SUBCELLULAR-DISTRIBUTION OF TIGHT JUNCTION-ASSOCIATED PROTEINS (OCCLUDIN, ZO-1, ZO-2) IN RODENT SKIN

Occludin is an integral membrane protein that is concentrated at tight junctions (zonulae occludentes) in simple epithelial cells. ZO-1 and ZO-2 are peripheral membrane proteins that are localized at tight junc tions in simple epithelial cells and at cadherin-based adherens juncti ons in nonepithelial cells. In this study, we investigated the express ion and subcellular distribution of occludin, ZO-1, and ZO-2 in rodent skin. Immunoblotting detected all of these molecules in isolated epid ermis, but the occludin/ZO-1 (or occludin/ZO-2) ratio was significantl y lower than that in cultured simple epithelial cells. In the epidermi s of adult skin, occludin was concentrated at cell-cell borders only i n the most superficial zone of the granular cell layer, whereas ZO-1 a nd ZO-2 were distributed in a much broader zone from the spinous to th e granular layers. During mouse skin development, this peculiar distri bution of occludin in the epidermis appeared when the periderm, a simp le epithelium bearing typical occludin-based tight junctions, was slou ghed off at embryonic day 16.5 of gestation. Freeze-fracture electron microscopy identified the so-called focal strands or maculae occludent es, i.e., spot tight junction-like structures, between adjacent granul ar cells, and anti-occludin monoclonal antibody exclusively labeled th ese focal strands. In hair follicles, occludin and ZO-1 were colocaliz ed at cell-cell borders in Henle's layer and the cornifying cuticle of the inner root sheath. In addition, ZO-1 but not occludin were locali zed weakly at the outer root sheath and intensely at the hair cortex/m atrix.