Studying the Fate of Tumor Extracellular Vesicles at High Spatiotemporal Resolution Using the Zebrafish Embryo

Tumor extracellular vesicles (EVs) mediate the communication between tumor and stromal cells mostly to the benefit of tumor progression. Notably, tumor EVs travel in the bloodstream, reach distant organs, and locally modify the microenvironment. However, visualizing these events in vivo still faces major hurdles. Here, we describe an approach for tracking circulating tumor EVs in a living organism: we combine chemical and genetically encoded probes with the zebrafish embryo as an animal model. We provide a first description of tumor EVs’ hemodynamic behavior and document their intravascular arrest. We show that circulating tumor EVs are rapidly taken up by endothelial cells and blood patrolling macrophages and subsequently stored in degradative compartments. Finally, we demonstrate that tumor EVs activate macrophages and promote metastatic outgrowth. Overall, our study proves the usefulness and prospects of zebrafish embryo to track tumor EVs and dissect their role in metastatic niches formation in vivo. [Display omitted] •MemBright allows for bright and specific staining of EVs•The zebrafish embryo allows tracking of tumor EVs at high spatiotemporal resolution•Circulating tumor EVs are mostly taken up by endothelial cells and patrolling macrophages•Zebrafish melanoma EVs favor metastatic outgrowth in zebrafish embryos Tumor extracellular vesicles (EVs) promote tumor progression. However, their behavior in body fluids remains mysterious. Hyenne et al. show that the zebrafish embryo can be used to track and assess the function of circulating tumor EVs in vivo and provide a high-resolution description of their dissemination and uptake.