1
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Altered tRNA processing is linked to a distinct and unusual La protein in Tetrahymena thermophila. Nat Commun 2022; 13:7332. [PMID: 36443289 PMCID: PMC9705548 DOI: 10.1038/s41467-022-34796-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Accepted: 11/07/2022] [Indexed: 11/29/2022] Open
Abstract
Nascent pre-tRNAs are transcribed by RNA polymerase III and immediately bound by La proteins on the UUU-3'OH sequence, using a tandem arrangement of the La motif and an adjacent RNA recognition motif-1 (RRM1), resulting in protection from 3'-exonucleases and promotion of pre-tRNA folding. The Tetrahymena thermophila protein Mlp1 has been previously classified as a genuine La protein, despite the predicted absence of the RRM1. We find that Mlp1 functions as a La protein through binding of pre-tRNAs, and affects pre-tRNA processing in Tetrahymena thermophila and when expressed in fission yeast. However, unlike in other examined eukaryotes, depletion of Mlp1 results in 3'-trailer stabilization. The 3'-trailers in Tetrahymena thermophila are uniquely short relative to other examined eukaryotes, and 5'-leaders have evolved to disfavour pre-tRNA leader/trailer pairing. Our data indicate that this variant Mlp1 architecture is linked to an altered, novel mechanism of tRNA processing in Tetrahymena thermophila.
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2
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Lv H, Hu L, Xu J, Bo T, Wang W. Identification and functional analysis of the mitochondrial cysteine synthase TtCsa2 from Tetrahymena thermophila. J Cell Biochem 2021; 122:1817-1831. [PMID: 34427342 DOI: 10.1002/jcb.30136] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2021] [Revised: 08/03/2021] [Accepted: 08/12/2021] [Indexed: 01/12/2023]
Abstract
Cysteine is a crucial component for all organisms and plays a critical role in the structure, stability, and catalytic functions of many proteins. Tetrahymena has reverse transsulfuration and de novo pathways for cysteine biosynthesis. Cysteine synthase is involved in the de novo cysteine biosynthesis and catalyzes the production of cysteine from O-acetylserine. The novel cysteine synthase TtCSA2 was identified from Tetrahymena thermophila. The TtCSA2 showed high expression levels at the log-phase and the sexual development stage. The TtCsa2 was localized on the outer mitochondrial membrane throughout different developmental stages. However, the truncated N-terminal signal peptide mutant TtCsa2-ΔN23 was localized into the mitochondria. His-TtCsa2 was expressed in Escherichia coli and purified using affinity chromatography. The His-TtCsa2 showed O-acetylserine sulfhydrylase and serine sulfhydrylase activities. Cysteine and glutathione contents decreased in the csa2KD mutant. Furthermore, mutant cells were sensitive to cadmium and copper stresses. This study indicated that the TtCSA2 was involved in the cysteine synthesis in mitochondria and related to heavy metal stresses resistance in Tetrahymena.
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Affiliation(s)
- Hongrui Lv
- School of Life Science, Shanxi University, Taiyuan, China.,Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan, China
| | - Lina Hu
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan, China
| | - Jing Xu
- School of Life Science, Shanxi University, Taiyuan, China.,Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan, China
| | - Tao Bo
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan, China
| | - Wei Wang
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan, China
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3
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Allen SE, Nowacki M. Roles of Noncoding RNAs in Ciliate Genome Architecture. J Mol Biol 2020; 432:4186-4198. [PMID: 31926952 PMCID: PMC7374600 DOI: 10.1016/j.jmb.2019.12.042] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Revised: 12/19/2019] [Accepted: 12/20/2019] [Indexed: 11/29/2022]
Abstract
Ciliates are an interesting model system for investigating diverse functions of noncoding RNAs, especially in genome defence pathways. During sexual development, the ciliate somatic genome undergoes massive rearrangement and reduction through removal of transposable elements and other repetitive DNA. This is guided by a multitude of noncoding RNAs of different sizes and functions, the extent of which is only recently becoming clear. The genome rearrangement pathways evolved as a defence against parasitic DNA, but interestingly also use the transposable elements and transposases to execute their own removal. Thus, ciliates are also a good model for the coevolution of host and transposable element, and the mutual dependence between the two. In this review, we summarise the genome rearrangement pathways in three diverse species of ciliate, with focus on recent discoveries and the roles of noncoding RNAs. Ciliate genomes undergo massive rearrangement and reduction during development. Transposon elimination is guided by small RNAs and carried out by transposases. New pathways for noncoding RNA production have recently been discovered in ciliates. Diverse ciliate species have different mechanisms for RNA-guided genome remodeling.
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Affiliation(s)
- Sarah E Allen
- Institute of Cell Biology, University of Bern, Switzerland
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4
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Nucleus-specific linker histones Hho1 and Mlh1 form distinct protein interactions during growth, starvation and development in Tetrahymena thermophila. Sci Rep 2020; 10:168. [PMID: 31932604 PMCID: PMC6957481 DOI: 10.1038/s41598-019-56867-0] [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: 07/19/2019] [Accepted: 11/14/2019] [Indexed: 02/07/2023] Open
Abstract
Chromatin organization influences most aspects of gene expression regulation. The linker histone H1, along with the core histones, is a key component of eukaryotic chromatin. Despite its critical roles in chromatin structure and function and gene regulation, studies regarding the H1 protein-protein interaction networks, particularly outside of Opisthokonts, are limited. The nuclear dimorphic ciliate protozoan Tetrahymena thermophila encodes two distinct nucleus-specific linker histones, macronuclear Hho1 and micronuclear Mlh1. We used a comparative proteomics approach to identify the Hho1 and Mlh1 protein-protein interaction networks in Tetrahymena during growth, starvation, and sexual development. Affinity purification followed by mass spectrometry analysis of the Hho1 and Mlh1 proteins revealed a non-overlapping set of co-purifying proteins suggesting that Tetrahymena nucleus-specific linker histones are subject to distinct regulatory pathways. Furthermore, we found that linker histones interact with distinct proteins under the different stages of the Tetrahymena life cycle. Hho1 and Mlh1 co-purified with several Tetrahymena-specific as well as conserved interacting partners involved in chromatin structure and function and other important cellular pathways. Our results suggest that nucleus-specific linker histones might be subject to nucleus-specific regulatory pathways and are dynamically regulated under different stages of the Tetrahymena life cycle.
