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dictyNews Volume 27 Number 03
dictyNews
Electronic Edition
Volume 27, number 3
August 4, 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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Delineation of the roles played by RasG and RasC in cAMP-dependent signal
transduction during the early development of Dictyostelium discoideum
Parvin Bolourani, George B. Spiegelman and Gerald Weeks
Department of Microbiology and Immunology, University of British Columbia
Vancouver, BC, V6T 1Z3, Canada
Corresponding author: Gerald Weeks
email: gerwee@interchange.ubc.ca
Tel: 604-822-6649
Fax: 604-822-6041
Mailing address:
Life Sciences Centre, 2350 Health Sciences Mall, University of British
Columbia
Vancouver, BC, V6T 1Z3, Canada
Molecular Biology of the Cell, in press
Upon starvation, the cellular slime mold Dictyostelium discoideum initiates
a program of development leading to formation of multicellular structures.
The initial cell aggregation requires chemotaxis to cyclic AMP (cAMP) and
relay of the cAMP signal by the activation of adenylyl cyclase (ACA), and it
has been shown previously that the Ras protein RasC is involved in both
processes. Insertional inactivation of the rasG gene resulted in delayed
aggregation and a partial inhibition of early gene expression, suggesting
that RasG also has a role in early development. Both chemotaxis and ACA
activation were reduced in the rasG- cells, but the effect on chemotaxis was
more pronounced. When the responses of rasG- cells to cAMP were compared
with the responses of rasC- and rasC- rasG- strains, generated in otherwise
isogenic backgrounds, these studies revealed that signal transduction through
RasG is more important in chemotaxis and early gene expression, but that
signal transduction through RasC is more important in ACA activation. Since
the loss of either of the two Ras proteins alone did not result in a total
loss of signal output down either of the branches of the cAMP signal-response
pathway, there appears to be some overlap of function.
Submitted by: Gerry Weeks [gerwee@interchange.ubc.ca]
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WASP-Interacting Protein (WIPa) is Important for Actin Filament Elongation
and Prompt Pseudopod Formation in Response to a Dynamic Chemoattractant
Gradient
Scott A. Myers, Laura R. Leper, and Chang Y. Chung
Department of Pharmacology, Vanderbilt University Medical Center, Nashville,
TN 37069
Molecular Biology of the Cell, In Press
The role of WASP-interacting protein (WIP) in the process of F-actin assembly
during chemotaxis of Dictyostelium was examined. Mutations of the WH1 domain
of WASP led to a reduction in binding to WIPa, a newly identified homolog of
mammalian WIP, a reduction of F-actin polymerization at the leading edge, and
a reduction in chemotactic efficiency. WIPa localizes to sites of new
pseudopod protrusion and colocalizes with WASP at the leading edge. WIPa
increases actin elongation in vivo and in vitro in a WASP-dependent manner.
WIPa overexpressing cells exhibit multiple microspike formation and defects
in chemotactic efficiency due to frequent changes of direction. WIPa
translocates to the cortical membrane upon uniform cAMP stimulation. This
translocation appears to be dependent upon cortical F-actin assembly.
Reduced expression of WIPa by expressing a hairpin WIPa (hp WIPa) construct
resulted in more polarized cells that exhibit a delayed response to a new
chemoattractant source due to delayed extension of pseudopod toward the new
gradient. These results suggest that WIPa is important for actin filament
elongation required for new pseudopod protrusion and prompt reorientation of
cells toward a new gradient by initiating localized bursts of actin
polymerization and/or elongation.
Submitted by: Chang Chung [chang.chung@vanderbilt.edu]
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[End dictyNews, volume 27, number 3] 
