Environmental Exosomes/Small Extracellular Vesicles: Evidence of Extracellular RNA Release by Aquatic Organisms

Aquatic organisms continuously interact with surrounding water, yet whether they release extracellular vesicles into this vast medium remains unknown. We hypothesized that pearl oysters (Pinctada fucata) release exosomes/small extracellular vesicles (sEVs) into the aquatic environment. To this end, we collected exosome/sEV-sized components by ultrafiltration from tank water and open-sea culture areas. Microscopy revealed abundant vesicles consistent with exosome/sEV size, and small RNA sequencing identified pearl oyster-specific PIWI-interacting RNAs (piRNAs) that matched sequences previously detected in hemolymph exosomes. These findings demonstrate that pearl oysters actively released exosomes containing species-specific nucleic acids into surrounding water, effectively protecting the RNA from rapid degradation. We propose referring to these vesicles as environmental exosomes/environmental sEVs (eExosomes/esEVs). These findings suggest that aquatic exosomes/sEVs serve as carriers of RNA and may contribute to inter-organismal communication networks. Beyond their functional role, eExosomes/esEVs also hold promise as highly stable, novel targets for environmental DNA/RNA (eDNA/eRNA) analysis, offering new opportunities for ecological monitoring and biodiversity research.