Tetrahymena pyriformis

Sonneborn, T. M.

doi:10.1007/978-1-4684-2994-7_19

Cited by 48 publications

(22 citation statements)

References 106 publications

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“…The importance of establishing the presence or absence of gene-sized pieces of macronuclear DNA in Tetrahymena is related to the phenomenon of genetic dislinkage during macronuclear assortment (2). Markers that are observed to segregate together in micronuclear meiosis appear unlinked during random assortment of the macronuclear genetic material (28,29).…”

Section: Discussionmentioning

confidence: 99%

Viscoelastic studies on Tetrahymena macronuclear DNA.

Williams¹,

Fleck²,

Hellier³

et al. 1978

Proc. Natl. Acad. Sci. U.S.A.

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We have used viscoelastometry in -an attempt to understand the physical organization of genetic material in Tetrahymena nuclei. The micronucleus or germ line nucleus is diploid. It divides mitotically during vegetative growth, and five pairs of chromosomes are seen in meiosis. The macronucleus, or somatic nucleus, is approximately 45-ploid, divides amitotically, and has no visible chromosomes at any stage. Viscoelastic analysis of Tetrahymena macronuclei reveals DNA molecules of 2-3 X 1010 daltons accounting for much, if not all, of the macronuclear DNA. Since the average chromosome in the micronucleus contains 2.4-2.7 X 1010 daltons of DNA, we deduce that the macronucleus of Tetrahymena contains chromosome-sized DNA molecules. The ciliated protozoa, Tetrahymena, are remarkable for their nuclear dimorphism; they possess a transcriptionally inactive, diploid, germinal micronucleus, and a transcriptionally active, polyploid, somatic macronucleus. During vegetative growth the micronucleus divides mitotically while the macronucleus divides amitotically. Sexual conjugation results in degeneration of the macronucleus while the micronucleus undergoes meiosis. Subsequent reciprocal exchange and fusion of two haploid gametic nuclei maintains the genetic continuity of the organism. From a daughter of the zygotic nucleus formed during conjugation a new macronucleus arises by amplification of the genetic material. Presumably, before macronuclear differentiation occurs the micronucleus and the macronuclear anlage contain identical genetic material. However, both go on to develop into quite different organelles with distinctly different functions. The mechanism by which Tetrahymena establish and maintain nuclear dimorphism remains an intriguing unsolved problem.At the present time the genetics and molecular architecture of the nuclei of Tetrahymena are being intensively studied (for reviews see refs. 1-4). The diploid micronucleus contains five pairs of approximately equal-sized chromosomes clearly visible during conjugation. Genetic markers on this germinal nucleus are distributed in the normal mendelian fashion. The macronucleus, by comparison, does not contain visible chromosomes, but rather many "chromatin bodies," and genetic markers are apparently segregated randomly during vegetative fission. On the basis of cytological (5), genetic (6), and cytospectrophotometric (7,8) evidence, the macronucleus appears to contain 45 haploid genomes after cell division, with each genome containing at least 90% of the sequences found in the micronuclear genome (9).Of central importance to an adequate understanding of Tetrahymena nuclear dimorphism is an explanation of how DNA is organized within the two types of nuclei. Conceivably, micronuclear DNA resembles DNA from other organisms in which chromosomes are visible, such as Drosophila (10) and yeast (11,12), in which chromosome-sized DNA molecules are observed, or dinoflagellates (13) and mice (14), in which large molecules somewhat smaller than chromosome size are observa...

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Section: Discussionmentioning

confidence: 99%

Viscoelastic studies on Tetrahymena macronuclear DNA.

Williams¹,

Fleck²,

Hellier³

et al. 1978

Proc. Natl. Acad. Sci. U.S.A.

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“…However, unlike the micronucleus, the macronucleus divides amitotically, being pinched apart during cytokinesis. The amitotic division of the macronucleus separates the somatic genome imperfectly and can lead to phenotypic assortment of a macronuclear allele (Sonneborn, 1974). Because the micronucleus is not transcribed, the accurate segregation of micronuclear chromosomes is not required for vegetative growth.…”

Section: Introductionmentioning

confidence: 99%

Gene Knockouts Reveal Separate Functions for Two Cytoplasmic Dyneins inTetrahymena thermophila

