Researchers solve piece of large-scale gene silenci...(-- DNA methylation which adds chemical f...)

Date:12/4/2008

-- DNA methylation, which adds chemical flags to genes, and histone modification, which alters the proteins that act as spools for DNA. The chemical inhibitors of silencing turned on the previously unexpressed set of parental genes, thereby demonstrated that the underlying mechanism of nucleolar dominance turns genes off, not on.

Since then, Pikaard and his collaborators have been working to disentangle the complex machinery behind this epigenetic on-off switch.

Using RNA to fight RNA

To determine the pathway regulating nucleolar dominance, Pikaard's team exploited a naturally occurring cellular mechanism known as RNA interference (RNAi).

Pikaard likens RNAi to a "search and destroy mission." Fragments of RNA known as small interfering RNAs (siRNAs) prevent specific genes from being expressed by guiding cleavage of matching RNA strands. Once these RNA strands are cut into smaller pieces, they can no longer be translated into proteins. RNAi has high specificity because the target RNA strand must have a genetic code that is complementary to the siRNA's nucleotide sequence.

In nature, cells use RNAi to silence "junk DNA," noncoding regions of the DNA, and "selfish DNA" such as virus-derived retrotransposons (jumping genes) that can be detrimental if activated.

In the lab, Pikaard and his collaborators use RNAi to "knockdown" expression of target genes.

Using a hybrid of two species of Arabidopsis, the plant version of a lab rat, Pikaard's team knocked down expression of genes coding for products that prior research had suggested might be involved in silencing. By knocking these suspects down one by one and assessing whether nucleolar dominance had been disrupted after each knockdown, Pikaard and his collaborators were able to determine which proteins and RNAs were necessary to keep the silenced parental genes off.

New clues

The RNAi knockdowns identified several ne
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Contact: Craig Pikaard pikaard@wustl.edu 314-935-7569 Washington University in St. Louis Source:Eurekalert

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