Localization of occludin, ZO-1, and pan-cadherin in rabbit ciliary epithelium and iris vascular endothelium

Previous studies have used conventional electron microscopy and freeze frac ture to identify the morphological equivalents of the blood-aqueous barrier in the mammalian eye. These equivalents are the tight junctions that form a part of the apicolateral junctional complex between adjacent non-pigmente d ciliary epithelial cells and the tight junctions present between endothel ial cells of the iris vasculature. Recent investigations have begun to unra vel the molecular assembly of the tight junction and some variability has b een found. Our goal in the present study was to probe the ciliary epitheliu m and iris vascular endothelium of the rabbit eye to determine if certain m olecular constituents associated with tight junctions in other tissues are also present as parts of the blood-aqueous barrier. The selected constituen ts were occludin, ZO-1, and a representative, adherens junction-related cad herin. Immunohistochemical and immunoelectron microscopic methods were used . The results showed that occludin was distributed exclusively at known loc ations of tight junctions. ZO-1 was also expressed at these locations but i ts distribution extended beyond that of occludin, along the adjacent membra nes. Pan-cadherin was expressed ubiquitously within the ciliary epithelium and negligibly in iris vascular endothelium. Our results demonstrate that o ccludin and ZO-1 are integral components of the blood-aqueous barrier of th e normal rabbit eye.