Master of Science (MS)


Biological Sciences

Document Type



RNA interference (RNAi) is a phylogenetically conserved gene regulation mechanism that modulates a wide variety of biological functions through suppressing gene expression at transcriptional or posttranscriptional levels (Bass 2000; Sharp 2001). One of the major natural functions of RNAi is antiviral defense in cytosol. RNAi directed viral immunity (RDVI) targets viral transcripts for destruction using small interfering RNAs (siRNAs) processed from viral replication intermediates, in the form of double-stranded RNA (dsRNA), as sequence guide (Lu, Maduro et al. 2005). Accumulating evidence suggests RDVI in the nematode worm Caenorhabditis elegans begins with the biogenesis of virus-derived siRNAs (viRNAs) by DCR-1 (Bernstein, Caudy et al. 2001; Duchaine, Wohlschlegel et al. 2006), a type III ribonuclease, and RDE-4, a dsRNA binding protein (Grishok, Pasquinelli et al. 2001; Knight and Bass 2001). Efficient destruction of viral transcripts guided by viRNAs is then orchestrated by several host factors that form distinct classes. Some of the known host factors downstream of viRNA biogenesis include Argonaute proteins (e.g. RDE-1) (Tabara, Sarkissian et al. 1999; Hammond, Boettcher et al. 2001; Parrish and Fire 2001), RNA-dependent RNA polymerases (e.g. RRF-1) and putative RNA helicases (e.g. DRH-1) (Tabara, Sarkissian et al. 1999). To better understand worm RDVI, we have recently performed a genetic screen aiming to isolate novel host factors in the RDVI pathway. RSD-2 is one of our top candidates whose function in RDVI has been confirmed using corresponding genetic mutants in this study. RSD-2 is a novel protein that is not conserved in fungi, plants, insects or vertebrates (Tijsterman and Plasterk 2004). When the level of viral replication was accessed in double mutants that contain both the rsd-2 null allele and null allele corresponding to rde-1, rde-4 or drh-1, enhanced viral replication, as compared to respective single mutants, was observed. Since viRNAs can be readily detected in double mutants corresponding to rde-4;rsd-2, these observations together suggested that RSD-2 functions in a RDE-4-independent pathway for virus silencing. Since RSD-2 appears to be unique to the nematode kingdom, our study on the function and mechanism of RSD-2 may help reveal some unique features of the worm RDVI.



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Committee Chair

Lu, Rui