Adherens Junctions: a Diverse Group of Homologous Cell Contacts

Adherens junctions (AJ) comprise a unique and widespread family of cellular contacts which displays a stable association, within the cells, with actin-containing microfilaments [Geiger et al., 19871. As discussed in several previous articles [Burridge et al., 1988; Woods and Couchman, 19881 AJ may be formed with different surfaces and assume a rather diverse morphology. They may be found in areas of plasmallemal contact with the surrounding extracellular matrix (ECM) as well as in regions of apparently direct intercellular interactions [Geiger et al., 19851. Examples for the former type include focal contacts of cultured cells [Burridge and Fath, 19891, myotendinous junctions [Tidball et al., 19861, dense plaques of smooth muscle [Geiger et al., 1981; Small, 198.51, basal adhesions to basement membranes (distinct from the intermediate filament-associated hemidesmosomes), etc. To the latter subfamily of AJ belong structures such as the zonula adhaerens of polar epithelia, also called “intermediate junctions” or “belt desmosomes” [Staehelin, 19741, endothelial junctions [Franke et al., 19881, fascia adhaerens of cardiac myocytes [Tokuyasu et al., 19811, and spot adhesions (or puncta adherentia) in other cell types. AJ are clearly distinct in structure, molecular composition, and function from tight junctions, gap junctions, and desmosomes [Staehelin, 1974; Geiger, 19831.