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      The nuclear F-actin interactome of Xenopus oocytes reveals an actin-bundling kinesin that is essential for meiotic cytokinesis

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          Abstract

          Nuclei of Xenopus laevis oocytes grow 100 000-fold larger in volume than a typical somatic nucleus and require an unusual intranuclear F-actin scaffold for mechanical stability. We now developed a method for mapping F-actin interactomes and identified a comprehensive set of F-actin binders from the oocyte nuclei. Unexpectedly, the most prominent interactor was a novel kinesin termed NabKin (Nuclear and meiotic actin-bundling Kinesin). NabKin not only binds microtubules but also F-actin structures, such as the intranuclear actin bundles in prophase and the contractile actomyosin ring during cytokinesis. The interaction between NabKin and F-actin is negatively regulated by Importin-β and is responsive to spatial information provided by RanGTP. Disconnecting NabKin from F-actin during meiosis caused cytokinesis failure and egg polyploidy. We also found actin-bundling activity in Nabkin's somatic paralogue KIF14, which was previously shown to be essential for somatic cell division. Our data are consistent with the notion that NabKin/KIF14 directly link microtubules with F-actin and that such link is essential for cytokinesis.

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          Most cited references58

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          Multiple sequence alignment with the Clustal series of programs.

          R Chenna (2003)
          The Clustal series of programs are widely used in molecular biology for the multiple alignment of both nucleic acid and protein sequences and for preparing phylogenetic trees. The popularity of the programs depends on a number of factors, including not only the accuracy of the results, but also the robustness, portability and user-friendliness of the programs. New features include NEXUS and FASTA format output, printing range numbers and faster tree calculation. Although, Clustal was originally developed to run on a local computer, numerous Web servers have been set up, notably at the EBI (European Bioinformatics Institute) (http://www.ebi.ac.uk/clustalw/).
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            Actin, a central player in cell shape and movement.

            The protein actin forms filaments that provide cells with mechanical support and driving forces for movement. Actin contributes to biological processes such as sensing environmental forces, internalizing membrane vesicles, moving over surfaces, and dividing the cell in two. These cellular activities are complex; they depend on interactions of actin monomers and filaments with numerous other proteins. Here, we present a summary of the key questions in the field and suggest how those questions might be answered. Understanding actin-based biological phenomena will depend on identifying the participating molecules and defining their molecular mechanisms. Comparisons of quantitative measurements of reactions in live cells with computer simulations of mathematical models will also help generate meaningful insights.
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              The interaction of Arp2/3 complex with actin: nucleation, high affinity pointed end capping, and formation of branching networks of filaments.

              The Arp2/3 complex is a stable assembly of seven protein subunits including two actin-related proteins (Arp2 and Arp3) and five novel proteins. Previous work showed that this complex binds to the sides of actin filaments and is concentrated at the leading edges of motile cells. Here, we show that Arp2/3 complex purified from Acanthamoeba caps the pointed ends of actin filaments with high affinity. Arp2/3 complex inhibits both monomer addition and dissociation at the pointed ends of actin filaments with apparent nanomolar affinity and increases the critical concentration for polymerization at the pointed end from 0.6 to 1.0 microM. The high affinity of Arp2/3 complex for pointed ends and its abundance in amoebae suggest that in vivo all actin filament pointed ends are capped by Arp2/3 complex. Arp2/3 complex also nucleates formation of actin filaments that elongate only from their barbed ends. From kinetic analysis, the nucleation mechanism appears to involve stabilization of polymerization intermediates (probably actin dimers). In electron micrographs of quick-frozen, deep-etched samples, we see Arp2/3 bound to sides and pointed ends of actin filaments and examples of Arp2/3 complex attaching pointed ends of filaments to sides of other filaments. In these cases, the angle of attachment is a remarkably constant 70 +/- 7 degrees. From these in vitro biochemical properties, we propose a model for how Arp2/3 complex controls the assembly of a branching network of actin filaments at the leading edge of motile cells.
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                Author and article information

                Journal
                EMBO J
                EMBO J
                The EMBO Journal
                Nature Publishing Group
                0261-4189
                1460-2075
                03 July 2013
                31 May 2013
                31 May 2013
                : 32
                : 13
                : 1886-1902
                Affiliations
                [1 ]Department of Cellular Logistics, MPI for Biophysical Chemistry , Göttingen, Germany
                [2 ]Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA) , Vienna, Austria
                [3 ]Systems Biology of Motor Proteins Group, MPI for Biophysical Chemistry , Göttingen, Germany
                [4 ]Bioanalytical Mass Spectrometry Group, MPI for Biophysical Chemistry , Göttingen, Germany
                Author notes
                [a ]Department of Cellular Logistics, MPI for Biophysical Chemistry , Am Fassberg 11, Göttingen 37077, Germany. Tel.:+49 551 201 2401; Fax:+49 551 201 2407; E-mail: goerlich@ 123456mpibpc.mpg.de
                Article
                emboj2013108
                10.1038/emboj.2013.108
                3981176
                23727888
                656970a9-9f56-4a90-a834-836f7a53e93a
                Copyright © 2013, European Molecular Biology Organization

                This article is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 Unported Licence. To view a copy of this licence visit http://creativecommons.org/licenses/by-nc-nd/3.0/.

                History
                : 10 March 2013
                : 23 April 2013
                Categories
                Article

                Molecular biology
                cytokinesis,kinesins,meiosis,nuclear actin,phalloidin
                Molecular biology
                cytokinesis, kinesins, meiosis, nuclear actin, phalloidin

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