RNAi-dependent formation of heterochromatin and its diverse functions

Expression profiling of eukaryotic genomes has revealed widespread transcription outside the confines of protein-coding genes, leading to production of antisense and non-coding RNAs (ncRNAs). Studies in Schizosaccharomyces pombe and multicellular organisms suggest that transcription and ncRNAs provide a framework for the assembly of heterochromatin, which has been linked to various chromosomal processes. In addition to gene regulation, heterochromatin is crucial for centromere function, cell fate determination as well as transcriptional and posttranscriptional silencing of repetitive DNA elements. Recently, heterochromatin factors have been shown to suppress antisense RNAs at euchromatic loci. These findings define conserved pathways that probably have major impact on the epigenetic regulation of eukaryotic genomes.