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Dieter Ammermann
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ABSTRACT: It was investigated whether (1) the number of cilia of the dorsal kineties 3 and 4 and (2) the cell length are species-specific characters which can be used to distinguish the sibling species S. mytilus and S. lemnae. The number of cilia of the dorsal kineties 3 and 4 is a relatively constant, reliable species-specific character in all investigated strains of both species and rather independent from the origin and the nutritional condition of the cells. The cell length is also a reliable species character, if strains of both species from Germany are compared (under identical nutritional conditions). However, all S. mytilus strains from China, Australia and Peru are significantly smaller forming one (or some) "small" subpopulations or subspecies, compared with a "big" subpopulation from Germany. The small ones cannot always be distinguished by size alone from S. lemnae cells. Thus the cell size in S. mytilus is not in all geographic regions a species character, but can be used to characterize subspecies.
European Journal of Protistology 07/2008; 44(4):263-8. · 1.97 Impact Factor
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ABSTRACT: ABSTRACTA new species, Pleurotricha indica n. sp., is described, characterized by an average size of 220 × 119 μm, a firm and inflexible body, six rows of dorsal kineties, one left and two right rows of marginal cirri, and an “Oxytricha-like” pattern of ventral cirri. The parts of the macronucleus are variable in shape and number. The comparison with other members of the genus shows that P. indica differs from other congeneric species in the combination of these characters.
Journal of Eukaryotic Microbiology 04/2007; 34(1):31 - 34. · 2.66 Impact Factor
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ABSTRACT: Ciliated protists are model organisms for a number of molecular phenomena including telomerase function, self-splicing introns, and an RNA interference-related mechanism in programmed DNA elimination. Despite this relevance, our knowledge about promoters and transcriptional regulation in these organisms is very limited. The macronuclear genome of stichotrichous ciliates consists of minichromosomes which typically encode a single gene. The 5' nontranscribed spacers are usually no longer than 400 bp and highly suitable for promoter characterizations. We used microinjection of two artificial and differently tagged alpha1 tubulin minichromosomes into the macronucleus of Stylonychia lemnae as a means to characterize in detail the corresponding promoter. Clonal cell lines that stably maintained both minichromosomes were generated, enabling comparative expression analysis by primer extension assays. Deletion and block substitution mutations of one of the minichromosomes revealed a TATA-like element, a putative initiator element, and two distinct upstream sequence elements (USEs). Determination of transcription initiation sites and a sequence alignment indicated that both TATA-like and initiator elements are conserved components of S. lemnae minichromosomes, whereas the USEs appear to be specific for the alpha1 tubulin minichromosome. The alpha2 tubulin minichromosome promoter is very short, comprising the two proximal elements but not the USEs. Despite the latter finding, up-regulation of alpha-tubulin expression in cells treated with concanavalin A activated the alpha2 but not the alpha1 tubulin promoter. These results therefore show that gene expression regulation in S. lemnae occurs at the level of transcription initiation on the basis of structurally different promoters.
Eukaryotic Cell 02/2007; 6(1):28-36. · 3.60 Impact Factor
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ABSTRACT: A sexually reproducing hypotrichous ciliates undergo senescence which is in general attributed to degenerative processes in the macronucleus, assuming that loss of viability is based on loss of genetic elements. It is generally accepted that the genetic elements in the macronucleus of hypotrichs segregate randomly, a process which potentially can lead to aneuploid imbalances in the distribution of gene copies. It is, however, unclear whether there are mechanisms which compensate for such imbalances such that each genetic element regains its predetermined copy number (regulatory model, conserving euploidy), or whether the genetic elements only double, so that genetic imbalances can be inherited to further generations (stochastic model, allowing aneuploidy). By means of mathematical modeling and simulations, we investigate these two models with respect to the number of generations a lineage of hypotrichs can survive under asexual conditions. Whereas the regulatory model cannot explain senescence in hypotrichs, the stochastic model provides plausible results which, however, strongly depend on the assumed distribution of copy numbers which we investigate by means of three examples. For both models, simple prediction formulae for the approximate survival time of asexually reproducing ciliates are provided.
