Cell-Substratum Interactions of Amoeba proteus: Old and New Open Questions

Abstract

Little is known about the mechanism of adhesion of free-living amoebae. Even though much has been learned about the motor functions of various proteins inside these cells, it remains conjectural whether there are specific molecular bridges binding their outside surfaces to the substrata, as well as which non-specific physical forces are involved in the interaction of both surfaces. In spite of the incomplete knowledge about the basic mechanism of adhesion, much more is known about relations of the motor functions of giant fresh water amoebae to their attachment to solid substrata. For example, in the case of Amoeba proteus:

• 1. Although the cortical actin cytoskeleton moves uniformly rearward in unattached cells, in adhering ones it is centripetally retracted toward the cell-substratum attachment sites (Grebecki 1984).

• 2. The absence of locomotion in enucleated amoebae has previously been attributed to a failure to adhere (Lorch 1969, Grebecka 1977). New observations indicate that the cortical cytoskeleton of enucleated amoebae is disorganized, but it can be repaired by cell attachment to highly adhesive substrata (Grebecka et al. in preparation).

• 3. Adhesion to the substratum is needed for phagocytosis, but it is missing during cation-induced pinocytosis (Opas 1981). Recently, it was clarified that the absence of adhesion is not a necessary condition but a result of pinocytosis (Klopocka et al. 1996).