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At least 19 recordsLinked to original sources
PubMed1995

Apoptosis in a unicellular eukaryote (Trypanosoma cruzi): implications for the evolutionary origin and role of programmed cell death in the control of cell proliferation, differentiation and survival.

The origin of programmed cell death (PCD) has been linked to the emergence of multicellular organisms. Trypanosoma cruzi, a member of one of the earliest diverging eukaryotes, is a protozoan unicellular parasite that undergoes three major differentiation changes and requires two different hosts. We report that the in vitro differentiation of the proliferating epimastigote stage into the G0/G1 arrested trypomastigote stage is associated with massive epimastigote death that shows the cytoplasmic and nuclear morphological features and DNA fragmentation pattern of apoptosis, the most frequent phenotype of PCD in multicellular organisms. Apoptosis could be accelerated or prevented by modifying culture conditions or cell density, indicating that extracellular signals influenced the epimastigote decision between life and death. Epimastigotes responded to complement-mediated immunological agression by undergoing apoptosis, while undergoing necrosis in response to nonphysiological saponin-mediated damage. PCD may participate into the optimal adaptation of T. cruzi to its different hosts, and the avoidance of a local competition between a G0/G1 arrested stage and its proliferating progenitor. The existence of a regulated cell death programme inducing an apoptotic phenotype in a unicellular eukaryote provides a paradigm for a widespread role for PCD in the control of cell survival, which extends beyond the evolutionary constraints that may be specific to multicellular organisms and raises the question of the origin and nature of the genes involved. Another implication is that PCD induction could represent a target for therapeutic strategies against unicellular pathogens.

Journal Article↗
PubMed2006

[The role of protein kinase cascades in stress signal transduction in unicellular eukaryotes].

The review summarizes current data on transduction mechanisms of stress signals by protein kinase cascades in unicellular eukaryotes. The role of sensor histidine kinases, tyrosine kinases, PKC, and cyclic nucleotid-dependent kinases are reviewed. Special attention is paid to a comparative analysis of transduction mechanisms of stress signals in vertebrates and unicellular eukaryotes.

Animals↗
PubMed2000

Compositional pressure and translational selection determine codon usage in the extremely GC-poor unicellular eukaryote Entamoeba histolytica.

It is widely accepted that the compositional pressure is the only factor shaping codon usage in unicellular species displaying extremely biased genomic compositions. This seems to be the case in the prokaryotes Mycoplasma capricolum, Rickettsia prowasekii and Borrelia burgdorferi (GC-poor), and in Micrococcus luteus (GC-rich). However, in the GC-poor unicellular eukaryotes Dictyostelium discoideum and Plasmodium falciparum, there is evidence that selection, acting at the level of translation, influences codon choices. This is a twofold intriguing finding, since (1) the genomic GC levels of the above mentioned eukaryotes are lower than the GC% of any studied bacteria, and (2) bacteria usually have larger effective population sizes than eukaryotes, and hence natural selection is expected to overcome more efficiently the randomizing effects of genetic drift among prokaryotes than among eukaryotes. In order to gain a new insight about this problem, we analysed the patterns of codon preferences of the nuclear genes of Entamoeba histolytica, a unicellular eukaryote characterised by an extremely AT-rich genome (GC = 25%). The overall codon usage is strongly biased towards A and T in the third codon positions, and among the presumed highly expressed sequences, there is an increased relative usage of a subset of codons, many of which are C-ending. Since an increase in C in third codon positions is 'against' the compositional bias, we conclude that codon usage in E. histolytica, as happens in D. discoideum and P. falciparum, is the result of an equilibrium between compositional pressure and selection. These findings raise the question of why strongly compositionally biased eukaryotic cells may be more sensitive to the (presumed) slight differences among synonymous codons than compositionally biased bacteria.

Animals↗
PubMed1998

Signaling in unicellular eukaryotes.

