dictyNews Electronic Edition Volume 30, number 1 January 4, 2008 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ========= Abstracts ========= Cytokinins induce sporulation in Dictyostelium Christophe Anjard and William F. Loomis* Center for Molecular Genetics, Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093-0368 Development, in press The social amoeba Dictyostelium discoideum diverged from the line leading to animals shortly after the separation of plants and animals but retained characteristics of both kingdoms. A GABAB-like receptor and a peptide, SDF-2, with homologs found only in animals, control sporulation, while cytokinins, which act as hormones in plants, keep spores dormant. When SDF-2 binds its receptor, DhkA, it reduces the activity of the cAMP phosphodiesterase RegA such that cAMP can increase. It has been proposed that the cytokinin, discadenine, also results in an increase in cAMP but acts through a different histidine kinase, DhkB. We have found that discadenine and its precursor, isopentenyl adenine, not only maintain spore dormancy but also initiate rapid encapsulation independently of the SDF-2 signal transduction pathway. DhkB and the adenylyl cyclase of late development, AcrA, are members of two component signal transduction families and both are required to transduce the cytokinin signal. As expected, strains lacking the isopentenyl-transferase enzyme chiefly responsible for cytokinin synthesis are defective in sporulation. It appears that SDF-2 and cytokinins are secreted during late development to trigger signal transduction pathways that lead to an increase in the activity of the cAMP dependent protein kinase, PKA, which triggers rapid encapsulation as well as ensures spore dormancy. Submitted by: Bill Loomis [wloomis@ucsd.edu] -------------------------------------------------------------------------------- GBF-dependent family genes morphologically suppress the partially active Dictyostelium STATa strain Nao Shimada, Naoko Kanno-Tanabe, Kakeru Minemura and Takefumi Kawata* Department of Biology, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan *Corresponding author Dev. Genes & Evol., In press Transcription factor Dd-STATa, a functional Dictyostelium homologue of metazoan Signal Transducers and Activators of Transcription (STAT) proteins, is necessary for culmination during development. We have isolated more than 18 putative multicopy suppressors of Dd-STATa using genetic screening. One was hssA gene, whose expression is known to be G-box binding factor (GBF)-dependent and which was specific to prestalk A (pst A) cells, where Dd-STATa is activated. Also, hssA mRNA was expressed in pstA cells in the Dd-STATa-null mutant. At least 40 hssA-related genes are present in the genome and constitute a multigene family. The tagged HssA protein was translated; hssA encodes an unusually high-glycine/serine-rich small protein (8.37 kDa), which has strong homology to previously reported cAMP-inducible 2C and 7E proteins. Overexpression of hssA mRNA as well as frame-shifted versions of hssA RNA suppressed the phenotype of the partially active Dd-STATa strain, suggesting that translation is not necessary for suppression. Although overexpression of prespore-specific genes among the family did not suppress the parental phenotype, prestalk-specific family members did. Although overexpression of the hssA did not revert the expression of Dd-STATa target genes, and although its suppression mechanism remains unknown, morphological reversion implies functional relationships between Dd-STATa and hssA. Submitted by: Takefumi Kawata [tkawata@bio.sci.toho-u.ac.jp] ============================================================== [End dictyNews, volume 30, number 1]