Claudin 5 (CLDN5)

Tight junctions are specialized regions of cell-cell contact that are particularly abundant in luminal epithelial cell sheets. In freeze-fracture electron micrographs, tight junctions are visualized as belt-like bands of anastomosing sealing strands (TJ strands) that completely encircle the lateral surfaces of each cell. TJ strands on adjacent cells are presumed to interact with each other to form a sort of "molecular gasket" that prevents ions, water and other molecules from leaking between cells and thus, from one side of the sheet to the other. In addition to this so-called "barrier" function, the "fence" function of tight junctions plays an important role in maintaining epithelial cell-polarity by blocking the diffusion of membrane proteins between apical (luminal) and basolateral cell surfaces. Confinement of the glucose symport to apical surfaces allows glucose to be transported vectorially from the lumen, through the cell, and into the bloodstream.\n\nSeveral peripheral membrane proteins are associated with tight junctions, including ZO-1, ZO-2, ZO-3, cingulin, the 7H6 antigen, Rab-3b, and symplekin.1-6 While their precise functions are not known, roles for these proteins have been suggested in tight junction assembly and maintenance; signal transduction; and the regulation of tight junction permeability. A growing body of evidence also suggests that actin filaments play a major role in regulating tight junction permeability. \n\nInitially, the only transmembrane protein known to be associated with tight junctions was occludin, a ~65kD protein with four transmembrane domains. Despite widespread expectation to the contrary, a critical structural role for occludin in TJ strands was ruled out by the observation of normal tight junctions formed between cells disrupted at both occludin alleles. Closer examination of isolated tight junctions uncovered two related, ~22kD, four-transmembrane domain proteins, claudin-1 and claudin-2, with no similarity to occludin. In contrast to occludin, which induces only a small number of short strands at cell-cell contact sites when introduced into fibroblasts lacking tight junctions, claudin-1 and -2 induce networks of strands characteristic of true tight junctions. These findings suggest that claudin-1 and-2 are major structural components of TJ strands and that occludin plays some other accessory role. Excitement in the tight junction field continues to rise following the recent discovery of claudins -3, -4, -5, -6, -7, and -8 and experiments suggesting that tight junctions in different tissues are comprised of different sets of claudin family proteins.\n\nApplications: \nSuitable for use in ELISA, Western Blot and Immunohistochemistry. Other applications not tested.\n\nRecommended Dilutions:\nELISA: 0.1-1ug/ml\nWestern Blot: 1-3ug/ml\nImmunohistochemistry (Human Colon): 5-10ug/ml\nNote: For best results in immunohistochemistry with formalin-fixed, paraffin-embedded (FFPE) tissues, heat induced epitope retrieval (HIER) with EDTA, pH 8.0, is required prior to staining.\nOptimal dilutions to be determined by the researcher.\n\nPositive Controls:\nRat lung, kidney, and small intestine homogenates and mouse lung homogenates\n\nStorage and Stability:\nMay be stored at 4 degrees C for short-term only. Aliquot to avoid repeated freezing and thawing. Store at -20 degrees C. Aliquots are stable for 12 months. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap.

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