Table 1.

Claudin-1, -3, -4, -5 and -7 expression and function in normal tissues.

Claudin	Function	Tissue specificity	Involvement in disease
Claudin-1	TJ-specific obliteration of the intercellular space through Ca2+-independent cell-adhesion activity. Acts as a co-receptor for HCV entry into hepatic cells	Strongly expressed in liver and kidney. Also expressed in heart, brain, spleen, lung and testis	Ichthyosis [61]
Claudin-3	TJ-specific obliteration of the intercellular space through Ca2+-independent cell-adhesion activity (CPE is the natural ligand)	Strongly expressed in ovary, lung, pancreas, salivary gland, kidney, adrenal, small intestine, colon and thyroid	Williams-Beuren syndrome [62]
Claudin-4	TJ-specific obliteration of the intercellular space (CPE is the natural ligand)	Strongly expressed in ovary, lung, pancreas, salivary gland, kidney, adrenal, small intestine, colon and thyroid	Williams-Beuren syndrome [62]
Claudin-5	Target molecule of hypoxia	Strongly expressed in vascular endothelial cells. Transiently expressed during development of RPE. Expressed in lung	Velocardiofacial syndrome [63]
Claudin-7	TJ-specific obliteration of the intercellular space. Co-localizes with EPCAM at the lateral cell membrane and TJ	Strongly expressed in kidney, GI tract, thyroid, adrenal gland and lung. Also expressed in prostate tissue	Related to ability of breast cancer cells to disseminate. Downregulation correlates with histological grade [57]