In vivo observations of myosin II dynamics support a role in rear retraction.
To investigate myosin II function in cell movement within a cell mass, we imaged green fluorescent protein-myosin heavy chain (GFP-MHC) cells moving within the tight mound of Dictyostelium discoideum. In the posterior cortex of cells undergoing rotational motion around the center of the mound, GFP-MHC cyclically formed a "C," which converted to a spot as the cell retracted its rear. Consistent with an important role for myosin in rotation, cells failed to rotate when they lacked the myosin II heavy chain (MHC-) or when they contained predominantly monomeric myosin II (3xAsp). In cells lacking the myosin II regulatory light chain (RLC-), rotation was impaired and eventually ceased. These rotational defects reflect a mechanical problem in the 3xAsp and RLC- cells, because these mutants exhibited proper rotational guidance cues. MHC- cells exhibited disorganized and erratic rotational guidance cues, suggesting a requirement for the MHC in organizing these signals. However, the MHC- cells also exhibited mechanical defects in rotation, because they still moved aberrantly when seeded into wild-type mounds with proper rotational guidance cues. The mechanical defects in rotation may be mediated by the C-to-spot, because RLC- cells exhibited a defective C-to-spot, including a slower C-to-spot transition, consistent with this mutant's slower rotational velocity.
Clow
P A
PA
Department of Biology and Institute for Biomedical Computing, Washington University, Box 1229, St. Louis, Missouri 63130, USA.
McNally
J G
JG
D000205:Actomyosin / Q000378:metabolism; D000818:Animals; D002448:Cell Adhesion; D002465:Cell Movement / Q000502:physiology*; D002478:Cells, Cultured / Q000166:cytology / Q000502:physiology; D002633:Chemotaxis / Q000502:physiology; D004023:Dictyostelium / Q000166:cytology*; D049452:Green Fluorescent Proteins; D007091:Image Processing, Computer-Assisted; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009154:Mutation; D009218:Myosins / Q000502:physiology*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
D008164:Luminescent Proteins; D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins; D000205:Actomyosin; D009218:Myosins