title: Molecular organization of cytokinesis nodes and contractile rings by super-resolution fluorescence microscopy of live fission yeast.
abstract: Cytokinesis in animals, fungi, and amoebas depends on the constriction of a contractile ring built from a common set of conserved proteins. Many fundamental questions remain about how these proteins organize to generate the necessary tension for cytokinesis. Using quantitative high-speed fluorescence photoactivation localization microscopy (FPALM), we probed this question in live fission yeast cells at unprecedented resolution. We show that nodes, protein assembly precursors to the contractile ring, are discrete structural units with stoichiometric ratios and distinct distributions of constituent proteins. Anillin Mid1p, Fes/CIP4 homology-Bin/amphiphysin/Rvs (F-BAR) Cdc15p, IQ motif containing GTPase-activating protein (IQGAP) Rng2p, and formin Cdc12p form the base of the node that anchors the ends of myosin II tails to the plasma membrane, with myosin II heads extending into the cytoplasm. This general node organization persists in the contractile ring where nodes move bidirectionally during constriction. We observed the dynamics of the actin network during cytokinesis, starting with the extension of short actin strands from nodes, which sometimes connected neighboring nodes. Later in cytokinesis, a broad network of thick bundles coalesced into a tight ring around the equator of the cell. The actin ring was ∼125 nm wide and ∼125 nm thick. These observations establish the organization of the proteins in the functional units of a cytokinetic contractile ring.
authors.affiliation: Department of Molecular Cellular and Developmental Biology, Yale University, New Haven, CT 06520.
authors.forename: Caroline
authors.initials: C
authors.lastname: Laplante
authors.affiliation: Department of Cell Biology, Yale University, New Haven, CT 06520.
authors.forename: Fang
authors.initials: F
authors.lastname: Huang
authors.affiliation: Department of Molecular Cellular and Developmental Biology, Yale University, New Haven, CT 06520; Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520.
authors.forename: Irene R
authors.initials: IR
authors.lastname: Tebbs
authors.affiliation: Department of Cell Biology, Yale University, New Haven, CT 06520; Department of Biomedical Engineering, Yale University, New Haven, CT 06520.
authors.forename: Joerg
authors.initials: J
authors.lastname: Bewersdorf
authors.affiliation: Department of Molecular Cellular and Developmental Biology, Yale University, New Haven, CT 06520; Department of Cell Biology, Yale University, New Haven, CT 06520; Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520; thomas.pollard@yale.edu.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Pollard
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D048749:Cytokinesis; D007399:Interphase; D008856:Microscopy, Fluorescence / Q000379:methods*; D008958:Models, Molecular; D010641:Phenotype; D012568:Schizosaccharomyces / Q000166:cytology* / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism
chemical_list: D000199:Actins; D029702:Schizosaccharomyces pombe Proteins
keywords: contractile ring; cytokinesis; cytokinetic nodes; fission yeast; super resolution