Visualization of actin filaments and monomers in somatic cell nuclei

In addition to its long-studied presence in the cytoplasm, actin is also found in the nuclei of eukaryotic cells. The function and form (monomer, filament, or noncanonical oligomer) of nuclear actin are hotly debated, and its localization and dynamics are largely unknown. To determine the distribution of nuclear actin in live somatic cells and evaluate its potential functions, we constructed and validated fluorescent nuclear actin probes. Monomeric actin probes concentrate in nuclear speckles, suggesting an interaction of monomers with RNA-processing factors. Filamentous actin probes recognize discrete structures with submicron lengths that are excluded from chromatin-rich regions. In time-lapse movies, these actin filament structures exhibit one of two types of mobility: 1) diffusive, with an average diffusion coefficient of 0.06–0.08 μm2/s, or (2) subdiffusive, with a mobility coefficient of 0.015 μm2/s. Individual filament trajectories exhibit features of particles moving within a viscoelastic mesh. The small size of nuclear actin filaments is inconsistent with a role in micron-scale intranuclear transport, and their localization suggests that they do not participate directly in chromatin-based processes. Our results instead suggest that actin filaments form part of a large, viscoelastic structure in the nucleoplasm and may act as scaffolds that help organize nuclear contents.

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GPCR-induced calcium transients trigger nuclear actin assembly for chromatin dynamics

Nature Communications ◽

10.1038/s41467-019-13322-y ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 16

Author(s):

Ying Wang ◽

Alice Sherrard ◽

Bing Zhao ◽

Michael Melak ◽

Jonathan Trautwein ◽

...

Keyword(s):

Actin Filaments ◽

Calcium Release ◽

Nuclear Actin ◽

Actin Assembly ◽

Filamentous Actin ◽

Cell Nuclei ◽

Chromatin Dynamics ◽

Surface Receptors ◽

Rapid Responses ◽

And Function

AbstractAlthough the properties of the actin cytoskeleton in the cytoplasm are well characterized, the regulation and function of nuclear actin filaments are only recently emerging. We previously demonstrated serum-induced, transient assembly of filamentous actin within somatic cell nuclei. However, the extracellular cues, cell surface receptors as well as underlying signaling mechanisms have been unclear. Here we demonstrate that physiological ligands for G protein-coupled receptors (GPCRs) promote nuclear F-actin assembly via heterotrimeric Gαq proteins. Signal-induced nuclear actin responses require calcium release from the endoplasmic reticulum (ER) targeting the ER-associated formin INF2 at the inner nuclear membrane (INM). Notably, calcium signaling promotes the polymerization of linear actin filaments emanating from the INM towards the nuclear interior. We show that GPCR and calcium elevations trigger nuclear actin-dependent alterations in chromatin organization, uncovering a general cellular mechanism by which physiological ligands and calcium promote nuclear F-actin assembly for rapid responses towards chromatin dynamics.

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The role of microfilaments in cytoplasmic streaming in Drosophila follicles

Journal of Cell Science ◽

10.1242/jcs.80.1.159 ◽

1986 ◽

Vol 80 (1) ◽

pp. 159-169 ◽

Cited By ~ 1

Author(s):

H.O. Gutzeit

Keyword(s):

Cell Membrane ◽

Nuclear Membrane ◽

Actin Filaments ◽

Cytoplasmic Streaming ◽

Nurse Cell ◽

Time Lapse ◽

Nurse Cells ◽

Cell Nuclei ◽

Cell Cytoplasm

During the last phase of oogenesis in Drosophila, nurse cell cytoplasm can be seen to be streaming into the growing oocyte when visualized in time-lapse films. This process can be reversibly inhibited by cytochalasins. The distribution of F-actin filaments in the nurse cells has been studied by staining with rhodamine-conjugated phalloidin. At the beginning of cytoplasmic streaming (stage 10B) increasingly thick bundles of microfilaments formed, many of which spanned the nurse cell cytoplasm from the cell membrane to the nuclear membrane. The association of F-actin with the nuclear membrane persisted when nurse cell nuclei were isolated mechanically. The experimental evidence suggests that microfilament contraction in the nurse cells leads to cytoplasmic streaming by pressure flow.

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Faculty Opinions recommendation of Visualization of actin filaments and monomers in somatic cell nuclei.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.717982313.793476991 ◽

2013 ◽

Author(s):

Jan Lammerding

Keyword(s):

Somatic Cell ◽

Actin Filaments ◽

Cell Nuclei

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Myofibrillar degeneration with diphtheria toxin

Turkish Journal of Biochemistry ◽

10.1515/tjb-2019-0109 ◽

2020 ◽

Vol 45 (4) ◽

pp. 351-357

Author(s):

Bilge Özerman Edis ◽

Muhammet Bektaş ◽

Rüstem Nurten

Keyword(s):

