation and deactivation of this calcium-activated chloride channel. The identification of multiple Tmem16a splice variants suggests that alternative splicing is an exquisite mechanism that operates to diversify TMEM16A channel function in both physiological and pathophysiological conditions.
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Affiliation(s)
- Kate E O'Driscoll
- Department of Physiology and Cell Biology, 1664 North Virginia Street, University of Nevada School of Medicine, Reno, Nevada 89557-0046, USA
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Lomelin D, Jorgenson E, Risch N. Human genetic variation recognizes functional elements in noncoding sequence. Genome Res 2009; 20:311-9. [PMID: 20032171 DOI: 10.1101/gr.094151.109] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Noncoding DNA, particularly intronic DNA, harbors important functional elements that affect gene expression and RNA splicing. Yet, it is unclear which specific noncoding sites are essential for gene function and regulation. To identify functional elements in noncoding DNA, we characterized genetic variation within introns using ethnically diverse human polymorphism data from three public databases-PMT, NIEHS, and SeattleSNPs. We demonstrate that positions within introns corresponding to known functional elements involved in pre-mRNA splicing, including the branch site, splice sites, and polypyrimidine tract show reduced levels of genetic variation. Additionally, we observed regions of reduced genetic variation that are candidates for distance-dependent localization sites of functional elements, possibly intronic splicing enhancers (ISEs). Using several bioinformatics approaches, we provide additional evidence that supports our hypotheses that these regions correspond to ISEs. We conclude that studies of genetic variation can successfully discriminate and identify functional elements in noncoding regions. As more noncoding sequence data become available, the methods employed here can be utilized to identify additional functional elements in the human genome and provide possible explanations for phenotypic associations.
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Affiliation(s)
- David Lomelin
- Institute for Human Genetics, University of California, San Francisco, San Francisco, California 94143, USA.
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Ohe K, Watanabe T, Harada SI, Munesue S, Yamamoto Y, Yonekura H, Yamamoto H. Regulation of alternative splicing of the receptor for advanced glycation endproducts (RAGE) through G-rich cis-elements and heterogenous nuclear ribonucleoprotein H. J Biochem 2009; 147:651-9. [PMID: 20028692 DOI: 10.1093/jb/mvp207] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Receptor for advanced glycation endproducts (RAGE) is a cell-surface receptor. The binding of ligands to membrane-bound RAGE (mRAGE) evokes cellular responses involved in various pathological processes. Previously, we identified a novel soluble form, endogenous secretory RAGE (esRAGE) generated by alternative 5' splice site selection in intron 9 that leads to extension of exon 9 (exon 9B). Because esRAGE works as an antagonistic decoy receptor, the elucidation of regulatory mechanism of the alternative splicing is important to understand RAGE-related pathological processes. Here, we identified G-rich cis-elements within exon 9B for regulation of the alternative splicing using a RAGE minigene. Mutagenesis of the G-rich cis-elements caused a drastic increase in the esRAGE/mRAGE ratio in the minigene-transfected cells and in loss of binding of the RNA motif to heterogenous nuclear ribonucleoprotein (hnRNP) H. On the other hand, the artificial introduction of a G-stretch in exon 9B caused a drastic decrease in the esRAGE/mRAGE ratio accompanied by the binding of hnRNP H to the RNA motif. Thus, the G-stretches within exon 9B regulate RAGE alternative splicing via interaction with hnRNP H. The findings should provide a molecular basis for the development of medicines for RAGE-related disorders that could modulate esRAGE/mRAGE ratio.
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Affiliation(s)
- Kazuyo Ohe
- Department of Biochemistry and Molecular Vascular Biology, Kanazawa University Graduate School of Medical Science, Kanazawa 920-8640, Japan
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Cheng D, MacArthur PS, Rong S, Parks JS, Shelness GS. Alternative splicing attenuates transgenic expression directed by the apolipoprotein E promoter-enhancer based expression vector pLIV11. J Lipid Res 2009; 51:849-55. [PMID: 19965599 DOI: 10.1194/jlr.d002709] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The plasmid vector pLIV11 is used commonly to achieve liver-specific expression of genes of interest in transgenic mice and rabbits. Expression is driven by the human apolipoprotein (apo)E 5' proximal promoter, which includes 5 kb of upstream sequence, exon 1, intron 1, and 5 bp of exon 2. A 3.8 kb 3' hepatic control region, derived from a region approximately 18 kb downstream of the apoE gene, enhances liver-specific expression. Here, we report that cDNA sequences inserted into the multiple cloning site (MCS) of pLIV11, which is positioned just downstream of truncated exon 2, can cause exon 2 skipping. Hence, splicing is displaced to downstream cryptic 3' splice acceptor sites causing deletion of cloned 5' untranslated mRNA sequences and, in some cases, deletion of the 5' end of an open reading frame. To prevent use of cryptic splice sites, the pLIV11 vector was modified with an engineered 3' splice acceptor site inserted immediately downstream of truncated apoE exon 2. Presence of this sequence fully shifted splicing of exon 1 from the native intron 1-exon 2 splice acceptor site to the engineered site. This finding confirmed that sequences inserted into the MCS of the vector pLIV11 can affect exon 2 recognition and provides a strategy to protect cloned sequences from alternative splicing and possible attenuation of transgenic expression.
