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dictyNews Volume 27 Number 12
dictyNews
Electronic Edition
Volume 27, number 12
October 13, 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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A Phg2-Adrm1 pathway participates in the nutrient-controlled developmental
response in Dictyostelium.
Cherix, N., Froquet, R., Charette, S.J., Blanc, C., Letourneur, F.,
Cosson, P.
Mol. Biol. Cell In press
ictyostelium amoebae grow as single cells but upon starvation they initiate
multicellular development. Phg2 was characterized previously as a kinase
controlling cellular adhesion and the organization of the actin
cytoskeleton. Here we report that Phg2 also plays a role during the
transition between growth and multicellular development, as evidenced by
the fact that phg2 mutant cells can initiate development even in the
presence of nutrients. Even at low cell density and in rich medium, phg2
mutant cells express discoidin, one of the earliest pre-developmental
markers. Complementation studies indicate that, in addition to the kinase
domain, the core region of Phg2 is involved in the initiation of
development. In this region, a small domain contiguous with a previously
described ras-binding domain, was found to interact with the Dictyostelium
ortholog of the mammalian adhesion-regulating molecule (ADRM1). In addition,
adrm1 knockout cells also exhibit abnormal initiation of development. These
results suggest that a Phg2-Adrm1 signaling pathway is involved in the
control of the transition from growth to differentiation in Dictyostelium.
Phg2 thus plays a dual role in the control of cellular adhesion and
initiation of development.
Submitted by: Pierre Cosson [Pierre.Cosson@medecine.unige.ch]
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Molecular systematics of Dictyostelids: 5.8S rDNA and internal transcribed
spacer region analyses.
Maria Romeralo, Ricardo Escalante, Leandro Sastre and Carlos Lado
Eukaryotic Cell, in press
The variability and adaptability of the amoeba from the class
Dictyosteliomycetes greatly complicate their systematics. The nucleotide
sequences of the Ribosomal Internal Transcribed Spacers (ITS) and the
5.8 S rDNA gene has been determined for twenty eight isolates and shown
their utility to discriminate between different species and genera.
Submitted by: Leandro Sastre [lsastre@iib.uam.es]
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Genetic evidence that the Acyl-CoA binding protein AcbA and the serine
protease/ABC transporter TagA function together in Dictyostelium discoideum
cell differentiation
Matthew Cabral1,2, Christophe Anjard3, William F. Loomis3, and Adam Kuspa1,2
1Departments of Molecular and Human Genetics, 2Biochemistry and Molecular
Biology, Baylor College of Medicine, Houston, Texas, USA, 77030. 3 Center
for Molecular Genetics, Division of Biological Sciences, University of
California San Diego, La Jolla, CA 92093.
Eukaryotic Cell, in press
The acyl-CoA binding protein AcbA is cleaved to form a peptide (SDF-2) that
coordinates spore encapsulation during the morphogenesis of Dictyostelium
fruiting bodies. We present genetic evidence that the misspecification of
cell types seen in mutants of the serine protease/ABC transporter TagA
results from the loss of normal interactions with AcbA. Developmental
phenotypes resulting from aberrant expression of the TagA protease domain,
such as the formation of supernumerary tips on aggregates and the
production of excess prestalk cells, are suppressed by null mutations in
the acbA gene. Phenotypes resulting from the deletion of tagA, such as
over-expresssion of the prestalk gene ecmB and the mis-expression of the
prespore gene cotB in stalk cells, are also observed in acbA mutants.
Moreover, tagA- mutants fail to produce SDF-2 during fruiting body
morphogenesis, but are able to do so if they are stimulated with exogenous
SDF-2. These results indicate that the developmental program depends on
TagA and AcbA working in concert with each other during cell type
differentiation and suggest that TagA is required for normal SDF-2
signaling during spore encapsulation.
Submitted by: Adam Kuspa [akuspa@bcm.tmc.edu]
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The monomeric clathrin assembly protein, AP180, regulates contractile
vacuole size in Dictyostelium discoideum
Irene Stavrou and Theresa J. O'Halloran
University of Texas, Austin
Mol. Biol. Cell In press
AP180, one of many assembly proteins and adaptors for clathrin, stimulates
the assembly of clathrin lattices on membranes, but its unique contribution
to clathrin function remains elusive. In this study we identified the
Dictyostelium discoideum ortholog of the adaptor protein AP180 and
characterized a mutant strain carrying a deletion in this gene. Imaging
GFP-labeled AP180 showed that it localized to punctae at the plasma
membrane, the contractile vacuole and cytoplasm and associated with
clathrin. AP180 null cells did not display defects characteristic of
clathrin mutants, and continued to localize clathrin punctae on their
plasma membrane and within the cytoplasm. However, like clathrin mutants,
AP180 mutants, were osmosensitive. When immersed in water, AP180 null
cells formed abnormally large contractile vacuoles. Furthermore, the cycle
of expansion and contraction for contractile vacuoles in AP80 null cells
was twice as long as that of wild type cells. Taken together, our results
suggest that AP180 plays a unique role as a regulator of contractile
vacuole morphology and activity in Dictyostelium.
Submitted by: Terry O'Halloran [t.ohalloran@mail.utexas.edu]
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[End dictyNews, volume 27, number 12] 
