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64 results for “Dictyostelium discoideum”
A role for myosin II cluster and membrane energy in cortex rupture for Dictyostelium discoideum cells
<p>Blebs, pressure driven protrusions of the cell membrane, facilitate the movement of eukaryotic cells such as the soil amoeba <em>Dictyostelium discoideum</em>, white blood cells and cancer cells. Blebs initiate when the cell membrane separates from the underlying cortex. A local rupture of the cortex, has been suggested as a mechanism by which blebs are initiated. However, much clarity is still needed about how cells inherently regulate rupture of the cortex in locations where blebs are expected to form. In this work, we examine the role of membrane energy and the motor protein myosin II (myosin) in facilitating the cell driven rupture of the cortex. We perform under-agarose chemotaxis experiments, using <em>Dictyostelium discoideum</em> cells, to visualize the dynamics of myosin and calculate changes in membrane energy in the blebbing region. To facilitate a rapid detection of blebs and analysis of the energy and myosin distribution at the cell front, we introduce an autonomous bleb detection algorithm that takes in discrete cell boundaries and returns the coordinate location of blebs with its shape characteristics. We are able to identify by microscopy naturally occurring gaps in the cortex prior to membrane detachment at sites of bleb nucleation. These gaps form at positions calculated to have high membrane energy, and are associated with areas of myosin enrichment. Myosin is also shown to accumulate in the cortex prior to bleb initiation and just before the complete disassembly of the cortex. Together our findings provide direct spatial and temporal evidence to support cortex rupture as an intrinsic bleb initiation mechanism and suggests that myosin clusters are associated with regions of high membrane energy where its contractile activity leads to a rupture of the cortex at points of maximal energy.</p>
Context-dependence in the symbiosis between Dictyostelium discoideum and Paraburkholderia
<p><span>Symbiotic interactions change with environmental context. Measuring these context-dependent effects in hosts and symbionts is critical to determining the nature of symbiotic interactions. We investigated context-dependence in the symbiosis between social amoeba hosts and their inedible </span><em>Paraburkholderia</em><span> bacterial symbionts, where the context is the abundance of host food bacteria. </span><em>Paraburkholderia</em><span> have been shown to harm hosts dispersed to food-rich environments, but aid hosts dispersed to food-poor environments by allowing hosts to carry food bacteria. Through measuring symbiont density and host spore production, we show that this food context matters in three other ways. First, it matters for symbionts, who suffer a greater cost from competition with food bacteria in the food-rich context. Second, it matters for host-symbiont conflict, changing how symbiont density negatively impacts host spore production. Third, data-based simulations show that symbiosis often provides a long-term fitness advantage for hosts after rounds of growth and dispersal in variable food-contexts, especially when conditions are harsh with little food. These results show how food context can have many consequences for the </span><em>Dictyostelium-Paraburkholderia</em><span> symbiosis and that both sides can frequently benefit.</span></p>
Context-dependence in the symbiosis between Dictyostelium discoideum and Paraburkholderia
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A role for myosin II cluster and membrane energy in cortex rupture for Dictyostelium discoideum cells
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Fluorescent (C)LSM image sequences of Dictyostelium discoideum (Ax2 - LifeAct mRFP) for cell track and cell contour analysis
<p>This data set is designed for cell contour and cell track analysis. Hence image sequences of moving Dictyostelium discoideum cells are recorded. For the purpose to facilitate the detection of the cell contour we take fluorescent images of the cortical protein actin to obtain a high contrast between background and cell body. In each image sequences several cells are recorded. This allows for an analysis of all cells at once or to crop single cell tracks.</p>
Wild Dictyostelium discoideum social amoebae show plastic responses to the presence of nonrelatives during multicellular development
<p>When multiple strains of microbes form social groups, such as the multicellular fruiting bodies of <em>Dictyostelium discoideum</em>, conflict can arise regarding cell fate. Both fixed and plastic differences among strains can contribute to cell fate, and plastic responses may be particularly important if social environments frequently change. We used RNA-sequencing and photographic time series analysis to detect possible conflict-induced plastic differences between wild <em>D. discoideum </em>aggregates formed by single strains compared to mixed pairs of strains (chimeras). We found one hundred and two differentially expressed genes that were enriched for biological processes including cytoskeleton organization and cyclic-AMP response (up-regulated in chimeras), and DNA replication and cell cycle (down-regulated in chimeras). In addition, our data indicate that in reference to a time series of multicellular development in the lab strain AX4, chimeras may be slightly behind clonal aggregates in their development. Finally, phenotypic analysis supported slower splitting of aggregates and a nonsignificant trend for larger group sizes in chimeras. The transcriptomic comparison and phenotypic analyses support discoordination among aggregate group members due to social conflict. These results are consistent with previously observed factors that affect cell fate decision in <em>D. discoideum </em>and provide evidence for plasticity in cAMP signaling and phenotypic coordination during development in response to social conflict in <em>D. discoideum </em>and similar microbial social groups.</p>