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5
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Jaspan VN, Taye ME, Carle CM, Chung JJ, Chalker DL. Boundaries of eliminated heterochromatin of Tetrahymena are positioned by the DNA-binding protein Ltl1. Nucleic Acids Res 2019; 47:7348-7362. [PMID: 31194876 PMCID: PMC6698652 DOI: 10.1093/nar/gkz504] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2018] [Revised: 05/16/2019] [Accepted: 06/10/2019] [Indexed: 12/19/2022] Open
Abstract
During differentiation of the Tetrahymena thermophila somatic nucleus, its germline-derived DNA undergoes extensive reorganization including the removal of ∼50 Mb from thousands of loci called internal eliminated sequences (IESs). IES-associated chromatin is methylated on lysines 9 and 27 of histone H3, marking newly formed heterochromatin for elimination. To ensure that this reorganized genome maintains essential coding and regulatory sequences, the boundaries of IESs must be accurately defined. In this study, we show that the developmentally expressed protein encoded by Lia3-Like 1 (LTL1) (Ttherm_00499370) is necessary to direct the excision boundaries of particular IESs. In ΔLTL1 cells, boundaries of eliminated loci are aberrant and heterogeneous. The IESs regulated by Ltl1 are distinct from those regulated by the guanine-quadruplex binding Lia3 protein. Ltl1 has a general affinity for double stranded DNA (Kd ∼ 350 nM) and binds specifically to a 50 bp A+T rich sequence flanking each side of the D IES (Kd ∼ 43 nM). Together these data reveal that Ltl1 and Lia3 control different subsets of IESs and that their mechanisms for flanking sequence recognition are distinct.
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Affiliation(s)
- Vita N Jaspan
- Biology Department, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Marta E Taye
- Biology Department, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Christine M Carle
- Biology Department, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Joyce J Chung
- Biology Department, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Douglas L Chalker
- Biology Department, Washington University in St. Louis, St. Louis, MO 63130, USA
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6
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Ashraf K, Nabeel-Shah S, Garg J, Saettone A, Derynck J, Gingras AC, Lambert JP, Pearlman RE, Fillingham J. Proteomic Analysis of Histones H2A/H2B and Variant Hv1 in Tetrahymena thermophila Reveals an Ancient Network of Chaperones. Mol Biol Evol 2019; 36:1037-1055. [PMID: 30796450 PMCID: PMC6502085 DOI: 10.1093/molbev/msz039] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Epigenetic information, which can be passed on independently of the DNA sequence, is stored in part in the form of histone posttranslational modifications and specific histone variants. Although complexes necessary for deposition have been identified for canonical and variant histones, information regarding the chromatin assembly pathways outside of the Opisthokonts remains limited. Tetrahymena thermophila, a ciliated protozoan, is particularly suitable to study and unravel the chromatin regulatory layers due to its unique physical separation of chromatin states in the form of two distinct nuclei present within the same cell. Using a functional proteomics pipeline, we carried out affinity purification followed by mass spectrometry of endogenously tagged T. thermophila histones H2A, H2B and variant Hv1.We identified a set of interacting proteins shared among the three analyzed histones that includes the FACT-complex, as well as H2A- or Hv1-specific chaperones. We find that putative subunits of T. thermophila versions of SWR- and INO80-complexes, as well as transcription-related histone chaperone Spt6Tt specifically copurify with Hv1. We also identified importin β6 and the T. thermophila ortholog of nucleoplasmin 1 (cNpl1Tt) as H2A–H2B interacting partners. Our results further implicate Poly [ADP-ribose] polymerases in histone metabolism. Molecular evolutionary analysis, reciprocal affinity purification coupled to mass spectrometry experiments, and indirect immunofluorescence studies using endogenously tagged Spt16Tt (FACT-complex subunit), cNpl1Tt, and PARP6Tt underscore the validity of our approach and offer mechanistic insights. Our results reveal a highly conserved regulatory network for H2A (Hv1)–H2B concerning their nuclear import and assembly into chromatin.
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Affiliation(s)
- Kanwal Ashraf
- Department of Biology, York University, Toronto, ON, Canada
| | - Syed Nabeel-Shah
- Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada.,Donnelly Centre, University of Toronto, Toronto, ON, Canada; Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Jyoti Garg
- Department of Biology, York University, Toronto, ON, Canada
| | - Alejandro Saettone
- Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada
| | - Joanna Derynck
- Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada
| | - Anne-Claude Gingras
- Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada.,Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON, Canada
| | - Jean-Philippe Lambert
- Department of Molecular Medicine and Cancer Research Centre, Université Laval, Québec, QC, Canada.,CHU de Québec Research Center, CHUL, Québec, QC, Canada
| | | | - Jeffrey Fillingham
- Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada
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7
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Lin CYG, Chao JL, Tsai HK, Chalker D, Yao MC. Setting boundaries for genome-wide heterochromatic DNA deletions through flanking inverted repeats in Tetrahymena thermophila. Nucleic Acids Res 2019; 47:5181-5192. [PMID: 30918956 PMCID: PMC6547420 DOI: 10.1093/nar/gkz209] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2018] [Revised: 03/03/2019] [Accepted: 03/26/2019] [Indexed: 12/13/2022] Open
Abstract
Eukaryotic cells pack their genomic DNA into euchromatin and heterochromatin. Boundaries between these domains have been shown to be set by boundary elements. In Tetrahymena, heterochromatin domains are targeted for deletion from the somatic nuclei through a sophisticated programmed DNA rearrangement mechanism, resulting in the elimination of 34% of the germline genome in ∼10,000 dispersed segments. Here we showed that most of these deletions occur consistently with very limited variations in their boundaries among inbred lines. We identified several potential flanking regulatory sequences, each associated with a subset of deletions, using a genome-wide motif finding approach. These flanking sequences are inverted repeats with the copies located at nearly identical distances from the opposite ends of the deleted regions, suggesting potential roles in boundary determination. By removing and testing two such inverted repeats in vivo, we found that the ability for boundary maintenance of the associated deletion were lost. Furthermore, we analyzed the deletion boundaries in mutants of a known boundary-determining protein, Lia3p and found that the subset of deletions that are affected by LIA3 knockout contained common features of flanking regulatory sequences. This study suggests a common mechanism for setting deletion boundaries by flanking inverted repeats in Tetrahymena thermophila.
