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Black CS, Whelan TA, Garside EL, MacMillan AM, Fast NM, Rader SD. Spliceosome assembly and regulation: insights from analysis of highly reduced spliceosomes. RNA (NEW YORK, N.Y.) 2023; 29:531-550. [PMID: 36737103 PMCID: PMC10158995 DOI: 10.1261/rna.079273.122] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Accepted: 01/06/2023] [Indexed: 05/06/2023]
Abstract
Premessenger RNA splicing is catalyzed by the spliceosome, a multimegadalton RNA-protein complex that assembles in a highly regulated process on each intronic substrate. Most studies of splicing and spliceosomes have been carried out in human or S. cerevisiae model systems. There exists, however, a large diversity of spliceosomes, particularly in organisms with reduced genomes, that suggests a means of analyzing the essential elements of spliceosome assembly and regulation. In this review, we characterize changes in spliceosome composition across phyla, describing those that are most frequently observed and highlighting an analysis of the reduced spliceosome of the red alga Cyanidioschyzon merolae We used homology modeling to predict what effect splicing protein loss would have on the spliceosome, based on currently available cryo-EM structures. We observe strongly correlated loss of proteins that function in the same process, for example, in interacting with the U1 snRNP (which is absent in C. merolae), regulation of Brr2, or coupling transcription and splicing. Based on our observations, we predict splicing in C. merolae to be inefficient, inaccurate, and post-transcriptional, consistent with the apparent trend toward its elimination in this lineage. This work highlights the striking flexibility of the splicing pathway and the spliceosome when viewed in the context of eukaryotic diversity.
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Affiliation(s)
- Corbin S Black
- Department of Chemistry and Biochemistry, University of Northern British Columbia, Prince George, British Columbia, Canada V2N 4Z9
- Department of Anatomy and Cell Biology, McGill University, Montréal, Quebec, Canada H3A 0C7
| | - Thomas A Whelan
- Biodiversity Research Center and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
| | - Erin L Garside
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Andrew M MacMillan
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Naomi M Fast
- Biodiversity Research Center and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
| | - Stephen D Rader
- Department of Chemistry and Biochemistry, University of Northern British Columbia, Prince George, British Columbia, Canada V2N 4Z9
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Van Etten J, Cho CH, Yoon HS, Bhattacharya D. Extremophilic red algae as models for understanding adaptation to hostile environments and the evolution of eukaryotic life on the early earth. Semin Cell Dev Biol 2023; 134:4-13. [PMID: 35339358 DOI: 10.1016/j.semcdb.2022.03.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2021] [Revised: 02/20/2022] [Accepted: 03/04/2022] [Indexed: 01/08/2023]
Abstract
Extremophiles have always garnered great interest because of their exotic lifestyles and ability to thrive at the physical limits of life. In hot springs environments, the Cyanidiophyceae red algae are the only photosynthetic eukaryotes able to live under extremely low pH (0-5) and relatively high temperature (35ºC to 63ºC). These extremophiles live as biofilms in the springs, inhabit acid soils near the hot springs, and form endolithic populations in the surrounding rocks. Cyanidiophyceae represent a remarkable source of knowledge about the evolution of extremophilic lifestyles and their genomes encode specialized enzymes that have applied uses. Here we review the evolutionary origin, taxonomy, genome biology, industrial applications, and use of Cyanidiophyceae as genetic models. Currently, Cyanidiophyceae comprise a single order (Cyanidiales), three families, four genera, and nine species, including the well-known Cyanidioschyzon merolae and Galdieria sulphuraria. These algae have small, gene-rich genomes that are analogous to those of prokaryotes they live and compete with. There are few spliceosomal introns and evidence exists for horizontal gene transfer as a driver of local adaptation to gain access to external fixed carbon and to extrude toxic metals. Cyanidiophyceae offer a variety of commercial opportunities such as phytoremediation to detoxify contaminated soils or waters and exploitation of their mixotrophic lifestyles to support the efficient production of bioproducts such as phycocyanin and floridosides. In terms of exobiology, Cyanidiophyceae are an ideal model system for understanding the evolutionary effects of foreign gene acquisition and the interactions between different organisms inhabiting the same harsh environment on the early Earth. Finally, we describe ongoing research with C. merolae genetics and summarize the unique insights they offer to the understanding of algal biology and evolution.
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Affiliation(s)
- Julia Van Etten
- Graduate Program in Ecology and Evolution, Rutgers University, New Brunswick, NJ 08901, USA.
| | - Chung Hyun Cho
- Department of Biological Sciences, Sungkyunkwan University, Suwon 16419, South Korea.
| | - Hwan Su Yoon
- Department of Biological Sciences, Sungkyunkwan University, Suwon 16419, South Korea.
| | - Debashish Bhattacharya
- Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ 08901, USA.
