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dictyNews Volume 26 Number 04
dictyNews
Electronic Edition
Volume 26, number 4
January 27, 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 retinoblastoma orthologue controls stalk/spore preference in Dictyostelium
Harry MacWilliams (1) Kimchi Doquang (1,2) Roberto Pedrola (3) Gytha
Dollman (1) Daniela Grassi (3) Thomas Peis (1) Adrian Tsang(2) and
Adriano Ceccarelli (3)
(1) Biozentrum der Ludwig-Maximilians-Universitt, Planegg-Martinsried,
Germany
(2) Centre for Structural and Functional Genomics, Concordia University,
Montreal, Quebec, Canada
(3) Dipartimento di Scienze Cliniche e Biologiche, Universit di Torino,
Ospedale S.Luigi, Torino, Italy
Development, in press
We describe rblA, the Dictyostelium ortholog of the retinoblastoma
susceptibility gene Rb. In the growth phase, rblA expression is correlated
with several factors which lead to ÒpreferenceÓ for the spore pathway.
During multicellular development, expression increases 200-fold in
differentiating spores. RblA-null strains differentiate stalk cells and
spores normally, but in chimeras with wild-type the mutant shows a strong
preference for the stalk pathway. RblA-null cells are hypersensitive to
the stalk morphogen DIF, suggesting that rblA normally suppresses the DIF
response in cells destined for the spore pathway. RblA overexpression
during growth leads to G1 arrest, but since growing Dictyostelium are
overwhelmingly G2, rblA does not seem to be important in the normal cell
cycle. RblA-null cells show reduced cell size and a premature
growth-development transition; the latter appears anomalous but may
reflect selection pressures acting on social ameba.
Submitted by: Harry MacWilliams [macw@zi.biologie.uni-muenchen.de]
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Single-molecule analysis of chemoattractant-stimulated membrane recruitment
of a PH domain-containing protein
Satomi Matsuoka(1), Miho Iijima(2), Tomonobu M. Watanabe(1), Hidekazu
Kuwayama(1), Toshio Yanagida(1), Peter N. Devreotes(2) and Masahiro Ueda(1)
(1)Laboratories for Nanobiology, Graduate School of Frontier Biosciences,
Osaka University, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan
(2)Department of Cell Biology, Johns Hopkins University School of Medicine
725 N. Wolfe St., 114 WBSB, Baltimore, Maryland, 21205, USA
Journal of Cell Science, in press
Molecular mechanisms of chemotactic response are highly conserved among
many eukaryotic cells including human leukocytes and Dictyostelium cells.
The cells can sense the differences in chemoattractant concentration across
the cell body and respond by extending pseudopods from the cell side facing
to a higher concentration. Pseudopod formation is regulated by binding of
pleckstrin homology-domain-containing proteins to phosphatidylinositol
3,4,5-trisphosphates localized at the leading edge of chemotaxing cells.
However, molecular mechanisms underlying dynamic features of a pseudopod
have not been fully explained by the known properties of pleckstrin
homology-domain-containing proteins. To investigate the mechanisms, we
visualized single molecules of green fluorescent protein tagged to Crac, a
pleckstrin homology-domain-containing protein in Dictyostelium discoideum
cells. Whereas populations of Crac molecules exhibited a stable steady-state
localization at pseudopods, individual molecules bound transiently to
phosphatidylinositol 3,4,5-trisphosphates for ~120 milliseconds, indicating
dynamic properties of pleckstrin homology-domain-containing protein.
Receptor stimulation did not alter the binding stability but regulated the
number of bound pleckstrin homology-domain molecules via
phosphatidylinositol 3,4,5-trisphosphates metabolisms. These results
demonstrate that the steady-state localization of pleckstrin
homology-domain-containing proteins at the leading edge of chemotaxing
cells is dynamically maintained by rapid recycling of individual pleckstrin
homology-domain-containing proteins. The short interaction between
pleckstrin homology-domain and phosphatidylinositol 3,4,5-trisphosphates
contributes to accurate and sensitive chemotactic movements through the
dynamic redistributions. These dynamic properties might be general for
signaling components involved in chemotaxis.
Submitted by: Satomi Matsuoka [matsuoka@phys1.med.osaka-u.ac.jp]
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Identification of Novel Centrosomal Proteins in Dictyostelium discoideum
by Comparative Proteomic Approaches
Yvonne Reinders, Irene Schulz, Ralph Graf, and Albert Sickmann*
Protein Mass Spectrometry and Functional Proteomics Group,
Rudolf-Virchow-Center for ExperimentalBiomedicine,
Julius-Maximilians-University Wuerzburg, Versbacher Strasse 9,
97078 Wuerzburg, Germany
Journal of Proteome Research, in press
The centrosome functions as the main microtubule-organization center of
the cell and is of importance for all microtubule-dependent processes such
as organelle transport and directionality of cell migration. One of the
major model organisms in centrosome research is the slime mold Dictyostelium
discoideum. Since only 10 centrosomal proteins are known so far in
Dictyostelium discoideum, the elucidation of new centrosomal components may
give a more comprehensive understanding of centrosomal function. To
distinguish between centrosomal and contaminating proteins we established
different separation and relative quantification strategies including
techniques such as iTRAQ and DIGE. In this work, we present the
identification of several known components as well as more than 70 new
candidatess currently subject of further investigationssfor the protein
inventory of the Dictyostelium centrosome. Among these protein
identifications, 44% represent hypothetical proteins of still unknown
function associated with the centrosome.
Submitted by: Ralph Graef [r.graef@zeiss.de]
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[End dictyNews, volume 26, number 4] 