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Affiliation(s)
- Chih-Yi Gabriela Lin
- Institute of Molecular Biology, Academia Sinica, 11529 Taipei, Taiwan
- Genome and Systems Biology Degree Program, National Taiwan University, 10617 Taipei, Taiwan
| | - Ju-Lan Chao
- Institute of Molecular Biology, Academia Sinica, 11529 Taipei, Taiwan
| | - Huai-Kuang Tsai
- Genome and Systems Biology Degree Program, National Taiwan University, 10617 Taipei, Taiwan
- Institute of Information Science, Academia Sinica, 11529 Taipei, Taiwan
| | - Douglas Chalker
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Meng-Chao Yao
- Institute of Molecular Biology, Academia Sinica, 11529 Taipei, Taiwan
- Genome and Systems Biology Degree Program, National Taiwan University, 10617 Taipei, Taiwan
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8
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Saettone A, Garg J, Lambert JP, Nabeel-Shah S, Ponce M, Burtch A, Thuppu Mudalige C, Gingras AC, Pearlman RE, Fillingham J. The bromodomain-containing protein Ibd1 links multiple chromatin-related protein complexes to highly expressed genes in Tetrahymena thermophila. Epigenetics Chromatin 2018. [PMID: 29523178 PMCID: PMC5844071 DOI: 10.1186/s13072-018-0180-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Background The chromatin remodelers of the SWI/SNF family are critical transcriptional regulators. Recognition of lysine acetylation through a bromodomain (BRD) component is key to SWI/SNF function; in most eukaryotes, this function is attributed to SNF2/Brg1. Results Using affinity purification coupled to mass spectrometry (AP–MS) we identified members of a SWI/SNF complex (SWI/SNFTt) in Tetrahymena thermophila. SWI/SNFTt is composed of 11 proteins, Snf5Tt, Swi1Tt, Swi3Tt, Snf12Tt, Brg1Tt, two proteins with potential chromatin-interacting domains and four proteins without orthologs to SWI/SNF proteins in yeast or mammals. SWI/SNFTt subunits localize exclusively to the transcriptionally active macronucleus during growth and development, consistent with a role in transcription. While Tetrahymena Brg1 does not contain a BRD, our AP–MS results identified a BRD-containing SWI/SNFTt component, Ibd1 that associates with SWI/SNFTt during growth but not development. AP–MS analysis of epitope-tagged Ibd1 revealed it to be a subunit of several additional protein complexes, including putative SWRTt, and SAGATt complexes as well as a putative H3K4-specific histone methyl transferase complex. Recombinant Ibd1 recognizes acetyl-lysine marks on histones correlated with active transcription. Consistent with our AP–MS and histone array data suggesting a role in regulation of gene expression, ChIP-Seq analysis of Ibd1 indicated that it primarily binds near promoters and within gene bodies of highly expressed genes during growth. Conclusions Our results suggest that through recognizing specific histones marks, Ibd1 targets active chromatin regions of highly expressed genes in Tetrahymena where it subsequently might coordinate the recruitment of several chromatin-remodeling complexes to regulate the transcriptional landscape of vegetatively growing Tetrahymena cells. Electronic supplementary material The online version of this article (10.1186/s13072-018-0180-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Alejandro Saettone
- Department of Chemistry and Biology, Ryerson University, 350 Victoria St., Toronto, M5B 2K3, Canada
| | - Jyoti Garg
- Department of Biology, York University, 4700 Keele St., Toronto, M3J 1P3, Canada
| | - Jean-Philippe Lambert
- Lunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital, Toronto, M5G 1X5, Canada.,Department of Molecular Medicine, Université Laval, Quebec, Canada.,Centre Hospitalier Universitaire de Québec Research Center, CHUL, 2705 Boulevard Laurier, Quebec, G1V 4G2, Canada
| | - Syed Nabeel-Shah
- Department of Chemistry and Biology, Ryerson University, 350 Victoria St., Toronto, M5B 2K3, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, M5S 1A8, Canada
| | - Marcelo Ponce
- SciNet HPC Consortium, University of Toronto, 661 University Ave, Suite 1140, Toronto, M5G 1M1, Canada
| | - Alyson Burtch
- Department of Chemistry and Biology, Ryerson University, 350 Victoria St., Toronto, M5B 2K3, Canada
| | - Cristina Thuppu Mudalige
- Department of Chemistry and Biology, Ryerson University, 350 Victoria St., Toronto, M5B 2K3, Canada
| | - Anne-Claude Gingras
- Lunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital, Toronto, M5G 1X5, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, M5S 1A8, Canada
| | - Ronald E Pearlman
- Department of Biology, York University, 4700 Keele St., Toronto, M3J 1P3, Canada
| | - Jeffrey Fillingham
- Department of Chemistry and Biology, Ryerson University, 350 Victoria St., Toronto, M5B 2K3, Canada.
