Super-Resolution Imaging of Tight and Adherens Junctions: Challenges and Open Questions

Abstract

The tight junction (TJ) and the adherens junction (AJ) bridge the paracellular cleft of epithelial and endothelial cells. In addition to their role as protective barriers against bacteria and their toxins they maintain ion homeostasis, cell polarity, and mechano-sensing. Their functional loss leads to pathological changes such as tissue inflammation, ion imbalance, and cancer. To better understand the consequences of such malfunctions, the junctional nanoarchitecture is of great importance since it remains so far largely unresolved, mainly because of major difficulties in dynamically imaging these structures at sufficient resolution and with molecular precision. The rapid development of super-resolution imaging techniques ranging from structured illumination microscopy (SIM), stimulated emission depletion (STED) microscopy, and single molecule localization microscopy (SMLM) has now enabled molecular imaging of biological specimens from cells to tissues with nanometer resolution. Here we summarize these techniques and their application to the dissection of the nanoscale molecular architecture of TJs and AJs. We propose that super-resolution imaging together with advances in genome engineering and functional analyses approaches will create a leap in our understanding of the composition, assembly, and function of TJs and AJs at the nanoscale and, thereby, enable a mechanistic understanding of their dysfunction in disease.

The Nanoscopic Organization of Synapse Structures: A Common Basis for Cell Communication

“…To be noted, SRFM has also been widely applied to other cell communication structures, namely epithelial cell junctions such as tight junctions, gap junctions, adherens junctions, desmosomes, and hemidesmosomes [ 145 , 146 , 147 ]. The superior resolution of SFRM techniques has enabled the detection of nanoclusters and subdomains of junction proteins, which could not be revealed with confocal microscopy.…”

An Experimental Workflow for Studying Barrier Integrity, Permeability, and Tight Junction Composition and Localization in a Single Endothelial Cell Monolayer: Proof of Concept

“…Recent advances in single molecule localization microscopy (SMLM) have provided opportunities for a more in-depth assessment of TJ changes with high spatial resolution as recently illustrated in studies involving ZO-1 in human endothelial cells [ 25 ]. This approach allows for the use of monolayers grown in filters after being subjected to TER, dextran leakage measurements, and immunostaining for specific TJ molecules [ 25 , 26 ]. Combining these methods in one experimental setting should circumvent inter-experimental variations and allow for combined analyses of specific TJ expression and localization, functional studies, and single molecule cluster analyses in a matched manner.…”

Evidence from ileum and liver transcriptomes of resistance to high-salt and water-deprivation conditions in camel

“…Cadherins compose a family of cell surface proteins that, using the adherens junction as a basis, participate in cell-cell adhesion, an essential process in tissue morphogenesis and integrity [73]. A previous study reported that adherens junctions form defensive barriers and maintain ion homeostasis, and that their functional deficiency triggers ion imbalance and tissue inflammation [74]. In intestinal epithelium, the selective barrier formed by adherens junction supervises absorption of fluid and solutes [75].…”