dictyNews Electronic Edition Volume 39, number 30 October 25, 2013 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 ========= Dictyostelium, a microbial model for brain disease S.J. Annesley, S. Chen, L.M. Francione, O. Sanislav, A.J. Chavan, C. Farah, S.W. De Piazza, C.L. Storey, J. Ilievska, S.G. Fernando, P.K. Smith, S.T. Lay , P.R. Fisher* Biochimica et Biophysica Acta - General Subjects, in press. Background Most neurodegenerative diseases are associated with mitochondrial dysfunction. In humans mutations in mitochondrial genes result in a range of phenotypic outcomes which do not correlate well with the underlying genetic cause. Other neurodegenerative diseases are caused by mutations that affect the function and trafficking of lysosomes, endosomes and autophagosomes. Many of the complexities of these human diseases can be avoided by studying them in the simple eukaryotic model Dictyostelium discoideum. Scope of Review This review describes research using Dictyostelium to study cytopathological pathways underlying a variety of neurodegenerative diseases including mitochondrial, lysosomal and vesicle trafficking disorders. Major Conclusions Generalized mitochondrial respiratory deficiencies in Dictyostelium produce a consistent pattern of defective phenotypes that are caused by chronic activation of a cellular energy sensor AMPK (AMP-activated protein kinase) and not ATP deficiency per se. Surprisingly, when individual subunits of Complex I are knocked out, both AMPK-dependent and AMPK-independent, subunit-specific phenotypes are observed. Many nonmitochondrial proteins associated with neurological disorders have homologues in Dictyostelium and are associated with the function and trafficking of lysosomes and endosomes. Conversely, some genes associated with neurodegenerative disorders do not have homologues in Dictyostelium and this provides a unique avenue for studying these mutated proteins in the absence of endogeneous protein. General Significance Using the Dictyostelium model we have gained insights into the sublethal cytopathological pathways whose dysregulation contributes to phenotypic outcomes in neurodegenerative disease. This work is beginning to distinguish correlation, cause and effect in the complex network of cross talk between the various organelles involved. Submitted by Paul Fisher [P.Fisher@latrobe.edu.au] --------------------------------------------------------------------------- Two Distinct Sensing Pathways Allow Recognition of Klebsiella pneumoniae by Dictyostelium Amoebae. Lima WC, Balestrino D, Forestier C, Cosson P. Cell Microbiol. 2013 Oct 15. [Epub ahead of print] Recognition of bacteria by metazoans is mediated by receptors that recognize different types of microorganisms and elicit specific cellular responses. The soil amoebae Dictyostelium discoideum feeds upon a variable mixture of environmental bacteria, and it is expected to recognize and adapt to various food sources. To date, however, no bacteria-sensing mechanisms have been described. In this study, we isolated a Dictyostelium mutant (fspA KO) unable to grow in the presence of non- capsulated Klebsiella pneumoniae bacteria, but growing as efficiently as wild-type cells in the presence of other bacteria, such as Bacillus subtilis. FspA KO cells were also unable to respond to K. pneumoniae and more specifically to bacterially secreted folate in a chemokinetic assay, while they responded readily to B. subtilis. Remarkably, both WT and fspA KO cells were able to grow in the presence of capsulated LM21 K. pneumoniae, and responded to purified capsule, indicating that capsule recognition may represent an alternative, FspA-independent mechanism for K. pneumoniae sensing. When LM21 capsule synthesis genes were deleted, growth and chemokinetic response were lost for fspA KO cells, but not for WT cells. Altogether, these results indicate that Dictyostelium amoebae use specific recognition mechanisms to respond to different K. pneumoniae elements. Submitted by Wanessa de Lima [wanessa.delima@unige.ch] --------------------------------------------------------------------------- The cyclic AMP phosphodiesterase RegA critically regulates encystation in social and pathogenic amoebas Qingyou Du, Christina Schilde, Elin Birgersson, Zhi-hui Chen, Stuart McElroy and Pauline Schaap Cellular Signalling, in press Amoebas survive environmental stress by differentiating into encapsulated cysts. As cysts pathogenic amoebas resist antibiotic treatment, which particularly counteracts treatment of vision-destroying Acanthamoeba keratitis. Limited genetic tractability of amoeba pathogens has left their encystation mechanisms unexplored. The social amoeba Dictyostelium discoideum forms spores in multicellular fruiting bodies to survive starvation, while other dictyostelids, such as Polysphondylium pallidum can additionally encyst as single cells. Sporulation is induced by cAMP acting on PKA with the cAMP phosphodiesterase RegA critically regulating cAMP levels. We show here that RegA is deeply conserved in social and pathogenic amoebas and that deletion of the RegA gene in P. pallidum causes precocious encystation and prevents cyst germination. We heterologously expressed and characterized Acanthamoeba RegA and performed a compound screen to identify RegA inhibitors. Two effective inhibitors increased cAMP levels and triggered Acanthamoeba encystation. Our results show that RegA critically regulates amoebozoan encystation and that components of the cAMP signalling pathway could be effective targets for therapeutic intervention with encystation. Submitted by Christina Schilde [c.schilde@dundee.ac.uk] ============================================================== [End dictyNews, volume 39, number 30]