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9
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Carle CM, Zaher HS, Chalker DL. A Parallel G Quadruplex-Binding Protein Regulates the Boundaries of DNA Elimination Events of Tetrahymena thermophila. PLoS Genet 2016; 12:e1005842. [PMID: 26950070 PMCID: PMC4780704 DOI: 10.1371/journal.pgen.1005842] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Accepted: 01/12/2016] [Indexed: 11/19/2022] Open
Abstract
Guanine (G)-rich DNA readily forms four-stranded quadruplexes in vitro, but evidence for their participation in genome regulation is limited. We have identified a quadruplex-binding protein, Lia3, that controls the boundaries of germline-limited, internal eliminated sequences (IESs) of Tetrahymena thermophila. Differentiation of this ciliate's somatic genome requires excision of thousands of IESs, targeted for removal by small-RNA-directed heterochromatin formation. In cells lacking LIA3 (ΔLIA3), the excision of IESs bounded by specific G-rich polypurine tracts was impaired and imprecise, whereas the removal of IESs without such controlling sequences was unaffected. We found that oligonucleotides containing these polypurine tracts formed parallel G-quadruplex structures that are specifically bound by Lia3. The discovery that Lia3 binds G-quadruplex DNA and controls the accuracy of DNA elimination at loci with specific G-tracts uncovers an unrecognized potential of quadruplex structures to regulate chromosome organization.
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Affiliation(s)
- Christine M. Carle
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Hani S. Zaher
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Douglas L. Chalker
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri, United States of America
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10
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Vogt A, Mochizuki K. The taming of the shrew: Regulation of a catalytically active domesticated transposase. Mob Genet Elements 2014; 4:e29383. [PMID: 25054083 PMCID: PMC4091102 DOI: 10.4161/mge.29383] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 05/26/2014] [Accepted: 05/27/2014] [Indexed: 01/08/2023] Open
Abstract
Transposons are mobile genetic elements that can be harmful for the host when mobilized. However, they are also genomic reservoirs for novel genes that can be evolutionarily beneficial. There are many examples of domesticated transposases, which play important roles in the hosts. In most cases domesticated transposases have lost their endonuclease activities and the hosts utilize their DNA-binding properties. However, some other domesticated transposases perform endonuclease activities for host biological processes. Because such a catalytically active transposase is potentially harmful for the integrity of the host genome, its activity should be tightly regulated. The catalytically active domesticated piggyBac transposase Tpb2p catalyzes programmed DNA elimination in the ciliate Tetrahymena. Here, we discuss the regulatory mechanism that prevents unintended DNA cleavage by Tpb2p and compare it to another well-studied catalytically active domesticated transposase, the RAG recombinase in V(D)J recombination. The regulatory mechanisms involve the temporarily regulated expression of the transposases, the target sequence preference of the endonuclease, and the recruitment of the transposases to locally restricted chromatin environments.
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Affiliation(s)
- Alexander Vogt
- European Molecular Biology Laboratory (EMBL); Heidelberg, Germany
| | - Kazufumi Mochizuki
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA); Vienna, Austria
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11
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Garg J, Lambert JP, Karsou A, Marquez S, Nabeel-Shah S, Bertucci V, Retnasothie DV, Radovani E, Pawson T, Gingras AC, Pearlman RE, Fillingham JS. Conserved Asf1-importin β physical interaction in growth and sexual development in the ciliate Tetrahymena thermophila. J Proteomics 2013; 94:311-26. [PMID: 24120531 DOI: 10.1016/j.jprot.2013.09.018] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2013] [Revised: 09/07/2013] [Accepted: 09/23/2013] [Indexed: 01/14/2023]
Abstract
UNLABELLED How the eukaryotic cell specifies distinct chromatin domains is a central problem in molecular biology. The ciliate protozoan Tetrahymena thermophila features a separation of structurally and functionally distinct germ-line and somatic chromatin into two distinct nuclei, the micronucleus (MIC) and macronucleus (MAC) respectively. To address questions about how distinct chromatin states are assembled in the MAC and MIC, we have initiated studies to define protein-protein interactions for T. thermophila chromatin-related proteins. Affinity purification followed by mass spectrometry analysis of the conserved Asf1 histone chaperone in T. thermophila revealed that it forms a complex with an importin β, ImpB6. Furthermore, these proteins co-localized to both the MAC and MIC in growth and development. We suggest that newly synthesized histones H3 and H4 in T. thermophila are transported via Asf1-ImpB6 in an evolutionarily conserved pathway to both nuclei where they then enter nucleus-specific chromatin assembly pathways. These studies set the stage for further use of functional proteomics to elucidate details of the characterization and functional analysis of the unique chromatin domains in T. thermophila. BIOLOGICAL SIGNIFICANCE Asf1 is an evolutionarily conserved chaperone of H3 and H4 histones that functions in replication dependent and independent chromatin assembly. Although Asf1 has been well studied in humans and yeast (members of the Opisthokonta lineage of eukaryotes), questions remain concerning its mechanism of function. To obtain additional insight into the Asf1 function we have initiated a proteomic analysis in the ciliate protozoan T. thermophila, a member of the Alveolata lineage of eukaryotes. Our results suggest that an evolutionarily conserved function of Asf1 is mediating the nuclear transport of newly synthesized histones H3 and H4.
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Affiliation(s)
- Jyoti Garg
- Department of Biology, York University, 4700 Keele St., Toronto M3J 1P3, Canada
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12
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Abstract
Nuclear dualism is a characteristic feature of the ciliated protozoa. Tetrahymena have two different nuclei in each cell. The larger, polyploid, somatic macronucleus (MAC) is the site of transcriptional activity in the vegetatively growing cell. The smaller, diploid micronucleus (MIC) is transcriptionally inactive in vegetative cells, but is transcriptionally active in mating cells and responsible for the genetic continuity during sexual reproduction. Although the MICs and MACs develop from mitotic products of a common progenitor and reside in a common cytoplasm, they are different from one another in almost every respect.
