Cortical actin filaments fragment and aggregate to form chloroplast-associated and free F-actin rings in mechanically isolatedZinnia mesophyll cells

PROTOPLASMA ◽  
1996 ◽  
Vol 194 (3-4) ◽  
pp. 195-207 ◽  
Author(s):  
Alexander O. Frost ◽  
Alison W. Roberts
Keyword(s):  
Actin Filaments ◽  
Cortical Actin ◽  
Mesophyll Cells ◽  
Actin Rings

scholarly journals Mechanism of the formation of contractile ring in dividing cultured animal cells. II. Cortical movement of microinjected actin filaments.

1990 ◽  
Vol 111 (5) ◽  
pp. 1905-1911 ◽  
Author(s):  
L G Cao ◽  
Y L Wang
Keyword(s):  
Actin Filaments ◽  
Average Rate ◽  
Rat Kidney ◽  
Equatorial Region ◽  
Cell Cortex ◽  
Polar Regions ◽  
Cortical Actin ◽  
Animal Cells ◽  
Contractile Ring ◽  
Directional Movement

The contractile ring in dividing animal cells is formed primarily through the reorganization of existing actin filaments (Cao, L.-G., and Y.-L. Wang. 1990. J. Cell Biol. 110:1089-1096), but it is not clear whether the process involves a random recruitment of diffusible actin filaments from the cytoplasm, or a directional movement of cortically associated filaments toward the equator. We have studied this question by observing the distribution of actin filaments that have been labeled with fluorescent phalloidin and microinjected into dividing normal rat kidney (NRK) cells. The labeled filaments are present primarily in the cytoplasm during prometaphase and early metaphase, but become associated extensively with the cell cortex 10-15 min before the onset of anaphase. This process is manifested both as an increase in cortical fluorescence intensity and as movements of discrete aggregates of actin filaments toward the cortex. The concentration of actin fluorescence in the equatorial region, accompanied by a decrease of fluorescence in polar regions, is detected 2-3 min after the onset of anaphase. By directly tracing the distribution of aggregates of labeled actin filaments, we are able to detect, during anaphase and telophase, movements of cortical actin filaments toward the equator at an average rate of 1.0 micron/min. Our results, combined with previous observations, suggest that the organization of actin filaments during cytokinesis probably involves an association of cytoplasmic filaments with the cortex, a movement of cortical filaments toward the cleavage furrow, and a dissociation of filaments from the equatorial cortex.

Barrier role of actin filaments in regulated mucin secretion from airway goblet cells

2005 ◽  
Vol 288 (1) ◽  
pp. C46-C56 ◽  
Author(s):  
Camille Ehre ◽  
Andrea H. Rossi ◽  
Lubna H. Abdullah ◽  
Kathleen De Pestel ◽  
Sandra Hill ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Actin Filaments ◽  
Fluorescent Protein ◽  
Secretory Granules ◽  
Yellow Fluorescent Protein ◽  
Goblet Cells ◽  
Actin Binding ◽  
Secretory Cells ◽  
Cortical Actin ◽  
Mucin Secretion

Airway goblet cells secrete mucin onto mucosal surfaces under the regulation of an apical, phospholipase C/Gq-coupled P2Y2receptor. We tested whether cortical actin filaments negatively regulate exocytosis in goblet cells by forming a barrier between secretory granules and plasma membrane docking sites as postulated for other secretory cells. Immunostaining of human lung tissues and SPOC1 cells (an epithelial, mucin-secreting cell line) revealed an apical distribution of β- and γ-actin in ciliated and goblet cells. In goblet cells, actin appeared as a prominent subplasmalemmal sheet lying between granules and the apical membrane, and it disappeared from SPOC1 cells activated by purinergic agonist. Disruption of actin filaments with latrunculin A stimulated SPOC1 cell mucin secretion under basal and agonist-activated conditions, whereas stabilization with jasplakinolide or overexpression of β- or γ-actin conjugated to yellow fluorescent protein (YFP) inhibited secretion. Myristoylated alanine-rich C kinase substrate, a PKC-activated actin-plasma membrane tethering protein, was phosphorylated after agonist stimulation, suggesting a translocation to the cytosol. Scinderin (or adseverin), a Ca2+-activated actin filament severing and capping protein was cloned from human airway and SPOC1 cells, and synthetic peptides corresponding to its actin-binding domains inhibited mucin secretion. We conclude that actin filaments negatively regulate mucin secretion basally in airway goblet cells and are dynamically remodeled in agonist-stimulated cells to promote exocytosis.

