dictyNews Electronic Edition Volume 41, number 2 January 16, 2015 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 ========= Mechanical stress and network structure drive protein dynamics during cytokinesis. Vasudha Srivastava and Douglas N. Robinson Curr. Biol. 2015, in press Cell shape changes associated with processes like cytokinesis and motility proceed on several second time-scales, but are derived from molecular events, including protein-protein interactions, assembly, and force generation by molecular motors, all of which occur much faster [1-4]. Therefore, defining the dynamics of such molecular machinery is critical for understanding cell shape regulation. In addition to signaling pathways, mechanical stresses also direct cytoskeletal protein accumulation [5-7]. A myosin II-based mechanosensory system controls cellular contractility and shape during cytokinesis and under applied stress [6, 8]. In Dictyostelium, this system tunes myosin II accumulation by feedback through the actin network, particularly through the crosslinker cortexillin I. Cortexillin-binding IQGAPs are major regulators of this system. Here, we defined the short time-scale dynamics of key cytoskeletal proteins during cytokinesis and under mechanical stress using fluorescence recovery after photobleaching and fluorescence correlation spectroscopy, to examine the dynamic interplay between these proteins. Equatorially enriched proteins including cortexillin I, IQGAP2, and myosin II recovered much more slowly than actin and polar crosslinkers. The mobility of equatorial proteins was greatly reduced at the furrow compared to the interphase cortex, suggesting their stabilization during cytokinesis. This mobility shift did not arise from a single biochemical event, but rather from a global inhibition of protein dynamics by mechanical stress-associated changes in the cytoskeletal structure. Mechanical tuning of contractile protein dynamics provides robustness to the cytoskeletal framework responsible for regulating cell shape and contributes to cytokinesis fidelity. Submitted by Doug Robinson [dnr@jhmi.edu] ---------------------------------------------------------------------- The centrosomal component CEP161 of Dictyostelium discoideum interacts with the Hippo signaling pathway Salil K. Sukumaran, Rosemarie Blau-Wasser, Meino Rohlfs, Christoph Gallinger, Michael Schleicher, Angelika A. Noegel Cell Cycle, in press CEP161 is a novel component of the Dictyostelium discoideum centrosome which was identified as binding partner of the pericentriolar component CP250. Here we show that the amino acids 1-763 of the 1381 amino acids CEP161 are sufficient for CP250 binding, centrosomal targeting and centrosome association. Analysis of AX2 cells over-expressing truncated and full length CEP161 proteins revealed defects in growth and development. By immunoprecipitation experiments we identified the Hippo related kinase SvkA (Hrk-svk) as binding partner for CEP161. Both proteins colocalize at the centrosome. In in vitro kinase assays the N-terminal domain of CEP161 (residues 1-763) inhibited the kinase activity of Hrk-svk. A comparison of D. discoideum Hippo kinase mutants with mutants overexpressing CEP161 polypeptides revealed similar defects. We propose that the centrosomal component CEP161 is a novel player in the Hippo signaling pathway and affects various cellular properties through this interaction Submitted by Angelika Noegel [noegel@uni-koeln.de] ---------------------------------------------------------------------- TipC and the chorea-acanthocytosis protein VPS13A regulate autophagy in Dictyostelium and human HeLa cells Sandra Munoz-Braceras, Rosa Calvo and Ricardo Escalante Autophagy, in press Deficient autophagy causes a distinct phenotype in Dictyostelium discoideum, characterized by the formation of multitips at the mound stage. This led us to analyze autophagy in a number of multitipped mutants described previously (tipAÐ, tipBÐ, tipCÐ, and tipDÐ). We found a clear autophagic dysfunction in tipCÐ and tipDÐ while the others showed no defects. tipD codes for a homologue of Atg16, which confirms the role of this protein in Dictyostelium autophagy and validates our approach. The tipC- encoded protein is highly similar to human VPS13A (also known as Chorein), whose mutations cause the chorea-acanthocytosis syndrome. No member of the VPS13 protein family has been previously related to autophagy despite the presence of a region of similarity to Atg2 at the C-terminus. This region also contains the conserved domain of unknown function DUF1162. Of interest, the expression of the TipC C-terminal coding sequence containing these two motifs largely complemented the mutant phenotype. Dictyostelium cells lacking TipC displayed a reduced number of autophagosomes visualized with the markers GFP-Atg18 and GFP-Atg8 and an impaired autophagic degradation as determined by a proteolytic cleavage assay. Downregulation of human VPS13A in HeLa cells by RNA interference confirmed the participation of the human protein in autophagy. VPS13A- depleted cells showed accumulation of autophagic markers and impaired autophagic flux. Submitted by Ricardo Escalante [rescalante@iib.uam.es] ============================================================== [End dictyNews, volume 41, number 2]