Microinjection into Acanthamoeba castellanii of monoclonal antibodies to myosin-II slows but does not stop cell locomotion.
To study the in vivo role of myosin-II in Acanthamoeba castellanii, motile cells were microinjected with monoclonal antibodies raised against the myosin-II heavy chain. All injected cells underwent a transient shock response. It was found that although injection of buffer alone or of an endogenous Acanthamoeba protein decreased the motility of injected cells from 7 microns/min to approximately 3 microns/min, injection of monoclonal antibodies specific for myosin-II decreased motility further to approximately 0.8 micron/min. This effect was seen whether or not the monoclonal antibody to myosin-II inhibited the actomyosin-II MgATPase activity in vitro. Levels of antibody far in excess of endogenous myosin-II concentrations could not completely block amoeboid movement. The morphology of moving antimyosin-II-injected cells was unusual, suggesting a greater defect in the ability to retract the trailing edge of the cell rather than to extend the leading edge. Endosomes frequently disappeared from injected cells, and although buffer-injected cells rapidly recovered visible endosomes (50% recovery at 5 min), endosomes were not seen in antimyosin-II-injected cells until, on the average, approximately 50 min after injection. Injection of a nonspecific antibody or of a nonspecific exogenous protein (ovalbumin) also decreased the mobility of the injected cells beyond that of buffer-injected cells (to approximately 1 micron/min). These cells tended to recover endosomes more rapidly (approximately 25 min) than cells injected with antimyosin-II monoclonal antibodies. The inability of antibodies to myosin-II to inhibit completely any of the movements studied suggests that although myosin-II probably plays a role in these motilities, the cell either routinely uses or can draw upon another cytoplasmic motor to maintain locomotion, organelle movement, contractile vacuole activity, and endocytosis.
Sinard
J H
JH
Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore.
Pollard
T D
TD
D000048:Acanthamoeba / Q000502:physiology*; D000199:Actins / Q000494:pharmacology / Q000502:physiology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage* / Q000276:immunology; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000032:analysis; D002465:Cell Movement / Q000187:drug effects; D003593:Cytoplasm / Q000032:analysis; D008274:Magnesium / Q000032:analysis; D008845:Microinjections; D015879:Myosin Subfragments; D009218:Myosins / Q000276:immunology / Q000502:physiology*; D010047:Ovalbumin / Q000494:pharmacology; D010446:Peptide Fragments / Q000276:immunology / Q000502:physiology*
D000199:Actins; D000911:Antibodies, Monoclonal; D015879:Myosin Subfragments; D010446:Peptide Fragments; D010047:Ovalbumin; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins; D008274:Magnesium; D002118:Calcium