Huljev, K. | bioRxiv Science

bioRxiv2022

Zinc-based Ultrasensitive Microscopic Barrier Assay (ZnUMBA): a live-imaging method for detecting epithelial barrier breaches with spatiotemporal precision

Epithelial barrier function is commonly analyzed using transepithelial electrical resistance (TER), which measures the ion flux across epithelia, or by adding traceable macromolecules to one side of the epithelium and monitoring their passage to the other side. While these methods effectively measure changes to global barrier function, they are not sensitive enough to detect local or transient disruptions in the barrier, and they do not reveal the location of barrier breaches within the context of cell or tissue morphology. Therefore, we developed a method that we named Zinc-based Ultrasensitive Microscopic Barrier Assay (ZnUMBA), which overcomes these limitations, allowing for detection of local tight junction (TJ) leaks with high spatial and temporal resolution (Stephenson et al., 2019; Varadarajan et al., 2021). Here, we present expanded applications for ZnUMBA. First, we show that ZnUMBA can be used in Xenopus embryos to measure the dynamics of barrier restoration and actin dynamics following laser injury of the junction. We also demonstrate that ZnUMBA can be effectively utilized in developing zebrafish embryos as well as cultured monolayers of Madin-Darby Canine Kidney II (MDCK II) epithelial cells. ZnUMBA is a powerful and flexible method that, with some optimization, can be applied to multiple systems to measure dynamic changes in barrier function with spatiotemporal precision.

cell biology↗

bioRxiv2020

Tension-dependent stabilization of E-cadherin limits cell-cell contact expansion

Tension of the actomyosin cell cortex plays a key role in determining cell-cell contact growth and size. The level of cortical tension outside of the cell-cell contact, when pulling at the contact edge, scales with the total size to which a cell-cell contact can grow1,2. Here we show in zebrafish primary germ layer progenitor cells that this monotonic relationship only applies to a narrow range of cortical tension increase, and that above a critical threshold, contact size inversely scales with cortical tension. This switch from cortical tension increasing to decreasing progenitor cell-cell contact size is caused by cortical tension promoting E-cadherin anchoring to the actomyosin cytoskeleton, thereby increasing clustering and stability of E-cadherin at the contact. Once tension-mediated E-cadherin stabilization at the contact exceeds a critical threshold level, the rate by which the contact expands in response to pulling forces from the cortex sharply drops, leading to smaller contacts at physiologically relevant timescales of contact formation. Thus, the activity of cortical tension in expanding cell-cell contact size is limited by tension stabilizing E-cadherin-actin complexes at the contact.

cell biology↗