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dictyNews Volume 24 Number 05
Dicty News
Electronic Edition
Volume 24, number 5
March 4, 2005
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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PldB, a putative phospholipase D homologue in Dictyostelium discoideum
mediates quorum sensing during development
Yi Chen, Vanessa Rodrick, Yi Yan, and Derrick Brazill*
Department of Biological Sciences
Hunter College
695 Park Avenue
New York, NY 10021
Eukaryotic Cell, in press
Quorum sensing, also known as cell-density sensing in the unicellular
eukaryote Dictyostelium discoideum, is required for efficient entry into
the differentiation and development segment of its life cycle. Quorum
sensing is accomplished by simultaneously secreting and sensing the
glycoprotein Conditioned Medium Factor, or CMF. When the density of
starving cells is high, CMF levels are high, which leads to aggregation
followed by development. Here, we describe the role of pldB, a gene coding
for a putative phospholipase D homologue, in quorum sensing. We find that
in submerged culture, adding butanol, an inhibitor of PLD-catalyzed
phosphatidic acid production, allows cells to bypass the requirement for
CMF mediated quorum sensing and aggregate at low cell density. Deletion of
pldB mimics the presence of butanol, allowing cells to aggregate at low cell
density. pldB- cells also initiate and finish aggregation rapidly.
Analysis of early developmental gene expression in pldB- cells reveals that
the cAMP receptor cAR1 is expressed at higher levels, earlier than in
wild type cells, which could explain the rapid aggregation phenotype. As
would be predicted, cells overexpressing pldB are unable to aggregate even
at high cell density. Adding CMF to these pldB-overexpressing cells does
not rescue aggregation. Both of these phenotypes are cell autonomous, as
mixing a small number of pldB- cells with wild-type cells does not cause
the wild type cells to behave like pldB- cells.
Submitted by: Derrick Brazill [brazill@genectr.hunter.cuny.edu]
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The Intracellular Role of Adenylyl Cyclase in the Regulation of Lateral
Pseudopod Formation During Dictyostelium Chemotaxis
Vesna Stepanovic, Deborah Wessels, Karla Daniels, William F. Loomis and
David R. Soll
W.M. Keck Dynamic Image Analysis Facility, Department of Biological Sciences,
The University of Iowa, Iowa City, IA 52242 and Department of Biology,
University of California-San Diego, La Jolla, CA 92037
Eukaryotic Cell, in press
Cyclic AMP (cAMP) functions as the extracellular chemoattractant in the
aggregation phase of Dictyostelium development. There is some question,
however, concerning what role, if any, it plays intracellularly in motility
and chemotaxis. To test for such a role, the behavior of null mutants of
acaA, the adenylyl cyclase gene which encodes the enzyme responsible for cAMP
synthesis during aggregation, was analyzed in buffer, and in response to
experimentally generated spatial and temporal gradients of extracellular cAMP.
acaA- cells were defective in suppressing lateral pseudopods in response to a
spatial gradient of cAMP and to an increasing temporal gradient of cAMP.
acaA- cells were unable to chemotax in natural waves of cAMP generated by
majority control cells in mixed cultures. These results indicate that
intracellular cAMP, and hence adenylate cyclase, plays an intracellular role
in the chemotactic response. The behavioral defects of acaA- cells were
surprisingly similar to those of cells of null mutants of regA, which encodes
the phosphodiesterase that hydrolyzes cAMP and, hence, functions opposite ACA.
This result is consistent with the hypothesis that ACA and REGA are components
of a receptor-regulated intracellular circuit that controls protein kinase A
activity. In this model, the suppression of lateral pseudopods in the front
of a natural wave depends on a complete circuit. Hence, deletion of any
component of the circuit (i.e., REGA or ACA) would result in the same
chemotactic defect.