Aspects of intercellular and intracellular signaling systems in cell survival, proliferation, differentiation, chemosensory behavior, and programmed cell death in free-living unicellular eukaryotes have been reviewed. Comparisons have been made with both bacteria and metazoa. The central organisms were flagellates (Trypanosoma, Leishmania, and Crithidia), slime molds (Dictyostelium), yeast cells (Saccharomyces cerevisiae), and ciliates (Paramecium, Euplotes, and Tetrahymena). There are two novel aspects in this review. First, cellular responses are viewed in an evolutionary perspective, rather than from the more prevailing one, in which the unicellular eukaryotes are seen by the mammalian organisms. Second, results obtained with cell cultures in minimal, chemically defined nutrient media at low cell densities where intercellular signaling is strongly reduced are discussed. These results shed light on control mechanisms and their cooperation inside the living cell. Intracellular systems have many common features in unicellular and multicellular organisms.

Animals↗
PubMed2003

Identification of organelles in bacteria similar to acidocalcisomes of unicellular eukaryotes.

Acidocalcisomes are acidic calcium storage compartments described in several unicellular eukaryotes, including trypanosomatid and apicomplexan parasites, algae, and slime molds. In this work, we report that the volutin granules of Agrobacterium tumefaciens possess properties similar to the acidocalcisomes. Transmission electron microscopy revealed that each intracellular granule was surrounded by a membrane. X-ray microanalysis of the volutin granules showed large amounts of phosphorus, magnesium, potassium, and calcium. Calcium in the volutin granules increased when the bacteria were incubated at high extracellular calcium concentration. Immunofluorescence and immunoelectron microscopy, using antisera raised against peptide sequences conserved in the A. tumefaciens proton pyrophosphatase, indicated localization in intracellular vacuoles. Purification of the volutin granules using iodixanol density gradients indicated a preferential localization of the pyrophosphatase activity in addition to high concentrations of phosphate, pyrophosphate, short- and long-chain polyphosphate, but lack of markers of the plasma membrane. The pyrophosphatase activity was potassium-insensitive and inhibited by the pyrophosphate analogs, amynomethylenediphosphonate and imidodiphosphate, by dicyclohexylcarbodiimide, and by the thiol reagent N-ethylmaleimide. Polyphosphate was also localized to the volutin granules by 4',6'-diamino-2-phenylindole staining. The organelles were acidic, as demonstrated by staining with LysoSensor blue DND-167, a dye especially used to detect very acidic compartments in cells, and cycloprodigiosin, a compound isolated from a marine bacterium that has been shown to uncouple proton pyrophosphatase activity acting as a chloride/proton symport. The results suggest that acidocalcisomes arose before the prokaryotic and eukaryotic lineages diverged.

Agrobacterium tumefaciens↗
PubMed1985

Further study on polyamines in primitive unicellular eukaryotic algae.

The possible usefulness of polyamines as chemotaxonomic markers has been investigated in eukaryotic algae. Polyamines were analyzed in 12 species of primitive unicellular eukaryotic algae including some anomalous species. Norspermidine and norspermine in addition to putrescine and spermidine are widely distributed in most unicellular species of the algae. However, neither norspermidine nor norspermine was found in the taxonomically conflicting algae, Cyanophora and Glaucocystis, which contain cyanellae, or in a primitive red alga, Porphyridium. A thermoacidophilic eukaryotic alga, Cyanidium, is rich in both norspermidine and norspermine. Appreciable amounts of spermine and sym-homospermidine were detected only in the species belonging to the Rhodophyta (red algae).

Eukaryota↗
PubMedDate not supplied

Evolutionary conservancy of the endocytic and trafficking machinery in the unicellular eukaryote Paramecium.

Molecular search for the homologues of the mammalian proteins in the unicellular eukaryote Paramecium involved in endocytosis and membrane trafficking is discussed. We cloned and sequenced the gene fragments encoding the following components participating in endosome formation, sorting and maturation of the proprotein precursors, respectively, dynamin 2, Rab7 and furin. There is a proof that all these genes are expressed in this unicellular organism. The function of the identified immunoanalogues of the above described components of Paramecium endocytic machinery as well as a high degree of sequence homology to the respective human counterparts points to the evolutionary conservancy of these pathways.

Animals↗
PubMed2002

On the evolution of programmed cell death: apoptosis of the unicellular eukaryote Leishmania major involves cysteine proteinase activation and mitochondrion permeabilization.

