Defining junctional complexes

There are four major types of cell–cell junctions in the polarized epithelial cells of vertebrates. Farquhar and Palade (1963) defined three of them.

The history of cell–cell contacts goes all the way back to the 1830s. For much of the 19th century an intercellular cement was thought to surround and bind cells over their entire surface area. The opposing idea of specific sites of adhesion was, however, hinted at even at the birth of the cell theory. Theodor Schwann (who with Matthias Schleiden enunciated cell theory in 1839) suggested that animal cells might fuse at specific points via cytoplasmic bridges. Several investigators singled out the spines of certain epidermal cells as contact points and potential...