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The Journal of Biological Chemistry Oct 2011Many transposon-related sequences are removed from the somatic macronucleus of ciliates during sexual reproduction. In the ciliate Tetrahymena, an RNAi-related mechanism... (Review)
Review
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.
Topics: DNA Transposable Elements; DNA, Protozoan; Heterochromatin; Macronucleus; Micronucleus, Germline; Tetrahymena
PubMed: 21914793
DOI: 10.1074/jbc.R111.276964 -
Experimental Cell Research Jan 1988Cytology, DNA and host-symbiont relationships of x-like endosymbionts from Paramecium caudatum are described. The symbionts (Caedibacter caryophila, sp. nov.) live in...
Cytology, DNA and host-symbiont relationships of x-like endosymbionts from Paramecium caudatum are described. The symbionts (Caedibacter caryophila, sp. nov.) live in the macronuclei of their hosts. They confer the killer trait upon their hosts and appear well adapted to their endonucleobiotic way of life. R bodies (proteinaceous ribbons associated with killing) are produced, but differ significantly from any of the four R-body classes previously described. C. caryophila and their R bodies were isolated. DNA was extracted from purified symbionts and used to demonstrate that one P. caudatum line harbors a natural mutant which is deficient in R-body production. Melting studies indicate a GC content of 34.6%. No sequence homology between the C. caryophila DNA and the coding sequence for type 51 R-body production was observed. C. caryophila is parasitic, causing the death of its hosts in starving cultures.
Topics: Animals; Bacteria; Cell Nucleus; DNA; DNA, Bacterial; Microscopy, Electron; Mutation; Paramecium; Symbiosis
PubMed: 3335230
DOI: 10.1016/0014-4827(88)90141-3 -
The Journal of Biophysical and... Jul 1956In a previous paper (8) an organized structure was described in the macronuclei of certain old organisms of Tokophrya infusionum. It was found that the same honeycomb...
In a previous paper (8) an organized structure was described in the macronuclei of certain old organisms of Tokophrya infusionum. It was found that the same honeycomb structure appears in great abundance in the macronuclei of overfed organisms. This permitted a better three-dimensional reconstruction of the described structure. Since the defined structure may be experimentally induced, it offers an opportunity for further more detailed studies as to its nature and meaning.
Topics: Animals; Cell Nucleus; Electrons; Eukaryota; Invertebrates; Kinetofragminophorea; Macronucleus; Microscopy; Microscopy, Electron; Porifera
PubMed: 13357580
DOI: 10.1083/jcb.2.4.425 -
Molecular Biology of the Cell Dec 2006The ribosomal DNA origin binding protein Tif1p regulates the timing of rDNA replication and is required globally for proper S-phase progression and division of the...
The ribosomal DNA origin binding protein Tif1p regulates the timing of rDNA replication and is required globally for proper S-phase progression and division of the Tetrahymena thermophila macronucleus. Here, we show that Tif1p safeguards chromosomes from DNA damage in the mitotic micronucleus and amitotic macronucleus. TIF1p localization is dynamically regulated as it moves into the micro- and macronucleus during the respective S phases. TIF1 disruption mutants are hypersensitive to hydroxyurea and methylmethanesulfonate, inducers of DNA damage and intra-S-phase checkpoint arrest in all examined eukaryotes. TIF1 mutants incur double-strand breaks in the absence of exogenous genotoxic stress, destabilizing all five micronuclear chromosomes. Wild-type Tetrahymena elicits an intra-S-phase checkpoint response that is induced by hydroxyurea and suppressed by caffeine, an inhibitor of the apical checkpoint kinase ATR/MEC1. In contrast, hydroxyurea-challenged TIF1 mutants fail to arrest in S phase or exhibit caffeine-sensitive Rad51 overexpression, indicating the involvement of TIF1 in checkpoint activation. Although aberrant micro- and macronuclear division occurs in TIF1 mutants and caffeine-treated wild-type cells, TIF1p bears no similarity to ATR or its substrates. We propose that TIF1 and ATR function in the same epistatic pathway to regulate checkpoint responses in the diploid mitotic micronucleus and polyploid amitotic macronucleus.
Topics: Animals; Caffeine; Chromosomes; DNA Damage; Diploidy; Gene Expression Regulation; Genomic Instability; Macronucleus; Meiosis; Methyl Methanesulfonate; Micronucleus, Germline; Mitosis; Mutation; Neomycin; Nuclear Proteins; Polyploidy; Protein Transport; RNA, Messenger; Rad51 Recombinase; S Phase; Tetrahymena; Transcription Factors
PubMed: 17005912
DOI: 10.1091/mbc.e06-05-0469 -
European Journal of Protistology Jun 1991Nuclear phenomena at conjugation of the multimicronucleate ciliate Blepharisma japonicum were investigated by using fluorescence microscopy. Several hours after cells...
