dictyNews Electronic Edition Volume 36, number 10 March 25, 2011 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. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= Identifying an uptake mechanism for the antiepileptic and bipolar disorder treatment valproic acid using the simple biomedical model Dictyostelium Nicole Terbach1, Rishita Shah2, Rachel Keleman2, Peter S. Klein2, Dmitri Gordienko3, Nigel A. Brown3, Christopher J. Wilkinson1, Robin S. B. Williams1,* 1 Centre for Biomedical Sciences, School of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, UK. 2 Department of Medicine, University of Pennsylvania School of Medicine, 415 Curie Boulevard, Philadelphia, PA 19104, U.S.A.. 3 Division of Basic Medical Sciences, St George's University of London, London SW17 0RE, UK Journal of Cell Science, in press Valproic acid (VPA) is the most highly prescribed epilepsy treatment worldwide and is also used to prevent bipolar disorder and migraine. Surprisingly, very little is known about its mechanisms of cellular uptake. Here we employ a range of cellular, molecular and genetic approaches to characterize VPA uptake using a simple biomedical model, Dictyostelium discoideum. We show that VPA is taken up against an electrochemical gradient in a dose-dependent manner. Transport is protein mediated, pH- and proton gradient-dependent and shows strong substrate structure specificity. Using a genetic screen, we identified a protein homologous to a mammalian solute carrier family 4 (SLC4) bicarbonate transporter that we show is involved in VPA uptake, since pharmacological and genetic ablation reduces the uptake of VPA and partially protects against VPA dependent developmental effects, and extracellular bicarbonate competes for VPA uptake in Dictyostelium. We further show that this uptake mechanism is likely to be conserved in both zebrafish (Danio rerio) and Xenopus laevis model systems. These results implicate, for the first time, a novel uptake mechanism for VPA through SLC4-catalysed activity. Submitted by Robin Williams [robin.williams@rhul.ac.uk] ------------------------------------------------------------------------------ Uncovering a role for the Dictyostelium discoideum SadA protein in cell-substrate adhesion: A Role for the Tail Anthony S. Kowal1,2,3 and Rex L. Chisholm2,3* Northwestern University Integrated Graduate Program in the Life Sciences1, Department of Cell and Molecular Biology2, The Center for Genetic Medicine3 Eukaryotic Cell, in press Previous work from our laboratory has shown that the Dictyostelium discoideum SadA protein plays a central role in cell-substrate adhesion. SadA null cells exhibit a loss of adhesion, a disrupted actin cytoskeleton and a cytokinesis defect. How SadA mediates these phenotypes is unknown. This work addresses the mechanism of SadA function, demonstrating an important role for the C-terminal cytoplasmic tail in SadA function. We found that a SadA tail-less mutant is unable to rescue the sadA adhesion deficiency, and overexpression of the SadA tail domain reduces adhesion in wild-type cells. We also show that SadA is closely associated with the actin cytoskeleton. Mutagenesis studies suggest that four serine residues in the tail - S924 / S925 and S940 / S941 - may regulate association of SadA with the actin cytoskeleton. GST pull-down assays identified at least one likely interaction partner of the SadA tail - Cortexillin I, a known actin bundling protein. Thus, our data demonstrate an important role for the carboxy terminal cytoplasmic tail in SadA function, and strongly suggest that a phosphorylation event in this tail regulates an interaction with Cortexillin I. Based on our data, we propose a model for the function of SadA. Submitted by Anthony Kowall [askowal@northwestern.edu] -------------------------------------------------------------------------------------- Dictyostelium hybrid polyketide synthase, SteelyA, produces 4-methyl-5-pentylbenzene-1,3-diol and induces spore maturation Takaaki B Narita1, Kota Koide2, Naoki Morita3 & Tamao Saito2* FEMS Microbiology Letters, in press The genome of Dictyostelium contains two novel hybrid-type polyketide synthases (PKSs) known as 'Steely'; the Steely enzyme is formed by the fusion of type I and type III PKSs. One of these enzymes, SteelyB, is known to be responsible for the production of the stalk cell-inducing factor DIF-1 in vivo. On the other hand, the product(s) and expression pattern of SteelyA are not clearly understood, because there are two different reports associated with the in vitro products of SteelyA and its expression pattern. To solve this problem, we first examined the expression pattern using two different primer sets and found that it was quite similar to that shown in the dictyExpress database. StlA expression peaked at approximately 3 hours and declined but showed a small peak around the end of development. Next we examined the in vivo product of SteelyA by the use of a stlA null mutant and found that the mutant lacked 4-methyl-5-pentylbenzene-1,3-diol (MPBD). This null mutant showed aberrant, glassy sori, and most of the cells in the sori remained amoeba-like without a cellwall. This defect was restored by adding 200 nM of MPBD to the agar. These results indicate that SteelyA produces MPBD in vivo and induces spore maturation. Submitted by Tamao Saito [tasaito@sophia.ac.jp] -------------------------------------------------------------------------------------------- DIF-1 regulates Dictyostelium basal disc differentiation by inducing the nuclear accumulation of a bZIP transcription factor Yoko Yamada, Beatriz Nunez-Corcuera and Jeffrey G. Williams+ College of Life Sciences, Welcome Trust Building, University of Dundee, Dow St.,Dundee DD1 5EH + corresponding author: tel 44 1382 385823 fax 44-1382 34421 j.g.williams@dundee.ac.uk Dev. Biol., in press Exposure of monolayer Dictyostelium cells to the signaling polyketide DIF-1 causes DimB, a bZIPtranscription factor, to accumulate in the nucleus where it induces prestalk gene expression. Here we analyse DimB signaling during normal development. In slugs DimB is specifically nuclear enriched in the pstB cells; a cluster of vital dye-staining cells located on the ventral surface of the posterior, prespore region. PstB cells move at culmination, to form the lower cup and the outer basal disc of the fruiting body, and DimB retains a high nuclear concentration in both these tissues. In a dimB null (dimB-) strain there are very few pstB or lower cup cells, as detected by neutral red staining, and it is known that the outer basal disc is absent or much reduced. In the dimB- strain ecmB, a marker of pstB differentiation, is not DIF inducible. Furthermore, ChIP analysis shows that DimB binds to the ecmB promoter in DIF-induced cells. These results suggest that the differentiation of pstB cells is caused by a high perceived level of DIF-1 signaling, leading to nuclear localization of DimB and direct activation of cell type-specific gene expression. Submitted by: Jeff Williams [j.g.williams@dundee.ac.uk] ============================================================== [End dictyNews, volume 36, number 10]