Dicty News Electronic Edition Volume 22, number 8 April 2, 2004 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 Dicty-News, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ============= Abstracts ============= A homologue of Cdk8 is required for spore cell differentiation in Dictyostelium Hsiu-Hsu Sophia Lin, Meenal Khosla, Hao-Jen Huang, Duen-Wei Hsu, Christine Michaelis, Gerald Weeks and Catherine Pears Dev Biol., in press The Cdk8 proteins are kinases which phosphorylate the carboxy terminal domain (CTD) of RNA polymerase II as well as some transcription factors and, therefore, are involved in the regulation of transcription. Here we report that a Cdk8 homologue from Dictyostelium discoideum is localised in the nucleus where it forms part of a high molecular weight complex that has CTD kinase activity. Insertional mutagenesis was used to abrogate gene function and analysis of the null strain revealed that the DdCdk8 protein plays an important role in spore formation during late development. As previously reported (Takeda, K., Saito, T. and Ochiai, H. 2002. Develop. Growth Differ. 44, 213-223) Ddcdk8- cells also exhibit impaired aggregation, although we report that the severity of the defect depends upon experimental conditions. When aggregation occurs, Ddcdk8- cells form abnormal terminally differentiated structures within which the Ddcdk8- cells differentiate into stalk cells but fail to form spores, indicating a role for DdCdk8 in cell differentiation. When Ddcdk8 is expressed from its own promoter the protein is able to rescue both the late developmental defect and the impaired aggregation. However, when expressed from an heterologous promoter only the impaired aggregation is rescued. This result demonstrates that the defect during late development is not a consequence of impaired aggregation and indicates a direct role for DdCdk8 in spore formation. Submitted by: Catherine Pears [catherine.pears@bioch.ox.ac.uk] ----------------------------------------------------------------------------- Chemoattractant induced Ras activation during Dictyostelium aggregation Helmut Kae, Chinten James Lim, George B. Spiegelman, Gerald Weeks Department of Microbiology and Immunology University of British Columbia, 300-6174 University Boulevard, Vancouver, British Columbia, Canada V6T 1Z3 EMBO Reports, in press Ras proteins are highly conserved molecular switches that regulate cellular response to external stimuli. Dictyostelium discoideum contains an extensive family of Ras proteins that function in regulation of mitosis, cytoskeletal function and motility, and the onset of development. Little is known about the events that lead to the activation of Ras proteins in Dictyostelium, primarily due to a lack of a biochemical assay to measure levels of activated Ras. We have adapted an assay used successfully to measure activated Ras in mammalian cells to monitor activation of two Dictyostelium Ras proteins, RasC and RasG. We have found that the Ras Binding Domain (RBD) of mammalian Raf1 was capable of binding to the activated form of RasG, but not to the activated form of RasC; however, the RBD of Schizosaccharomyces pombe Byr2 was capable of binding preferentially to the activated forms of both RasC and RasG. Using this assay, we discovered that RasC and RasG showed a rapid and transient activation when aggregation competent cells were stimulated with the chemoattractant cAMP, and this activation did not occur in a number of cAMP signalling mutants. This data provides further evidence of a role for both RasC and RasG in the early development of Dictyostelium. Submitted by: Helmut Kae [hkae@interchange.ubc.ca] ----------------------------------------------------------------------------- Ecological succession of dictyostelid slime molds on the island of Hawaii Andrew R. Swanson(1), John D. Shadwick(1), Don E. Hemmes(2) and Frederick W. Spiegel(1) (1)Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas, 72701, USA (2)Department of Biology, University of Hawaii, Hilo, Hawaii, 96720, USA Systematics and Geography of Plants, in press Patterns of ecological succession have been demonstrated for decomposer communities, but the details of such patterns with respect to the role of eumycetozoans have not been addressed. Successional patterns can be inferred from a sequence of closely located sites which differ only in age, but are controlled for other sources of variation. Hawaii, the largest and youngest of the Hawaiian Islands, offers an ideal site for such studies, consisting of variously-aged landforms underlain by similar substrates, and influenced by similar climates and biotic communities. Soil/litter samples were collected from nine montane mesic sites of similar elevation and rainfall, but ranging in substrate age from 67 to 10,000 ybp. Samples were processed to recover dictyostelid (cellular) slime molds according to established protocols. Results suggest that slightly different assemblages of dictyostelids occupy the soil/litter derived from different-aged parent materials. The density and species diversity of dictyostelids was higher in soil/litter samples from the youngest sites. The time necessary for dictyostelids to colonize a site is less than 67 years. It is hypothesized that colonization of the soil/litter by dictyostelids is followed by the arrival of predators, particularly nematodes, which adversely affect the density and species diversity of soil amoebae in general, and dictyostelids in particular. Submitted by: Andrew R. Swanson [arswans@uark.edu] =============================================================================== [End Dicty News, volume 22, number 8]