Dicty News Electronic Edition Volume 17, number 15 December 22, 2001 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 ============= A Novel Dictyostelium Gene Encoding Multiple Repeats of Adhesion Inhibitor- Like Domains has Effects on Cell-Cell and Cell-Substrate Adhesion. Timothy R. Varney, Elisabeth Casademunt, Hoa N. Ho, Chere' Petty, Jayne Dolman, and Daphne D. Blumberg* Department of Biological Sciences, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250 Developmental Biology in press Abstract The Dictyostelium protein AmpA (Adhesion modulation protein A) is encoded by the gene originally identified by the D11 cDNA clone. AmpA contains repeated domains homologous to a variety of proteins that influence cell adhesion. The protein accumulates during development, reaching a maximal level at the finger stage. Much of the AmpA protein is found extracellularly during development, and in culminants AmpA is found in association with Anterior-Like Cells. Characterization of an ampA- strain generated by gene replacement reveals a significant increase in cell-cell clumping when cells are starved in non-nutrient buffer suspensions. Developing ampA- cells are also more adhesive to the underlying substrate and are delayed in developmental progression, with the severity of the delay increasing as cells are grown in the presence of bacteria or on tissue culture dishes rather than in suspension culture. Reintroduction of the ampA gene rescues the developmental defects of ampA- cells however expression of additional copies of the gene in wild type cells results in more severe developmental delays and decreased clumping in suspension culture. We propose that the AmpA protein functions as an anti-adhesive to limit cell-cell and cell-substrate adhesion during development and thus facilitate cell migration during morphogenesis. ----------------------------------------------------------------------------- A Gene Encoding a Novel Anti-Adhesive Protein is Expressed in Growing Cells and Restricted to Anterior-Like Cells During Development of Dictyostelium. Elisabeth Casademunt, Timothy R. Varney, Jayne Dolman, Chere' Petty and Daphne D. Blumberg* Department of Biological Sciences, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250 Differentiation, in press Abstract The Dictyostelium gene ampA, initially identified by the D11 cDNA, encodes a novel anti-adhesive-like protein. The ampA gene product inhibits premature cell agglutination during growth and modulates cell-cell and cell- substrate adhesion during development. Analysis of the promoter indicates that cap site-proximal sequence directs ampA expression during both growth and early development. Expression following tip formation is controlled by more distal sequence, which contains TTGA repeats known to regulate prestalk cell gene expression in other promoters. Comparison of reporter gene expression and endogenous mRNA accumulation indicate that during growth the ampA gene is expressed in an increasing number of cells as a function of density. The number of cells expressing the ampA gene drops as development initiates, but the cells that continue to express the gene do so at high levels. These cells are initially scattered throughout the entire aggregate. By the tip formation stage however, the majority of ampA-expressing cells are localized to the mound periphery, with only a few cells remaining scattered in the upper portion of the mound. In the final culminant, ampA is expressed only in the upper cup, lower cup and basal disc. Although reporter expression is observed in cells that migrate anteriorly to a banded region just posterior to the tip, expression is rarely observed in the extreme tip. AmpA protein however, is localized to the tip as well as to ALCs during late development. The results presented here suggest that ampA gene expression is shut off in ALCs that continue along the prestalk differentiation pathway before they are added to the primordial stalk. ----------------------------------------------------------------------------- Deducing the Origin of Soluble Adenylyl Cyclase, a Gene Lost in Multiple Lineages Jeroen Roelofs and Peter J.M. Van Haastert Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands Molecular Biology and Evolution, in press The family of eukaryotic adenylyl cyclases consists of a very large group of twelve transmembrane adenylyl cyclases and a very small group of soluble adenylyl cyclase (sAC). Orthologs of human sAC are present in rat, Dictyostelium and bacteria, but absent from the completely sequenced genomes of Drosophila melanogaster, Caenorhabditis elegans, Arabidopsis thaliana and Saccharomyces cereviciae. sAC consists of two cyclase domains and a long ~1000 amino acid C-terminal (sCKH) region. This sCKH region and one cyclase domain have been found in only four bacterial genes; the sCKH region was also detected in bacterial Lux transcription factors and in complex bacterial and fungal kinases. The phylogenies of the kinase and cyclase domains are identical to the phylogeny of the corresponding sCKH domain, suggesting that the sCKH region fused with the other domains early during evolution in bacteria. The amino acid sequences of sAC proteins yield divergence times from the human lineage for rat and Dictyostelium that are close to the reported divergence times of many other proteins in these species. The combined results suggest that the sCKH region was fused with one cyclase domain in bacteria, and a second cyclase domain was added in bacteria or early eukaryotes. The sAC was retained in a few bacteria and during the entire evolution of the human lineage, but lost independently from many bacteria and in the lineages to plants, yeast, worms and flies. We conclude that within the family of adenylyl cyclases, soluble AC was poorly fixed during evolution while membrane bound AC has expanded to form the subgroups of prevailing adenylyl and guanylyl cyclases. ----------------------------------------------------------------------------- [End Dicty News, volume 17, number 15]