Extracellular vesicles mediate stem cell signaling and systemic RNAi in planarians

Planarian flatworms are known for their remarkable regenerative capacity; however, the precise intercellular communication mechanisms underlying this process remain unsolved. Here, we report the discovery and characterization of abundant extracellular vesicles (EVs) in planarians. Using imaging and molecular analysis, we show conservation of biogenesis, morphology, and protein composition of planarian EVs. Environmental stressors significantly elevate EV release, indicating that planarians dynamically regulate vesicle production. Functionally, planarian EVs mediate intercellular communication by transferring regulatory signals: We find that they shuttle small RNAs that effect systemic RNA interference (RNAi) throughout the organism. Notably, gene knockdown experiments reveal a crucial role for AGO-3, a member of the Argonaute family of proteins, in modulating the association of small interfering RNAs with EVs, linking the intracellular RNAi machinery to EV-based signaling. These findings highlight EVs as pivotal mediators of cell-cell communication in planarians, with broad implications for understanding the coordination of gene regulation and tissue regeneration in animals.