dictyNews
Electronic Edition
Volume 34, number 5
February 12, 2010

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=========
Abstracts
=========

A cytohesin homolog in Dictyostelium amoebae

Maria Christina Shina1, Rolf Müller1, Rosemarie Blau-Wasser1, Gernot  
Glöckner1,2,
Michael Schleicher3, Ludwig Eichinger1, Angelika A. Noegel1, Waldemar  
Kolanus4

1 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,
2 Leibniz Institute for Age Research -Fritz-Lipmann-Institute e.V.,  
Jena, Germany,
3 Institute of Anatomy and Cell Biology and Center for Integrated  
Protein Science
(CIPSM), Ludwig-Maximilians-University, Muenchen, Germany,
4 Laboratory of Molecular Immunology, LIMES Institute of the  
University of Bonn,
Bonn, Germany


PLoS ONE

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.

Principle 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 which is important for development is not  
affected.
Accordingly, multicellular development proceeds normally in the  
mutant. During
chemotaxis secG-minus 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.



Submitted by Angelika Nögel [[log in to unmask]]
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The prespore cell inducing factor, psi factor (PsiA), controls both  
prestalk
and prespore gene expression in Dictyostelium development

Yoko Yamada1†, Hiroshi Minamisawa2, Masashi Fukuzawa3,
Takefumi Kawata2, Akiko A. Oohata1*


Dev.Growth Differ., in press

PsiA (psi factor), encoded by the psiA gene of Dictyostelium, is a  
secreted
signal glycoprotein that induces prespore cell differentiation when  
added to
monolayer cultures. In situ hybridization during normal development  
showed
that the psiA gene is highly expressed in scattered cells at the mound  
stage
and in prespore cells at the onset of culmination. The conventional
prespore-cell marker genes, cotC and pspA, were expressed normally in
psiA- and psiA overexpressing strains. Expressions of rnrB and cudA are
repressed in the prestalk cells of a wild type slug to render prespore  
specific
pattern. However, a promoter-reporter fusion gene, rnrB:gal, showed an
ectopic  expression in the prestalk cells of psiA- strain while  
cudA:gal did
so in those of psiA overexpressing strain. Overexpression of psiA  
delayed
expression of the prestalk specific gene, ecmB, during development,  
while
knocking out psiA promoted its expression. In addition, overexpression
inhibited DIF-induced stalk formation in monolayer cultures. Together  
with
the known prespore inducing activity, the results indicate that PsiA  
regulates
both prespore and prestalk/stalk cell differentiation. These results  
indicate
that PsiA is also involved in prestalk cell differentiation.


Submitted by Akiko Oohata [[log in to unmask]]
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[End dictyNews, volume 34, number 5]