Dicty News Electronic Edition Volume 14, number 11 May 13, 2000 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 ============= Towards a molecular understanding of cytokinesis Douglas N. Robinson and James A. Spudich Department of Biochemistry, Beckman Center, Rm. B-400, Stanford University, Stanford, CA 94305-5307, USA Trends in CELL BIOLOGY 10: 228-237. June, 2000 In this review, we focus on recent discoveries regarding the molecular basis of cleavage furrow positioning and contractile ring assembly and contraction during cytokinesis. However, some of these mechanisms might have different degrees of importance in different organisms. This synthesis attempts to uncover common themes and to reveal potential relationships that might contribute to the biochemical and mechanical aspects of cytokinesis. Because the information about cytokinesis is still fairly rudimentary, our goal is not to present a definitive model but to present testable hypotheses that might lead to a better mechanistic understanding of the process. ---------------------------------------------------------------------------- Loss of a member of the aquaporin gene family, aqpA affects spore dormancy in Dictyostelium Biswa Nath Mitra, Ryuji Yoshino, Takahiro Morio, Masako Yokoyama1, Mineko Maeda1, Hideko Urushihara and Yoshimasa Tanaka Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan and 1 Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Gnee, in press. Abstract We isolated and characterized a gene from Dictyostelium discoideum which encodes a protein of 279 amino acids (30.6 kDa) containing six transmembrane domains with two highly conserved motifs of asparagine-proline-alanine (NPA) found in the aquaporin family of water channel proteins, although the second motif of the protein has been modified into NPV (asparagine-proline-valine). The deduced amino acid sequences of the gene, which we have named aqpA, is 39% identical to D. discoideum WacA, 26% identical to human Aqp5, 26% identical to Oryza sativa PIP2a, 25% identical to yeast Aqy1 and 24% identical to E.coli AqpZ. Southern analyses indicated that aqpA is present as a single copy in the genome. Northern blot analysis showed that the developmentally regulated 1-kb mRNA transcript first appears at tight mound stage (12 h), and is abundant in fingers (16 h) and late culminants (20 h). In situ hybridization of slugs revealed that aqpA mRNA accumulated in cells of the prespore region but not in those of the prestalk region. Disruption of aqpA by homologous recombination did not significantly affect growth or developmental morphogenesis. Although mutant spores were viable, when assayed soon after encapsulation, they became permeable to propidium iodide and lost viability after a week on the top of a fruiting body. Thus AqpA is essential to maintain spore dormancy perhaps through the regulation of water flow. ---------------------------------------------------------------------------- Developmental Cheating and The Evolutionary Biology of Dictyostelium and Myxococcus Dee N. Dao, Richard H. Kessin, and Herbert L. Ennis Department of Anatomy and Cell Biology, Columbia University 630 West 168th St., N.Y., N.Y. 10032, USA Microbiology, in press. Abstract Although widely separated in phylogeny, Dictyostelium and Myxococcus species have a developmental strategy in common. They both collect cells from a certain volume of soil and therefore, within their developmental structures, not all cells are necessarily genetically equivalent. While laboratory strains are genetically uniform, there is no reason to expect clonal aggregation in the wild. Twenty percent of cells die to form the stalk during development of Dictyostelium discoideum and a higher percentage of aggregating cells die during fruiting body formation of Myxococcus xanthus. In this situation, it is likely that cheaters will arise that form only viable spores and avoid cell fates that lead to death. Such cheating variants have now been found in M. xanthus and in D. discoideum. This review discusses the common features of cheater mutants and how organisms that create multi-cellular structures by aggregation must solve the problem of parasitism that is avoided in animals that form from zygotes. ---------------------------------------------------------------------------- Molecular characterization of a calmodulin-like Dictyostelium protein CalB Daniel Rösel, Frantisek Puta, Anna Blahuskova, Petr Smykal#, Petr Folk Department of Physiology and Developmental Biology, #Department of Plant Physiology, Charles University, Vinicna 7, Praha 2, 128 00, Czech Republic FEBS Letters, in press. A gene named calB was cloned and characterized in Dictyostelium. A relationship to calmodulin (CaM) is suggested by sequence identity (50%), similar exon-intron structure and cross-reactivity with anti-CaM sera. The level of calB mRNA is developmentally regulated with maxima during aggregation and in spores. CalB null cells grow normally, develop and produce viable spores. We demonstrated the capacity of tagged CalB to bind Ca2+ using the 45Ca2+ overlay assay and showed that its mobility on SDS-PAGE is dependent on Ca2+/EGTA pretreatment. ---------------------------------------------------------------------------- Suppression of the Growth/Differentiation Transition in Dictyostelium Development by Transient Expression of a Novel Gene, Dia1 Shigenori Hirose, Yuji Inazu, Soo-Cheon Chae2 and Yasuo Maeda Biological Institute, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan Development, in press. SUMMARY In Dictyostelium discoideum Ax-2 cells, a specific check-point (PS-point) from which cells enter the differentiation phase in response to starvation has been specified in the cell cycle. Using the differential display method, we isolated a novel gene, dia1 (differentiation-associated gene 1), as being specifically expressed in cells differentiating from the PS-point. The dia1 mRNA has an open reading flame of 1,368 bp and is deduced to code for a 48.6 kDa protein (DIA1). The DIA1 protein is highly serine-rich and the serine residues are predominantly located in the C-terminal region. After the PSORT search, the protein is predicted to be GPI-anchored at the plasma membrane. Unexpectedly, the dia1-overexpression rather impaired the progression of differentiation, possibly coupling with the reduced expression of early genes such as cAMP receptor1 (car1). The inhibitory effect of dia1-expression on early differentiation was almost completely nullified by externally applied cAMP pulses. In contrast to the dia1-overexpression, antisense RNA-mediated dia1 inactivation was found to enhance the initial step of cell differentiation, as exemplified by precocious expressions of car1 and other early genes. We discuss the unique structure and function of DIA1 and its relation with cooperative development of cells during the establishment of multicellular organization. ---------------------------------------------------------------------------- [End Dicty News, volume 14, number 11]