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Bétermier M, Klobutcher LA, Orias E. Programmed chromosome fragmentation in ciliated protozoa: multiple means to chromosome ends. Microbiol Mol Biol Rev 2023; 87:e0018422. [PMID: 38009915 PMCID: PMC10732028 DOI: 10.1128/mmbr.00184-22] [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] [Indexed: 11/29/2023] Open
Abstract
SUMMARYCiliated protozoa undergo large-scale developmental rearrangement of their somatic genomes when forming a new transcriptionally active macronucleus during conjugation. This process includes the fragmentation of chromosomes derived from the germline, coupled with the efficient healing of the broken ends by de novo telomere addition. Here, we review what is known of developmental chromosome fragmentation in ciliates that have been well-studied at the molecular level (Tetrahymena, Paramecium, Euplotes, Stylonychia, and Oxytricha). These organisms differ substantially in the fidelity and precision of their fragmentation systems, as well as in the presence or absence of well-defined sequence elements that direct excision, suggesting that chromosome fragmentation systems have evolved multiple times and/or have been significantly altered during ciliate evolution. We propose a two-stage model for the evolution of the current ciliate systems, with both stages involving repetitive or transposable elements in the genome. The ancestral form of chromosome fragmentation is proposed to have been derived from the ciliate small RNA/chromatin modification process that removes transposons and other repetitive elements from the macronuclear genome during development. The evolution of this ancestral system is suggested to have potentiated its replacement in some ciliate lineages by subsequent fragmentation systems derived from mobile genetic elements.
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Affiliation(s)
- Mireille Bétermier
- Department of Genome Biology, Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell, Gif-sur-Yvette, France
| | - Lawrence A. Klobutcher
- Department of Molecular Biology and Biophysics, UCONN Health (University of Connecticut), Farmington, Connecticut, USA
| | - Eduardo Orias
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, California, USA
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Han X, Yan G, Ma Y, Miao W, Wang G. Sequencing and characterization of the macronuclear rDNA minichromosome of the protozoan Tetrahymena pyriformis. Int J Biol Macromol 2020; 147:576-581. [PMID: 31931068 DOI: 10.1016/j.ijbiomac.2020.01.063] [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: 10/12/2019] [Revised: 12/06/2019] [Accepted: 01/06/2020] [Indexed: 10/25/2022]
Abstract
Tetrahymena ribosomal DNA (rDNA) is an ideal system for studying eukaryotic DNA replication and gene transcription. In this study, we developed a new method to isolate rDNA from Tetrahymena cells and used it to sequence and annotate the complete 19,670 bp macronuclear rDNA minichromosome of Tetrahymena pyriformis, a species that lacks the germ-line micronucleus and is unable to undergo sexual reproduction. The key features of T. pyriformis and Tetrahymena thermophila rDNA sequences were then compared. Our results showed (i) the short inverted repeats (M repeats) essential for formation of rDNA minichromosome palindromic structure during sexual reproduction in Tetrahymena are highly conserved in T. pyriformis; (ii) in contrast to T. thermophila, which has two tandem domains that coordinately regulate rDNA replication, T. pyriformis has only a single domain; (iii) the 35S pre-rRNA precursor has 80.25% similarity between the two species; and (iv) the G + C content is higher in the transcribed region than the non-transcribed region in both species, but the GC-skew is more stable in T. pyriformis. The new isolation method and annotated information for the T. pyriformis rDNA minichromosome will provide a useful resource for studying DNA replication and chromosome copy number control in Tetrahymena.