Experimental evolution of Dictyostelium discoideum cheating under relaxed selection
<p>Many microbes interact with one another, but the difficulty of directly observing these interactions in nature makes interpreting their adaptive value complicated. The social amoeba <em>Dictyostelium discoideum </em>forms aggregates<em> </em>wherein some cells are sacrificed for the benefit of others. Within chimeric aggregates containing multiple unrelated lineages, cheaters can gain an advantage by undercontributing, but the extent to which wild <em>D. discoideum </em>has adapted to cheat is not fully clear. In this study, we experimentally evolved <em>D. discoideum </em>in an environment where there were no selective pressures to cheat or resist cheating in chimeras. <em>D. discoideum </em>lines grown in this environment evolved reduced competitiveness within chimeric aggregates and reduced ability to migrate during the slug stage. By contrast, we did not observe a reduction in cell number, a trait for which selection was not relaxed. The observed loss of traits that our laboratory conditions had made irrelevant suggests that these traits were adaptations driven and maintained by selective pressures <em>D. discoideum </em>faces in its natural environment. Our results suggest that <em>D. discoideum</em> faces social conflict in nature, and illustrate a general approach that could be applied to searching for social or non-social adaptations in other microbes.</p>
Facultative symbiont virulence determines horizontal transmission rate without host specificity in Dictyostelium discoideum social amoebas
<p>In facultative symbioses, only a fraction of hosts are associated with symbionts. Specific host and symbiont pairings may be the result of host-symbiont coevolution driven by reciprocal selection, or priority effects pertaining to which potential symbiont became associated with a host first. Distinguishing between these possibilities is important for understanding the evolutionary forces that affect facultative symbioses. We used the social amoeba <em>Dictyostelium discoideum</em> and its symbiont <em>Paraburkholderia bonniea </em>to determine whether ongoing coevolution affects which host-symbiont strain pairs naturally co-occur within a facultative symbiosis. Relative to other <em>Paraburkholderia</em>,<em> </em>including another symbiont of <em>D. discoideum</em>, <em>P. bonniea</em> features a reduced genome size that indicates a significant history of coevolution with its host. We hypothesized that ongoing host-symbiont coevolution would lead to higher fitness for naturally co-occurring (native) host and symbiont pairings compared to novel pairings. We show for the first time that <em>P. bonniea</em> symbionts can horizontally transmit to new amoeba hosts when hosts aggregate together during the social stage of their life cycle. Here we find evidence for a virulence-transmission trade-off without host specificity. Although symbiont strains were significantly variable in virulence and horizontal transmission rate, hosts and symbionts responded similarly to associations in native and novel pairings. We go on to identify candidate virulence factors in the genomes of <em>P. bonniea </em>strains that may contribute to variation in virulence. We conclude that ongoing coevolution is unlikely for <em>D. discoideum </em>and <em>P. bonniea. </em>The system instead appears to represent a stable facultative symbiosis in which naturally co-occurring <em>P. bonniea </em>host and symbiont pairings are the result of priority effects.</p>
Data from: In the social amoeba Dictyostelium discoideum, shortened stalks may limit obligate cheater success even when exploitable partners are available
<p>Cooperation is widespread across life, but its existence can be threatened by exploitation. The rise of obligate social cheaters that are incapable of contributing to a necessary cooperative function can lead to the loss of that function. In the social amoeba <em>Dictyostelium discoideum</em>, obligate social cheaters cannot form dead stalk cells and in chimeras instead form living spore cells. This gives them a competitive advantage within chimeras. However, obligate cheaters of this kind have thusfar not been found in nature, probably because they are often enough in clonal populations that they need to retain the ability to produce stalks. In this study we discovered an additional cost to obligate cheaters. Even when there are wild-type cells to parasitize, the chimeric fruiting bodies that result have shorter stalks and these are disadvantaged in spore dispersal. The inability of obligate cheaters to form fruiting bodies when they are on their own combined with the lower functionality of fruiting bodies when they are not represent limits on obligate social cheating as a strategy<em>.</em></p>
Dictyostelium discoideum cells retain nutrients when the cells are about to outgrow their food source
<p><em>Dictyostelium discoideum</em> is a unicellular eukaryote that eats bacteria, and eventually overgrows the bacteria. <em>D. discoideum</em> cells accumulate extracellular polyphosphate (polyP), and the polyP concentration increases as the local cell density increases. At high cell densities, the correspondingly high extracellular polyP concentrations allow cells to sense that they are about to overgrow their food supply and starve, causing the <em>D. discoideum</em> cells to inhibit their proliferation. In this report, we show that high extracellular polyP inhibits exocytosis of undigested or partially digested nutrients. PolyP decreases plasma membrane recycling and apparent cell membrane fluidity, and this requires the G protein-coupled polyP receptor GrlD, the polyphosphate kinase Ppk1, and the inositol hexakisphosphate kinase I6kA. PolyP alters protein contents in detergent-insoluble crude cytoskeletons, but does not significantly affect random cell motility, cell speed, or F-actin levels. Together, these data suggest that <em>D. discoideum</em> cells use polyP as a signal to sense their local cell density and reduce cell membrane fluidity and membrane recycling, perhaps as a mechanism to retain ingested food when the cells are about to starve.</p>