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Wong DK, Grisdale CJ, Slat VA, Rader SD, Fast NM. The evolution of pre-mRNA splicing and its machinery revealed by reduced extremophilic red algae. J Eukaryot Microbiol 2023; 70:e12927. [PMID: 35662328 DOI: 10.1111/jeu.12927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The Cyanidiales are a group of mostly thermophilic and acidophilic red algae that thrive near volcanic vents. Despite their phylogenetic relationship, the reduced genomes of Cyanidioschyzon merolae and Galdieria sulphuraria are strikingly different with respect to pre-mRNA splicing, a ubiquitous eukaryotic feature. Introns are rare and spliceosomal machinery is extremely reduced in C. merolae, in contrast to G. sulphuraria. Previous studies also revealed divergent spliceosomes in the mesophilic red alga Porphyridium purpureum and the red algal derived plastid of Guillardia theta (Cryptophyta), along with unusually high levels of unspliced transcripts. To further examine the evolution of splicing in red algae, we compared C. merolae and G. sulphuraria, investigating splicing levels, intron position, intron sequence features, and the composition of the spliceosome. In addition to identifying 11 additional introns in C. merolae, our transcriptomic analysis also revealed typical eukaryotic splicing in G. sulphuraria, whereas most transcripts in C. merolae remain unspliced. The distribution of intron positions within their host genes was examined to provide insight into patterns of intron loss in red algae. We observed increasing variability of 5' splice sites and branch donor regions with increasing intron richness. We also found these relationships to be connected to reductions in and losses of corresponding parts of the spliceosome. Our findings highlight patterns of intron and spliceosome evolution in related red algae under the pressures of genome reduction.
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Affiliation(s)
- Donald K Wong
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, BC, Canada
| | - Cameron J Grisdale
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, BC, Canada.,Michael Smith Genome Sciences Centre, Vancouver, BC, Canada
| | - Viktor A Slat
- Department of Chemistry, University of Northern British Columbia, Prince George, BC, Canada
| | - Stephen D Rader
- Department of Chemistry, University of Northern British Columbia, Prince George, BC, Canada
| | - Naomi M Fast
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, BC, Canada
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Schärfen L, Zigackova D, Reimer KA, Stark MR, Slat VA, Francoeur NJ, Wells ML, Zhou L, Blackshear PJ, Neugebauer KM, Rader SD. Identification of Alternative Polyadenylation in Cyanidioschyzon merolae Through Long-Read Sequencing of mRNA. Front Genet 2022; 12:818697. [PMID: 35154260 PMCID: PMC8831791 DOI: 10.3389/fgene.2021.818697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Accepted: 12/22/2021] [Indexed: 12/04/2022] Open
Abstract
Alternative polyadenylation (APA) is widespread among metazoans and has been shown to have important impacts on mRNA stability and protein expression. Beyond a handful of well-studied organisms, however, its existence and consequences have not been well investigated. We therefore turned to the deep-branching red alga, Cyanidioschyzon merolae, to study the biology of polyadenylation in an organism highly diverged from humans and yeast. C. merolae is an acidothermophilic alga that lives in volcanic hot springs. It has a highly reduced genome (16.5 Mbp) and has lost all but 27 of its introns and much of its splicing machinery, suggesting that it has been under substantial pressure to simplify its RNA processing pathways. We used long-read sequencing to assess the key features of C. merolae mRNAs, including splicing status and polyadenylation cleavage site (PAS) usage. Splicing appears to be less efficient in C. merolae compared with yeast, flies, and mammalian cells. A high proportion of transcripts (63%) have at least two distinct PAS’s, and 34% appear to utilize three or more sites. The apparent polyadenylation signal UAAA is used in more than 90% of cases, in cells grown in both rich media or limiting nitrogen. Our documentation of APA for the first time in this non-model organism highlights its conservation and likely biological importance of this regulatory step in gene expression.
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Affiliation(s)
- Leonard Schärfen
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
| | - Dagmar Zigackova
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
| | - Kirsten A. Reimer
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
| | - Martha R. Stark
- Department of Chemistry, University of Northern British Columbia, Prince George, BC, Canada
| | - Viktor A. Slat
- Department of Chemistry, University of Northern British Columbia, Prince George, BC, Canada
| | - Nancy J. Francoeur
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Melissa L. Wells
- The Signal Transduction Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, Durham, NC, United States
| | - Lecong Zhou
- Integrative Bioinformatics Support Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, Durham, NC, United States
| | - Perry J. Blackshear
- The Signal Transduction Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, Durham, NC, United States
| | - Karla M. Neugebauer
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
- *Correspondence: Stephen D. Rader, ; Karla M. Neugebauer,
| | - Stephen D. Rader
- Department of Chemistry, University of Northern British Columbia, Prince George, BC, Canada
- *Correspondence: Stephen D. Rader, ; Karla M. Neugebauer,
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