dictyNews Electronic Edition Volume 37, number 17 December 23, 2011 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 ========= Understanding the Cooperative Interaction between Myosin II and Actin Crosslinkers Mediated by Actin Filaments during Mechanosensation Tianzhi Luo,1, Krithika Mohan,3 Vasudha Srivastava,1,4 Yixin Ren,1 Pablo A. Iglesias,3 and Douglas N. Robinson1,2,4 1 Department of Cell Biology and 2 Department of Pharmacology and Molecular Science, School of Medicine, Johns Hopkins University, Baltimore, MD, 21205, USA 3 Department of Electrical and Computer Engineering and 4 Department of Chemical and Biomolecular Engineering, Whiting School of Engineering, Johns Hopkins University, Baltimore, MD, 21218, USA Biophysical Journal, in press Myosin II is a central mechanoenzyme in a wide range of cellular morphogenic processes. Its cellular localization is dependent not only on signal transduction pathways, but also on mechanical stress. We suggest that this stress-dependent distribution is the result of both the force-dependent binding to actin filaments and cooperative interactions between bound myosin heads. By assuming that the binding of myosin heads induces and/or stabilizes local conformational changes in the actin filaments which enhances myosin II binding locally, we successfully simulate the cooperative binding of myosin to actin observed experimentally. In addition, we can interpret the cooperative interactions between myosin and actin-crosslinking proteins observed in cellular mechanosensation, provided that a similar mechanism operates among different proteins. Finally, we present a model that couples cooperative interactions to the assembly dynamics of myosin bipolar thick filaments and that accounts for the transient behaviors of the myosin II accumulation during mechanosensation. This mechanism is likely to be general for a range of myosin II-dependent cellular mechanosensory processes. Submitted by Doug Robinson [dnr@jhmi.edu>] -------------------------------------------------------------------------------------- A New Biological Strategy for Drug Delivery: Eucaryotic Cell-Derived Nanovesicles Irne Tatischeff 1, Annette Alfsen2 1 Laboratoire Acides Nucliques et Biophotonique (CNRS, UPMC), F-75252 Paris, France 2 CNRS UMR8104, INSERM, U567, Institut Cochin, Dpartement de Biologie Cellulaire, Universit Paris-Descartes, F-75014 Paris, France Journal of Biomaterials and Nanobiotechnology, Special Issue on Drug Delivery, in press. An efficient drug delivery is the prerequisite of the successful chemotherapeutic treatments of many human diseases. Despite a great number of approaches, the improvement of drug cell internalization remains an actual research challenge. We propose a new biological delivery system based on the extracellular vesicles released by a non-pathological eukaryotic microorganism, Dictyostelium discoideum. After a summary of the main characteristics of these extracellular vesicles, including of their lipid bilayer that appears as a good candidate for initiating membrane fusion, followed by delivery of their encapsulated drug, the capacity of these vesicles to convey drugs into human cells was demonstrated in vitro on two tumor cell lines, resistant leukaemia K562r and cervix carcinoma HeLa cells. A comparison with other extracellular vesicles, like exosomes or bacteria-derived particles, stresses the unique properties of Dictyostelium extracellular nanovesicles for drug delivery. Submitted by Irene Tatischeff [irene.tatischeff@upmc.fr] -------------------------------------------------------------------------------------- Pleiotropic Roles of a Ribosomal Protein in Dictyostelium discoideum Smita Amarnath 1, Trupti Kawli 1, Smita Mohanty 3, Narayanaswamy Srinivasan 3 and Vidyanand Nanjundiah 2 1Joint first authors; e-mail: smita-nms@mail.utexas.edu and trupti@stanford.edu) 2Department of Molecular Reproduction, Development and Genetics 3 Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, INDIA PLOS One, accepted When expressed in Saccharomyces cerevisiae, a D. discoideum cDNA that encodes the ribosomal protein S4 (DdS4) can rescue the phenotypic effects of mutations in three cell cycle genes. The products of the genes