text: For more than 20 years, microRNAs have been known to act in the cytoplasm to degrade transcriptional expression of specific target gene messenger RNAs (see microRNA history).  However, recently, Gagnon et al. showed that as many as 75% of microRNAs may be shuttled back into the nucleus of cells.  Some nuclear microRNAs have been shown to mediate transcriptional gene activation or transcriptional gene inhibition.