Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Folic acid attracts vegetative amoebae of Dictyostelium discoideum. Secreted by bacteria, it may act as a food-seeking device. The inactivation of this attractant is catalyzed by a deaminase. As assay has been developed to measure the folic acid deaminase activity. In addition to cell-surface an intracellular deaminase, the amoebae of D. discoideum release the enzyme into the medium. The pH optimum of the extracellular enzyme was 6.0, and higher for the cell-associated deaminases. The extracellular enzyme was secreted maximally by vegetative amoebae, and its activity diminished during cell differentiation. The cell-surface bound enzyme was less active than the extracellular enzyme, and its activity decreased twofold during a 6-h starvation period. The enzyme activity of homogenates and 48,000 x g pellets diminished during this period 35 to 40%. The supernatant of a homogenate had a higher deaminase activity than the homogenate itself or its pellet; this suggests the presence of an inhibitor in the particulate fraction. The underlying mechanism for inactivation of folic acid has similar characteristics as that for inactivation of cyclic adenosine monophosphate.
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PMID:Folic acid deaminase activity during development in Dictyostelium discoideum. 740 95

Development of the cellular slime mould Dictyostelium discoideum strain NC4, in the presence of alpha-chymotrypsin (3 mg/ml) is reversibly arrested at the tight aggregate stage (10/12 h). Pronase has a similar effect, but trypsin only retards normal development by about five hours. Normally developing cells are susceptible to alpha-chymotrypsin if they are transferred into its presence at any time up to the tight aggregate stage (10-12 h). Transfer after this stage does not affect the appearance of fruiting body structures in the normal time (24 h). Electron microscopy showed the ultrastructure of alpha-chymotrypsin-blocked aggregates after starvation for 24 h to be consistent with a block at 10-12 h of normal development. Poorly developed prespore vacuoles, having thin incomplete walls and a paucity of electron-dense material, are present in some cells. No angular vacuolated cells characteristic of stalk cells are visible. Fruiting bodies formed in the presence of a alpha-chymotrypsin, either as minority structures when the enzyme is added before 10-12 h of normal development, or as the majority structures on later enzyme addition, were found to be abnormal. Normal stalks were formed but the spores were immature. Prespore vacuoles were present, though disrupted, and the cells were not encapsulated by spore walls. The electronegativity of intact slime mould amoebae was significantly reduced, and material containing L-[6-3H]-fucose and [1-14C]leucine was removed from the cell surface on alpha-chymotrypsin treatment. Few plasma membrane proteins were affected, however, and staining of polyacrylamide gels for glycopeptides using Con A-peroxide binding also showed little change.
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PMID:The effect of chymotrypsin on the development of Dictyostelium discoideum. 743 Sep 29

The rap1 gene of Dictyostelium discoideum is a member of the ras-gene superfamily of low molecular weight GTPase proteins. The rap1 gene is expressed both during growth and development in D. discoideum. To examine the action of the Rap1 protein in D. discoideum, the rap1 cDNA was expressed under the control of the inducible discoidin promoter. Treatment with conditioned media, which induces the discoidin promoter, increased Rap1 protein levels in vegetative cells approximately six fold. Overexpression of the Rap1 protein correlated with the appearance of morphologically aberrant vegetative amoebae: cells were extensively spread and flattened. The distribution of F-actin was altered in these cells, with an increase in actin staining around the cell periphery. Induction of the discoidin promoter by starvation in the rap1 transformants also resulted in spread flat cells. When starved D. discoideum amoebae are refed with HL5 media, the cells rapidly respond by rounding up. By contrast, the rap1 transformant cells showed a pronounced delay in rounding up. Rapid tyrosine phosphorylation of a p45 protein occurred in both control cells and the rap1 transformant upon refeeding, implying that the signal transduction pathway leading to tyrosine phosphorylation remained functional in the rap1 transformant. We propose that the Rap1 protein functions in the regulation of cell morphology in D. discoideum.
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PMID:Altered morphology of vegetative amoebae induced by increased expression of the Dictyostelium discoideum ras-related gene rap1. 750 18

Although Dictyostelium differentiation occurs in the absence of external nutrients, two periods of mitosis occur, one during early development and one during the formation of the migrating pseudoplasmodium. We showed previously that cyclin B mRNA levels vary in a cell cycle dependent manner during vegetative cell growth. In the present study, we report that cyclin B mRNA levels change dramatically during development, reaching a maximum at the tipped aggregate stage. However, amounts of cyclin B protein vary only slightly, peaking during early development and decreasing during late aggregation and pseudoplasmodial formation. Cdc2 protein levels also remain relatively constant during development. Cdc2-histone H1 kinase activity was considerably higher in vegetative cell extracts of transformants that expressed large amounts of truncated cyclin B protein in comparison to extracts of the parental Ax-2 cells. These results suggest that Cdc2 kinase activity is dependent upon the level of cyclin B in vegetative cells. This result is consistent with the idea that variations in the level of cyclin B during growth regulate the cell cycle. When Cdc2 histone H1 kinase activity was determined during development, it was also found that activity correlated reasonably well with the amount of cyclin B protein. Thus, there was an increase in Cdc2 histone H1 kinase activity early in development, and then levels decreased as development progressed. The increase in Cdc2 histone H1 kinase activity that occurs early in development following starvation may be important in accelerating G2-phase cells through into mitosis. There was no increase in Cdc2 histone H1 kinase that accompanied the previously reported late developmental mitosis.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cyclin B and Cdc2 expression and Cd2 kinase activity during Dictyostelium differentiation. 757 76

