title: Effects of the actin-binding protein DNAase I on cytoplasmic streaming and ultrastructure of Amoeba proteus. An attempt to explain amoeboid movement.
abstract: Microinjection of DNAase I, which is known to form a specific complex with G-actin, induces characteristic changes in cytoplasmic streaming, locomotion and morphology of the contractile apparatus of A. proteus. Light microscopical studies show pronounced streaming originating from the uroid and/or the retracting pseudopods, which ceases 10--15 min after injection of DNAase I, at a time when ultrasctructural studies show that the actin filament system is very much reduced. These results suggest that a controlled reversible equilibrium between soluble and polymerized forms of actin is a necessary requirement for amoeboid movement. The topographic distribution of contractile filaments beneath the plasma membrane visualized by correlated light- and electron microscopy of DNAase I-injected cells establishes the importance of the membrane-bound filamentous layer for three major aspects of streaming: (1) Streaming originates by local contractions of a cell membrane-associated filament layer at the uroid and/or retracting pseudopods, creating a pressure flow. (2) This flow continues beneath the membrane, which is stabilized by filaments in the lateral regions between the posterior end, with a high hydrostatic pressure, and the anterior end, with a low hydrostatic pressure. (3) Pseudopods or extending areas are created by a local destabilization of the cell periphery caused by the separation of the filamentous layer from the plasma membrane.
mesh_terms: D000656:Amoeba / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D000818:Animals; D003593:Cytoplasm / Q000648:ultrastructure; D003595:Cytoplasmic Streaming / Q000187:drug effects*; D003599:Cytoskeleton / Q000648:ultrastructure*; D003851:Deoxyribonucleases / Q000494:pharmacology*; D009068:Movement / Q000187:drug effects; D011554:Pseudopodia / Q000648:ultrastructure
chemical_list: D003851:Deoxyribonucleases