title: The F-actin bundler α-actinin Ain1 is tailored for ring assembly and constriction during cytokinesis in fission yeast.
abstract: The actomyosin contractile ring is a network of cross-linked actin filaments that facilitates cytokinesis in dividing cells. Contractile ring formation has been well characterized in Schizosaccharomyces pombe, in which the cross-linking protein α-actinin SpAin1 bundles the actin filament network. However, the specific biochemical properties of SpAin1 and whether they are tailored for cytokinesis are not known. Therefore we purified SpAin1 and quantified its ability to dynamically bind and bundle actin filaments in vitro using a combination of bulk sedimentation assays and direct visualization by two-color total internal reflection fluorescence microscopy. We found that, while SpAin1 bundles actin filaments of mixed polarity like other α-actinins, SpAin1 has lower bundling activity and is more dynamic than human α-actinin HsACTN4. To determine whether dynamic bundling is important for cytokinesis in fission yeast, we created the less dynamic bundling mutant SpAin1(R216E). We found that dynamic bundling is critical for cytokinesis, as cells expressing SpAin1(R216E) display disorganized ring material and delays in both ring formation and constriction. Furthermore, computer simulations of initial actin filament elongation and alignment revealed that an intermediate level of cross-linking best facilitates filament alignment. Together our results demonstrate that dynamic bundling by SpAin1 is important for proper contractile ring formation and constriction.
authors.affiliation: Committee on Genetics, Genomics and Systems Biology, University of Chicago, Chicago, IL 60637.
authors.forename: Yujie
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637.
authors.forename: Jenna R
authors.initials: JR
authors.lastname: Christensen
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637.
authors.forename: Kaitlin E
authors.initials: KE
authors.lastname: Homa
authors.affiliation: Department of Chemistry, James Franck Institute, Institute for Biophysical Dynamics, and Computation Institute, University of Chicago, Chicago, IL 60637.
authors.forename: Glen M
authors.initials: GM
authors.lastname: Hocky
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637.
authors.forename: Alice
authors.initials: A
authors.lastname: Fok
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Sees
authors.affiliation: Department of Chemistry, James Franck Institute, Institute for Biophysical Dynamics, and Computation Institute, University of Chicago, Chicago, IL 60637.
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Voth
authors.affiliation: Committee on Genetics, Genomics and Systems Biology, University of Chicago, Chicago, IL 60637 Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637 Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637 drkovar@uchicago.edu.
authors.forename: David R
authors.initials: DR
authors.lastname: Kovar
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000185:Actinin / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000205:Actomyosin / Q000378:metabolism; D048749:Cytokinesis / Q000502:physiology*; D006801:Humans; D012568:Schizosaccharomyces / Q000166:cytology* / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*
chemical_list: D000199:Actins; D029702:Schizosaccharomyces pombe Proteins; C430383:ain1 protein, S pombe; D000185:Actinin; D000205:Actomyosin