WORCESTER, MA Organisms employ a fascinating array of strategies to identify and restrain invasive pieces of foreign DNA, such as those introduced by viruses. For example, many viruses produce double-stranded (ds)RNA during their life cycle and the RNA interference (RNAi) mechanism is thought to recognize this structural feature to initiate a silencing response.
Now, UMass Medical School researchers have identified a mechanism related to RNAi that scans for intruders not by recognizing dsRNA or some other aberrant feature of the foreign sequence, but rather by comparing the foreign sequences to a memory of previously expressed native RNA. Once identified, an "epigenetic memory" of the foreign DNA fragments is created and can be passed on from one generation to the next, permanently silencing the gene.
A remarkable feature of this RNAi-related phenomenon (referred to as RNA-induced epigenetic silencing, or RNAe), is that the animal carries a memory of previous gene expression. This memory of active genes serves as an "anti-silencing" signal, which protects native genes from RNAe and under some circumstances appears to adopt foreign genes as self. These findings, described in three studies (including a study by Eric Miska and colleagues of the Gurdon Institute, University of Cambridge and Wellcome Trust, UK) published online yesterday and to appear in the July 6 issue of Cell, provide new insights into how identical organisms can have the same DNA sequence but opposite patterns of gene expression and thus dramatically different phenotypes.
"If a worm modulates gene expression by carrying a memory of the genes it expressed in previous generations, perhaps other organisms (including humans) can as well. If so, mechanisms of this type could have an important impact on evolution," said Craig C. Mello, PhD, Howard Hughes Medical Institute Investigator, Blais University Chair in Molecular Medicine and distinguished professor of mole
|Contact: Jim Fessenden|
University of Massachusetts Medical School