Epigenetic regulation of gene expression in human cells by noncoding RNAs.

Emerging evidence has begun to suggest that a vast array of noncoding RNAs is operative in human cells, with some containing the ability to directly modulate gene transcription. While observations of noncoding-RNA-based epigenetic regulation of gene expression were in the past relegated to imprinted or X-linked genes, it is now becoming apparent that several different genes in differentiated cells may be under some form of RNA-based regulatory control. Studies have begun to discern certain aspects of an underlying mechanism of action whereby noncoding RNAs modulate gene transcription. Much of the evidence suggests that noncoding RNAs are functional in controlling gene transcription by the targeted recruitment of epigenetic silencing complexes to homology-containing loci in the genome. The results of these studies, as well as the implications that a vast array of noncoding-RNA-based regulatory networks may be operative in human cells, are discussed. Knowledge of this emerging RNA-based epigenetic regulatory network has implications in cellular evolution as well as in an entirely new area of pharmacopeia.