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  • 1
    ISSN: 1432-041X
    Keywords: Transcription ; Ribosomal RNA ; Macronuclear development ; Tetrahymena ; Nucleoli
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Conjugation inTetrahymena, as in other ciliated protozoa is both a necessary tool for genetic studies and a potential model system in development. Conjugation is an ordered sequence of events which involves pair formation between two cells of different mating types followed by a precise sequence of nuclear events leading to the establishment of a new recombinant germinal nucleus (micronucleus) and then to the development of a new somatic nucleus (macronnucleus) from the germinal nucleus. The whole process takes about 20 h at 30°C and can be performed with large volumes of cells. The synthesis of ribosomal RNA during macronuclear development was studied in cultures of conjugatingTetrahymena thermophila by following the incorporation of3H-uridine into whole cells and purified ribosomal and pre-ribosomal RNA as well as by measuring bulk-RNA accumulation. In starving cultures and conjugating cultures refed with growth medium during late conjugation, some (background) ribosomal RNA synthesis was detectable 11–12 h after mixing the cells, which is the time when conjugating cells come apart but the macronnucleus is still developing. However, the major burst of rRNA accumulation occurred 13–18 h in refed conjugants. Observation of the conjugating cells by transmission electron microscopy showed that development of nucleoli took place in the macronuclear analagen concomitantly with the major burst of ribosomal RNA synthesis (13–18 h). A nucleolar organization similar to that found in vegetative cells was attained in the macronuclear anlagen 18 h after mixing of the cells.
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  • 2
    ISSN: 1430-3418
    Keywords: Concanavalin A receptors ; Recognition ; Chemosensory behaviour ; Tetrahymena
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between concanavalin A (ConA) receptors and the chemosensory behaviour of the ciliated protozoan Tetrahymena thermophila was studied using the peptide chemoattractants proteose peptone and fibroblast growth factor. Studies on the chemosensory behaviour in semisolid methylcellulose showed that 50 μg/ml ConA selectively inhibited the persistent element of swimming behaviour by reducing time runs of cells responding to proteose peptone from 12.2±4.5 min to 0.8±0.3 min. Methyl-alpha-D-mannoside, but not methyl-alpha-D-galactoside, abolished the inhibitory effect of ConA, suggesting that mannoside-containing ConA receptors are involved in maintaining a persistent swimming behaviour. Control experiments, carried out in liquids where persistent swimming is less important for cellular behaviour, showed that ConA did not affect proteose-peptone-induced chemoattraction under these conditions as measured by a two-phase assay for chemoattraction. Also, no inhibitory effect of ConA could be found on swimming rates when individual velocities of ConA-treated cells were determined. When tested in liquid chemoattraction assays, ConA was found to be a weak but significant chemoattractant. Studies of the cellular location of ConA receptors on the plasma membrane of starved cells showed an unequal distribution. A preferential clustering of receptors at the anterior end of the cell was observed when determined at high concentrations (100 μg/ml) of fluorescent ConA. Methyl-alpha-D-mannoside but not methyl-alpha-D-galactoside abolished the fluorescent ConA labelling, indicating a preferential clustering of these mannoside-containing receptors at the anterior part of the plasma membrane and cilia. At lower concentrations (25 μg/ml), FITC-ConA produced more general labelling of the entire cell membrane. The results suggest that ConA receptors are necessary for the persistent element of swimming and that binding of ConA to its receptors interferes with processes related to signal transduction rather than by limiting the free movement of cilia required for locomotion. The gradient of receptors seen at high FITC-ConA concentrations may be important for a putative spatial chemosensory mechanism, i.e. chemotaxis.
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 217 (1968), S. 1153-1155 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] We have looked for a correlation between the maximal growth rates of different micro-organisms and their contents of DNA, RNA and protein. The organisms tested included twelve bacteria, a haploid and a diploid strain of yeast and a ciliate protozoon, selected to cover a range of generation times ...
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The role of the cilia in the locomotion (“gliding”) of Tetrahymena thermophila in a semi-solid medium has been studied when cells were migrating in gradients of attractant. Video recordings and computer-aided motion analysis of migrating cells and their ciliary activity show that Tetrahymena thermophila migrate by swimming forward in semi-solid methyl cellulose, using their cilia. Ciliary reversals occur at certain intervals and cause a termination (“stop”) of cellular migration. Cells with reversed cilia resume forward migration when normal ciliary beating resumes. In gradients of attractants, cells migrating towards the attractant suppress ciliary reversals, which leads to longer runs between stops than in control cells. Cells migrating away from the attractant have a higher frequency of ciliary reversals than the control cells resulting in shorter runs. Stimulated cells adapt to a particular ambient concentration of attractant several times during migration in the gradient. Adaptation is followed by de-adaptation, which occurs during the “stop”. In the presence of cycloheximide, a strong inhibitor of chemoattraction, the attractant-induced suppression of ciliary reversal is abolished (cells become desensitized to the attractant). It is concluded that Tetrahymena has a short-term memory during adaptation. This is important for the efficiency of migration towards an attractant.
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  • 5
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Starved Tetrahymena thermophila (or cells growing in Holz's defined medium) are attracted by a chemosensory response to complex peptide mixtures as proteose peptone, yeast extract, and extracts of blood platelets containing platelet-derived growth factor. Starved cells are also significantly attracted by mixtures of amino acids and of nucleosides of Holz's defined medium; however, no individual amino acid or nucleoside could be identified as the major chemo-attractant.The positive chemosensory response can be abolished by cycloheximide (CHX) but is insensitive to actinomycin D and puromycin, possibly indicating that de novo RNA and protein synthesis are not necessary for a change in chemosensory behavior. Three mutants resistant to CHX show normal response in the presence of the drug.The possible role of peptides as naturally occurring food signals of Tetrahymena is discussed.
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