Pamela M. Carroll

Epigenetic Blocking of an Enhancer Region Controls Irradiation-Induced Proapoptotic Gene Expression in Drosophila Embryos

Drosophila embryos are highly sensitive to gamma-ray-induced apoptosis at early but not later, more differentiated stages during development. Two proapoptotic genes, reaper and hid, are upregulated rapidly following irradiation. However, in post-stage-12 embryos, in which most cells have begun differentiation, neither proapoptotic gene can be induced by high doses of irradiation. Our study indicates that the sensitive-to-resistant transition is due to epigenetic blocking of the irradiation-responsive enhancer region (IRER), which is located upstream of reaper but is also required for the induction of hid in response to irradiation. This IRER, but not the transcribed regions of reaper/hid, becomes enriched for trimethylated H3K27/H3K9 and forms a heterochromatin-like structure during the sensitive-to-resistant transition. The functions of histone-modifying enzymes Hdac1(rpd3) and Su(var)3-9 and PcG proteins Su(z)12 and Polycomb are required for this process. Thus, direct epigenetic regulation of two proapoptotic genes controls cellular sensitivity to cytotoxic stimuli.

Model Organisms in Drug Discovery

List of contributors.Acknowledgments.1. Introduction to Model Systems in Drug Discovery (Kevin Fitzgerald and Pamela M. Carroll).2. Growing Yeast for Fun and Profit: Use of Saccharomyces cerevisiae as a Model System in Drug Discovery (Petra Ross-Macdonald).3. Caenorhabditis elegans Functional Genomics in Drug Discovery: Expanding Paradigms (Titus Kaletta, Lynn Butler and Thierry Bogaert).4. Drosophila as a Tool for Drug Discovery (Hao Li and Dan Garza).5. Drosophila - a Model System for Targets and Lead Identification in Cancer and Metabolic Disorders (Corina Schutt, Barbara Froesch and Ernst Hafen).6. Mechanism of Action in Model Organisms: Interfacing Chemistry, Genetics and Genomics (Pamela M. Carroll, Kevin Fitzgerald and Rachel Kindt).7. Gene tics and Genomics in the Zebrafish: from Gene to Function and Back (Stefan Schulte-Merker).8. Lipid Metabolism and Signaling in Zebrafish (Shiu-Ying Ho, Steven A. Farber and Michael Pack).9. Chemical Mutagenesis in the Mouse: a Powerful Tool in Drug Target Identification and Validation (Andreas Russ, Neil Dear, Geert Mudde, Gabriele Stumm, Johannes Grosse, Andreas Schroder, Reinhard Sedlmeier, Sigrid Wattler and Michael Nehls).10. Saturation Screening of the Druggable Mammalian Genome (Hector Beltrandelrio, Francis Kern, Thomas Lanthorn, Tamas Oravecz, James Piggott, David Powell, Ramiro Ramirez-Solis, Arthur T. Sands and Brian Zambrowicz).Index.

Chemical Genetics Reveals an RGS/G-Protein Role in the Action of a Compound

We report here on a chemical genetic screen designed to address the mechanism of action of a small molecule. Small molecules that were active in models of urinary incontinence were tested on the nematode Caenorhabditis elegans, and the resulting phenotypes were used as readouts in a genetic screen to identify possible molecular targets. The mutations giving resistance to compound were found to affect members of the RGS protein/G-protein complex. Studies in mammalian systems confirmed that the small molecules inhibit muscarinic G-protein coupled receptor (GPCR) signaling involving G-αq (G-protein alpha subunit). Our studies suggest that the small molecules act at the level of the RGS/G-αq signaling complex, and define new mutations in both RGS and G-αq, including a unique hypo-adapation allele of G-αq. These findings suggest that therapeutics targeted to downstream components of GPCR signaling may be effective for treatment of diseases involving inappropriate receptor activation.