CSM News Electronic Edition Volume 6, number 3 February 3, 1996 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.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" ----------------------------------------- Address of CSM-News and WEB Page Changed ----------------------------------------- Please note that the address for the computer that runs the Web page, the anonymous ftp site and the email server has changed. The new address is "worms.cmb.nwu.edu". Please make a note of this change. ========== Dicty 96 ========== The 2nd announcement on the International Dictyostelium Conference '96 in Sendai, Japan The next Dicty meeting will be held in Sendai from October 13 (Sunday) to October 18 (Wednesday), 1996. The brief schedule has been set up as follows: Date Morning Afternoon Evening (9:00-12:00) (13:30-18:00) (18:00-21:00) Oct. 13 Resistration Welcome party (Sun) (Washington Hotel) (Washington Hotel) Oct. 14 Oral presentation Oral presentation free (Mon) (Sendai City Hole) (Sendai City Hole) Oct. 15 Oral presentation Oral presentation and free (Tue) (Sendai City Hole) poster session (Sendai City Hole) Oct. 16 Oral presentation Excursion to a hot Conference Banquet (Wed) (Sendai City Hole) spring resort "Akiu" Oct. 17 Oral presentation Oral presentation and free (Thu) (Sendai City Hole) poster session Oct. 18 Oral presentation meeting ends (Fri) (Sendai City Hole) The meeting will be partly supported by a fund from the Yamada Science Foundation. For this, the registration fee will be reduced to about 50,000 (Japanese yen), being about a half of that in regular meetings. This will include a welcome party on October 13 (Sunday), hotel charge (Washington Hotel), breakfast and lunch from Monday to Friday noon, and also expenses for the excursion to a hot spring resort "Akiu", a Conference banquet and stay in Hotel "Sakan" of Japanese style on October 16 (Wednesday). Oral and poster sessions will be held in Sendai City Hole located within 15 min of walk from Washington Hotel. A resistration form will be mailed in the near future. Maybe, the DEADLINE FOR RESISTRATION will be set up around JULY 1st, 1996. The ABSTRACT submission deadline is AUGUST 1st, 1996. Hoping to see you next October in Sendai. Yasuo Maeda Organizer of the International Dictyostelium Conference '96 ============================================================================== =========== Abstracts =========== Cell-cell Adhesion Prevents Mutant Cells Lacking Myosin II from Penetrating Aggregation Streams of Dictyostelium Xiaoxin Susan Xu+, Adam Kuspa*, Danny Fuller*, William F. Loomis* and David A. Knecht+ +Department of Molecular and Cell Biology, University of Connecticut Storrs, CT 06269 * Department of Biology, University of California San Diego, La Jolla, CA 92093 Develop. Biol. (in press) Abstract When a small number of fluorescently labeled myosin II mutant cells (mhcA-) are mixed with wild-type cells and development of the chimeras observed by confocal microscopy, the mutant cells can be seen to be excluded to the edges of aggregation streams and mounds. Moreover, the mutant cells stick to wild type cells and become distorted (Shelden and Knecht, 1995). Two independent adhesion mechanisms, Contact Sites A and Contact Sites B, function during the aggregation stage and either one or both might be responsible for excluding the myosin II null cells. We have mixed mhcA- cells with cells in which the appearance of Contact Sites B is delayed (strain TL72) as well as cells which lack Contact Sites A (strain GT10) and double mutants in which both adhesion mechanisms are affected (strain TL73). In all chimera's, the mhcA- cells were distorted by interactions with the adhesion mutant cells indicating that it does not require significant adhesive interaction to distort the flaccid cortex of mhcA- cells. mhcA- cells were excluded from streams composed of cells lacking either Contact Sites A or Contact Sites B but mixed randomly with cells lacking both adhesion systems. By 10 hours of development, cells of strain TL73 acquire Contact Sites B adhesion. If cells of this strain were mixed with labeled mhcA- cells, allowed to develop for 9 hours and then dissociated before replating, the myosin II null cells were seen to be distorted and excluded from the reaggregates. Thus the exclusion of mhcA- cells from streams can be accomplished by either Contact Sites A or B. When chimeras of labeled TL73 and wild-type cells were made, the TL73 cells were found to be randomly mixed into aggregation streams. This result indicates that adhesive sorting does not function during aggregation and so cannot account for the exclusion of mhcA- cells from streams. We hypothesize that the flaccid cortex of mhcA- cells cannot generate sufficient protrusive force to break the contacts between adhered cells in aggregation streams but can enter streams where the cells are weakly adherent. ---------------------------------------------------------------------------- Mutations in the Dictyostelium heterotrimetic G protein alpha subunit Ga5 alter the kinetics of tip morphogenesis Jeffrey A. Hadwiger, Kanchana Natarajan, and Richard A. Firtel Development, in press SUMMARY Tip morphogenesis during the Dictyostelium