1
|
Perchlik M, Sasse A, Mostafavi S, Fields S, Cuperus JT. Impact on splicing in Saccharomyces cerevisiae of random 50-base sequences inserted into an intron. RNA (NEW YORK, N.Y.) 2023; 30:52-67. [PMID: 37879864 PMCID: PMC10726166 DOI: 10.1261/rna.079752.123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Accepted: 10/18/2023] [Indexed: 10/27/2023]
Abstract
Intron splicing is a key regulatory step in gene expression in eukaryotes. Three sequence elements required for splicing-5' and 3' splice sites and a branchpoint-are especially well-characterized in Saccharomyces cerevisiae, but our understanding of additional intron features that impact splicing in this organism is incomplete, due largely to its small number of introns. To overcome this limitation, we constructed a library in S. cerevisiae of random 50-nt (N50) elements individually inserted into the intron of a reporter gene and quantified canonical splicing and the use of cryptic splice sites by sequencing analysis. More than 70% of approximately 140,000 N50 elements reduced splicing by at least 20%. N50 features, including higher GC content, presence of GU repeats, and stronger predicted secondary structure of its pre-mRNA, correlated with reduced splicing efficiency. A likely basis for the reduced splicing of such a large proportion of variants is the formation of RNA structures that pair N50 bases-such as the GU repeats-with other bases specifically within the reporter pre-mRNA analyzed. However, multiple models were unable to explain more than a small fraction of the variance in splicing efficiency across the library, suggesting that complex nonlinear interactions in RNA structures are not accurately captured by RNA structure prediction methods. Our results imply that the specific context of a pre-mRNA may determine the bases allowable in an intron to prevent secondary structures that reduce splicing. This large data set can serve as a resource for further exploration of splicing mechanisms.
Collapse
Affiliation(s)
- Molly Perchlik
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195, USA
| | - Alexander Sasse
- Paul G. Allen School of Computer Science and Engineering, University of Washington, Seattle, Washington 98195, USA
| | - Sara Mostafavi
- Paul G. Allen School of Computer Science and Engineering, University of Washington, Seattle, Washington 98195, USA
| | - Stanley Fields
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195, USA
- Department of Medicine, University of Washington, Seattle, Washington 98195, USA
| | - Josh T Cuperus
- Department of Genome Sciences, University of Washington, Seattle, Washington 98195, USA
| |
Collapse
|
2
|
Pan B, Ye F, Li T, Wei F, Warren A, Wang Y, Gao S. Potential role of N 6-adenine DNA methylation in alternative splicing and endosymbiosis in Paramecium bursaria. iScience 2023; 26:106676. [PMID: 37182097 PMCID: PMC10173741 DOI: 10.1016/j.isci.2023.106676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2022] [Revised: 12/02/2022] [Accepted: 04/11/2023] [Indexed: 05/16/2023] Open
Abstract
N6-adenine DNA methylation (6mA), a rediscovered epigenetic mark in eukaryotic organisms, diversifies in abundance, distribution, and function across species, necessitating its study in more taxa. Paramecium bursaria is a typical model organism with endosymbiotic algae of the species Chlorella variabilis. This consortium therefore serves as a valuable system to investigate the functional role of 6mA in endosymbiosis, as well as the evolutionary importance of 6mA among eukaryotes. In this study, we report the first genome-wide, base pair-resolution map of 6mA in P. bursaria and identify its methyltransferase PbAMT1. Functionally, 6mA exhibits a bimodal distribution at the 5' end of RNA polymerase II-transcribed genes and possibly participates in transcription by facilitating alternative splicing. Evolutionarily, 6mA co-evolves with gene age and likely serves as a reverse mark of endosymbiosis-related genes. Our results offer new insights for the functional diversification of 6mA in eukaryotes as an important epigenetic mark.
