CONTACTUS ADHERENS, A SPECIAL TYPE OF PLAQUE-BEARING ADHERING JUNCTION CONTAINING M-CADHERIN, IN THE GRANULE CELL LAYER OF THE CEREBELLAR GLOMERULUS

In the glomeruli of the granule cell layer of mammalian cerebellum, ne uronal extensions are interconnected by numerous small, nearly isodiam etric (diameters up to 0.1 mu m), junctions previously classified as p uncta adherentia related to the vinculina-containing, actin microfilam ent-anchoring junctions of the zonula adherens of epithelial and certa in other cells. Using immunofluorescence and immunoelectron microscopy , we have found, however, that these junctions are negative for E- and VE-cadherin, for desmosomal cadherins, and also for vinculin, alpha-a ctinin, and desmoplakin, but they do contain, in addition to the prote in plakoglobin common to all forms of adhering junctions, the plaque p roteins alpha- and beta-catenin and the transmembrane glycoprotein M-c adherin previously found as a spread-i.e., not junction bound-plasma m embrane protein in certain fetal and regenerating muscle cells and in satellite cells of adult skeletal muscle. We conclude that these M-cad herin-containing junctions of the granule cell layer represent a speci al type of adhering junction, for which we propose the term contactus adherens (from the Latin contactus, for touch, site of bordering upon, also influence), and we discuss the differences between the various a dhering junctions on the basis of their molecular constituents.