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Affiliation(s)
- Dongmei Cheng
- Department of Pathology Section on Lipid Sciences, Wake Forest University School of Medicine, Winston Salem, NC 27157, USA
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33
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Disassembly of Exon Junction Complexes by PYM. Cell 2009; 137:536-48. [DOI: 10.1016/j.cell.2009.02.042] [Citation(s) in RCA: 142] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2008] [Revised: 12/31/2008] [Accepted: 02/18/2009] [Indexed: 11/22/2022]
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Conservation of the protein composition and electron microscopy structure of Drosophila melanogaster and human spliceosomal complexes. Mol Cell Biol 2008; 29:281-301. [PMID: 18981222 DOI: 10.1128/mcb.01415-08] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Comprehensive proteomics analyses of spliceosomal complexes are currently limited to those in humans, and thus, it is unclear to what extent the spliceosome's highly complex composition and compositional dynamics are conserved among metazoans. Here we affinity purified Drosophila melanogaster spliceosomal B and C complexes formed in Kc cell nuclear extract. Mass spectrometry revealed that their composition is highly similar to that of human B and C complexes. Nonetheless, a number of Drosophila-specific proteins were identified, suggesting that there may be novel factors contributing specifically to splicing in flies. Protein recruitment and release events during the B-to-C transition were also very similar in both organisms. Electron microscopy of Drosophila B complexes revealed a high degree of structural similarity with human B complexes, indicating that higher-order interactions are also largely conserved. A comparison of Drosophila spliceosomes formed on a short versus long intron revealed only small differences in protein composition but, nonetheless, clear structural differences under the electron microscope. Finally, the characterization of affinity-purified Drosophila mRNPs indicated that exon junction complex proteins are recruited in a splicing-dependent manner during C complex formation. These studies provide insights into the evolutionarily conserved composition and structure of the metazoan spliceosome, as well as its compositional dynamics during catalytic activation.
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Gao K, Masuda A, Matsuura T, Ohno K. Human branch point consensus sequence is yUnAy. Nucleic Acids Res 2008; 36:2257-67. [PMID: 18285363 PMCID: PMC2367711 DOI: 10.1093/nar/gkn073] [Citation(s) in RCA: 170] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2007] [Revised: 01/17/2008] [Accepted: 02/05/2008] [Indexed: 11/18/2022] Open
Abstract
Yeast carries a strictly conserved branch point sequence (BPS) of UACUAAC, whereas the human BPS is degenerative and is less well characterized. The human consensus BPS has never been extensively explored in vitro to date. Here, we sequenced 367 clones of lariat RT-PCR products arising from 52 introns of 20 human housekeeping genes. Among the 367 clones, a misincorporated nucleotide at the branch point was observed in 181 clones, for which we can precisely pinpoint the branch point. The branch points were comprised of 92.3% A, 3.3% C, 1.7% G and 2.8% U. Our analysis revealed that the human consensus BPS is simply yUnAy, where the underlined is the branch point at position zero and the lowercase pyrimidines ('y') are not as well conserved as the uppercase U and A. We found that the branch points are located 21-34 nucleotides upstream of the 3' end of an intron in 83% clones. We also found that the polypyrimidine tract spans 4-24 nucleotides downstream of the branch point. Our analysis demonstrates that the human BPSs are more degenerative than we have expected and that the human BPSs are likely to be recognized in combination with the polypyrimidine tract and/or the other splicing cis-elements.