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Affiliation(s)
- Xiaojie Han
- College of Fisheries and Life Science, Dalian Ocean University, Dalian 116023, China; Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Guanxiong Yan
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yang Ma
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Wei Miao
- College of Fisheries and Life Science, Dalian Ocean University, Dalian 116023, China; Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China; State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; CAS Center for Excellence in Animal Evolution and Genetics, Kunming 650223, China
| | - Guangying Wang
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
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3
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Pontremoli C, Forni D, Cagliani R, Pozzoli U, Clerici M, Sironi M. Evolutionary rates of mammalian telomere-stability genes correlate with karyotype features and female germline expression. Nucleic Acids Res 2018; 46:7153-7168. [PMID: 29893967 PMCID: PMC6101625 DOI: 10.1093/nar/gky494] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Revised: 05/17/2018] [Accepted: 05/22/2018] [Indexed: 12/26/2022] Open
Abstract
Telomeres protect the ends of eukaryotic chromosomes and are essential for cell viability. In mammals, telomere dynamics vary with life history traits (e.g. body mass and longevity), suggesting differential selection depending on physiological characteristics. Telomeres, in analogy to centromeric regions, also represent candidate meiotic drivers and subtelomeric DNA evolves rapidly. We analyzed the evolutionary history of mammalian genes implicated in telomere homeostasis (TEL genes). We detected widespread positive selection and we tested two alternative hypotheses: (i) fast evolution is driven by changes in life history traits; (ii) a conflict with selfish DNA elements at the female meiosis represents the underlying selective pressure. By accounting for the phylogenetic relationships among mammalian species, we show that life history traits do not contribute to shape diversity of TEL genes. Conversely, the evolutionary rate of TEL genes correlates with expression levels during meiosis and episodes of positive selection across mammalian species are associated with karyotype features (number of chromosome arms). We thus propose a telomere drive hypothesis, whereby (sub)telomeres and telomere-binding proteins are engaged in an intra-genomic conflict similar to the one described for centromeres.
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Affiliation(s)
- Chiara Pontremoli
- Bioinformatics, Scientific Institute IRCCS E. MEDEA, 23842 Bosisio Parini, Italy
| | - Diego Forni
- Bioinformatics, Scientific Institute IRCCS E. MEDEA, 23842 Bosisio Parini, Italy
| | - Rachele Cagliani
- Bioinformatics, Scientific Institute IRCCS E. MEDEA, 23842 Bosisio Parini, Italy
| | - Uberto Pozzoli
- Bioinformatics, Scientific Institute IRCCS E. MEDEA, 23842 Bosisio Parini, Italy
| | - Mario Clerici
- Department of Physiopathology and Transplantation, University of Milan, 20090 Milan, Italy
- Don C. Gnocchi Foundation ONLUS, IRCCS, 20148 Milan, Italy
| | - Manuela Sironi
- Bioinformatics, Scientific Institute IRCCS E. MEDEA, 23842 Bosisio Parini, Italy
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4
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Feng L, Wang G, Hamilton EP, Xiong J, Yan G, Chen K, Chen X, Dui W, Plemens A, Khadr L, Dhanekula A, Juma M, Dang HQ, Kapler GM, Orias E, Miao W, Liu Y. A germline-limited piggyBac transposase gene is required for precise excision in Tetrahymena genome rearrangement. Nucleic Acids Res 2017; 45:9481-9502. [PMID: 28934495 PMCID: PMC5766162 DOI: 10.1093/nar/gkx652] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Accepted: 07/15/2017] [Indexed: 12/20/2022] Open
Abstract
Developmentally programmed genome rearrangement accompanies differentiation of the silent germline micronucleus into the transcriptionally active somatic macronucleus in the ciliated protozoan Tetrahymena thermophila. Internal eliminated sequences (IES) are excised, followed by rejoining of MAC-destined sequences, while fragmentation occurs at conserved chromosome breakage sequences, generating macronuclear chromosomes. Some macronuclear chromosomes, referred to as non-maintained chromosomes (NMC), are lost soon after differentiation. Large NMC contain genes implicated in development-specific roles. One such gene encodes the domesticated piggyBac transposase TPB6, required for heterochromatin-dependent precise excision of IES residing within exons of functionally important genes. These conserved exonic IES determine alternative transcription products in the developing macronucleus; some even contain free-standing genes. Examples of precise loss of some exonic IES in the micronucleus and retention of others in the macronucleus of related species suggest an evolutionary analogy to introns. Our results reveal that germline-limited sequences can encode genes with specific expression patterns and development-related functions, which may be a recurring theme in eukaryotic organisms experiencing programmed genome rearrangement during germline to soma differentiation.
