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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of starvation on the cell morphology of Dictyostelium discoideum were studied with different cytochemical techniques, and with a morphometric method by which the surface areas of the cell membrane and of the digestive system can be determined. During the first 2 h, the cell membrane becomes very wrinkled and many phagocytic cups and filopods are formed. These changes are in accord with the 40 percent increase in the cell surface area to cytoplasmic volume ratio observed, which is mainly due to a strong decrease in the cytoplasmic volume. At this time of starvation, cells are able to ingest twice as many yeast as during growth. Afterwards, while the phagocytic ability decreases, the phagocytic cups disappear, and all the cells become bristled with many thin filopods. In spite of these morphological changes, no quantitative or topological differences have been observed concerning the polysaccharide content of the plasma membrane, whether it was stained with phosphotungstic acid, silver proteinate, or ruthenium red. During this time, the digestive vacuoles imbricate one into the other. Part of the vacuoles are degraded by this process, thus leading to an atrophy of the digestive apparatus. The digestive apparatus is progressively replaced by an autophagic system. Polysaccharide stainings and morphological observations show that the cytosegresomes seem to originate from the food vacuoles which flatten and sequester portions of cytoplasm. After 5 h of starvation, the digestive system is entirely transformed into an autophagic apparatus. The cell population appears to be homogeneous with respect to these changes. Therefore, potential precursors of prestalk and prespore cells were not observed.
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PMID:Changes of the cell surface and of the digestive apparatus of Dictyostelium discoideum during the staruation period triggering aggregation. 14 40

Cyclic adenosine 3':5'-monophosphate added to the starvation media of Dictyostelium discoideum amoebae induces both intracellular and extracellular phosphodiesterase activities of these cells. The induced enzyme activity appears several hours earlier than that in starved cells which have not been induced with cyclic nucleotide. In both cases, the appearance of enzyme is inhibited by cycloheximide, and actinomycin D, and daunomycin. The KmS for the extracellular enzyme(s) of nucleotide-induced and uninduced control cells are identical. The induction of enzyme activity seems specific for cyclic adenosine 3':5'-monophosphate since cyclic guanosine 3':5'-monophosphate, as well as other nucleotides, have no effect. No differences in the activity or excretion of either N-acetylglucosaminidase or the inhibitory of the extracellular phosphodiesterase are observed between cyclic adenosine 3':5'-monophosphate-induced and control cells. A direct activation of phosphodiesterase by cyclic adenosine 3':5'-monophosphate can be excluded, since the addition of this nucleotide to cell lysates has no effect on the enzyme activity.
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PMID:Induction of phosphodiesterase by cyclic adenosine 3':5'-monophosphate in differentiating Dictyostelium discoideum amoebae. 17 Feb 56

During the first few hours of starvation, Dictyostelium discoideum amoebae excrete a macromolecule, probably a glycoprotein, which stimulates cell differentiation to aggregation competence. 3':5'-Cyclic AMP pulses, which mimic the chemotactic signal, and this factor (differentiation stimulating factor) are shown to exert a cooperative effect in inducing cell differentiation. Data suggest that the appearance of the factor determines the moment amoebae become responsive to cyclic AMP pulses.
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PMID:A differentiation stimulating factor induces cell sensitivity to 3':5'-cyclic AMP pulses in dictyostelium discoideum. 17 82

1. Rapid labelling occurs when myxamoebae of Dictyostelium discoideum strain AX2 are incubated with [1,4-14C]putrescine. Labelling is energy-dependent. 2. The label enters a pool from which rapid exchange with extracellular putrescine does not occur, and labelling is believed to represent uptake into the cells. 3. The concentration-dependence of putrescine uptake indicates that a number of systems are involved, at least one of which is saturable, with a Km of 9.1 micro M-putrescine. At high putrescine concentrations the overall uptake process is non-saturable. 4. Significant metabolism of putrescine and loss of intracellular putrescine to the medium only occurred when cells were incubated with millimolar concentrations of extracellular putrescine. 5. Putrescine uptake was inhibited by diamines, polyamines, bivalent metal ions and omega-aminocarboxylic acids. 6. The ability to take up putrescine at low concentrations decreased during starvation of myxamoebae. 7. The results are interpreted in terms of a model for putrescine uptake involving adsorptive pinocytosis at low concentrations and fluid-phase pinocytosis at high concentrations.
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PMID:Putrescine uptake by the cellular slime mould dictyostelium discoideum. 48 95