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Affiliation(s)
| | | | | | - Kinji Ohno
- Division of Neurogenetics, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan
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36
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Palazzo AF, Springer M, Shibata Y, Lee CS, Dias AP, Rapoport TA. The signal sequence coding region promotes nuclear export of mRNA. PLoS Biol 2008; 5:e322. [PMID: 18052610 PMCID: PMC2100149 DOI: 10.1371/journal.pbio.0050322] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2007] [Accepted: 10/19/2007] [Indexed: 11/19/2022] Open
Abstract
In eukaryotic cells, most mRNAs are exported from the nucleus by the transcription export (TREX) complex, which is loaded onto mRNAs after their splicing and capping. We have studied in mammalian cells the nuclear export of mRNAs that code for secretory proteins, which are targeted to the endoplasmic reticulum membrane by hydrophobic signal sequences. The mRNAs were injected into the nucleus or synthesized from injected or transfected DNA, and their export was followed by fluorescent in situ hybridization. We made the surprising observation that the signal sequence coding region (SSCR) can serve as a nuclear export signal of an mRNA that lacks an intron or functional cap. Even the export of an intron-containing natural mRNA was enhanced by its SSCR. Like conventional export, the SSCR-dependent pathway required the factor TAP, but depletion of the TREX components had only moderate effects. The SSCR export signal appears to be characterized in vertebrates by a low content of adenines, as demonstrated by genome-wide sequence analysis and by the inhibitory effect of silent adenine mutations in SSCRs. The discovery of an SSCR-mediated pathway explains the previously noted amino acid bias in signal sequences and suggests a link between nuclear export and membrane targeting of mRNAs. In eukaryotic cells, precursors of messenger RNAs (mRNAs) are synthesized and processed in the nucleus. During processing, noncoding introns are spliced out, and a cap and poly-adenosine sequence are added to the beginning and end of the transcript, respectively. The resulting mature mRNA is exported from the nucleus to the cytoplasm by crossing the nuclear pore. Both the introns and the cap help to recruit factors that are necessary for nuclear export of an mRNA. Here we provide evidence for a novel mRNA export pathway that is specific for transcripts coding for secretory proteins. These proteins contain signal sequences that target them for translocation across the endoplasmic reticulum membrane. We made the surprising observation that the signal sequence coding region (SSCR) can serve as a nuclear export signal of an mRNA that lacks an intron or functional cap. Even the export of an intron-containing natural mRNA was enhanced by its SSCR. The SSCR export signal appears to be characterized in vertebrates by a low content of adenines. Our discovery of an SSCR-mediated pathway explains the previously noted amino acid bias in signal sequences, and suggests a link between nuclear export and membrane targeting of mRNAs. Signal sequences, which target newly synthesized secretory proteins to the endoplasmic reticulum, are encoded by adenine-depleted nucleotide sequences that promote the nuclear export of the mRNAs.
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Affiliation(s)
- Alexander F Palazzo
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Michael Springer
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Yoko Shibata
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Chung-Sheng Lee
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Anusha P Dias
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Tom A Rapoport
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
- * To whom correspondence should be addressed. E-mail:
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37
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Kim DS, Gusti V, Dery KJ, Gaur RK. Ligand-induced sequestering of branchpoint sequence allows conditional control of splicing. BMC Mol Biol 2008; 9:23. [PMID: 18267036 PMCID: PMC2275289 DOI: 10.1186/1471-2199-9-23] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2007] [Accepted: 02/12/2008] [Indexed: 12/24/2022] Open
Abstract
Background Despite tremendous progress in understanding the mechanisms of constitutive and alternative splicing, an important and widespread step along the gene expression pathway, our ability to deliberately regulate gene expression at this step remains rudimentary. The present study was performed to investigate whether a theophylline-dependent "splice switch" that sequesters the branchpoint sequence (BPS) within RNA-theophylline complex can regulate alternative splicing. Results We constructed a series of pre-mRNAs in which the BPS was inserted within theophylline aptamer. We show that theophylline-induced sequestering of BPS inhibits pre-mRNA splicing both in vitro and in vivo in a dose-dependent manner. Several lines of evidence suggest that theophylline-dependent inhibition of splicing is highly specific, and thermodynamic stability of RNA-theophylline complex as well as the location of BPS within this complex affects the efficiency of splicing inhibition. Finally, we have constructed an alternative splicing model pre-mRNA substrate in which theophylline caused exon skipping both in vitro and in vivo, suggesting that a small molecule-RNA interaction can modulate alternative splicing. Conclusion These findings provide the ability to control splicing pattern at will and should have important implications for basic, biotechnological, and biomedical research.
