dictyNews Electronic Edition Volume 26, number 11 April 14, 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 ============= GABA induces terminal differentiation of Dictyostelium through a GABAB type receptor Christophe Anjard and William F. Loomis Center for Molecular Genetics, Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093-0368 Development, in press When prespore cells approach the top of the stalk in a Dictyostelium fruiting body, they rapidly encapsulate in response to the signalling peptide, SDF-2. Glutamate decarboxylase, the product of the gadA gene, generates GABA from glutamate. gadA is expressed exclusively in prespore cells late in development. We found that GABA induces the release of the precursor of SDF-2, AcbA, from prespore cells. GABA also induces exposure of the protease domain of TagC on the surface of prestalk cells where it can convert AcbA to SDF-2. The receptor for GABA in Dictyostelium, GrlE, is a seven-transmembrane G-protein coupled receptor that is most similar to GABA-B type receptors. The signal transduction pathway from GABA/ GrlE appears to be mediated by PI3 kinase and the PKB related protein kinase PkbR1. Glutamate acts as a competitive inhibitor of GABA functions in Dictyostelium and is also able to inhibit induction of sporulation by SDF-2. The signal transduction pathway from SDF-2 is independent of the GABA/ glutamate signal transduction pathway but the two appear to converge to control release of AcbA and exposure of TagC protease. These results indicate that GABA is not only a neurotransmitter but also an ancient intercellular signal. Submitted by: Bill Loomis [wloomis@ucsd.edu] ----------------------------------------------------------------------------- Filopodia Formation in the Absence of Functional WAVE and Arp2/3 Complexes Anika Steffen 1, Jan Faix 2, Guenter P. Resch 3, Joern Linkner 2, Juergen Wehland 1, J. Victor Small 3, Klemens Rottner 1, and Theresia E.B. Stradal 1 1) Signalling and Motility Group, Cytoskeleton Dynamics Group, and Department of Cell Biology, German Research Centre for Biotechnology, D-38124 Braunschweig, Germany; 2)Institute of Biophysical Chemistry, Hannover Medical School, D-30623 Hannover, Germany; 3) Institute of Molecular Biotechnology, Austrian Academy of Sciences, A-1030 Vienna, Austria Mol. Biol. Cell, in press. Cell migration is initiated by plasma membrane protrusions, in the form of lamellipodia and filopodia. The latter rod-like projections may exert sensory functions and are found in organisms as distant in evolution as mammals and amoeba like Dictyostelium discoideum. In mammals, lamellipodia protrusion downstream of the small GTPase Rac1 requires a multimeric protein assembly, the WAVE-complex, which activates Arp2/3-mediated actin filament nucleation and actin network assembly. A current model of filopodia formation postulates that these structures arise from a dendritic network of lamellipodial actin filaments by selective elongation and bundling. Here we have analyzed filopodia formation in mammalian cells abrogated in expression of essential components of the lamellipodial actin polymerization machinery. Cells depleted of the WAVE-complex component Nap1 and, in consequence, of lamellipodia, exhibited normal filopodia protrusion. Likewise, the Arp2/3-complex, which is essential for lamellipodia protrusion, is dispensable for filopodia formation. Moreover, genetic disruption of nap1 or the WAVE-orthologue scar (suppressor of cAMP receptor) in Dictyostelium was also ineffective in preventing filopodia protrusion. These data suggest that the molecular mechanism of filopodia formation is conserved throughout evolution from Dictyostelium to mammals and show that lamellipodia and filopodia formation are functionally separable. Submitted by: Hans Faix [faix@bpc.mh-hannover.de] ----------------------------------------------------------------------------- Transcriptional regulation of Dictyostelium pattern formation Jeffrey G. Williams School of Life Sciences University of Dundee Dow Street Dundee DD1 5EH UK j.g.williams@dundee.ac.uk EMBO reports, in press On starvation, Dictyostelium cells form a terminally differentiated structure, the fruiting body, which comprises stalk cells and spore cells. Their precursorsÑprestalk and prespore cellsÑare spatially separated and accessible in a migratory structure known as the slug. This simplicity and manipulability has made Dictyostelium attractive to both experimental and theoretical developmental biologists. However, this outward simplicity conceals a surprising degree of developmental sophistication. Multiple prestalk sub-types are formed and they undertake a co-ordinated series of morphogenetic cell movements to generate the fruiting body. This review describes recent advances in understanding the signalling pathways that generate prestalk cell heterogeneity, focusing on the roles of the prestalk cell inducer differentiation-inducing factor-1 (DIF-1), the tip inducer cAMP and the transcription factors that mediate their action. These include signal transducers and activators of transcription (STAT) proteins, basic leucine zipper (bZIP) proteins and a Myb protein of a class previously only described in plants. Submitted by: jeff Williams [j.g.williams@dundee.ac.uk] ----------------------------------------------------------------------------- The Dictyostelium genome William F. Loomis Cell and Developmental Biology, Division of Biology, University of California San Diego, La Jolla, CA 92093 Curr. Issues in Mol. Biol., in press The 34 Mb genome of Dictyostelium discoideum is carried on 6 chromosomes and has been fully sequenced by an international consortium. The sequence was assembled on the classical and physical maps that had been built up over the years and refined by HAPPY mapping. Annotation of the sequence predicted about 12,000 genes for proteins of at least 50 amino acids in length. The total number of amino acids encoded (the proteome) is more than double that in yeast and rivals that of metazoans. The genome sequence shows all the proteins available to Dictyostelium as well as definitively showing which domains have been lost since Dictyostelium diverged from the line leading to metazoans. Genomics opens the door to determining the expression patterns of all the genes during growth and development using microarrays. This approach has already uncovered a wealth of new markers for the stages of development and the various cell types. Transcription factors and their cis-regulatory sites that account for the surprising complexity of Dictyostelium development can be analyzed much more easily now that we have the complete sequence. Submitted by: Bill Loomis [wloomis@ucsd.edu] ============================================================================== [End dictyNews, volume 26, number 11]