In vivo imaging of EVs in zebrafish: New perspectives from "the waterside"

Abstract

To harmoniously coordinate the activities of all its different cell types, a multicellular organism critically depends on intercellular communication. One recently discovered mode of intercellular cross-talk is based on the exchange of "extracellular vesicles" (EVs). EVs are nano-sized heterogeneous lipid bilayer vesicles enriched in a variety of biomolecules that mediate short- and long-distance communication between different cells, and between cells and their environment. Numerous studies have demonstrated important aspects pertaining to the dynamics of their release, their uptake, and sub-cellular fate and roles in vitro. However, to demonstrate these and other aspects of EV biology in a relevant, fully physiological context in vivo remains challenging. In this review we analyze the state of the art of EV imaging in vivo, focusing in particular on zebrafish as a promising model to visualize, study, and characterize endogenous EVs in real-time and expand our understanding of EV biology at cellular and systems level.

Keywords: exosomes; extracellular vesicles; homeostasis; live‐imaging; zebrafish.

FIGURE 1

EV sub‐populations released by a single cell, with their respective diameters. EV, extracellular vesicles; MVB, multivesicular body; N, nucleus

FIGURE 2

Zebrafish (ZF) embryos as comprehensive model to investigate EV‐biology in vivo. Live‐imaging of genetically labelled endogenous EVs in the ZF embryo allows to (1) study their release by producing cells, (2) follow their journey in the bloodstream and interstitial compartments, (3) follow their uptake by their natural targets and (4) characterize their intracellular fate. EV, extracellular vesicles

FIGURE 3

Visualization and mapping of the endogenous “inter organ EV‐interactome” in the ZF embryo. Tissue‐specific expression of EV (‐subpopulation) reporter‐proteins as well as cargo‐transfer reporter systems could help unravel EV‐mediated communication pathways existing between different tissues and organs. EV, extracellular vesicles; ZF, zebrafish

FIGURE 4

Options to interfere with endogenous EV biology in vivo. To better understand and pinpoint the (patho) physiological roles of endogenous EVs in vivo, various developments are necessary. (Upper half) Hypothetical model of the various steps during the normal life‐span of endogenous EVs in vivo. (Lower half) Opportunities to interfere. (1) Spatial‐ and/or temporal modulation of EV secretion. (2) Modulation of the natural “default” EVs trajectory toward a different, ectopic target. (3) Genetic control of endocytosis and of the intracellular fate in recipient cells. EV, extracellular vesicles