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PubMed1961

Infective organisms in the cytoplasm of Amoeba proteus.

Evidence from electron and phase microscopy is given which shows that infective organisms are present in the cytoplasm of Amoeba proteus. Vesicles containing living organisms have been observed after repeated washing and starvation of the amebae for a period of 2 weeks. Exposure to gamma-radiation in conjunction with starvation, repeated washing, isolation of single amebae, refeeding with contaminant-free Tetrahymena, and clone selection has produced clones with reduced cytoplasmic infection. These findings are discussed in regard to the autoradiographic studies of other investigators on Amoeba proteus. The controversies over whether DNA and RNA are synthesized in the cytoplasm may be resolved by the finding of cytoplasmic infection.

Amoeba↗
PubMed1956

Electron microscopy of the nuclear membrane of Amoeba proteus.

An electron microscope study of the nuclear membrane of Amoeba proteus by thin sectioning techniques has revealed an ultrastructure in the outer layer of the membrane that is homologous to the pores and annuli observed in the nuclear membranes of many other cell types studied by these techniques. An inner honeycombed layer apparently unique to Amoeba proteus is also described.

Amoeba↗
PubMed2006

Effects of chemoattractant pteridines upon speed of D. discoideum vegetative amoebae.

Movements of D. discoideum vegetative amoebae responding to pteridine chemoattractants, folate acid and pterin, were recorded. A vector analysis of these images was performed to partition the speed and orientation components of these motility patterns. This study demonstrates that in addition to orientation (chemotaxis), stimulated speed (chemokinesis) is an important component of the directed migration of these amoebae. Furthermore, the primary difference in their response to folate versus pterin is in speed rather than orientation. The data support a model of directed migration of these cells in which there are (1) separate signal translation pathways consequent from folate versus pterin reception and (2) specific pathways leading to increase in orientation versus speed.

Amoeba↗
PubMed1975

Microfibrillar structures in the nucleus and cytoplasm of amoeba proteus.

The presence of microfibrillar structures in the nucleus and cytoplasm of Amoeba proteus has been described after glutaraldehyde and osmium fixation. The possible roles of cytoplasmic microfibrils in the contraction process of amoeba and nuclear microfibrils in the formation of the honeycomb nuclear lamina are discussed.

Amoeba↗
PubMed1996

A Ca(2+)-dependent early functional heterogeneity in amoebae of Dictyostelium discoideum, revealed by flow cytometry.

When freshly starved amoebae of Dictyostelium discoideum are loaded with the Ca(2+)-specific dye indo-1/ AM and analyzed in a fluorescence-activated cell sorter, they exhibit a quasi-bimodal distribution of fluorescence. This permits a separation of the population into two classes: H, or "high Ca(2+)-indo-1 fluorescence," and L, or "low Ca(2+)-indo-1 fluorescence." Simultaneous monitoring of Ca(2+)-indo-1 and Ca(2+)-chlortetracycline fluorescence shows that by and large the same cells tend to have high (or low) levels of both cytoplasmic and sequestered Ca2+. Next we label H cells with tetramethylrhodamine isothiocyanate (TRITC) and mix them in a 1:4 ratio with L cells. In the slugs that result, TRITC fluorescence is confined mainly to the anterior prestalk region. This implies that amoebae with relatively high Ca2+ at the vegetative stage tend to develop into prestalk cells and those with low Ca2+ into prespores. Polysphondylium violaceum, a cellular slime mold that does not possess prestalk and prespore cells, also does not display a Ca(2+)-dependent heterogeneity at the vegetative stage or in slugs. Finally, confirming earlier findings with the fluorophore fura-2 (Azhar et al., Curr. Sci. 68, 337-342 (1995)), a prestalk-prespore difference in cellular Ca2+ is present in the cells of the slug in vivo. These findings are discussed in light of the possible roles of Ca2+ for cell differentiation in D. discoideum.

Amoeba↗
PubMed1983

Dynamics of the cytoskeleton in Amoeba proteus. I. Redistribution of microinjected fluorescein-labeled actin during locomotion, immobilization and phagocytosis.