Actin filaments regulate epithelial Na+ channel activity

1991 ◽  
Vol 261 (5) ◽  
pp. C882-C888 ◽  
Author(s):  
H. F. Cantiello ◽  
J. L. Stow ◽  
A. G. Prat ◽  
D. A. Ausiello
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Functional Role ◽  
Cytochalasin D ◽  
Actin Binding ◽  
Na Channel ◽  
Na Channels ◽  
Channel Activity ◽  
Cortical Actin ◽  
Excised Patches

The functional role of the cytoskeleton in the control of ion channel activity is unknown. In the present study, immunocolocalization of Na+ channels with specific antibodies and fluorescein isothiocyanate-phalloidin to stain the cortical cytoskeleton indicates that actin is always present in close proximity to apical Na+ channels in A6 cells. The patch-clamp technique was used to assess the effect of cortical actin networks on apical Na+ channels in these A6 epithelial cells. The actin filament disrupter, cytochalasin D (5 micrograms/ml), induced Na+ channel activity in cell-attached patches within 5 min of addition. Cytochalasin D also induced and/or increased Na+ channel activity in 90% of excised patches tested within 2 min. Addition of short actin filaments (greater than 5 microM) to excised patches also induced channel activity. This effect was enhanced by addition of ATP and/or cytochalasin D. The effect of actin on Na+ channel activity was reversed by addition of the G actin-binding protein DNase I or completely prevented by treatment of the excised patches with this enzyme. Addition of the actin-binding protein, filamin, reversibly inhibited both spontaneous and actin-induced Na+ channels. Thus actin filament networks, achieved by either depolymerizing endogenous actin filaments by treatment with cytochalasin D, the addition of exogenous short actin filaments plus ATP, or actin plus cytochalasin D, regulate apical Na+ channel activity. This conclusion was supported by the observation that the addition of short actin filaments in the form of actin-gelsolin complexes in molar ratios less than 8:1 was also effective in activating Na+ channels. We have thus demonstrated a functional role for the cortical actin network in the regulation of epithelial Na+ channels that may complement a structural role for membrane protein targetting and assembly.

scholarly journals Stress fibers are embedded in a contractile cortical network

2020 ◽  
Author(s):  
Timothée Vignaud ◽  
Calina Copos ◽  
Christophe Leterrier ◽  
Qingzong Tseng ◽  
Laurent Blanchoin ◽  
...  
Keyword(s):  
Cell Fate ◽  
Actin Filaments ◽  
Mechanical Response ◽  
Force Production ◽  
Traction Force ◽  
Cortical Network ◽  
Cortical Actin ◽  
Cell Fate Decisions ◽  
Production And Distribution ◽  
Intracellular Forces

ABSTRACTContractile actomyosin networks generate intracellular forces essential for the regulation of cell shape, migration, and cell-fate decisions, ultimately leading to the remodeling and patterning of tissues. Although actin filaments aligned in bundles represent the main source of traction-force production in adherent cells, there is increasing evidence that these bundles form interconnected and interconvertible structures with the rest of the intracellular actin network. In this study, we explored how these bundles are connected to the surrounding cortical network and the mechanical impact of these interconnected structures on the production and distribution of traction forces on the extracellular matrix and throughout the cell. By using a combination of hydrogel micropatterning, traction-force microscopy and laser photoablation, we measured the relaxation of the cellular traction field in response to local photoablations at various positions within the cell. Our experimental results and modeling of the mechanical response of the network revealed that bundles were fully embedded along their entire length in a continuous and contractile network of cortical filaments. Moreover, the propagation of the contraction of these bundles throughout the entire cell was dependent on this embedding. In addition, these bundles appeared to originate from the alignment and coalescence of thin and unattached cortical actin filaments from the surrounding mesh.

scholarly journals The ATP binding cassette transporter, ABCG1, localizes to cortical actin filaments

