CSM News Electronic Edition Volume 4, number 22 June 17, 1995 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 at the URL "http://worms.cmsbio.nwu.edu/dicty.html" =========== Abstracts =========== Spiral and concentric waves organize multicellular Dictyostelium mounds Florian Siegert* & Cornelis J. Weijer Zoologisches Institut, Universitat Munchen, Luisenstr. 14, 80333 Munchen 2, Germany. Tel. 0049-89-5902469, FAX 0049-89-5902450 Current Biology, in press. ABSTRACT Background: It is known for more 20 years that periodic waves of cAMP instruct the cells to collect in the aggregation center during early aggregation of Dictyostelium. Although it has been hypothesised that cAMP waves are involved in the organisation of multicellular morphogenesis nobody has been able to show wave propagation in the later stages of development. Results: We have developed special optical and digital image processing techniques which allow us to visualize propagating waves of chemotactic activity in multicellular aggregates (mounds). These experiments directly demonstrate signal propagation in a multicellular stage of Dictyostelium discoideum. Within mounds these waves can propagate as concentric rings, as single armed spirals or as multi-armed spirals. The spontaneous appearance of the latter structures is new and completely unexpected. The geometry of wave propagation is strain specific. Strain XP55 predominantly shows concentric ring waves while spiral waves are typical for a derivative of XP55, streamer F mutant NP377 and the widely used axenic strain AX-3. The different geometry of the signals is reflected by distinct cell movement patterns and different cell movement speeds. First, cells in AX-3 mounds organized by spiral waves move faster than cells in XP55 mounds. Second, spiral waves are always accompagnied by rotational cell movement while cells in XP55 mounds move towards the aggregation center. Conclusion: The same principles - wave propagation and chemotaxis - that control aggregation also govern the morphogenesis of the mound stage. Mounds behave as a highly excitable system in which a diverse range of signal propagation geometries creates the same biological structure - a migrating slug. --------------------------------------------------------------------- Regulation of Dictyostelium Early Development Genes in Signal Transduction Mutants Lin Wu (1), Dane Hansen (2), Jakob Franke (1), Richard H. Kessin (1), and Gregory J. Podgorski (2)* 1) Department of Anatomy and Cell Biology, Columbia University, New York, NY 10032; 2) Department of Biology, Utah State University, Logan, UT 84322-5305 * Corresponding Author Developmental Biology, in press Abstract The secreted cyclic nucleotide phosphodiesterase (PDE) and its glycoprotein inhibitor (PDI) are among the first genes expressed when Dictyostelium amoebae begin their development. We used a series of mutants with defects in signal transduction to ask whether cAMP receptors 1 and 3, Galpha2, Gbeta, adenylyl cyclase (ACA), or the protein kinase A catalytic subunit (PKAcat) are required for the initial appearance or later regulation of the PDE and the PDI transcripts. The PDE gene produces a 1.9-kb transcript during vegetative growth and then a 2.4-kb transcript during the early hours of development. Regulation of the 2.4-kb transcript in CAR1, Galpha2, Gbeta, and ACA mutants is similar to that of isogenic parental strains, although its level is reduced in strains that carry the CAR1 mutation. CAR1/CAR3 double mutants also produce less PDE transcript, but the PDE gene remains inducible by cAMP. The PKAcat mutant produces the 2.4-kb PDE transcript, but in this mutant the vegetative transcript is retained in development. CAR1 and CAR3 are not required for transcription of the PDI gene, but deleting CAR1 leads to overproduction of the PDI transcript. Induction or repression of the PDI gene does not require Galpha2, Gbeta or ACA. PKAcat is required for synthesis of the PDI transcript. The results suggest a two stage regulation of these early genes through a Galpha2/Gbeta independent mechanism and an absolute dependence of PDI on the PKAcat. ----------------------------------------------------------------------- LOCALIZATION OF CYCLIC-AMP RECEPTORS WITH ACIDOSOMES IN DICTYOSTELIUM DISCOIDEUM Harish Padh1 and Shashikala Tanjore Center for Biotechnology, Northwestern University, Evanston, IL 60208, U.S.A. FEBS Letters, in press Abstract Earlier studies have shown that in Dictyostelium discoideum, a buoyant membrane fraction contained ~90% of the vacuolar proton pump (V-H+-ATPase) activity, leading to its designation acidosomes. It was proposed that acidosomes may be involved in endocytosis, specially in the acidification of endosomes. In this study we further investigated the putative function(s) of acidosomes. The findings suggest that acidosomes contain abundant receptors for cyclic AMP (CAR1) and that it may be the site for recycling of internalized receptors. Acidosomes also contain an abundance of Rab4 (Bush et al. 1994), a marker for early endosomes. By these criteria, we suggest that the acidosomes are analogous to early or recycling endosome present in mammalian cells. These findings suggest that the structure earlier defined biochemically, morphologically and immunologically as acidosomes may represent early and/or recycling endosomes in this protist. --------------------------------------------------------------------- [End CSM News, volume 4, number 22]