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dictyNews Volume 18 Number 09
Dicty News
Electronic Edition
Volume 18, number 9
May 25, 2002
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu.
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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Identification of four candidate cGMP targets in Dictyostelium.
Goldberg JM, Bosgraaf L, Van Haastert PJ, Smith JL.
Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA
02472-2829;
and Department of Biochemistry, University of Groningen, Nijenborgh 4,
9747 AG, Groningen, The Netherlands.
Proc Natl Acad Sci U S A 2002 May 14;99(10):6749-54
In Dictyostelium, a transient increase in intracellular cGMP is important
for cytoskeletal rearrangements during chemotaxis. There must be cGMP-
binding proteins in Dictyostelium that regulate key cytoskeletal components
after treatment with chemoattractants, but to date, no such proteins have
been identified. Using a bioinformatics approach, we have found four
candidate cGMP-binding proteins (GbpA-D). GbpA and -B have two tandem
cGMP-binding sites downstream of a metallo beta-lactamase domain, a
superfamily that includes cAMP phosphodiesterases. GbpC contains the
following nine domains (in order): leucine-rich repeats, Ras, MEK kinase,
Ras guanine nucleotide exchange factor N-terminal (RasGEF-N), DEP, RasGEF,
cGMP-binding, GRAM, and a second cGMP-binding domain. GbpD is related to
GbpC, but is much shorter; it begins with the RasGEF-N domain, and lacks
the DEP domain. Disruption of the gbpC gene results in loss of all high-
affinity cGMP-binding activity present in the soluble cellular fraction.
GbpC mRNA levels increase dramatically 8 h after starvation is initiated.
GbpA, -B, and -D mRNA levels show less dramatic changes, with gbpA mRNA
levels highest 4 h into starvation, gbpB mRNA levels highest in vegetative
cells, and gbpD levels highest at 8 h. The identification of these genes is
the first step in a molecular approach to studying downstream effects of
cGMP signaling in Dictyostelium.
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A Comparative Analysis of Spore Coat Formation, Structure and Function in
Dictyostelium
Christopher M. West
Deptartment of Anatomy & Cell Biology, University of Florida College of
Medicine, 1600 SW Archer Road, Gainesville, FL 32610-0235 USA
Telephone: 352-392-3329, Fax: 352-392-3305, Email: westcm@ufl.edu
Int. Rev. Cyt., in press
Dictyostelium produces spores at the end of its developmental cycle to
propagate the lineage. The spore coat is an essential feature of spore
biology contributing a semipermeable chemical and physical barrier to
protect the enclosed amoeaba. The coat is assembled from proteins and a
branched polysaccharide that are secreted and from cellulose produced at
the cell surface. They are organized into a polarized molecular sandwich
with proteins forming layers surrounding the microfibrillar cellulose
core. Genetic and biochemical studies are beginning to provide insight
into how the delivery of protein and cellulose to the cell surface are
coordinated, and how cysteine-rich domains of the proteins interact to
form the layers. A multi-domain inner layer protein, SP85/PsB, has a
central role in regulating coat assembly and contributing to a core
structural module that bridges proteins to cellulose. Coat formation
and structure have many parallels in walls from plant, algal, yeast,
protist and animal cells.
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The different components of a multisubunit cell number-counting factor have
both unique and overlapping functions
Debra A. Brock, R. Diane Hatton, Dan-Victor Giurgiutiu, Brenton Scott, Robin
Ammann, and Richard H. Gomer
Howard Hughes Medical Institute and Department of Biochemistry and Cell
Biology, MS-140, Rice University, 6100 S. Main Street, Houston, TX 77005-1892
Development, in press
Summary
Dictyostelium aggregation streams break up into groups of 103 to 2 x 104
cells. The cells sense the number of cells in a stream or group by the
level of a secreted counting factor (CF). CF is a complex of at least 5
polypeptides. When the gene encoding countin (one of the CF polypeptides)
was disrupted, the cells could not sense each other's presence, resulting
in non-breaking streams that coalesced into abnormally large groups. To
understand the function of the components of CF, we have isolated cDNA
sequences encoding a second component of CF, CF50. CF50 is 30% identical
to lysozyme (but has very little lysozyme activity) and contains distinctive
serine-glycine motifs. Transformants with a disrupted cf50 gene, like
countin cells, form abnormally large groups. Addition of recombinant CF50
protein to developing cf50 cells rescues their phenotype by decreasing
group size. Abnormalities seen in aggregating countin cells (such as high
cell-cell adhesion and low motility) are also observed in the cf50 cells.
Western blot analysis of conditioned medium sieve column fractions showed
that the CF50 protein is present in the same fraction as the 450 KD CF
complex. In the absence of CF50, secreted countin is degraded, suggesting
that one function of CF50 may be to protect countin from degradation.
However, unlike countin cells, cf50 cells differentiate into an abnormally
high percentage of prespore cells, and this difference can be rescued by
exposing cells to recombinant CF50. These observations indicate that unlike
other known multisubunit factors, CF contains subunits with both overlapping
and unique properties.
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[End Dicty News, volume 18, number 9]
