Slime mould dictyostelium discoideum

Studies in yeasts (Saccharomyces cerevisiae, Schizo-saccharomyces pombe), slime mould (,Dictyostelium discoideum), worm (Caenorhabditis elegans), fly (Drosophila melanogaster) and mammalian systems have all contributed to our understanding of TOR signalling. 

The chemotactic response to cAMP of the slime mould Dictyostelium discoideum is presented as an example. When these cells are starving, they sense cAMP signals, and in response to the hunger signal, cAMP, the cells differentiate (reviewed in ref. 67). In Dictyostelium discoideum the response to cAMP is mediated by G-protein-coupled hepta-helical receptors and is transmitted by the Py subunits of a heterotrimeric G protein. In response to the chemoattractant, cAMP, a homologue of PKB (protein kinase B) is rapidly activated by phosphorylation througji a Ptdins kinase specific for the 3-OH position (see also Chapter 4). 

In the slime mould, Dictyostelium discoideum, a STAT-like DNA-binding protein, DIF (the differentiation-inducing factor), is expressed. DIF is about 700 amino-acid residues long, and has substantial homology with mammalian STATs. DIF is, like STAT, activated by phosphorylation of tyrosines. It is essential for differentiation of the stalk cells of D. discoideum A The long evolutionary path that the STATs have travelled from Dictyostelium to mammals underlines their conserved and essential role as signal transmitters and transcriptional activators in early development. 

Two compounds common in plant metabolism are believed to be precursors of isoprenoid cytokinins in plants adenosine-5 -monophosphate (AMP) and A -isopentenylpyrophos-phate (iPP). As a final product of the mevalonate pathway, the latter substance serves also as a precursor for a wide spectrum of metabolites including some other plant hormones, as abscisic acid, gibberellins and brassinosteroids. The hypothetical scheme of reactions resulting in the formation of iPA, Z and DHZ is given in Fig. 2. The enzyme of entry into isoprenoid cytokinin formation is A -isopentenylpyrophosphate 5 -AMP-A -iso-pentenyltransferase (EC 2.5.1.8, trivially named cytokinin synthetase ). This enzyme activity was first detected in a cell-free preparation from the slime mould Dictyostelium discoideum [7,8]. Later the enzyme from higher plants (cytokinin-independent tobacco callus [9,10] and immature Zea mays kernels [11]) was described and the data were recently summarised in [12], The enzyme is very specific as far as the substrate is concerned [13,14] only the nucleotide AMP can be converted and only iPP (with a double bond in A position) may function as a side chain donor. 

In the slime mould Dictyostelium discoideum, a portion of the cellular NDPK has been shown to be plasma membrane-associated. Furthermore Dictyostelium p>ossesses surface cAMP-receptors, which couple to a G-protein, but NDPK activity appears to be activated by the receptor followed by G-protein activation [22]. This activation could be eliminated by the addition of antibodies against NDPK and it was proposed that NDPK was supplying GTP for G-protein activation. 

Biological rhythms occur only under precise conditions, and variations in a control parameter can bring about their disappearance. In a symmetrical manner, the variation of such a parameter can lead to the appearance of a rhythm in the course of development. There is no example as yet where the molecular basis of the ontogenesis of a biological rhythm is known in detail. The rhythm of intercellular communication in the slime mould Dictyostelium discoideum provides us with a prototype for the study of this question. 

Alcantara, F. M. Monk. 1974. Signal propagation during aggregation in the slime mould Dictyostelium discoideum. J. Gen. Microbiol 85 321-34. 

Martiel, J.L. A. Goldbeter. 1985. Autonomous chaotic behaviour of the slime mould Dictyostelium discoideum predicted by a model for cyclic AMP signalling. Nature 313 590-2. 

Monk, P.B. H.G. Othmer. 1990. Wave propagation in aggregation fields of the cellular slime mould Dictyostelium discoideum. Proc. R. Soc. Lond. B 240 555-89. 

Shaffer, B.M. 1975. Secretion of cyclic AMP induced by cyclic AMP in the cellular slime mould Dictyostelium discoideum. Nature 255 549-52. 

Siegert, F. C. Weijer. 1991. Analysis of optical density wave propagation and cell movement in the cellular slime mould Dictyostelium discoideum. Physica 49D 224-32. 

Williams, K.L. P.C. Newell. 1976. A genetic study of aggregation in the cellular slime mould Dictyostelium discoideum using complementary analysis. Genetics 82 287-307. 

The specific growth rate of a microbial predator (X) was found to be dependent upon the ratio of the prey (H) to predator (P) population densities rather than the prey density alone. Predatory amoebae of the cellular slime mould Dictyostelium discoideum were grown in single-stage and two-stage chemostat cultures with the gut bacterium, Escherichia coli as their source of food. Predator growth in the cultures was compared to each of three functions which have been proposed for X. ... 

The goal of the research we report here was to determine whether the specific growth rate of predatory amoebae of the cellular slime mould Dictyostelium discoideum feeding on the gut bacteria, Escherichia coli was dependent upon prey density alone or upon the ratio of prey to predator. Two experimental systems were employed, both based on the chemostat type of continuous culture. A chemostat is a continuously stirred tank reactor in which microorganisms grow in a homogeneous environment and are supplied with nutrient solution at the same volumetric rate at... 

The eukaryotic cellular slime mould Dictyostelium discoideum is a widely used model organism as its lifecycle involves both unicellular and multicellular stages. This has made D. discoideum an excellent... 

D-Glucose could be transferred from UDP-D-glucose to endogenous receptors by a particulate enzyme fraction from the cellular slime mould, Dictyostelium discoideum When H4-edta was incorporated into the medium, the sole product was a mono-D-glucosylceramide that contained a hydroxy fatty acid. Divalent cations were not essential but they could stimulate the reaction, whereas other sugars had little effect on the reaction. 

More complicated structures have been reported in the literature. Coupling of flows with reaction-diffusion yields interesting travelling stmctures. The addition of flow to chemical reaction-diffusion system provides a robust pattern forming mechanism which is expected to occur in a wide variety of natural and artificial systems [56]. Typical examples are (i) Ca + waves in the slime mould dictyostelium discoideum,... 

The transition of the cellular slime mould Dictyostelium discoideum from the amoebal phase to the aggregation phase initiates the production of discoidin, a cell-surface lectin. This lectin has been resolved into two components that differ in the way that they are regulated during development. 

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