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