CSM News Electronic Edition Volume 3, number 11 October 1, 1994 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to CSM-News@worms.cmsbio.nwu.edu. Back issues of CSM-News, the CSM Reference database and other useful information is available by anonymous ftp from worms.cmsbio.nwu.edu [165.124.233.50], via Gopher at the same address, or by World Wide Web through www.nwu.edu. =============== Announcements =============== The next International Dictyostelium Conference will be held in 1995 in Paris from June 25th to June 30th. It will be organized jointly by Michel Satre from the CEA in Grenoble and by Michel Veron from the Institut Pasteur in Paris. In 1996, the Dictyostelium meeting will be in Japan. A first circular will be sent through the Dicty E.mail network within three months. We hope to wellcome you in Paris next year. Michel Satre & Michel Veron =========== Abstracts =========== Protein kinase A is a positive regulator of spore coat gene transcription in Dictyostelium Neil A. Hopper 1, Glenn M. Sanders 2, Kathy L. Fosnaugh 2, Jeffrey G. Williams 1 and William F. Loomis 2. 1MRC Laboratory For Molecular Cell Biology, University College London, Gower St, London WC1E 6BT, Tel: +44 (71) 380 7254, Fax: +44 (71) 380 7805 2 Center for Molecular Biology, Department of Biology, University of California San Diego, La Jolla, California 92093, USA. Tel: (619) 534-2543, Fax: (619) 534-0053 ABSTRACT The cotA, cotB, and cotC genes encode the major spore coat proteins of Dictyostelium. All three cot genes are coordinately expressed as aggregation is nearing completion. Induction and maintenance of their expression is dependent upon the presence of extracellular cAMP. We show that expression of a dominant inhibitor of the cAMP dependent protein kinase (PKA) in prespore cells greatly reduces the transcription rates of the cotB and cotC genes. All three cot genes contain, in their upstream regulatory regions, short sequence elements that have a high content of cytosine and adenosine residues. These CA-rich sequences are essential for optimal cot gene transcription. We show that expression of the dominant PKA inhibitor results in a greatly reduced level of the activity that recognizes the CA-rich sequences upstream of the cotB gene. Thus PKA acts, either directly or indirectly, to control expression of the cot genes and it may do so by modulating the activity of a DNA binding protein. However, we find that mutant cells where PKA is constitutively active still require exogenous cAMP for optimal cot gene expression in dissociated cells, suggesting that a separate, PKA-independent, signalling pathway is also involved in the regulation of cot gene expression by extracellular cAMP. ------------------------------------------------------------------------- Comparison of the Dictyostelium rasD and ecmA genes reveals two distinct mechanisms whereby an mRNA may become enriched in prestalk cells. Keith Jermyn and Jeffrey Williams. Imperial Cancer Research Fund, Clare Hall Laboratory, S. Mimms, Herts EN6 3LD. Summary The Dictyostelium ras gene, rasD, encodes an mRNA that is more abundant in prestalk than prespore cells in the migratory slug. Its expression is inducible by extracellular cAMP but is not inducible by the prestalk and stalk cell morphogen DIF. We show that a rasD-lacZ fusion gene is first expressed in approximately one half of the cells in the aggregate, including some cells that also express a prespore-specific marker. The amount of rasD-lacZ fusion protein in prespore cells then diminishes as the slug is formed. Analysis of a rasD-lacZ fusion protein with an N terminal substitution that reduces protein stability within the cell provides strong confirmatory evidence that the ras gene product becomes enriched in prestalk cells by selective repression of gene expression in prespore cells. In contrast, the DIF-inducible ecmA gene is expressed only in those cells that will become prestalk cells in the migratory slug. These results show that there are two different ways in which an mRNA may become enriched in prestalk cells and support the view that DIF is the inducer of prestalk cell differentiation. ---------------------------------------------------------------------- [End CSM-News, volume 3, number 11]