developmental life cycle is a process by which prestalk cells sort to form the anterior region of the multicellular organism. We show that the temporal regulation of this morphological process is dependent on the copy number of the Dictyostelium Ga5 gene. Tip formation is delayed in aggregates of ga5 null mutant cells and accelerated in aggregates overexpressing the Ga5 gene compared to tip formation in wild-type cells. The onset of cell-type-specific gene expression associated with mound formation and tip morphogenesis is also temporally altered in Ga5 mutants. Tip morphogenesis in chimeric organisms of Ga5 mutants and wild-type cells is dependent on the copy number of the Ga5 gene, indicating that Ga5 function plays an integral role in the intercellular signaling of this stage of development. The Ga5 gene encodes a Ga subunit that has 51% identity to the Dictyostelium Ga4 subunit. Like the Ga4 gene, the Ga5 gene is expressed in a subset of cells distributed throughout the multicellular organism, with a distribution that is similar to the anterior-like cell population. Amino acid substitutions in the Ga5 subunit analogous to substitutions altering guanine nucleotide binding and hydrolysis in other Ga subunits had no apparent effect on the rate of tip formation when a single copy of the mutant gene was used to replace the wild-type gene. Overexpression of these mutant Ga5 genes by increased gene dosage resulted in cell death, suggesting that high levels of the altered subunits have detrimental effects during vegetative growth. ----------------------------------------------------------------------------- PLANT PROFILINS RESCUE THE ABERRANT PHENOTYPE OF PROFILIN-DEFICIENT DICTYOSTELIUM CELLS Iakowos Karakesisoglou, Michael Schleicher, Bryan C. Gibbon* and Christopher J. Staiger*+ Adolf-Butenandt-Institut / Zellbiologie, Ludwig-Maximilians-Universitaet Muenchen, Schillerstr. 42, 80336 Muenchen, Federal Republic of Germany *Dept. of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA +author for correspondence Fax: 317-496-1496 e-mail: cstaiger@bilbo.bio.purdue.edu Cell Motility and Cytoskeleton, in press. Abstract To characterize the function of plant profilins in vivo, we expressed two pollen-specific Zea mays (maize) profilin isoforms in profilin-minus Dictyostelium discoideum mutants. In maize, profilins exist as a multigene family containing 4 or more members which are highly similar to each other but substantially less similar to profilins from animals and lower eukaryotes. Previously we have shown that D. discoideum profilin-minus cells have an aberrant phenotype due to defects in cell shape, cytokinesis and development. These defects could be rescued by introducing the pollen-specific profilins 1 or 2 from maize using a newly constructed expression vector. Expression of the heterologous profilins in Dictyostelium clones was assayed by affinity purification of the pollen profilins with poly-L-proline agarose and by immunoblotting with a polyclonal antiserum raised against maize pollen profilin. In contrast to the profilin-minus mutants, Dictyostelium cells expressing plant profilins showed normal cell shape, contained less F-actin, and were able to form fruiting bodies. These data provide genetic evidence that maize pollen profilins, even though they are specific for a distinct developmental stage, share functional properties with profilin from a lower eukaryote and apparently act as G-actin-sequestering proteins in this system. ----------------------------------------------------------------------------- Targeted disruption of genes for gp138, a cell-fusion-related protein in Dictyostelium discoideum, revealed the existence of a third gene Nobuyuki Yamaguchi, Mikihiko Higa, Kazuhiro Aiba, Hui Fang, Yoshimasa Tanaka and Hideko Urushihara Institute of Biological Sciences, University of Tsukuba Tsukuba, Ibaraki 305 JAPAN TEL: 0298-53-4910 FAX: 0298-53-6614 e-mail: d402hu@sakura.cc.tsukuba.ac.jp Development, Growth & Differentiation. in press ABSTRACT The sexual cycle of the cellular slime mold, Dictyostelium discoideum, offers a suitable experimental system to analyze sexual cell interactions. We have been analyzing molecular mechanisms involved in sexual cell fusion using complementary heterothallic strains in D. discoideum and have identified several cell surface proteins involved in the process. One of them, gp138, is present in strains of both mating types and considered to be responsible for membrane fusion itself. Two genes with high mutual homology, GP138A and GP138B, have been identified so far as encoding this protein. Expression of antisense RNA for GP138B has been shown to suppress sexual cell fusion, confirming the critical importance of these genes in sexual cell fusion. However, neither functional relationship of the two gp138 genes nor possibility of the existence of more genes which encode gp138 has been determined yet. In the present study, GP138A and GP138B were disrupted by homologous recombination in an effort to clarify the se points. Analysis of the double knock-out mutants suggested the presence of a third gene for gp138. ------------------------------------------------------------------------ [End CSM News, volume 6, number 3]