CSM News Electronic Edition Volume 8, number 7 March 22, 1997 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to CSM-News@worms.cmb.nwu.edu. Back issues of CSM-News, the CSM Reference database and other useful information is available by anonymous ftp from worms.cmb.nwu.edu [165.124.233.50], via Gopher at the same address, or by World Wide Web at the URL "http://worms.cmb.nwu.edu/dicty.html" ************** Editor's Note ************** Since the current list of Dictyostelium Email Directory is always available on the Web site (http://worms.cmb.nwu.edu/dicty.html) I propose to discontinue to practice of sending it out monthly. If you have comments or concerns regarding this change in practice, or if you do not have access to the web site please contact me at CSM-News@worms.cmb.nwu.edu. =========== Abstracts =========== Characterisation of a Dictyostelium factor that acts synergistically with DIF to induce terminal stalk cell differentiation Yohko Yamada1,2, Koji Okamoto1 and Jeffrey Williams2 1 Department of Botany, Division of Biological Sciences, Graduate School of Science, Kyoto University, Kyoto 606-01, Japan 2 MRC Laboratory of Molecular Cell Biology and Department of Biology, University College London, Gower Street, London WC1E 6BT, UK Dev Biol., in press. The differentiation of Dictyostelium prestalk cells is induced by the chlorinated hexaphenone DIF-1 and their maturation into stalk cells at culmination occurs by activation of the cAMP dependent protein kinase (PKA). Medium harvested from developing Dictyostelium cells will act synergistically with DIF-1 to induce prestalk cell differentiation in a low density monolayer assay (Yamada and Okamoto, 1994). Using HPLC, we have partially purified from such conditioned medium an activity we term STIF (stalk inducing factor). It is hydrophilic and of low molecular weight. There are multiple classes of prestalk cells, that are defined by their patterns of expression of the ecmA and ecmB genes and that can be further sub-categorized because they utilize different elements within the promoters of the two genes. We show that, in a monolayer assay, STIF acts synergistically with DIF-1 to induce ecmB gene expression via promoter elements that are normally activated strongly only in cells that have entered the stalk tube and which are therefore committed to differentiate into stalk cells. The combination of STIF and DIF-1 also induces morphological maturation of prestalk cells into stalk cells but does not efficiently induce expression of ecmA: a gene that is selectively expressed in cells within the anterior, prestalk region of the slug. Inactivation of PKA, by cell type specific expression of a dominant inhibitor, represses the action of STIF. These data suggest that STIF is an extracellular signal that acts to induce the terminal differentiation of stalk cells. ------------------------------------------------------------------------- The Role of Dictyostelium racE in Cytokinesis: Mutational Analysis and Localization Studies by Use of Green Fluorescent Protein Denis A. Larochelle, Kalpa K. Vithalani and Arturo De Lozanne Department of Cell Biology, Duke University Medical Center Durham, NC 27710 Mol. Biol. Cell, in press. ABSTRACT The small GTPase racE is essential for cytokinesis in Dictyostelium but its precise role in cell division is not known. To determine the molecular mechanism of racE function we undertook a mutational analysis of racE. The exogenous expression of either wild-type racE or a constitutively active V20racE mutant effectively rescues the cytokinesis deficiency of racE null cells. In contrast, a constitutively inactive N25racE mutant fails to rescue the cytokinesis deficiency. Thus, cytokinesis requires only the activation of racE by GTP and not the inactivation of racE by hydrolysis of GTP. To determine the spatial distribution of racE we created a fusion protein with the green fluorescent protein (GFP) at the amino terminus of racE. Remarkably, GFP-racE fusion protein was fully competent to rescue the phenotype of racE null cells and therefore, must reside in the same location as native racE. We found that GFP-racE localized to the plasma membrane of the cell throughout the entire cell cycle. ----------------------------------------------------------------------- [End CSM News, volume 8, number 7]