title: The ultrastructural organization of actin and myosin II filaments in the contractile ring: new support for an old model of cytokinesis.
abstract: Despite recent advances in our understanding of the components and spatial regulation of the contractile ring (CR), the precise ultrastructure of actin and myosin II within the animal cell CR remains an unanswered question. We used superresolution light microscopy and platinum replica transmission electron microscopy (TEM) to determine the structural organization of actin and myosin II in isolated cortical cytoskeletons prepared from dividing sea urchin embryos. Three-dimensional structured illumination microscopy indicated that within the CR, actin and myosin II filaments were organized into tightly packed linear arrays oriented along the axis of constriction and restricted to a narrow zone within the furrow. In contrast, myosin II filaments in earlier stages of cytokinesis were organized into small, discrete, and regularly spaced clusters. TEM showed that actin within the CR formed a dense and anisotropic array of elongate, antiparallel filaments, whereas myosin II was organized into laterally associated, head-to-head filament chains highly reminiscent of mammalian cell stress fibers. Together these results not only support the canonical "purse-string" model for contractile ring constriction, but also suggest that the CR may be derived from foci of myosin II filaments in a manner similar to what has been demonstrated in fission yeast.
authors.affiliation: Department of Biology, Dickinson College, Carlisle, PA 17013 henson@dickinson.edu.|Friday Harbor Laboratories, University of Washington, Friday Harbor, WA 98250.
authors.forename: John H
authors.initials: JH
authors.lastname: Henson
authors.affiliation: Department of Biology, Dickinson College, Carlisle, PA 17013.
authors.forename: Casey E
authors.initials: CE
authors.lastname: Ditzler
authors.affiliation: Department of Biology, Dickinson College, Carlisle, PA 17013.
authors.forename: Aphnie
authors.initials: A
authors.lastname: Germain
authors.affiliation: Department of Biology, Dickinson College, Carlisle, PA 17013.
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Irwin
authors.affiliation: Department of Biology, Dickinson College, Carlisle, PA 17013.
authors.forename: Eric T
authors.initials: ET
authors.lastname: Vogt
authors.affiliation: Department of Biology, Dickinson College, Carlisle, PA 17013.
authors.forename: Shucheng
authors.initials: S
authors.lastname: Yang
authors.affiliation: National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20824.
authors.forename: Xufeng
authors.initials: X
authors.lastname: Wu
authors.affiliation: Friday Harbor Laboratories, University of Washington, Friday Harbor, WA 98250.|Department of Biology, New Mexico State University, Las Cruces, NM 88003.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Shuster
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure*; D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D048749:Cytokinesis / Q000502:physiology; D004625:Embryo, Nonmammalian / Q000166:cytology; D046529:Microscopy, Electron, Transmission / Q000379:methods; D024462:Myosin Type II / Q000737:chemistry / Q000378:metabolism*; D012617:Sea Urchins; D062211:Spatio-Temporal Analysis
chemical_list: D000199:Actins; D024462:Myosin Type II