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dictyNews Volume 40 Number 22
dictyNews
Electronic Edition
Volume 40, number 22
September 5, 2014
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 dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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=========
Abstracts
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PTEN Redundancy: Overexpressing lpten, a Homolog of Dictyostelium discoideum
ptenA, the Ortholog of Human PTEN, Rescues All Behavioral Defects of the
Mutant ptenA- .
Daniel F. Lusche, Deborah Wessels, Nicole A. Richardson, Kanoe B. Russell,
Brett M. Hanson, Benjamin A. Soll, Benjamin H. Lin and David R. Soll.
Monoclonal Antibody Research Institute and Developmental Studies Hybridoma
Bank Department of Biology, The University of Iowa, Iowa City, IA 52242
PloS ONE, in press
Mutations in the tumor suppressor gene PTEN are associated with a significant
proportion of human cancers. Because the human genome also contains several
homologs of PTEN, we considered the hypothesis that if a homolog, functionally
redundant with PTEN, can be overexpressed, it may rescue the defects of a
PTEN mutant. We have performed an initial test of this hypothesis in the model
system Dictyostelium discoideum, which contains an ortholog of human PTEN,
ptenA. Deletion of ptenA results in defects in motility, chemotaxis, aggregation
and multicellular morphogenesis. D. discoideum also contains lpten, a newly
discovered homolog of ptenA. Overexpressing lpten completely rescues all
developmental and behavioral defects of the D. discoideum mutant ptenA-.
This hypothesis must now be tested in human cells.
Submitted by Daniel Lusche [daniel-lusche@uiowa.edu]
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Cell substratum adhesion during early development of Dictyostelium discoideum
Marco Tarantola, Albert Bae, Danny Fuller, Eberhard Bodenschatz,
Wouter-Jan Rappel and William F. Loomis
PLoS ONE' in press
Vegetative and developed amoebae of Dictyostelium discoideum gain traction
and move rapidly on a wide range of substrata without forming focal adhesions.
We used two independent assays to quantify cell-substrate adhesion in mutants
and in wild-type cells as a function of development. Using a microfluidic device
that generates a range of hydrodynamic shear stress, we found that substratum
adhesion decreases at least 10 fold during the first 6 hr of development of wild
type cells. This result was confirmed using a single-cell assay in which cells
were attached to the cantilever of an atomic force probe and allowed to adhere
to untreated glass surfaces before being retracted. Both of these assays showed
that the decrease in substratum adhesion was dependent on the cAMP receptor
CAR1 which triggers development. Vegetative cells missing talin as the result of
a mutation in talA exhibited slightly reduced adhesive properties compared to
vegetative wild-type cells. In sharp contrast to wild-type cells, however, these
talA mutant cells did not show further reduction of adhesion during development
such that after 5 hr of development they were significantly more adhesive than
developed wild type cells. In addition, both assays showed that substrate
adhesion was reduced in 0hr cells when the actin cytoskeleton was disrupted by
latrunculin. Consistent with previous observations, substrate adhesion was also
reduced in 0hr cells lacking the membrane proteins SadA or SibA as the result
of mutations in sadA or sibA. However, there was no difference in the adhesion
properties between wild type AX3 cells and these mutant cells after 6 hr of
development, suggesting that neither SibA nor SadA play an essential role in
substratum adhesion during aggregation. Our results provide a quantitative
framework for further studies of cell substratum adhesion in Dictyostelium.
Submitted by Bill Loomis [wloomis@ucsd.edu]
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Defective lysosome maturation and Legionella pneumophila replication in
Dictyostelium ArfGAP ACAP-A mutant cells
Nathalie Bailo, Pierre Cosson, Steve J. Charette, Valerie E. Paquet,
Patricia Doublet, and Franois Letourneur
J Cell Sci , doi:10.1242/jcs.154559
http://jcs.biologists.org/content/early/2014/09/01/jcs.154559.abstract
Dictyostelium discoideum ACAP-A is an Arf-GTPase-activating protein involved
in cytokinesis, cell migration and actin cytoskeleton dynamics. In mammalian
cells, ACAP family members regulate endocytic protein trafficking. Here we
explored the function of ACAP-A in the endocytic pathway of D. discoideum. In
the absence of ACAP-A, reduced fusion efficacy of post-lysosomes with the
plasma membrane resulted in the accumulation of post-lysosomes. Moreover,
internalized fluid-phase showed extended intracellular transit time and transfer
kinetics of phagocyted particles from lysosomes to post-lysosomes was reduced.
Neutralization of lysosomal pH, one essential step in lysosome maturation, was
also delayed. Whereas expression of ACAP-A-GFP in acapA- cells
restored normal particle transport kinetics, a mutant ACAP-A protein with no GAP
activity towards the small GTPase ArfA failed to complement this defect. Together
these data support a role for ACAP-A in maturation of lysosomes into
post-lysosomes through an ArfA-dependent mechanism. In addition, we reveal
that ACAP-A is required for efficient intracellular growth of Legionella pneumophila,
a pathogen known to subvert the endocytic host cell machinery for replication.
This further emphasizes the role of ACAP-A in the endocytic pathway.
Submitted by Francois Letourneur [francois.letourneur@univ-montp2.fr]
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[End dictyNews, volume 40, number 22]