Collapse
Affiliation(s)
- Bo Pan
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China
- Laboratory for Marine Biology and Biotechnology, Laoshan Laboratory, Qingdao 266237, China
- MOE Key Laboratory of Marine Genetics and Breeding, College of Marine Life Science, Ocean University of China, Qingdao 266003, China
| | - Fei Ye
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China
- Laboratory for Marine Biology and Biotechnology, Laoshan Laboratory, Qingdao 266237, China
| | - Tao Li
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China
- Laboratory for Marine Biology and Biotechnology, Laoshan Laboratory, Qingdao 266237, China
| | - Fan Wei
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China
- Laboratory for Marine Biology and Biotechnology, Laoshan Laboratory, Qingdao 266237, China
| | - Alan Warren
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
| | - Yuanyuan Wang
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China
- Laboratory for Marine Biology and Biotechnology, Laoshan Laboratory, Qingdao 266237, China
- Corresponding author
| | - Shan Gao
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China
- Laboratory for Marine Biology and Biotechnology, Laoshan Laboratory, Qingdao 266237, China
- MOE Key Laboratory of Marine Genetics and Breeding, College of Marine Life Science, Ocean University of China, Qingdao 266003, China
| |
Collapse
|
3
|
Singh A, Maurer‐Alcalá XX, Solberg T, Häußermann L, Gisler S, Ignarski M, Swart EC, Nowacki M. Chromatin remodeling is required for sRNA-guided DNA elimination in Paramecium. EMBO J 2022; 41:e111839. [PMID: 36221862 PMCID: PMC9670198 DOI: 10.15252/embj.2022111839] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 09/14/2022] [Accepted: 09/19/2022] [Indexed: 01/13/2023] Open
Abstract
Small RNAs mediate the silencing of transposable elements and other genomic loci, increasing nucleosome density and preventing undesirable gene expression. The unicellular ciliate Paramecium is a model to study dynamic genome organization in eukaryotic cells, given its unique feature of nuclear dimorphism. Here, the formation of the somatic macronucleus during sexual reproduction requires eliminating thousands of transposon remnants (IESs) and transposable elements scattered throughout the germline micronuclear genome. The elimination process is guided by Piwi-associated small RNAs and leads to precise cleavage at IES boundaries. Here we show that IES recognition and precise excision are facilitated by recruiting ISWI1, a Paramecium homolog of the chromatin remodeler ISWI. ISWI1 knockdown substantially inhibits DNA elimination, quantitatively similar to development-specific sRNA gene knockdowns but with much greater aberrant IES excision at alternative boundaries. We also identify key development-specific sRNA biogenesis and transport proteins, Ptiwi01 and Ptiwi09, as ISWI1 cofactors in our co-immunoprecipitation studies. Nucleosome profiling indicates that increased nucleosome density correlates with the requirement for ISWI1 and other proteins necessary for IES excision. We propose that chromatin remodeling together with small RNAs is essential for efficient and precise DNA elimination in Paramecium.
Collapse
Affiliation(s)
- Aditi Singh
- Institute of Cell BiologyUniversity of BernBernSwitzerland,Graduate School for Cellular and Biomedical SciencesUniversity of BernBernSwitzerland,Max Planck Institute for BiologyTubingenGermany
| | | | - Therese Solberg
- Institute of Cell BiologyUniversity of BernBernSwitzerland,Graduate School for Cellular and Biomedical SciencesUniversity of BernBernSwitzerland
| | | | - Silvan Gisler
- Institute of Cell BiologyUniversity of BernBernSwitzerland
| | | | - Estienne C Swart
- Institute of Cell BiologyUniversity of BernBernSwitzerland,Max Planck Institute for BiologyTubingenGermany
| | | |
Collapse
|
4
|
Broad domains of histone marks in the highly compact Paramecium macronuclear genome. Genome Res 2022; 32:710-725. [PMID: 35264449 PMCID: PMC8997361 DOI: 10.1101/gr.276126.121] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Accepted: 03/04/2022] [Indexed: 11/25/2022]
Abstract
The unicellular ciliate Paramecium contains a large vegetative macronucleus with several unusual characteristics, including an extremely high coding density and high polyploidy. As macronculear chromatin is devoid of heterochromatin, our study characterizes the functional epigenomic organization necessary for gene regulation and proper Pol II activity. Histone marks (H3K4me3, H3K9ac, H3K27me3) reveal no narrow peaks but broad domains along gene bodies, whereas intergenic regions are devoid of nucleosomes. Our data implicate H3K4me3 levels inside ORFs to be the main factor associated with gene expression, and H3K27me3 appears in association with H3K4me3 in plastic genes. Silent and lowly expressed genes show low nucleosome occupancy, suggesting that gene inactivation does not involve increased nucleosome occupancy and chromatin condensation. Because of a high occupancy of Pol II along highly expressed ORFs, transcriptional elongation appears to be quite different from that of other species. This is supported by missing heptameric repeats in the C-terminal domain of Pol II and a divergent elongation system. Our data imply that unoccupied DNA is the default state, whereas gene activation requires nucleosome recruitment together with broad domains of H3K4me3. In summary, gene activation and silencing in Paramecium run counter to the current understanding of chromatin biology.
Collapse
|