TALIN-NULL CELLS OF DICTYOSTELIUM ARE STRONGLY DEFECTIVE IN ADHESION TO PARTICLE AND SUBSTRATE SURFACES AND SLIGHTLY IMPAIRED IN CYTOKINESIS

Dictyostelium discoideum contains a full-length homologue of talin, a protein implicated in linkage of the actin system to sites of cell-to- substrate adhesion in fibroblasts and neuronal growth cones. Gene repl acement eliminated the talin homologue in Dictyostelium and led to def ects in phagocytosis and cell-to-substrate interaction of moving cells , two processes dependent on a continuous cross talk between the cell surface and underlying cytoskeleton. The up-take rate of yeast particl es was reduced, and only bacteria devoid of the carbohydrate moiety of cell surface lipopolysaccharides were adhesive enough to be recruited by talin-null cells in suspension and phagocytosed. Cell-to-cell adhe sion of undeveloped cells was strongly impaired in the absence of tali n, in contrast with the cohesion of aggregating cells mediated by the phospholipid-anchored contact site A glycoprotein, which proved to be less talin dependent. The mutant cells were still capable of moving an d responding to a chemoattractant, although they attached only loosely to a substrate via small areas of their surface. With their high prop ortion of binucleated cells, the talin-null mutants revealed interacti ons of the mitotic apparatus with the cell cortex that were not obviou s in mononucleated cells.