NEUROGLIAN-MEDIATED CELL-ADHESION INDUCES ASSEMBLY OF THE MEMBRANE SKELETON AT CELL CONTACT SITES

The protein ankyrin links integral membrane proteins to the spectrin-b ased membrane skeleton. Ankyrin is often concentrated within restricte d membrane domains of polarized epithelia and neurons, but the mechani sms responsible for membrane targeting and its segregation within a co ntinuous lipid bilayer remain unexplained. We provide evidence that ne uroglian, a cell adhesion molecule related to L1 and neurofascin, can transmit positional information directly to ankyrin and thereby polari ze its distribution in Drosophila S2 tissue culture cells. Ankyrin was not normally associated with the plasma membrane of these cells. Upon expression of an inducible neuroglian minigene, however, cells aggreg ated into large clusters and ankyrin became concentrated at sites of c ell-cell conSpectrin was also recruited to sites of cell contact in re sponse to neuroglian expression. The accumulation of ankyrin at cell c ontacts required the presence of the cytoplasmic domain of neuroglian since a glycosyl phosphatidylinositol-linked form of neuroglian failed to recruit ankyrin to sites of cell-cell contact. Double-labeling exp eriments revealed that, whereas ankyrin was strictly associated with s ites of cell-cell contact, neuroglian was more broadly distributed ove r the cell surface. A direct interaction between neuroglian and ankyri n was demonstrated using yeast two-hybrid analysis. Thus, neuroglian a ppears to be activated by extracellular adhesion so that ankyrin and t he membrane skeleton selectively associate with sites of cell contact and not with other regions of the plasma membrane.