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.


=========
Abstracts
=========



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 mek1�), 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 PP4C�s 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]
--------------------------------------------------------------------------------


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]
--------------------------------------------------------------------------------


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]
============================================================
[End dictyNews, volume 28, number 7]