dictyNews Electronic Edition Volume 30, number 9 March 10, 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 ========= Live imaging of the Dictyostelium cell cycle reveals widespread S-phase during development, a G2 bias in spore differentiation and a premitotic checkpoint Tetsuya Muramoto and Jonathan R. Chubb Division of Cell and Developmental Biology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK Development, in press The regulation of the Dictyostelium cell cycle has remained ambiguous due to difficulties in long term imaging of motile cells and a lack of markers for defining cell cycle phases. There is controversy over whether cells replicate their DNA during development, and whether spores are in G1 or G2 of the cell cycle. We have introduced a living cell S-phase marker into Dictyostelium cells, which allows us to precisely define cycle phase. We show that during multicellular development, a large proportion of cells undergo nuclear DNA synthesis. Germinating spores enter S-phase only after their first mitosis, indicating spores are in G2. In addition, we demonstrate that Dictyostelium heterochromatin is copied late in S-phase, and replicates via accumulation of replication factors, rather than recruitment of DNA to pre-existing factories. Analysis of variability in cycle times indicates regulation of the cycle manifests at a single random transition in G2, and we present the first identified checkpoint in the organism, which operates at the G2/M transition in response to DNA damage. Submitted by: Jonathan Chubb [j.chubb@dundee.ac.uk] -------------------------------------------------------------------------------- Cell type specificity of a diffusible inducer is determined by a GATA family transcription factor Thomas Keller and Christopher R.L. Thompson* Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester, M13 9PT *Author for correspondence (christopher.thompson@manchester.ac.uk) Development, in press One poorly understood mechanism of developmental patterning involves the intermingled differentiation of different cell types that then sort out to generate pattern. Examples of this are known in nematodes and vertebrates, and in Dictyostelium it is the major mechanism. However, a general problem with this mechanism is whether different inducers are required for each cell type that arises independently of positional information. Consistent with this idea, in Dictyostelium the signaling molecule DIF acts as a position independent signal and was thought to only regulate the differentiation of a single cell type (pstO). The results presented here challenge this idea. In a novel genetic selection to isolate genes required for DIF signal transduction we found a mutant (dimC-) that is a hypomorphic allele of a GATA family transcription factor (gtaC). gtaC expression is directly regulated by DIF and GtaC rapidly translocates to the nucleus in response to DIF. gtaC- null cells showed some hallmark DIF signaling defects. Surprisingly, other aspects of the mutant were distinct from those of other DIF signaling mutants, suggesting that gtaC regulates a subset of DIF responses. For example, pstO cell differentiation appeared normal. However we found that pstB cells were mislocalised and the pstB derived basal disc was much reduced or missing. These defects are due to a failure to respond to DIF as they are phenocopied in other DIF signaling mutants. These findings therefore identify a novel small molecule activated GATA factor that is required to regulate the cell type specific effects of DIF. They also reveal that a non-positional signal can regulate the differentiation of multiple cell types through differential interpretation in receiving cells. Submitted by: Chris Thompson [christopher.thompson@manchester.ac.uk] ============================================================== [End dictyNews, volume 30, number 9]