Protist 04/2004; 155(1):45-52. · 3.14 Impact Factor
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ABSTRACT: The small subunit rDNAs of five species belonging to the Euplotidae and eight species of the Oxytrichidae were sequenced to obtain a more detailed picture of the phylogenetic relationships within the Spirotrichea (Ciliophora). Various tree reconstruction algorhythms yielded nearly identical topologies. All Euplotidae were separated from the other Spirotrichea by a deep split. Further, a large genetic distance between the marine genus Moneuplotes and the freshwater species of Euplotoides was found. Differences between the methods used occurred only within the Oxytrichidae. Whereas the monophyly of the Stylonychinae was supported in all trees, the monophyly of the Oxytrichinae was not. However, the molecular data support the morphological and ontogenetic evidence that the pattern of 18 frontal–ventral–transversal cirri evolved in the stemline of the Oxytrichidae and was modified several times independently. Our results are also in agreement with taxonomic revisions: the separation of both Sterkiella nova from Oxytricha and Tetmemena pustulata from Stylonychia.
Molecular Phylogenetics and Evolution 11/2001; · 3.61 Impact Factor
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ABSTRACT: All Stylonychia mytilus-like ciliates which were collected and sent to us during the last 20 years belonged either to S. mytilus or to a new species, S. lemnae, which is described here. The only morphological differences are the shape and the size. Stylonychia mytilus that have been starved for one day average 300 μm in length, and S. lemnae starved for a day are 230 μm long. The occurrence of mating types is described.
Journal of Eukaryotic Microbiology 04/1983; 30(2):290 - 294. · 2.66 Impact Factor
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ABSTRACT: A differentiation, based on morphological characters, between Stylonychia mytilus and Stylonychia lemnae is very difficult, especially for non-specialists. These two sibling species were considered as one species, S. mytilus, until detailed cytological and genetic studies could show the existence of two genetically isolated varieties. Further morphological and biochemical analyses verified the separation and finally in 1983 a new species S. lemnae was described. The examination of several isoenzymes revealed unambiguous differences in the banding pattern of isocitrate dehydrogenase (IDH) between these two species. Therefore, the IDH gene of 30 isolates of S. lemnae and S. mytilus coming from various regions all over the world were amplified and sequenced. The sequence analyses revealed intraspecific as well as interspecific substitutions, which were used for the development of species-specific PCR primers for both species. Application of these species-specific primer pairs now allows a very easy and clear identification of both sibling species.
Journal of Eukaryotic Microbiology 53(5):343-7. · 2.66 Impact Factor
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ABSTRACT: Stylonychia lemnae (Ciliophora, Spirotrichea), a member of the Stylonychia mytilus complex, shows a global distribution, occurring in many temperate fresh waters. As there are few descriptions of biogeographical patterns of ubiquitously occurring ciliated protozoans, we report a distinct sequence difference within the small subunit ribosomal DNA gene, which occurs only in the clones of S. lemnae isolated from the surroundings of Ithaca (USA) in comparison with clones of the same species from different regions in Europe, Asia, and South Africa.
Journal of Eukaryotic Microbiology 53(4):308-9. · 2.66 Impact Factor
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ABSTRACT: Macronuclei of Stylonychia lemnae contain millions of gene sized minichromosomes. These minichromosomes in general harbour only one gene. Their nontranscribed regions are usually less than 400 bp long and most likely carry the signals for DNA replication and transcription. Therefore, S. lemnae seems to be an ideal object to study these processes in a protist organism. By microinjecting defined linear minichromosomal DNA directly into macronuclei of vegetative cells, we have developed a suitable in vivo assay system for S. lemnae. Transfections were carried out with α1 tubulin minichromosomes whose gene was internally tagged by a 19 bp-long insertion. Although the endogenous ocl tubulin minichromosome is present in approximately 100,000 copies per cell, clonal cell lines were generated which stably contained tagged minichromosomes in up to a fivefold excess of endogenous copy numbers. As demonstrated by Southern blot analysis, the copy number of endogenous α1 tubulin minichromosomes was not reduced in these cell lines, and transfected minichromosomes were not noticeably rearranged by the cells. Moreover, tagged ocl tubulin genes were unequivocally expressed. Transcription of these genes was initiated correctly, and the amount of transcript present in steady-state RNA correlated with gene copy number.
European Journal of Protistology. 35(1):70-80.