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Affiliation(s)
- Kathleen M Karrer
- Department of Biological Sciences, Marquette University, Milwaukee, Wisconsin, USA
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13
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Schoeberl UE, Mochizuki K. Keeping the soma free of transposons: programmed DNA elimination in ciliates. J Biol Chem 2011; 286:37045-52. [PMID: 21914793 DOI: 10.1074/jbc.r111.276964] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Many transposon-related sequences are removed from the somatic macronucleus of ciliates during sexual reproduction. In the ciliate Tetrahymena, an RNAi-related mechanism produces small noncoding RNAs that induce heterochromatin formation, which is followed by DNA elimination. Because RNAi-related mechanisms repress transposon activities in a variety of eukaryotes, the DNA elimination mechanism of ciliates might have evolved from these types of transposon-silencing mechanisms. Nuclear dimorphism allows ciliates to identify any DNA that has invaded the germ-line micronucleus using small RNAs and a whole genome comparison of the micronucleus and the somatic macronucleus.
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Affiliation(s)
- Ursula E Schoeberl
- Institute of Molecular Biotechnology, Austrian Academy of Sciences (IMBA), A-1030 Vienna, Austria
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14
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Chalker DL, Yao MC. DNA elimination in ciliates: transposon domestication and genome surveillance. Annu Rev Genet 2011; 45:227-46. [PMID: 21910632 DOI: 10.1146/annurev-genet-110410-132432] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Ciliated protozoa extensively remodel their somatic genomes during nuclear development, fragmenting their chromosomes and removing large numbers of internal eliminated sequences (IESs). The sequences eliminated are unique and repetitive DNAs, including transposons. Recent studies have identified transposase proteins that appear to have been domesticated and are used by these cells to eliminate DNA not wanted in the somatic macronucleus. This DNA elimination process is guided by meiotically produced small RNAs, generated in the germline nucleus, that recognize homologous sequences leading to their removal. These scan RNAs are found in complexes with PIWI proteins. Before they search the developing genome for IESs to eliminate, they scan the parental somatic nucleus and are removed from the pool if they match homologous sequences in that previously reorganized genome. In Tetrahymena, the scan RNAs target heterochromatin modifications to mark IESs for elimination. This DNA elimination pathway in ciliates shares extensive similarity with piRNA-mediated silencing of metazoans and highlights the remarkable ability of homologous RNAs to shape developing genomes.
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Affiliation(s)
- Douglas L Chalker
- Department of Biology, Washington University, St. Louis, Missouri 63130, USA.
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15
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Motl JA, Chalker DL. Subtraction by addition: domesticated transposases in programmed DNA elimination. Genes Dev 2009; 23:2455-60. [PMID: 19884252 DOI: 10.1101/gad.1864609] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The ciliate Paramecium tetraurelia must eliminate approximately 60,000 short sequences from its genome to generate uninterrupted coding sequences in its somatic macronucleus. In this issue of Genes & Development, Baudry and colleagues (pp. 2478-2483) identify the protein that excises these noncoding sequences: a domesticated piggyBac transposase that has been adapted to remove what are likely the remnants of transposon insertions. This new study reveals how addition of a transposase to small RNA-directed silencing machinery can guide major genome reorganization.
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Affiliation(s)
- Jason A Motl
- Biology Department, Washington University in St. Louis, St. Louis, Missouri 63130, USA
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16
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Aronica L, Bednenko J, Noto T, DeSouza LV, Siu KM, Loidl J, Pearlman RE, Gorovsky MA, Mochizuki K. Study of an RNA helicase implicates small RNA-noncoding RNA interactions in programmed DNA elimination in Tetrahymena. Genes Dev 2008; 22:2228-41. [PMID: 18708581 PMCID: PMC2518816 DOI: 10.1101/gad.481908] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2008] [Accepted: 06/25/2008] [Indexed: 12/17/2022]
Abstract
Tetrahymena eliminates micronuclear-limited sequences from the developing macronucleus during sexual reproduction. Homology between the sequences to be eliminated and approximately 28-nucleotide small RNAs (scnRNAs) associated with an Argonaute family protein Twi1p likely underlies this elimination process. However, the mechanism by which Twi1p-scnRNA complexes identify micronuclear-limited sequences is not well understood. We show that a Twi1p-associated putative RNA helicase Ema1p is required for the interaction between Twi1p and chromatin. This requirement explains the phenotypes of EMA1 KO strains, including loss of selective down-regulation of scnRNAs homologous to macronuclear-destined sequences, loss of H3K9 and K27 methylation in the developing new macronucleus, and failure to eliminate DNA. We further demonstrate that Twi1p interacts with noncoding transcripts derived from parental and developing macronuclei and this interaction is greatly reduced in the absence of Ema1p. We propose that Ema1p functions in DNA elimination by stimulating base-pairing interactions between scnRNAs and noncoding transcripts in both parental and developing new macronuclei.
