dictyNews Electronic Edition Volume 38, number 27 October 26, 2012 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 Note from Guenther Gerisch: During the production process of the paper Gerisch et al "PIP3 Waves and PTEN Dynamics in the Emergence of Cell Polarity", Biophysical Journal, Volume 103, Issue 6, 1170-1178, 19 September 2012,the Movies had been aligned at random, such that none of the links opened the right Movie.These errors have now been corrected. ========= Abstracts ========= Comparative genomics in the Amoebozoa clade Gernot Gloeckner and Angelika A. Noegel Biological Reviews, in press Amoeboid life forms can be found throughout the evolutionary tree. The greatest proportion of these life forms is found in the Amoebozoa clade, one of the six major eukaryote evolutionary branches. Despite its common origin this clade exhibits a wide diversity of lifestyles including free-living and parasitic species and species with multicellular and multinucleate life stages. In this group, development, cooperation, and social behaviour can be studied in addition to traits common to unicellular organisms. To date, only a few Amoebozoa genomes have been sequenced completely, however a number of expressed sequence tags (ESTs) and complete and draft genomes have become available recently for several species that represent some of the major evolutionary lineages in this clade. This resource allows us to compare and analyse the evolutionary history and fate of branch-specific genes if properly exploited. Despite the large evolutionary time scale since the emergence of the major groups the genomic organization in Amoebozoa has retained common features. The number of Amoebozoa-specific genetic inventions seems to be rather small. The emergence of subgroups is accompanied by gene and domain losses and acquisitions of bacterial gene material. The sophisticated developmental cycles of Myxogastria and Dictyosteliida likely have a common origin and are deeply rooted in amoebozoan evolution. In this review we describe initial approaches to comparative genomics in Amoebozoa, summarize recent findings, and identify goals for further studies. Submitted by Gernot Gloeckner [gernot.gloeckner@uni-koeln.de] --------------------------------------------------------------------------- Delineating the Core Regulatory Elements Critical for Directed Cell Migration by Examining Folic Acid-Mediated Responses Srinivasan, K.(a), Wright, G.(a), Hames, N.(a), Housman, M.(a), Roberts, A.(a), Aufderheide, K.J.(b), and Chris Janetopoulos(a) (a) Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA. (b) Department of Biology, Texas A&M University, College Station, TX 77843, USA. J Cell Sci., in press Dictyostelium discoideum shows chemotaxis towards folic acid (FA) throughout vegetative growth, and towards cAMP during development. We determined the spatio-temporal localization of cytoskeletal and signaling molecules and investigated the FA-mediated responses in a number of signaling mutants to further our understanding of the core regulatory elements that are critical for cell migration. Proteins enriched in the pseudopods during chemotaxis also re-localize transiently to the plasma membrane (PM) during uniform FA stimulation. Alternatively, proteins that are absent from the pseudopods during migration re-distribute transiently from the PM to the cytosol when cells are globally stimulated with FA. These chemotactic responses to FA were also examined in cells lacking the GTPases Ras C and G. While Ras and Phosphoinositide 3-Kinase activity were significantly decreased in Ras G and Ras C/G nulls, these mutants still migrated to FA, indicating that other pathways must support FA-mediated chemotaxis. We also examined the spatial movements of PTEN to uniform FA and cAMP stimulation in Phospholipase C (PLC) null cells. The lack of PLC strongly influences the localization of PTEN in response to FA, but not cAMP. In addition, we compared the gradient sensing behavior of polarized cells migrating towards cAMP to that of unpolarized cells migrating towards FA. The majority of polarized cells make U turns when the cAMP gradient is switched from the front of the cell to the rear. Conversely, unpolarized cells immediately extend pseudopods towards the new FA source. We also observed that PM PI(3,4,5)P3 levels oscillate in unpolarized cells treated with Latrunculin-A, while polarized cells had stable PM PI(3,4,5)P3 responses toward the chemoattractant gradient source. Similar findings were found in 4 hour starved cells where there was a mixture of polarized and unpolarized cells responding to cAMP. Taken together, these findings suggest that similar components control gradient sensing during FA and cAMP-mediated motility, but polarized cells have an easier time forming a stabilized response which ultimately helps maintain their directionality. Submitted by Chris Janetopoulos [c.janetopoulos@vanderbilt.edu] --------------------------------------------------------------------------- A kinesin-mediated mechanism that couples centrosomes to nuclei Tikhonenko, I, Magidson, V, Graef, R, Khodjakov, A, and Koonce, M.P. Division of Translational Medicine,Wadsworth Center and Department of Cell Biology, University of Potsdam, Cell Mol Life Science, in press The M-type kinesin isoform, Kif9, has recently been implicated in maintaining a physical connection between the centrosome and nucleus in Dictyostelium discoideum. However, the mechanism by which Kif9 functions to link these two organelles remains obscure. Here we demonstrate that the Kif9 protein is localized to the nuclear envelope and is concentrated in the region underlying the centrosome point of attachment. Nuclear anchorage appears mediated through a specialized transmembrane domain located in the carboxyl terminus. Kif9 interacts with microtubules in in vitro binding assays and effects an endwise depolymerization of the polymer. These results suggest a model whereby Kif9 is anchored to the nucleus and generates a pulling force that reels the centrosome up against the nucleus. This is a novel activity for a kinesin motor, one important for progression of cells into mitosis and to ensure centrosome-nuclear parity in a multinuclear environment. Submitted by Mike Koonce [koonce@wadsworth.org] --------------------------------------------------------------------------- The adhesion modulation protein, AmpA localizes to an endocytic compartment and influences substrate adhesion, actin polymerization and endocytosis in vegetative Dictyostelium cells Noratel, E.F., Petty, C.L. Kelsey, J.S., Cost, H.H., Basappa, N. and Blumberg, D.D. Department of Biological Sciences, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250 BMC-Cell Biology, in press Background: AmpA is a secreted 24Kd protein that has pleiotropic effects on Dictyostelium development. Null mutants delay development at the mound stage with cells adhering too tightly to the substrate. Prestalk cells initially specify as prespore cells and are delayed in their migration to the mound apex. Extracellular AmpA can rescue these defects, but AmpA is also necessary in a cell autonomous manner for anterior like cells (ALCs) to migrate to the upper cup. The ALCs are only 10% of the developing cell population making it difficult to study the cell autonomous effect of AmpA on the migration of these cells. AmpA is also expressed in growing cells, but, while it contains a hydrophobic leader sequence that is cleaved, it is not secreted from growing cells. This makes growing cells an attractive system for studying the cell autonomous function of AmpA. Results: In growing cells AmpA plays an environment dependent role in cell migration. Excess AmpA facilitates migration on soft, adhesive surfaces but hinders migration on less adhesive surfaces. AmpA also effects the level of actin polymerization. Knockout cells polymerize less actin while over expressing cells polymerize more actin than wild type. Overexpression of AmpA also causes an increase in endocytosis that is traced to repeated formation of multiple endocytic cups at the same site on the membrane. Immunofluorescence analysis shows that AmpA is found in the Golgi and colocalizes with calnexin and the slow endosomal recycling compartment marker, p25, in a perinuclear compartment. AmpA is found on the cell periphery and is endocytically recycled to the perinuclear compartment. Conclusion: AmpA is processed through the secretory pathway and traffics to the cell periphery where it is endocytosed and localizes to what has been defined as a slow endosomal recycling compartment. AmpA plays a role in actin polymerization and cell substrate adhesion. Submitted by Daphne Blumberg [blumberg@umbc.edu] ============================================================== [End dictyNews, volume 38, number 27]