title: Dynamics of antigenic membrane sites relating to cell aggregation in Dictyostelium discoideum.
abstract: Membrane interaction in aggregating cells of Dictyostelium discoideum can be blocked by univalent antibodies directed against specific membrane sites. Using a quantitative technique for measuring cell association, two classes of target sites for blocking antibodies were distinguished and their developmental dynamics studied. One class of these sites is specific for aggregation-competent cells, their quantity rising from virtually 0-level during growth, with a steep increase shortly before cell aggregation. The serological activity of these structures is species specific; they are not detectable in a nonaggregating mutant, but present in a revertant undergoing normal morphogenesis. Patterns of cell assembly in the presence of antibodies show that selective blockage of these membrane sites abolishes the preference for end-to-end association which is typical for aggregating cells. A second class of target sites is present in comparable quantities in particle fractions from both growth-phase and aggregation-competent cells. Blockage of these sites leads to aggregation patterns in which the side-by-side contacts of aggregating cells are abolished. The target sites of aggregation-inhibiting antibodies are suggested to be identical or associated with the molecular units of the cell membrane that mediate cell-to-cell contacts during aggregation. The results indicate that in one cell, two independent classes of contact sites can be simultaneously active.
mesh_terms: D001666:Binding Sites, Antibody; D002448:Cell Adhesion; D002449:Cell Aggregation; D002454:Cell Differentiation; D002462:Cell Membrane / Q000276:immunology*; D004492:Edetic Acid; D009235:Myxomycetes / Q000166:cytology*
chemical_list: D004492:Edetic Acid