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dictyNews Volume 28 Number 07
dictyNews
Electronic Edition
Volume 28, number 7
March 23, 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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MEK1 and Protein Phosphatase 4 Coordinate Dictyostelium Development and
Chemotaxis
Michelle C. Mendoza, Ezgi O. Booth, Gad Shaulsky,
and Richard A. Firtel
Mol. Cell Bio. in press
The MEK and ERK/MAPK proteins are established regulators of multicellular
development and cell movement. By combining traditional genetic and biochemical
assays with statistical analysis of global gene-expression profiles, we
discerned a genetic interaction between Dictyostelium mek1, smkA (suppressor
of mek1Ð), and pppC (protein phosphatase 4 catalytic subunit). We found that
during development and chemotaxis, both mek1 and smkA regulate pppC function.
In other organisms, the protein phosphatase 4 catalytic subunit, PP4C,
functions in complex with the PP4R2 and PP4R3 regulatory subunits to control
recovery from DNA damage. Here, we show that catalytically active PP4C is
also required for development, chemotaxis, and the expression of numerous
genes. smkA (SMEK) functions as the Dictyostelium PP4R3 homolog and
positively regulates a subset of PP4CÕs functions: PP4C-mediated developmental
progression, chemotaxis, and the expression of genes specifically involved in
cell stress responses and cell movement. We also demonstrate that SMEK does
not control the absolute level of PP4C activity and suggest that SMEK regulates
PP4C by controlling its localization to the nucleus. These data define a novel
genetic pathway in which mek1 functions upstream of pppC/smkA to control
multicellular development and chemotaxis.
Submitted by Rick Firtel [rafirtel@ucsd.edu]
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The BEACH protein LvsB is localized on lysosomes and postlysosomes and limits
their fusion with early endosomes.
Elena Kypri, Christian Schmauch, Markus Maniak, and Arturo De Lozanne
Section of Molecular Cell & Developmental Biology and Institute for Cellular
and Molecular Biology, University of Texas at Austin, Austin, TX 78712 and
Zellbiologie, Universitaet Kassel, Kassel, Germany
Traffic, in press
The Chediak-Higashi Syndrome is a genetic disorder caused by the loss of the
BEACH protein Lyst. Impaired lysosomal function in CHS patients results in
many physiological problems, including immunodeficiency, albinism and
neurological problems. Dictyostelium LvsB is the ortholog of mammalian Lyst
and is also important for lysosomal function. A knock-in approach was used to
tag LvsB with GFP and express it from its single chromosomal locus. GFP-LvsB
was observed on late lysosomes and postlysosomes. Loss of LvsB resulted in
enlarged postlysosomes, in the abnormal localization of proton pumps on
postlysosomes and their abnormal acidification. The abnormal postlysosomes
in LvsB null cells were produced by the inappropriate fusion of early endosomal
compartments with postlysosomal compartments. The intermixing of compartments
resulted in a delayed transit of fluid phase marker through the endolysosomal
system. These results support the model that LvsB and Lyst proteins act as
negative regulators of fusion by limiting the heterotypic fusion of early
endosomes with postlysosomal compartments.
Submitted by Arturo De Lozanne [a.delozanne@mail.utexas.edu]
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Profilin isoforms in Dictyostelium discoideum
Rajesh Arasada (1), Annika Gloss (1), Budi Tunggal (2), Jayabalan M. Joseph (1),
Daniela Rieger (1), Subhanjan Mondal (2), Michael Schleicher (1) and
Angelika A. Noegel (2,3)
(1) Adolf-Butenandt-Institut / Zellbiologie, Ludwig-Maximilians-Universitaet,
80336 Muenchen, Germany; (2) Institut f. Biochemie, Med. Fak., (3) Zentrum
Molekulare Medizin Koeln, Universitaet zu Koeln, 50931 Koeln, Germany.
Biochim. Biophys. Acta (Mol. Cell Res.), in press
Eukaryotic cells contain a large number of actin binding proteins of different
functions, locations and conconcentrations. They bind either to monomeric actin
(G-actin) or to actin filaments (F-actin) and thus regulate the dynamic
rearrangement of the actin cytoskeleton. The Dictyostelium discoideum genome
harbors representatives of all G-actin binding proteins including actobindin,
twinfilin, and profilin. A phylogenetic analysis of all profilins suggests that
two distinguishable groups emerged very early in evolution and comprise either
vertebrate and viral profilins or profilins from all other organisms. The newly
discovered profilin III isoform in D. discoideum shows all functions that are
typical for a profilin. However, the concentration of the third isoform in wild
type cells reaches only about 0.5% of total profilin. In a yeast-2-hybrid assay
profilin III was found to bind specifically to the proline-rich region of the
cytoskeleton-associated vasodilator-stimulated phosphoprotein (VASP).
Immunolocalization studies showed similar to VASP the profilin III isoform in
filopodia and an enrichment at their tips. Cells lacking the profilin III
isoform show defects in cell motility during chemotaxis. The low abundance and
the specific interaction with VASP argue against a significant actin
sequestering function of the profilin III isoform.
Submitted by: Michael Schleicher [schleicher@lrz.uni-muenchen.de]
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[End dictyNews, volume 28, number 7]
