1
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Ng AYE, Chan SN, Pek JW. Genetic compensation between ribosomal protein paralogs mediated by a cognate circular RNA. Cell Rep 2024; 43:114228. [PMID: 38735045 DOI: 10.1016/j.celrep.2024.114228] [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] [Received: 03/01/2024] [Revised: 04/19/2024] [Accepted: 04/26/2024] [Indexed: 05/14/2024] Open
Abstract
Inter-regulation between related genes, such as ribosomal protein (RP) paralogs, has been observed to be important for genetic compensation and paralog-specific functions. However, how paralogs communicate to modulate their expression levels is unknown. Here, we report a circular RNA involved in the inter-regulation between RP paralogs RpL22 and RpL22-like during Drosophila spermatogenesis. Both paralogs are mutually regulated by the circular stable intronic sequence RNA (sisRNA) circRpL22(NE,3S) produced from the RpL22 locus. RpL22 represses itself and RpL22-like. Interestingly, circRpL22 binds to RpL22 to repress RpL22-like, but not RpL22, suggesting that circRpL22 modulates RpL22's function. circRpL22 is in turn controlled by RpL22-like, which regulates RpL22 binding to circRpL22 to indirectly modulate RpL22. This circRpL22-centric inter-regulatory circuit enables the loss of RpL22-like to be genetically compensated by RpL22 upregulation to ensure robust male germline development. Thus, our study identifies sisRNA as a possible mechanism of genetic crosstalk between paralogous genes.
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Affiliation(s)
- Amanda Yunn Ee Ng
- Temasek Life Sciences Laboratory, 1 Research Link National University of Singapore, Singapore 117604, Singapore; Department of Biological Sciences, National University of Singapore, 14 Science Drive Singapore 117543, Singapore
| | - Seow Neng Chan
- Temasek Life Sciences Laboratory, 1 Research Link National University of Singapore, Singapore 117604, Singapore
| | - Jun Wei Pek
- Temasek Life Sciences Laboratory, 1 Research Link National University of Singapore, Singapore 117604, Singapore; Department of Biological Sciences, National University of Singapore, 14 Science Drive Singapore 117543, Singapore.
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2
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Li H, Zhang Y, Bing J, Han J, Hu J, Zhao H, Sun X. Intron-capture RNA-seq reveals the landscape of intronic RNAs in Arabidopsis. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2023; 196:75-88. [PMID: 36701993 DOI: 10.1016/j.plaphy.2023.01.040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Accepted: 01/19/2023] [Indexed: 06/17/2023]
Abstract
Intronic RNAs have been overlooked for a long time: They are functional, but treated as "junk." In this work, we designed a new sequencing strategy to investigate intronic RNAs. By using intron-capture RNA-seq, we systematically analyzed the intronic RNAs in Arabidopsis by zooming into the intronic regions an order of magnitude deeper than in previous work. Our key findings include: (1) Intron-capture RNA-seq is a much more efficient approach to analyze intronic RNAs than total RNA-seq and mRNA-seq. (2) We identified three types of intronic RNAs, and found that the GC pattern differs significantly between the introns with and without intronic RNAs. (3) We detected many hidden elements in introns, including circular RNAs, splice junctions, and transcripts that have previously been overlooked. (4) The expression of these intronic RNAs varies during the time course of pathogen infection, which indicates that an unknown mechanism may exist for these RNAs. (5) We also demonstrated that most of intronic RNAs are detectable in both Arabidopsis and rice, suggesting that these non-coding molecules are conserved. Taken together, this work proposes an efficient strategy to analyze intronic RNAs, and provides an unprecedented view of this essential component in biological pathways.
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Affiliation(s)
- Han Li
- Agricultural Big-Data Research Center, College of Information Science and Engineering, Shandong Agricultural University, Taian, China
| | - Yimai Zhang
- Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Nanjing, China
| | - Jianhao Bing
- Agricultural Big-Data Research Center, College of Information Science and Engineering, Shandong Agricultural University, Taian, China
| | - Jinyu Han
- Agricultural Big-Data Research Center, College of Information Science and Engineering, Shandong Agricultural University, Taian, China
| | - Jiming Hu
- Agricultural Big-Data Research Center, College of Information Science and Engineering, Shandong Agricultural University, Taian, China
| | - Hongwei Zhao
- Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Nanjing, China.
| | - Xiaoyong Sun
- Agricultural Big-Data Research Center, College of Information Science and Engineering, Shandong Agricultural University, Taian, China.
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3
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Muzafar S, Sharma RD, Chauhan N, Prasad R. Intron distribution and emerging role of alternative splicing in fungi. FEMS Microbiol Lett 2021; 368:6414529. [PMID: 34718529 DOI: 10.1093/femsle/fnab135] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Accepted: 10/28/2021] [Indexed: 12/16/2022] Open
Abstract
Spliceosomal introns are noncoding sequences that are spliced from pre-mRNA. They are ubiquitous in eukaryotic genomes, although the average number of introns per gene varies considerably between different eukaryotic species. Fungi are diverse in terms of intron numbers ranging from 4% to 99% genes with introns. Alternative splicing is one of the most common modes of posttranscriptional regulation in eukaryotes, giving rise to multiple transcripts from a single pre-mRNA and is widespread in metazoans and drives extensive proteome diversity. Earlier, alternative splicing was considered to be rare in fungi, but recently, increasing numbers of studies have revealed that alternative splicing is also widespread in fungi and has been implicated in the regulation of fungal growth and development, protein localization and the improvement of survivability, likely underlying their unique capacity to adapt to changing environmental conditions. However, the role of alternative splicing in pathogenicity and development of drug resistance is only recently gaining attention. In this review, we describe the intronic landscape in fungi. We also present in detail the newly discovered functions of alternative splicing in various cellular processes and outline areas particularly in pathogenesis and clinical drug resistance for future studies that could lead to the development of much needed new therapeutics.
