1
|
Müller R, Herr C, Sukumaran SK, Omosigho NN, Plomann M, Riyahi TY, Stumpf M, Swaminathan K, Tsangarides M, Yiannakou K, Blau-Wasser R, Gallinger C, Schleicher M, Kolanus W, Noegel AA. The cytohesin paralog Sec7 of Dictyostelium discoideum is required for phagocytosis and cell motility. Cell Commun Signal 2013; 11:54. [PMID: 23915312 PMCID: PMC3737031 DOI: 10.1186/1478-811x-11-54] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Accepted: 07/29/2013] [Indexed: 12/26/2022] Open
Abstract
Background Dictyostelium harbors several paralogous Sec7 genes that encode members of three subfamilies of the Sec7 superfamily of guanine nucleotide exchange factors. One of them is the cytohesin family represented by three members in D. discoideum, SecG, Sec7 and a further protein distinguished by several transmembrane domains. Cytohesins are characterized by a Sec7-PH tandem domain and have roles in cell adhesion and migration. Results We study here Sec7. In vitro its PH domain bound preferentially to phosphatidylinositol 3,4-bisphosphate (PI(3,4)P2), phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3). When following the distribution of GFP-Sec7 in vivo we observed the protein in the cytosol and at the plasma membrane. Strikingly, when cells formed pseudopods, macropinosomes or phagosomes, GFP-Sec7 was conspicuously absent from areas of the plasma membrane which were involved in these processes. Mutant cells lacking Sec7 exhibited an impaired phagocytosis and showed significantly reduced speed and less persistence during migration. Cellular properties associated with mammalian cytohesins like cell-cell and cell-substratum adhesion were not altered. Proteins with roles in membrane trafficking and signal transduction have been identified as putative interaction partners consistent with the data obtained from mutant analysis. Conclusions Sec7 is a cytosolic component and is associated with the plasma membrane in a pattern distinctly different from the accumulation of PI(3,4,5)P3. Mutant analysis reveals that loss of the protein affects cellular processes that involve membrane flow and the actin cytoskeleton.
Collapse
Affiliation(s)
- Rolf Müller
- Institute of Biochemistry I, Medical Faculty, Center for Molecular Medicine Cologne and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, 50931 Köln, Germany
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
2
|
Sillo A, Matthias J, Konertz R, Bozzaro S, Eichinger L. Salmonella typhimurium is pathogenic for Dictyostelium cells and subverts the starvation response. Cell Microbiol 2011; 13:1793-811. [PMID: 21824247 DOI: 10.1111/j.1462-5822.2011.01662.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
In unicellular amoebae, such as Dictyostelium discoideum, bacterial phagocytosis is a food hunting device, while in higher organisms it is the first defence barrier against microbial infection. In both cases, pathogenic bacteria exploit phagocytosis to enter the cell and multiply intracellularly. Salmonella typhimurium, the agent of food-borne gastroenteritis, is phagocytosed by both macrophages and Dictyostelium cells. By using cell biological assays and global transcriptional analysis with DNA microarrays covering the Dictyostelium genome, we show here that S. typhimurium is pathogenic for Dictyostelium cells. Depending on the degree of virulence, which in turn depended on bacterial growth conditions, Salmonella could kill Dictyostelium cells or inhibit their growth and development. In the early phase of infection in non-nutrient buffer, the ingested bacteria escaped degradation, induced a starvation-like transcriptional response but inhibited selectively genes required for chemotaxis and aggregation. This way differentiation of the host cells into spore and stalk cells was blocked or delayed, which in turn is likely to be favourable for the establishment of a replicative niche for Salmonella. Inhibition of the aggregation competence and chemotactic streaming of aggregation-competent cells in the presence of Salmonella suggests interference with cAMP signalling.
Collapse
Affiliation(s)
- Alessio Sillo
- Department of Clinical and Biological Sciences, University of Turin, AOU S. Luigi, 10043 Orbassano (Torino), Italy
| | | | | | | | | |
Collapse
|
3
|
Shina MC, Müller R, Blau-Wasser R, Glöckner G, Schleicher M, Eichinger L, Noegel AA, Kolanus W. A cytohesin homolog in Dictyostelium amoebae. PLoS One 2010; 5:e9378. [PMID: 20186335 PMCID: PMC2826412 DOI: 10.1371/journal.pone.0009378] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2009] [Accepted: 02/02/2010] [Indexed: 01/28/2023] Open
Abstract
BACKGROUND Dictyostelium, an amoeboid motile cell, harbors several paralogous Sec7 genes that encode members of three distinct subfamilies of the Sec7 superfamily of Guanine nucleotide exchange factors. Among them are proteins of the GBF/BIG family present in all eukaryotes. The third subfamily represented with three members in D. discoideum is the cytohesin family that has been thought to be metazoan specific. Cytohesins are characterized by a Sec7 PH tandem domain and have roles in cell adhesion and migration. PRINCIPAL FINDINGS Dictyostelium SecG exhibits highest homologies to the cytohesins. It harbors at its amino terminus several ankyrin repeats that are followed by the Sec7 PH tandem domain. Mutants lacking SecG show reduced cell-substratum adhesion whereas cell-cell adhesion that is important for development is not affected. Accordingly, multicellular development proceeds normally in the mutant. During chemotaxis secG(-) cells elongate and migrate in a directed fashion towards cAMP, however speed is moderately reduced. SIGNIFICANCE The data indicate that SecG is a relevant factor for cell-substrate adhesion and reveal the basic function of a cytohesin in a lower eukaryote.
