New Live-Imaging Technique Reveals Rho’s Role in Repair

Epithelial cells are sheets of cells that coat our organs, creating wall-like barriers that protect us from bacteria, viruses, and other disease-causing invaders. And when potentially harmful gaps between these cells emerge, a molecular switch gets flipped to call the repair crew to fix the leaks.

Using a novel live-imaging technique, University of Michigan researchers have achieved the first direct detection of short-lived leaks in epithelial tissues as they occur. The new assay could help provide insights into the mechanisms of diseases that target the epithelial barrier—ailments caused by microbes and allergens, as well as various inflammatory states, immune disorders, diabetes, and even cancers. And the assay could potentially be used to screen drugs to treat those afflictions. The team’s findings were published today in Developmental Cell.

“An important unanswered question about epithelial tissues is: How are the junctions between cells able to maintain the biological barrier function even as cells change shape?” says senior author Ann Miller.

During embryonic development, many epithelial cells work together to bend and fold tissues. Using their new microscopy assay, Zinc-based Ultrasensitive Microscopic Barrier Assay (ZnUMBA), the researchers studied what happens at the cellular level of live frog embryos when epithelial cell–cell junctions are stretched. It turns out that leaks are formed but are short-lived, suggesting that there is an active repair mechanism. Upon further investigation, the researchers discovered that the repair mechanism involves local activation of the protein Rho in a sudden burst of activity they dubbed a “Rho flare.”

“We discovered that cells are normally very proactive when it comes to maintaining the barrier. This repair mechanism happens quickly and is carried out very locally, affecting only a small part of the cell junction, rather than multiple cells or the whole tissue,” says first author Rachel Stephenson. “We think that this proactive approach is what gives our cells the flexibility to move and change shape without compromising the barrier function of the tissue. Diseases involving a leaky barrier might be due to a faulty repair mechanism or the cells’ inability to detect leaks and flip the switch.”

Stephenson and other members of the Miller Lab are now working to determine how the switch gets flipped to turn on Rho at the right time and place and to identify other proteins that are part of the cellular repair crew.