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Affiliation(s)
- Suraya Muzafar
- Amity Institute of Integrative Sciences and Health, Amity University Gurgaon, Gurgaon 122413, Haryana, India
| | - Ravi Datta Sharma
- Amity Institute of Integrative Sciences and Health, Amity University Gurgaon, Gurgaon 122413, Haryana, India
| | - Neeraj Chauhan
- Public Health Research Institute, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ 07103, USA
| | - Rajendra Prasad
- Amity Institute of Integrative Sciences and Health, Amity University Gurgaon, Gurgaon 122413, Haryana, India
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4
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Gao W, Jones TA, Rivas E. Discovery of 17 conserved structural RNAs in fungi. Nucleic Acids Res 2021; 49:6128-6143. [PMID: 34086938 PMCID: PMC8216456 DOI: 10.1093/nar/gkab355] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Revised: 03/25/2021] [Accepted: 04/21/2021] [Indexed: 11/13/2022] Open
Abstract
Many non-coding RNAs with known functions are structurally conserved: their intramolecular secondary and tertiary interactions are maintained across evolutionary time. Consequently, the presence of conserved structure in multiple sequence alignments can be used to identify candidate functional non-coding RNAs. Here, we present a bioinformatics method that couples iterative homology search with covariation analysis to assess whether a genomic region has evidence of conserved RNA structure. We used this method to examine all unannotated regions of five well-studied fungal genomes (Saccharomyces cerevisiae, Candida albicans, Neurospora crassa, Aspergillus fumigatus, and Schizosaccharomyces pombe). We identified 17 novel structurally conserved non-coding RNA candidates, which include four H/ACA box small nucleolar RNAs, four intergenic RNAs and nine RNA structures located within the introns and untranslated regions (UTRs) of mRNAs. For the two structures in the 3' UTRs of the metabolic genes GLY1 and MET13, we performed experiments that provide evidence against them being eukaryotic riboswitches.
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Affiliation(s)
- William Gao
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, USA
| | - Thomas A Jones
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, USA
- Howard Hughes Medical Institute, Harvard University, Cambridge, USA
| | - Elena Rivas
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, USA
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5
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Lim CS, Weinstein BN, Roy SW, Brown CM. Analysis of fungal genomes reveals commonalities of intron gain or loss and functions in intron-poor species. Mol Biol Evol 2021; 38:4166-4186. [PMID: 33772558 PMCID: PMC8476143 DOI: 10.1093/molbev/msab094] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Previous evolutionary reconstructions have concluded that early eukaryotic ancestors including both the last common ancestor of eukaryotes and of all fungi had intron-rich genomes. By contrast, some extant eukaryotes have few introns, underscoring the complex histories of intron–exon structures, and raising the question as to why these few introns are retained. Here, we have used recently available fungal genomes to address a variety of questions related to intron evolution. Evolutionary reconstruction of intron presence and absence using 263 diverse fungal species supports the idea that massive intron reduction through intron loss has occurred in multiple clades. The intron densities estimated in various fungal ancestors differ from zero to 7.6 introns per 1 kb of protein-coding sequence. Massive intron loss has occurred not only in microsporidian parasites and saccharomycetous yeasts, but also in diverse smuts and allies. To investigate the roles of the remaining introns in highly-reduced species, we have searched for their special characteristics in eight intron-poor fungi. Notably, the introns of ribosome-associated genes RPL7 and NOG2 have conserved positions; both intron-containing genes encoding snoRNAs. Furthermore, both the proteins and snoRNAs are involved in ribosome biogenesis, suggesting that the expression of the protein-coding genes and noncoding snoRNAs may be functionally coordinated. Indeed, these introns are also conserved in three-quarters of fungi species. Our study shows that fungal introns have a complex evolutionary history and underappreciated roles in gene expression.
