dictyNews Electronic Edition Volume 32, number 9 April 3, 2009 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 ========= Dictyostelium discoideum Paxillin Regulates Actin-Based Processes M. Berenice Duran, Asif Rahman, Max Colten and Derrick Brazill Department of Biological Sciences, Center for the Study of Gene Structure and Function Hunter College of the City University of New York, New York, NY 10021 Protist, in press Paxillin is a key player in integrating the actin cytoskeleton with adhesion, and thus is essential to numerous cellular processes including proliferation, differentiation and migration in animal cells. PaxB, the Dictyostelium discoideum orthologue of paxillin, has been shown to be important for adhesion and development, much like its mammalian counterpart. Here, we use the overproduction of PaxB to gain better insight into its role in regulating the actin cytoskeleton and adhesion. We find that PaxB overexpressing (PaxBOE) cells can aggregate and form mounds normally, but are blocked in subsequent development. This arrest can be rescued by addition of wild-type cells, indicating a non-cell autonomous role for PaxB. PaxBOE cells also have alterations in several actin-based processes, including adhesion, endocytosis, motility and chemotaxis. PaxBOE cells exhibit an EDTA-sensitive increase in cell-cell cohesion, suggesting that PaxB-mediated adhesion is Ca2+ or Mg2+ dependent. Interestingly, cells overexpressing paxB are less adhesive to the substratum. In addition, PaxBOE cells display decreased motility under starved conditions, decreased endocytosis, and are unable to efficiently chemotax up a folate gradient. Taken together, the data suggest that proper expression of PaxB is vital for the regulation of development and actin-dependent processes. Submitted by: Derrick Brazill [brazill@genectr.hunter.cuny.edu] -------------------------------------------------------------------------------- Activated cAMP receptors switch encystation into sporulation Yoshinori Kawabe1, Takahiro Morio2, John L. James1, Alan R. Prescott1, Yoshimasa Tanaka2 and Pauline Schaap1* 1College of Life Sciences, University of Dundee, Dundee, Angus, DD15EH, UK. 2Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, 305-8572, Japan. PNAS, in press Metazoan embryogenesis is controlled by a limited number of signalling modules that are used repetitively at succesive developmental stages. The development of social amoebas shows similar reiterated use of cAMP-mediated signalling. In the model Dictyostelium discoideum, secreted cAMP acting on 4 cAMP receptors (cARs1-4) coordinates cell movement during aggregation and fruiting body formation, and induces the expression of aggregation and sporulation genes at consecutive developmental stages. To identify hierarchy in the multiple roles of cAMP, we investigated cAR heterogeneity and function across the social amoeba phylogeny. The gene duplications that yielded cARs 2-4 occurred late in evolution. Many species have only a cAR1 ortholog, that duplicated independently in the Polysphondylids and Acytostelids. Disruption of both cAR genes of Polysphondylium pallidum did not affect aggregation, but caused complete collapse of fruiting body morphogenesis. The stunted structures contained disorganized stalk cells, which supported a mass of cysts instead of spores. cAMP triggered spore gene expression in P.pallidum, but not in the cAR null mutant, explaining its sporulation defect. Encystation is the survival strategy of solitary amoebas, and basal taxa, like P.pallidum, can still encyst as single cells. Recent findings showed that intracellular cAMP accumulation suffices to trigger encystation, whereas it is a complementary requirement for sporulation. Combined, the data suggest that cAMP signalling in social amoebas evolved from cAMP-mediated encystation in solitary amoebas. cAMP secretion in aggregates prompted the starving cells to form spores and not cysts, and additionally organized fruiting body morphogenesis. cAMP-mediated aggregation was the most recent innovation. Submitted by: Pauline Schaap [p.schaap@dundee.ac.uk] ============================================================== [End dictyNews, volume 32, number 9]

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