Maelstrom and Gtsf1 are essential for piwi-mediated transcriptional silencing of transposable elements in Drosophila
Başlık çevirisi mevcut değil.
- Tez No: 402373
- Danışmanlar: DR. JULIUS BRENNECKE
- Tez Türü: Doktora
- Konular: Biyoloji, Biology
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2014
- Dil: İngilizce
- Üniversite: Universität Wien
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Moleküler Biyoloji Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 146
Özet
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Özet (Çeviri)
The piRNA pathway, a small RNA based gene silencing mechanism, acts in animal gonads and protects the genome against the deleterious influence of transposable elements (TEs). At the center of the pathway act PIWI clade Argonaute proteins loaded with PIWI interacting RNAs (piRNAs). piRNAs act as sequencespecific guides to target PIWI-piRNA complexes (Piwi-RNA Induced Silencing Complex (Piwi-RISC)) to complementary TE transcripts. Many piRNA pathway members are important for PIWI-RISC formation through their roles in piRNA biogenesis and/or PIWI loading. Loss of these factors leads to a reduction in PIWI protein levels due to instability of unloaded PIWI proteins. Much less is known about how mature PIWI-RISCs silence TEs. This is especially true for the only nuclear Drosophila PIWI family protein Piwi. Towards this end, we have identified a group of piRNA pathway members that do not affect Piwi stability or Piwi-RISC formation yet are essential for Piwi-mediated TE silencing. The aim of my thesis was to characterize two such proteins named Maelstrom and Gtsf1. Both of these proteins are expressed specifically in gonads and are evolutionarily conserved in mammals where they are also essential for TE silencing. We first demonstrated that both factors act clearly downstream of Piwi-RISC formation. Using genetics and genomics approaches we then show that Piwi-mediated TE silencing is transcriptional and that this process depends on both, Maelstrom and Gtsf1. Our data show that Piwi-RISC silences TE targets in trans and it is accompanied by deposition of histone H3 Lys9 tri-methylation (H3K9me3) at targeted TE insertion sites. Importantly, Gtsf1 directly interacts with Piwi and is required for Piwi guided H3K9 methylation suggesting a direct function of Gtsf1 in the Piwi-RISC. In contrast, Maelstrom is not required for H3K9-methylation at target loci. We conclude that Maelstrom acts in an unknown silencing process downstream of H3K9 methylation. Our work lies the genetic and conceptual foundation to mechanistically dissect a small RNA directed transcriptional silencing process in a higher eukaryote.
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