Data for: Self-cleaving 2A peptides allow for expression of multiple genes in Dictyostelium discoideum
<p>The social amoeba <em>Dictyostelium discoideum</em> is a model for a wide range of biological processes including chemotaxis, cell-cell communication, phagocytosis, and development. Interrogating these processes with modern genetic tools often requires the expression of multiple transgenes. While it is possible to transfect multiple transcriptional units, the use of separate promoters and terminators for each gene leads to large plasmid sizes and possible interference between units. In many eukaryotic systems this challenge has been addressed through polycistronic expression mediated by 2A viral peptides, permitting efficient, co-regulated gene expression. Here, we screen the most commonly used 2A peptides, porcine teschovirus-1 2A (P2A), <em>Thosea asigna</em> virus 2A (T2A), equine rhinitis A virus 2A (E2A), and foot-and-mouth disease virus 2A (F2A), for activity in <em>D. discoideum</em> and find that all the screened 2A sequences are effective. However, combining the coding sequences of two proteins into a single transcript leads to notable strain-dependent decreases in expression level, suggesting additional factors regulate gene expression in <em>D. discoideum</em> that merit further investigation. Our results show that P2A is the optimal sequence for polycistronic expression in <em>D. discoideum</em>, opening up new possibilities for genetic engineering in this model system.</p>
Data from: In the social amoeba Dictyostelium discoideum, shortened stalks may limit obligate cheater success even when exploitable partners are available
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Fluorescent (C)LSM image sequences of Dictyostelium discoideum (Ax2 - LifeAct mRFP) for cell track and cell contour analysis
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Data for: Self-cleaving 2A peptides allow for expression of multiple genes in Dictyostelium discoideum
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Experimental evolution of Dictyostelium discoideum cheating under relaxed selection
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Facultative symbiont virulence determines horizontal transmission rate without host specificity in Dictyostelium discoideum social amoebas
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Dictyostelium discoideum cells retain nutrients when the cells are about to outgrow their food source
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Wild Dictyostelium discoideum social amoebae show plastic responses to the presence of nonrelatives during multicellular development
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Data from: Sentinel cells, symbiotic bacteria, and toxin resistance in the social amoeba Dictyostelium discoideum
The social amoeba Dictyostelium discoideum is unusual among eukaryotes in having both unicellular and multicellular stages. In the multicellular stage, some cells, called sentinels, ingest toxins, waste, and bacteria. The sentinel cells ultimately fall away from the back of the migrating slug, thus removing these substances from the slug. However, some D. discoideum clones called farmers carry commensal bacteria through the multicellular stage while others called non-farmers do not. Farmers profit from their beneficial bacteria. To prevent the loss of these bacteria, we hypothesize that sentinel cell numbers may be reduced in farmers and thus farmers may have a diminished capacity to respond to pathogenic bacteria or toxins. In support, we found that farmers have fewer sentinel cells compared to non-farmers. However, farmers produced no fewer viable spores when challenged with a toxin. These results are consistent with the beneficial bacteria, Burkholderia, providing protection against toxins. The farmers did not vary in spore production with and without a toxin challenge the way the non-farmers did, which suggests the costs of Burkholderia may be fixed while sentinel cells may be inducible. Therefore, the costs for non-farmers are only paid in the presence of the toxin. When the farmers were cured of their symbiotic bacteria with antibiotics, they behaved just like non-farmers in response to a toxin challenge. Thus, the advantages farmers gain from carrying bacteria include not just food and protection against competitors, but also protection against toxins.
Data from: Sex ratio and gamete size across eastern North America in Dictyostelium discoideum, a social amoeba with three sexes
Theory indicates that numbers of mating types should tend towards infinity or remain at two. The social amoeba, Dictyostelium discoideum, however, has three mating types. It is therefore a mystery how this species has broken the threshold of two mating types, but has not increased towards a much higher number. Frequency dependent selection on rare types in combination with isogamy, a form of reproduction involving gametes similar in size, could explain the evolution of multiple mating types in this system. Other factors, such as drift, may be preventing the evolution of more than three. We first looked for evidence of isogamy by measuring gamete size associated with each type. We found no evidence of size dissimilarities between gametes. We then looked for evidence of balancing selection, by examining mating type distributions in natural populations and comparing genetic differentiation at the mating type locus to that at more neutral loci. We found that mating type frequency varied among the three populations we examined, with only one of the three showing an even sex ratio, which does not support balancing selection. However, we found more population structure at neutral loci than the mating type locus, suggesting that the three mating types are indeed maintained at intermediate frequencies by balancing selection. Overall, the data are consistent with balancing selection acting on D. discoideum mating types, but with a sufficiently weak rare sex advantage to allow for drift, a potential explanation for why these amoebae have only three mating types.
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