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Affiliation(s)
- Chun Shen Lim
- Department of Biochemistry, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
| | - Brooke N Weinstein
- Quantitative & Systems Biology, School of Natural Sciences, University of California-Merced, Merced, CA, USA.,Department of Biology, San Francisco State University, San Francisco, CA, USA
| | - Scott W Roy
- Quantitative & Systems Biology, School of Natural Sciences, University of California-Merced, Merced, CA, USA.,Department of Biology, San Francisco State University, San Francisco, CA, USA
| | - Chris M Brown
- Department of Biochemistry, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
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6
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Cha S, Hong CP, Kang HA, Hahn JS. Differential activation mechanisms of two isoforms of Gcr1 transcription factor generated from spliced and un-spliced transcripts in Saccharomyces cerevisiae. Nucleic Acids Res 2021; 49:745-759. [PMID: 33367825 PMCID: PMC7826247 DOI: 10.1093/nar/gkaa1221] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 11/27/2020] [Accepted: 12/03/2020] [Indexed: 12/19/2022] Open
Abstract
Gcr1, an important transcription factor for glycolytic genes in Saccharomyces cerevisiae, was recently revealed to have two isoforms, Gcr1U and Gcr1S, produced from un-spliced and spliced transcripts, respectively. In this study, by generating strains expressing only Gcr1U or Gcr1S using the CRISPR/Cas9 system, we elucidate differential activation mechanisms of these two isoforms. The Gcr1U monomer forms an active complex with its coactivator Gcr2 homodimer, whereas Gcr1S acts as a homodimer without Gcr2. The USS domain, 55 residues at the N-terminus existing only in Gcr1U, inhibits dimerization of Gcr1U and even acts in trans to inhibit Gcr1S dimerization. The Gcr1S monomer inhibits the metabolic switch from fermentation to respiration by directly binding to the ALD4 promoter, which can be restored by overexpression of the ALD4 gene, encoding a mitochondrial aldehyde dehydrogenase required for ethanol utilization. Gcr1U and Gcr1S regulate almost the same target genes, but show unique activities depending on growth phase, suggesting that these isoforms play differential roles through separate activation mechanisms depending on environmental conditions.
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Affiliation(s)
- Seungwoo Cha
- School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
| | - Chang Pyo Hong
- Theragen Bio Co., Ltd, 145 Gwanggyo-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 16229, Republic of Korea
| | - Hyun Ah Kang
- Department of Life Science, College of Natural Science, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea
| | - Ji-Sook Hahn
- School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
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7
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Balarezo-Cisneros LN, Parker S, Fraczek MG, Timouma S, Wang P, O’Keefe RT, Millar CB, Delneri D. Functional and transcriptional profiling of non-coding RNAs in yeast reveal context-dependent phenotypes and in trans effects on the protein regulatory network. PLoS Genet 2021; 17:e1008761. [PMID: 33493158 PMCID: PMC7886133 DOI: 10.1371/journal.pgen.1008761] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Revised: 02/16/2021] [Accepted: 12/19/2020] [Indexed: 12/19/2022] Open
Abstract
Non-coding RNAs (ncRNAs), including the more recently identified Stable Unannotated Transcripts (SUTs) and Cryptic Unstable Transcripts (CUTs), are increasingly being shown to play pivotal roles in the transcriptional and post-transcriptional regulation of genes in eukaryotes. Here, we carried out a large-scale screening of ncRNAs in Saccharomyces cerevisiae, and provide evidence for SUT and CUT function. Phenotypic data on 372 ncRNA deletion strains in 23 different growth conditions were collected, identifying ncRNAs responsible for significant cellular fitness changes. Transcriptome profiles were assembled for 18 haploid ncRNA deletion mutants and 2 essential ncRNA heterozygous deletants. Guided by the resulting RNA-seq data we analysed the genome-wide dysregulation of protein coding genes and non-coding transcripts. Novel functional ncRNAs, SUT125, SUT126, SUT035 and SUT532 that act in trans by modulating transcription factors were identified. Furthermore, we described the impact of SUTs and CUTs in modulating coding gene expression in response to different environmental conditions, regulating important biological process such as respiration (SUT125, SUT126, SUT035, SUT432), steroid biosynthesis (CUT494, SUT053, SUT468) or rRNA processing (SUT075 and snR30). Overall, these data capture and integrate the regulatory and phenotypic network of ncRNAs and protein-coding genes, providing genome-wide evidence of the impact of ncRNAs on cellular homeostasis. A quarter of the yeast genome comprises non-coding RNA molecules (ncRNAs), which do not translate into proteins but are involved in the regulation of gene expression. ncRNAs can affect nearby genes by physically interfering with their transcription (cis mode of action), or they interact with DNA, proteins or other RNAs to regulate the expression of distant genes (trans mode of action). Examples of cis-acting ncRNAs have been broadly described, however, genome-wide studies to identify functional trans-acting ncRNAs involved in global gene regulation are still lacking. Here, we used a ncRNA yeast deletion collection to score ncRNA impact on cellular function in different environmental conditions. A group of 20 ncRNA deletion mutants with broad fitness diversity were selected to investigate the ncRNA effect on the protein and ncRNA expression network. We showed a high correlation between altered phenotypes and global transcriptional changes, in an environmental dependent manner. We confirmed the trans acting regulation of ncRNAs in the genome and their role in altering the expression of transcription factors. These findings support the notion of the involvement of ncRNAs in fine tuning cellular expression via regulation of transcription factors, as an advantageous RNA-mediated mechanism that can be fast and cost-effective for the cells.
