dictyNews Electronic Edition Volume 38, number 7 March 2, 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 ========= Ca2+ signaling regulates ecmB expression, cell differentiation and slug regeneration in Dictyostelium Yekaterina Poloz and Danton H. O'Day Differentiation, in press Ca2+ regulates cell differentiation and morphogenesis in a diversity of organisms and dysregulation of Ca2+ signal transduction pathways leads to many cellular pathologies. In Dictyostelium Ca2+ induces ecmB expression and stalk cell differentiation in vitro. Here we have analyzed the pattern of ecmB expression in intact and bisected slugs and the effect of agents that affect Ca2+ levels or antagonize calmodulin (CaM) on this expression pattern. We have shown that Ca2+ and CaM regulate ecmB expression and pstAB/pstB cell differentiation in vivo. Agents that increase intracellular Ca2+ levels increased ecmB expression and/or pstAB and pstB cell differentiation, while agents that decrease intracellular Ca2+ or antagonize CaM decreased it. In isolated slug tips agents that affect Ca2+ levels and antagonize CaM had differential effect on ecmB expression and cell differentiation in the anterior versus posterior zones. Agents that increase intracellular Ca2+ levels increased the number of ecmB expressing cells in the anterior region of slugs, while agents that decrease intracellular Ca2+ levels or antagonize CaM activity increased the number of ecmB expressing cells in the posterior. We have also demonstrated that agents that affect Ca2+ levels or antagonize CaM affect cells motility and regeneration of shape in isolated slug tips and backs and regeneration of tips in isolated slug backs. To our knowledge, this is the first study detailing the pattern of ecmB expression in regenerating slugs as well as the role of Ca2+ and CaM in the regeneration process and ecmB expression. Submitted by Danton H. O'Day [danton.oday@utoronto.ca] -------------------------------------------------------------------------------------- A mechanosensory system governs myosin II accumulation in dividing cells Kee YS, Ren Y, Dorfman D, Iijima M, Firtel RA, Iglesias PA, Robinson DN Mol. Biol. Cell 2012, in press. The mitotic spindle is generally considered the initiator of furrow ingression. However, recent studies suggest that furrows can form without spindles, particularly during asymmetric cell division. In Dictyostelium, the mechanoenzyme myosin II and the actin crosslinker cortexillin I form a mechanosensor that responds to mechanical stress, which could account for spindle-independent contractile protein recruitment. Here, we show that the regulatory and contractility network, composed of myosin II, cortexillin I, IQGAP2, kinesin-6 (kif12) and INCENP, is a mechanical stress-responsive system. Myosin II and cortexillin I form the core mechanosensor, and mechanotransduction is mediated by IQGAP2 to kif12 and INCENP. Additionally, IQGAP2 is antagonized by IQGAP1 to modulate the mechanoresponsiveness of the system, suggesting a possible mechanism for discriminating between mechanical and biochemical inputs. Furthermore, IQGAP2 is important for maintaining spindle morphology and kif12 and myosin II cleavage furrow recruitment. Cortexillin II is not directly involved in myosin II mechanosensitive accumulation, but without cortexillin I, cortexillin IIÕs role in membrane-cortex attachment is revealed. Finally, the mitotic spindle is dispensable for the system. Overall, this mechanosensory system is structured like a control system characterized by mechanochemical feedback loops that regulate myosin II localization at sites of mechanical stress and the cleavage furrow. Submitted by Douglas Robinson [dnr@jhmi.edu] -------------------------------------------------------------------------------------- Deconvolution of the cellular force-generating subsystems that govern cytokinesis furrow ingression Poirier C, Ng WP, Robinson DN, Iglesias PA. PLoS Comp. Biol, in press. Abstract: Cytokinesis occurs through the coordinated action of several biochemically-mediated stresses acting on the cytoskeleton. Here, we develop a computational model of cellularmechanics, and using a large number of experimentally measured biophysical parameters, we simulate cell division under a number of different scenarios. We demonstrate that traction-mediated protrusive forces or contractile forces due to myosin II are sufficient to initiate furrow ingression. Furthermore, we show that passive forces due to the cellÕs cortical tension and surface curvature allow the furrow to complete ingression. We compare quantitatively the furrow thinning trajectories obtained from simulation with those observed experimentally in both wild-type and myosin II null Dictyostelium cells. Our simulations highlight the relative contributions of different biomechanical subsystems to cell shape progression during cell division. Submitted by Douglas Robinson [dnr@jhmi.edu] ============================================================== [End dictyNews, volume 38, number 7]