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Affiliation(s)
- Lucia Aronica
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), A-1030 Vienna, Austria
| | - Janna Bednenko
- Department of Biology, University of Rochester, Rochester, New York 14627, USA
| | - Tomoko Noto
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), A-1030 Vienna, Austria
| | - Leroi V. DeSouza
- Department of Chemistry and Center for Research in Mass Spectrometry, York University, Toronto, Ontario M3J 1P3, Canada
| | - K.W. Michael Siu
- Department of Chemistry and Center for Research in Mass Spectrometry, York University, Toronto, Ontario M3J 1P3, Canada
| | - Josef Loidl
- Department of Chromosome Biology, Max F. Perutz Laboratories, University of Vienna, A-1030 Vienna, Austria
| | - Ronald E. Pearlman
- Department of Biology and Center for Research in Mass Spectronomy, York University, Toronto, Ontario M3J 1P3, Canada
| | - Martin A. Gorovsky
- Department of Biology, University of Rochester, Rochester, New York 14627, USA
| | - Kazufumi Mochizuki
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), A-1030 Vienna, Austria
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17
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Fillingham JS, Garg J, Tsao N, Vythilingum N, Nishikawa T, Pearlman RE. Molecular genetic analysis of an SNF2/brahma-related gene in Tetrahymena thermophila suggests roles in growth and nuclear development. EUKARYOTIC CELL 2007; 5:1347-59. [PMID: 16896218 PMCID: PMC1539136 DOI: 10.1128/ec.00149-06] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We used a reverse genetic approach to identify three members of the SNF2 superfamily of chromatin remodeling genes in the ciliated protozoan Tetrahymena thermophila in order to investigate possible functions of ATP-dependent chromatin remodeling factors in growth and nuclear development. Comparative sequence analysis of the gene product of the Tetrahymena brahma-related gene (TtBRG1) indicates it is a member of the SNF2/BRM subgroup of the SNF2 superfamily. Northern analysis suggests that TtBRG1 has roles in growth and nuclear development in Tetrahymena. Indirect immunofluorescence analysis during nuclear development indicates that TtBrg1p localizes to both the parental and developing macronucleus of Tetrahymena during the time period corresponding to genome rearrangements. We generated germ line knockout heterokaryons for TtBRG1 and demonstrated that expression of the gene is required to complete nuclear development of Tetrahymena. In addition, the formation of distinct Pdd1p-containing structures is disturbed during the late stages of conjugation in TtBRG1 germ line knockout heterokaryons. We discuss these results in light of possible roles of SNF2-related proteins in growth and nuclear development of Tetrahymena.
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Affiliation(s)
- Jeffrey S Fillingham
- Department of Biology, York University, 4700 Keele St, Toronto, Ontario, Canada M3J 1P3
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18
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Juranek SA, Lipps HJ. New Insights into the Macronuclear Development in Ciliates. INTERNATIONAL REVIEW OF CYTOLOGY 2007; 262:219-51. [PMID: 17631190 DOI: 10.1016/s0074-7696(07)62005-1] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
During macronuclear differentiation in ciliated protozoa, most amazing "DNA gymnastics" takes place, which includes DNA excision, DNA elimination, DNA reorganization, and DNA-specific amplification. Although the morphological events occurring during macronuclear development are well described, a detailed knowledge of the molecular mechanisms and the regulation of this differentiation process is still missing. However, recently several models have been proposed for the molecular regulation of macronuclear differentiation, but these models have yet to be verified experimentally. The scope of this review is to summarize recent discoveries in different ciliate species and to compare and discuss the different models proposed. Results obtained in these studies are not only relevant for our understanding of nuclear differentiation in ciliates, but also for cellular differentiation in eukaryotic organisms in general as well as for other disciplines such as bioinformatics and computational biology.
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Affiliation(s)
- Stefan A Juranek
- Howard Hughes Medical Institute, Laboratory of RNA Molecular Biology, Rockefeller University, New York, New York 10021, USA
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19
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Kowalczyk CA, Anderson AM, Arce-Larreta M, Chalker DL. The germ line limited M element of Tetrahymena is targeted for elimination from the somatic genome by a homology-dependent mechanism. Nucleic Acids Res 2006; 34:5778-89. [PMID: 17053100 PMCID: PMC1635302 DOI: 10.1093/nar/gkl699] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
A RNA interference (RNAi) like mechanism is involved in elimination of thousands of DNA segments from the developing somatic macronucleus of Tetrahymena, yet how specific internal eliminated sequences (IESs) are recognized remains to be fully elucidated. To define requirements for DNA rearrangement, we performed mutagenesis of the M element, a well-studied IES. While sequences within the macronucleus-retained DNA are known to determine the excision boundaries, we show that sequences internal to these boundaries are required to promote this IES's rearrangement. However, this element does not contain any specific sequence required in cis as removal of its entire left or right side was insufficient to abolish all rearrangement. Instead, rearrangement efficiency correlated with the overall size of the M element sequence within a given construct, with a lower limit of nearly 300 bp. Also, the observed minimal region necessary to epigenetically block excision supports this size limit. Truncated M element constructs that exhibited impaired rearrangement still showed full transcriptional activity, which suggests that their defect was due to inefficient recognition. This study indicates that IESs are targeted for elimination upon their recognition by homologous small RNAs and further supports the idea that DNA elimination is a RNAi-related mechanism involved in genome surveillance.
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Affiliation(s)
| | | | | | - Douglas L. Chalker
- To whom correspondence should be addressed. Tel: +1 314 935 8838; Fax: +1 314 935 4432; E-mail:
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20
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Malone CD, Anderson AM, Motl JA, Rexer CH, Chalker DL. Germ line transcripts are processed by a Dicer-like protein that is essential for developmentally programmed genome rearrangements of Tetrahymena thermophila. Mol Cell Biol 2005; 25:9151-64. [PMID: 16199890 PMCID: PMC1265777 DOI: 10.1128/mcb.25.20.9151-9164.2005] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Abundant approximately 28-nucleotide RNAs that are thought to direct histone H3 lysine 9 (H3K9) methylation and promote the elimination of nearly 15 Mbp of DNA from the developing somatic genome are generated during Tetrahymena thermophila conjugation. To identify the protein(s) that generates these small RNAs, we studied three Dicer-related genes encoded within the Tetrahymena genome, two that contain both RNase III and RNA helicase motifs, Dicer 1 (DCR1) and DCR2, and a third that lacks the helicase domain, Dicer-like 1 (DCL1). DCL1 is expressed upon the initiation of conjugation, and the protein localizes to meiotic micronuclei when bidirectional germ line transcription occurs and small RNAs begin to accumulate. Cells in which we disrupted the DCL1 gene (DeltaDCL1) grew normally and initiated conjugation as wild-type cells but arrested near the end of development and eventually died, unable to resume vegetative growth. These DeltaDCL1 cells failed to generate the abundant small RNAs but instead accumulated germ line-limited transcripts. Together, our findings demonstrate that these transcripts are the precursors of the small RNAs and that DCL1 performs RNA processing within the micronucleus. Postconjugation DeltaDCL1 cells die without eliminating the germ line-limited DNA sequences from their newly formed somatic macronuclei, a result that shows that this Dicer-related gene is required for programmed DNA rearrangements. Surprisingly, DeltaDCL1 cells were not deficient in overall H3K9 methylation, but this modification was not enriched on germ line-limited sequences as it is in wild-type cells, which clearly demonstrates that these small RNAs are essential for its targeting to specific loci.
