DEVELOPMENT OF THE BLOOD-RETINAL BARRIER IN-VITRO - FORMATION OF TIGHT JUNCTIONS AS REVEALED BY OCCLUDIN AND ZO-1 CORRELATES WITH THE BARRIER FUNCTION OF CHICK RETINAL-PIGMENT EPITHELIAL-CELLS

To elucidate the molecular mechanisms of the blood-retinal barrier (BR B), we examined chick retinal tissues histochemically using antibodies against tight junction proteins such as ZO-1, 7H6 antigen, and occlud in. Retinal pigment epithelial (RPE) cells in situ in chickens and lat e chick embryos expressed all of the tight junctional proteins examine d, showing that tight junctions seal the cell borders of chick RPE cel ls in vivo. On the other hand, RPE cells isolated from late chick embr yos and transferred in vitro did not express occludin, ZO-1 and 7H6 an tigen. The effects of differentiation-inducing agents, such as retinoi c acid, dexamethasone and dimethyl sulfoxide (DMSO) were tested. Only DMSO induced an increase in transepithelial electrical resistance (TER ) in a time-dependent manner. Under supplementation with DMSO, immunof luorescently demonstrable occludin and ZO-1 were induced progressively at cell borders in parallel with the increase in TER that occurred wi th decreases in inulin and dextran permeability. Electron microscopica lly tight junction-like junctional apparatus were induced in RPE cells . These results indicated that tight junctions of RPE cells play an im portant role in the formation of the BRB. (C) 1995 Academic Press Limi ted