Collapse
Affiliation(s)
- Maria Christina Shina
- Center for Biochemistry, Medical Faculty, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Köln, Germany
| | - Rolf Müller
- Center for Biochemistry, Medical Faculty, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Köln, Germany
| | - Rosemarie Blau-Wasser
- Center for Biochemistry, Medical Faculty, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Köln, Germany
| | - Gernot Glöckner
- Center for Biochemistry, Medical Faculty, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Köln, Germany
- Leibniz Institute for Age Research - Fritz-Lipmann-Institute e.V., Jena, Germany
| | - Michael Schleicher
- Institute of Anatomy and Cell Biology and Center for Integrated Protein Science (CIPSM), Ludwig-Maximilians-University, Muenchen, Germany
| | - Ludwig Eichinger
- Center for Biochemistry, Medical Faculty, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Köln, Germany
| | - Angelika A. Noegel
- Center for Biochemistry, Medical Faculty, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Köln, Germany
- * E-mail: (AAN); (WK)
| | - Waldemar Kolanus
- Laboratory of Molecular Immunology, LIMES Institute of the University of Bonn, Bonn, Germany
- * E-mail: (AAN); (WK)
| |
Collapse
|
4
|
Involvement of Sib proteins in the regulation of cellular adhesion in Dictyostelium discoideum. EUKARYOTIC CELL 2008; 7:1600-5. [PMID: 18676957 DOI: 10.1128/ec.00155-08] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Molecular mechanisms ensuring cellular adhesion have been studied in detail in Dictyostelium amoebae, but little is known about the regulation of cellular adhesion in these cells. Here, we show that cellular adhesion is regulated in Dictyostelium, notably by the concentration of a cellular secreted factor accumulating in the medium. This constitutes a quorum-sensing mechanism allowing coordinated regulation of cellular adhesion in a Dictyostelium population. In order to understand the mechanism underlying this regulation, we analyzed the expression of recently identified Dictyostelium adhesion molecules (Sib proteins) that present features also found in mammalian integrins. sibA and sibC are both expressed in vegetative Dictyostelium cells, but the expression of sibC is repressed strongly in conditions where cellular adhesion decreases. Analysis of sibA and sibC mutant cells further suggests that variations in the expression levels of sibC account largely for changes in cellular adhesion in response to environmental cues.
Collapse
|
5
|
Arigoni M, Bracco E, Lusche DF, Kae H, Weeks G, Bozzaro S. A novel Dictyostelium RasGEF required for chemotaxis and development. BMC Cell Biol 2005; 6:43. [PMID: 16336640 PMCID: PMC1325028 DOI: 10.1186/1471-2121-6-43] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2005] [Accepted: 12/07/2005] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Ras proteins are guanine-nucleotide-binding enzymes that couple cell surface receptors to intracellular signaling pathways controlling cell proliferation and differentiation, both in lower and higher eukaryotes. They act as molecular switches by cycling between active GTP and inactive GDP-bound states, through the action of two classes of regulatory proteins: a) guanine nucleotide exchange factor (GEFs) and b) GTP-ase activating proteins (GAPs). Genome wide analysis of the lower eukaryote Dictyostelium discoideum revealed a surprisingly large number of Ras Guanine Nucleotide Exchange Factors (RasGEFs). RasGEFs promote the activation of Ras proteins by catalyzing the exchange of GDP for GTP, thus conferring to RasGEFs the role of main activator of Ras proteins. Up to date only four RasGEFs, which are all non-redundant either for growth or development, have been characterized in Dictyostelium. We report here the identification and characterization of a fifth non-redundant GEF, RasGEFM. RESULTS RasGEFM is a multi-domain protein containing six poly-proline stretches, a DEP, RasGEFN and RasGEF catalytic domain. The rasGEFM gene is differentially expressed during growth and development. Inactivation of the gene results in cells that form small, flat aggregates and fail to develop further. Expression of genes required for aggregation is delayed. Chemotaxis towards cAMP is impaired in the mutant, due to inability to inhibit lateral pseudopods. Endogenous cAMP accumulates during early development to a much lower extent than in wild type cells. Adenylyl cyclase activation in response to cAMP pulses is strongly reduced, by contrast guanylyl cyclase is stimulated to higher levels than in the wild type. The actin polymerization response to cAMP is also altered in the mutant. Cyclic AMP pulsing for several hours partially rescues the mutant. In vitro experiments suggest that RasGEFM acts downstream of the cAMP receptor but upstream of the G protein. CONCLUSION The data indicate that RasGEFM is involved in the establishment of the cAMP relay system. We propose that RasGEFM is a component of a Ras regulated pathway, which integrate signals acting as positive regulator for adenylyl cyclase and negative regulator for guanylyl cyclase. Altered guanylyl cyclase, combined with defective regulation of actin polymerization, results in altered chemotaxis.
