dictyNews Electronic Edition Volume 40, number 20 August 22, 2014 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 ========= Huntingtin supplies a csaA-independent function essential for EDTA-resistant homotypic cell adhesion in Dictyostelium discoideum Morgan N. Thompson, Marcy E. MacDonald, James F. Gusella and Michael A. Myre Center for Human Genetic Research, Massachusetts General Hospital, Harvard Medical School. Boston, MA, 02114 USA The Journal of HuntingtonÕs Disease, in press Background: The CAG triplet repeat expansion mutation in the HTT locus, which results in neurodegeneration in HuntingtonÕs disease, elongates a polyglutamine tract in huntingtin, a HEAT/HEAT-like protein that has been highly structurally conserved through evolution. In several organisms, huntingtin is necessary for proper cell-cell adhesion and normal development. Objective: Dictyostelium discoideum huntingtin null (htt-) cells display a variety of developmental abnormalities and completely fail to acquire EDTA-resistant homotypic cell adhesion during starvation in suspension culture. Methods: Here, we have assessed the hypothesis that Htt may be a genetic interactor of csaA, a major regulator of EDTA-resistant homotypic cell adhesion in D. discoideum. Immunoblot analysis demonstrated that csaA protein expression is dysregulated in htt- cells. Results: Unexpectedly, csaA overexpression, previously shown to rescue csaA- cell adhesion, failed to rescue the htt- adhesion defect. Thus, while htt was required for proper expression of the csaA protein, csaA overexpression was not sufficient to confer EDTA-resistant adhesion in the context of the htt- genetic background in contrast to parental cells. This implies a novel role for Htt in conferring csaA-dependent, EDTA- resistant cell adhesion that warrants further investigation. Calcium supplementation restored both endogenous csaA protein levels and EDTA-resistant adhesion in htt- cells. Conclusions: Our data suggests the existence of an additional mechanism that overcomes the EDTA-resistant adhesion defect of htt- cells in the early development of D. discoideum. Submitted by Michael Myre [myre@chgr.mgh.harvard.edu] --------------------------------------------------------------------------- Huntingtin Regulates Ca2+ Chemotaxis and K+-facilitated cAMP Chemotaxis, in Conjunction with the Monovalent Cation/H+ Exchanger Nhe1, in a Model Developmental System: Insights into its Possible Role in Huntington's Disease Deborah Wessels, Daniel F. Lusche, Amanda Scherer, Spencer Kuhl, Michael A. Myre* and David Soll Developmental Studies Hybridoma Bank, Department of Biology, University of Iowa, Iowa City, Iowa 52242; *Center for Human Genetic Research, Massachusetts General Hospital, Boston, Harvard Medical School, Boston MA, 02114 USA Developmental Biology, in press. HuntingtonÕs disease is a neurodegenerative disorder, attributable to an expanded trinucleotide repeat in the coding region of the human HTT gene, which encodes the protein huntingtin. These mutations lead to huntingtin fragment inclusions in the striatum of the brain. However, the exact function of normal huntingtin and the defect causing the disease remain obscure. Because there are indications that huntingtin plays a role in Ca2+ homeostasis, we studied the deletion mutant of the HTT ortholog in the model developmental system Dictyostelium discoideum, in which Ca2+ plays a role in receptor- regulated behavior related to the aggregation process that leads to multicellular morphogenesis. In D.discoideum, the htt- mutant failed to undergo both K+-facilitated chemotaxis in spatial gradients of the major chemoattractant cAMP, and chemotaxis up a spatial gradient of Ca2+, but behaved normally in Ca2+-facilitated cAMP chemotaxis and Ca2+-dependent flow-directed motility. This was the same phenotypic profile of the null mutant of Nhel, a monovalent cation/H+exchanger. The htt- mutant also failed to orient correctly during natural aggregation, as was the case for the Nhel mutant. Moreover, in a K+-based buffer the normal localization of actin was similarly defective in both htt- and nhe1- cells in a K+-based buffer, and the normal localization of Nhe1 was disrupted in the htt- mutant. These observations demonstrate that Htt and Nhel play roles in the same specific cation-facilitated behaviors and that Nhel localization is directly or indirectly regulated by Htt. Similar cation-dependent behaviors and a similar relationship between Htt and Nhe1 have not been reported for mammalian neurons and deserves investigation, especially as it may relate to HuntingtonÕs disease. Submitted by Michael Myre [myre@chgr.mgh.harvard.edu] --------------------------------------------------------------------------- A cyanobacterial light activated adenylylcyclase partially restores development of a Dictyostelium Discoideum, adenylyl cyclase A null mutant Zhi-hui Chen1, Sarah Raffelberg2, Aba Losi3, Pauline Schaap1* , Wolfgang GŠrtner2* 1 College of Life Sciences, University of Dundee, Dundee UK 2 MPI Chemical Energy Conversion, MŸlheim, Germany 3 Dept. of Physics and Earth Sciences, University of Parma, Parma, Italy *to whom correspondence should be addressed: p.schaap@dundee.ac.uk; Wolfgang.gaertner@cec.mpg.de Journal of Biotechnology, in press Abstract: A light-regulated adenylyl cyclase, mPAC, was previously identified from the cyanobacterium Microcoleus chthonoplastes PCC7420. MPAC consists of a flavin-based blue light-sensing LOV domain and a catalytic domain. In this work, we expressed mPAC in an adenylate cyclase A null mutant (aca-) of the eukaryote Dictyostelium discoideum and tested to what extent light activation of mPAC could restore the cAMP-dependent developmental programme of this organism. Amoebas of Dictyostelium, a well- established model organism, generate and respond to cAMP pulses, which cause them to aggregate and construct fruiting bodies. mPAC