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Affiliation(s)
- Laura Natalia Balarezo-Cisneros
- Manchester Institute of Biotechnology, Faculty of Biology Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
| | - Steven Parker
- Manchester Institute of Biotechnology, Faculty of Biology Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
| | - Marcin G. Fraczek
- Manchester Institute of Biotechnology, Faculty of Biology Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
| | - Soukaina Timouma
- Manchester Institute of Biotechnology, Faculty of Biology Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
| | - Ping Wang
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
| | - Raymond T. O’Keefe
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
| | - Catherine B. Millar
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
- * E-mail: (CM); (DD)
| | - Daniela Delneri
- Manchester Institute of Biotechnology, Faculty of Biology Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
- * E-mail: (CM); (DD)
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8
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Roy B, Granas D, Bragg F, Cher JAY, White MA, Stormo GD. Autoregulation of yeast ribosomal proteins discovered by efficient search for feedback regulation. Commun Biol 2020; 3:761. [PMID: 33311538 PMCID: PMC7732827 DOI: 10.1038/s42003-020-01494-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2020] [Accepted: 11/15/2020] [Indexed: 11/13/2022] Open
Abstract
Post-transcriptional autoregulation of gene expression is common in bacteria but many fewer examples are known in eukaryotes. We used the yeast collection of genes fused to GFP as a rapid screen for examples of feedback regulation in ribosomal proteins by overexpressing a non-regulatable version of a gene and observing the effects on the expression of the GFP-fused version. We tested 95 ribosomal protein genes and found a wide continuum of effects, with 30% showing at least a 3-fold reduction in expression. Two genes, RPS22B and RPL1B, showed over a 10-fold repression. In both cases the cis-regulatory segment resides in the 5’ UTR of the gene as shown by placing that segment of the mRNA upstream of GFP alone and demonstrating it is sufficient to cause repression of GFP when the protein is over-expressed. Further analyses showed that the intron in the 5’ UTR of RPS22B is required for regulation, presumably because the protein inhibits splicing that is necessary for translation. The 5’ UTR of RPL1B contains a sequence and structure motif that is conserved in the binding sites of Rpl1 orthologs from bacteria to mammals, and mutations within the motif eliminate repression. Here, the authors screen for feedback regulation of ribosomal proteins by overexpressing a non- regulatable version of a gene and observing its effects on the expression of the GFP-fused version. They find that 30% show at least a 3-fold reduction in expression and two genes show a 10-fold reduction with the regulatory site being in the 5’ untranslated region of the gene.
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Affiliation(s)
- Basab Roy
- Department of Genetics and Center for Genome Sciences and Systems Biology, Washington University School of Medicine, St Louis, MO, 63110, USA.
| | - David Granas
- Department of Genetics and Center for Genome Sciences and Systems Biology, Washington University School of Medicine, St Louis, MO, 63110, USA
| | - Fredrick Bragg
- Department of Genetics and Center for Genome Sciences and Systems Biology, Washington University School of Medicine, St Louis, MO, 63110, USA
| | - Jonathan A Y Cher
- Department of Genetics and Center for Genome Sciences and Systems Biology, Washington University School of Medicine, St Louis, MO, 63110, USA
| | - Michael A White
- Department of Genetics and Center for Genome Sciences and Systems Biology, Washington University School of Medicine, St Louis, MO, 63110, USA
| | - Gary D Stormo
- Department of Genetics and Center for Genome Sciences and Systems Biology, Washington University School of Medicine, St Louis, MO, 63110, USA.
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9
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de Witt RN, Kroukamp H, Van Zyl WH, Paulsen IT, Volschenk H. QTL analysis of natural Saccharomyces cerevisiae isolates reveals unique alleles involved in lignocellulosic inhibitor tolerance. FEMS Yeast Res 2020; 19:5528620. [PMID: 31276593 DOI: 10.1093/femsyr/foz047] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2019] [Accepted: 07/03/2019] [Indexed: 12/13/2022] Open
Abstract
Decoding the genetic basis of lignocellulosic inhibitor tolerance in Saccharomyces cerevisiae is crucial for rational engineering of bioethanol strains with enhanced robustness. The genetic diversity of natural strains present an invaluable resource for the exploration of complex traits of industrial importance from a pan-genomic perspective to complement the limited range of specialised, tolerant industrial strains. Natural S. cerevisiae isolates have lately garnered interest as a promising toolbox for engineering novel, genetically encoded tolerance phenotypes into commercial strains. To this end, we investigated the genetic basis for lignocellulosic inhibitor tolerance of natural S. cerevisiae isolates. A total of 12 quantitative trait loci underpinning tolerance were identified by next-generation sequencing linked bulk-segregant analysis of superior interbred pools. Our findings corroborate the current perspective of lignocellulosic inhibitor tolerance as a multigenic, complex trait. Apart from a core set of genetic variants required for inhibitor tolerance, an additional genetic background-specific response was observed. Functional analyses of the identified genetic loci revealed the uncharacterised ORF, YGL176C and the bud-site selection XRN1/BUD13 as potentially beneficial alleles contributing to tolerance to a complex lignocellulosic inhibitor mixture. We present evidence for the consideration of both regulatory and coding sequence variants for strain improvement.
