dictyNews Electronic Edition Volume 25, number 12 November 18, 2005 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 ============= Comparing the Dictyostelium and Entamoeba Genomes Reveals an Ancient Split in the Conosa Lineage J. Song, Q. Xu, R. Olsen, W. F. Loomis, G. Shaulsky, A. Kuspa and R. Sucgang Verna and Marrs McLean Department of Biochemistry and Molecular Biology, The Department of Human Genetics, and The Graduate Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA Section of Cell and Developmental Biology, Division of Biology, University of California, San Diego, La Jolla, California 92093, USA PLoS Computational Biology, in press The Amebozoa are a sister clade to the fungi and the animals, but are poorly sampled for completely sequenced genomes. The social amoeba Dictyostelium discoideum and a mitochondriate pathogen Entamoeba histolytica are the first Amoebozoa with genomes completely sequenced. Both organisms are classified under the Conosa subphylum. To identify Amoebozoa-specific genomic elements, we compared these two genomes to each other and to other eukaryotic genomes. An expanded phylogenetic tree, built from the complete predicted proteomes of 23 eukaryotes places the two amoebae in the same lineage, although the divergence is estimated to be greater than that between animals and fungi, and probably happened shortly after the Amoebozoa split from the opisthokont lineage. Most of the 1500 orthologous gene families shared between the two amoebae are also shared with plant, animal, and fungal genomes. We found that only 42 gene families are distinct to the amoeba lineage, among these are a large number of proteins the encode repeats of the FNIP domain, and a transcription factor essential for proper cell type differentiation in D. discoideum. These Amoebozoa-specific genes may be useful in the design of novel diagnostics and therapies for amoebal pathologies. Supplementary data is available from http://dictygenome.org/supplement/rsucgang/song_2005 . Submitted by: Richard Sucgang [rsucgang@bcm.tmc.edu] ----------------------------------------------------------------------------- Dictyostelium myosin-IE is a fast molecular motor involved in phagocytosis Ulrike Duerrwang1, Setsuko Fujita-Becker1, Muriel Erent1, F. Jon Kull2, Georgios Tsiavaliaris1,4, Michael A. Geeves3, and Dietmar J. Manstein1,4 1 Abteilung Biophysik, Max-Planck Institut fuer medizinische Forschung, Jahnstr. 29, D-69120 Heidelberg, Germany 2 Dartmouth College, Department of Chemistry, 6128 Burke Laboratory, Hanover, NH 03755 3 Department of Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom 4 Institut fuer Biophysikalische Chemie, OE 4350, Medizinische Hochschule Hannover, Carl-Neuberg-Strasse 1, D-30623 Hannover, Germany Journal Of Cell Science, in press Class-I myosins are single-headed motor proteins, implicated in various motile processes including organelle translocation, ion-channel gating, and cytoskeleton reorganization. Here we describe the cellular localization of myosin-IE and its role in the phagocytic uptake of solid particles and cells. A complete analysis of the kinetic and motor properties of Dictyostelium discoideum myosin-IE was achieved by the use of motor domain constructs with artificial lever arms. Class-I myosins belonging to subclass-IC like myosin-IE are thought to be tuned for tension maintenance or stress sensing. Different from this prediction, our results show myosin-IE to be a fast motor. Myosin-IE motor activity is regulated by TEDS-site phosphorylation, which increases the coupling efficiency between the actin and nucleotide binding sites 10-fold and the motile activity more than 5-fold. Changes in the level of free Mg2+-ions, which are within the physiological range, are shown to modulate the motor activity of myosin-IE by inhibiting ADP-release. Submitted by: Dietmar Manstein [manstein@bpc.mh-hannover.de] ----------------------------------------------------------------------------- On the effects of cycloheximide on cell motility and polarisation in Dictyostelium discoideum Authors: Margaret Clotworthy* and David Traynor. MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH, England. BioMed Central Cell Biology, in press Background Cycloheximide is a protein synthesis inhibitor that acts specifically on the 60S subunit of eukaryotic ribosomes. It has previously been shown that a short incubation of Dictyostelium discoideum amoebae in cycloheximide eliminates fluid phase endocytosis. Results We found that treatment with cycloheximide also causes the amoebae to retract their pseudopodia, round up and cease movement. Furthermore, fluid phase endocytosis, phagocytosis and capping cease in the presence of 2mM cycloheximide, although membrane uptake, as measured using FM1-43, is unaffected. In the presence of cycloheximide, aggregation-competent amoebae sensitive to cAMP, although round, can still localise CRAC, ABP120, PI3K and actin polymerisation in response to a micropipette filled with cAMP. The behaviour of wild-type amoebae in the presence of cycloheximide is surprisingly similar to that of amoebae having a temperature-sensitive version of NSF at the restrictive temperature. Conclusions Our results may suggest that, upon cycloheximide treatment, either a labile protein required for polarised membrane recycling is lost, or a control mechanism linking protein synthesis to membrane recycling is activated. Submitted by: Margaret Clotworthy [clotworm@mrc-lmb.cam.ac.uk] ----------------------------------------------------------------------------- Transcriptional regulation of post-aggregation genes in Dictyostelium by a feed-forward loop involving GBF and LagC Negin Iranfar, Danny Fuller, and William F. Loomis Cell and Developmental Biology Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093 Developmental Biology, in press Expression profiles of developmental genes in Dictyostelium were determined on microarrays during development of wild type cells and mutant cells lacking either the DNA binding protein GBF or the signaling protein LagC. We found that the mutant strains developed in suspension with added cAMP expressed the pulse-induced and early adenylyl cyclase (ACA) dependent genes, but not the later ACA dependent, post-aggregation genes. Since expression of lagC itself is dependent on GBF, expression of the post-aggregation genes might be controlled only by signaling from LagC. However, expression of lagC in a GBF-independent manner in a gbfA- null strain did not result in expression of the post-aggregation genes. Since GBF is necessary for accumulation of LagC and both the DNA binding protein and the LagC signal transduction pathway are necessary for expression of post-aggregation genes, GBF and LagC form a feed-forward loop. Such network architecture is a common motif in diverse organisms and can act as a filter for noisy inputs. Breaking the feed-forward loop by expressing lagC in a GBF independent manner in a gbfA+ strain does not significantly affect the patterns of gene expression for cells developed in suspension with added cAMP, but results in a significant delay at the mound stage and asynchronous development on solid supports. This feed-forward loop can integrate temporal information with morphological signals to ensure that post-aggregation genes are only expressed after cell contacts have been made. Submitted by: Bill Loomis [wloomis@ucsd.edu] ============================================================================== [End dictyNews, volume 25, number 12]