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Elvis Pandzic ◽  
Ingrid C. Gelissen ◽  
Renee Whan ◽  
Philip J. Barter ◽  
Dmitri Sviridov ◽  
...  
Keyword(s):  
Actin Filaments ◽  
Atp Binding ◽  
Cortical Actin ◽  
Atp Binding Cassette Transporter ◽  
Atp Binding Cassette

scholarly journals Cortical Actin Filaments Form Rapidly during Photopolarization and Are Required for the Development of Calcium Gradients in Pelvetia compressa Zygotes

2000 ◽  
Vol 222 (2) ◽  
pp. 440-449 ◽  
Author(s):  
Rongsun Pu ◽  
Michele Wozniak ◽  
Kenneth R. Robinson
Keyword(s):  
Actin Filaments ◽  
Cortical Actin ◽  
Pelvetia Compressa

scholarly journals Filopodia formation and endosome clustering induced by mutant plus-end–directed myosin VI

2017 ◽  
Vol 114 (7) ◽  
pp. 1595-1600 ◽  
Author(s):  
Thomas A. Masters ◽  
Folma Buss
Keyword(s):  
Actin Filaments ◽  
Leucine Zipper ◽  
Adaptor Protein ◽  
Cell Cortex ◽  
Myosin Vi ◽  
Actin Network ◽  
Ph Domain ◽  
Cortical Actin ◽  
Directed Movement ◽  
Interacting Protein

Myosin VI (MYO6) is the only myosin known to move toward the minus end of actin filaments. It has roles in numerous cellular processes, including maintenance of stereocilia structure, endocytosis, and autophagosome maturation. However, the functional necessity of minus-end–directed movement along actin is unclear as the underlying architecture of the local actin network is often unknown. To address this question, we engineered a mutant of MYO6, MYO6+, which undergoes plus-end–directed movement while retaining physiological cargo interactions in the tail. Expression of this mutant motor in HeLa cells led to a dramatic reorganization of cortical actin filaments and the formation of actin-rich filopodia. MYO6 is present on peripheral adaptor protein, phosphotyrosine interacting with PH domain and leucine zipper 1 (APPL1) signaling endosomes and MYO6+ expression causes a dramatic relocalization and clustering of this endocytic compartment in the cell cortex. MYO6+ and its adaptor GAIP interacting protein, C terminus (GIPC) accumulate at the tips of these filopodia, while APPL1 endosomes accumulate at the base. A combination of MYO6+ mutagenesis and siRNA-mediated depletion of MYO6 binding partners demonstrates that motor activity and binding to endosomal membranes mediated by GIPC and PI(4,5)P2 are crucial for filopodia formation. A similar reorganization of actin is induced by a constitutive dimer of MYO6+, indicating that multimerization of MYO6 on endosomes through binding to GIPC is required for this cellular activity and regulation of actin network structure. This unique engineered MYO6+ offers insights into both filopodia formation and MYO6 motor function at endosomes and at the plasma membrane.

scholarly journals Functional Characterization and Localization of theAspergillus nidulans Formin SEPA

2002 ◽  
Vol 13 (2) ◽  
pp. 469-479 ◽  
Author(s):  
Kathryn E. Sharpless ◽  
Steven D. Harris
Keyword(s):  
Fusion Protein ◽  
Actin Filaments ◽  
Functional Characterization ◽  
Scaffold Proteins ◽  
Molecular Pathways ◽  
Null Mutant ◽  
Localization Pattern ◽  
Amino Terminal ◽  
Gfp Fusion Protein ◽  
Actin Rings

Formins are a family of multidomain scaffold proteins involved in actin-dependent morphogenetic events. In Aspergillus nidulans, the formin SEPA participates in two actin-mediated processes, septum formation and polarized growth. In this study, we use a new null mutant to demonstrate that SEPA is required for the formation of actin rings at septation sites. In addition, we find that a functional SEPA::GFP fusion protein localizes simultaneously to septation sites and hyphal tips, and that SEPA colocalizes with actin at each site. Using live imaging, we show that SEPA localization at septation sites and hyphal tips is dynamic. Notably, at septation sites, SEPA forms a ring that constricts as the septum is deposited. Moreover, we demonstrate that actin filaments are required to maintain the proper localization pattern of SEPA, and that the amino-terminal half of SEPA is sufficient for localization at septation sites and hyphal tips. In contrast, only localization at septation sites is affected by loss of the sepH gene product. We propose that specific morphological cues activate common molecular pathways to direct SEPA localization to the appropriate morphogenetic site.

