dictyNews Electronic Edition Volume 30, number 14 May 2, 2008 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 ========= MPL1, the novel phosphatase with Leucine-Rich-Repeats, is essential for proper ERK2 phosphorylation and cell motility. Marbelys Rodriguez*, Bohye Kim*, Nam-Sihk Lee, Sudhakar Veeranki, and Leung Kim# Dept of Biological Sciences, Florida International University, Miami, FL 33199 * Equal contributing authors. # Corresponding Author: Dept of Biological Sciences, Florida International University, Health and Life Science Building, Rm 218C Miami, FL 33199 Tel: 305-348-7315 FAX: 305-348-1986 email: kiml@fiu.edu Eukaryotic Cell, In press The novel Dictyostelium phosphatase Mpl1 contains six Leucine-Rich-Repeats at the amino-terminal end and a phosphatase domain at the carboxyl end. Similarly architectured phosphatases exist among other protozoa such as Entamoeba histolytica, Leishmania major, and Trypanosoma cruzi. Mpl1 was strongly induced after 5 hours of development; ablation by homologous recombination led to defective streaming and aggregation during development. In addition, cAMP pulsed mpl1- cells showed reduced random and directional motility. At the molecular level, mpl1- cells displayed higher prestimulus and persistent post-stimulus ERK2 phosphorylation in response to cAMP stimulation. Consistent with their phenotype of persistent ERK2 phosphorylation, mpl1- cells also displayed an aberrant pattern of cAMP production, resembling that of the regA- cells. Reintroduction of a full length Mpl1 into mpl1- cells restored aggregation, ERK2 regulation, random and directional motility, and cAMP production similar to wild type cells. We propose that MPL1 is a novel phosphatase essential for proper regulation of ERK2 phosphorylation and optimal motility during development. Submitted by: Leung Kim [kiml@fiu.edu] -------------------------------------------------------------------------------- Endocytosis and the actin cytoskeleton in Dictyostelium discoideum Francisco Rivero The Hull York Medical School. University of Hull, Hull HU6 7RX, United Kingdom Int. Rev. Cell Mol. Biol, 276, in press Endocytosis, an essential process of all eukaryotic cells, requires the actin cytoskeleton for proper functioning. The soil amoeba Dictyostelium discoideum is well known for its contribution to the actin cytoskeleton field. The genetic tractability and the availability of appropriate tools have made of Dictyostelium an attractive model for studies of endocytosis and vesicle trafficking as well. These tools include a large palette of fluorescent protein fusions and the combination of improved fractionation methods with high throughput techniques along with the recently propagated use of the amoeba as a host for microbial pathogens. In this review I discuss in a comprehensive manner the evidence accumulated in the literature towards a participation of components of the microfilament system of D. discoideum in endocytic trafficking and conclude with a model that describes the sequence of events and the components involved during the well investigated uptake phase of the endocytic process in the soil amoeba. Submitted by: Francisco Rivero [francisco.rivero@uni-koeln.de] -------------------------------------------------------------------------------- A secreted protein is a Dictyostelium chalone Deenadayalan Bakthavatsalam, Debra A. Brock, N. Neda Nikravan, Kevin D. Houston, R. Diane Hatton, and Richard H. Gomer Department of Biochemistry and Cell Biology, MS-140, Rice University, Houston, TX 77005 J. Cell Science, in press Dictyostelium discoideum cells secrete CfaD, a protein with similarity to cathepsin proteases. Cells lacking cfaD proliferate faster and reach a higher stationary phase density than wild-type, while cells overexpressing CfaD proliferate slowly and reach stationary phase at a low cell density. On a per nucleus basis, CfaD affects proliferation but not growth. The drawback to not having CfaD is a reduced spore viability. Recombinant CfaD has no detectable protease activity, but when added to cells, inhibits the proliferation of wild-type and cfaD¯ cells. The secreted protein AprA also inhibits proliferation. AprA is necessary for the effect of CfaD on proliferation. Sieving gel chromatography indicates that in conditioned growth medium, the 60 kDa CfaD is part of a ~150 kDa complex, and both chromatography and pull-down assays suggest that CfaD interacts with AprA. These results suggest that two interacting proteins may function together as a chalone signal in a negative feedback loop that slows Dictyostelium cell proliferation. Submitted by: Richard Gomer [richard@rice.edu] ============================================================== [End dictyNews, volume 30, number 14]