The cellular mechanics of gene silencing by RNAi was largely misunderstood or even unknown until the work of Andrew Fire and Craig Mello with the nematode Caenorhabditis elegans [5]. RNAi regulates gene expression through small noncoding RNAs (sRNAs). The sRNAs of ~21–25 bp long dsRNA molecules have ~2 nt 3′ overhangs that allow them to be recognized by enzymes from the RNAi machinery, which subsequently leads to homology-dependent degradation of target mRNA. There are two primary classes for sRNAs in the RNAi pathway, the micro-RNAs (miRNAs) and the short-interfering RNAs (siRNAs).