Inhaltszusammenfassung

The Piwi pathway is a germline-specific defence mechanism that animals have evolved to silence transposable elements, in order to preserve genome integrity and ensure survival of a species. In C. elegans, the Piwi protein PRG-1 forms a complex together with its 21U RNA co-factor, in order to recognize and silence a target RNA. Upon target recognition, an RNA-dependent RNA polymerase is recruited to the target RNA to use it as a template and synthetize secondary siRNAs. These so-called 22G RNA...The Piwi pathway is a germline-specific defence mechanism that animals have evolved to silence transposable elements, in order to preserve genome integrity and ensure survival of a species. In C. elegans, the Piwi protein PRG-1 forms a complex together with its 21U RNA co-factor, in order to recognize and silence a target RNA. Upon target recognition, an RNA-dependent RNA polymerase is recruited to the target RNA to use it as a template and synthetize secondary siRNAs. These so-called 22G RNAs are then loaded onto secondary Argonaute proteins, such as WAGO-1 and HRDE-1, to amplify the silencing reaction. In some cases, the silencing mediated by HRDE-1 can become independent from PRG-1 and is accompanied by the deposition of heterochromatic marks at the targeted locus. This form of silencing is extremely stable and can be transmitted for several generations; it depends on HRDE-1 as well as mutator proteins, and it is called RNAe. RNAe establishes in a stochastic manner, but the mechanisms behind this decision are not known. We therefore investigated how PRG-1 mediated silencing is connected to RNAe. In chapter 2, we show that maternally provided 21U RNAs are essential for establishing de novo 22G RNAs production. The parental contribution of both 21U RNAs and RNAe silencing memory is necessary to instruct the silencing machinery in the next generation, to ensure appropriate gene silencing as well as gene expression; this is an essential requirement to guarantee gonad development and fertility. In chapter 3, we use a transgenic 21U RNA target and define that maternal 21U RNAs are not only necessary, but also sufficient to initiate de novo silencing. Moreover, in some cases, maternal 21U RNAs can trigger RNAe. This silencing can also affect endogenous targets, thereby causing variability in the transcriptome among different individuals. In chapter 4, we describe the characterization of a novel factor, which we named PID-2. PID-2 is required to establish de novo target silencing initiated by maternal 21U RNAs, in particular to boost the production of secondary 22G RNAs and to establish RNAe. PID-2 is also involved in Tc1 silencing, acting just downstream of PRG-1. PID-2 interacts with two novel Tudor proteins, PID-4 and PID-5, and together they are required for maintenance of an immortal germline over generations. These factors are linking PRG-1 mediated silencing to RNAe, therefore we started to unravel the requirements for establishing this very stable form of silencing.» weiterlesen» einklappen

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DDC Sachgruppe:
Biowissenschaften, Biologie