Unusually high evolutionary rate of the elongation factor 1 alpha genes from the Ciliophora and its impact on the phylogeny of eukaryotes.
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The elongation factor 1 alpha (EF-1 alpha) has become widely employed as a phylogenetic marker for studying eukaryotic evolution. However, a disturbing problem, the artifactual polyphyly of ciliates, is always observed. It has been suggested that the addition of new sequences will help to circumvent this problem. Thus, we have determined 15 new ciliate EF-1 alpha sequences, providing for a more comprehensive taxonomic sampling of this phylum. These sequences have been analyzed together with a representation of eukaryotic sequences using distance-, parsimony-, and likelihood-based phylogenetic methods. Such analyses again failed to recover the monophyly of Ciliophora. A study of the substitution rate showed that ciliate EF-1 alpha genes exhibit a high evolutionary rate, produced in part by an increased number of variable positions. This acceleration could be related to alterations of the accessory functions acquired by this protein, likely to those involving interactions with the cytoskeleton, which is very modified in the Ciliophora. The high evolutionary rate of these sequences leads to an artificial basal emergence of some ciliates in the eukaryotic tree by effecting a long-branch attraction artifact that produces an asymmetric topology for the basal region of the tree. The use of a maximum-likelihood phylogenetic method (which is less sensitive to long-branch attraction) and the addition of sequences to break long branches allow retrieval of more symmetric topologies, which suggests that the asymmetric part of the tree is most likely artifactual. Therefore, the sole reliable part of the tree appears to correspond to the apical symmetric region. These kinds of observations suggest that the general eukaryotic evolution might have consisted of a massive radiation followed by an increase in the evolutionary rates of certain groups that emerge artificially as early branches in the asymmetric base of the tree. Ciliates in the case of the EF-1 alpha genes would offer clear evidence for this hypothesis. (+info)
Ultrastructure of meiosis-inducing (heterotypic) and non-inducing (homotypic) cell unions in conjugation of Blepharisma.
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Cells of mating types I and II of Blepharisma japonicum interact with each other and unite in heterotypic (type I-type II) or homotypic (type I-type I, type II-type II) pairs. Heterotypic pairs undergo meiosis and other nuclear changes of conjugation, while homotypic pairs remain united for days without the nuclear changes taking place. We compared cell unions of these two kinds of pairs at the ultrastructural level. In the homotypic union, cell membranes are closely juxtaposed, separated by a distance of about 20 nm. This arrangement is interrupted in some places by vacuoles and small cytoplasmic bridges. Saccule-like structures tend to be more abundant near the united surfaces. Microtubules running at right or slightly obtuse angles with the cell surface (PACM microtubules) are characteristically present at the united region of cells. These structures are very similar to those observed in earlier stages of the heterotypic union. However, in homotypic pairs, cells unite only at the anterior half of the peristome, while in heterotypic pairs cells unite also at the posterior half of the peristome, where the cell membrane totally disappears in later stages. PACM microtubules persist for at least 18 h in homotypic unions, while they disappear within a few hours in heterotypic unions. These differences between the two kinds of cell union are discussed in relation to the initiation mechanism of meiosis and other nuclear changes of conjugation. Similarities between homotypic union and cell junctions in multicellular organisms are also discussed. (+info)
Dermatitis with invasive ciliated protozoa in dolphins that died during the 1987-1988 Atlantic Bottlenose Dolphin morbilliviral epizootic.
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Dermatitis with intradermal cilated protozoa was identified in 18 of 95 (19%) Atlantic Bottlenose Dolphins (Tursiops truncatus) that died during the 1987-1988 Atlantic-dolphin morbillivirus epizootic. The lesions were characterized by focally extensive suppurative and histiocytic dermatitis and cellulitis with ulceration and variable numbers of dermal and hypodermal ciliates. Vasculitis, thrombosis, and/or intravascular ciliates were rarely present. In one dolphin, there was an associated lymphadenitis with ciliates, and in another, bronchopneumonia with rare intrabronchiolar ciliates. Ten of the dolphins were female, and eight were male. The animals ranged in length from 148 to 260 cm. Eleven were from Virginia, four were from New Jersey, and three were from Florida. In 13 dolphins, results of immunohistochemical and/or polymerase chain reaction (PCR) tests were positive for morbillivirus infection. Results of immunohistochemical tests were negative in four dolphins that were not also tested with PCR. Results were also negative in one dolphin tested using both methods. Nine dolphins had concomitant bacterial, fungal, and/or other protozoal infections. Fourteen other dolphins with ciliate-associated dermatitis were identified from 414 Atlantic bottlenose dolphin cases (3%) archived at the Armed Forces Institute of Pathology. The incidence of dermatitis with invasive ciliates is much greater in dolphins that died during the 1987-1988 epizootic. (+info)
Rumen ciliate protozoal fauna of native sheep, friesian cattle and dromedary camel in Libya.
