dictyNews Electronic Edition Volume 40, number 17 July 18, 2014 Please submit abstracts of your papers as soon as they have been accepted for publication by by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit or by sending them to dicty@northwestern.edu 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 ========= How blebs and pseudopods cooperate during chemotaxis Richard A. Tyson, Evgeny Zatulovskiy, Robert R. Kay, Till Bretschneider PNAS, accepted Two motors can drive extension of the leading edge of motile cells: actin polymerization, and myosin-driven contraction of the cortex, producing fluid pressure and the formation of blebs. Dictyostelium cells can move with both blebs and actin-driven pseudopods at the same time, and blebs, like pseudopods, can be orientated by chemotactic gradients. Here we ask how bleb sites are selected and how the two forms of projection cooperate. We show that membrane curvature is an important, yet overlooked, factor. Dictyostelium cells were observed moving under agarose, which efficiently induces blebbing, and the dynamics of membrane deformations analysed. Blebs preferentially originate from negatively curved regions, generated on the flanks of either extending pseudopods or blebs themselves. This is true of cells at different developmental stages, chemotaxing to either folate or cyclic-AMP, and moving with both blebs and pseudopods, or blebs only. A physical model of blebbing suggests that detachment of the cell membrane is facilitated in concave areas of the cell, where membrane tension produces an outward directed force, as opposed to pulling inwards in convex regions. Our findings assign a new role to membrane tension which can spatially couple blebs and pseudopods, thus contributing to clustering protrusions to the cell front. Submitted by Till Bretschneider [T.Bretschneider@warwick.ac.uk] --------------------------------------------------------------------------- The social amoeba Polysphondylium pallidum loses encystation and sporulation, but can still erect fruiting bodies in the absence of cellulose. Qingyou Du and Pauline Schaap1 1corresponding author Phone: 44 1382 388078; Fax 44 1382 345386. College of Life Sciences, University of Dundee, MSI/WTB/JBC complex, Dow Street, Dundee, DD15EH, UK. E-mail: q.du@dundee.ac.uk; p.schaap@dundee.ac.uk Protist, accepted Amoebas and other freely moving protists differentiate into walled cysts when exposed to stress. As cysts, amoeba pathogens are resistant to biocides, preventing treatment and eradication. Lack of gene modification procedures has left the mechanisms of encystation largely unexplored. Genetically tractable Dictyostelium discoideum amoebas require cellulose synthase for formation of multicellular fructifications with cellulose-rich stalk and spore cells. Amoebas of its distant relative Polysphondylium pallidum (Ppal), can additionally encyst individually in response to stress. Ppal has two cellulose synthase genes, DcsA and DcsB, which we deleted individually and in combination. Dcsa- mutants formed fruiting bodies with normal stalks, but their spores and cyst walls lacked cellulose, which obliterated stress- resistance of spores and rendered cysts entirely non-viable. A dcsa-/dcsb- mutant made no walled spores, stalk cells or cysts, although simple fruiting structures were formed with a droplet of amoeboid cells resting on an sheathed column of decaying cells. DcsB is expressed in prestalk and stalk cells, while DcsA is additionally expressed in spores and cysts. We conclude that cellulose is essential for encystation and that cellulose synthase may be a suitable target for drugs to prevent encystation and render amoeba pathogens susceptible to conventional antibiotics. Submitted by Pauline Schaap [p.schaap@dundee.ac.uk] ============================================================== [End dictyNews, volume 40, number 17]