scholarly journals Actin filament dynamics are dominated by rapid growth and severing activity in the Arabidopsis cortical array

2009 ◽  
Vol 184 (2) ◽  
pp. 269-280 ◽  
Author(s):  
Christopher J. Staiger ◽  
Michael B. Sheahan ◽  
Parul Khurana ◽  
Xia Wang ◽  
David W. McCurdy ◽  
...  
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Stochastic Dynamics ◽  
Actin Dynamics ◽  
Epifluorescence Microscopy ◽  
Actin Assembly ◽  
Cortical Actin ◽  
Filament Dynamics ◽  
Cortical Array

Metazoan cells harness the power of actin dynamics to create cytoskeletal arrays that stimulate protrusions and drive intracellular organelle movements. In plant cells, the actin cytoskeleton is understood to participate in cell elongation; however, a detailed description and molecular mechanism(s) underpinning filament nucleation, growth, and turnover are lacking. Here, we use variable-angle epifluorescence microscopy (VAEM) to examine the organization and dynamics of the cortical cytoskeleton in growing and nongrowing epidermal cells. One population of filaments in the cortical array, which most likely represent single actin filaments, is randomly oriented and highly dynamic. These filaments grow at rates of 1.7 µm/s, but are generally short-lived. Instead of depolymerization at their ends, actin filaments are disassembled by severing activity. Remodeling of the cortical actin array also features filament buckling and straightening events. These observations indicate a mechanism inconsistent with treadmilling. Instead, cortical actin filament dynamics resemble the stochastic dynamics of an in vitro biomimetic system for actin assembly.

scholarly journals Unconventional Myosins in Inner-Ear Sensory Epithelia

1997 ◽  
Vol 137 (6) ◽  
pp. 1287-1307 ◽  
Author(s):  
Tama Hasson ◽  
Peter G. Gillespie ◽  
Jesus A. Garcia ◽  
Richard B. MacDonald ◽  
Yi-dong Zhao ◽  
...  
Keyword(s):  
Inner Ear ◽  
Hair Cells ◽  
Actin Filaments ◽  
Structural Integrity ◽  
Myosin Vi ◽  
Cortical Actin ◽  
Unconventional Myosin ◽  
Myosin Isozymes ◽  
Cuticular Plate ◽  
Myosin Viia

To understand how cells differentially use the dozens of myosin isozymes present in each genome, we examined the distribution of four unconventional myosin isozymes in the inner ear, a tissue that is particularly reliant on actin-rich structures and unconventional myosin isozymes. Of the four isozymes, each from a different class, three are expressed in the hair cells of amphibia and mammals. In stereocilia, constructed of cross-linked F-actin filaments, myosin-Iβ is found mostly near stereociliary tips, myosin-VI is largely absent, and myosin-VIIa colocalizes with crosslinks that connect adjacent stereocilia. In the cuticular plate, a meshwork of actin filaments, myosin-Iβ is excluded, myosin-VI is concentrated, and modest amounts of myosin-VIIa are present. These three myosin isozymes are excluded from other actin-rich domains, including the circumferential actin belt and the cortical actin network. A member of a fourth class, myosin-V, is not expressed in hair cells but is present at high levels in afferent nerve cells that innervate hair cells. Substantial amounts of myosins-Iβ, -VI, and -VIIa are located in a pericuticular necklace that is largely free of F-actin, squeezed between (but not associated with) actin of the cuticular plate and the circumferential belt. Our localization results suggest specific functions for three hair-cell myosin isozymes. As suggested previously, myosin-Iβ probably plays a role in adaptation; concentration of myosin-VI in cuticular plates and association with stereociliary rootlets suggest that this isozyme participates in rigidly anchoring stereocilia; and finally, colocalization with cross-links between adjacent stereocilia indicates that myosin-VIIa is required for the structural integrity of hair bundles.

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