The growth of the eucaryotic microorganism Dictyostelium discoideum in liquid culture was completely inhibited by the aspartic acid analog hadacidin (N-formylhydroxyamino-acetic acid). Growth arrest occurred both in chemically defined medium and in complex growth medium containing aspartic acid and AMP precursors such as adenine and adenosine. Although these compounds could not overcome the effect of hadacidin, growth was restored if cells were washed and resuspended in fresh growth medium. Additional experiments showed that D. discoideum contains adenylosuccinate synthetase, the enzyme which catalyzes the synthesis of adenylosuccinate from IMP, aspartic acid, and GTP in the de novo biosynthesis of purines. A partially purified preparation of this enzyme was obtained, and the effect of hadacidin on its activity was studied. We found that maximum inhibition of the D. discoideum activity occurs at a ratio of aspartic acid to hadacidin of 5:1, suggesting that the affinity of the drug for this enzyme is less than for the enzyme from rabbit muscle and plants but greater than for that from Escherichia coli. The effect of the drug can be overcome by a 10-fold excess of aspartic acid, suggesting that the drug acts as a competitive inhibitor. A comparison of the adenylosuccinate synthetase activity levels at various stages of growth showed that its specific activity decreases about 60% as cells enter the stationary growth phase, and decreases about 75% after starvation for 2 h. Further studies showed that in cells treated with hadacidin the rate of uptake of exogenous nutrients is reduced about 75% and that these cells are more resistant to rupture by osmotic shock. While the results of this study are consistent with the proposal that growth arrest is contingent upon inhibition of adenylosuccinate synthetase activity, they also suggest that, as a consequence of this inhibition, some physiological properties of the cell have been altered.
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PMID:Effect of hadacidin on growth and adenylosuccinate synthetase activity of Dictyostelium discoideum. 56 51

Throughout growth, Dictyostelium cells continuously produce an autocrine factor, PSF, that accumulates in proportion to cell density. Production of PSF declines rapidly when cells are shifted to starvation conditions, and the properties of PSF are distinct from those of regulatory factors produced by starving cells. During late exponential growth, PSF induces expression of several early developmental genes, including those for proteins important in cAMP signaling and cell aggregation. Examples are the aggregation stage cAMP receptor (cAR1), the aggregation-specific form of cyclic nucleotide phosphodiesterase, and gp24 (contact sites B). Through PSF, growing cells detect environmental conditions (cell number high, food approaching depletion) that are appropriate for production of the gene products needed to initiate aggregation and development.
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PMID:Expression of early developmental genes in Dictyostelium discoideum is initiated during exponential growth by an autocrine-dependent mechanism. 131 52

A number of phosphoinositide-specific phospholipases C (PLC) of different species have recently been cloned. The predicted amino acid sequences of these isoforms contain two highly conserved domains. Here we report the identification of a PLC gene of Dictyostelium by using the polymerase chain reaction. Primers were designed coding for highly conserved amino acid regions located within one of the conserved domains of PLCs. Cloning and sequencing of the polymerase chain reaction product revealed one unique PLC-like sequence. This sequence was used to screen a library and isolate several overlapping cDNA clones. The complete cDNA was expressed in Dictyostelium cells resulting in increased basal levels of inositol 1,4,5-trisphosphate and enhanced PLC activity. The identified Dictyostelium PLC, DdPLC, encodes a protein with a calculated molecular mass of 91 kDa. The deduced amino acid sequence contains the two conserved domains found in other PLC isoforms, separated by a short variable region. The C-terminal part of the protein shows strong homology with the mammalian PLC-delta isoform. DdPLC is expressed at all stages of development, with an increase in transcription during starvation and in the culminating fruiting body.
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PMID:Molecular cloning and expression of a phosphoinositide-specific phospholipase C of Dictyostelium discoideum. 132 23

