A substantial and growing body of evidence highlights extracellular vesicles as critical components in cell-to-cell communication pathways. The visualization of EVs is fundamental to our understanding of the role of EVs in all aspects of cellular transmission; from the packaging of signaling molecules and nucleic acids during vesicle biogenesis, to tracking of their uptake and fate after internalization within selected target cells or tissues.
Challenges in Visualizing Extracellular Vesicles
Extracellular vesicles originating from different cells or tissues are destined for specific target sites where they carry out particular functions. As EVs vary greatly in both size and protein content, it is believed that the presence of specific biomarkers (including tetraspanins, integrins and other proteins) on different sub-groups of EVs may be the root cause of this selectivity (Lyden et al 2015). However, characterizing these biomarkers on individual EVs poses a significant challenge to researchers in the field.
While electron microscopy techniques have the capability to resolve individual EVs, they do not easily allow detection of multiple markers at the same time, and are limited to fixed cells. With conventional light microscopy techniques, a number of proteins can be labeled but the small size of EVs means that the majority fall well below the resolution limit of light microscopy, restricting the usefulness of these techniques in identifying different sub-populations of vesicles.
Super-resolution for Extracellular Vesicle characterization
Super-resolution microscopy surpasses the resolution barrier of conventional light microscopes and enables detection and quantification of single proteins and nucleic acids at the sub-vesicular level. Furthermore, the structural composition of vesicle membranes can be reconstructed with single-molecule localization microscopy (SMLM) reaching 20 nm resolution and can be used to identify the specific biomolecules involved in EV signalling and targeting.
The application of super-resolution imaging techniques has high value in identifying and visualizing sub-populations of EVs and may additionally provide important information into the role EVs play in disease progression. Read more about visualizing extracellular vesicles