scholarly journals Bistability in the actin cortex

2010 ◽  
Vol 3 (1) ◽  
Author(s):  
Carsten Beta
Keyword(s):  
Actin Cortex

scholarly journals Microtubule–microtubule sliding by kinesin-1 is essential for normal cytoplasmic streaming in Drosophila oocytes

2016 ◽  
Vol 113 (34) ◽  
pp. E4995-E5004 ◽  
Author(s):  
Wen Lu ◽  
Michael Winding ◽  
Margot Lakonishok ◽  
Jill Wildonger ◽  
Vladimir I. Gelfand
Keyword(s):  
Cytoplasmic Streaming ◽  
Cell Types ◽  
Nurse Cells ◽  
Wild Type ◽  
Actin Cortex ◽  
Microtubule Motor ◽  
Multiple Cell ◽  
Cytoplasmic Microtubules ◽  
Two Populations

Cytoplasmic streaming in Drosophila oocytes is a microtubule-based bulk cytoplasmic movement. Streaming efficiently circulates and localizes mRNAs and proteins deposited by the nurse cells across the oocyte. This movement is driven by kinesin-1, a major microtubule motor. Recently, we have shown that kinesin-1 heavy chain (KHC) can transport one microtubule on another microtubule, thus driving microtubule–microtubule sliding in multiple cell types. To study the role of microtubule sliding in oocyte cytoplasmic streaming, we used a Khc mutant that is deficient in microtubule sliding but able to transport a majority of cargoes. We demonstrated that streaming is reduced by genomic replacement of wild-type Khc with this sliding-deficient mutant. Streaming can be fully rescued by wild-type KHC and partially rescued by a chimeric motor that cannot move organelles but is active in microtubule sliding. Consistent with these data, we identified two populations of microtubules in fast-streaming oocytes: a network of stable microtubules anchored to the actin cortex and free cytoplasmic microtubules that moved in the ooplasm. We further demonstrated that the reduced streaming in sliding-deficient oocytes resulted in posterior determination defects. Together, we propose that kinesin-1 slides free cytoplasmic microtubules against cortically immobilized microtubules, generating forces that contribute to cytoplasmic streaming and are essential for the refinement of posterior determinants.

scholarly journals A Model System for the Reconstitution of the Cellular Actin Cortex

2017 ◽  
Vol 112 (3) ◽  
pp. 561a
Author(s):  
Or Gill ◽  
Anne Bernheim-Groswasser
Keyword(s):  
Model System ◽  
Actin Cortex

scholarly journals The actin cortex as an active wetting layer

2013 ◽  
Vol 36 (5) ◽  
Author(s):  
J. -F. Joanny ◽  
K. Kruse ◽  
J. Prost ◽  
S. Ramaswamy
Keyword(s):  
Wetting Layer ◽  
Actin Cortex

scholarly journals Myosin-II activity generates a dynamic steady state with continuous actin turnover in a minimal actin cortex

2018 ◽  
Author(s):  
Sonal ◽  
Kristina A. Ganzinger ◽  
Sven K. Vogel ◽  
Jonas Mücksch ◽  
Philipp Blumhardt ◽  
...  
Keyword(s):  
Steady State ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Fine Tuning ◽  
Cellular Functions ◽  
Actin Cortex ◽  
Actin Turnover ◽  
Cytoskeletal Dynamics

ABSTRACTDynamic reorganization of the actomyosin cytoskeleton allows a fine-tuning of cell shape that is vital to many cellular functions. It is well established that myosin-II motors generate the forces required for remodeling the cell surface by imparting contractility to actin networks. An additional, less understood, role of myosin-II in cytoskeletal dynamics is believed to be in the regulation of actin turnover; it has been proposed that myosin activity increases actin turnover in various cellular contexts, presumably by contributing to disassembly. In vitro reconstitution of actomyosin networks has confirmed the role of myosin in actin network disassembly, but factors such as diffusional constraints and the use of stabilized filaments have thus far limited the observation of myosin-assisted actin turnover in these networks. Here, we present the reconstitution of a minimal dynamic actin cortex where actin polymerization is catalyzed on the membrane in the presence of myosin-II activity. We demonstrate that myosin activity leads to disassembly and redistribution in this simplified cortex. Consequently, a new dynamic steady state emerges in which actin filaments undergo constant turnover. Our findings suggest a multi-faceted role of myosin-II in fast remodeling of the eukaryotic actin cortex.