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Affiliation(s)
- R N de Witt
- Department of Microbiology, Stellenbosch University, De Beer Street, Stellenbosch 7600, Western Cape, South Africa
| | - H Kroukamp
- Department of Molecular Sciences, Macquarie University, Balaclava Rd, North Ryde, NSW 2109, Australia
| | - W H Van Zyl
- Department of Microbiology, Stellenbosch University, De Beer Street, Stellenbosch 7600, Western Cape, South Africa
| | - I T Paulsen
- Department of Molecular Sciences, Macquarie University, Balaclava Rd, North Ryde, NSW 2109, Australia
| | - H Volschenk
- Department of Microbiology, Stellenbosch University, De Beer Street, Stellenbosch 7600, Western Cape, South Africa
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10
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Hewitt SK, Duangrattanalert K, Burgis T, Zeef LAH, Naseeb S, Delneri D. Plasticity of Mitochondrial DNA Inheritance and its Impact on Nuclear Gene Transcription in Yeast Hybrids. Microorganisms 2020; 8:microorganisms8040494. [PMID: 32244414 PMCID: PMC7232527 DOI: 10.3390/microorganisms8040494] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 03/25/2020] [Accepted: 03/29/2020] [Indexed: 12/15/2022] Open
Abstract
Mitochondrial DNA (mtDNA) in yeast is biparentally inherited, but colonies rapidly lose one type of parental mtDNA, thus becoming homoplasmic. Therefore, hybrids between the yeast species possess two homologous nuclear genomes, but only one type of mitochondrial DNA. We hypothesise that the choice of mtDNA retention is influenced by its contribution to hybrid fitness in different environments, and the allelic expression of the two nuclear sub-genomes is affected by the presence of different mtDNAs in hybrids. Saccharomyces cerevisiae/S. uvarum hybrids preferentially retained S. uvarum mtDNA when formed on rich media at colder temperatures, while S. cerevisiae mtDNA was primarily retained on non-fermentable carbon source, at any temperature. Transcriptome data for hybrids harbouring different mtDNA showed a strong environmentally dependent allele preference, which was more important in respiratory conditions. Co-expression analysis for specific biological functions revealed a clear pattern of concerted allelic transcription within the same allele type, which supports the notion that the hybrid cell works preferentially with one set of parental alleles (or the other) for different cellular functions. Given that the type of mtDNA retained in hybrids affects both nuclear expression and fitness, it might play a role in driving hybrid genome evolution in terms of gene retention and loss.
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Affiliation(s)
- Sarah K Hewitt
- Manchester Institute of Biotechnology, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M1 7DN, UK
- Division of Evolution and Genomic Science, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PL, UK
| | - Kobchai Duangrattanalert
- Manchester Institute of Biotechnology, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M1 7DN, UK
- Division of Evolution and Genomic Science, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PL, UK
| | - Tim Burgis
- Division of Evolution and Genomic Science, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PL, UK
| | - Leo A H Zeef
- Division of Evolution and Genomic Science, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PL, UK
| | - Samina Naseeb
- Manchester Institute of Biotechnology, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M1 7DN, UK
- Division of Evolution and Genomic Science, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PL, UK
| | - Daniela Delneri
- Manchester Institute of Biotechnology, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M1 7DN, UK
- Division of Evolution and Genomic Science, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PL, UK
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11
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De Nijs Y, De Maeseneire SL, Soetaert WK. 5' untranslated regions: the next regulatory sequence in yeast synthetic biology. Biol Rev Camb Philos Soc 2019; 95:517-529. [PMID: 31863552 DOI: 10.1111/brv.12575] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 11/08/2019] [Accepted: 11/28/2019] [Indexed: 01/10/2023]
Abstract
When developing industrial biotechnology processes, Saccharomyces cerevisiae (baker's yeast or brewer's yeast) is a popular choice as a microbial host. Many tools have been developed in the fields of synthetic biology and metabolic engineering to introduce heterologous pathways and tune their expression in yeast. Such tools mainly focus on controlling transcription, whereas post-transcriptional regulation is often overlooked. Herein we discuss regulatory elements found in the 5' untranslated region (UTR) and their influence on protein synthesis. We provide not only an overall picture, but also a set of design rules on how to engineer a 5' UTR. The reader is also referred to currently available models that allow gene expression to be tuned predictably using different 5' UTRs.
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Affiliation(s)
- Yatti De Nijs
- Faculty of Bioscience Engineering, Centre for Industrial Biotechnology and Biocatalysis (InBio.be), Department Biotechnology, Ghent University, Coupure Links 653, 9000, Ghent, Belgium
| | - Sofie L De Maeseneire
- Faculty of Bioscience Engineering, Centre for Industrial Biotechnology and Biocatalysis (InBio.be), Department Biotechnology, Ghent University, Coupure Links 653, 9000, Ghent, Belgium
| | - Wim K Soetaert
- Faculty of Bioscience Engineering, Centre for Industrial Biotechnology and Biocatalysis (InBio.be), Department Biotechnology, Ghent University, Coupure Links 653, 9000, Ghent, Belgium
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12
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Parenteau J, Abou Elela S. Introns: Good Day Junk Is Bad Day Treasure. Trends Genet 2019; 35:923-934. [PMID: 31668856 DOI: 10.1016/j.tig.2019.09.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Revised: 08/28/2019] [Accepted: 09/19/2019] [Indexed: 02/01/2023]
Abstract
Introns are ubiquitous in eukaryotic transcripts. They are often viewed as junk RNA but the huge energetic burden of transcribing, removing, and degrading them suggests a significant evolutionary advantage. Ostensibly, an intron functions within the host pre-mRNA to regulate its splicing, transport, and degradation. However, recent studies have revealed an entirely new class of trans-acting functions where the presence of intronic RNA in the cell impacts the expression of other genes in trans. Here, we review possible new mechanisms of intron functions, with a focus on the role of yeast introns in regulating the cell growth response to starvation.
