Understanding the mechanism of Piwi-induced transcriptional silencing Project summary Maintaining genomic integrity is crucial for the survival of all species. Piwi proteins and their small RNA partners, the piwi-interacting RNAs (piRNAs), repress transposon activity in the germline to ensure genomic integrity. In the cytoplasm of germline cells, piwi proteins ? guided by piRNAs ? recognize and cleave transposon mRNAs. We have recently shown that the Piwi protein is active in the nuclei of Drosophila cells: Piwi silences transposons by inducing transcriptional repression and establishing a repressive chromatin state at its genomic targets. Neither the mechanism of Piwi-induced transcriptional silencing nor the components of the molecular machinery involved in this process downstream of Piwi is known. In this proposal we will comprehensively investigate the mechanism of Piwi-induced transcriptional repression. We will comprehensively characterize changes in chromatin marks and chromatin factors. These experiments will direct further analyses to identify factors responsible for Piwi-mediated transcriptional repression. We will also establish a reporter system for piRNA-independent recruitment of Piwi to specific sites on the genome. We will use this reporter system to identify factors that are required for Piwi-mediated transcriptional silencing. We will also evaluate the role of the N-terminal region of Piwi in transcriptional silencing. Piwi proteins and the associated piRNAs are maternally deposited into the embryo and accumulate in the pole plasm that later gives rise to the developing gonads. The functional relevance of the deposited piRNAs is not known. We will test the role of the piRNA pathway in transgenerational epigenetic silencing in the somatic and germline tissues of the offspring. The proposed studies will significantly advance our knowledge of RNA-mediated regulation of chromatin structure and transcriptional activity in animals. Mechanistic insights into Piwi-mediated transcriptional repression and an understanding of how these processes are involved in transmitting epigenetic information to the progeny will aid in the design of targeted treatment of human sterility caused by deregulation of the Piwi- piRNA pathway.

Public Health Relevance

The aim of this application is to understand the biological impacts of small RNAs in establishing epigenetic states. Small RNAs regulate gene expression on several levels and they impact disease states ranging from cancer to neurodegeneration. They also serve as tools for understanding normal and aberrant biological processes and will perhaps transform clinical practice by serving as the basis for a new generation of therapeutic agents.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular Genetics A Study Section (MGA)
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Carter, Anthony D
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California Institute of Technology
Schools of Arts and Sciences
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Rogers, Alicia K; Situ, Kathy; Perkins, Edward M et al. (2017) Zucchini-dependent piRNA processing is triggered by recruitment to the cytoplasmic processing machinery. Genes Dev 31:1858-1869
Huang, Xiawei; Fejes Tóth, Katalin; Aravin, Alexei A (2017) piRNA Biogenesis in Drosophila melanogaster. Trends Genet 33:882-894
Chen, Yung-Chia Ariel; Stuwe, Evelyn; Luo, Yicheng et al. (2016) Cutoff Suppresses RNA Polymerase II Termination to Ensure Expression of piRNA Precursors. Mol Cell 63:97-109
Tóth, Katalin Fejes; Pezic, Dubravka; Stuwe, Evelyn et al. (2016) The piRNA Pathway Guards the Germline Genome Against Transposable Elements. Adv Exp Med Biol 886:51-77
Marinov, Georgi K; Wang, Jie; Handler, Dominik et al. (2015) Pitfalls of mapping high-throughput sequencing data to repetitive sequences: Piwi's genomic targets still not identified. Dev Cell 32:765-71