Fluorescein-labeled muscle actin was microinjected into Amoeba proteus and followed during intracellular redistribution by means of the image-intensification technique. The fully polymerization-competent protein becomes part of the endogenous actomyosin system undergoing dynamic changes over time periods of several hours. Single-frame analysis of long-term sequences enabled the direct demonstration of both the contractile activities and morphological transformations of microfilaments in normally locomoting, immobilized and phagocytozing specimens. In normally locomoting cells the filament layer undergoes continuous changes in spatial distribution depending on the actual pattern of cytoplasmic streaming and cell shape. The highest degree of differentiation is always maintained in the intermediate region between the front and the uroid, thus indicating this segment of the cortex to be the most important site in generating motive force for pseudopodium formation and ameboid movement. In immobilized cells contracted by the application of ruthenium red or relaxed by different anesthetics, the filament layer forms a continuous thick sheath beneath the cell surface or becomes completely disintegrated. In phagocytozing cells the local polymerization of actin at the tip of pseudopodia forming the food-cup and around the nascent phagosome points to a significant participation of the actomyosin system in the process of capturing and constricting prey organisms. Although our results provide clear evidence for the overall importance of motive force generation according to the hydraulic pressure theory, some motile phenomena exist in Amoeba proteus that cannot exclusively be explained by this mechanism.

Actins↗
PubMed1975

Effects of induced pinocytotic activity and extreme temperatures on the morphology of Golgi bodies in Amoeba proteus.

The morphology of the Golgi apparatus of Amoeba proteus can be influenced by substances inducing pinocytotic activity as well as by extreme temperatures. During the ingestion of a solution of 0.5% egg white the number of Golgi bodies decreases from 100% measured in control cells to 82% measured in cells showing induced pinocytosis. Simultaneously the ratio of the surface area of the cisternae at the proximal face to that of the vesicles at the distal face of single dictyosomes remains constant (1.74-1.72). The decrease and increase of the temperature of the culture medium to 4 degrees C and 30 degrees C respectively, causes the disappearance of most of the dictyosomes. After keeping the cells for 3-10 h at these temperatures the number of Golgi bodies was only 5-10% of the controls. A continued treatment with cold or warm culture medium leads to a partial reorganization of dictyosomes. After 15 h the number of Golgi bodies counted per cell returned to 57% at 4 degrees C and 38% at 30 degrees C. The ratio of the surface area of the Golgi cisternae to the surface area of the Golgi vesicles also alters under the influence of extreme temperatures. The values measured after treating the cells for 3h, 4 h 10 h and 15 h at 4 degrees C and 30 degrees C amounted to 0.75, 0.85, 1.14 1.53 and 0.93, 0.38, 0.88, 1.60, respectively, compared to 1.72 of control amoebae. The different values of the ratio of the surface area of cisternae to that of vesicles indicate that there are strong morphological changes of single dictyosomes.

Amoeba↗
PubMed1978

Diaminobenzidine reactions in control and treated Amoeba proteus.

Cytochrome oxidase activity was demonstrated in Amoeba proteus by diaminobenzidine (DAB) cytochemistry. Deposition of the reaction product occurred on the inner mitochondrial membranes and the cristae. The reaction was abolished by cyanide incubations. Positive reactions were produced with both unfixed and fixed cells: although staining potential was destroyed by any prefixatives which included glutaraldehyde. Cells prefixed with 4% formaldehyde, to raise structural preservation, retained staining ability. Amoebae subjected to prolonged anaerobiosis or to treatment with the carcinogen N-methyl-N-nitrosourethane (MNU) displayed a reduction in DAB reactivity. A positive reaction was only produced in incubations of unfixed cells and even in these the intensity of cristal staining was depleted. The possible use of DAB reactions where lesions in mitochondrial functioning have occurred is considered.

3,3'-Diaminobenzidine↗
PubMed1999

Primary and secondary structure of the small-subunit ribosomal RNA of the naked, marine amoeba Vannella anglica: phylogenetic implications.

The primary and secondary structure of the small-subunit ribosomal RNA (ssrRNA) gene from the naked, marine amoeba, Vannella anglica (subclass Gymnamoebia), was determined. The ssrRNA is 1962 nucleotides in length, with a low G+C content of 37.1%. The ssrRNA is composed of several uncommon secondary structure features including helix E8-1, which may be a useful target for rRNA probes for the direct identification of isolates in mixed culture. Phylogenetic analysis of sequence data showed that V. anglica branched prior to the rapid diversification of the eukaryotes. It did not associate with the other naked, lobose amoebae represented by Acanthamoeba and Hartmannella, indicating that Vannella represents a separate amoeboid lineage and the subclass Gymnamoebia is polyphyletic.

