RNAi-mediated gene silencing in fishes?

The recent discovery that small regulatory RNAs have diverse roles in eukaryotic intracellular life, such as fine tuners of endogenous gene expression, as inhibitors of viral replication and as suppressors of transposon activity, is now widely recognized as a major breakthrough in the understanding of cellular biology. The pathways used by these small RNAs seem to build upon a few central mechanisms in which small double-stranded RNAs (dsRNAs) are generated from various precursor RNAs of exogenous or endogenous origin and used for inhibiting expression of genes with sequence complementarity to the small RNA. In particular, one class of small gene-regulatory RNAs, known as small interfering RNAs (siRNAs), has the potential for highly specific gene silencing. These are c. 21 nucleotide perfectly complementary dsRNAs with 3′ end overhangs. They are produced by cleavage of long dsRNA believed to be of viral origin. Subsequently, a large cytoplasmic protein complex known as the RNA-induced silencing complex (RISC) uses the antisense strand of the siRNAs for targeting complementary mRNA strands followed by cleavage of these transcripts in the mechanism called RNA interference (RNAi). Accordingly, synthetic siRNAs may have a potential for treating diseases caused by intracellular pathogens like viruses by specifically targeting the expression of their molecular components. Furthermore, as target sequences need not be of viral origin, siRNAs hold a promise for the treatment of various cellular diseases and as a tool in reverse genetic studies. SiRNAs are currently exploited for such purposes in diverse organisms ranging from plants and invertebrates to human beings. But due to initial difficulties, when using RNAi for gene silencing in fishes, only a few such studies have been conducted in fishes. The purpose of this review is to inspire further experimental work.