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Affiliation(s)
- Dong-Suk Kim
- Division of Molecular Biology, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA.
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38
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Zhang Z, Krainer AR. Splicing remodels messenger ribonucleoprotein architecture via eIF4A3-dependent and -independent recruitment of exon junction complex components. Proc Natl Acad Sci U S A 2007; 104:11574-9. [PMID: 17606899 PMCID: PMC1913901 DOI: 10.1073/pnas.0704946104] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Pre-mRNA splicing not only removes introns and joins exons to generate spliced mRNA but also results in remodeling of the spliced messenger ribonucleoprotein, influencing various downstream events. This remodeling includes the loading of an exon-exon junction complex (EJC). It is unclear how the spliceosome recruits the EJC onto the mRNA and whether EJC formation or EJC components are required for pre-mRNA splicing. Here we immunodepleted the EJC core component eIF4A3 from HeLa cell nuclear extract and found that eIF4A3 is dispensable for pre-mRNA splicing in vitro. However, eIF4A3 is required for the splicing-dependent loading of the Y14/Magoh heterodimer onto mRNA, and this activity of human eIF4A3 is also present in the Drosophila ortholog. Surprisingly, the loading of six other EJC components was not affected by eIF4A3 depletion, suggesting that their binding to mRNA involves different or redundant pathways. Finally, we found that the assembly of the EJC onto mRNA occurs at the late stages of the splicing reaction and requires the second-step splicing and mRNA-release factor HRH1/hPrp22. The EJC-dependent and -independent recruitment of RNA-binding proteins onto mRNA suggests a role for the EJC in messenger ribonucleoprotein remodeling involving interactions with other proteins already bound to the pre-mRNA, which has implications for nonsense-mediated mRNA decay and other mRNA transactions.
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Affiliation(s)
- Zuo Zhang
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724
| | - Adrian R. Krainer
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724
- *To whom correspondence should be addressed at:
Cold Spring Harbor Laboratory, P.O. Box 100, Cold Spring Harbor, NY 11724. E-mail:
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Charron M, Chern JY, Wright WW. The cathepsin L first intron stimulates gene expression in rat sertoli cells. Biol Reprod 2007; 76:813-24. [PMID: 17229931 DOI: 10.1095/biolreprod.106.057851] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Large amounts of cathepsin L (CTSL), a cysteine protease required for quantitatively normal spermatogenesis, are synthesized by mouse and rat Sertoli cells during stages VI to VII of the cycle of the seminiferous epithelium. We previously demonstrated that all of the regulatory elements required in vivo for both Sertoli cell- and stage-specific expression of the Ctsl gene are present within a ~3-kb genomic fragment that contains 2065 nucleotides upstream of the transcription start site and 977 nucleotides of downstream sequence. Most of the downstream region encodes the first intron. In this study, transient transfection assays using primary Sertoli cell cultures and the TM4 Sertoli cell line established that the Ctsl first intron increased reporter gene activity by ~5-fold. While the intron-mediated enhancement in reporter gene activity was not restricted to the Ctsl promoter, positioning the first intron upstream of the Ctsl promoter in either orientation abolished its stimulatory activity, suggesting that it does not contain a typical enhancer. Mutating the 5'-splice site of the Ctsl first intron or replacing the first intron by the Ctsl fourth intron abolished the stimulatory effect. Finally, the intron-dependent increase in reporter gene activity could be explained in part by an increase in the amounts of total RNA and transcript polyadenylation. Results from this study suggest that the stimulatory effect mediated by the Ctsl first intron may explain in part why Sertoli cells in seminiferous tubules at stages VI to VII produce high levels of CTSL.
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Affiliation(s)
- Martin Charron
- Division of Reproductive Biology, Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, Maryland 21205, USA.
