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. RNA interference (RNAi) and the Polycomb system are two well-conserved gene silencing pathways. 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. Both mechanisms are involved in specific epigenetic processes like cosuppression in Drosophila melanogaster and the formation of C. elegans mes and SOP-2 complexes. There are molecular links between RNAi components and Polycomb-mediated silencing in human cells and in 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. Several microRNAs and non coding RNAs have been found in human and fly HOX gene loci. They may regulate HOX gene expression both post-trascriptionally and co-transcriptionally.

from Portoso and Cavalli in RNA and the Regulation of Gene Expression (Chapter 3)

Labels: Drosophila, epigenetics, polycomb, regulation, RNA, RNAi