Development of piRNAs for target-specific methylation

University Of Michigan At Ann Arbor, Ann Arbor MI

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Abstract

? DESCRIPTION (provided by applicant): Currently available tools to modify the epigenome are blunt instruments rather than the precise editors in great demand for both researchers and clinicians. Existing targeted approaches rely on creating transgenic animals or gene therapy, and therefore face a difficult path for translation to the clinic. Thus, new technology for targete epigenetic manipulation is needed that should be both gene-specific and easy to administer. With these qualities in mind, our challenge is to develop a suite of tools, based on the Piwi-interacting RNA (piRNA) system, to accurately induce DNA methylation of targeted loci in adult tissues, applicable to all mammals. PIWI-interacting RNAs (piRNAs) represent a fascinating adaptive mechanism and a potentially ready made tool for innovation in gene-specific repression. Originally piRNAs and their associated proteins were thought to be expressed only in germ cells, however, mounting evidence finds the expression of piRNAs in somatic tissues as diverse as brain and kidney in animals from sea slug to mouse to macaque. Activating the piRNA pathway in adult mammals holds promise in closing the gap between basic research and human application. The crucial difference in silencing by piRNAs compared to widely used miRNA/siRNA treatment is that piRNAs offer sensitive sequence specificity and induce DNA methylation. We will use this class of RNA to develop the technology to target specific genes and loci for stable, mitotically heritable, silencing at pre-determined genomic locations. While much is known about global silencing by piRNAs in germ cells, much less is known about their activity in adult somatic tissues. Our studies will validate their use as a technological platform or targeted epigenetics in any gene for all mammalian species. Choice of model organism is critical in the testing of potential epigenetic therapeutics. For these studies, we will use the Agouti viable yellow mouse, which varies in coat color concomitantly with DNA methylation at a single locus. Induced methylation targeted to the Avy transposon will provide direct visual semi-quantitative evidence of systemic molecular silencing at this locus. Additional experiments will verify the site specificity and degree of silencing. Further, we will adapt the piRNA suppression system in the soma to target genic regions as well as transposons. The research generated will provide sorely needed evidence clarifying the roles and activity of piRNA in somatic tissues of mammals and will be used to develop piRNA targeted methylation for the wider research and therapeutic communities.