| Description |
In contrast to DNA, which functions to store genetic information, RNA effectuates genetic information. The versatility of RNA is evident in the multiple cellular functions RNA fulfills. RNA molecules are structural elements, catalysts, adaptors, messengers and regulators. Accordingly, RNA shows great diversity in nucleotide composition and structure. This dissertation explores how sequence and structural features of RNA influence the fate of RNA in nematode cells and impact the entire organism. First, the C. elegans noncoding transcript rncs-1 is characterized. Throughout development, rncs-1 is expressed in intestine and hypodermis. Upon starvation, transcription of rncs-1 is upregulated by an ELT-2-dependent mechanism. A feature of the rncs-1 transcript is its extended double-stranded structure. Double-stranded RNA is a substrate for the RNase III enzyme Dicer, which cleaves long RNA duplexes into ~23-nucleotide products that subsequently silence cognate messages. Surprisingly, rncs-1 RNA is resistant to Dicer cleavage in vitro, and additional studies demonstrate that secondary structural elements in rncs-1 occlude access of Dicer to the double-stranded region. While not a cleavage substrate for Dicer in vitro, rncs-1 inhibits Dicer activity. Significantly, overexpression of rncs-1 modulates expression of endogenous Dicer silencing targets in vivo. This result represents a previously uncharacterized cellular function of noncoding RNAs. Second, the effect of RNA editing on the subcellular localization of RNA is examined. Deamination of adenosine to inosine within double-stranded RNA is catalyzed by adenosine deaminases that act on RNA (ADARs). The majority of cellular inosine is found in noncoding sequences, but the function of inosine in noncoding regions of RNA is unknown. In contradiction to existing models for nuclear retention of ADAR-edited RNA, research presented here confirms that endogenous editing substrates of C. elegans are exported to the cytoplasm. Finally, in continuation of previous behavioral studies that revealed chemotaxis defects of C. elegans ADAR-mutants, the response of editing-deficient worms to dauer-inducing pheromone is assayed. Dauer pheromone controls the entry of C. elegans into a specialized, highly resistant alternative larval stage called dauer. Nematodes lacking ADARs are found to show wildtype dauer formation, indicating that ADAR activity is dispensable for response to dauer pheromone. |
