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dictyNews Volume 26 Number 08
dictyNews
Electronic Edition
Volume 26, number 8
March 10, 2006
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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Blebbing of Dictyostelium cells in response to chemoattractant
Paul D Langridge and Robert R. Kay
Experimental Cell Research
Stimulation of Dictyostelium cells with a high uniform concentration of
the chemoattractant cyclic-AMP induces a series of morphological changes,
including cell rounding and subsequent extension of pseudopodia in random
directions. Here we report that cyclic-AMP also elicits blebs and analyse
their mechanism of formation. The surface area and volume of cells remain
constant during blebbing indicating that blebs form by the redistribution
of cytoplasm and plasma membrane rather than the exocytosis of internal
membrane coupled to a swelling of the cell. Blebbing occurs immediately
after a rapid rise and fall in submembraneous F-actin, but the blebs
themselves contain little F-actin as they expand. A mutant with a partially
inactivated Arp2/3 complex has a greatly reduced rise in F-actin content,
yet shows a large increase in blebbing. This suggests that bleb formation
is not enhanced by the preceding actin dynamics, but is actually inhibited
by them. In contrast, cells that lack myosin-II completely fail to bleb.
We conclude that bleb expansion is likely to be driven by hydrostatic
pressure produced by cortical contraction involving myosin-II. As blebs
are induced by chemoattractant we speculate that hydrostatic pressure is
one of the forces driving pseudopod extension during movement up a
gradient of cyclic-AMP.
Submitted by: Paul Langridge [pl@mrc-lmb.cam.ac.uk]
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The Dictyostelium KinomeÑAnalysis of the Protein Kinases from a Simple
Model Organism
Jonathan M. Goldberg1*, Gerard Manning2*, Allen Liu1, Petra Fey3,
Karen E. Pilcher3, Yanji Xu1, Janet L. Smith1
*These authors contributed equally to this work.
1 Boston Biomedical Research Institute, Watertown, Massachusetts,USA
2 Razavi-Newman Center for Bioinformatics, Salk Institute for
Biological Studies, La Jolla, California, USA
3 Center for Genetic Medicine, Northwestern University, Chicago,
Illinois, USA
PLoS Genetics, in press
Dictyostelium discoideum is a widely studied model organism with both
unicellular and multicellular forms in its developmental cycle. The
Dictyostelium genome encodes 285 predicted protein kinases, similar to the
count of the much more advanced Drosophila. It contains members of most
kinase classes shared by fungi and metazoans, as well as many previously
thought to be metazoan specific, indicating that they have been secondarily
lost from the fungal lineage. This includes the entire tyrosine kinaseÐlike
(TKL) group, which is expanded in Dictyostelium and includes several novel
receptor kinases. Dictyostelium lacks tyrosine kinase group kinases, and
most tyrosine phosphorylation appears to be mediated by TKL kinases. About
half of Dictyostelium kinases occur in subfamilies not present in yeast
and metazoa, suggesting that protein kinases have played key roles in the
adaptation of Dictyostelium to its habitat. This study offers insights into
kinase evolution and provides a focus for signaling analysis in this system.
Submitted by: Janet Smith [janet.l.smith@gmail.com]
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[End dictyNews, volume 26, number 8] 
