poly(UG)-tailed RNAs and Transgenerational Epigenetic Inheritance in C. elegans
Author
Shukla, Aditi
Metadata
Show full item recordCitation
Shukla, Aditi. 2020. poly(UG)-tailed RNAs and Transgenerational Epigenetic Inheritance in C. elegans. Doctoral dissertation, Harvard University Graduate School of Arts and Sciences.Abstract
Small noncoding RNAs (small RNAs) such as Piwi-interacting RNAs (piRNAs), microRNA (miRNAs), and short-interfering RNAs (siRNAs) are important regulators of gene expression. Small RNAs are bound by Argonaute proteins and, together, this complex locates complementary target mRNAs and mediates their silencing. Known roles of siRNAs include protecting genomes from mobile genetic elements called transposons and mediating gene silencing in response to exogenous double-stranded RNAs (dsRNAs). RDE-3 is a ribonucleotidyltransferase required for the silencing of transposon RNAs and dsRNA-targeted mRNAs in Caenorhabditis elegans (C. elegans). In heterologous expression systems, RDE-3 adds long stretches of alternating, non-templated uridine (U) and guanosine (G) ribonucleotides to the 3′ termini of RNAs (designated poly(UG) or pUG tails). In Chapter 2 of my dissertation, we show that, in its natural context in C. elegans, RDE-3 adds pUG tails to mRNA targets of exogenous dsRNA, as well as to transposon RNAs. RNA fragments attached to pUG tails with more than 16 perfectly alternating 3′ U and G nucleotides become potent mediators of gene silencing. pUG tails promote gene silencing by recruiting RNA-dependent RNA polymerases, which use pUG-tailed RNAs (pUG RNAs) as templates to synthesize gene-silencing siRNAs.In C. elegans, siRNAs can promote gene silencing for several generations. This multigenerational silencing is a robust example of transgenerational epigenetic inheritance (TEI). Chapter 2 of my dissertation shows that cycles of pUG RNA-templated siRNA synthesis and siRNA-directed pUG RNA biogenesis (pUG RNA/siRNA cycling) underlie siRNA-directed TEI in the C. elegans germline. How C. elegans ensures accuracy and fidelity to this feed-forward, heritable and, therefore, inherently dangerous gene regulatory system is not well understood. Chapter 3 of my dissertation demonstrates that C. elegans piRNAs are one system that prevents the wrong germline-expressed mRNAs from becoming permanently inactivated by pUG RNA/siRNA cycling. In the absence of piRNAs, a subset of germline-expressed genes that are not normally subjected to TEI enter a state of permanent silencing. Entry into the silenced state is irreversible, and genes thus silenced are paramutagenic. Taken together, this work reports a new 3’ RNA modification that turns RNA fragments into potent mediators of gene silencing within and across generations and identifies one mechanism that C. elegans uses to ensure that this potentially dangerous modification is added to the correct RNAs.
Terms of Use
This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAACitable link to this page
https://nrs.harvard.edu/URN-3:HUL.INSTREPOS:37369477
Collections
- FAS Theses and Dissertations [6136]
Contact administrator regarding this item (to report mistakes or request changes)