Vertebrate animal models unravel physiological roles for zonula occludens tight junction adaptor proteins.

Tight junctions (TJs) contribute to the maintenance of epithelial cell polarity and endothelial and epithelial barrier functions. Structurally, TJs are composed of integral membrane proteins, which are tethered to the actin cytoskeleton through adaptor or scaffolding proteins. Three related members of the membrane associated guanylate kinase (MAGUK) protein family--ZO-1, ZO-2, and ZO-3--have been extensively studied in cell culture systems, yet their relevance to TJ structure and function have only recently started to be elucidated. Vertebrate animal models--in particular, mouse and zebrafish--have contributed to the unraveling of the physiological importance of these proteins in vivo. Here we discuss recent findings on the importance of ZO-2 in mouse development and the role of ZO-3 in barrier function of the skin of zebrafish embryos.