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House dust mites are common pests with an unusual evolutionary history. They are tiny, free-living animals that evolved from a parasitic ancestor, which in turn evolved from free-living organisms millions of years ago. A new genetic study suggests that, as a consequence of its tumultuous evolutionary history, the house dust mite developed a novel way to protect its genome from internal disruptions.
All animals and plants face a threat from transposable elements, pieces of non-coding DNA that can change their position in the genome, often causing mutations and disease. Organisms have evolved complex ways to watch for, target and silence transposable elements. In most animals, this surveillance mission is carried out by small RNA fragments that find and break offending genetic sequences. The mechanism is called the piwi-associated RNA pathway -- named for the protein Piwi, first discovered in fruit flies. Researchers found that house dust mites do not have Piwi proteins or the associated small RNAs that most animals use to control transposable elements. Instead, dust mites have replaced the Piwi pathway with a completely different small RNA mechanism that uses small-interfering RNAs.Image credit: G. Bauchan and R. Ochoa