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Rumen ciliate species and composition were surveyed on the native sheep, Friesian-cattle and dromedary (one-humped) camels kept in Libya. As a result of survey, 5 genera including 14 species with 5 formae in native sheep, 9 genera including 27 species with 6 formae in Friesian-cattle and 6 genera including 13 species and 7 formae in dromedary camels were identified. All of the ciliate species and their percentage composition detected from the Libyan sheep and cattle in this examination were similar to those found from corresponding animals in the other countries. Libyan camels lacked some peculiar ciliate species found from camels in the other countries, but had many cosmopolitan species common with those in the domestic ruminants, suggesting that ciliate faunae of camel are easily affected by the other domestic ruminants kept together. The ciliate density was estimated as 105/ml in every host species. (+info)
Factors affecting the uptake and metabolism of soluble carbohydrates by the rumen ciliate Dasytricha ruminantium isolated from ovine rumen contents by filtration.
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A filtration technique is described whereby metabolically-active suspensions of Dasytricha ruminantium can be isolated from rumen contents with negligible contamination by bacteria or other protozoa. The effects of environmental factors and of the diurnal cycle of the rumen on the uptake and metabolism of soluble carbohydrates by these isolated cells were examined. The principal contribution of the protozoan metabolic end-products to the host ruminant is the supply of lactic, acetic and butyric acids during periods when soluble sugars are in excess. (+info)
Anti-immunoglobulin antisera used in an ELISA to detect antibodies in barramundi Lates calcarifer to Cryptocaryon irritans.
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Immunoglobulins (Ig) in serum from barramundi vaccinated with bovine serum albumin (BSA) were purified by ammonium sulphate precipitation and affinity chromatography using BSA as the ligand. The BSA-binding activity of eluted putative Ig fractions was assessed by enzyme-linked immunosorbent assay (ELISA) before being pooled and characterised by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Double affinity purification did not improve the purity of the Ig preparation compared to single affinity purification. Barramundi Ig were injected into sheep to produce anti-Ig antisera which were assessed in an indirect ELISA as the secondary antibody to detect serum Ig in barramundi vaccinated with Cryptocaryon irritans theronts. Affinity-purified Ig induced a more specific reagent for use as secondary antibody in ELISA than did normal whole-barramundi sera. The heavy (H) chain of barramundi Ig had an apparent molecular weight of 70 kDa while that of the light (L) chain was 27 kDa in SDS-PAGE studies. Under non-reducing conditions 2 putative populations of Ig were identified, at 768 and 210 kDa. The N-terminal sequence of the barramundi Ig H chain showed 78% homology with channel catfish Ictalurus punctatus Ig H chain sequence. (+info)
Graviresponses of certain ciliates and flagellates.
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Protozoa are eukaryotic cells and represent suitable model systems to study the mechanisms of gravity perception and signal transduction due to their clear gravity-induced responses (gravitaxis and gravikinesis). Among protists, parallel evolution for graviperception mechanisms have been identified: either sensing by distinct stato-organelles (e.g., the Muller vesicles of the ciliate Loxodes) or by sensing the density difference between the whole cytoplasm and the extracellular medium (as proposed for Paramecium and Euglena). These two models are supported by experiments in density-adjusted media, as the gravitaxis of Loxodes was not affected, whereas the orientation of Paramecium and Euglena was completely disturbed. Both models include the involvement of ion channels in the cell membrane. Diverse experiments gave new information on the mechanism of graviperception in unicellular systems, such as threshold values in the range of 10% of gravity, relaxation of the responses after removal of the stimulus, and no visible adaptation phenomena during exposure to hypergravity or microgravity conditions for up to 12 days. (+info)
A subtelomeric DNA sequence is required for correct processing of the macronuclear DNA sequences during macronuclear development in the hypotrichous ciliate Stylonychia lemnae.
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During macronuclear differentiation in ciliated protozoa a series of programed DNA reorganization processes occur. These include the elimination of micronuclear-specific DNA sequences, the specific fragmentation of the genome into small gene-sized DNA molecules, the de novo addition of telomeric sequences to these DNA molecules and the specific amplification of the remaining DNA molecules. Recently we constructed a vector containing the modified micronuclear version of macronuclear destined DNA sequences that was correctly fragmented and telomeres were added de novo after injection into the developing macronucleus. It therefore must contain all the cis- acting sequences required for these processes. We made a series of vectors deleting different sequences from the original vector. It could be shown that at least in the case studied here no micronuclear-specific sequences are required for specific fragmentation of the genome and telomere addition. However, a short subtelomeric sequence at the 3[prime]-end is essential for these processes, whereas no specific cut seems to occur at the 5[prime]-end. In addition, we can show that the processing activity is restricted to a short period of time during macronuclear differentiation and that a preceding transcription is required for correct processing of macronuclear-destined DNA sequences. Possible mechanisms of these processes will be discussed. (+info)