Collapse
Affiliation(s)
- Maddalena Arigoni
- Department of Clinical and Biological Sciences, University of Torino, Regione Gonzole 10, 10043 Orbassano, Italy
| | - Enrico Bracco
- Department of Clinical and Biological Sciences, University of Torino, Regione Gonzole 10, 10043 Orbassano, Italy
| | - Daniel F Lusche
- Faculty of Biology, University of Konstanz, 78457 Konstanz, Germany
| | - Helmut Kae
- Dept. Microbiology and Immunology, University of British Columbia, Canada V6T1Z3
| | - Gerald Weeks
- Dept. Microbiology and Immunology, University of British Columbia, Canada V6T1Z3
| | - Salvatore Bozzaro
- Department of Clinical and Biological Sciences, University of Torino, Regione Gonzole 10, 10043 Orbassano, Italy
| |
Collapse
|
6
|
Bowers-Morrow VM, Ali SO, Williams KL. Comparison of molecular mechanisms mediating cell contact phenomena in model developmental systems: an exploration of universality. Biol Rev Camb Philos Soc 2004; 79:611-42. [PMID: 15366765 DOI: 10.1017/s1464793103006389] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Are there universal molecular mechanisms associated with cell contact phenomena during metazoan ontogenesis? Comparison of adhesion systems in disparate model systems indicates the existence of unifying principles. Requirements for multicellularity are (a) the construction of three-dimensional structures involving a crucial balance between adhesiveness and motility; and (b) the establishment of integration at molecular, cellular, tissue, and organismal levels of organization. Mechanisms for (i) cell-cell and cell-substrate adhesion, (ii) cell movement, (iii) cell-cell communication, (iv) cellular responses, (v) regulation of these processes, and (vi) their integration with patterning, growth, and other developmental processes are all crucial to metazoan development, and must have been present for the emergence and radiation of Metazoa. The principal unifying themes of this review are the dynamics and regulation of cell contact phenomena. Our knowledge of the dynamic molecular mechanisms underlying cell contact phenomena remains fragmentary. Here we examine the molecular bases of cell contact phenomena using extant model developmental systems (representing a wide range of phyla) including the simplest i.e. sponges, and the eukaryotic protist Dictyostelium discoideum, the more complex Drosophila melanogaster, and vertebrate systems. We discuss cell contact phenomena in a broad developmental context. The molecular language of cell contact phenomena is complex; it involves a plethora of structurally and functionally diverse molecules, and diverse modes of intermolecular interactions mediated by protein and/or carbohydrate moieties. Reasons for this are presumably the necessity for a high degree of specificity of intermolecular interactions, the requirement for a multitude of different signals, and the apparent requirement for an increasingly large repertoire of cell contact molecules in more complex developmental systems, such as the developing vertebrate nervous system. However, comparison of molecular models for dynamic adhesion in sponges and in vertebrates indicates that, in spite of significant differences in the details of the way specific cell-cell adhesion is mediated, similar principles are involved in the mechanisms employed by members of disparate phyla. Universal requirements are likely to include (a) rapidly reversible intermolecular interactions; (b) low-affinity intermolecular interactions with fast on-off rates; (c) the compounding of multiple intermolecular interactions; (d) associated regulatory signalling systems. The apparent widespread employment of molecular mechanisms involving cadherin-like cell adhesion molecules suggests the fundamental importance of cadherin function during development, particularly in epithelial morphogenesis, cell sorting, and segregation of cells.
Collapse
|
7
|
Abstract
The development of most multicellular organisms involves differential movement of cells resulting in the formation of tissues. The principles governing these movements are poorly understood. One exception is the formation of the slug in the social amoebae Dictyostelium discoideum. The slug forms by the chemotactic aggregation of up to 10(5) starving cells, it is motile and migrates in response to light and temperature gradients to the surface of the soil to form a fruiting body consisting of a stalk supporting a spore head. Slug migration and behaviour result from coordinated chemotactic movement of the individual cells in the slug. Waves of a chemoattractant, most likely cAMP, are periodically initiated in the tip of the slug and propagate towards the back of the slug resulting in periodic forward movement of individual cells as well as the whole slug. Here we develop a model to investigate how wave propagation and cell movement interacts to result in migration and shape changes of the slug. The slug tissue is modelled as an incompressible liquid, in which waves of chemoattractant are generated in an excitable manner. The liquid is "active", i.e. it is able to generate body forces in response to the gradients of the chemoattractant. These forces lead to the formation of flows (representing chemotactically moving cells) and result in slug movement and shape changes. The model provides a theoretical framework for the understanding of the interactions between cell-cell signalling and cell movement, which govern slug behaviour and tissue morphogenesis.