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Affiliation(s)
- Lifang Feng
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA.,Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.,School of Food Science and Biotechnology, Zhejiang Gongshang University, Hangzhou 310018, China
| | - Guangying Wang
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Eileen P Hamilton
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106, USA
| | - Jie Xiong
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Guanxiong Yan
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Kai Chen
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Xiao Chen
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Wen Dui
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Amber Plemens
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Lara Khadr
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Arjune Dhanekula
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Mina Juma
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Hung Quang Dang
- Department of Molecular and Cellular Medicine, Texas A&M University Health Science Center, College Station, TX 77843, USA
| | - Geoffrey M Kapler
- Department of Molecular and Cellular Medicine, Texas A&M University Health Science Center, College Station, TX 77843, USA
| | - Eduardo Orias
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106, USA
| | - Wei Miao
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Yifan Liu
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
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5
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Tetrahymena as a Unicellular Model Eukaryote: Genetic and Genomic Tools. Genetics 2017; 203:649-65. [PMID: 27270699 DOI: 10.1534/genetics.114.169748] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Accepted: 04/08/2016] [Indexed: 12/12/2022] Open
Abstract
Tetrahymena thermophila is a ciliate model organism whose study has led to important discoveries and insights into both conserved and divergent biological processes. In this review, we describe the tools for the use of Tetrahymena as a model eukaryote, including an overview of its life cycle, orientation to its evolutionary roots, and methodological approaches to forward and reverse genetics. Recent genomic tools have expanded Tetrahymena's utility as a genetic model system. With the unique advantages that Tetrahymena provide, we argue that it will continue to be a model organism of choice.
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6
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Hamilton EP, Kapusta A, Huvos PE, Bidwell SL, Zafar N, Tang H, Hadjithomas M, Krishnakumar V, Badger JH, Caler EV, Russ C, Zeng Q, Fan L, Levin JZ, Shea T, Young SK, Hegarty R, Daza R, Gujja S, Wortman JR, Birren BW, Nusbaum C, Thomas J, Carey CM, Pritham EJ, Feschotte C, Noto T, Mochizuki K, Papazyan R, Taverna SD, Dear PH, Cassidy-Hanley DM, Xiong J, Miao W, Orias E, Coyne RS. Structure of the germline genome of Tetrahymena thermophila and relationship to the massively rearranged somatic genome. eLife 2016; 5. [PMID: 27892853 PMCID: PMC5182062 DOI: 10.7554/elife.19090] [Citation(s) in RCA: 109] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 11/14/2016] [Indexed: 12/30/2022] Open
Abstract
The germline genome of the binucleated ciliate Tetrahymena thermophila undergoes programmed chromosome breakage and massive DNA elimination to generate the somatic genome. Here, we present a complete sequence assembly of the germline genome and analyze multiple features of its structure and its relationship to the somatic genome, shedding light on the mechanisms of genome rearrangement as well as the evolutionary history of this remarkable germline/soma differentiation. Our results strengthen the notion that a complex, dynamic, and ongoing interplay between mobile DNA elements and the host genome have shaped Tetrahymena chromosome structure, locally and globally. Non-standard outcomes of rearrangement events, including the generation of short-lived somatic chromosomes and excision of DNA interrupting protein-coding regions, may represent novel forms of developmental gene regulation. We also compare Tetrahymena's germline/soma differentiation to that of other characterized ciliates, illustrating the wide diversity of adaptations that have occurred within this phylum.
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Affiliation(s)
- Eileen P Hamilton
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, United States
| | - Aurélie Kapusta
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, United States
| | - Piroska E Huvos
- Biochemistry and Molecular Biology, Southern Illinois University, Carbondale, United States
| | | | - Nikhat Zafar
- J. Craig Venter Institute, Rockville, United States
| | - Haibao Tang
- J. Craig Venter Institute, Rockville, United States
| | | | | | | | | | - Carsten Russ
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Qiandong Zeng
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Lin Fan
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Joshua Z Levin
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Terrance Shea
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Sarah K Young
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Ryan Hegarty
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Riza Daza
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Sharvari Gujja
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Jennifer R Wortman
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Bruce W Birren
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Chad Nusbaum
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Jainy Thomas
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, United States
| | - Clayton M Carey
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, United States
| | - Ellen J Pritham
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, United States
| | - Cédric Feschotte
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, United States
| | - Tomoko Noto
- Institute of Molecular Biotechnology, Vienna, Austria
| | | | - Romeo Papazyan
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, United States
| | - Sean D Taverna
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, United States
| | - Paul H Dear
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | | | - Jie Xiong
- Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
| | - Wei Miao
- Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
| | - Eduardo Orias
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, United States
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7
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Lin CYG, Lin IT, Yao MC. Programmed Minichromosome Elimination as a Mechanism for Somatic Genome Reduction in Tetrahymena thermophila. PLoS Genet 2016; 12:e1006403. [PMID: 27806059 PMCID: PMC5091840 DOI: 10.1371/journal.pgen.1006403] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 10/04/2016] [Indexed: 01/12/2023] Open
Abstract
The maintenance of chromosome integrity is crucial for genetic stability. However, programmed chromosome fragmentations are known to occur in many organisms, and in the ciliate Tetrahymena the five germline chromosomes are fragmented into hundreds of minichromosomes during somatic nuclear differentiation. Here, we showed that there are different fates of these minichromosomes after chromosome breakage. Among the 326 somatic minichromosomes identified using genomic data, 50 are selectively eliminated from the mature somatic genome. Interestingly, many and probably most of these minichromosomes are eliminated during the growth period between 6 and 20 doublings right after conjugation. Genes with potential conjugation-specific functions are found in these minichromosomes. This study revealed a new mode of programmed DNA elimination in ciliates similar to those observed in parasitic nematodes, which could play a role in developmental gene regulation.