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40
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Wang Y, Silverman SK. Efficient one-step synthesis of biologically related lariat RNAs by a deoxyribozyme. Angew Chem Int Ed Engl 2006; 44:5863-6. [PMID: 16086354 PMCID: PMC1513635 DOI: 10.1002/anie.200501643] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
| | - Scott K. Silverman
- Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL 61801 (USA), Phone: (+1) 217-244-4489, Fax: (+1) 217-244-8024, E-mail:
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41
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Cass DM, Berglund JA. The SF3b155 N-Terminal Domain Is a Scaffold Important for Splicing. Biochemistry 2006; 45:10092-101. [PMID: 16906767 DOI: 10.1021/bi060429o] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Recruitment of U2 snRNP to the branch point sequence of introns is a necessary step in pre-mRNA splicing. In the current model, U2AF65, bound at the polypyrimidine tract of the intron, recruits U2 snRNP to the branch point sequence by interacting with the U2 snRNP protein SF3b155. We demonstrate that the N-terminal domain of SF3b155 contains multiple U2AF65 binding sites that are distinct from the binding site for the U2 snRNP protein p14, mapped to amino acids 396-424 of SF3b155. The N-terminal domain of SF3b155 appears to adopt a primarily unfolded structure but is functional to inhibit splicing in vitro. RNA binding studies show that the N-terminal domain of SF3b155 binds RNA nonspecifically and that the sites for U2AF65 binding and RNA binding are overlapping (or the same) within SF3b155. We propose that the N-terminal domain of SF3b155 adopts a primarily unfolded structure that functions as a scaffold to facilitate SF3b155's multiple protein-protein and protein-RNA interactions. The multiple U2AF65 binding sites on SF3b155 suggest a model in which multiple U2AF65 molecules bound to the intron could enhance U2 snRNP recruitment to the branch point sequence.
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Affiliation(s)
- Danielle M Cass
- Department of Chemistry and Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA
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42
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Wang Y, Silverman SK. Efficient One-Step Synthesis of Biologically Related Lariat RNAs by a Deoxyribozyme. Angew Chem Int Ed Engl 2005. [DOI: 10.1002/ange.200501643] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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43
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Dietrich RC, Fuller JD, Padgett RA. A mutational analysis of U12-dependent splice site dinucleotides. RNA (NEW YORK, N.Y.) 2005; 11:1430-40. [PMID: 16043500 PMCID: PMC1370826 DOI: 10.1261/rna.7206305] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Introns spliced by the U12-dependent minor spliceosome are divided into two classes based on their splice site dinucleotides. The /AU-AC/ class accounts for about one-third of U12-dependent introns in humans, while the /GU-AG/ class accounts for the other two-thirds. We have investigated the in vivo and in vitro splicing phenotypes of mutations in these dinucleotide sequences. A 5' A residue can splice to any 3' residue, although C is preferred. A 5' G residue can splice to 3' G or U residues with a preference for G. Little or no splicing was observed to 3' A or C residues. A 5' U or C residue is highly deleterious for U12-dependent splicing, although some combinations, notably 5' U to 3' U produced detectable spliced products. The dependence of 3' splice site activity on the identity of the 5' residue provides evidence for communication between the first and last nucleotides of the intron. Most mutants in the second position of the 5' splice site and the next to last position of the 3' splice site were defective for splicing. Double mutants of these residues showed no evidence of communication between these nucleotides. Varying the distance between the branch site and the 3' splice site dinucleotide in the /GU-AG/ class showed that a somewhat larger range of distances was functional than for the /AU-AC/ class. The optimum branch site to 3' splice site distance of 11-12 nucleotides appears to be the same for both classes.
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Affiliation(s)
- Rosemary C Dietrich
- Department of Molecular Genetics, NE-20, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, OH 44195, USA
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44
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Zhang XHF, Leslie CS, Chasin LA. Dichotomous splicing signals in exon flanks. Genome Res 2005; 15:768-79. [PMID: 15930489 PMCID: PMC1142467 DOI: 10.1101/gr.3217705] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2004] [Accepted: 03/04/2005] [Indexed: 02/06/2023]
Abstract
Intronic elements flanking the splice-site consensus sequences are thought to play a role in pre-mRNA splicing. However, the generality of this role, the catalog of effective sequences, and the mechanisms involved are still lacking. Using molecular genetic tests, we first showed that the approximately 50-nt intronic flanking sequences of exons beyond the splice-site consensus are generally important for splicing. We then went on to characterize exon flank sequences on a genomic scale. The G+C content of flanks displayed a bimodal distribution reflecting an exaggeration of this base composition in flanks relative to the gene as a whole. We divided all exons into two classes according to their flank G+C content and used computational and statistical methods to define pentamers of high relative abundance and phylogenetic conservation in exon flanks. Upstream pentamers were often common to the two classes, whereas downstream pentamers were totally different. Upstream and downstream pentamers were often identical around low G+C exons, and in contrast, were often complementary around high G+C exons. In agreement with this complementarity, predicted base pairing was more frequent between the flanks of high G+C exons. Pseudo exons did not exhibit this behavior, but rather tended to form base pairs between flanks and exon bodies. We conclude that most exons require signals in their immediate flanks for efficient splicing. G+C content is a sequence feature correlated with many genetic and genomic attributes. We speculate that there may be different mechanisms for splice site recognition depending on G+C content.
