RNA-Dependent Gene Silencing and Epigenetics in Animals.

In animals noncoding RNAs are involved in a large variety of gene silencing mechanisms. These include post-transcriptional RNA interference (RNAi) that is mediated by small double-stranded RNAs and results in degradation of messenger RNAs as well as epigenetic silencing of genes. RNAi as a naturally occurring silencing mechanism has been well investigated in various eukaryotic organisms. Sequencing of the human and mouse genomes and careful analyses of the related transcriptomes led to the identification of some hundred microRNAs that might regulate endogenous gene expression by RNAi-like mechanisms or repression of translation. In mammals the major protein components of the RNAi machinery have been identified, and RNAi has become a tool for artificial gene silencing in mammalian systems. There is also evidence that in mammalian cells genes can be regulated by noncoding antisense transcripts that are transcribed from the opposite DNA strand. Besides their potential roles in RNAi and repression of translation, short double-stranded RNAs and also long noncoding RNAs are involved in epigenetic gene silencing. In this chapter we give an overview of prominent features of naturally occurring RNAi and also of the potential role of RNAs in epigenetic gene silencing mechanisms in animals, especially in mammals. [ABSTRACT FROM AUTHOR]