Lee

Wisniewski

Dentler

et al. 1999

MBoC

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In many organisms, there are multiple isoforms of cytoplasmic dynein heavy chains, and division of labor among the isoforms would provide a mechanism to regulate dynein function. The targeted disruption of somatic genes in Tetrahymena thermophila presents the opportunity to determine the contributions of individual dynein isoforms in a single cell that expresses multiple dynein heavy chain genes. Substantial portions of two Tetrahymena cytoplasmic dynein heavy chain genes were cloned, and their motor domains were sequenced. Tetrahymena DYH1 encodes the ubiquitous cytoplasmic dynein Dyh1, and DYH2 encodes a second cytoplasmic dynein isoform, Dyh2. The disruption of DYH1, but not DYH2, resulted in cells with two detectable defects: 1) phagocytic activity was inhibited, and 2) the cells failed to distribute their chromosomes correctly during micronuclear mitosis. In contrast, the disruption of DYH2 resulted in a loss of regulation of cell size and cell shape and in the apparent inability of the cells to repair their cortical cytoskeletons. We conclude that the two dyneins perform separate tasks in Tetrahymena. INTRODUCTIONDynein is a molecular motor that transduces chemical energy into mechanical motion along microtubules. There are two functional classes of dynein: axonemal dynein that produces the propagated bending of cilia and of eukaryotic flagella and nonaxonemal or "cytoplasmic" dynein that performs functions other than ciliary beating. Cytoplasmic dynein is implicated in a variety of intracellular movements, including fast retrograde transport (Schroer et al., 1989;Muresan et al., 1996), slow axonal transport (Cleveland and Hoffman, 1991;Dillman et al., 1996), mediation of the trafficking of membrane-bounded organelles (Corthesy-Theulaz et al., 1992;Aniento et al., 1993;Fath et al., 1994;Oda et al., 1995;Holleran et al., 1996), the organization and separation of the bipolar mitotic spindle (Verde et al., 1991;Vaisberg et al., 1993;Saunders et al., 1995;Echeverri et al., 1996), and postmitotic nuclear migrations in yeast and filamentous fungi (Eshel et al., 1993;Li et al., 1993;Plamann et al., 1994;Xiang et al., 1994;Inoue et al., 1998).The realization that dynein performs so many different tasks and the discovery that many organisms express multiple dynein heavy chain genes lead to the hypothesis that different dynein isoforms perform different cellular tasks (reviewed in Asai, 1996). Cilia and eukaryotic flagella provide clear examples of dynein functional specialization (Piperno, 1990). The close coordination of ϳ12 distinct axonemal dynein heavy chains produces axonemal bending (e.g., Piperno and Ramanis, 1991;Mastronarde et al., 1992; reviewed in Brokaw, 1994).The functional specialization of the cytoplasmic dyneins is not well understood. All eukaryotes examined express homologues of the ubiquitous Dyh1 (also called MAP1C, cDHC1, DHC1a), and some organisms, including Saccharomyces, Aspergillus, Neurospora, and Dictyostelium, apparently have only this dynein. In the analysis of the family of dynein gen...

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“…All cells which completed mating (crosses A and B, Table 5) were sensitive to BUdR, indicating that the phenotype is recessive. After phenotypic assortment (26), BUdR-resistant cells could be isolated.…”

Section: Resultsmentioning

confidence: 99%

Mutant strains of Tetrahymena thermophila defective in thymidine kinase activity: biochemical and genetic characterization.

Cornish¹,

Pearlman²

1982

Mol. Cell. Biol.

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Three mutant strains, one conditional, of Tetrahymena thermophila were defective in thymidine phosphorylating activity in vivo and in thymidine kinase activity in vitro. Nucleoside phosphotransferase activity in mutant cell extracts approached wild-type levels, suggesting that thymidine kinase is responsible for most, if not all, thymidine phosphorylation in vivo. Thymidine kinase activity in extracts of the conditional mutant strain was deficient when the cells were grown or assayed or both at the permissive temperature, implying a structural enzyme defect. Analysis of the reaction products from in vitro assays with partially purified enzymes showed that phosphorylation by thymidine kinase and nucleoside phosphotransferase occurred at the 5' position. Genetic analyses showed that the mutant phenotype was recessive and that mutations in each of the three mutant strains did not complement, suggesting allelism.

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Tetrahymena pyriformis

Cited by 48 publications

References 106 publications

Viscoelastic studies on Tetrahymena macronuclear DNA.

Viscoelastic studies on Tetrahymena macronuclear DNA.

Gene Knockouts Reveal Separate Functions for Two Cytoplasmic Dyneins inTetrahymena thermophila

Mutant strains of Tetrahymena thermophila defective in thymidine kinase activity: biochemical and genetic characterization.

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