title: Visualization of actin polymerization and depolymerization cycles during polyamine-induced cytokinesis in living Amoeba proteus.
abstract: Microinjection of spermine induces cytokinesis of Amoeba proteus. Within 30--60 s after spermine injection cells form one, or less commonly, two cleavage furrows and within the following 4--10 min the constrictions are completed. The resulting nucleated cell parts show normal streaming and locomotion, whereas the non-nucleated cell parts remain stationary and later degenerate. The intracellular distribution of fully polymerization-competent fluorescently labelled muscle actin was followed by image intensification. Double injection experiments initially using labelled action and 30 min later spermine revealed a ring-like structure of enhanced fluorescence corresponding to the constricting cleavage furrow. Immediately after cleavage was completed, the ring disappeared. Electron microscopy of cells fixed during spermine-induced cytokinesis showed numerous well aligned actin and myosin filaments in the developing cleavage furrow. These filaments are a specialized manifestation of the cell cortex. The results demonstrate that cycles of actin and myosin polymerization and depolymerization and the parallel alignment of preexisting filaments (crosslinking) represent a basic mechanism in the generation of the motive force during cytokinesis.
mesh_terms: D000199:Actins / Q000378:metabolism; D000205:Actomyosin / Q000502:physiology*; D000656:Amoeba / Q000166:cytology / Q000502:physiology*; D008124:Locomotion; D008854:Microscopy, Electron; D009218:Myosins / Q000378:metabolism; D011108:Polymers / Q000378:metabolism; D013096:Spermine / Q000494:pharmacology*
chemical_list: D000199:Actins; D011108:Polymers; D013096:Spermine; D000205:Actomyosin; D009218:Myosins