Tight junctions

Tight junctions are those which link cells together; an example of this is epithelial cells to prevent the lipid and protein domains from interacting.  They are located between the lateral membranes of cells.  This linking means that the cells can form a tissue, for example, the skin consists of many layers of epithelial cells which hold together due to the tight junctions between the cells.

Function of Tight Junctions

Tight junctions are thought to prevent interaction between lipid and proteins laterally across the two domains of the membrane.  It is also a barrier to prevent certain molecules from leaving the basolateral side or entering via the apical side of the cells.  

There have been several studies which have provided evidence that there is interaction of the two domains in the absence of tight junctions. For example, sphingomyelin, which is lipophilic, is labelled with bodipy and inserted into the apical membrane of the epithelial cell.  In the presence of the tight junctions the sphingomyelin will remain in the apical membrane and not interact with the basolateral surfaces.  However, if the tight junctions are disrupted then the sphingomyelin is seen to move to the basolateral membranes thus suggesting that the tight junctions are the reason for the maintanance of the cells polarity.  These results are analysed using confocal imaging.