MicroRNAs control gene expression in a single-celled alga, reports a paper in this week's Nature. The finding suggests that microRNAs evolved earlier than previously thought, according to the authors. "This is a very important result," said Scott Poethig of the University of Pennsylvania in Philadelphia, who wasn't an author on the paper. "This is the first single-celled organism in which microRNAs have been discovered."A recent paper in Genes and Development also reported finding microRNAs in the same alga.Previous studies have found short interfering RNAs (siRNAs) in unicellular organisms, but not microRNAs, according to David Baulcombe of the Sainsbury Laboratory in Norwich, UK, senior author of the Nature paper. Some researchers have suggested that microRNAs evolved along with multicellularity, "playing a role in that evolution, perhaps independently in plants and animals," Heriberto Cerutti of the University of Nebraska in Lincoln, who was not involved in the work, told...

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