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dictyNews Volume 23 Number 09
Dicty News
Electronic Edition
Volume 23, number 9
september 10, 2004
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 Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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Disruption of the NCS-1/frequenin-related ncsA gene in Dictyostelium
discoideum accelerates development
Barrie Coukell*, Anne Cameron, Stephen Perusini1, Katharine Shim
Department of Biology, York University,4700 Keele St.,
Toronto, ON, M3J 1P3, CANADA
Develop. Growth Differ., in press
To learn more about the function of intracellular Ca2+ in Dictyostelium
discoideum, we searched databases for sequences encoding potential members
of the neuronal calcium sensor (NCS) family of Ca2+-binding proteins. As a
result, genes for five new putative Ca2+-binding proteins were identified.
Based on amino acid sequence alignments and phylogenetic analyses, one of
these genes (ncsA) was determined to be closely related to NCS-1/frequenin
genes in other organisms. The protein product of ncsA (NcsA) binds 45Ca2+
and exhibits a dramatic gel mobility shift in the presence of Ca2+,
suggesting that it is a Ca2+ sensor. ncsA-null cells grow normally in
axenic culture. However, on bacterial lawns, the ncsA-null clones expand
slowly and development begins prematurely within the plaques. In larger
clones, ncsA-null cells form narrow growth zones with evenly spaced
aggregrates along the inner edge, and closely packed fruiting bodies.
An analysis of intracellular cAMP levels, developmental timing on PBS agar,
and stage-specific gene expression indicate that development of ncsA-null
cells is accelerated by 3-4 h. Together, these results suggest that NcsA
might function in Dictyostelium to prevent cells from entering development
prematurely in the presence of environmental nutrients.
Submitted by: Barrie Coukell [bcoukell@yorku.ca]
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Evidence that the Dictyostelium STAT protein Dd-STATa plays a role in the
differentiation of inner basal disc cells and identification of a promoter
element essential for expression in these cells
Nao Shimada1, Toshinari Maruo2, Mineko Maeda2, Hideko Urushihara3 and
Takefumi Kawata1, 4
1 Department of Biology, Faculty of Science, Toho University, 2-2-1 Miyama,
Funabashi, Chiba 274-8510, Japan
2Department of Biology, Graduate School of Science, Osaka University,
Toyonaka, Osaka 560-0043
3 Graduate School of Life and Environmental Sciences, University of Tsukuba,
Tsukuba, Ibaraki 305-8572
4 Corresponding author
E-mail: tkawata@bio.sci.toho-u.ac.jp
Differentiation, in press
Abstract Dd-STATa, a Dictyostelium homologue of the metazoan STATs (signal
transducers and activators of transcription) proteins, is necessary in the
slug for correct entry into culmination. Dd-STATa-null mutant fails to
culminate and its phenotype correlates with the loss of a funnel-shaped
core region, the pstAB core region, which expresses both the ecmA and ecmB
genes. To understand how the differentiation of pstAB core cells is
regulated, we identified an EST that is expressed in the core cells of
normal slugs but down-regulated in the Dd-STATa-null mutant. This EST,
SSK348, encodes a close homologue of the Dictyostelium acetyl-CoA synthetase
(ACS). A promoter fragment of the cognate gene, aslA (acetyl-CoA
synthetase-like A), was fused to a lacZ reporter and the expression pattern
determine. As expected from the behaviour of the endogenous aslA gene, the
aslA:lacZ fusion gene is not expressed in Dd-STATa-null slugs. In parental
cells, the aslA promoter is first activated in the funnel-shaped core cells
located at the slug anterior; the ãpstAB coreä. During culmination, the
pstAB core cells move down, through the prespore cells, to form the inner
part of the basal disc. As the spore mass climbs the stalk the aslA gene
comes to be expressed in cells of the upper and lower cups; structures that
cradle the spore head. Deletion and point mutation analyses of the promoter
identified an AT-rich sequence that is necessary for expression in the pstAB
core. This acts in combination with repressor regions that prevent ectopic
aslA expression in the prestalk regions of slugs and the stalks of culminants.
Thus this study confirms that Dd-STATa is necessary for the differentiation
of pstAB core cells, by showing that it is needed for the activation of the
aslA gene. It also identifies aslA promoter elements that are likely to be
regulated, directly or indirectly, by Dd-STATa.
Submitted by: Takefumi Kawata [tkawata@bio.sci.toho-u.ac.jp]
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Molecular structure of the rod domain of Dictyostelium filamin
Grzegorz M. Popowicz, Rolf Mueller, Angelika A. Noegel, Michael Schleicher,
Robert Huber and Tad A. Holak
J. Mol. Biol, in press
Dictyostelium discoideum filamin (ddFLN) is a two-chain F-actin
crosslinking protein with an N-terminal actin-binding domain and a rod
domain constructed from six tandem repeats of a 100-residue motif that has
an immunoglobulin (Ig) fold. We report the 2.8 resolution crystal
structure of a homodimer of rod repeats 4, 5 and 6. The two chains are
arranged in an antiparallel fashion and form an elongated element, which
is shortened, however, compared to a fully extended, linear configuration
because the long axis of each Ig domain is arranged at an angle to the long
axis of the rod. Same arrangement of repeats should also be present in the
rod domain of human FLNa, much longer than Dictyostelium FLN, which forms a
straight and long rigid structure able to crosslink F-actin chains over
distances of more than 1000 .
Submitted by: Michael Schleicher [schleicher@lrz.uni-muenchen.de]
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[End Dicty News, volume 23, number 9] 