The expression of the discoidin I genes in Dictyostelium discoideum is regulated by the concerted action of the extracellular factors cyclic adenosine monophosphate (cAMP), folate, prestarvation factor (PSF) and conditioned media factor (CMF). However, the pathways by which these signals are transduced and the interactions between the pathways have been unexplored so far. We have analysed wild-type and mutant cells with defined lesions in signal transduction to elucidate these regulatory processes, and shown that different pathways are used for the down-regulation and induction of these genes. The cAMP receptor cARI is required for the cAMP-mediated down-regulation of discoidin I gene expression but not for the induction of discoidin I expression during development. Surprisingly, induction of the discoidin I genes requires G alpha 2, the G-protein subunit which is generally believed to couple to cARI, to control the expression of cAMP-inducible genes. Thus, our data suggest that G alpha 2 interacts with different receptors to regulate gene expression in early development. Furthermore, the analysis shows that discoidin induction in bacterially grown cells occurs in two sequential steps. The first is a low basal induction which occurs in late log-phase growth prior to starvation. PSF can induce the basal level, and the induction is independent of G alpha 2. The developmental induction following starvation is much stronger, dependent on G alpha 2 and probably signaled by CMF, which is secreted at that time.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Multiple signal transduction pathways regulate discoidin I gene expression in Dictyostelium discoideum. 764 76

Dictyostelium amoebae that lack myosin II (mhcA-) are unable to undergo morphogenesis. The cells aggregate slowly to form hemispherical mounds, but the mounds never extend a tip upward. Expression of developmentally regulated genes appears normal in the absence of morphogenesis. When mixed with an excess of wild-type cells, some mutant cells form differentiated spores; however, rescue is extremely inefficient (Knecht and Loomis, 1988). In order to assess how morphogenesis is normally accomplished and why mutants lacking myosin II cannot develop, a new method has been developed that allows individual amoebae to be localized and tracked at high resolution within the multicellular organism during development. Amoebae are labeled with a fluorescent dye at the beginning of starvation, mixed with an excess of unlabeled cells, and allowed to develop. The three-dimensional position of labeled cells in the multicellular organism is then determined using a laser scanning confocal microscope. Using this methodology, we have shown that labeled wild-type cells are randomly distributed throughout the organism and complete development normally. When labeled mhcA- mutant cells are mixed with a 20-fold excess of wild-type cells, they are non-randomly localized even at the earliest stages of development. Mutant cells in aggregation streams are found primarily at the edges of the streams and many cells never become part of the streams or are left behind as the wild-type cells complete aggregation. Those that are incorporated into the aggregate are found at the edge and base, the backs of slugs and the base of the fruiting bodies. A few mutant cells can be found in the sorus, where they presumably become spores. The segregation of mhcA- mutant cells to the outside of the wild-type aggregation streams argues that the mutant cells are unable to penetrate a mass of adhered, wild-type cells. We hypothesize that mutant cells lacking cortical integrity are unable to generate sufficient protrusive force to break the adhesion of wild-type cells to each other. This would make the mutants incapable of moving through a mass of cells (either mutant or wild type) or of changing shape when adhered to other cells. We propose that mutants lacking myosin II are unable to accomplish morphogenesis because they cannot move correctly in a three-dimensional mass of adhered cells.
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PMID:Three-dimensional localization of wild-type and myosin II mutant cells during morphogenesis of Dictyostelium. 764 74

When Dictyostelium cells that have initiated their developmental program upon starvation are returned to growth medium, there is a rapid and transient de novo tyrosine phosphorylation of a 43-kilodalton protein. This protein was found to be actin. Most of the phosphorylation occurred in a single, minor acidic isoform of actin. Developing cells that had been returned to growth medium lost their pseudopod extensions, became round, and had reduced adhesion to the substratum. These effects occurred with kinetics that matched the increase in tyrosine phosphorylation of actin. In mutant cell lines in which the gene for the phosphotyrosine phosphatase PTP1 had been disrupted, tyrosine phosphorylation of actin was rapid and more prolonged. These cells responded with proportionally accelerated kinetics of cell rounding. Cell lines overexpressing PTP1 had diminished amplitude and duration of actin tyrosine phosphorylation and exhibited diminished cell-shape change and an accelerated return to the extended cell-shape morphology seen in starved cells.
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PMID:Tyrosine phosphorylation of actin in Dictyostelium associated with cell-shape changes. 767 70

