High resolution microscopy reveals claudin-18 as a basolateral and not a tight junction-associated protein in stomach (1111.6)

Background: Claudin-18 (Cldn18) is the most highly expressed tight junction protein in the stomach. Cldn18, however, also localizes to the basolateral membrane of gastric epithelial cells. We aimed to determine whether cldn18 is actually a tight junction protein using high resolution microscopy techniques. Methods: Immunostaining for cldn18 and for ZO-1, a well-established protein that is limited to tight junctions, was done on sections from mouse stomach. Structured illumination microscopy (SIM) was used to examine the high resolution 3-D pattern of cldn18 and ZO-1 localization in parietal and chief cells. Results: 3-D SIM data revealed that cldn18 is solely a basolateral membrane-associated cldn that runs in discontinuous anastomosing bundles along the basolateral membrane (in a basket-like configuration) to completely enclose parietal cells. Although still present, the discontinuous bundles of cldn18 are spaced further apart in chief cells. ZO-1 in parietal cells localizes to a shallow cleft bounded by...