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Affiliation(s)
- Colin D Malone
- Biology Department, Washington University, St. Louis, MO 63130, USA
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21
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Liu Y, Song X, Gorovsky MA, Karrer KM. Elimination of foreign DNA during somatic differentiation in Tetrahymena thermophila shows position effect and is dosage dependent. EUKARYOTIC CELL 2005; 4:421-31. [PMID: 15701804 PMCID: PMC549336 DOI: 10.1128/ec.4.2.421-431.2005] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In the ciliate Tetrahymena thermophila, approximately 15% of the germ line micronuclear DNA sequences are eliminated during formation of the somatic macronucleus. The vast majority of the internal eliminated sequences (IESs) are repeated in the micronuclear genome, and several of them resemble transposable elements. Thus, it has been suggested that DNA elimination evolved as a means for removing invading DNAs. In the present study, bacterial neo genes introduced into the germ line micronuclei were eliminated from the somatic genome. The efficiency of elimination from two different loci increased dramatically with the copy number of the neo genes in the micronuclei. The timing of neo elimination is similar to that of endogenous IESs, and they both produce bidirectional transcripts of the eliminated element, suggesting that the deletion of neo occurred by the same mechanism as elimination of endogenous IESs. These results indicate that repetition of an element in the micronucleus enhances the efficiency of its elimination from the newly formed somatic genome of Tetrahymena thermophila. The implications of these data in relation to the function and mechanism of IES elimination are discussed.
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Affiliation(s)
- Yifan Liu
- Department of Biology, University of Rochester, Rochester, New York, USA
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22
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Fillingham JS, Pearlman RE. Role of micronucleus-limited DNA in programmed deletion of mse2.9 during macronuclear development of Tetrahymena thermophila. EUKARYOTIC CELL 2004; 3:288-301. [PMID: 15075259 PMCID: PMC387634 DOI: 10.1128/ec.3.2.288-301.2004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Extensive programmed DNA rearrangements occur during the development of the somatic macronucleus from the germ line micronucleus in the sexual cycle of the ciliated protozoan Tetrahymena thermophila. Using an in vivo processing assay, we analyzed the role of micronucleus-limited DNA during the programmed deletion of mse2.9, an internal eliminated sequence (IES). We identified a 200-bp region within mse2.9 that contains an important cis-acting element which is required for the targeting of efficient programmed deletion. Our results, obtained with a series of mse2.9-based chimeric IESs, led us to suggest that the cis-acting elements in both micronucleus-limited and macronucleus-retained flanking DNAs stimulate programmed deletion to different degrees depending on the particular eliminated sequence. The mse2.9 IES is situated within the second intron of the micronuclear locus of the ARP1 gene. We show that the expression of ARP1 is not essential for the growth of Tetrahymena. Our results also suggest that mse2.9 is not subject to epigenetic regulation of DNA deletion, placing possible constraints on the scan RNA model of IES excision.
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23
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Fillingham JS, Thing TA, Vythilingum N, Keuroghlian A, Bruno D, Golding GB, Pearlman RE. A non-long terminal repeat retrotransposon family is restricted to the germ line micronucleus of the ciliated protozoan Tetrahymena thermophila. EUKARYOTIC CELL 2004; 3:157-69. [PMID: 14871946 PMCID: PMC329501 DOI: 10.1128/ec.3.1.157-169.2004] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The ciliated protozoan Tetrahymena thermophila undergoes extensive programmed DNA rearrangements during the development of a somatic macronucleus from the germ line micronucleus in its sexual cycle. To investigate the relationship between programmed DNA rearrangements and transposable elements, we identified several members of a family of non-long terminal repeat (LTR) retrotransposons (retroposons) in T. thermophila, the first characterized in the ciliated protozoa. This multiple-copy retrotransposon family is restricted to the micronucleus of T. thermophila. The REP (Tetrahymena non-LTR retroposon) elements encode an ORF2 typical of non-LTR elements that contains apurinic/apyrimidinic endonuclease (APE) and reverse transcriptase (RT) domains. Phylogenetic analysis of the RT and APE domains indicates that the element forms a deep-branching clade within the non-LTR retrotransposon family. Northern analysis with a probe to the conserved RT domain indicates that transcripts from the element are small and heterogeneous in length during early macronuclear development. The presence of a repeated transposable element in the genome is consistent with the model that programmed DNA deletion in T. thermophila evolved as a method of eliminating deleterious transposons from the somatic macronucleus.