Nuclear phenomena at conjugation of the multimicronucleate ciliate Blepharisma japonicum were investigated by using fluorescence microscopy. Several hours after cells united in pairs, micronuclei differentiated into meiotic micronuclei and "somatomicronuclei". Meiotic micro-nuclei participated in conventional sexual processes producing new micro- and macronuclei through meiosis, karyogamy and postkaryogamic mitoses. On the other hand, somatomicronuclei participated in characteristic asexual processes in which each micronucleus differentiated into a macronucleus without undergoing any nuclear division and karyogamy. These two paths of macronucleus differentiation, one sexual and the other asexual, proceeded side by side in each cell, but eventually one path dominated the other. The sexual path regularly dominated in crossing conjugation which was induced by mixing clones of complementary mating types I and II. However, if macronuclear anlagen in the sexual path were removed, the asexual path took over to form macronuclei, indicating that the asexual path serves as a reserve path of macronucleus formation. The asexual path regularly dominated in intraclonal conjugation of high-frequency selfers, suggesting that it functions in reducing the genetic effect of inbreeding. These findings not only clarify nuclear phenomena at conjugation in Blepharisma, but also provide a new opportunity for the study of macronucleus differentiation.
PubMed: 23194710
DOI: 10.1016/S0932-4739(11)80340-8 -
PloS One 2012Ciliated protozoans possess two types of nuclei; a transcriptionally silent micronucleus, which serves as the germ line nucleus, and a transcriptionally active...
Ciliated protozoans possess two types of nuclei; a transcriptionally silent micronucleus, which serves as the germ line nucleus, and a transcriptionally active macronucleus, which serves as the somatic nucleus. The macronucleus is derived from a new diploid micronucleus after mating, with epigenetic information contributed by the parental macronucleus serving to guide the formation of the new macronucleus. In the stichotrichous ciliate Oxytricha trifallax, the macronuclear DNA is highly processed to yield gene-sized nanochromosomes with telomeres at each end. Here we report that soon after mating of Oxytricha trifallax, abundant 27 nt small RNAs are produced that are not present prior to mating. We performed next generation sequencing of Oxytricha small RNAs from vegetative and mating cells. Using sequence comparisons between macronuclear and micronuclear versions of genes, we found that the 27 nt RNA class derives from the parental macronucleus, not the developing macronucleus. These small RNAs are produced equally from both strands of macronuclear nanochromosomes, but in a highly non-uniform distribution along the length of the nanochromosome, and with a particular depletion in the 30 nt telomere-proximal positions. This production of small RNAs from the parental macronucleus during macronuclear development stands in contrast to the mechanism of epigenetic control in the distantly related ciliate Tetrahymena. In that species, 28-29 nt scanRNAs are produced from the micronucleus and these micronuclear-derived RNAs serve as epigenetic controllers of macronuclear development. Unlike the Tetrahymena scanRNAs, the Oxytricha macronuclear-derived 27 mers are not modified by 2'O-methylation at their 3' ends. We propose models for the role of these "27macRNAs" in macronuclear development.
Topics: Gene Expression Regulation; Genome, Protozoan; Macronucleus; Oxytricha; RNA, Protozoan; RNA, Small Nuclear; Sequence Analysis, RNA; Telomere
PubMed: 22900016
DOI: 10.1371/journal.pone.0042371 -
Methods in Cell Biology 2012Tetrahymena thermophila is both a cell and an organism, which combines great intracellular complexity with a remarkable accessibility to investigation using many... (Review)
Review
Tetrahymena thermophila is both a cell and an organism, which combines great intracellular complexity with a remarkable accessibility to investigation using many different approaches. In this review, we start with a description of the elaborate cortical organization of the Tetrahymena cell, and then proceed inward to consider the mitochondria and then the nuclei. For each of these cellular organelles and organelle-systems, first we familiarize the reader with its location in the cell and its structure and ultrastructure, and then we analyze the molecular mechanisms associated with organelle assembly, function, and subdivision. This analysis includes a molecular inventory of the organelle or organelle system, as well as a review of the consequences of modification, disruption or overexpression of important molecular components of each structure or system. Relevant comparisons to results obtained with other well-studied organisms, from Paramecium to Homo sapiens, are also included. Our goal is to provide investigators, in particular those who are new to this organism, both the background and the motivation to work with this model system and achieve further insight into its organization and dynamics.
Topics: Apoptosis Inducing Factor; Cell Membrane; Cell Nucleus Shape; Cilia; DNA Fragmentation; Eukaryotic Cells; Genes, Protozoan; Genome, Mitochondrial; Macronucleus; Micronucleus, Germline; Microscopy, Electron, Transmission; Mitochondria; Protein Transport; Protozoan Proteins; Tetrahymena thermophila
PubMed: 22444144
DOI: 10.1016/B978-0-12-385967-9.00005-0 -
The EMBO Journal Aug 1991Genetic and biochemical studies have shown that cdc2 protein kinase plays a pivotal role in a highly conserved mechanism controlling the entry of cells into mitosis. It...