Amino Acid Sequence↗
PubMed2003

Characteristics of trajectory in the migration of Amoeba proteus.

We investigated the behavior of migration of Amoeba proteus in an isotropic environment. We found that the trajectory in the migration of A. proteus is smooth in the observation time of 500-1000 s, but its migration every second (the cell velocity) on the trajectory randomly changes. Stochastic analysis of the cell velocity and the turn angle of the trajectory has shown that the histograms of the both variables well fit to Gaussian curves. Supposing a simple model equation for the cell motion, we have estimated the motive force of the migrating cell, which is of the order of piconewton. Furthermore, we have found that the cell velocity and the turn angle have a negative cross-correlation coefficient, which suggests that the amoeba explores better environment by changing frequently its migrating direction at a low speed and it moves rectilinearly to the best environment at a high speed. On the other hand, the model equation has simulated the negative correlation between the cell velocity and the turn angle. This indicates that the apparently rational behavior comes from intrinsic characteristics in the dynamical system where the motive force is not torquelike.

Amoeba↗
PubMed1982

Protein migration from transplanted nuclei in Amoeba proteus. I. The relation to the cell cycle and RNA migration, as studied by autoradiography.

Autoradiography has been used to examine the migration of proteins from a radioactively labelled amoeba nucleus following transplantation into an unlabelled homophasic amoeba. Nuclei were transferred at three times in the cell cycle coinciding with DNA synthesis (4 h post-division); a peak of RNA synthesis (25 h); and a relative lull in synthetic activity (43 h). Six amino acids were added individually to the culture medium to label the nuclear proteins. Migration of the proteins from the donor nucleus was found to be greatest following the transfer of [3H]aspartic acid-labelled nuclei and least with protein labelled with the basic amino acids. All amino acids exhibited the greatest extent of migration following the 25-h transfers, i.e., coinciding with a peak of RNA synthesis at 26-27.5 h. Actinomycin D (actD) inhibition of RNA synthesis reduced, but did not eliminate the extent of protein migration from the transplanted nucleus, thus indicating the existence of two classes of migratory proteins. Firstly, proteins, associated with RNA transport, which migrated mainly into the host cytoplasm. The second class migrated into the host nucleus from the transplanted nucleus, irrespective of RNa synthesis. The shuttling character of the latter class of proteins is consistent with a role of regulation of nuclear activity.

Amoeba↗
PubMed1984

Selective inhibition of calcium-stimulated cation-induced pinocytosis by starvation and inhibitors of protein synthesis in Amoeba proteus.

The capacity of Amoeba proteus to form pinocytotic channels after pretreatment with either puromycin, cycloheximide, emetine or a long period of starvation was studied. The effect on pinocytosis of the three inhibitors of protein synthesis was similar. They preferentially affected pinocytosis induced by Na+ with little effect on K+-induced pinocytosis. In Ca2+-deficient media, Na+-induced pinocytosis was inhibited, while the addition of Ca2+ restored channel formation. The degree of inhibition of Na+-induced pinocytosis was influenced by the concentration of Ca2+ in the inducing solution. Selective Ca2+-reversible inhibition of Na+-induced pinocytosis also occurred after starvation or treatment with a proteolytic enzyme, subtilisin. The membrane potential in starved or emetine-treated cells in culture medium was normal and their depolarising response to inducers was not diminished in solutions containing Na+. The resting input resistance of these cells was higher than in normal amoebae, but no significant difference in electrical parameters was observed after pinocytosis was induced. It is suggested that starvation, inhibition of protein synthesis, and enzyme digestion deplete the membrane of structures which are necessary for normal Ca2+ functions during induction of pinocytosis by Na+-like inducers.

Amoeba↗
PubMed1984

Activation of the capacity for sodium-induced pinocytosis in Amoeba proteus.

Amoebae treated with cycloheximide or starved for 8-10 days lose their pinocytotic response to Na+. Their capacity for Na+-induced pinocytosis was activated after application of various physical or chemical stimuli (electrical stimulation, mechanical shearing forces, osmotic pressure, UV-light, alkali metal ions, capsaicin, and indole). The degree of activation was related to the intensity and duration of the stimulus and lasted several hours after the stimulus had been withdrawn. The dose-response curves of activating stimuli were always biphasic. Strong activating agents reduced the sensitivity of the amoeba to the inducer. At concentrations lower than those which induced pinocytosis, but in the same order of efficacy, inorganic cations were potent activating agents. Like induction of pinocytosis, activation by cations required minute amounts of Ca2+ and was inhibited by high concentrations of this ion. Activation may therefore be an early event during the induction of pinocytosis. Capsaicin and indole were potent activators, indicating that specific chemical stimuli may increase the capacity for pinocytosis. The activation may be the result of a secretory process adding area and structures to the old membrane which are necessary for the induction of pinocytosis.