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24
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Huvos P. Modular structure in developmentally eliminated DNA in Tetrahymena may be a consequence of frequent insertions and deletions. J Mol Biol 2004; 336:1075-86. [PMID: 15037070 DOI: 10.1016/j.jmb.2003.12.065] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2003] [Revised: 12/15/2003] [Accepted: 12/17/2003] [Indexed: 11/28/2022]
Abstract
The work reported here describes insertion-deletion (Indel) polymorphisms in two internally eliminated sequences (IESs, that are deleted during development in Tetrahymena): a 1.8 kb Indel at one end of the 1.1 kb H1 IES and a 0.5 kb Indel inside the 1.4 kb calmodulin (C) IES. These two IESs are located in the proximity of the H1 histone and calmodulin genes, respectively, and are among the ten IESs that have been fully sequenced out of an estimated total of 6000. Three hundred base-pairs of the 1.8 kb H1 Indel are retained in the macronucleus. Both the +Indel and the -Indel variants of the H1 and C IESs that occur in different strains are eliminated during development. Thus, a drastic change involving over half of the deleted sequence and 300 bp of flanking sequence does not disable developmental elimination of the H1 IES, which may indicate a lack of requirement for specific sequences on the Indel side of the IES. The H1 Indel is a composite of three sequence elements: a unique segment and two other sections containing members of different repeat families. One of these, a 0.5 kb repetitive component, is 75% similar to another 0.5 kb sequence that constitutes the C Indel, a sequence present in the middle of the calmodulin IES in some strains, but not in others. Therefore, the C Indel sequence is likely to have been part of a mobile unit, even though it has no obvious features of a transposon. However, sequences similar to the C Indel are present in about 100 copies in the genome. The results suggest that IESs may consist, at least in part, of relatively short modules of repeated sequences that are the source of insertion-deletion polymorphisms among strains of Tetrahymena thermophila.
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Affiliation(s)
- Piroska Huvos
- Department of Biochemistry and Molecular Biology, Southern Illinois University, Carbondale, IL 62901, USA
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25
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Huvos P. A member of a repeat family is the source of an insertion-deletion polymorphism inside a developmentally eliminated sequence of Tetrahymena thermophila. J Mol Biol 2004; 336:1061-73. [PMID: 15037069 DOI: 10.1016/j.jmb.2003.12.064] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2003] [Revised: 12/15/2003] [Accepted: 12/17/2003] [Indexed: 11/21/2022]
Abstract
In Tetrahymena thermophila, the development of a transcriptionally active macronucleus from a transcriptionally inert micronucleus is accompanied by the elimination of numerous DNA segments, called internally eliminated sequences (IESs), many of which belong to dispersed repetitive sequence families. To examine the relationship between the insertion and deletion events expected to occur during evolution of the repeats and the developmental elimination process, IESs were compared among different Tetrahymena strains. A 600 base-pair DNA segment, the R Indel, was discovered inside the R IES, one of the ten sequenced IESs out of an estimated 6000 total in the Tetrahymena genome. The R Indel was found in strains B3 and C2 but not in several other strains examined, indicating that the Indel was probably present in a progenitor of strains B3 and C2. The R Indel was found to belong to a moderately large sequence family of about 200 members; however, BLAST searches did not reveal meaningful similarities with other mobile elements. Sequence comparisons revealed that a 300 base-pair stretch, very closely related to the first half of the R Indel, was present inside the previously described B IES, another of the ten sequenced IESs. This is the first example of shared sequences between two of the known IESs.
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Affiliation(s)
- Piroska Huvos
- Department of Biochemistry and Molecular Biology, Southern Illinois University, Carbondale, IL 62901, USA.
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26
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Wuitschick JD, Karrer KM. Diverse sequences within Tlr elements target programmed DNA elimination in Tetrahymena thermophila. EUKARYOTIC CELL 2003; 2:678-89. [PMID: 12912887 PMCID: PMC178349 DOI: 10.1128/ec.2.4.678-689.2003] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Tlr elements are a novel family of approximately 30 putative mobile genetic elements that are confined to the germ line micronuclear genome in Tetrahymena thermophila. Thousands of diverse germ line-limited sequences, including the Tlr elements, are specifically eliminated from the differentiating somatic macronucleus. Macronucleus-retained sequences flanking deleted regions are known to contain cis-acting signals that delineate elimination boundaries. It is unclear whether sequences within deleted DNA also play a regulatory role in the elimination process. In the current study, an in vivo DNA rearrangement assay was used to identify internal sequences required in cis for the elimination of Tlr elements. Multiple, nonoverlapping regions from the approximately 23-kb Tlr elements were independently sufficient to stimulate developmentally regulated DNA elimination when placed within the context of flanking sequences from the most thoroughly characterized family member, Tlr1. Replacement of element DNA with macronuclear or foreign DNA abolished elimination activity. Thus, diverse sequences dispersed throughout Tlr DNA contain cis-acting signals that target these elements for programmed elimination. Surprisingly, Tlr DNA was also efficiently deleted when Tlr1 flanking sequences were replaced with DNA from a region of the genome that is not normally associated with rearrangement, suggesting that specific flanking sequences are not required for the elimination of Tlr element DNA.
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Affiliation(s)
- Jeffrey D Wuitschick
- Department of Biological Sciences, Marquette University, Milwaukee, Wisconsin 53201-1881, USA
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27
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Wuitschick JD, Gershan JA, Lochowicz AJ, Li S, Karrer KM. A novel family of mobile genetic elements is limited to the germline genome in Tetrahymena thermophila. Nucleic Acids Res 2002; 30:2524-37. [PMID: 12034842 PMCID: PMC117186 DOI: 10.1093/nar/30.11.2524] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
In the ciliated protozoan Tetrahymena thermophila, extensive DNA elimination is associated with differentiation of the somatic macronucleus from the germline micronucleus. This study describes the isolation and complete characterization of Tlr elements, a family of approximately 30 micronuclear DNA sequences that are efficiently eliminated from the developing macronucleus. The data indicate that Tlr elements are comprised of an approximately 22 kb internal region flanked by complex and variable termini. The Tlr internal region is highly conserved among family members and contains 15 open reading frames, some of which resemble genes encoded by transposons and viruses. The Tlr termini appear to be long inverted repeats consisting of (i) a variable region containing multiple direct repeats which differ in number and sequence from element to element and (ii) a conserved terminal 47 bp sequence. Taken together, these results suggest that Tlr elements comprise a novel family of mobile genetic elements that are confined to the Tetrahymena germline genome. Possible mechanisms of developmentally programmed Tlr elimination are discussed.
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