Occludin and claudins in tight-junction strands: leading or supporting players?

Tight junctions have attracted much interest from cell biologists, especially electron microscopists, since on freeze-fracture electron microscopy they appear as a well-developed network of continuous, anastomosing intramembranous strands (tight-junction strands). These strands might be directly involved in the 'barrier' as well as 'fence' functions in epithelial and endothelial cell sheets, hut until recently little war; known of their constituents. This review discusses current understanding of the molecular architecture of tight-junction strands, focusing on the recent discovery of two distinct types of tight-junction-specific integral membrane proteins, occludin and claudins.