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Dissertation
piRNA Biogenesis and Transposon Silencing in Drosophila: A Dissertation
GSBS Dissertations and Theses
  • Zhao Zhang, University of Massachusetts Medical School
Date of Completion
11-6-2013
Document Type
Doctoral Dissertation
Department
RNA Therapeutics Institute
First Thesis Advisor
Phillip Zamore, PhD
Keywords
  • Small Interfering RNA,
  • RNA Interference,
  • DNA Transposable Elements,
  • Drosophila Proteins
Subject Categories
Subjects
Dissertations, UMMS; RNA, Small Interfering; RNA Interference; DNA Transposable Elements; Drosophila Proteins
Abstract
piRNAs guide PIWI proteins to silence transposons in animal germ cells. In Drosophila, the heterochromatic piRNA clusters transcribe piRNA precursors to be transported into nuage, a perinuclear structure for piRNA production and transposon silencing. At nuage, reciprocal cycles of piRNA-directed RNA cleavage—catalyzed by the PIWI proteins Aubergine (Aub) and Argonaute3 (Ago3) in Drosophila—destroy the sense transposon mRNA and expand the population of antisense piRNAs in response to transposon expression, a process called the Ping-Pong cycle. Heterotypic Ping-Pong between Aub and Ago3 ensures that antisense piRNAs predominate. My thesis research mainly focuses on two fundamental questions about the piRNA production: How does the germ cell differentiate piRNA precursor from mRNAs for piRNA biogenesis? And what is the mechanism to impose Aub Ping-Pong with Ago3? For the first question, we show that the HP1 homolog protein Rhino marks the piRNA cluster regions in the genome for piRNA biogenesis. Rhino seems to anchor a nuclear complex that suppresses cluster transcript splicing, which may differentiate piRNA precursors from mature mRNAs. Moreover, LacI::Rhino fusion protein binding suppresses splicing of a reporter transgene and is sufficient to trigger de novo piRNA production from a trans combination of sense and antisense transgenes. For the second question, we show that Qin, a new piRNA pathway factor contains both E3 ligase and Tudor domains, colocalizes with Aub and Ago3 in nuage, enforces heterotypic Ping- Pong between Aub and Ago3. Loss of qinleads to less Ago3 binding to Aub, futile Aub:Aub homotypic Ping-Pong prevails, antisense piRNAs decrease, many families of mobile genetic elements are reactivated, DNA damage accumulates in the germ cells and flies are sterile.
DOI
10.13028/M2888D
Rights and Permissions
Copyright is held by the author, with all rights reserved.
Citation Information
Zhao Zhang. "piRNA Biogenesis and Transposon Silencing in Drosophila: A Dissertation" (2013)
Available at: http://works.bepress.com/zhao-zhang/20/