Humans and other animals carry rogue sequences of DNA in their genomes called transposable elements (TEs). To prevent passing TEs to their offspring, they employ the piRNA pathway in their reproductive organs to block the elements from being active in their sperm and eggs. With a new study in flies, Brown University biologists are the first to show that the anti-TE activity of the piRNA pathway also operates in a normal non-reproductive body tissue, the fly fat body, and that it helps to sustain the life of the animal. "It's required for normal health and longevity," said Dr. Stephen Helfand, senior author of the study in Nature Communications and a Professor of Biology at Brown University. The open-access article is titled “A Somatic piRNA Pathway in the Drosophila Fat Body Ensures Metabolic Homeostasis and Normal Lifespan. Most previous reports of piRNA at work outside of reproductive organs were in cancer or stem cells, with one study suggesting it may also be present in a subset of adult fly neurons, but no one had ever measured its consequences in normal health and aging. In experiments led by Brown graduate student Brian Jones, the research team tracked several components of the pathway, such as the presence of piRNAs and the expression of associated "piwi" and "flamenco" genes, in the fat body tissue of flies. The fat body is akin to adipose and liver tissues in mammals and also contributes to flies' immune systems. Once the researchers confirmed that the piRNA pathway was active in a normal, mature body tissue, they conducted several experiments to see what happened in the flies when they knocked out components of the pathway. For example, with the piwi gene gone, flies had significantly fewer piRNAs than flies who had a copy.
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