Expression and distribution of ZO-3, a tight junction MAGUK protein, in mouse tissues.

Background: Three related MAGUK proteins, ZO-1, ZO-2 and ZO-3, are concentrated at the cytoplasmic surface of tight junctions. However, in contrast to ZO-1/ZO-2, our knowledge of the expression and distribution of ZO-3 is still fragmentary, partly due to a lack of antibodies that specifically distinguish ZO-3 from ZO-1 and ZO-2.

Results: We generated one pAb and one mAb that specifically recognized ZO-3 on Western blotting. The immunofluorescence signals obtained with these antibodies completely disappeared from ZO-1/ZO-2-positive tight junctions in the liver of ZO-3-deficient mice, indicating that the antibodies can be used to localize ZO-3 in various tissues by immunofluorescence microscopy. Immunofluorescence microscopy with these antibodies revealed that ZO-3 was concentrated at tight junctions in various types of epithelium, but not in endothelium or at cadherin-based cell-cell adhesion sites (spot adherens junctions of fibroblasts and intercalated discs of cardiac muscle cells), where ZO-1 and ZO-2 are concentrated.

Conclusions: We conclude that ZO-3 is expressed in a more epithelium-specific manner than ZO-1 and ZO-2. These observations provide for a better understanding of the functions of tight junction-associated MAGUKs.