dictyNews Electronic Edition Volume 26, number 16 May 26, 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. ============= Abstracts ============= Staying in shape with formins Jan Faix(1) and Robert Grosse(2) (1) Institute for Biophysical Chemistry, Hannover Medical School, 30623 Hannover, Germany. (2) Institute of Pharmacology, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany. Developmental Cell, in press Formins constitute a diverse protein family present in all eukaryotes examined. They are defined by the presence of a formin homology 2 (FH2) domain, which possesses intrinsic and conserved functions regulating cytoskeletal dynamics. Over the past few years formins have become recognized as potent nucleators of linear actin filaments that control a large variety of cellular and morphogenetic functions. Here, we review the molecular principles of formin-induced cytoskeletal rearrangements and their consequences for a growing number of biological processes. Submitted by: Hans Faix [faix@bpc.mh-hannover.de] ----------------------------------------------------------------------------- Dictyostelium RacH regulates endocytic vesicular trafficking and is required for localization of vacuolin Baggavalli P. Somesh (1), Carola Neffgen (1), Miho Iijima (2), Peter Devreotes (2) and Francisco Rivero (1). 1. Center for Biochemistry and Center for Molecular Medicine Cologne, Medical Faculty, University of Cologne. Joseph-Stelzmann-Strasse 52, D-50931 Koeln, Germany 2. Department of Cell Biology, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore MD, 21205, USA Traffic, in press Dictyostelium RacH localizes predominantly to membranes of the nuclear envelope, ER and Golgi apparatus. To investigate the role of this protein we generated knockout and overexpressor strains. RacH-deficient cells displayed 50% reduced fluid phase uptake and a moderate exocytosis defect, but phagocytosis was unaffected. Detailed examination of the endocytic pathway revealed defective acidification of early endosomes and reduced secretion of acid phosphatase in the presence of sucrose. The distribution of the post-lysosomal marker vacuolin was altered, with a high proportion of cells showing a diffuse vesicular pattern in contrast to the wild type strain, where few intensely stained vacuoles predominate. Cytokinesis, cell motility, chemotaxis and development appeared largely unaffected. In a cell-free system RacH stimulates actin polymerization, suggesting that this protein is involved in actin-based trafficking of vesicular compartments. We also investigated the determinants of subcellular localization of RacH by expression of GFP-tagged chimeras in which the C-terminus of RacH and the plasma membrane targeted RacG were exchanged, the insert region was deleted or the net positive charge of the hypervariable region was increased. We show that several regions of the molecule, not only the hypervariable region, determine targeting of RacH. Overexpression of mis-targeted RacH mutants did not recapitulate the phenotypes of a strain overexpressing non mutated RacH, indicating that the function of this protein is in great part related to its subcellular localization. Submitted by: Francisco Rivero [francisco.rivero@uni-koeln.de] ============================================================================== [End dictyNews, volume 26, number 16]