was expressed under control of a constitutive actin-15 promoter in D. discoideum and displayed low basal adenylyl cyclase activity in darkness that was about five-fold stimulated by blue light. mPAC expression in aca- cells marginally restored aggregation and fruiting body formation in darkness. However, more and larger fruiting bodies were formed when mPAC expressing cells were incubated in light. Extending former applications of light-regulated AC, these results demonstrate that mPAC can be used to manipulate multicellular development in eukaryotes in a light dependent manner. Submitted by Zhihui Chen [z.y.chen@dundee.ac.uk] --------------------------------------------------------------------------- Two Dictyostelium Tyrosine Kinase-Like kinases function in parallel, stress-induced STAT activation pathways Tsuyoshi Araki*, Linh Hai Vu , Norimitsu Sasakiā, Takefumi Kawataā, Ludwig Eichinger  and Jeffrey G. Williams*¤ * College of Life Sciences, Welcome Trust Biocentre, University of Dundee, Dow St., Dundee, DD1 5EH, UK   Center for Biochemistry Institute of Biochemistry I Joseph-Stelzmann-Str. 52 50931 Cologne Germany ā Department of Biology, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan ¤ j.g.williams@dundee.ac.uk Molecular Biology of the Cell,, in press When Dictyostelium cells are hyper-osmotically stressed STATc is activated by tyrosine phosphorylation. Unusually, activation is regulated by serine phosphorylation and consequent inhibition of a tyrosine phosphatase: PTP3. The identity of the cognate tyrosine kinase is unknown and we show that two Tyrosine Kinase-Like (TKL) enzymes, Pyk2 and Pyk3, share this function; thus for stress-induced STATc activation, single null mutants are only marginally impaired but the double mutant is non-activatable. When cells are stressed Pyk2 and Pyk3 undergo increased auto-catalytic tyrosine phosphorylation. The site(s) that are generated bind the SH2 domain of STATc and then STATc becomes the target of further kinase action. The signalling pathways that activate Pyk2 and Pyk3 are only partially overlapping and there may be a structural basis for this difference because Pyk3 contains both a TKL domain and a pseudokinase domain. The latter functions, like the JH2 domain of metazoan JAKs, as a negative regulator of the kinase domain. The fact that two differently regulated kinases catalyse the same phosphorylation event may facilitate specific targeting because under stress Pyk3 and Pyk2 accumulate in different parts of the cell; Pyk3 moves from the cytosol to the cortex while Pyk2 accumulates in cytosolic granules that co-localise with PTP3. The University of Dundee is a registered Scottish Charity, No: SC015096 Submitted by Jeff Williams [j.g.williams@dundee.ac.uk] --------------------------------------------------------------------------- Dictyostelium uses ether-linked inositol phospholipids for intracellular signalling Jonathan Clark, Robert R Kay, Anna Kielkowska, Izabella Niewczas, Louise Fets, David Oxley, Len R Stephens, Phillip T Hawkins Signalling Programme and Babraham Biosciences Technology, Babraham Research Campus, Babraham, Cambridge, CB22 3AT, UK. MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK Authors for correspondence: Rob Kay, Len Stephens and Phillip Hawkins EMBO J, in press Inositol phospholipids are critical regulators of membrane biology throughout eukaryotes. The general principle by which they perform these roles is conserved across species and involves binding of differentially phosphorylated inositol headgroups to specific protein domains. This interaction serves to both recruit and regulate the activity of several different classes of protein which act on membrane surfaces. In mammalian cells, these phosphorylated inositol headgroups are predominantly borne by a C38:4 diacyl glycerol backbone. We show here that the inositol phospholipids of Dictyostelium are different, being highly enriched in an unusual C34:1e lipid backbone, 1- hexadecyl -2-(11Z-octadecenoyl)-sn-glycero-3-phospho-(1'-myo-inositol), in which the sn-1 position contains an ether-linked C16:0 chain; they are thus plasmanylinositols. These plasmanylinositols respond acutely to stimulation of cells with chemoattractants and their levels are regulated by PIPKs, PI3Ks and PTEN. In mammals and now in Dictyostelium, the hydrocarbon chains of inositol phospholipids are a highly selected subset of those available to other phospholipids, suggesting that different molecular selectors are at play in these organisms but serve a common, evolutionary conserved purpose. Submitted by Rob Kay [rrk@mrc-lmb.cam.ac.uk] --------------------------------------------------------------------------- Evolutionary reconstruction of pattern formation in 98 Dictyostelium species reveals that cell-type specialization by lateral inhibition is a derived trait Christina Schilde, Anna Skiba and Pauline Schaap College of Life Sciences, University of Dundee, UK EvoDevo, in press Multicellularity provides organisms with opportunities for cell-type specialization, but requires novel mechanisms to position correct proportions of different cell types throughout the organism. Dictyostelid social amoebas display an early form of multicellularity, where amoebas aggregate to form fruiting bodies, which contain only spores or up to four additional cell-types. These cell types will form the stalk and support structures for the stalk and spore head. Phylogenetic inference subdivides Dictyostelia into four major groups, with the model organism D.discoideum residing in group 4. Differentiation of its five cell types is dominated in D.discoideum by lateral inhibition-type mechanisms that trigger scattered cell differentiation, with tissue patterns being formed by cell sorting. Submitted by Christina Schilde [c.schilde@dundee.ac.uk] ============================================================== [End dictyNews, volume 40, number 20]