in question, cdc24, cdc42 and bem-1, affect morphogenesis in yeast via a coordinated moulding of the cytoskeleton during bud site selection. Computational analysis and mutational studies indicate how this might be achieved: an SH3 domain in the yeast scaffold protein Bem-1p is central to constructing the bud site selection complex, and a C-terminal domain in DdS4 is the functional equivalent of the SH3 domain. In D. discoideum itself, cells that over- or under-express DdS4 do not show detectable changes in protein synthesis. However, they display developmental aberrations that are both similar and graded according to the extent of over- or under-expression. This suggested to us that DdS4 might influence morphogenesis via a stoichiometric effect specifically, by taking part in a multimeric complex similar to the one involving Cdc24p, Cdc42p and Bem-1p in yeast. In support of the hypothesis, the S. cerevisiae proteins Cdc24p, Cdc42p and Bem-1p as well as their D. discoideum cognates could be co-precipitated with antibodies to DdS4. The implication is that DdS4 has at least two functions in the cell. The first, vital, role is as part of the small subunit of the ribosome. The second, moonlighting, role of DdS4 is as part of another multi-protein complex. An adaptation that (presumably) evolved for the second role enables it fortuitously to rescue a set of cell cycle mutants in yeast. We speculate that the second role acts as a built-in safeguard against the potentially lethal consequences of sub-optimal ribosomal activity that might be caused by spontaneous variations in DdS4 levels. Submitted by Smita Amarnath [smita.smitar@gmail.com] -------------------------------------------------------------------------------------- Colchicine affects cell motility, pattern formation and stalk cell differentiation in Dictyostelium by altering calcium signaling Yekaterina Poloz 1 and Danton H. O'Day 1,2 1 Department of Cell & Systems Biology, 25 Harbord Street, University of Toronto, Toronto, ON, Canada M5S 3G5 2 Department of Biology, University of Toronto at Mississauga, 3359 Mississauga Road Mississauga, ON, Canada L5L 1C6 Differentiation, in press Previous work, verified here, showed that colchicine affects Dictyostelium pattern formation, disrupts morphogenesis, inhibits spore differentiation and induces terminal stalk cell differentiation. Here we show that colchicine specifically induces ecmB expression and enhances accumulation of ecmB-expressing cells at the posterior end of multicellular structures. Colchicine did not induce a nuclear translocation of DimB, a DIF-1 responsive transcription factor in vitro. It also induced terminal stalk cell differentiation in a mutant strain that does not produce DIF-1 (dmtA-) and after the treatment of cells with DIF-1 synthesis inhibitor cerulenin (100 uM). This suggests that colchicine induces the differentiation of ecmB-expressing cells independent of DIF-1 production and likely through a signaling pathway that is distinct from the one that is utilized by DIF-1. Depending on concentration, colchicine enhanced random cell motility, but not chemotaxis, by 3-5 fold (10-50 mM colchicine, respectively) through a Ca+2-mediated signaling pathway involving phospholipase C, calmodulin and heterotrimeric G proteins. Colchicines effects were not due to microtubule depolymerization as other microtubule-depolymerizing agents did not have these effects. Finally normal morphogenesis and stalk and spore cell differentiation of cells treated with 10 mM colchicine were rescued through chelation of Ca+2 by BAPTA-AM and EDTA and calmodulin antagonism by W-7 but not PLC inhibition by U-73122. Morphogenesis or spore cell differentiation of cells treated with 50 mM colchicine could not be rescued by the above treatments but terminal stalk cell differentiation was inhibited by BAPTA-AM, EDTA and W-7, but not U-73122. Thus colchicine disrupts morphogenesis and induces stalk cell differentiation through a Ca+2-mediated signaling pathway involving specific changes in gene expression and cell motility. Submitted by Danton H. O'Day [danton.oday@utoronto.ca] ============================================================== [End dictyNews, volume 37, number 17]