Dicty News Electronic Edition Volume 9, number 15 December 6, 1997 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@nwu.edu. Back issues of Dicty-News, the Dicty Reference database and other useful information is available at the Dictyostelium Web Page "http://dicty.cmb.nwu.edu/dicty/dicty.html" =========== Abstracts =========== A cAMP-Phosphodiesterase Controls PKA-Dependent Differentiation Gad Shaulsky, Danny Fuller and William F. Loomis Center for Molecular Genetics, Department of Biology, University of California San Diego, La Jolla, CA 92093 Development, in press SUMMARY A cAMP-specific phosphodiesterase was found that is stimulated by binding to the regulatory subunit of cAMP dependent protein kinase, PKA-R, from either Dictyostelium or mammals. The phosphodiesterase is encoded by the regA gene of Dictyostelium that was recovered in a mutant screen for strains that sporulate in the absence of signals from prestalk cells. The sequence of RegA predicts that it will function as a member of a two component system. Genetic analyses indicate that inhibition of the phosphodiesterase results in an increase in the activity of PKA that acts at a check point for terminal differentiation. Conserved components known to affect memory, learning and differentiation in flies and vertebrates suggest that a similar circuitry functions in higher eukaryotes. ------------------------------------------------------------------------- Rapid patterning of Dictyostelium discoideum cells under confined geometry and its relation to differentiation Yasuji Sawada, 1* Yoshiki Maeda, 1 Ikuo Takeuchi, 2 Jeff Williams3 and Yasuo Maeda4 1Research Institute of Electrical Communication, Tohoku University, Katahira, Sendai 980-77, Japan, 2Okazaki National Research Institute, Myodaiji, Okazaki 444, Japan, 3MRC Laboratory of Molecular and Cell Biology, University College London, Gower Street, London, WC1E 6BT, UK, and 4Biological Institute,Graduate School of Science, Tohoku University, Aoba, Sendai 980-77, Japan. Develop. Growth Differ., in press Abstract: The following was recently reported by Bonner et al. (1995) : 1) Rapid differentiation occurred into two zones in Dictyostelium discoideum cells confined in a fine glass capillary. The cells in the anterior zone exposed to theair appear similar to prestalk cells, while the posterior zone isolated from the air mimicks prespore cells, 2) The volumes of the two zones are proportional to each other for different-sized cell masses, and the proportion is the same as that in normal migrating slugs. We investigated the nature of this newly found rapid differentiation in a slightly modified geometry. Exponentially growing cells were harvested, washed to remove external nutrients, and pelleted by centrifugation. Subsequently, a small drop of the pelleted (starved) cells was placed on a slide glass and then confined in a two-dimensional space between the slide glass and a coverslip, with help of spacers whose thickness varied from 25 to 100 um. As a result, a dark zone which looked optically different emerged within several minutes in the periphery of the disc of the confined cells, corresponding to the zonation in a capillary as previously reported (Bonner et al. 1995). When the width of the peripheral zone was measured for more than 30 samples of different diameters for each thickness of the spacers, the width was found to be always about 100 um , irrespective of the size difference of the cell mass placed. This fact seems to be contradictory to the previous observation made by Bonner et al. (1995). Wealso examined oxygen concentration dependence on the zone width. The zone width was found to be independent of the oxygen concentration at low concentrations, but increased rapidly at high concentrations. We discuss a diffusion-reaction mechanism for formation of the zone and possible involvement of atmospheric oxygen (O2) in the initial steps of cell differentiation and pattern formation. ------------------------------------------------------------------------- A mitochondrion as the structural basis of formation of a cell-type specific organelle in Dictyostelium development Shin-Ichi Matsuyama1 and Yasuo Maeda* Biological Institute, Graduate School of Science, Tohoku University, Aoba, S endai 980-77, Japan. 1Present address: Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030-3498, USA. Protoplasama, in press Abstract: The mitochondrion has been mainly given attention as a self- reproductive and respiratory organelle. We report here that the mitochondrion may participate in the formation of a cell-type specific organelle, coupling with the Golgi complex. During the development of Dictyostelium discoideum, the two-types of cells, i.e. the anterior prestalk cells and the posterior prespore ce lls form a polarized cell mass. Prespore differentiation is characterized by the presence of unique vacuoles named PSVs (prespore-specific vacuoles) in the cytoplasm. Thus the PSV is the most essential organelle to understand the structural basis of cell differention in this organism. In differentiating prespore cells, the mitochondrion exerts a remarkable transformation to form a sort of vacuole (M-vacuole). Using a PSV-specific antibody, it was immuno- cytochemically shown that a PSV-antigen (C-10) is localized in the M-vacuole as well as in the lining membrane of PSV. Interestingly, the C-10 antigen was also noticed in the Golgi cisternae that had fused with M-vacuole. Based on these findings, we propose here a promising model which suggests how both mitochondria and Golgi cisternae may be coordinately involved in the PSV-formation. This model will provide a new aspect of mitochondrial functions in cell differentiation. ------------------------------------------------------------------------- [End Dicty News, volume 9, number 15]