Studies of the cohesion mechanism of axenic dictyostelium discoideum cells

Abstract

The cohesive behaviour of slime mould cells during axenic growth has been studied. Axenically-grown log phase Ax-2 cells cohere rapidly when shaken in phosphate buffer. After 3.5 days in stationary phase, cells become completely non cohesive however, stationary phase cells form mutual contacts with both log phase and aggregation-competent cells. Mixed cohesions of these 2 cell types is inhibited by both EDTA and a low-molecular-weight inhibitory factor present in stationary phase medium. The effect of this factor seems to be specific against contact sites B-mediated cohesion. Plasma membranes isolated from log phase Ax-2 cells inhibit cohesion of homologous cells completely, and partially inhibit cohesion of aggregation-competent cells. Evidence is presented which suggests that these inhibitory effects are directed against contact sites B, mediated by tyccp'o4eivo and non-specific for other species. A soluble extract obtained from log cell membranes with lithium diiodosalicylate (LIS), contains an active component which inhibits cohesion of log phase cells completely, and that of aggregation-competent cells only partially. The active material is sensitive to periodate, stable against heat and binds to Con A-Agarose, beads, suggesting it is a glycoprotein. Evidence is presented to suggest that the extractable inhibitory activity binds to the surface of intact log phase cells. A ligand(glycoprotein) -receptor (carbohydrate-binding protein) model is proposed for the cohesion mechanism of vegetative slime mould cells, and the evidence discussed in relation to known aspects of behaviour in these cells.

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