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Affiliation(s)
- Chih-Yi Gabriela Lin
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
- Genome and Systems Biology Degree Program, National Taiwan University, Taipei, Taiwan
| | - I-Ting Lin
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Meng-Chao Yao
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
- Genome and Systems Biology Degree Program, National Taiwan University, Taipei, Taiwan
- * E-mail:
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Abstract
Ciliates are champions in programmed genome rearrangements. They carry out extensive restructuring during differentiation to drastically alter the complexity, relative copy number, and arrangement of sequences in the somatic genome. This chapter focuses on the model ciliate Tetrahymena, perhaps the simplest and best-understood ciliate studied. It summarizes past studies on various genome rearrangement processes and describes in detail the remarkable progress made in the past decade on the understanding of DNA deletion and other processes. The process occurs at thousands of specific sites to remove defined DNA segments that comprise roughly one-third of the genome including all transposons. Interestingly, this DNA rearranging process is a special form of RNA interference. It involves the production of double-stranded RNA and small RNA that guides the formation of heterochromatin. A domesticated piggyBac transposase is believed to cut off the marked chromatin, and the retained sequences are joined together through nonhomologous end-joining processes. Many of the proteins and DNA players involved have been analyzed and are described. This link provides possible explanations for the evolution, mechanism, and functional roles of the process. The article also discusses the interactions between parental and progeny somatic nuclei that affect the selection of sequences for deletion, and how the specific deletion boundaries are determined after heterochromatin marking.
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Elde NC, Roach KC, Yao MC, Malik HS. Absence of positive selection on centromeric histones in Tetrahymena suggests unsuppressed centromere: drive in lineages lacking male meiosis. J Mol Evol 2011; 72:510-20. [PMID: 21643829 PMCID: PMC3144370 DOI: 10.1007/s00239-011-9449-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2011] [Accepted: 05/19/2011] [Indexed: 12/20/2022]
Abstract
Centromere-drive is a process where centromeres compete for transmission through asymmetric "female" meiosis for inclusion into the oocyte. In symmetric "male" meiosis, all meiotic products form viable germ cells. Therefore, the primary incentive for centromere-drive, a potential transmission bias, is believed to be missing from male meiosis. In this article, we consider whether male meiosis also bears the primary cost of centromere-drive. Because different taxa carry out different combinations of meiotic programs (symmetric + asymmetric, symmetric only, asymmetric only), it is possible to consider the evolutionary consequences of centromere-drive in the context of these differing systems. Groups with both types of meiosis have large, rapidly evolving centromeric regions, and their centromeric histones (CenH3s) have been shown to evolve under positive selection, suggesting roles as suppressors of centromere-drive. In contrast, taxa with only symmetric male meiosis have shown no evidence of positive selection in their centromeric histones. In this article, we present the first evolutionary analysis of centromeric histones in ciliated protozoans, a group that only undergoes asymmetric "female" meiosis. We find no evidence of positive selection acting on CNA1, the CenH3 of Tetrahymena species. Cytological observations of a panel of Tetrahymena species are consistent with dynamic karyotype evolution in this lineage. Our findings suggest that defects in male meiosis, and not mitosis or female meiosis, are the primary selective force behind centromere-drive suppression. Our study raises the possibility that taxa like ciliates, with only female meiosis, may therefore undergo unsuppressed centromere drive.