Leishmania major is a protozoan parasite from one of the most ancient phylogenic branches of unicellular eukaryotes, and containing only one giant mitochondrion. Here we report that staurosporine, that induces apoptosis in all mammalian nucleated cells, also induces in L. major a death process with several cytoplasmic and nuclear features of apoptosis, including cell shrinkage, phosphatidyl serine exposure, maintenance of plasma membrane integrity, mitochondrial transmembrane potential (DeltaPsim) loss and cytochrome c release, nuclear chromatin condensation and fragmentation, and DNA degradation. Nuclear apoptosis-like features were prevented by cysteine proteinase inhibitors, and cell free assays using dying L. major cytoplasmic extracts indicated that the cysteine proteinases involved (i) also induced nuclear apoptosis-like features in isolated mammalian nuclei, and (ii) shared at least two nuclear substrates, but no cleavage site preference, with human effector caspases. Finally, isolated L. major mitochondria released cytochrome c and cysteine proteinases with nuclear pro-apoptotic activity when incubated with human recombinant Bax, even (although much less efficiently) when Bax was deleted of its transmembrane domain required for insertion in mitochondrial outermembranes, implying that L. major mitochondrion may express proteins able to interact with Bax. The recruitment of cysteine proteinases and mitochondria to the cell death machinery may be of very ancient evolutionary origin. Alternately, host/parasite interactions may have exerted selective pressures on the cell death phenotype of kinetoplastid parasites, resulting in the more recent emergence of an apoptotic machinery through a process of convergent evolution.

Animals↗
PubMedDate not supplied

Immunoanalogue of vertebrate beta-adrenergic receptor in the unicellular eukaryote Paramecium.

Cell fractionation, SDS-PAGE, quantitative Western blot, confocal immunolocalization and immunogold labelling were performed to find an interpretation of the physiological response of the unicellular eukaryote Paramecium to beta-adrenergic ligands. The 69 kDa polypeptide separated by SDS-PAGE in S2 and P2 Paramecium subcellular fractions cross-reacted with antibody directed against human beta2-adrenergic receptor. This was detected by Western blotting followed by chemiluminescent detection. Quantitative image analysis showed that beta-selective adrenergic agonist (-)-isoproterenol--previously shown to enhance phagocytic activity--evoked redistribution of the adrenergic receptor analogue from membraneous (P2) to cytosolic (S2) fraction. The relative increase in immunoreactive band intensity in S2 reached 80% and was paralleled by a 59% decrease in P2 fraction. Confocal immunofluorescence revealed beta2-adrenergic receptor sites on the cell surface and at the ridge of the cytopharynx--where nascent phagosomes are formed. This localization was confirmed by immunoelectron microscopy. These results indicate that the 69 kDa Paramecium polypeptide immunorelated to vertebrate beta2-adrenergic receptor appeared in this evolutionary ancient cell as a nutrient receptor.

Animals↗
PubMed2005

Are yeasts free-living unicellular eukaryotes?

Yeasts are defined as unicellular fungi, yet many recent observations suggest their whole lifestyle is anything but unicellular. This review surveys the evidence that yeasts are really social organisms with cell-to-cell communication.

Cell Communication↗
PubMed1988

Partial phylogeny of the unicellular eukaryotes based on rapid sequencing of a portion of 28S ribosomal RNA.

Using a rapid rRNA sequencing technique, we have determined the sequence of the 400 nucleotides located at the 5' end of the large subunit rRNA molecule from eight species of unicellular eukaryotes (protists). This region contains a pair of conservative domains well-suited for long-range phylogenetic evaluations among eukaryotes, due both to their substantia, length and to their intrinsic rate of sequence variation during evolution. It also comprises a central more rapidly evolving portion, which allows for a fine tuning of distance evaluation between closely related species. Molecular distances were computed between the aligned nucleotides of all presently available protist sequences and were used to derive a tentative dendrogram. Within the limitations inherent to this approach, a number of interesting observations emerge: The various protist groups appear to have separated very early from each other. The most deeply divergent protists belong to a number of orders of flagellates (mastigotes), suggesting a very ancient origin for organelles containing a 9 + 2 microtubular arrangement. Ciliates emerged late among eukaryotes, suggesting that their peculiar genetic code was derived secondarily. Moreover, a dinoflagellate clusters with ciliates, thus making it likely that the unusual features of nuclear organization and mitosis of this group are not primitive but derived characters. Finally, within groups, taxonomic and evolutionary inferences appear to be feasible using this portion of the rRNA.