Genetic and biochemical studies have shown that cdc2 protein kinase plays a pivotal role in a highly conserved mechanism controlling the entry of cells into mitosis. It is generally believed that one function of cdc2 kinase is to phosphorylate histone H1 which in turn promotes mitotic chromosome condensation. However, direct evidence linking H1 phosphorylation to mitotic chromatin condensation is limited and the exact cellular function(s) of H1 phosphorylation remains unclear. In this study, we show that mammalian cdc2 kinase phosphorylates H1 from the amitotic macronucleus of Tetrahymena with remarkable fidelity. Furthermore, we demonstrate that macronuclei from Tetrahymena contain a growth-associated H1 kinase activity which closely resembles cdc2 kinase from other eukaryotes. Using polyclonal antibodies raised against yeast p34cdc2, we have detected a 36 kd immunoactive polypeptide in macronuclei which binds to Suc1 (p13)-coated beads and closely follows H1 kinase activity. Since macronuclei divide without mitotic chromosome condensation, these data demonstrate that H1 phosphorylation by cdc2 kinase may be necessary, but is not sufficient to promote mitotic chromatin condensation. The fact that an activity which strongly resembles mammalian cdc2 kinase is active during cell growth in a nucleus which does not undergo mitosis and chromosome condensation suggests that other factors are needed for a true mitotic division to occur. These data also reinforce the notion that H1 phosphorylation has important functions outside mitosis both in Tetrahymena and in mammalian cells.
Topics: Animals; Blotting, Western; CDC2 Protein Kinase; Cell Nucleus; Electrophoresis, Polyacrylamide Gel; HeLa Cells; Histones; Humans; Immunohistochemistry; Mitosis; Phosphorylation; Substrate Specificity; Tetrahymena
PubMed: 2065655
DOI: 10.1002/j.1460-2075.1991.tb07738.x -
Science China. Life Sciences Oct 2013Most eukaryotes employ a variety of mechanisms to defend the integrity of their genome by recognizing and silencing parasitic mobile nucleic acids. However, recent... (Review)
Review
Most eukaryotes employ a variety of mechanisms to defend the integrity of their genome by recognizing and silencing parasitic mobile nucleic acids. However, recent studies have shown that genomic DNA undergoes extensive rearrangements, including DNA elimination, fragmentation, and unscrambling, during the sexual reproduction of ciliated protozoa. Non-coding RNAs have been identified to program and regulate genome rearrangement events. In Paramecium and Tetrahymena, scan RNAs (scnRNAs) are produced from micronuclei and transported to vegetative macronuclei, in which scnRNA elicits the elimination of cognate genomic DNA. In contrast, Piwi-interacting RNAs (piRNAs) in Oxytricha enable the retention of genomic DNA that exhibits sequence complementarity in macronuclei. An RNA interference (RNAi)-like mechanism has been found to direct these genomic rearrangements. Furthermore, in Oxytricha, maternal RNA templates can guide the unscrambling process of genomic DNA. The non-coding RNA-directed genome rearrangements may have profound evolutionary implications, for example, eliciting the multigenerational inheritance of acquired adaptive traits.
Topics: Ciliophora; DNA, Protozoan; Evolution, Molecular; Gene Rearrangement; Genome, Protozoan; RNA Interference; RNA, Protozoan; RNA, Small Interfering; RNA, Untranslated; Species Specificity
PubMed: 24008384
DOI: 10.1007/s11427-013-4539-4 -
Medecine Sciences : M/S Apr 2005Since the middle of the last century, Paramecium has appeared as an intriguing genetic model, displaying a variety of heritable characters which do not follow the Mendel... (Review)
Review
Since the middle of the last century, Paramecium has appeared as an intriguing genetic model, displaying a variety of heritable characters which do not follow the Mendel laws but are cytoplasmically inherited. The analysis of the hereditary mechanisms at play in this eukaryotic unicellular organism has provided new insight into epigenetics mechanisms. Interestingly, the revealing phenomena concern two pecularities of Paramecium, its highly elaborate surface structure (with thousands of ciliary basal bodies as cytoskeleton organizers), and its nuclear dualism (coexistence of a diploid "germline" micronucleus and a highly polyploid somatic macronucleus devoted to transcription, which contains a rearranged version of the germline genome). Analysis of variant cortical organization has led to the concept of structural inheritance, implying that assembly of new organelles and supramolecular protein complexes is guided by pre-existing organization. Analysis of other cytoplasmically inherited characters revealed that the developing macronucleus is epigenetically programmed by the maternal macronucleus through RNA-mediated, homology-dependent effects, suggesting the transcriptome should be recognized as a third actor in cellular inheritance, along with the "structurome" and the genome.
Topics: Animals; Cell Nucleus; Epigenesis, Genetic; Paramecium
PubMed: 15811302
DOI: 10.1051/medsci/2005214377