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Affiliation(s)
- Julie Parenteau
- Département de microbiologie et d'infectiologie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, QC J1E 4K8, Canada
| | - Sherif Abou Elela
- Département de microbiologie et d'infectiologie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, QC J1E 4K8, Canada.
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13
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Excised linear introns regulate growth in yeast. Nature 2019; 565:606-611. [PMID: 30651636 DOI: 10.1038/s41586-018-0828-1] [Citation(s) in RCA: 92] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Accepted: 11/27/2018] [Indexed: 12/31/2022]
Abstract
Spliceosomal introns are ubiquitous non-coding RNAs that are typically destined for rapid debranching and degradation. Here we describe 34 excised introns in Saccharomyces cerevisiae that-despite being rapidly degraded in log-phase growth-accumulate as linear RNAs under either saturated-growth conditions or other stresses that cause prolonged inhibition of TORC1, which is a key integrator of growth signalling. Introns that become stabilized remain associated with components of the spliceosome and differ from other spliceosomal introns in having a short distance between their lariat branch point and 3' splice site, which is necessary and sufficient for their stabilization. Deletion of these unusual introns is disadvantageous in saturated conditions and causes aberrantly high growth rates in yeast that are chronically challenged with the TORC1 inhibitor rapamycin. The reintroduction of native or engineered stable introns suppresses this aberrant rapamycin response. Thus, excised introns function within the TOR growth-signalling network of S. cerevisiae and, more generally, excised spliceosomal introns can have biological functions.
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14
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Stable Intronic Sequence RNAs (sisRNAs): An Expanding Universe. Trends Biochem Sci 2018; 44:258-272. [PMID: 30391089 DOI: 10.1016/j.tibs.2018.09.016] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Revised: 09/11/2018] [Accepted: 09/21/2018] [Indexed: 12/26/2022]
Abstract
Intronic sequences are often regarded as 'nonsense' transcripts that are rapidly degraded. We highlight here recent studies on intronic sequences that play regulatory roles as long noncoding RNAs (lncRNAs) which are classified as sisRNAs. Interestingly, sisRNAs come in different forms and are produced via a variety of ways. They regulate genes at the DNA, RNA, and protein levels, and frequently engage in autoregulatory feedback loops to ensure cellular homeostasis under normal and stress conditions. Future directions, evolutionary insights, and potential implications of dysregulated sisRNAs are also discussed, especially in relation to human pathogenesis.
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15
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Wong JT, Akhbar F, Ng AYE, Tay MLI, Loi GJE, Pek JW. DIP1 modulates stem cell homeostasis in Drosophila through regulation of sisR-1. Nat Commun 2017; 8:759. [PMID: 28970471 PMCID: PMC5624886 DOI: 10.1038/s41467-017-00684-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Accepted: 07/19/2017] [Indexed: 01/09/2023] Open
Abstract
Stable intronic sequence RNAs (sisRNAs) are by-products of splicing and regulate gene expression. How sisRNAs are regulated is unclear. Here we report that a double-stranded RNA binding protein, Disco-interacting protein 1 (DIP1) regulates sisRNAs in Drosophila. DIP1 negatively regulates the abundance of sisR-1 and INE-1 sisRNAs. Fine-tuning of sisR-1 by DIP1 is important to maintain female germline stem cell homeostasis by modulating germline stem cell differentiation and niche adhesion. Drosophila DIP1 localizes to a nuclear body (satellite body) and associates with the fourth chromosome, which contains a very high density of INE-1 transposable element sequences that are processed into sisRNAs. DIP1 presumably acts outside the satellite bodies to regulate sisR-1, which is not on the fourth chromosome. Thus, our study identifies DIP1 as a sisRNA regulatory protein that controls germline stem cell self-renewal in Drosophila. Stable intronic sequence RNAs (sisRNAs) are by-products of splicing from introns with roles in embryonic development in Drosophila. Here, the authors show that the RNA binding protein DIP1 regulates sisRNAs in Drosophila, which is necessary for germline stem cell homeostasis.
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Affiliation(s)
- Jing Ting Wong
- Ngee Ann Polytechnic, 535 Clementi Road, Singapore, 599489, Singapore
| | - Farzanah Akhbar
- Temasek Polytechnic, 21 Tampines Avenue 1, Singapore, 529757, Singapore
| | - Amanda Yunn Ee Ng
- Temasek Life Sciences Laboratory, 1 Research Link National University of Singapore, Singapore, 117604, Singapore
| | - Mandy Li-Ian Tay
- Temasek Life Sciences Laboratory, 1 Research Link National University of Singapore, Singapore, 117604, Singapore
| | - Gladys Jing En Loi
- National University of Singapore, 21 Lower Kent Ridge Road, Singapore, 119077, Singapore
| | - Jun Wei Pek
- Temasek Life Sciences Laboratory, 1 Research Link National University of Singapore, Singapore, 117604, Singapore.