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Affiliation(s)
- Xiang H-F Zhang
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
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45
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Kupfer DM, Drabenstot SD, Buchanan KL, Lai H, Zhu H, Dyer DW, Roe BA, Murphy JW. Introns and splicing elements of five diverse fungi. EUKARYOTIC CELL 2005; 3:1088-100. [PMID: 15470237 PMCID: PMC522613 DOI: 10.1128/ec.3.5.1088-1100.2004] [Citation(s) in RCA: 202] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Genomic sequences and expressed sequence tag data for a diverse group of fungi (Saccharomyces cerevisiae, Schizosaccharomyces pombe, Aspergillus nidulans, Neurospora crassa, and Cryptococcus neoformans) provided the opportunity to accurately characterize conserved intronic elements. An examination of large intron data sets revealed that fungal introns in general are short, that 98% or more of them belong to the canonical splice site (ss) class (5'GU...AG3'), and that they have polypyrimidine tracts predominantly in the region between the 5' ss and the branch point. Information content is high in the 5' ss, branch site, and 3' ss regions of the introns but low in the exon regions adjacent to the introns in the fungi examined. The two yeasts have broader intron length ranges and correspondingly higher intron information content than the other fungi. Generally, as intron length increases in the fungi, so does intron information content. Homologs of U2AF spliceosomal proteins were found in all species except for S. cerevisiae, suggesting a nonconventional role for U2AF in the absence of canonical polypyrimidine tracts in the majority of introns. Our observations imply that splicing in fungi may be different from that in vertebrates and may require additional proteins that interact with polypyrimidine tracts upstream of the branch point. Theoretical protein homologs for Nam8p and TIA-1, two proteins that require U-rich regions upstream of the branch point to function, were found. There appear to be sufficient differences between S. cerevisiae and S. pombe introns and the introns of two filamentous members of the Ascomycota and one member of the Basidiomycota to warrant the development of new model organisms for studying the splicing mechanisms of fungi.
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Affiliation(s)
- Doris M Kupfer
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, P.O. Box 26901, BMSB 1053, Oklahoma City, OK 73190, USA
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Ibrahim EC, Schaal TD, Hertel KJ, Reed R, Maniatis T. Serine/arginine-rich protein-dependent suppression of exon skipping by exonic splicing enhancers. Proc Natl Acad Sci U S A 2005; 102:5002-7. [PMID: 15753297 PMCID: PMC555999 DOI: 10.1073/pnas.0500543102] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The 5' and 3' splice sites within an intron can, in principle, be joined to those within any other intron during pre-mRNA splicing. However, exons are joined in a strict 5' to 3' linear order in constitutively spliced pre-mRNAs. Thus, specific mechanisms must exist to prevent the random joining of exons. Here we report that insertion of exon sequences into an intron can inhibit splicing to the downstream 3' splice site and that this inhibition is independent of intron size. The exon sequences required for splicing inhibition were found to be exonic enhancer elements, and their inhibitory activity requires the binding of serine/arginine-rich splicing factors. We conclude that exonic enhancers can act as barriers to prevent exon skipping and thereby may play a key role in ensuring the correct 5' to 3' linear order of exons in spliced mRNA.