The Schizosaccharomyces pombe gpa2 gene was cloned by hybridization with a cDNA for Dictyostelium discoideum G alpha 1. It encodes a homolog of G-protein alpha-subunits with 354 amino acids and a predicted molecular mass of 40,522. Disruption of gpa2 slows cell growth but is not lethal. Cells defective in gpa2 mate and sporulate readily in the presence of plentiful nutrition, bypassing the requirement of nitrogen starvation for the initiation of sexual development. These phenotypes mimic those of cells defective in cyr1 encoding adenylyl cyclase. The level of cAMP in gpa2 null mutants is only one-third of the wild-type level. Mutations in gpa2 that are likely to inhibit the GTPase activity of the gene product cause a slight increase in intracellular cAMP levels and result in leaky sterility. The cAMP level reaches 20 times as high as the wild-type level if a cell carries both this type of gpa2 mutation and a null mutation in pde1 encoding phosphodiesterase. Cells defective in gpa2 fail to produce cAMP in response to glucose stimulation. These results suggest that Gpa2 is involved in the determination of the cAMP level according to nutritional conditions, most likely as a positive regulator of adenylyl cyclase.
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PMID:Characterization of a fission yeast gene, gpa2, that encodes a G alpha subunit involved in the monitoring of nutrition. 134 Apr 62

To investigate the intracellular role of the clathrin heavy chain in living cells, we have used "antisense" RNA to engineer mutant Dictyostelium discoideum cells that are severely deficient in clathrin heavy chain expression. Immunoblots stained with an anti-clathrin heavy chain antiserum revealed that mutant cells contained undetectable amounts of clathrin heavy chain protein. Similarly, Northern blots showed an absence of clathrin heavy chain mRNA. Clathrin heavy chain-deficient Dictyostelium cells were viable, but exhibited growth rates twofold slower than parental cells. Whereas many morphological features of the mutant cells were normal, mutant cells lacked coated pits and coated vesicles. Clathrin-deficient cells were also missing large translucent vacuoles that serve as endosomes and contractile vacuoles. In the absence of clathrin heavy chain, mutant cells displayed three distinct functional defects: (a) impairment in endocytosis of fluid phase markers, but competence in another endocytic pathway, the phagocytosis of solid particles; (b) defects in osmoregulation; and (c) inability to complete the starvation-induced development cycle.
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PMID:Clathrin heavy chain is required for pinocytosis, the presence of large vacuoles, and development in Dictyostelium. 152 12

The cellular slime mold Dictyostelium discoideum is a microorganism in which growth and development are strictly separated. Starvation initiates a developmental program in which extracellular cAMP plays a major role as a signal molecule. In response to cAMP several second messengers are produced, including cAMP, cGMP and inositol 1,4,5-trisphosphate, (Ins(1,4,5)P3). Ins(1,4,5)P3 levels are controlled by the activation of phosphoinositidase C and the activity of the Ins(1,4,5)P3-degrading phosphatases. In Dictyostelium discoideum two major routes for the dephosphorylation of Ins(1,4,5)P3 are present: a 5-phosphatase, which hydrolyses Ins(1,4,5)P3 at the 5-position producing Ins(1,4)P2 as in vertebrate cells, and a 1-phosphatase which removes the 1-phosphate, giving Ins(4,5)P2, as in plants. In this paper we show that at the onset of development both the 1-phosphatase and the 5-phosphatase are present in equal amounts. During development the 5-phosphatase disappears leaving the 1-phosphatase as the single enzyme to remove Ins(1,4,5)P3. We conclude that during development Dictyostelium discoideum switches from a mixed type of Ins(1,4,5)P3 degradation to a more plant-like degradation pathway.
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PMID:Developmental regulation of the inositol 1,4,5-trisphosphate phosphatases in Dictyostelium discoideum. 164 36


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