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Affiliation(s)
- Nels C. Elde
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N. A2-205, Seattle, WA 98109 USA
- Present Address: Department of Human Genetics, University of Utah, Salt Lake City, UT 84112 USA
| | - Kevin C. Roach
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N. A2-205, Seattle, WA 98109 USA
- Department of Genome Sciences, University of Washington, Seattle, WA 98195 USA
| | - Meng-Chao Yao
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 11529
| | - Harmit S. Malik
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N. A2-205, Seattle, WA 98109 USA
- HHMI, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N. A2-205, Seattle, WA 98109 USA
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Microarray analyses of gene expression during the Tetrahymena thermophila life cycle. PLoS One 2009; 4:e4429. [PMID: 19204800 PMCID: PMC2636879 DOI: 10.1371/journal.pone.0004429] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2008] [Accepted: 12/18/2008] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The model eukaryote, Tetrahymena thermophila, is the first ciliated protozoan whose genome has been sequenced, enabling genome-wide analysis of gene expression. METHODOLOGY/PRINCIPAL FINDINGS A genome-wide microarray platform containing the predicted coding sequences (putative genes) for T. thermophila is described, validated and used to study gene expression during the three major stages of the organism's life cycle: growth, starvation and conjugation. CONCLUSIONS/SIGNIFICANCE Of the approximately 27,000 predicted open reading frames, transcripts homologous to only approximately 5900 are not detectable in any of these life cycle stages, indicating that this single-celled organism does indeed contain a large number of functional genes. Transcripts from over 5000 predicted genes are expressed at levels >5x corrected background and 95 genes are expressed at >250x corrected background in all stages. Transcripts homologous to 91 predicted genes are specifically expressed and 155 more are highly up-regulated in growing cells, while 90 are specifically expressed and 616 are up-regulated during starvation. Strikingly, transcripts homologous to 1068 predicted genes are specifically expressed and 1753 are significantly up-regulated during conjugation. The patterns of gene expression during conjugation correlate well with the developmental stages of meiosis, nuclear differentiation and DNA elimination. The relationship between gene expression and chromosome fragmentation is analyzed. Genes encoding proteins known to interact or to function in complexes show similar expression patterns, indicating that co-ordinate expression with putative genes of known function can identify genes with related functions. New candidate genes associated with the RNAi-like process of DNA elimination and with meiosis are identified and the late stages of conjugation are shown to be characterized by specific expression of an unexpectedly large and diverse number of genes not involved in nuclear functions.
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11
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Hamilton EP, Williamson S, Dunn S, Merriam V, Lin C, Vong L, Russell-Colantonio J, Orias E. The highly conserved family of Tetrahymena thermophila chromosome breakage elements contains an invariant 10-base-pair core. EUKARYOTIC CELL 2006; 5:771-80. [PMID: 16607024 PMCID: PMC1459666 DOI: 10.1128/ec.5.4.771-780.2006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
As a typical ciliate, Tetrahymena thermophila is a unicellular eukaryote that exhibits nuclear dimorphism: each cell contains a diploid, germ line micronucleus (MICN) and a polyploid, somatic macronucleus (MACN). During conjugation, when a new MACN differentiates from a mitotic descendant of the diploid fertilization nucleus, the five MICN chromosomes are site-specifically fragmented into 250 to 300 MACN chromosomes. The classic chromosome breakage sequence (CBS) is a 15-bp element (TAAACCAACCTCTTT) reported to be necessary and sufficient for chromosome breakage. To determine whether a CBS is present at every site of chromosome fragmentation and to assess the range of sequence variation tolerated, 31 CBSs were isolated without preconception as to the sequence of the chromosome breakage element. Additional CBS-related sequences were identified in the whole-genome sequence by their similarities to the classic CBS. Forty CBS elements behaved as authentic chromosome breakage sites. The CBS nucleotide sequence is more diverse than previously thought: nearly half of the CBS elements identified by unbiased methods have a variant of the classic CBS. Only an internal 10-bp core is completely conserved, but the entire 15-bp chromosome breakage sequence shows significant sequence conservation. Our results suggest that any one member of the CBS family provides a necessary and sufficient cis element for chromosome breakage. No chromosome breakage element totally unrelated to the classic CBS element was found; such elements, if they exist at all, must be rare.