Action Potentials↗
PubMed1985

Recycling of membrane proteins during endo- and exocytosis in amoebae.

The fate of a membrane protein of the amoeba plasmalemma was studied by means of 125I iodination by lactoperoxidase, gel electrophoresis, radioautography and gamma counting. There was only one iodinatable polypeptide group with a molecular weight (MW) of 175 000 on the external surface of the plasmalemma. Two hours or more after induced phagocytosis, isolated phagolysosomal membranes contained two other smaller polypeptides with MWs of 70 000 and 35 000, respectively, suggesting that the 175 000 polypeptide was broken down to these smaller components during endocytosis. After 22 h of induced phagocytosis, isolated plasmalemma contained a 35 000 polypeptide group in addition to the 175 000 polypeptide species. The results suggested that some of the iodinatable membrane proteins were altered and recycled during endo- and exocytosis in amoebae, while others were recycled intact.

Amoeba↗
PubMed1989

The effects of vasopressin and related peptides on osmoregulation in Amoeba proteus.

We describe the effects of arginine-vasopressin (AVP) and five related peptides on the contractile vacuole, the osmoregulatory organelle of the fresh water Amoeba proteus. Arginine-vasopressin, lysine-vasopressin, and SKF 101926, a synthetic antagonist of vasopressin, cause a significant increase in the rate of output of the contractile vacuole. Deamino-vasopressin (dAVP), oxytocin, and arginine-vasotocin have no such activity, although dAVP interferes with the action of AVP when present in equimolar concentration. Relatively high concentrations are required and the effect of active peptides is readily reversible. When the normal, hypotonic medium (a synthetic pond water) is replaced by isotonic sucrose, the action of AVP on the vacuole is abolished. Thus vasopressin is believed to act by increasing permeability of the Amoeba plasma membrane to water.

Amoeba↗
PubMed1993

External ions and direct membrane effects of enkephalins on Amoeba proteus.

We have shown that amphiphilic hormones like vasopressins and endorphins increase water permeability and activate the contractile vacuole (CV) in Amoeba by direct action on the plasma membrane. Using our standard CV assay, the effects of nine opioids, morphine, naloxone and 7 enkephalin derivatives, have been compared in normal, ion-containing growth medium (Chalkley's) and in glass-distilled water. While the absence of external ions does not affect the activity of molecules with net positive charges, opioids with no net charge are devoid of action in glass-distilled water. This shows that, in addition to amphiphilicity, which permits insertion into the lipid core of the membrane, electrostatic interactions with ions and with negative charges of phospholipids membrane and glycocalyx, the thick glycoproteic cell coat of Amoeba, are important in the direct action of these compounds.

Amino Acid Sequence↗
PubMed1985

Photophobic and phototactic responses of Amoeba proteus in KCN and SHAM solutions.

The effects of the metabolic inhibitors KCN and SHAM on phototaxis and photophobic response in Amoeba proteus have been studied. Both drugs neither change amoebae photophobic response nor the phototactic reaction. The results indicate clearly that the negative phototactic orientation is not impaired by impediment of respiration thus it is not directly coupled to the differences in energy production in different parts of A. proteus body.

Amoeba↗
PubMed1996

The s29x gene of symbiotic bacteria in Amoeba proteus with a novel promoter.

Gram-symbiotic bacteria (called X-bacteria), present in the xD strain of Amoeba proteus as required cell components, synthesize and export a large amount of a 29-kDa protein, S29x. S29x is exported into the host's cytoplasm across the bacterial membranes and the symbiosome membrane. The complete nucleotide (nt) sequence of the s29x gene of X-bacteria has been determined, and the promoter sequence and tsp have also been identified. The gene has a nonconventional promoter with putative nt sequences different from the known consensus sequences. When Escherichia coli cells are transformed with s29x, the gene is expressed and the product is secreted into the culture medium. Functions of S29x are not fully known, but it is suspected that S29x plays an important role in the symbiotic relationship between amoebae and X-bacteria.

Amino Acid Sequence↗