Submitted by: Deborah Wessels [deborah-wessels@uiowa.edu]
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The genome of the social amoeba Dictyostelium discoideum
L. Eichinger1, , J.A. Pachebat2,1, , G. Glckner3, , M.-A. Rajandream4, ,
R. Sucgang5, , M. Berriman4, J. Song5, R. Olsen6, K. Szafranski3, Q. Xu7, 8,
B. Tunggal1, S. Kummerfeld2, M. Madera2, B. A. Konfortov2, F. Rivero1,
A. T. Bankier2, R. Lehmann3, N. Hamlin4, R. Davies4, P. Gaudet9, P. Fey9 ,
K. Pilcher9, G. Chen5, D. Saunders4, E. Sodergren7,10, P. Davis4, A. Kerhornou4,
X. Nie5, N. Hall4, a, C. Anjard6, L. Hemphill5, N. Bason4, P. Farbrother1,
B. Desany5, E. Just9, T. Morio11, R. Rost12, C. Churcher4, J. Cooper4,
S. Haydock13, N. van Driessche7, A. Cronin4, I. Goodhead4, D. Muzny10,
T. Mourier4, A. Pain4, M. Lu5, D. Harper4, R. Lindsay5, H. Hauser4, K. James4,
M. Quiles10, M. Madan Babu2, T. Saito14, C. Buchrieser15, A. Wardroper16, 2,
M. Felder3, M. Thangavelu17, D. Johnson4, A. Knights4, H. Loulseged10,
K. Mungall4, K. Oliver4, C. Price4, M.A. Quail4, H. Urushihara11,
J. Hernandez10, E. Rabbinowitsch4, D. Steffen10, M. Sanders4, J. Ma10,
Y. Kohara18, S. Sharp4, M. Simmonds4, S. Spiegler4, A. Tivey4, S. Sugano19,
B. White4, D. Walker4, J. Woodward4, T. Winckler20, Y. Tanaka11,
G. Shaulsky7,8, M. Schleicher12, G. Weinstock7, 10, A. Rosenthal3, E.C. Cox21,
R. L. Chisholm9, R. Gibbs7, 10, W. F. Loomis6, M. Platzer3, à, R. R. Kay2, à,
J. Williams22, à, P. H. Dear2, à,¤, A. A. Noegel1, à, B. Barrell4, à and
A. Kuspa5, 7, à
1Center for Biochemistry and Center for Molecular Medicine Cologne, University
of Cologne, Joseph-Stelzmann-Str. 52, 50931 Cologne, Germany
2Laboratory of Molecular Biology, MRC Centre, Cambridge CB2 2QH, UK
3Genome Analysis, Institute for Molecular Biotechnology, Beutenbergstr. 11,
D-07745 Jena, Germany
4The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton,
Cambridgeshire CB10 1SA, UK
5Verna and Marrs McLean Department of Biochemistry and Molecular Biology,
Baylor College of Medicine, Houston, TX77030, USA
6Section of Cell and Developmental Biology, Division of Biology, University
of California, San Diego, La Jolla, CA 92093, USA
7Dept. of Human and Molecular Genetics, Baylor College of Medicine, Houston,
TX 77030, USA
8Graduate Program in Structural and Computational Biology and Molecular
Biophysics, Baylor College of Medicine, Houston TX 77030, USA
9dictyBase, Center for Genetic Medicine, Northwestern University,
303 E Chicago Ave, Chicago, IL 60611, USA
10Human Genome Sequencing Center, Baylor College of Medicine, Houston,
TX 77030, USA
11Graduate School of Life and Environmental Sciences, University of Tsukuba,
Tsukuba, Ibaraki 305-8572, Japan
12Adolf-Butenandt-Institute/Cell Biology, Ludwig-Maximilians-University,
80336 Munich, Germany
13Biochemistry Department, University of Cambridge, Cambridge CB2 1QW, UK.
14Division of Biological Sciences, Graduate School of Science, Hokkaido
University, Sapporo 060-0810 Japan
15Unit de Genomique des Microorganismes Pathogenes, Institut Pasteur,
28 rue du Dr. Roux, 75724 Paris Cedex 15, France.
16Department of Biology, University of York, York YO10 5YW, UK.
17MRC Cancer Cell Unit, Hutchison/MRC Research Centre, Hills Road,
Cambridge CB2 2XZ, UK.
18Centre for Genetic Resource Information, National Institute of Genetics,
Mishima, Shizuoka 411-8540, Japan
19Department of Medical Genome Sciences, Graduate School of Frontier Sciences,
The University of Tokyo, Minato, Tokyo 108-8639, Japan
20Institut fr Pharmazeutische Biologie, Universitt Frankfurt (Biozentrum),
Frankfurt am Main, 60439, Germany
21Department of Molecular Biology, Princeton University, Princeton,
NJ08544-1003, USA
22School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
aPresent address: The Institute for Genomic Research, 9712 Medical Center Drive,
Rockville MD 20850, USA
These authors contributed equally.
àCo-senior authors
¤Corresponding author.
Telephone: [0044] 1223 402190
Fax: [0044] 1223 412178
Email: phd@mrc-lmb.cam.ac.uk
Nature, in press
The social amoebae are exceptional in their ability to alternate between
unicellular and multicellular forms. Here we describe the genome of the
best-studied member of this group, Dictyostelium discoideum. The gene-dense
chromosomes encode ~12,500 predicted proteins, a high proportion of which
have long repetitive amino acid tracts. There are many genes for polyketide
synthases and ABC transporters, suggesting an extensive secondary metabolism
for producing and exporting small molecules. The genome is rich in complex
repeats, one class of which is clustered and may serve as centromeres.
Partial copies of the extrachromosomal rDNA element are found at the ends
of each chromosome, suggesting a novel telomere structure and the use of a
common mechanism to maintain both the rDNA and chromosomal termini. A
proteome-based phylogeny shows that the amoebozoa diverged from the
animal/fungal lineage after the plant/animal split, but Dictyostelium appears
to have retained more of the diversity of the ancestral genome than either
of these two groups.
Submitted by: Paul Dear [phd@mrc-lmb.cam.ac.uk]
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[End Dicty News, volume 24, number 5] 