Collapse
Affiliation(s)
- Bakhtier Vasiev
- Division of Cell and Developmental Biology, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, UK.
| | | |
Collapse
|
8
|
Queller DC, Ponte E, Bozzaro S, Strassmann JE. Single-gene greenbeard effects in the social amoeba Dictyostelium discoideum. Science 2003; 299:105-6. [PMID: 12511650 DOI: 10.1126/science.1077742] [Citation(s) in RCA: 182] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Selection can favor reproductive altruism if an altruism allele aids copies of itself by helping relatives. The alternative "greenbeard" mechanism, in which an allele directly recognizes and aids copies of itself in others, is generally thought to be too complex for a single gene to carry out. The csA gene in Dictyostelium discoideum acts as a single-gene greenbeard. When wild-type cells are mixed with csA-knockout cells, the wild type is more altruistic, but is also able preferentially to direct the benefits to other wild-type cells. Both properties derive directly from homophilic cell adhesion of the protein encoded by csA.
Collapse
Affiliation(s)
- David C Queller
- Department of Ecology and Evolution, MS-170, Rice University, Post Office Box 1892, Houston, TX 77251-1892, USA.
| | | | | | | |
Collapse
|
9
|
Décavé E, Garrivier D, Bréchet Y, Fourcade B, Bruckert F. Shear flow-induced detachment kinetics of Dictyostelium discoideum cells from solid substrate. Biophys J 2002; 82:2383-95. [PMID: 11964228 PMCID: PMC1302030 DOI: 10.1016/s0006-3495(02)75583-5] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Using Dictyostelium discoideum as a model organism of specific and nonspecific adhesion, we studied the kinetics of shear flow-induced cell detachment. For a given cell, detachment occurs for values of the applied hydrodynamic stress above a threshold. Cells are removed from the substrate with an apparent first-order rate constant that strongly depends on the applied stress. The threshold stress depends on cell size and physicochemical properties of the substrate, but is not affected by depolymerization of the actin and tubulin cytoskeleton. In contrast, the kinetics of cell detachment is almost independent of cell size, but is strongly affected by a modification of the substrate and the presence of an intact actin cytoskeleton. These results are interpreted in the framework of a peeling model. The threshold stress and the cell-detachment rate measure the local equilibrium energy and the dissociation rate constant of the adhesion bridges, respectively.
Collapse
Affiliation(s)
- Emmanuel Décavé
- Département de Biologie Moléculaire et Structurale/BBSI, Commissariat à l'Energie Atomique Grenoble, 38054 Grenoble cedex 9, France
| | | | | | | | | |
Collapse
|
10
|
Tatischeff I, Petit PX, Grodet A, Tissier JP, Duband-Goulet I, Ameisen JC. Inhibition of multicellular development switches cell death of Dictyostelium discoideum towards mammalian-like unicellular apoptosis. Eur J Cell Biol 2001; 80:428-41. [PMID: 11484934 DOI: 10.1078/0171-9335-00172] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The multicellular development of the single celled eukaryote Dictyostelium discoideum is induced by starvation and consists of initial aggregation of the isolated amoebae, followed by their differentiation into viable spores and dead stalk cells. These stalk cells retain their structural integrity inside a stalk tube that support the spores in the fruiting body. Terminal differentiation into stalk cells has been shown to share several features with programmed cell death (Cornillon et al. (1994), J. Cell Sci. 107, 2691-2704). Here we report that, in the absence of aggregation and differentiation, D. discoideum can undergo another form of programmed cell death that closely resembles apoptosis of most mammalian cells, involves loss of mitochondrial transmembrane potential, phosphatidylserine surface exposure, and engulfment of dying cells by neighboring D. discoideum cells. This death has been studied by various techniques (light microscopy and scanning or transmission electron microscopy, flow cytometry, DNA electrophoresis), in two different conditions inhibiting D. discoideum multicellular development. The first one, corresponding to an induced unicellular cell death, was obtained by starving the cells in a "conditioned" cell-free buffer, prepared by previous starvation of another D. discoideum cell population in potassium phosphate buffer (pH 6.8). The second one, corresponding to death of D. discoideum after axenic growth in suspension, was obtained by keeping stationary cells in their culture medium. In both cases of these unicellular-specific cell deaths, microscopy revealed morphological features known as hallmarks of apoptosis for higher eukaryotic cells and apoptosis was further corroborated by flow cytometry. The occurrence in D. discoideum of programmed cell death with two different phenotypes, depending on its multicellular or unicellular status, is further discussed.
