Live tracking of inter-organ communication by endogenous exosomes in vivo

SUMMARY Extracellular vesicles (EVs) are released by most cell types but the definitive demonstration of their functional relevance remains challenging due to the lack of appropriate model organisms. Here we developed an in vivo model to study EV physiology by expressing CD63-pHluorin in zebrafish embryos. A combination of microscopy techniques and proteomic analysis allowed us to study the biogenesis, composition, transfer, uptake and fate of individual endogenous EVs in vivo . We identified an exosome population released in a syntenin-dependent manner from the Yolk Syncytial Layer into the blood circulation. These exosomes were specifically captured, endocytosed and degraded by patrolling macrophages and endothelial cells in the Caudal Vein Plexus (CVP) in a scavenger receptor and dynamin-dependent manner. Interference with exosome secretion affected CVP growth, supporting their trophic role. Altogether, our work provides a unique model to track in vivo inter-organ communication by endogenous exosomes at individual vesicle level and high spatio-temporal accuracy. Highlights - Single endogenous EVs can be live-visualized in the whole embryo with CD63-pHluorin - In the YSL, syntenin regulates exosome release into the blood for their propagation - YSL exosomes reach the tail to be taken up by macrophages and endothelial cells - Uptake is scavenger receptor and dynamin-dependent and provides trophic support Blurb We propose zebrafish embryos expressing a fluorescent reporter for exosomes as a relevant model organism to live-track production, journey and fate of individual extracellular vesicles in vivo. Our model allows investigation of the composition of EVs and the molecular mechanisms controlling their biogenesis and fate and functions in receiving cells.