The tight junction is a cell-to-cell adhesion structure in epithelial cells that constitutes the epithelial junctional complex with adherens junctions and desmosomes. Tight junctions seal cells to create a primary barrier to the diffusion of solutes across the cellular sheet and also function as a boundary between the apical and basolateral membrane domains to produce cellular polarization.

  1. Tight junction strands are mainly composed of claudins, occludin, and JAM.
  2. The scaffold proteins ZO-1, ZO-2, and ZO-3 are concentrated at the cytoplasmic surfaces of the junctional complexes, and determine the specialization and localization of junctions. The zona occludens (ZO) proteins form the plaque structures underlying plasma membranes together with proteins such as cingulin, symplekin, the Par-3/Par-6/atypical protein kinase C complex, ZONAB, and guanine nucleotide exchange factor-H1/Lfc.
  3. All three ZO proteins have three PDZ domains, one Src homology 3 domain, and one guanylate kinase-like homologue domain, characterizing them as membrane-associated guanylate kinase-like homologues (MAGUKs).
  4. A recent study reported that low levels of ZO-1 expression correlate with poor patient prognosis in breast cancer.
  5. Another study observed aberrant ZO-1 expression in synovial sarcoma samples.
  6. ZO-1 antibodies are useful markers of tight junctions between cells, due to the exclusive localization of ZO-1 there.

Immunofluorescent co-localization (yellow) of ZO-1 (green) and Occludin (red) in Caco-2 (top row) and MDCK II (bottom row) cells using rabbit anti-ZO-1 (Mid) polyclonal antibody. Image courtesy of Jacey Bennis and Dr. James Anderson, University of North Carolina at Chapel Hill.

Immunofluorescent staining of blood vessels in mouse heart tissue using rabbit anti-ZO-1 (N-term) polyclonal antibody. Image courtesy of James I Nagy, PhD, University of Manitoba, Canada.

Western blot analysis of (A) MDCK II, (B) A431, (C) Caco-2, (D) Rat-1, and (E) NRK-52E cell lysates using rabbit anti-ZO-1 (Mid) polyclonal antibody.


  1. Anderson JM and Van Itallie CM. Am J Physiol 269:G467-G475, 1995.
  2. Umeda K, et al. J Biol Chem 279(43):44785-44794, 2004.
  3. Itoh M, et al. J Cell Biol 121:491-502, 1993.
  4. Martin TA, et al. Eur J Cancer 40(18):2717-2725, 2004.
  5. Billings SD, et al. Mod Pathol 17(2):141-149, 2004.

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