Collapse
Affiliation(s)
- I Tatischeff
- Laboratoire de Physicochimie Biomoléculaire et Cellulaire, CNRS ESA 7033, Université Pierre et Marie Curie, Paris, France.
| | | | | | | | | | | |
Collapse
|
11
|
Yuan A, Siu CH, Chia CP. Calcium requirement for efficient phagocytosis by Dictyostelium discoideum. Cell Calcium 2001; 29:229-38. [PMID: 11243931 DOI: 10.1054/ceca.2000.0184] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Extracellular EDTA suppressed in a dose-dependent manner the phagocytosis of yeast particles by Dictyostelium discoideum cells. Activity was restored fully by the addition of Ca(2+), and partially by the addition of Mn(2+)or Zn(2+), but Mg(2+)was ineffective. The pH-sensitive, Ca(2+)-specific chelator EGTA also inhibited phagocytosis at pH 7.5, but not at pH 5, and Ca(2+)restored the inhibited phagocytosis. In contrast, pinocytosis was unaffected by EDTA. Consistent with the idea that Ca(2+)was required for phagocytosis, D. discoideum growth on bacteria was inhibited by EDTA, which was then restored by the addition of Ca(2+). It is concluded that Ca(2+)was needed for efficient phagocytosis by D. discoideum amoebae. A search for Ca(2+)-dependent membrane proteins enriched in phagosomes revealed the presence of p24, a Ca(2+)-dependent cell-cell adhesion molecule-1 (DdCAD-1) that could be the target of the observed EDTA and EGTA inhibition. DdCAD-1-minus cells, however, had normal phagocytic activity. Furthermore, phagocytosis was inhibited by EDTA and rescued by Ca(2+)in the mutant just as in wild type. Thus, DdCAD-1 was not responsible for the observed Ca(2+)-dependence of phagocytosis, indicating that one or more different Ca(2+)-dependent molecule(s) was involved in the process.
Collapse
Affiliation(s)
- A Yuan
- School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68588-0118, USA.
| | | | | |
Collapse
|
12
|
Marée AF, Hogeweg P. How amoeboids self-organize into a fruiting body: multicellular coordination in Dictyostelium discoideum. Proc Natl Acad Sci U S A 2001; 98:3879-83. [PMID: 11274408 PMCID: PMC31146 DOI: 10.1073/pnas.061535198] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2000] [Indexed: 11/18/2022] Open
Abstract
When individual amoebae of the cellular slime mold Dictyostelium discoideum are starving, they aggregate to form a multicellular migrating slug, which moves toward a region suitable for culmination. The culmination of the morphogenesis involves complex cell movements that transform a mound of cells into a globule of spores on a slender stalk. The movement has been likened to a "reverse fountain," whereby prestalk cells in the upper part form a stalk that moves downwards and anchors to the substratum, while prespore cells in the lower part move upwards to form the spore head. So far, however, no satisfactory explanation has been produced for this process. Using a computer simulation that we developed, we now demonstrate that the processes that are essential during the earlier stages of the morphogenesis are in fact sufficient to produce the dynamics of the culmination stage. These processes are cAMP signaling, differential adhesion, cell differentiation, and production of extracellular matrix. Our model clarifies the processes that generate the observed cell movements. More specifically, we show that periodic upward movements, caused by chemotactic motion, are essential for successful culmination, because the pressure waves they induce squeeze the stalk downwards through the cell mass. The mechanisms revealed by our model have a number of self-organizing and self-correcting properties and can account for many previously unconnected and unexplained experimental observations.
Collapse
Affiliation(s)
- A F Marée
- Theoretical Biology and Bioinformatics, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands.
| | | |
Collapse
|
13
|
Colosimo ME, Katz ER. Altered prestarvation response in a nystatin resistant Dictyostelium discoideum mutant. Differentiation 2001; 67:1-11. [PMID: 11270118 DOI: 10.1046/j.1432-0436.2001.067001001.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Wild-type Dictyostelium amoebae secrete an autocrine, prestarvation factor (PSF) that allows them to measure the amount of food bacteria compared to their cell density. When the ratio of PSF to bacteria reaches a threshold, the cells are signaled to prepare for eventual starvation. This prestarvation response (PSR) usually starts three to four generations before the end of exponential growth, leading to the accumulation of several aggregation specific genes during growth. We characterize a nystatin-resistant mutant, HK19, that expresses the PSR genes three generations earlier than wild type but has an otherwise wild-type PSR. Although HK19 has a full PSR during growth, HK19 continues to grow at the wild-type rate and reaches normal cell densities. Because HK19 temporally separates the PSR from starvation, it became possible to test whether starvation is required for development. Since HK19 growing at low density can be induced to clump with either cAMP or folate, it appears that the PSR and an external signal are sufficient for entry into development. These data suggest that the PSR is a complex genetic pathway that induces genes involved in the exit from growth and the entry into development.