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Affiliation(s)
- Eileen P Hamilton
- Department of Molecular, Cellular and Developmental Biology, University of California at Santa Barbara, Santa Barbara, CA 93106, USA.
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12
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Yao MC, Chao JL. RNA-guided DNA deletion in Tetrahymena: an RNAi-based mechanism for programmed genome rearrangements. Annu Rev Genet 2006; 39:537-59. [PMID: 16285871 DOI: 10.1146/annurev.genet.39.073003.095906] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Ciliated protozoan are unicellular eukaryotes. Most species in this diverse group display nuclear dualism, a special feature that supports both somatic and germline nuclei in the same cell. Probably due to this unique life style, they exhibit unusual nuclear characteristics that have intrigued researchers for decades. Among them are large-scale DNA rearrangements, which restructure the somatic genome to become drastically different from its germline origin. They resemble the classical phenomenon of chromatin diminution in some nematodes discovered more than a century ago. The mechanisms of such rearrangements, their biological roles, and their evolutionary origins have been difficult to understand. Recent studies have revealed a clear link to RNA interference, and begin to shed light on these issues. Using the simple ciliate Tetrahymena as a model, this chapter summarizes the physical characterization of these processes, describes recent findings that connect them to RNA interference, and discusses the details of their mechanisms, potential roles in genome defense, and possible occurrences in other organisms.
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Affiliation(s)
- Meng-Chao Yao
- Institute of Molecular Biology, Academia Sinica, Nankang, Taipei 11529, Taiwan, Republic of China.
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Yakisich JS, Kapler GM. Deletion of the Tetrahymena thermophila rDNA replication fork barrier region disrupts macronuclear rDNA excision and creates a fragile site in the micronuclear genome. Nucleic Acids Res 2006; 34:620-34. [PMID: 16449202 PMCID: PMC1356531 DOI: 10.1093/nar/gkj466] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
During macronuclear development the Tetrahymena thermophila ribosomal RNA gene is excised from micronuclear chromosome 1 by site-specific cleavage at chromosome breakage sequence (Cbs) elements, rearranged into a ‘palindromic’ 21 kb minichromosome and extensively amplified. Gene amplification initiates from origins in the 5′ non-transcribed spacer, and forks moving toward the center of the palindrome arrest at a developmentally regulated replication fork barrier (RFB). The RFB is inactive during vegetative cell divisions, suggesting a role in the formation or amplification of macronuclear rDNA. Using micronuclear (germline) transformation, we show that the RFB region facilitates Cbs-mediated excision. Deletion of the RFB inhibits chromosome breakage in a sub-population of developing macronuclei and promotes alternative processing by a Cbs-independent mechanism. Remarkably, the RFB region prevents spontaneous breakage of chromosome 1 in the diploid micronucleus. Strains heterozygous for ΔRFB and wild-type rDNA lose the ΔRFB allele and distal left arm of chromosome 1 during vegetative propagation. The wild-type chromosome is subsequently fragmented near the rDNA locus, and both homologs are progressively eroded, suggesting that broken micronuclear chromosomes are not ‘healed’ by telomerase. Deletion of this 363 bp segment effectively creates a fragile site in the micronuclear genome, providing the first evidence for a non-telomere cis-acting determinant that functions to maintain the structural integrity of a mitotic eukaryotic chromosome.
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Affiliation(s)
| | - G. M. Kapler
- To whom correspondence should be addressed. Tel: +1 979 847 8690; Fax: +1 979 847 9481;
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Hamilton E, Bruns P, Lin C, Merriam V, Orias E, Vong L, Cassidy-Hanley D. Genome-wide characterization of tetrahymena thermophila chromosome breakage sites. I. Cloning and identification of functional sites. Genetics 2005; 170:1611-21. [PMID: 15956677 PMCID: PMC1449750 DOI: 10.1534/genetics.104.031401] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2004] [Accepted: 05/10/2005] [Indexed: 11/18/2022] Open
Abstract
The chromosomes of the macronuclear (expressed) genome of Tetrahymena thermophila are generated by developmental fragmentation of the five micronuclear (germline) chromosomes. This fragmentation is site specific and directed by a conserved 15-bp chromosome breakage sequence (Cbs element). This article reports the construction of a library enriched for chromosome breakage junctions and the development of a successful scheme for the genome-wide isolation and characterization of functional Cbs junctions. Twenty-three new Cbs junctions were characterized and each was assigned to a specific micronuclear chromosome or chromosome arm. Two distinct previously unreported variant chromosome breakage sequences were found, each in two or more functional Cbs elements. Analysis of natural Cbs junctions confirmed that microheterogeneity in the macronuclear telomere addition site is associated with chromosome fragmentation. The physical and genetic characterization of these functional chromosome breakage junctions is reported in the accompanying article in this issue. The whole-genome shotgun sequencing and auto-assembly phase of the Tetrahymena Genome Initiative has recently been completed at The Institute for Genome Research (TIGR). By providing unique sequence from the natural ends of macronuclear chromosomes, Cbs junctions characterized in the work reported here will serve as useful sequence tags for relating macro- and micronuclear genetic, physical, and sequence maps.
