Dicty News Electronic Edition Volume 22, number 6 March 5, 2004 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 Dicty-News, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ============= Abstracts ============= Tissue-specific G1 phase cell cycle arrest prior to terminal differentiation in Dictyostelium. Guokai Chen, Gad Shaulsky and Adam Kuspa Verna and Marrs McLean Department of Biochemistry and Molecular Biology, and Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston TX 77030. Development, in press The cell cycle status of developing Dictyostelium cells remains unresolved because previous studies have led to conflicting interpretations. We propose a new model of cell cycle events during development that accounts for most of the previous data and is based on experiments in which multiple parameters of cell cycle status were monitored. We observe little mitosis during the first twelve hours of development, followed by division of fifty percent of the cells between twelve and eighteen hours of development. Cellular DNA content profiles obtained by flow cytometry and quantification of extra-chromosomal and chromosomal DNA suggest that the daughter cells have half the chromosomal DNA of vegetative cells. Furthermore, we detect little chromosomal DNA synthesis during development indicating that no S phase occurs and suggesting that dividing cells arrest within the G1 phase of the cell cycle. The DNA content in cells sorted by fluorescent tissue-specific reporters indicates that prespore cells divide first and later encapsulate as G1-arrested spores. Consistent with this, we show by fluorescence in situ hybridization that germinating spores have one copy of their chromosomes and they replicate their chromosomes before mitosis of the emergent amoebea. The DNA content of mature stalk cells suggests that they also attain a G1 state prior to terminal differentiation. Since prestalk cells appear to be in G2 up to 22 hours of development, our data suggests that they divide just prior to stalk formation. Our results suggest tissue-specific regulation of G1 phase cell cycle arrest prior to terminal differentiation in Dictyostelium. Submitted by: Adam Kuspa [akuspa@bcm.tmc.edu] ----------------------------------------------------------------------------- Overexpression of sphingosine-1-phosphate lyase or inhibition of sphingosine kinase in Dictyostelium discoideum results in a selective increase in sensitivity to platinum based chemotherapy drugs Junxia Min, Andrew L. Stegner, Hannah Alexander and Stephen Alexander Division of Biological Sciences, University of Missouri, Columbia, MO 65211-7400 Eukaryotic Cell, in press The efficacy of the chemotherapy drug cisplatin is often limited due to resistance of the tumors to the drug, and increasing the potency of cisplatin, without increasing its concentration could prove beneficial. A previously characterized Dictyostelium discoideum mutant with increased resistance to cisplatin was defective in the gene encoding sphingosine-1-phosphate (S-1-P) lyase, which catalyzes the breakdown of S-1-P, an important regulatory molecule in cell function and development and the regulation of cell fate. We hypothesized that the increased resistance to cisplatin was due to an elevation of S-1-P, and predicted that lowering levels of S-1-P should increase sensitivity to the drug. We generated three strains that stably overexpress different levels of the S-1-P lyase. The overexpressor strains have reduced growth rate, and confirming the hypothesis, showed an expression dependent increase in sensitivity to cisplatin. Consistently, treating the cells with D-erythro N,N, dimethylsphingosine, a known inhibitor of sphingosine kinase, increased the sensitivity of mutant and parent cells to cisplatin, while addition of exogenous of S-1-P or 8-Br-cAMP made the cells more resistant to cisplatin. The increased sensitivity of the overexpressors to cisplatin was also observed with the cisplatin analog carboplatin. In contrast, the response to doxorubicin, 5-flurouracil or etoposide was unaffected, indicating that the involvement of the sphingolipid metabolic pathway in modulating the response to cisplatin is not part of a global genotoxic stress response. The augmented sensitivity to cisplatin appears to be the result of an intracellular signaling function of S-1-P, since D. discoideum does not appear to have EDG(S-1-P) receptors. Overall, the results show that modulation of the sphingolipid pathway at multiple points can result in increased sensitivity to cisplatin, and has the potential for increasing the clinical usefulness of this important drug. Submitted by: Hannah Alexander [alexanderh@missouri.edu] =============================================================================== [End Dicty News, volume 22, number 6]