dictyNews Electronic Edition Volume 38, number 4 February 3, 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 ========= Abstracts ========= Evolution of self-organisation in Dictyostelia by adaptation of a non-selective phosphodiesterase and a matrix component for regulated cAMP degradation Yoshinori Kawabe, Karin E. Weening, Jacques Marquay-Markiewicz and Pauline Schaap* College of Life Sciences, University of Dundee, Dundee DD15EH, UK Development, in press Dictyostelium discoideum amoebas coordinate aggregation and morphogenesis by secreting cAMP pulses that propagate as waves through fields of cells and multicellular structures. To retrace how this mechanism for self-organisation evolved, we studied the origin of the cAMP phosphodiesterase PdsA and its inhibitor PdiA, which are essential for cAMP wave propagation. D.discoideum and other species that use cAMP to aggregate reside in group 4 of the four major groups of Dictyostelia. We found that groups 1-3 express a non-specific, low affinity ortholog of PdsA, which gained cAMP selectivity and increased 200-fold in affinity in group 4. A low affinity group 3 PdsA only partially restored aggregation of a D.discoideum pdsA null mutant, but was more effective at restoring fruiting body morphogenesis. Deletion of a group 2 PdsA gene resulted in disruption of fruiting body morphogenesis, but left aggregation unaffected. Together, these results show that groups 1-3 use a low affinity PdsA for morphogenesis that is neither suited nor required for aggregation. PdiA belongs to a family of matrix proteins that are present in all Dictyostelia and consist mainly of cysteine-rich repeats. However, in its current form with several extensively modified repeats, PdiA is only present in the group 4. PdiA is essential for initiating spiral cAMP waves, which, by organizing large territories, generate the large fruiting structures that characterize group 4. We conclude that efficient cAMP-mediated aggregation in group 4 evolved by recruitment and adaptation of a non-selective phosphodiesterase and a matrix component into a system for regulated cAMP degradation. Submitted by Pauline Schaap [p.schaap@dundee.ac.uk] -------------------------------------------------------------------------------------- Regulation of aggregate size and pattern by adenosine and caffeine in cellular slime molds. Jaiswal P, Soldati T, Thewes S, Baskar R. BMC Dev Biol. 2012 Jan 23;12(1):5. BACKGROUND: Multicellularity in cellular slime molds is achieved by aggregation of several hundreds to thousands of cells. In the model slime mold Dictyostelium discoideum, adenosine is known to increase the aggregate size and its antagonist caffeine reduces the aggregate size. However, it is not clear if the actions of adenosine and caffeine are evolutionarily conserved among other slime molds known to use structurally unrelated chemoattractants. RESULTS: We have examined how the known factors affecting aggregate size are modulated by adenosine and caffeine. Result: Adenosine and caffeine induced the formation of large and small aggregates respectively, in evolutionarily distinct slime molds known to use diverse chemoattractants for their aggregation. Due to its genetic tractability, we chose D. discoideum to further investigate the factors affecting aggregate size. The changes in aggregate size are caused by the effect of the compounds on several parameters such as cell number and size, cell-cell adhesion, cAMP signal relay and cell counting mechanisms. While some of the effects of these two compounds are opposite to each other, interestingly, both compounds increase the intracellular glucose level and strengthen cell-cell adhesion. These compounds also inhibit the synthesis of cAMP phosphodiesterase (PdsA), weakening the relay of extracellular cAMP signal. Adenosine as well as caffeine rescue mutants impaired in stream formation (pde4- and pdiA-) and colony size (smlA- and ctnA-) and restore their parental aggregate size. CONCLUSION: Adenosine increased the cell division timings thereby making large number of cells available for aggregation and also it marginally increased the cell size contributing to large aggregate size. Reduced cell division rates and decreased cell size in the presence of caffeine makes the aggregates smaller than controls. Both the compounds altered the speed of the chemotactic amoebae causing a variation in aggregate size. Our data strongly suggests that cytosolic glucose and extracellular cAMP levels are the other major determinants regulating aggregate size and pattern. Importantly, the aggregation process is conserved among different lineages of cellular slime molds despite using unrelated signalling molecules for aggregation. Submitted by R. Baskar [rbaskar@IITM.AC.IN] -------------------------------------------------------------------------------------- ZizB, a novel RacGEF regulates development, cell motility and cytokinesis in Dictyostelium Nicholl K. Pakes*, Douwe Veltman*, Francisco Rivero, Jamal Nasir, Robert Insall, and Robin S.B. Williams J. Cell Sci., in press Dock (Dedicator of Cytokinesis) proteins represent a family of Guanine nucleotide Exchange Factors (GEFs) that include the well studied Dock180 family and the poorly characterised zizimin family. Our current understanding of Dock180 function is to regulate Rho small GTPases, playing a role in a number of cell processes including cell migration, development and division. Here, we have employed a tractable model for cell motility research, Dictyostelium discoideum, to help elucidate the role of the related zizimin proteins. We show that gene ablation of zizA causes no change in development whereas ablation of zizB gives rise to an aberrant developmental morphology and a reduction in cell directionality and velocity, and altered cell shape. Fluorescently labeled ZizA protein associates with the microtubule organizing centre (MTOC), whereas the ZizB protein exhibits cortical enrichment. Overexpression of ZizB also causes an increase in the number filopodia and a partial inhibition of cytokinesis. Analysis of ZizB protein binding partners indicates a direct binding to Rac1a and a range of actin-interacting proteins. In conclusion our work provides the first insight into the molecular and cellular functions of zizimin GEF proteins playing a role in cell movement, filopodia formation and cytokinesis. Submitted by Robin Williams [Robin.Williams@rhul.ac.uk] ============================================================== [End dictyNews, volume 38, number 4]