dictyNews Volume 26 Number 16

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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 
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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] 
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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] 
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[End dictyNews, volume 26, number 16]