This website was created as a project for Genetics 677, an undergraduate course at UW Madison.
RNA interference (RNAi)
RNAi is a mechanism found naturally within cells that regulates gene expression. The RNAi phenomenon was discovered in 1998 by Andrew Fire and Craig Mello, and has since become a valuable tool for understanding gene function. RNAi works by knocking down gene expression via double-stranded RNA that activates an enzyme called Dicer (in humans called DICER1). Dicer cleaves the double-stranded RNA into shorter fragments which are called small-interfering RNAs (siRNAs). The siRNA then separates into short, single-stranded RNA that binds to the complementary mRNA sequence, also triggering the formation of an RNA-induced silencing complex (RISC). If the siRNA is partially homologous to the target mRNA, RISC will bind and prevent translation of the peptide and therefore inhibit the formation of the protein encoded by the gene. In instances where the siRNA is perfectly homologous to the target mRNA, the RISC complex will bind and cleave the mRNA, destroying the message. It is important to understand that in order for researchers to use RNAi as a genetic tool, the DNA sequence of a gene must be known in order to create the target complementary RNA sequence. Additionally, because the siRNA binds to mRNA, the initial DNA sequence of the gene remains intact, preserving any regulatory interactions that could potentially be disrupted by knocking out the gene. The double-stranded RNA can be introduced to the organism by feeding bacteria expressing double-stranded RNA specific to the desired gene of interest, although organisms vary in their ability to uptake foreign double-stranded RNA for use in the RNAi mechanism.
RNAi detection of a WRN orthologue in C. elegans
The gene wrn-1 (F18C5.2) is a C. elegans orthologue (a gene in a different species that evolved from a common ancestral gene via speciation) of the WRN gene found in humans. This gene was located using an RNAi database called WormBase. As in humans, when wrn-1 is mutated in C. elegans, it leads to Werner syndrome. This is significant as it identifies a potential model organism in which to study the disease, as orthologues typically retain the same function during the course of evolution. The use of RNAi suppression could elucidate further information regarding elements within wrn-1 that may be useful in understanding human WRN, although the lower sequence homology in wrn-1 may prove problematic when comparing the two homologs. I was unsuccessful in finding any other RNAi information from Phenobank or the RNAi Database. The following video displays the wild-type phenotype of the wrn-1 gene during cell division in C. elegans.
| C. elegans ortholog phenotype |
A larger video can be viewed here.
References
1. Representative phenotype recording [video on the internet]. Cenix bioscience, MPI-CPG, editor; Cenix Bioscience, MPI-CBG, producer. : Phenobank: gene view F18C5.2; 2009 September [cited 2010 Feb 25]; 33 sec. Available from http://www.worm.mpi-cbg.de/phenobank2/cgi-bin/GenePage.py?GeneID=478
2. Representative phenotype recording [video on the internet]. Cenix bioscience, MPI-CPG, editor; Cenix Bioscience, MPI-CBG, producer. : Phenobank: gene view F18C5.2; 2009 September [cited 2010 Feb 25]; 33 sec. Available from http://worm-srv3.mpi-cbg.de/ceimages/204/204-c12-1-d5-5.mov
3. Fire A, Xu S, Montgomery M, Kostas S, Driver S, Mello C (1998). "Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans". Nature 391 (6669): 806–11. doi:10.1038/35888. PMID 9486653
2. Representative phenotype recording [video on the internet]. Cenix bioscience, MPI-CPG, editor; Cenix Bioscience, MPI-CBG, producer. : Phenobank: gene view F18C5.2; 2009 September [cited 2010 Feb 25]; 33 sec. Available from http://worm-srv3.mpi-cbg.de/ceimages/204/204-c12-1-d5-5.mov
3. Fire A, Xu S, Montgomery M, Kostas S, Driver S, Mello C (1998). "Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans". Nature 391 (6669): 806–11. doi:10.1038/35888. PMID 9486653
