dictyNews Electronic Edition Volume 38, number 10 April 6, 2012 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. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= Live imaging of nascent RNA dynamics reveals distinct types of transcriptional pulse regulation Tetsuya Muramoto1, Danielle Cannon1,4, Marek Gierlinski2,3, Adam Corrigan1,4, Geoffrey J Barton2,3 and Jonathan R Chubb1,4 Divisions of Cell and Developmental Biology1 Biological Chemistry and Drug Discovery2 Wellcome Trust Centre for Gene Regulation and Expression3, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK. 4Present address: Department of Cell and Developmental Biology and MRC Laboratory for Molecular Cell Biology, University College London, Gower Street, London, WC1E 6BT, UK. PNAS, in press Transcription of genes can be discontinuous, occurring in pulses or bursts. It is not clear how properties of transcriptional pulses vary between different genes. We compared the pulsing of 5 housekeeping and 5 developmentally- induced genes by direct imaging of single gene transcriptional events in individual living Dictyostelium cells. Each gene displayed its own transcriptional signature, differing in probability of firing and pulse duration, frequency and intensity. In contrast to the prevailing view from both prokaryotes and eukaryotes that transcription displays binary behaviour, strongly expressed housekeeping genes altered the magnitude of their transcriptional pulses during development. These non-binary 'tunable' responses may be better suited than stochastic switch behaviour for housekeeping functions. Analysis of RNA synthesis kinetics using fluorescence recovery after photobleaching implied modulation of housekeeping gene pulse strength occurs at the level of transcription initiation, rather than elongation. In addition, disparities between single cell and population measures of transcript production suggested differences in RNA stability between gene classes. Analysis of stability using RNAseq revealed no major global differences in stability between developmental and housekeeping transcripts, although strongly induced RNAs showed unusually rapid decay, indicating tight regulation of expression. Submitted by Jonathan Chubb [j.chubb@ucl.ac.uk] -------------------------------------------------------------------------------------- Valentina Lo Sardo, Chiara Zuccato, Germano Gaudenzi, Barbara Vitali , Catarina Ramos, Marzia Tartari, Michael A. Myre, James A. Walker, Anna Pistocchi, Luciano Conti, Marta Valenza, Binia Drung, Boris Schmidt, James Gusella, Scott Zeitlin, Franco Cotelli, Elena Cattaneo An evolutionary recent neuroepithelial cell adhesion function of huntingtin implicates ADAM10-Ncadherin Nature Neuroscience, in press The Huntington's disease gene product, huntingtin, is indispensable for neural tube formation but its role is obscure. We studied neurulation in htt-null embryonic stem cells and htt-morpholino zebrafish embryos, and found a novel, evolutionarily-recent function for this ancient protein. We show that htt is essential for homotypic interactions between neuroepithelial cells; it permits neurulation and rosette-formation by regulating metalloprotease ADAM10-activity and Ncadherin-cleavage. This function is embedded in the htt N-terminus and phenocopied by treatment ofhtt-knock-down zebrafish with an ADAM10 inhibitor. Notably, in htt-null cells, reversion of the rosetteless phenotype occurs only with expression of evolutionarily-recent htt heterologues from deuterostome organisms. Conversely, all heterologues tested, including htt from Drosophila melanogaster and Dictyostelium discoideum, exhibit anti-apoptotic activity. Thus, anti-apoptosis may have been one of htt's ancestral function(s) but, in deuterostomes, htt evolved to acquire a unique regulatory activity for controlling neural adhesion via ADAM10-Ncadherin, with implications for brain evolution and development. Submitted by Michael Myre [myre@chgr.mgh.harvard.edu] -------------------------------------------------------------------------------------- Michael A. Myre Clues to Gamma-secretase, huntingtin and Hirano body normal function using the model organism Dictyostelium discoideum Journal of Biomedical Science, in press Many neurodegenerative disorders, although related by their destruction of brain function, display remarkable cellular and/or regional pathogenic specificity likely due to a deregulated functionality of the mutant protein. However, neurodegenerative disease genes, for example huntingtin (HTT), the ataxins, the presenilins (PSEN1/PSEN2) are not simply localized to neurons but are ubiquitously expressed throughout peripheral tissues; it is therefore paramount to properly understand the earliest precipitating events leading to neuronal pathogenesis to develop effective long-term therapies. This means, in no unequivocal terms, it is crucial to understand the gene's normal function. Unfortunately, many genes are often essential for embryogenesis which precludes their study in whole organisms. This is true for HTT, the beta-amyloid precursor protein (APP) and presenilins, responsible for early onset Alzheimer's disease (AD). To better understand neurological disease in humans, many lower and higher eukaryotic models have been established. So the question arises: how reasonable is the use of organisms to study neurological disorders when the model of choice does not contain neurons? Here we will review the surprising, and novel emerging use of the model organism Dictyostelium discoideum, a species of soil-living amoeba, as a valuable biomedical tool to study the normal function of neurodegenerative genes. Historically, the evidence on the usefulness of simple organisms to understand the etiology of cellular pathology cannot be denied. But using an organism without a central nervous system to understand diseases of the brain? We will first introduce the life cycle of Dictyostelium, the presence of many disease genes in the genome and how it has provided unique opportunities to identify mechanisms of disease involving actin pathologies, mitochondrial disease, human lysosomal and trafficking disorders and host-pathogen interactions. Secondly, I will highlight recent studies on the function of HTT, presenilin gamma-secretase and Hirano bodies conducted in Dictyostelium. I will then outline the limitations and future directions in using Dictyostelium to study disease, and finally conclude that given the evolutionary conservation of genes between Dictyostelium and humans and the organisms' genetic tractability, that this system provides a fertile environment for discovering normal gene function related to neurodegeneration and will permit translational studies in higher systems. Submitted by Michael Myre [myre@chgr.mgh.harvard.edu] ============================================================== [End dictyNews, volume 38, number 10]