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Affiliation(s)
- El Chérif Ibrahim
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
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47
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Liao HJ, Baker CC, Princler GL, Derse D. cis-Acting and trans-acting modulation of equine infectious anemia virus alternative RNA splicing. Virology 2004; 323:131-40. [PMID: 15165825 DOI: 10.1016/j.virol.2003.12.028] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2003] [Revised: 12/11/2003] [Accepted: 12/22/2003] [Indexed: 11/22/2022]
Abstract
Equine infectious anemia virus (EIAV), a lentivirus distantly related to HIV-1, encodes regulatory proteins, EIAV Tat (ETat) and Rev (ERev), from a four-exon mRNA. Exon 3 of the tat/rev mRNA contains a 30-nucleotide purine-rich element (PRE) which binds both ERev and SF2/ASF, a member of the SR family of RNA splicing factors. To better understand the role of this element in the regulation of EIAV pre-mRNA splicing, we quantified the effects of mutation or deletion of the PRE on exon 3 splicing in vitro and on alternative splicing in vivo. We also determined the branch point elements upstream of exons 3 and 4. In vitro splicing of exon 3 to exon 4 was not affected by mutation of the PRE, and addition of purified SR proteins enhanced splicing independently of the PRE. In vitro splicing of exon 2 to exon 3 was dependent on the PRE; under conditions of excess SR proteins, either the PRE or the 5' splice site of exon 3 was sufficient to activate splicing. We applied isoform-specific primers in real-time RT-PCR reactions to quantitatively analyze alternative splicing in cells transfected with rev-minus EIAV provirus constructs. In the context of provirus with wild-type exon 3, greater than 80% of the viral mRNAs were multiply spliced, and of these, less than 1% excluded exon 3. Deletion of the PRE resulted in a decrease in the relative amount of multiply spliced mRNA to about 40% of the total and approximately 39% of the viral mRNA excluded exon 3. Ectopic expression of ERev caused a decrease in the relative amount of multiply spliced mRNA to approximately 50% of the total and increased mRNAs that excluded exon 3 to about 4%. Over-expression of SF2/ASF in cells transfected with wild-type provirus constructs inhibited splicing but did not significantly alter exon 3 skipping.
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Affiliation(s)
- Huey-Jane Liao
- Basic Research Program, SAIC-Frederick, Frederick, MD 21702, USA
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48
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Chamary JV, Hurst LD. Similar rates but different modes of sequence evolution in introns and at exonic silent sites in rodents: evidence for selectively driven codon usage. Mol Biol Evol 2004; 21:1014-23. [PMID: 15014158 DOI: 10.1093/molbev/msh087] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
In mammals divergence at fourfold degenerate sites in codons (K(4)) and intronic sequence (K(i)) are both used to estimate the mutation rate, under the supposition that both evolve neutrally. Does it matter which of these we use? Using either class of sequence can be defended because (1) K(4) is the same as K(i) (at least in rodents) and (2) there is no selectively driven codon usage (hence no systematic selection on third sites). Here we re-examine these findings using 560 introns (for 136 genes) in the mouse-rat comparison, aligned by eye and using a new maximum likelihood protocol. We find that the rate of evolution at fourfold sites and at intronic sites is similar in magnitude, but only after eliminating putatively constrained sites from introns (first introns and sites flanking intron-exon junctions). Any approximate congruence between the two rates is not, however, owing to an underlying similarity in the mode of sequence evolution. Some dinucleotides are hypermutable and differently abundant in exons and introns (e.g., CpGs). More importantly, after controlling for relative abundance, all dinucleotides starting with A or T are more prevalent in mismatches in exons than in introns, whereas C-starting dinucleotides (except CG) are more common in introns. Although C content at intronic sites is lower than at flanking fourfold sites, G content is similar, demonstrating that there exists a strong strand-specific preference for C nucleotides that is unique to exons. Transcription-coupled mutational processes and biased gene conversion cannot explain this, as they should affect introns and flanking exons equally. Therefore, by elimination, we propose this to be strong evidence for selectively driven codon usage in mammals.
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Affiliation(s)
- Jean-Vincent Chamary
- Department of Biology and Biochemistry, University of Bath, Bath, United Kingdom
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49
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Su Y, Testaverde JR, Davis CN, Hayajneh WA, Adair R, Colberg-Poley AM. Human cytomegalovirus UL37 immediate early target minigene RNAs are accurately spliced and polyadenylated. J Gen Virol 2003; 84:29-39. [PMID: 12533698 DOI: 10.1099/vir.0.18700-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The human cytomegalovirus (HCMV) UL36-38 immediate early (IE) locus encodes proteins required for virus growth. The UL37 IE promoter drives production of differentially spliced and unspliced RNAs. To study their post-transcriptional processing, we generated target minigenes encoding each UL37 RNA splicing substrate. Target 1 RNA, spanning UL37 exon 1 (x1) donor and 2 (x2) acceptor as well as adjacent intronic sequences, but not the UL38 gene, accurately reproduced UL37 x1/x2 RNA splicing in transfected permissive cells. Surprisingly, deletion of distal intronic sequences nt -82 to -143 from the UL37x2 acceptor resulted in aberrant splicing to an upstream non-consensus exonic donor. Target 1 RNAs carry the UL37x1 polyadenylation (PA) signal and site as well as a downstream SV40 early PA signal. Both the UL37x1 and SV40 PA signals are used in wild-type target 1 RNAs but inhibited in UL37x1 PA signal mutants. Alternative RNA splicing of UL37 exons 2 to 3 or 3A as well as exons 3 to 4, observed in HCMV mature UL37 and UL36 spliced RNAs, is accurately reproduced with target minigene RNAs carrying the corresponding UL37 exonic and intronic sequences. Moreover, alternative splicing using two novel UL37 exon 3 consensus splice donors (di and dii) was found in target and in HCMV-infected cell RNA. These results demonstrate that: (i) target minigene RNAs accurately recapitulate the processing of UL37 IE RNAs in the HCMV-infected cell; (ii) precise UL37x1 donor selection is modulated by 3'-distal UL37 intronic sequences; and (iii) UL37 exon 3 contains multiple alternative consensus splice donors.
