Dicty News Electronic Edition Volume 21, number 7 September 5, 2003 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu. Back issues of Dicty-News, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ============= Abstracts ============= Cell sorting by differential cell motility: a model for pattern formation in Dictyostelium Tamiki Umeda* and Kei Inouye# *Department of Marine Engineering, Kobe University of Mercantile Marine, Kobe 658-0022, Japan #Department of Botany, Division of Biological Science, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan J. theor. Biol., in press In the slug stage of the cellular slime mold Dictyostelium discoideum, prespore cells and four types of prestalk cells show a well-defined spatial distribution in a migrating slug. We have developed a continuous mathematical model for the distribution pattern of these cell types based on the balance of force in individual cells. In the model, cell types are assumed to have different properties in cell motility, i.e., different motive force, the rate of resistance against cell movement, and diffusion coefficient. Analysis of the stationary solution of the model shows that combination of these parameters and slug speed determines the 3-dimensional shape of a slug and cell distribution pattern within it. Based on experimental data of slug motive force and velocity measurements, appropriate sets of parameters were chosen so that the cell-type distribution at stationary state matches the distribution in real slugs. With these parameters, we performed numerical calculation of the model in 2-dimensional space using a moving particle method. The results reproduced many of the basic features of slug morphogenesis, i.e., cell sorting, translocation of the prestalk region, elongation of the slug, and its steady migration. Submitted by: Kei Inouye [inoue@cosmos.bot.kyoto-u.ac.jp] ------------------------------------------------------------------------------- Structure of the N-Terminal Domain of the Adenylyl Cyclase-Associated Protein (CAP) from Dictyostelium discoideum Dorota Ksiazek, Hans Brandstetter, Lars Israel, Gleb P. Bourenkov, Galina Katchalova, Klaus-Peter Janssen, Hans D. Bartunik, Angelika A. Noegel, Michael Schleicher and Tad A. Holak Structure, in press Cyclase-associated proteins (CAPs) are widely distributed and highly conserved proteins that regulate actin remodeling in response to cellular signals. The N-terminus of CAPs plays a role in Ras signaling and binds adenylyl cyclase; the C-terminus binds to G-actin and thus alters the dynamic rearrangements of the microfilament system. We report here the X-ray structure of the N-terminal domain of the CAP from Dictyostelium discoideum determined by a combination of single isomorphous replacement with anomalous scattering (SIRAS) of iridium-soaked crystals. The overall structure of this domain consists of an a-helix bundle composed of six antiparallel helices and is found in the monomeric and Mg2+-induced dimeric states. Together with gel filtration, cross-linking experiments, the structural CAP adata suggest a multimeric state of the whole CAP molecule. The presented structure is the first for an N-terminal domain of any CAP and can be useful for defining specific functions for these domains. Submitted by: Michael Schleicher [schleicher@lrz.uni-muenchen.de] ------------------------------------------------------------------------------- Unique behavior and function of the mitochondrial ribosomal protein S4 (RPS4) in early Dictyostelium development Koh-ichi Hosoya, Aiko Amagai, Junji Chida, and Yasuo Maeda* Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan Zoological Science (in press) Certain proteins encoded by mitochondrial DNA (mt-DNA), including mt-ribosomal protein S4 (rps4), appear to play important roles in the initiation of cell differentiation. Partial disruption of rps4 in Dictyostelium discoideum Ax-2 cells by means of homologous recombination greatly impairs the progression of differentiation, while the the rps4OE cells in which the rps4 mRNA was overexpressed in the extra-mitochondrial cytoplasm exhibit enhanced differentiation (Inazu et al., 1999). We have prepared a specific anti-RPS4 antibody and generated transformants (rps4AS cells) by antisense-mediated gene inactivation of rps4. Surprisingly, in the rps4AS cells the progress of differentiation was found to be markedly inhibited, suggesting that the antisense rps4 RNA synthesized in the extra-mitochondrial cytoplasm might be as effective as the partial disruption of rps4 gene. Immunostaining of the rps4OE cells with the anti-RPS4 antibody demonstrated that the RPS4 protein synthesized in the extra-mitochondrial cytoplasm is capable of moving to the nucleus, as predicted by PSORTII. Taken together with the results obtained using immunostained Ax-2 cells, we propose a possible pathway of RPS4 translocation coupled with differentiation. Submitted by: Yasuo Maeda [ymaeda@mail.cc.tohoku.ac.jp] =============================================================================== [End Dicty News, volume 21, number 7]