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Affiliation(s)
- Eileen Hamilton
- Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, California 93106, USA.
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15
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LUSHAI GUGS, LOXDALE HUGHD, ALLEN JOHNA. The dynamic clonal genome and its adaptive potential. Biol J Linn Soc Lond 2003. [DOI: 10.1046/j.1095-8312.2003.00189.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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16
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Abstract
The germline genomes of ciliated protozoa are dynamic structures, undergoing massive DNA rearrangement during the formation of a functional macronucleus. Macronuclear development involves chromosome fragmentation coupled with de novo telomere synthesis, numerous DNA splicing events that remove internal segments of DNA, and, in some ciliates, the reordering of scrambled gene segments. Despite the fact that all ciliates share similar forms of DNA rearrangement, there appears to be great diversity in both the nature of the rearranged DNA and the molecular mechanisms involved. Epigenetic effects on rearrangement have also been observed, and recent work suggests that chromatin differentiation plays a role in specifying DNA segments either for rearrangement or for elimination.
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Affiliation(s)
- Carolyn L Jahn
- Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
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17
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Huang H, Smothers JF, Wiley EA, Allis CD. A nonessential HP1-like protein affects starvation-induced assembly of condensed chromatin and gene expression in macronuclei of Tetrahymena thermophila. Mol Cell Biol 1999; 19:3624-34. [PMID: 10207086 PMCID: PMC84163 DOI: 10.1128/mcb.19.5.3624] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Heterochromatin represents a specialized chromatin environment vital to both the repression and expression of certain eukaryotic genes. One of the best-studied heterochromatin-associated proteins is Drosophila HP1. In this report, we have disrupted all somatic copies of the Tetrahymena HHP1 gene, which encodes an HP1-like protein, Hhp1p, in macronuclei (H. Huang, E. A. Wiley, R. C. Lending, and C. D. Allis, Proc. Natl. Acad. Sci. USA 95:13624-13629, 1998). Unlike the Drosophila HP1 gene, HHP1 is not essential in Tetrahymena spp., and during vegetative growth no clear phenotype is observed in cells lacking Hhp1p (DeltaHHP1). However, during a shift to nongrowth conditions, the survival rate of DeltaHHP1 cells is reduced compared to that of wild-type cells. Upon starvation, Hhp1p becomes hyperphosphorylated concomitant with a reduction in macronuclear volume and an increase in the size of electron-dense chromatin bodies; neither of these morphological changes occurs in the absence of Hhp1p. Activation of two starvation-induced genes (ngoA and CyP) is significantly reduced in DeltaHHP1 cells while, in contrast, the expression of several growth-related or constitutively expressed genes is comparable to that in wild-type cells. These results suggest that Hhp1p functions in the establishment and/or maintenance of a specialized condensed chromatin environment that facilitates the expression of certain genes linked to a starvation-induced response.
