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.
Yonezawa et al. (Sat,) studied this question.