Claudins are a family of proteins that control the flow of molecules in the intercellular space between epithelial cells. They are the most important components of tight junctions—a type of cell-to-cell adhesion that forms continuous seals around cells. Tight junctions act as a physical barrier to prevent solutes and water from passing freely through the paracellular space. Claudins have four transmembrane domains, with the N-terminus and the C-terminus in the cytoplasm. Over 24 members of the claudin family have been identified in humans. In mouse, claudin-1, -2, -6, -7, and -15 are expressed at high levels in liver and kidney, while claudin-5 is expressed in vascular endothelial cells.
Claudin-1 is also known as CLD1, senescence-associated epithelial membrane protein 1 (SEMP1), and ILVASC. Knockout mice lacking claudin-2 show defects in the leaky and cation-selective paracellular permeability properties of renal proximal tubules.
Claudin-2 is also critical for vitamin D-dependent Ca2+ absorption between enterocytes. Claudin-2 is also known as SP82 and AL022813.
Knockout mice lacking the CLDN5 gene have a lethal disruption of the blood-brain barrier. Claudin-5 is expressed at high levels in normal lung endothelium and plays a regulatory role in acrolein-induced acute lung injury. Claudin-5 is also known as MBEC1, BEC1, CPETRL1, transmembrane protein deleted in velocardiofacial syndrome (Tmvcf), AWAL, and AI854493.
Claudin-6 is essential for blastocyst formation in preimplantation mouse embryos, and for the formation and maintenance of the epidermal permeability barrier. It is also known as skullin and AL024037. Claudin-6 has been identified as a novel diagnostic marker for primitive germ cell tumors and other tumors with primitive phenotypes. Expression of claudin-6 protein is significantly down-regulated in breast invasive ductal carcinomas.
Differential expression of the human CLDN7 gene has been associated with breast cancer, ovarian cancer, hepatocellular carcinomas, urinary tumors, prostate cancer, lung cancer, head and neck cancers, and thyroid cancer. Claudin-7 is expressed constitutively in the mammary epithelium throughout development, and is essential for NaCl homeostasis in distal nephrons. It is also known as clostridium perfringens enterotoxin receptor-like 2 (CPETRL2) and CEPTRL2.
Differential expression of the human CLDN8 gene has been associated with colorectal carcinoma and renal cell tumors. Claudin-8 is an immunohistochemical marker for the differential diagnosis of chromophobe renal cell carcinoma and renal oncocytoma. It is also known as AI648025.
The human CLDN12 gene is expressed in the inner ear and bladder epithelium, and is over-expressed in colorectal carcinomas. Claudin-12 is critical for vitamin D-dependent Ca2+ absorption in enterocytes. It is also known as RGD1561053.
Claudin-15 deficiency is associated with decreased intestinal epithelial paracellular ion permeability. The CLDN15 gene is a direct target for hepatocyte-nuclear-factor-4alpha (HNF4-alpha), and CLDN15 expression is downregulated in inflammatory bowel disease. Claudin-15 is also known as BB107105 and 2210009B08Rik.
Antibodies for Claudin Detection
These products are affinity-purified IgG antibodies that recognize claudin protein variants. The antibodies were raised in rabbit using a synthetic peptide, and can be used for Western blot (WB) detection, immunohistochemical (IHC) detection, and immunocytochemical (ICC) detection.