The Role of RNAi and Noncoding RNAs in Polycomb Mediated Control of Gene Expression and Genomic Programming
Manuela Portoso and Giacomo Cavalli
from: RNA and the Regulation of Gene Expression: A Hidden Layer of Complexity (Edited by: Kevin V. Morris). Caister Academic Press, U.K. (2008)
Regulation of gene expression is a complex, multi-layered process that is crucial to correctly drive and maintain cell identity during development and adult life. In this chapter, we discuss the functional and molecular links between two well-conserved gene silencing pathways, RNA interference (RNAi) and Polycomb. RNAi participates in post transcriptional as well as transcriptional gene silencing of natural genes as well as transposons and viruses. Polycomb group (PcG) proteins are well-known for their role in silencing HOX genes through modulation of chromatin structure. However, both mechanisms were found to be involved in specific epigenetic processes like cosuppression in Drosophila melanogaster and the formation of C elegans mes and SOP-2 complexes. Recent work has uncovered molecular links between RNAi components and Polycomb-mediated silencing in human cells and Drosophila. RNA polymerase II and Argonaute 1 interact to bring about chromatin modifications on endogenous Polycomb target gene promoters in human cells, while Drosophila RNAi components modulate the nuclear organization of PcG target DNA elements, thereby affecting the strength of PcG-mediated silencing. Finally, we discuss the findings of several microRNAs and non coding RNAs in human and fly HOX gene loci, where they may regulate HOX gene expression both post-trascriptionally and co-transcriptionally read more ...