RNAa

Small double-stranded RNA (dsRNA) has been found to silence gene expression by an evolutionally conserved mechanism known as RNA interference or RNAi. Such dsRNAs are called small interfering RNAs or siRNA. RNAi can occur at both transcriptional and post-transcriptional levels. Surprisingly, two recent studies have found that dsRNA can also activate gene expression, a mechanism that has been termed "small RNA-induced gene activation" or RNAa. It has been shown that dsRNAs targeting gene promoters induce potent transcriptional activation of associated genes. Both studies demonstrate RNAa in human cells using synthetic dsRNAs termed small activating RNAs (saRNAs). Endogenous miRNA that cause RNAa has also been found in humans. It is currently unknown if RNAa is conserved in other organisms.

Another surprising observation is that gene activation by RNAa is long-lasting. Induction of gene expression has been seen to last for over ten days. The prolonged effect of RNAa could be attributed to epigenetic changes at dsRNA target sites.