Collapse
Affiliation(s)
- M E Colosimo
- Department of Molecular Genetics and Microbiology, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
| | | |
Collapse
|
14
|
Palmieri SJ, Nebl T, Pope RK, Seastone DJ, Lee E, Hinchcliffe EH, Sluder G, Knecht D, Cardelli J, Luna EJ. Mutant Rac1B expression in Dictyostelium: effects on morphology, growth, endocytosis, development, and the actin cytoskeleton. CELL MOTILITY AND THE CYTOSKELETON 2000; 46:285-304. [PMID: 10962483 DOI: 10.1002/1097-0169(200008)46:4<285::aid-cm6>3.0.co;2-n] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Rac1 is a small G-protein in the Ras superfamily that has been implicated in the control of cell growth, adhesion, and the actin-based cytoskeleton. To investigate the role of Rac1 during motile processes, we have established Dictyostelium cell lines that conditionally overexpress epitope-tagged Dictyostelium discoideum wild-type Rac1B (DdRac1B) or a mutant DdRac1B protein. Expression of endogenous levels of myc- or GFP-tagged wild-type DdRac1B had minimal effect on cellular morphologies and behaviors. By contrast, expression of a constitutively active mutant (G12-->V or Q61-->L) or a dominant negative mutant (T17-->N) generated amoebae with characteristic cellular defects. The morphological appearance of actin-containing structures, intracellular levels of F-actin, and cellular responses to chemoattractant closely paralleled the amount of active DdRac1B, indicating a role in upregulating actin cytoskeletal activities. Expression of any of the three mutants inhibited cell growth and cytokinesis, and delayed multicellular development, suggesting that DdRac1B plays important regulatory role(s) during these processes. No significant effects were observed on binding or internalization of latex beads in suspension or on intracellular membrane trafficking. Cells expressing DdRac1B-G12V exhibited defects in fluid-phase endocytosis and the longest developmental delays; DdRac1B-Q61L produced the strongest cytokinesis defect; and DdRac1B-T17N generated intermediate phenotypes. These conditionally expressed DdRac1B proteins should facilitate the identification and characterization of the Rac1 signaling pathway in an organism that is amenable to both biochemical and molecular genetic manipulations.
Collapse
Affiliation(s)
- S J Palmieri
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, UK
| | | | | | | | | | | | | | | | | | | |
Collapse
|
15
|
Ponte E, Rivero F, Fechheimer M, Noegel A, Bozzaro S. Severe developmental defects in Dictyostelium null mutants for actin-binding proteins. Mech Dev 2000; 91:153-61. [PMID: 10704840 DOI: 10.1016/s0925-4773(99)00292-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
The actin cytoskeleton is implicated in many cellular processes, such as cell adhesion, locomotion, contraction and cytokinesis, which are central to any development. The extent of polymerization, cross-linking, and bundling of actin is regulated by several actin-binding proteins. Knock-out mutations in these proteins have revealed in many cases only subtle, if any, defects in development, suggesting that the actin system is redundant, with multiple proteins sharing overlapping functions. The apparent redundancy may, however, reflect limitations of available laboratory assays in assessing the developmental role of a given protein. By using a novel assay, which reproduces conditions closer to the natural ones, we have re-examined the effects of disruption of many actin-binding proteins, and show here that deletion of alpha-actinin, interaptin, synexin, 34-kDa actin-bundling protein, and gelation factor affect to varying degrees the efficiency of Dictyostelium cells to complete development and form viable spores. No phenotypic defects were found in hisactophilin or comitin null mutants.
Collapse
Affiliation(s)
- E Ponte
- Dipartimento di Scienze Cliniche e Biologiche, Università di Torino, Ospedale S. Luigi, 10043-, Orbassano, Italy
| | | | | | | | | |
Collapse
|
16
|
|
17
|
Leys SP. Introduction to studies on cell adhesion using invertebrate models. Microsc Res Tech 1999; 44:201-3. [PMID: 10098922 DOI: 10.1002/(sici)1097-0029(19990215)44:4<201::aid-jemt1>3.0.co;2-o] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- S P Leys
- Department of Zoology, University of Queensland, Brisbane, Australia
| |
Collapse
|
18
|
Abstract
The ability of a microorganism to adhere to a solid support and to initiate a colony is often the first stage of microbial infections. To date, studies on S. cerevisiae cell-cell and cell-solid support interactions concerned only cell agglutination during mating and flocculation. Colony formation has not been studied before probably because this species is not pathogenic. However, S. cerevisiae can be a convenient model to study this process, thanks to well-developed genetics and the full knowledge of its nucleotide sequence. A preliminary characterization of the recently cloned essential IRR1 gene indicated that it may participate in cell-cell/substrate interactions. Here we show that lowering the level of expression of IRR1 (after fusion with a regulatory catalase A gene promoter) affects colony formation and disturbs zygote formation and spore germination. All these processes involve cell-cell or cell-solid support contacts. The IRR1 protein is localized in the cytosol as verified by immunofluorescence microscopy, and confirmed by cell fractionation and Western blotting. This indicates that Irr1p is not directly involved in the cell-solid support adhesion, but may be an element of a communication pathway between the cell and its surroundings.
