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 fracture 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-pigmented ciliary epithelial cells and the tight junctions present between endothelial cells of the iris vasculature. Recent investigations have begun to unravel the molecular assembly of the tight junction and some variability has been found. Our goal in the present study was to probe the ciliary epithelium and iris vascular endothelium of the rabbit eye to determine if certain molecular constituents associated with tight junctions in other tissues are also present as parts of the blood-aqueous barrier. The selected constituents were occludin, ZO-1, and a representative, adherens junction-related cadherin. Immunohistochemical and immunoelectron microscopic methods were used. The results showed that occludin was distributed exclusively at known locations of tight junctions. ZO-1 was also expressed at these locations but its distribution extended beyond that of occludin, along the adjacent membranes. Pan-cadherin was expressed ubiquitously within the ciliary epithelium and negligibly in iris vascular endothelium. Our results demonstrate that occludin and ZO-1 are integral components of the blood-aqueous barrier of the normal rabbit eye.