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Affiliation(s)
- Yan Su
- Center for Cancer and Immunology Research, Room 5720, Children's Research Institute, George Washington University School of Medicine and Health Sciences, 111 Michigan Avenue, NW, Washington, DC 20010, USA
| | - James R Testaverde
- Center for Cancer and Immunology Research, Room 5720, Children's Research Institute, George Washington University School of Medicine and Health Sciences, 111 Michigan Avenue, NW, Washington, DC 20010, USA
| | - Candice N Davis
- Center for Cancer and Immunology Research, Room 5720, Children's Research Institute, George Washington University School of Medicine and Health Sciences, 111 Michigan Avenue, NW, Washington, DC 20010, USA
| | - Wail A Hayajneh
- Department of Infectious Diseases, Children's National Medical Center, George Washington University School of Medicine and Health Sciences, 111 Michigan Avenue, NW, Washington, DC 20010, USA
- Center for Cancer and Immunology Research, Room 5720, Children's Research Institute, George Washington University School of Medicine and Health Sciences, 111 Michigan Avenue, NW, Washington, DC 20010, USA
| | - Richard Adair
- Center for Cancer and Immunology Research, Room 5720, Children's Research Institute, George Washington University School of Medicine and Health Sciences, 111 Michigan Avenue, NW, Washington, DC 20010, USA
| | - Anamaris M Colberg-Poley
- Department of Pediatrics, George Washington University School of Medicine and Health Sciences, 111 Michigan Avenue, NW, Washington, DC 20010, USA
- Center for Cancer and Immunology Research, Room 5720, Children's Research Institute, George Washington University School of Medicine and Health Sciences, 111 Michigan Avenue, NW, Washington, DC 20010, USA
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50
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Barrow LL, van Bokhoven H, Daack-Hirsch S, Andersen T, van Beersum SEC, Gorlin R, Murray JC. Analysis of the p63 gene in classical EEC syndrome, related syndromes, and non-syndromic orofacial clefts. J Med Genet 2002; 39:559-66. [PMID: 12161593 PMCID: PMC1735218 DOI: 10.1136/jmg.39.8.559] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
EEC syndrome is an autosomal dominant disorder with the cardinal signs of ectrodactyly, ectodermal dysplasia, and orofacial clefts. EEC syndrome has been linked to chromosome 3q27 and heterozygous p63 mutations were detected in unrelated EEC families. In addition, homozygous p63 null mice exhibit craniofacial abnormalities, limb truncations, and absence of epidermal appendages, such as hair follicles and tooth primordia. In this study, we screened 39 syndromic patients, including four with EEC syndrome, five with syndromes closely related to EEC syndrome, and 30 with other syndromic orofacial clefts and/or limb anomalies. We identified heterozygous p63 mutations in three unrelated cases of EEC syndrome, two Iowa white families and one sporadic case in a Filipino boy. One family is atypical for EEC and has features consistent with Hay-Wells syndrome. In this family, the mutation ablates a splice acceptor site and, in the other two, mutations produce amino acid substitutions, R280C and R304Q, which alter conserved DNA binding sites. Germline mosaicism was detected in the founder of the mutation in one case. These three cases show significant interfamilial and intrafamilial variability in expressivity. We also screened p63 in 62 patients with non-syndromic orofacial clefts, identifying an intronic single nucleotide polymorphism but finding no evidence of mutations that would explain even a subset of non-syndromic orofacial clefts. This study supports a common role for p63 in classical EEC syndrome, both familial and sporadic, but not in other related or non-syndromic forms of orofacial clefts.
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Affiliation(s)
- L L Barrow
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa, Iowa City, IA 52242, USA
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