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Affiliation(s)
- H Huang
- Department of Biology, Syracuse University, Syracuse, New York 13244, USA
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18
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Klobutcher LA, Gygax SE, Podoloff JD, Vermeesch JR, Price CM, Tebeau CM, Jahn CL. Conserved DNA sequences adjacent to chromosome fragmentation and telomere addition sites in Euplotes crassus. Nucleic Acids Res 1998; 26:4230-40. [PMID: 9722644 PMCID: PMC147820 DOI: 10.1093/nar/26.18.4230] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
During the formation of a new macronucleus in the ciliate Euplotes crassus, micronuclear chromosomes are reproducibly broken at approximately 10 000 sites. This chromosome fragmentation process is tightly coupled with de novo telomere synthesis by the telomerase ribonucleoprotein complex, generating short linear macronuclear DNA molecules. In this study, the sequences of 58 macronuclear DNA termini and eight regions of the micronuclear genome containing chromosome fragmentation/telomere addition sites were determined. Through a statistically based analysis of these data, along with previously published sequences, we have defined a 10 bp conserved sequence element (E-Cbs, 5'-HATTGAAaHH-3', H = A, C or T) near chromosome fragmentation sites. The E-Cbs typically resides within the DNA destined to form a macronuclear DNA molecule, but can also reside within flanking micronuclear DNA that is eliminated during macronuclear development. The location of the E-Cbs in macronuclear-destined versus flanking micronuclear DNA leads us to propose a model of chromosome fragmentation that involves a 6 bp staggered cut in the chromosome. The identification of adjacent macronuclear-destined sequences that overlap by 6 bp provides support for the model. Finally, our data provide evidence that telomerase is able to differentiate between newly generated ends that contain partial telomeric repeats and those that do not in vivo.
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Affiliation(s)
- L A Klobutcher
- Department of Biochemistry, University of Connecticut Health Center, Farmington, CT 06030, USA.
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Kuo MT, Sen S, Hittelman WN, Hsu TC. Chromosomal fragile sites and DNA amplification in drug-resistant cells. Biochem Pharmacol 1998; 56:7-13. [PMID: 9698083 DOI: 10.1016/s0006-2952(98)00040-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
It has been well established that DNA amplification is one of the important mechanisms by which cultured cells acquire resistance to many cytotoxic compounds. Amplification of important genes including those encoding oncoproteins, growth factors, their receptors and cell-cycle regulators has been reported in human neoplasms. Yet, despite intensive research since the first description of DNA amplification in cultured cells about 20 years ago, the mechanisms of DNA amplification remain largely unknown. Many models have been proposed to account for the diverse manifestations of amplified DNA in many different cell sources. It is not the intention of this commentary to review these many different models. Rather, we wil focus on the recent advances in this area of research, made mainly via the fluorescence in situ hybridization technique, that have revealed a fairly common chromosomal manifestation of amplified DNA in the drug-resistant hamster cell lines and have demonstrated the association of chromosomal fragile site breakage with early events in DNA amplification. These new developments underscore the importance of future research toward understanding the molecular bases of chromosomal fragile sites, including mechanisms involved in DNA strand breakage and repair, chromosomal translocations, and deletions, which may, in turn, provide important new insights into genomic plasticity and neoplastic transformation.
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Affiliation(s)
- M T Kuo
- Department of Molecular Pathology, The University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
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Campbell C, Romero DP. Identification and characterization of the RAD51 gene from the ciliate Tetrahymena thermophila. Nucleic Acids Res 1998; 26:3165-72. [PMID: 9628914 PMCID: PMC147671 DOI: 10.1093/nar/26.13.3165] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The RAD51 gene is a eukaryotic homolog of rec A, a critical component in homologous recombination and DNA repair pathways in Escherichia coli . We have cloned the RAD51 homolog from Tetrahymena thermophila , a ciliated protozoan. Tetrahymena thermophila RAD51 encodes a 36.3 kDa protein whose amino acid sequence is highly similar to representative Rad51 homologs from other eukaryotic taxa. Recombinant Rad51 protein was purified to near homogeneity following overproduction in a bacterial expression system. The purified protein binds to both single- and double-stranded DNA, possesses a DNA-dependent ATPase activity and promotes intermolecular ligation of linearized plasmid DNA. While steady-state levels of Rad51 mRNA are low in normally growing cells, treatment with UV light resulted in a >100-fold increase in mRNA levels. This increase in mRNA was time dependent, but relatively independent of UV dose over a range of 1400-5200 J/m2. Western blot analysis confirmed that Rad51 protein levels increase upon UV irradiation. Exposure to the alkylating agent methyl methane sulfonate also resulted in substantially elevated Rad51 protein levels in treated cells, with pronounced localization in the macronucleus. These data are consistent with the hypothesis that ciliates such as T.thermophila utilize a Rad51-dependent pathway to repair damaged DNA.
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Affiliation(s)
- C Campbell
- Department of Pharmacology, Medical School, University of Minnesota, 3-249 Millard Hall, 435 Delaware Street SE, Minneapolis, MN 55455, USA
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