Animals↗
PubMed1980

Evolutionary origins of vertebrate hormones: substances similar to mammalian insulins are native to unicellular eukaryotes.

Tetrahymena pyriformis, Neurospora crassa, and Aspergillus fumigatus that had been grown in simple defined media were extracted with acid ethanol by a classic method for recovering insulin from pancreas. After filtration of the extracts on Sephadex G-50, distinct peaks of insulin immunoreactivity were recovered in the region typical of insulin. The gel-filtered material from the Tetrahymena had reactivity in the pork insulin radioimmunoassay about equal to its reactivity in the insulin bioassay (stimulation of lipogenesis in isolated rat adipocytes), and the gel-filtered material from neurospora had an immunoreactivity-to-bioactivity ratio of about 1:3. The material that stimulated lipogenesis could be neturalized by anti-insulin sera (i.e., 75-95% of the Tetrahymena material and 60% of the Neurospora material). Bioactive and immunoactive insulin was found in the conditioned medium equal in amount to that in the cells. The findings suggest that insulin did not arise evolutionarily in the intestinal or neural tissues of primitive vertebrates or complex invertebrates but rather has its molecular origins at least as far back as the simplest unicellular eukaryotes.

Aspergillus↗
PubMedDate not supplied

[Gravitational sensitivity of eukaryotic unicellular organisms].

Unicellular organisms are viewed as the best suitable objects for studying environmental effects, including the field of gravity, on living beings at the cellular level. Investigations of unicellular free-living eukaryotic organisms in gravitational and space biology help resolve both theoretical problems and practical problems associated with the design and development of biological life support systems. This paper presents experimental data about the effect of hypergravity on the structure, function and behavior of unicellular organisms--Tetrahymena pyriformis and Euglena gracilis. They were centrifuged at a rate of 87, 108 or 142 rpm to produce acceleration of 2, 3 or 5 G. The following parameters were measured: time course variations in the culture growth, rate of biomass accumulation, cell shape and size. It was found that as the gravity level grew from 2 to 5 G the culture growth was first stimulated and then inhibited. Biomass accumulation as well as the cell size and volume of Tetrahymena pyriformis and Euglena gracilis also decreased. It was demonstrated that the functional activity of cells was inversely proportional to the gravity magnitude. Potential mechanisms of the effect of hypergravity on the cell structure and function are discussed.

Animals↗
PubMed2004

Human platelet dense granules contain polyphosphate and are similar to acidocalcisomes of bacteria and unicellular eukaryotes.

Inorganic polyphosphate (polyP) has been identified and measured in human platelets. Millimolar levels (in terms of Pi residues) of short chain polyP were found. The presence of polyP of approximately 70-75 phosphate units was identified by 31P NMR and by urea-polyacrylamide gel electrophoresis of platelet extracts. An analysis of human platelet dense granules, purified using metrizamide gradient centrifugation, indicated that polyP was preferentially located in these organelles. This was confirmed by visualization of polyP in the dense granules using 4',6-diamidino-2-phenylindole and by its release together with pyrophosphate and serotonin upon thrombin stimulation of intact platelets. Dense granules were also shown to contain large amounts of calcium and potassium and both bafilomycin A1-sensitive ATPase and pyrophosphatase activities. In agreement with these results, when human platelets were loaded with the fluorescent calcium indicator Fura-2 acetoxymethyl ester to measure their intracellular Ca2+ concentration ([Ca2+]i), they were shown to possess a significant amount of Ca2+ stored in an acidic compartment. This was indicated by the following: 1) the increase in [Ca2+]i induced by nigericin, monensin, or the weak base, NH4Cl, in the nominal absence of extracellular Ca2 and 2) the effect of ionomycin, which could not take Ca2+ out of acidic organelles and was more effective after alkalinization of this compartment by the previous addition of nigericin, monensin, or NH4Cl. All of these characteristics of the platelet dense granules, together with their known acidity and high density (both by weight and by electron microscopy), are similar to those of acidocalcisomes (volutin granules, polyP bodies) of bacteria and unicellular eukaryotes. The results suggest that acidocalcisomes have been conserved during evolution from bacteria to humans.

