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dictyNews Volume 29 Number 08
dictyNews
Electronic Edition
Volume 29, number 8
Sptember 15, 2007
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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A GPCR involved in post aggregation events in Dictyostelium discoideum
Yogikala Prabhu, Subhanjan Mondal, Ludwig Eichinger and Angelika A. Noegel
Center for Biochemistry, Medical Faculty and Center for Molecular Medicine
Cologne, University of Cologne, Joseph-Stelzmann-Str. 52,
50931 Koeln, Germany
Developmental Biology, in press
Dictyostelium has 55 genes encoding seven-transmembrane G-protein-coupled
receptors (GPCR) that belong to five of the six GPCR families. GrlA is one
of the 17 family 3 GPCRs in Dictyostelium all of which resemble GABAB
receptors from higher eukaryotes. GrlA is a 90 kDa protein present on the
plasma membrane and on membranes of the ER. It has a large extracellular
domain with homology to bacterial periplasmic proteins. The GrlA message
is present throughout development and shows increased levels during the
post aggregation stages. Inactivation of the grlA gene does not severely
affect the growth phase, however, it leads to a delay in the development
at the post aggregation stage. GrlA deficient strains show an altered DIF-1
response specific to the prestalk specific ecmA and ecmB gene, reduced car2
and pkaC transcript levels and form a reduced number of spores. Germination
of the spores was as in wild type. Transcriptional profiling supported the
defect in the sporulation pathway as a large number of genes involved in
the biogenesis and organization of the extracellular matrix and the
sporulation process were significantly down regulated in the mutant.
Submitted by: Angelika Noegel [noegel@uni-koeln.de]
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Expression of zinc transporter family genes in Dictyostelium
Nobuya Sunaga†, Meri Monna, Nao Shimada, Mai Tsukamoto and
Takefumi Kawata1,*
1Department of Biology, Faculty of Science, Toho University, 2-2-1
Miyama, Funabashi, Chiba 274-8510, Japan
TEL & FAX: +81-47-472-5156
†Present address: Department of Biological Sciences, Graduate School
of Science, Tokyo Metropolitan University, Minami-Ohsawa 1-1, Hachioji,
Tokyo 192-0397, Japan
*Corresponding author
Int. J. Dev. Biol., in press
Regulation of the zinc ion concentration is physiologically important to
control the activities of a variety of cellular molecules. A BLAST search
against a conserved domain of known zinc transporters identified twelve
putative zinc transporter family genes in the Dictyostelium genome.
Phylogenetic analysis revealed the presence of three zinc transporter
subfamilies in Dictyostelium. One subfamily of proteins, the ZntA-D
proteins, has weak homology to the STAT3-inducible LIV-1 protein. In
addition, in situ hybridization revealed that Dd-STATa is necessary for
the differentiation of pstAB cells, which are where zntA~D genes are
expressed. Thus, Dd-STATa may control stalk cell differentiation through
some members of the zinc transporter family genes during Dictyostelium
development.
Submitted by: Takefumi Kawatae [tkawata@bio.sci.toho-u.ac.jp]
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Developmental Commitment in Dictyostelium discoideum
Mariko Katoh, Guokai Chen, Emily Roberge, Gad Shaulsky and Adam Kuspa
Departments of Genetics and Biochemistry, Baylor College of Medicine,
Houston, TX, USA
Eukaryotic Cell, in press
Upon starvation, Dictyostelium cells halt cell proliferation, aggregate
into multicellular organisms, form migrating slugs and undergo morphogenesis
into fruiting bodies while differentiating into dormant spores and dead
stalk cells. At almost any developmental stage cells can be forced to
dedifferentiate when they are dispersed and diluted into nutrient broth.
However, migrating slugs can traverse lawns of bacteria for days without
dedifferentiating, ignoring abundant nutrients and continuing development.
We now show that developing Dictyostelium cells revert to the growth phase
only when bacteria are supplied during the first 4-6 hours of development,
but after this time, cells continue to develop regardless of the presence
of food. We postulate that the cells’ inability to revert to the growth
phase after 6 hours represents a commitment to development. We show that
the onset of commitment correlates with the cells’ loss of phagocytic
function. By examining mutant strains, we also show that commitment
requires extracellular cAMP signaling. Moreover, cAMP pulses are sufficient
to induce both commitment and the loss of phagocytosis in starving cells,
whereas starvation alone is insufficient. Finally, we show that inhibition
of development by food prior to commitment is independent of contact between
the cells and the bacteria and that small soluble molecules, probably amino
acids, inhibit development first few hours and subsequently the cells become
unable to react to the molecules and commit to development. We propose that
commitment serves as a checkpoint that ensures the completion of cooperative
aggregation of developing Dictyostelium cells once it has begun, dampening
the response to nutritional cues that might inappropriately block development.
Submitted by: Gad Shaulsky [gadi@bcm.tmc.edu]
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Dictyostelium Hip1r contributes to spore shape and requires epsin for
phosphorylation and localization
Shannon Lea Repass1, Rebecca J. Brady1, and Theresa J. O'Halloran1,*
1 Department of Molecular Cell and Developmental Biology, The University of
Texas at Austin, Austin, TX 78712
*corresponding author
Journal of Cell Science, in press
Clathrin-coated pits assemble on the plasma membrane to select and sequester
proteins within coated vesicles for delivery to intracellular compartments.
While a host of clathrin associated proteins have been identified, much less
is known regarding the interactions between clathrin associated proteins or
how individual proteins influence the function of other proteins. In this study,
we present evidence of a functional relationship between two clathrin associated
proteins in Dictyostelium, Hip1r and epsin. Hip1r null cells form fruiting
bodies that yield defective spores that lack the organized fibrils typical of
wild type spores. This spore coat defect leads to round, rather than ovoid,
spores in Hip1r null cells that exhibit decreased viability. Like Hip1r null
cells, epsin null cells also construct fruiting bodies with round spores, but
these spores are more environmentally robust. Double null cells that harbor
deletions in both epsin and Hip1r form fruiting bodies with spores identical
in shape and viability to Hip1r single null cells. In growing amoeba, Hip1r
is phosphorylated and localizes to punctae on the plasma membrane that also
contain epsin. Both the phosphorylation state and localization of Hip1r into
membrane punctae require epsin. Moreover, expression of the NH2-terminal
ENTH domain of epsin is sufficient to restore both the phosphorylation and the
restricted localization of Hip1r within plasma membrane punctae. Results from
this study reveal a novel interaction between two clathrin associated proteins
during cellular events in both growing and developing Dictyostelium cells.
Submitted by: Terry O'Halloran [t.ohalloran@mail.utexas.edu]
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[End dictyNews, volume 29, number 8]