Collapse
Affiliation(s)
- A Kurlandzka
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warszawa, Poland
| | | | | | | |
Collapse
|
19
|
Jiang Y, Levine H, Glazier J. Possible cooperation of differential adhesion and chemotaxis in mound formation of Dictyostelium. Biophys J 1998; 75:2615-25. [PMID: 9826586 PMCID: PMC1299937 DOI: 10.1016/s0006-3495(98)77707-0] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
In the mound stage of Dictyostelium discoideum, pre-stalk cells sort and form a tip at the apex. How this pattern forms is as yet unknown. A cellular level model allows us to simulate both differential cell adhesion and chemotaxis, to show that with differential adhesion only, pre-stalk cells move to the surface of the mound but form no tip. With chemotaxis driven by an outgoing circular wave only, a tip forms but contains both pre-stalk and pre-spore cells. Only for a narrow range of relative strengths between differential adhesion and chemotaxis can both mechanisms work in concert to form a tip containing only pre-stalk cells. The simulations provide a method to determine the processes necessary for patterning and suggest a series of further experiments.
Collapse
Affiliation(s)
- Y Jiang
- Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA.
| | | | | |
Collapse
|
20
|
Ponte E, Bracco E, Faix J, Bozzaro S. Detection of subtle phenotypes: the case of the cell adhesion molecule csA in Dictyostelium. Proc Natl Acad Sci U S A 1998; 95:9360-5. [PMID: 9689085 PMCID: PMC21343 DOI: 10.1073/pnas.95.16.9360] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Dictyostelium amoebae aggregate into a multicellular organism by cAMP-driven chemotaxis and cell-cell adhesion. Cell adhesion is mediated by an EDTA-sensitive and an EDTA-resistant adhesion system. The latter is developmentally regulated and triggered by homophilic interactions of the membrane glycoprotein csA; on disruption of the encoding gene, EDTA-resistant contacts fail to form. Nevertheless, csA-null cells under usual laboratory conditions aggregate normally and complete development. By using experimental conditions that reproduce more closely the habitat of Dictyostelium amoebae, evidence is provided that csA is required for development and that its expression confers a selective advantage to populations of wild-type cells over csA-null mutants. The latter display reduced cell-cell adhesion, increased adhesiveness to the substratum, and slower motility, which lead to their sorting out from aggregating wild-type cells. It is proposed that the experimental conditions commonly used in the laboratory are not stringent enough to assess the developmental role of csA and other proteins. The assay described can be used to detect subtle phenotypes, to reexamine the developmental role of apparently nonessential genes, and to test the validity of recent models on emergence and maintenance of apparent genetic redundancy.
Collapse
Affiliation(s)
- E Ponte
- Dipartimento di Scienze Cliniche e Biologiche, Università di Torino, Ospedale S. Luigi, 10043-Orbassano, Italy
| | | | | | | |
Collapse
|
21
|
Peracino B, Borleis J, Jin T, Westphal M, Schwartz JM, Wu L, Bracco E, Gerisch G, Devreotes P, Bozzaro S. G protein beta subunit-null mutants are impaired in phagocytosis and chemotaxis due to inappropriate regulation of the actin cytoskeleton. J Cell Biol 1998; 141:1529-37. [PMID: 9647646 PMCID: PMC2133009 DOI: 10.1083/jcb.141.7.1529] [Citation(s) in RCA: 102] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/1998] [Revised: 05/27/1998] [Indexed: 02/08/2023] Open
Abstract
Chemotaxis and phagocytosis are basically similar in cells of the immune system and in Dictyostelium amebae. Deletion of the unique G protein beta subunit in D. discoideum impaired phagocytosis but had little effect on fluid-phase endocytosis, cytokinesis, or random motility. Constitutive expression of wild-type beta subunit restored phagocytosis and normal development. Chemoattractants released by cells or bacteria trigger typical transient actin polymerization responses in wild-type cells. In beta subunit-null cells, and in a series of beta subunit point mutants, these responses were impaired to a degree that correlated with the defect in phagocytosis. Image analysis of green fluorescent protein-actin transfected cells showed that beta subunit- null cells were defective in reshaping the actin network into a phagocytic cup, and eventually a phagosome, in response to particle attachment. Our results indicate that signaling through heterotrimeric G proteins is required for regulating the actin cytoskeleton during phagocytic uptake, as previously shown for chemotaxis. Inhibitors of phospholipase C and intracellular Ca2+ mobilization inhibited phagocytosis, suggesting the possible involvement of these effectors in the process.