Adenosine Triphosphatases↗
PubMed2003

The circadian clock of the unicellular eukaryotic model organism Chlamydomonas reinhardtii.

The green unicellular alga Chlamydomonas reinhardtii, also called 'green yeast', emerged in the past years as a model organism for specific scientific questions such as chloroplast biogenesis and function, the composition of the flagella including its basal apparatus, or the mechanism of the circadian clock. Sequencing of its chloroplast and mitochondrial genomes have already been completed and a first draft of its nuclear genome has also been released recently. In C. reinhardtii several circadian rhythms are physiologically well characterized, and one of them has even been shown to operate in outer space. Circadian expression patterns of nuclear and plastid genes have been studied. The mode of regulation of these genes occurs at the transcriptional level, although there is also evidence for posttranscriptional control. A clock-controlled, phylogenetically conserved RNA-binding protein was characterized in this alga, which interacts with several mRNAs that all contain a common cis-acting motif. Its function within the circadian system is currently under investigation. This review summarizes the current state of the knowledge about the circadian system in C. reinhardtii and points out its potential for future studies.

Animals↗
PubMedDate not supplied

A rhodopsin is the functional photoreceptor for phototaxis in the unicellular eukaryote Chlamydomonas.

Rhodopsin is a visual pigment ubiquitous in multicellular animals. If visual pigments have a common ancient origin, as is believed, then some unicellular organisms might also use a rhodopsin photoreceptor. We show here that the unicellular alga Chlamydomonas does indeed use a rhodopsin photoreceptor. We incorporated analogues of its retinal chromophore into a blind mutant; normal photobehaviour was restored and the colour of maximum sensitivity was shifted in a manner consistent with the nature of the retinal analogue added. The data suggest that 11-cis-retinal is the natural chromophore and that the protein environment of this retinal is similar to that found in bovine rhodopsin, suggesting homology with the rhodopsins of higher organisms. This is the first demonstration of a rhodopsin photoreceptor in an alga or eukaryotic protist and also the first report of behavioural spectral shifts caused by exogenous synthetic retinals in a eukaryote. A survey of the morphology and action spectra of other protists suggests that rhodopsins may be common photoreceptors of chlorophycean, prasinophycean and dinophycean algae. Thus, Chlamydomonas represents a useful new model for studying photoreceptor cells.

Cell Movement↗
PubMed2005

Prokaryotic and eukaryotic unicellular chronomics.

An impeccable time series, published in 1930, consisting of hourly observations on colony advance in a fluid culture of E. coli, was analyzed by a periodogram and power spectrum in 1961. While the original senior author had emphasized specifically periodicity with no estimate of period length, he welcomed further analyses. After consulting his technician, he knew of no environmental periodicity related to human schedules other than an hourly photography. A periodogram analysis in 1961 showed a 20.75-h period. It was emphasized that "... the circadian period disclosed is not of exactly 24-h length." Confirmations notwithstanding, a committee ruled out microbial circadian rhythms based on grounds that could have led to a different conclusion, namely first, the inability of some committee members to see (presumably by eyeballing) the rhythms in their own data, and second, what hardly follows, that there were "too many analyses" in the published papers. Our point in dealing with microbes and humans is that analyses are indispensable for quantification and for discovering a biologically novel spectrum of cyclicities, matching physical ones. The scope of circadian organization estimated in 1961 has become broader, including about 7-day, about half-yearly, about-yearly and ex-yearly and decadal periodisms, among others. Microbial circadians have become a field of their own with eyeballing, yet time-microscopy can quantify characteristics with their uncertainties and can assess broad chronomes (time structures) with features beyond circadians. As yet only suggestive differences between eukaryotes and prokaryotes further broaden the perspective and may lead to life's sites of origin and to new temporal aspects of life's development as a chronomic tree by eventual rhythm dating in ontogeny and phylogeny.

Acetabularia↗