We identified and purified an actin monomer-binding protein of apparent molecular weight of 15,000 from Dictyostelium discoideum. The 15-kDa protein depolymerized actin filaments in a pH-dependent manner. The protein also had an activity to decrease apparent viscosity of actin solutions in a dose-dependent manner. This activity was inhibited by phosphatidyl inositides. Molecular cloning of genes encoding this protein revealed that the protein is 42% identical in its primary sequence to yeast cofilin. We concluded that the 15-kDa protein is cofilin of this organism. D. discoideum cells contain two cofilin genes (DCOF1 and DCOF2) whose nucleotide sequences were entirely identical in their exsons while the promoter and intron regions were different. Promoter assay experiments revealed that DCOF1 is expressed both in vegetative and differentiating cells and that DCOF2 is not expressed under any conditions examined. Gene disruption experiments suggested that DCOF1 might be essential for the proliferation of D. discoideum cells whereas the disruption of DCOF2 was proven not to alter any phenotypes. Indirect immunofluorescence microscopic observations showed that cofilin is distributed diffusely throughout cytoplasm in vegetative cells. In flattened cells under starvation stress, cofilin localized at dramatically reorganizing actin-cytoskeletons in ruffling membranes of the leading edge, but not at rigid actin meshwork in focal adhesion plaques. These results suggest that cofilin may be involved in dynamic reorganization of membranous actin cytoskeletons.
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PMID:Identification, characterization, and intracellular distribution of cofilin in Dictyostelium discoideum. 773 34

Cell differentiation and proliferation are mutually exclusive processes in many cases. The transition of starving Dictyostelium cells from growth to differentiation phase has been shown to occur at a particular position (putative shift point; PS-point) in the cell cycle of D. discoideum Ax-2. The significance of phosphorylation states of proteins such as 101 kDa, 90 kDa, and 32 kDa phosphoproteins has been argued, particularly around the PS-point. In this study we examined effects of the protein kinase inhibitors and activators on the transition of Ax-2 cells from growth to differentiation. K252a, a potent inhibitor of protein kinases, inhibited growth possibly through the blockage of pinocytotic activity of cells, and promoted the progress of development after starvation when applied to Ax-2 cells at the growth phase. Such a K252a-effect was most pronouncedly exhibited on the cells located near the PS-point. Unexpectedly, however, the development of starved cells was found to be considerably delayed by staurosporine bearing a structural and functional resemblance to K252a when it was applied during the growth phase. Pulse-labelings of growing Ax-2 cells with inorganic 32P (32Pi) showed that K252a induces the disappearance of a 48 kDa phosphoprotein and the appearance of a 50 kDa phosphoprotein, specifically in the cells located around the PS-point. Phosphorylation of 32 kDa and 24 kDa proteins was also inhibited by K252a, but this inhibition was not necessarily specific to the K252a-treatment and occurred independently of the cell-cycle phases. The possible significance of these results is discussed in relation to a breakaway of cells from proliferation to differentiation at the PS-point.
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PMID:K252a, a potent inhibitor of protein kinases, promotes the transition of Dictyostelium cells from growth to differentiation. 776 85

Conventional myosin has two different light chains bound to the neck region of the molecule. It has been suggested that the light chains contribute to myosin function by providing structural support to the neck region, therefore amplifying the conformational changes in the head following ATP hydrolysis (Rayment et al., 1993). The regulatory light chain is also believed to be important in regulating the actin-activated ATPase and myosin motor function as assayed by an in vitro motility assay (Griffith et al., 1987). Despite extensive in vitro biochemical study, little is known regarding RMLC function and its regulatory role in vivo. To better understand the importance and contribution of RMLC in vivo, we engineered Dictyostelium cell lines with a disrupted RMLC gene. Homologous recombination between the introduced gene disruption vector and the chromosomal RMLC locus (mlcR) resulted in disruption of the RMLC-coding region, leading to cells devoid of both the RMLC transcript and the 18-kD RMLC polypeptide. RMLC-deficient cells failed to divide in suspension, becoming large and multinucleate, and could not complete development following starvation. These results, similar to those from myosin heavy chain mutants (DeLozanne et al., 1987; Manstein et al., 1989), suggest the RMLC subunit is required for normal cytokinesis and cell motility. In contrast to the myosin heavy chain mutants, however, the mlcR cells are able to cap cell surface receptors following concanavilin A treatment. By immunofluorescence microscopy, RMLC null cells exhibited myosin localization patterns different from that of wild-type cells. The myosin localization in RMLC null cells also varied depending upon whether the cells were cultured in suspension or on a solid substrate. In vitro, purified RMLC- myosin assembled to form thick filaments comparable to wild-type myosin, but the filaments then exhibit abnormal disassembly properties. These results indicate that in vivo RMLC is necessary for myosin function.
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PMID:Targeted disruption of the Dictyostelium RMLC gene produces cells defective in cytokinesis and development. 780 58


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