dictyNews
Electronic Edition
Volume 43, number 3
February 3, 2017
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Abstracts
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In Memoriam: Maurice Sussman (1922–2016)
Steve Alexander, Jakob Franke, Herb Ennis, Hannah Alexander
Developmental Biology: http://www.sciencedirect.com/science/article/pii/S0012160616305978
submitted by: Steve Alexander [[log in to unmask]]
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Effects of deletion of the receptor CrlA on Dictyostelium aggregation
and MPBD mediated responses are strain-dependent and not evident in
strain Ax2
Takaaki B. Narita*, Pauline Schaap, Tamao Saito
FEMS Microbiology Letters, in press
The polyketide MPBD (4-methyl-5-pentylbenzene-1, 3-diol) is produced
by the polyketide synthase SteelyA (StlA) in Dictyostelium discoideum.
MPBD is required for appropriate expression of cAMP signalling genes
involved in cell aggregation and additionally induces the spore maturation
at the fruiting body stage. The MPBD signalling pathway for regulation of
cell aggregation is unknown, but MPBD effects on sporulation were
reported to be mediated by the G-protein coupled receptor CrlA in D.
discoideum KAx3. In this study, we deleted the crlA gene from the same
parental strain (Ax2) that was used to generate the MPBD-less mutant.
We found that unlike the MPBD-less mutant, Ax2-derived crlA- mutants
exhibited normal cell aggregation, indicating that in Ax2 MPBD effects on
early development do not require CrlA. We also found that the Ax2/crlA-
mutant formed normal spores in fruiting bodies. When transformed with
PkaC, both Ax2 and Ax2/crlA- similarly responded to MPBD in vitro with
spore encapsulation. Our data make it doubtful that CrlA acts as the
receptor for MPBD signalling during the development of D. discoideum
Ax2.
submitted by: Takaaki Narita [[log in to unmask]]
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Coupled Excitable Ras and F-actin activation mediate spontaneous
pseudopod formation and directed cell movement.
Peter J.M. van Haastert, Ineke Keizer-Gunnink and Arjan Kortholt
Department of Cell Biochemistry, University of Groningen,
Nijenborgh 7, 9747 AG Groningen, The Netherlands.
Molecular Biology of the Cell, in press
Many eukaryotic cells regulate their mobility by external cues. Genetic
studies have identified more than hundred components that participate in
chemotaxis, which hinders to identify the conceptual framework how cells
sense and respond to shallow chemical gradients. The activation of Ras
occurs during basal locomotion, and is an essential connector between
receptor and the cytoskeleton during chemotaxis. Using a sensitive assay
for activated Ras we show here that activation of Ras and F-actin form two
excitable systems that are coupled through mutual positive feedback and
memory. This coupled excitable system leads to short-lived patches of
activated Ras and associated F-actin that precede the extension of
protrusions. In buffer excitability starts frequently with Ras activation in
the back/side of the cell or with F-actin in the front of the cell. In a shallow
gradient of chemoattractant local Ras activation triggers full excitation of
Ras and subsequently F-actin at the side of the cell facing the
chemoattractant , leading to directed pseudopod extension and
chemotaxis. A computational model shows that the coupled excitable
Ras/F-actin system forms the driving heart for the ordered-stochastic
extension of pseudopods in buffer and for efficient directional extension
of pseudopods in chemotactic gradients.
submitted by: Peter van Haastert [[log in to unmask]]
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[End dictyNews, volume 43, number 3]
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