scholarly journals Coupled myosin VI motors facilitate unidirectional movement on an F-actin network

2009 ◽  
Vol 187 (1) ◽  
pp. 53-60 ◽  
Author(s):  
Sivaraj Sivaramakrishnan ◽  
James A. Spudich
Keyword(s):  
Single Molecule ◽  
Membrane Trafficking ◽  
Cell Periphery ◽  
Myosin Vi ◽  
Actin Network ◽  
Cortical Actin ◽  
Actin Cortex ◽  
Unidirectional Movement ◽  
Transport Vesicle ◽  
Pointed End

Unconventional myosins interact with the dense cortical actin network during processes such as membrane trafficking, cell migration, and mechanotransduction. Our understanding of unconventional myosin function is derived largely from assays that examine the interaction of a single myosin with a single actin filament. In this study, we have developed a model system to study the interaction between multiple tethered unconventional myosins and a model F-actin cortex, namely the lamellipodium of a migrating fish epidermal keratocyte. Using myosin VI, which moves toward the pointed end of actin filaments, we directly determine the polarity of the extracted keratocyte lamellipodium from the cell periphery to the cell nucleus. We use a combination of experimentation and simulation to demonstrate that multiple myosin VI molecules can coordinate to efficiently transport vesicle-size cargo over 10 µm of the dense interlaced actin network. Furthermore, several molecules of monomeric myosin VI, which are nonprocessive in single molecule assays, can coordinate to transport cargo with similar speeds as dimers.

scholarly journals Zebrafish vasa RNA but Not Its Protein Is a Component of the Germ Plasm and Segregates Asymmetrically before Germline Specification

2000 ◽  
Vol 149 (4) ◽  
pp. 875-888 ◽  
Author(s):  
Holger Knaut ◽  
Francisco Pelegri ◽  
Kerstin Bohmann ◽  
Heinz Schwarz ◽  
Christiane Nüsslein-Volhard
Keyword(s):  
Germ Cell ◽  
Germ Plasm ◽  
Primordial Germ Cell ◽  
Subcellular Structure ◽  
Actin Cortex ◽  
Maternal Effect Gene ◽  
Close Proximity ◽  
Hybrid Fish ◽  
Vasa Gene ◽  
Effect Gene

Work in different organisms revealed that the vasa gene product is essential for germline specification. Here, we describe the asymmetric segregation of zebrafish vasa RNA, which distinguishes germ cell precursors from somatic cells in cleavage stage embryos. At the late blastula (sphere) stage, vasa mRNA segregation changes from asymmetric to symmetric, a process that precedes primordial germ cell proliferation and perinuclear localization of Vasa protein. Analysis of hybrid fish between Danio rerio and Danio feegradei demonstrates that zygotic vasa transcription is initiated shortly after the loss of unequal vasa mRNA segregation. Blocking DNA replication indicates that the change in vasa RNA segregation is dependent on a maternal program. Asymmetric segregation is impaired in embryos mutant for the maternal effect gene nebel. Furthermore, ultrastructural analysis of vasa RNA particles reveals that vasa RNA, but not Vasa protein, localizes to a subcellular structure that resembles nuage, a germ plasm organelle. The structure is initially associated with the actin cortex, and subsequent aggregation is inhibited by actin depolymerization. Later, the structure is found in close proximity of microtubules. We previously showed that its translocation to the distal furrows is microtubule dependent. We propose that vasa RNA but not Vasa protein is a component of the zebrafish germ plasm. Triggered by maternal signals, the pattern of germ plasm segregation changes, which results in the expression of primordial germ cell–specific genes such as vasa and, consequently, in germline fate commitment.

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