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dictyNews Volume 20 Number 11
Dicty News
Electronic Edition
Volume 20, number 11
June 20, 2003
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu.
Back issues of Dicty-News, the Dicty Reference database and other
useful information is available at DictyBase--http://dictybase.org.
============================================
Special Note to the Dictyostelium community
============================================
We have just published within Science's STKE Web site two connection maps.
One pertaining to the events associated with the chemotaxis response in
early aggregation (http://stke.sciencemag.org/cgi/cm/stkecm;CMP_7918)
and the other with the G protein-independent signaling that occurs
through the cAR1 receptor (http://stke.sciencemag.org/cgi/cm/stkecm;CMP_11471).
A ViewPoint published in the June 6, 2003 issue of Science accompanies
the two connection maps. In addition, animators at Science helped design
a movie depicting the signaling events that occur in response to cAMP
(http://stke.sciencemag.org/cgi/content/full/sigtrans;CMP_7918/DC1).
Partial access to STKE is free. To fully benefit the annotated pathways,
you must be AAAS member
(see http://www.sciencemag.org/subscriptions/accessinfo-stke.dtl for more
information). Most Universities and Research Institutes have Institutional
Subscriptions.
The pathways were based on an intense review of the literature. However,
since we are far from perfect, we might have overseen/oversimplified
some aspects. We encourage the Dictyostelium community to access the
pathways and forward any comments to either of us. We have access to
the database and intend to continuously update it. We hope that this
will add to the many tools the community possesses and that it will
become a central arena for discussion about signaling pathways.
Alan Kimmel and Carole Parent
=============
Abstracts
=============
Revamp a model - status and prospects of the Dictyostelium genome project
Ludwig Eichinger
Center for Biochemistry, Medical Faculty, University of Cologne,
Joseph-Stelzmann-Str. 52, 50931 Koeln, FRG
Curr. Gen., in press
Abstract
International efforts are underway that aim at determining the complete
genome sequence of the social amoeba Dictyostelium discoideum. As strategy
a whole chromosome shotgun (WCS) approach has been chosen and each of the
six Dictyostelium chromosomes has been assigned to project partners. The
project is well advanced, chromosome 2 has recently been published, and it
is expected that the sequences of chromosomes 1 and 6 and a gene catalogue
for the complete genome will be available at the end of this year. The
genome sequence together with powerful molecular genetic tools will
undoubtedly further accelerate Dictyostelium research into a number of
fundamental biological processes that are common to a wide range of
eukaryotes. Furthermore, it will constitute the basis for genome-wide
functional analyses. The integration of results from these studies should
ultimately lead to a better understanding of the complex networks that
govern cellular behaviour and development.
Submitted by: Ludwig Eichinger [ludwig.eichinger@uni-koeln.de]
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Gene regulation during early development of Dictyostelium using genome-wide
expression analyses
Negin Iranfar, Danny Fuller, and William F. Loomis
Cell and Developmental Biology, Division of Biology, University of
California San Diego, La Jolla, CA 92093
Eucaryotic Cell, in press
Using genome-wide microarrays we have recognized 172 genes that are highly
expressed at one stage or another during multicellular development of
Dictyostelium discoideum. When developed in shaken suspension, 125 of
these genes were expressed if the cells were treated with cAMP pulses at
6 minute intervals between 2 and 6 hours of development followed by high
levels of exogenous cAMP. In the absence of cAMP treatment, only 3 genes,
carA, gbaB and pdsA, were consistantly expressed. Surprisingly, 14 other
genes were induced by cAMP treatment of mutant cells lacking the
activatable adenylyl cyclase, ACA. However, these genes were not cAMP
induced if both of the developmental adenylyl cyclases, ACA and ACR, were
disrupted showing that they depend on an internal source of cAMP.
Constitutive activity of the cAMP dependent protein kinase, PKA, was
found to bypass the requirement of these genes for adenyly cyclase and
cAMP pulses demonstrating the critical role of PKA in transducing the
cAMP signal to early gene expression. In the absence of constitutive
PKA activity expression of later genes was strictly dependent on ACA in
pulsed cells.
Submitted by: Bill Loomis [wloomis@ucsd.edu]
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Leading the way:
Directional sensing through phosphatidylinositol 3-kinase (PI3K) and other
signaling pathways
Sylvain Merlot and Richard A. Firtel
J. Cell Science (review), in press
ABSTRACT
Chemoattractant-responsive cells are able to translate a shallow
extracellular chemical gradient into a steep intracellular gradient resulting
in the localization of F-actin assembly at the front and an actomyosin
network at the rear that moves the cell forward. Recent evidence suggests
that one of the first asymmetric cellular responses is the localized
accumulation of PtdIns(3,4,5)P3, the product of Class I PI3K at the site of
the new leading edge. The strong accumulation of PtdIns(3,4,5)P3 results
from the localized activation of PI3K, but also to feedback loops that amplify
PtdIns(3,4,5)P3 synthesis at the front and control its degradation at the
side and back of cells. This review examines these different pathways and
discusses several questions about how these pathways are temporally and
spatially regulated and integrate with other signaling pathway during
directional sensing and chemotaxis.
Submitted by: Rick Firtel [rafirtel@ucsd.edu]
-----------------------------------------------------------------------------
THE SIGNAL TO MOVE: D. discoideum go orienteering
Alan R. Kimmel* and Carole A. Parent+#
* Laboratory of Cellular and Developmental Biology, NIDDK
+ Laboratory of Cellular and Molecular Biology, NCI
National Institutes of Health, Bethesda, MD 20892
Science 300: 1525 (2003)
Cells migrating directionally toward a chemoattractant source display a
highly polarized cytoskeletal organization, with F-actin localized
predominantly at the anterior and myosin II at the lateral and posterior
regions. Dictyostelium discoideum has proven a useful system for elucidating
signaling pathways that regulate this chemotactic response. During development,
extracellular adenosine 3', 5' monophosphate (cAMP) functions as a primary
signal to activate cell surface cAMP receptors (cARs). These receptors
transduce different signals depending on whether or not they are coupled
to heterotrimeric guanine nucleotide -binding proteins (G proteins) (see
the STKE Connections Maps). Multiple G protein-stimulated pathways interact
to establish polarity in chemotaxing D. discoideum cells by localizing
F-actin at their leading edge and by regulating the phosphorylation state
and assembly of myosin II. Many of the molecular interactions described are
fundamental to the regulation of chemotaxis in other eukaryotic cells.
Submitted by: Carole Parent [parentc@helix.nih.gov]
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[End Dicty News, volume 20, number 11]