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16
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Naseeb S, Ames RM, Delneri D, Lovell SC. Rapid functional and evolutionary changes follow gene duplication in yeast. Proc Biol Sci 2017; 284:20171393. [PMID: 28835561 PMCID: PMC5577496 DOI: 10.1098/rspb.2017.1393] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Accepted: 07/13/2017] [Indexed: 12/22/2022] Open
Abstract
Duplication of genes or genomes provides the raw material for evolutionary innovation. After duplication a gene may be lost, recombine with another gene, have its function modified or be retained in an unaltered state. The fate of duplication is usually studied by comparing extant genomes and reconstructing the most likely ancestral states. Valuable as this approach is, it may miss the most rapid evolutionary events. Here, we engineered strains of Saccharomyces cerevisiae carrying tandem and non-tandem duplications of the singleton gene IFA38 to monitor (i) the fate of the duplicates in different conditions, including time scale and asymmetry of gene loss, and (ii) the changes in fitness and transcriptome of the strains immediately after duplication and after experimental evolution. We found that the duplication brings widespread transcriptional changes, but a fitness advantage is only present in fermentable media. In respiratory conditions, the yeast strains consistently lose the non-tandem IFA38 gene copy in a surprisingly short time, within only a few generations. This gene loss appears to be asymmetric and dependent on genome location, since the original IFA38 copy and the tandem duplicate are retained. Overall, this work shows for the first time that gene loss can be extremely rapid and context dependent.
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Affiliation(s)
- Samina Naseeb
- School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Ryan M Ames
- School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Daniela Delneri
- School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Simon C Lovell
- School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Oxford Road, Manchester M13 9PT, UK
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17
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Parker S, Fraczek MG, Wu J, Shamsah S, Manousaki A, Dungrattanalert K, de Almeida RA, Estrada-Rivadeneyra D, Omara W, Delneri D, O'Keefe RT. A resource for functional profiling of noncoding RNA in the yeast Saccharomyces cerevisiae. RNA (NEW YORK, N.Y.) 2017; 23:1166-1171. [PMID: 28468764 PMCID: PMC5513061 DOI: 10.1261/rna.061564.117] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 05/01/2017] [Indexed: 06/07/2023]
Abstract
Eukaryotic genomes are extensively transcribed, generating many different RNAs with no known function. We have constructed 1502 molecular barcoded ncRNA gene deletion strains encompassing 443 ncRNAs in the yeast Saccharomyces cerevisiae as tools for ncRNA functional analysis. This resource includes deletions of small nuclear RNAs (snRNAs), transfer RNAs (tRNAs), small nucleolar RNAs (snoRNAs), and other annotated ncRNAs as well as the more recently identified stable unannotated transcripts (SUTs) and cryptic unstable transcripts (CUTs) whose functions are largely unknown. Specifically, deletions have been constructed for ncRNAs found in the intergenic regions, not overlapping genes or their promoters (i.e., at least 200 bp minimum distance from the closest gene start codon). The deletion strains carry molecular barcodes designed to be complementary with the protein gene deletion collection enabling parallel analysis experiments. These strains will be useful for the numerous genomic and molecular techniques that utilize deletion strains, including genome-wide phenotypic screens under different growth conditions, pooled chemogenomic screens with drugs or chemicals, synthetic genetic array analysis to uncover novel genetic interactions, and synthetic dosage lethality screens to analyze gene dosage. Overall, we created a valuable resource for the RNA community and for future ncRNA research.
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Affiliation(s)
| | | | - Jian Wu
- Division of Molecular and Cellular Function, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, United Kingdom
| | - Sara Shamsah
- Division of Molecular and Cellular Function, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, United Kingdom
| | | | | | - Rogerio Alves de Almeida
- Division of Molecular and Cellular Function, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, United Kingdom
| | - Diego Estrada-Rivadeneyra
- Division of Molecular and Cellular Function, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, United Kingdom
| | - Walid Omara
- Division of Molecular and Cellular Function, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, United Kingdom
- Department of Microbiology and Immunology, Faculty of Pharmacy, Minia University, Minya 11432, Egypt
| | | | - Raymond T O'Keefe
- Division of Molecular and Cellular Function, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, United Kingdom
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18
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Wallace EWJ, Beggs JD. Extremely fast and incredibly close: cotranscriptional splicing in budding yeast. RNA (NEW YORK, N.Y.) 2017; 23:601-610. [PMID: 28153948 PMCID: PMC5393171 DOI: 10.1261/rna.060830.117] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
RNA splicing, an essential part of eukaryotic pre-messenger RNA processing, can be simultaneous with transcription by RNA polymerase II. Here, we compare and review independent next-generation sequencing methods that jointly quantify transcription and splicing in budding yeast. For many yeast transcripts, splicing is fast, taking place within seconds of intron transcription, while polymerase is within a few dozens of nucleotides of the 3' splice site. Ribosomal protein transcripts are spliced particularly fast and cotranscriptionally. However, some transcripts are spliced inefficiently or mainly post-transcriptionally. Intron-mediated regulation of some genes is likely to be cotranscriptional. We suggest that intermediates of the splicing reaction, missing from current data sets, may hold key information about splicing kinetics.
