dictyNews Electronic Edition Volume 31, number 5 Aug 1, 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. Upon publication of your paper, please send strains and plamids to the Dicty Stock Center. For more information see http://dictybase.org/StockCenter/Deposit.html. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ========= Abstracts ========= A Protein with Similarity to PTEN Regulates Aggregation Territory Size by Decreasing cAMP Pulse Size during Dictyostelium Development Yitai Tang and Richard H. Gomer* Department of Biochemistry and Cell Biology, Rice University, Houston, Texas Eukaryotic Cell, in press An interesting but largely unanswered biological question is how eukaryotic organisms regulate the size of multicellular tissues. During development, a lawn of Dictyostelium cells breaks up into territories, and within the territories the cells aggregate in dendritic streams to form groups of ~20,000 cells. Using random insertional mutagenesis to search for genes involved in group size regulation, we found that an insertion in the cnrN gene affects group size. Cells lacking CnrN (cnrN–) form abnormally small groups, which can be rescued by the expression of exogenous CnrN. Relayed pulses of extracellular adenosine 3’5’-cyclic monophosphate (cAMP) direct cells to aggregate by chemotaxis to form aggregation territories and streams. cnrN– cells over-accumulate cAMP during development and form small territories. Decreasing the cAMP pulse size by treating cnrN– cells with cAMP phosphodiesterase (PDE) or starving cnrN– cells at a low density rescues the small territory phenotype. The predicted CnrN sequence has similarity to phosphatase and tensin homolog (PTEN), which in Dictyostelium inhibits cAMP-stimulated phosphatidylinositol 3’ kinase (PI3K) signaling pathways. CnrN inhibits cAMP-stimulated PIP3 accumulation, Akt activation, actin polymerization, and cAMP production. Our results suggest that CnrN is a protein with some similarities to PTEN, and regulates cAMP signal transduction to regulate territory size. Submitted by: Yitai Tang [yttang@rice.edu] -------------------------------------------------------------------------------- Dictyostelium myosin-5b is a conditional processive motor Manuel H. Taft, Falk K. Hartmann, Agrani Rump, Heiko Keller, Igor Chizhov, Dietmar J. Manstein, and Georgios Tsiavaliaris Institute for Biophysical Chemistry, Hannover Medical School, Hannover D-30625 Corresponding Author: gtsiaval@bpc.mh-hannover.de JBC, in press Dictyostelium myosin-5b is the gene product of myoJ and one of two closely related myosin-5 isoenzymes produced in Dictyostelium discoideum. Here we report a detailed investigation of the protein’s kinetic and functional properties. In standard assay buffer conditions, Dictyostelium myosin-5b displays high actin affinity in the presence of ADP, fast ATP hydrolysis, and a high steady-state ATPase activity in the presence of actin that is rate limited by ADP release. These properties are typical for a processive motor that can move over long distances along actin filaments without dissociating. Our results show that a physiological decrease in the concentration of free Mg2+-ions leads to an increased rate of ADP release and shortening of the fraction of time the motor spends in the strong actin binding states. Consistently, the ability of the motor to efficiently translocate actin filaments at very low surface densities decreases with decreasing concentrations of free Mg2+-ions. In addition, we provide evidence that the observed changes in Dd myosin-5b motor activity are of physiological relevance and propose a mechanism by which this molecular motor can switch between processive and non-processive movement. Submitted by: Georgios Tsiavaliaris [gtsiaval@bpc.mh-hannover.de] -------------------------------------------------------------------------------- A Dictyostelium homologue of the metazoan Cbl proteins regulates STAT signalling (Dictyostelium Cbl and STAT regulation) Judith Langenick, Tsuyoshi Araki, Yoko Yamada and Jeffrey G. Williams+ University of Dundee, School of Life Sciences, Dow Street, Dundee DD1 5EH , UK J Cell Sci, in press Cbl proteins down-regulate metazoan signalling pathways by ubiquitylating receptor tyrosine kinases, thereby targeting them for degradation. They contain a phosphotyrosine-binding region, comprised of an EF-hand and an SH2 domain, linked to an E3 ubiquitin-ligase domain. CblA, a Dictyostelium homologue of the Cbl proteins, contains all three conserved domains. In a cblA- strain early development occurs normally but migrating cblA- slugs frequently fragment and the basal disc of the culminants that are formed are absent or much reduced. These are characteristic features of mutants in signalling by DIF-1: the low molecular weight, prestalk and stalk cell inducer. Tyrosine phosphorylation of STATc is induced by DIF-1 but in the cblA- strain this response is attenuated relative to parental cells. We present evidence that CblA fulfils this function, as a positive regulator of STATc tyrosine phosphorylation, by down-regulating PTP3: the protein tyrosine phosphatase responsible for de-phosphorylating STATc. Thus Cbl proteins have an ancient origin but, while metazoan Cbl proteins regulate tyrosine kinases, the Dictyostelium Cbl regulates via a a tyrosine phosphatase. Submitted by: Jeff Williams [j.g.williams@dundee.ac.uk] ============================================================== [End dictyNews, volume 31, number 5]