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dictyNews Volume 31 Number 01
dictyNews
Electronic Edition
Volume 31, number 1
July 4, 2008
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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3’-phosphoinositides regulate the coordination of speed and accuracy
during chemotaxis
Gruver, J. S., J. P. Wikswo, and C. Y. Chung
1Department of Pharmacology, Vanderbilt University Medical Center
2Departments of Physics and Astronomy, Biomedical Engineering, and
Molecular Physiology and Biophysics, Vanderbilt University, Nashville TN 37232
Biophysical J., in press
The PI3K/PTEN pathway, as the regulator of 3'-phosphoinositide (3'-PI)
dynamics, has emerged as a key regulator of chemoattractant gradient sensing
during chemotaxis in Dictyostelium and other cell types. Previous results
have shown 3'-PIs to be important for regulating basal cell motility and sensing
the direction and strength of the chemoattractant gradient. We examined
the chemotaxis of wild-type cells and cells lacking PTEN or PI3K1 and 2 using
analytical methods that allow us to quantitatively discern differences
between the genotypes ability to sense and efficiently respond to changes in
gradient steepness during chemotaxis. We find that cells are capable of
increasing their chemotactic accuracy and speed as they approach a micropipette
in a manner that is dependent on the increasing strength of the concentration
gradient and 3’-PI signaling. Further, our data shows that 3'-PI signaling
affects a cell's ability to coordinate speed and direction in order to increase
chemotactic efficiency. Using a new measurement of chemotactic efficiency
that reveals the degree of coordination between speed and accuracy, we find
that cells also have the capacity to increase their chemotactic efficiency as they
approach the micropipette. Like directional accuracy and speed, the increase in
chemotactic efficiency of cells with increased gradient strength is sensitive to
3'-PI dysregulation. Our evidence suggests that receptor-driven 3'-PI signaling
regulates the ability of the cell to capitalize on stronger directional inputs as
well as minimize the effects of inaccurate turns in order to increase
chemotactic efficiency.
Submitted by: Chang Chung [chang.chung@vanderbilt.edu]
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Functional analysis of spontaneous cell movement under different physiological
conditions
Hiroaki Takagi 1,2,3, Masayuki J. Sato 1,3, Toshio Yanagida 1, Masahiro Ueda 1,3
1. Laboratories for Nanobiology, Graduate School of Frontier Biosciences,
Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
2. Department of Physics, School of Medicine, Nara Medical University,
Nara, 634-8521, Japan.
3. JST, CREST, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.
PLoS ONE, in press
Cells can show not only spontaneous movement but also tactic responses to
environmental signals. Since the former can be regarded as the basis to realize
the latter, playing essential roles in various cellular functions, it is
important to investigate spontaneous movement quantitatively at different
physiological conditions in relation to a cell's physiological functions. For
that purpose, we observed a series of spontaneous movements by Dictyostelium
cells at different developmental periods by using a single cell tracking system.
Using statistical analysis of these traced data, we found that cells showed
complex dynamics with anomalous diffusion and that their velocity distribution
had power-law tails in all conditions. Furthermore, as development proceeded,
average velocity and persistency of the movement increased and as too did the
exponential behavior in the velocity distribution. Based on these results, we
succeeded in applying a generalized Langevin model to the experimental data.
With this model, we discuss the relation of spontaneous cell movement to
cellular physiological function and its relevance to behavioral strategies
for cell survival.
Submitted by: Hiroaki Takagi [takagi@naramed-u.ac.jp]
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Dictyostelium transcriptional responses to Pseudomonas aeruginosa: common and
specific effects from PAO1 and PA14 strains
Sergio Carilla-Latorre1*, Javier Calvo-Garrido1*, Gareth Bloomfield2,
Jason Skelton3, Robert R. Kay2, Alasdair Ivens3, Jose L. Martinez4
and Ricardo Escalante1
1 Instituto de Investigaciones Biomedicas Alberto Sols. Universidad Autonoma
de Madrid-Consejo Superior de Investigaciones Cientificas. Madrid. Spain.
2 MRC Laboratory of Molecular Biology, Cambridge. UK.
3 Wellcome Trust Sanger Institute, Hinxton. UK.
4 Centro Nacional de Biotecnología. CSIC. Madrid and CIBERESP Spain.
BMC-Microbiology, in press
Background
Pseudomonas aeruginosa is one of the most relevant human opportunistic
bacterial pathogens. Two strains (PAO1 and PA14) have been mainly used as
models for studying virulence of P. aeruginosa. The strain PA14 is more
virulent than PAO1 in a wide range of hosts including insects, nematodes
and plants. Whereas some of the differences might be attributable to concerted
action of determinants encoded in pathogenicity islands present in the genome
of PA14, a global analysis of the differential host responses to these
P. aeruginosa strains has not been addressed. Little is known about the host
response to infection with P. aeruginosa and whether or not the global host
transcription is being affected as a defense mechanism or altered in the
benefit of the pathogen. Since the social amoeba Dictyostelium discoideum
is a suitable host to study virulence of P. aeruginosa and other pathogens,
we used available genomic tools in this model system to study the
transcriptional host response to P. aeruginosa infection.
Results
We have compared the virulence of the P. aeruginosa PAO1 and PA14 using
D. discoideum and studied the transcriptional response of the amoeba upon
infection. Our results showed that PA14 is more virulent in Dictyostelium
than PA01using different plating assays. For studying the differential
response of the host to infection by these model strains, D. discoideum
cells were exposed to either P. aeruginosa PAO1 or P. aeruginosa PA14
(mixed with an excess of the non-pathogenic bacterium Klebsiella aerogenes
as food supply) and after 4 hours, cellular RNA extracted. A three-way
comparison was made using whole-genome D. discoideum microarrays between
RNA samples from cells treated with the two different strains and control
cells exposed only to K. aerogenes. The transcriptomic analyses have shown
the existence of common and specific responses to infection. The expression
of 364 genes changed in a similar way upon infection with one or another
strain, whereas 169 genes were differentially regulated depending on whether
the infecting strain was either P. aeruginosa PAO1 or PA14. Effects on
metabolism, signalling, stress response and cell cycle can be inferred from
the genes affected.
Conclusions
Our results show that pathogenic Pseudomonas strains invoke both a common
transcriptional response from Dictyostelium and a strain specific one,
indicating that the infective process of bacterial pathogens can be
strain-specific and is more complex than previously thought.
Submitted by: Ricardo Escalante [rescalante@iib.uam.es]
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[End dictyNews, volume 31, number 1]