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Affiliation(s)
- Edward W J Wallace
- School of Informatics, University of Edinburgh, EH8 9AB, United Kingdom
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, EH9 3BF, United Kingdom
| | - Jean D Beggs
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, EH9 3BF, United Kingdom
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Workflow for Genome-Wide Determination of Pre-mRNA Splicing Efficiency from Yeast RNA-seq Data. BIOMED RESEARCH INTERNATIONAL 2016; 2016:4783841. [PMID: 28050562 PMCID: PMC5168555 DOI: 10.1155/2016/4783841] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Accepted: 11/02/2016] [Indexed: 11/17/2022]
Abstract
Pre-mRNA splicing represents an important regulatory layer of eukaryotic gene expression. In the simple budding yeast Saccharomyces cerevisiae, about one-third of all mRNA molecules undergo splicing, and splicing efficiency is tightly regulated, for example, during meiotic differentiation. S. cerevisiae features a streamlined, evolutionarily highly conserved splicing machinery and serves as a favourite model for studies of various aspects of splicing. RNA-seq represents a robust, versatile, and affordable technique for transcriptome interrogation, which can also be used to study splicing efficiency. However, convenient bioinformatics tools for the analysis of splicing efficiency from yeast RNA-seq data are lacking. We present a complete workflow for the calculation of genome-wide splicing efficiency in S. cerevisiae using strand-specific RNA-seq data. Our pipeline takes sequencing reads in the FASTQ format and provides splicing efficiency values for the 5′ and 3′ splice junctions of each intron. The pipeline is based on up-to-date open-source software tools and requires very limited input from the user. We provide all relevant scripts in a ready-to-use form. We demonstrate the functionality of the workflow using RNA-seq datasets from three spliceosome mutants. The workflow should prove useful for studies of yeast splicing mutants or of regulated splicing, for example, under specific growth conditions.
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20
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Fasken MB, Corbett AH. Links between mRNA splicing, mRNA quality control, and intellectual disability. RNA & DISEASE 2016; 3:e1448. [PMID: 27868086 PMCID: PMC5113822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023] Open
Abstract
In recent years, the impairment of RNA binding proteins that play key roles in the post-transcriptional regulation of gene expression has been linked to numerous neurological diseases. These RNA binding proteins perform critical mRNA processing steps in the nucleus, including splicing, polyadenylation, and export. In many cases, these RNA binding proteins are ubiquitously expressed raising key questions about why only brain function is impaired. Recently, mutations in the ZC3H14 gene, encoding an evolutionarily conserved, polyadenosine RNA binding protein, have been linked to a nonsyndromic form of autosomal recessive intellectual disability. Thus far, research on ZC3H14 and its Nab2 orthologs in budding yeast and Drosophila reveals that ZC3H14/Nab2 is important for mRNA processing and neuronal patterning. Two recent studies now provide evidence that ZC3H14/Nab2 may function in the quality control of mRNA splicing and export and could help to explain the molecular defects that cause neuronal dysfunction and lead to an inherited form of intellectual disability. These studies on ZC3H14/Nab2 reveal new clues to the puzzle of why loss of the ubiquitously expressed ZC3H14 protein specifically affects neurons.
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Affiliation(s)
- Milo B Fasken
- Department of Biology, Emory University, 1510 Clifton Rd., NE RRC 1021, Atlanta, GA 30322, U.S.A
| | - Anita H Corbett
- Department of Biology, Emory University, 1510 Clifton Rd., NE RRC 1021, Atlanta, GA 30322, U.S.A
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The Evolutionarily-conserved Polyadenosine RNA Binding Protein, Nab2, Cooperates with Splicing Machinery to Regulate the Fate of pre-mRNA. Mol Cell Biol 2016; 36:2697-2714. [PMID: 27528618 PMCID: PMC5064217 DOI: 10.1128/mcb.00402-16] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Numerous RNA binding proteins are deposited onto an mRNA transcript to modulate post-transcriptional processing events ensuring proper mRNA maturation. Defining the interplay between RNA binding proteins that couple mRNA biogenesis events is crucial for understanding how gene expression is regulated. To explore how RNA binding proteins control mRNA processing, we investigated a role for the evolutionarily conserved polyadenosine RNA binding protein, Nab2, in mRNA maturation within the nucleus. This work reveals that nab2 mutant cells accumulate intron-containing pre-mRNA in vivo We extend this analysis to identify genetic interactions between mutant alleles of nab2 and genes encoding the splicing factor, MUD2, and the RNA exosome, RRP6, with in vivo consequences of altered pre-mRNA splicing and poly(A) tail length control. As further evidence linking Nab2 proteins to splicing, an unbiased proteomic analysis of vertebrate Nab2, ZC3H14, identifies physical interactions with numerous components of the spliceosome. We validated the interaction between ZC3H14 and U2AF2/U2AF65 Taking all the findings into consideration, we present a model where Nab2/ZC3H14 interacts with spliceosome components to allow proper coupling of splicing with subsequent mRNA processing steps contributing to a kinetic proofreading step that allows properly processed mRNA to exit the nucleus and escape Rrp6-dependent degradation.
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