Introduction of foreign nucleic acids into an organism induces frequently silencing of the homologous sequences. In some cases silencing is the result of a repression of transcription (transcriptional gene silencing or TGS). In other cases the silenced genes are transcribed but transcripts are nearly undetectable (post-transcriptional gene silencing or PIGS). Recent work has focused attention on double stranded RNA as a trigger for both TGS and PIGS (RNA silencing). So far RNA-mediated TGS has only been reported in plants, but PTGS-related phenomena have been described in plants, fungi and animals. Some results indicate that RNA silencing is a host defence system protecting organisms against parasitic sequences such as transposable elements and viruses. Given the importance of these sequences in the genomes, the elucidation of the mechanisms involved in their taming is a challenging question. One of the most exciting aspects of PIGS is that it seems that one common mechanism acts in diverse organisms, maybe in all eukaryotes, indicating that they are very important processes. The possibility that RNA-induced genome modifications (methylation, chromatin structure) are common to eukaryotes is still an open question, but the increasing detection of non-coding or antisense RNAs in epigenetic phenomena involving DNA or chromatin modifications (sex chromosome dosage compensation, imprinting) suggests widespread occurrence. The participants to this network have decided to join their efforts to elucidate by a combination of genetic and biochemical approaches the mechanisms underlying PTGS and RNA-mediated TGS in a variety of organisms (plants, fungi and animals), to determine the relationships between these two types silencing, the similarities and differences in the mechanisms of RNA silencing in various kingdoms and how they may be responsible for the protection of eukaryotes against the propagation of transposable elements and viruses.
Funding SchemeNET - Research network contracts
3584 CT Utrecht
NR4 7UH Norwich
EH9 3Jr Edinburgh