Collapse
Affiliation(s)
- B Peracino
- Dipartimento di Scienze Cliniche e Biologiche, Università di Torino, Ospedale S. Luigi, 10043 Orbassano, Italy
| | | | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Sesaki H, Wong EF, Siu CH. The cell adhesion molecule DdCAD-1 in Dictyostelium is targeted to the cell surface by a nonclassical transport pathway involving contractile vacuoles. J Cell Biol 1997; 138:939-51. [PMID: 9265658 PMCID: PMC2138044 DOI: 10.1083/jcb.138.4.939] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/1997] [Revised: 05/14/1997] [Indexed: 02/05/2023] Open
Abstract
DdCAD-1 is a 24-kD Ca2+-dependent cell- cell adhesion molecule that is expressed soon after the initiation of development in Dictyostelium cells. DdCAD-1 is present on the cell surface as well as in the cytosol. However, the deduced amino acid sequence of DdCAD-1 lacks a hydrophobic signal peptide or any predicted transmembrane domain, suggesting that it may be presented on the cell surface via a nonclassical transport mechanism. Here we report that DdCAD-1 is transported to the cell surface via contractile vacuoles, which are normally involved in osmoregulation. Immunofluorescence microscopy and subcellular fractionation revealed a preferential association of DdCAD-1 with contractile vacuoles. Proteolytic treatment of isolated contractile vacuoles degraded vacuole-associated calmodulin but not DdCAD-1, demonstrating that DdCAD-1 was present in the lumen. The use of hyperosmotic conditions that suppress contractile vacuole activity led to a dramatic decrease in DdCAD-1 accumulation on the cell surface and the absence of cell cohesiveness. Shifting cells back to a hypotonic condition after hypertonic treatments induced a rapid increase in DdCAD-1-positive contractile vacuoles, followed by the accumulation of DdCAD-1 on the cell membrane. 7-chloro-4-nitrobenzo-2-oxa-1, 3-diazole, a specific inhibitor of vacuolar-type H+-ATPase and thus of the activity of contractile vacuoles, also inhibited the accumulation of DdCAD-1 on the cell surface. Furthermore, an in vitro reconstitution system was established, and isolated contractile vacuoles were shown to import soluble DdCAD-1 into their lumen in an ATP-stimulated manner. Taken together, these data provide the first evidence for a nonclassical protein transport mechanism that uses contractile vacuoles to target a soluble cytosolic protein to the cell surface.
Collapse
Affiliation(s)
- H Sesaki
- Banting and Best Department of Medical Research, University of Toronto, Ontario, Canada
| | | | | |
Collapse
|
23
|
Yang C, Brar SK, Desbarats L, Siu CH. Synthesis of the Ca(2+)-dependent cell adhesion molecule DdCAD-1 is regulated by multiple factors during Dictyostelium development. Differentiation 1997; 61:275-84. [PMID: 9342838 DOI: 10.1046/j.1432-0436.1997.6150275.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In Dictyostelium discoideum, the cadA gene encodes the cell adhesion molecule DdCAD-1, a protein of M(r) 24,000, which mediates Ca(2+)-dependent cell-cell adhesion during development. We have examined the effects of cAMP, cell-cell contact, and growth conditions on cadA expression. cadA has a unique pattern of expression, which appears to be a combination of the expression patterns of early genes and aggregation-stage genes. Expression of the cadA gene in bacterially grown cells is activated at the beginning of the developmental cycle, followed by a period of rapid DdCAD-1 accumulation. The mRNA level reaches its maximum at 9 h of development and then declines to the basal level at approximately 18 h, while the protein level remains constant after reaching its maximum at 12 h. Pulse-chase experiments have demonstrated that DdCAD-1 has a significantly longer half-life than the average cellular protein. Transcription of the cadA gene is stimulated by exogenous cAMP pulses, leading to a 3- to 5-fold increase in the transcription rate. In the fgdA mutant, which lacks a functional G alpha 2, cAMP fails to enhance cadA expression, suggesting that cAMP stimulates cadA transcription via a G protein-dependent pathway. However, inhibition of cell-cell contact has no effect on the synthesis of DdCAD-1. Growth conditions also have a major influence on cadA expression. Axenically grown cells produce a high level of cadA transcripts during vegetative growth. The mRNA level shows a steady decrease during development and is reduced to the basal level by 12 h. In contrast, the level of DdCAD-1 remains relatively high throughout development, suggesting that axenic growth affects the accumulation of cadA mRNA but not the stability of the protein. These results indicate that multiple mechanisms are involved to maintain a high level of DdCAD-1 during development.
Collapse
Affiliation(s)
- C Yang
- Banting and Best Department of Medical Research, University of Toronto, Ontario, Canada
| | | | | | | |
Collapse
|