Frontiers of RNA Silencing Mechanisms
Tuesday, October 5, 2004
Presented by the RNAi Discussion Group
Organizer: Tom Tuschl, Rockefeller University
The RNAi Discussion Group is a part of the Frontiers of Science Program under which the Academy is starting a series of discussion groups.
Oliver Hobert, Columbia University, "Control of Neuronal Development by Small Regulatory RNAs."
Markus Stoffel, Rockefeller University, "Role of MicroRNAs in Insulin Secretion and Diabetes."
Tariq Rana, University of Massachusetts Medical School, "RNAi in Human Cells: Mechanism and Therapeutic Application."
"Control of Neuronal Development by Small Regulatory RNAs"
Animal microRNAs (miRNAs) are gene regulatory factors that prevent expression of specific messenger RNA targets by binding to their 3’ untranslated region. In each species examined, miRNAs constitute at least 1% of the predicted genes in the respective genome. Since the abundance of miRNAs has only recently been recognized, there is still a large gap in our understanding of the biological functions of miRNAs. We have found that the C. elegans lsy-6 miRNA (for lateral symmetry defective) functions in a poorly understood developmental context, the generation of neuronal diversity along the left/right (L/R) axis of an animal. lsy-6 repressed the expression of the cog-1 transcription factor, which in turn controls the L/R asymmetric expression of putative chemoreceptors. lsy-6 is only expressed in a selected set of neurons. In one neuron, its expression is controlled by the die-1 Zn finger transcription factors, whose expression itself is controlled by a miRNA, mir-273. In conclusion, sequentially acting miRNAs control the expression of transcription factors that govern the L/R asymmetric properties of the worm chemosensory system.
"Role of MicroRNAs in Insulin Secretion and Diabetes"
MicroRNAs (miRNAs) constitute a growing class of noncoding RNAs that are thought to regulate gene expression by translational repression. We have identified a novel, evolutionarily conserved and islet-specific miRNA (miR-375). Overexpression of miR-375 suppressed glucose-induced insulin secretion, and, conversely, inhibition of endogenous miR-375 function enhanced insulin secretion. The mechanism by which secretion is modified by miR-375 is independent of changes in glucose metabolism or intracellular Ca2+-signaling but correlated with a direct effect on insulin exocytosis. Myotropin (Mtpn) was predicted and validated as a target of miR-375. Inhibition of Mtpn by siRNA mimicked the effects of miR-375 on glucose-stimulated insulin secretion and exocytosis. Thus, miR-375 is a regulator of insulin secretion and thereby may constitute a novel pharmacological target for the treatment of diabetes.
"RNAi in Human Cells: Mechanism and Therapeutic Application"
RNAi interference (RNAi) is the process whereby double-stranded RNA (dsRNA) induces the sequence-specific degradation of homologous mRNA. We have investigated the mechanism of RNAi in human cells and addressed a number of basic questions. Various chemical modifications were created in short-interfering RNAs (siRNAs) to determine the biochemical properties required for RNA interference. Rules for designing effective siRNA for in vitro and in vivo applications will be discussed. In addition, results showing the applications of modified siRNA to silence human genes involved in regulating HIV-1 replication will be presented.