Protein Synthesis ◽

Actin Filaments ◽

Diphtheria Toxin ◽

Cardiac Tissue ◽

Culture Conditions ◽

Bacterial Toxin ◽

Filamentous Actin ◽

Cardiac Damage ◽

Tissue Samples

AbstractObjectivesCardiac damage in patient with diphtheritic myocarditis is reported as the leading cause of mortality. Diphtheria toxin (DTx) is a well-known bacterial toxin inducing various cytotoxic effects. Mainly, catalytic fragment inhibits protein synthesis, induces cytotoxicity, and depolymerizes actin filaments. In this study, we aimed to demonstrate the extent of myofibrillar damage under DTx treatment to porcine cardiac tissue samples.MethodsTissue samples were incubated with DTx for 1–3 h in culture conditions. To analyze whole toxin (both fragments) distribution, conjugation of DTx with FITC was performed. Measurements were carried out with fluorescence spectrophotometer before and after dialysis. Immunofluorescence microscopy was used to show localization of DTx-FITC (15 nM) on cardiac tissue incubated for 2 h. Ultrastructural characterization of cardiac tissue samples treated with DTx (15 or 150 nM) was performed with transmission electron microscopy.ResultsDTx exerts myofibrillar disorganization. Myofilament degeneration, mitochondrial damage, vacuolization, and abundant lipid droplets were determined with 150 nM of DTx treatment.ConclusionsThis finding is an addition to depolymerization of actin filaments as a result of the DTx-actin interactions in in vitro conditions, indicating that myofilament damage can occur with DTx directly besides protein synthesis inhibition. Ultrastructural results support the importance of filamentous actin degeneration at diphtheritic myocarditis.

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Effect of Modification on the Fluid Diffusion Coefficient in Silica Nanochannels

Molecules ◽

10.3390/molecules26134030 ◽

2021 ◽

Vol 26 (13) ◽

pp. 4030

Author(s):

Gengbiao Chen ◽

Zhiwen Liu

Keyword(s):

Diffusion Coefficient ◽

Diffusion Coefficients ◽

Surface Effect ◽

Bulk Water ◽

Self Diffusion ◽

Average Diffusion Coefficient ◽

Average Diffusion ◽

Chain Lengths ◽

Fluid Diffusion ◽

Self Diffusion Coefficient

The diffusion behavior of fluid water in nanochannels with hydroxylation of silica gel and silanization of different modified chain lengths was simulated by the equilibrium molecular dynamics method. The diffusion coefficient of fluid water was calculated by the Einstein method and the Green–Kubo method, so as to analyze the change rule between the modification degree of nanochannels and the diffusion coefficient of fluid water. The results showed that the diffusion coefficient of fluid water increased with the length of the modified chain. The average diffusion coefficient of fluid water in the hydroxylated nanochannels was 8.01% of the bulk water diffusion coefficient, and the diffusion coefficients of fluid water in the –(CH2)3CH3, –(CH2)7CH3, and –(CH2)11CH3 nanochannels were 44.10%, 49.72%, and 53.80% of the diffusion coefficients of bulk water, respectively. In the above four wall characteristic models, the diffusion coefficients in the z direction were smaller than those in the other directions. However, with an increase in the silylation degree, the increased self-diffusion coefficient due to the surface effect could basically offset the decreased self-diffusion coefficient owing to the scale effect. In the four nanochannels, when the local diffusion coefficient of fluid water was in the range of 8 Å close to the wall, Dz was greater than Dxy, and beyond the range of 8 Å of the wall, the Dz was smaller than Dxy.

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To be or not to be assembled: progressing into nuclear actin filaments

Nature Reviews Molecular Cell Biology ◽

10.1038/nrm3681 ◽

2013 ◽

Vol 14 (11) ◽

pp. 693-697 ◽

Cited By ~ 73

Author(s):

Robert Grosse ◽

Maria K. Vartiainen

Keyword(s):

Actin Filaments ◽

Nuclear Actin

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Molten Slag Structure and Diffusion Coefficients of Cr3+ and Si4+ during Micro-Carbon Cr-Fe Alloy Production

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.79.77 ◽

2011 ◽

Vol 79 ◽

pp. 77-82

Author(s):

Yi Min ◽

Jian Huang ◽

Cheng Jun Liu ◽

Mao Fa Jiang

Keyword(s):

Diffusion Coefficient ◽

Diffusion Coefficients ◽

Molten Slag ◽

Optimization Method ◽

Structure Theory ◽

Average Diffusion Coefficient ◽

Slag Structure ◽

Initial Stage ◽

Silicate Structure ◽

Average Diffusion

Based on the silicate structure theory, the molten slag structure and the existential state of and during micro-carbon Cr-Fe alloy production process were analysised, and then their diffusion coefficients were calculated. The results showed that, during the initial stage, the average diffusion coeffecient of and is close to the , the reaction process is controlled by the diffusion of () and corporately, during the later stage, the diffusion coefficient of is less than average diffusion coefficient of and , the controlling step is the diffusion of . According to the evolution of diffusion coefficient, molten slag composition optimization method was advised to increase the diffusion ability of and for enhancing the reaction efficiency and the recovery rate of chromium.

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αE-catenin actin-binding domain alters actin filament conformation and regulates binding of nucleation and disassembly factors

Molecular Biology of the Cell ◽

10.1091/mbc.e13-07-0388 ◽

2013 ◽

Vol 24 (23) ◽

pp. 3710-3720 ◽

Cited By ~ 62

Author(s):

Scott D. Hansen ◽

Adam V. Kwiatkowski ◽

Chung-Yueh Ouyang ◽

HongJun Liu ◽

Sabine Pokutta ◽

...

Keyword(s):

Actin Filament ◽

Actin Filaments ◽

Binding Domain ◽

Actin Binding ◽

Filamentous Actin ◽

Filament Structure ◽

Actin Binding Domain ◽

Filament Bundles ◽

Underlying Mechanisms ◽

Cell Cell

The actin-binding protein αE-catenin may contribute to transitions between cell migration and cell–cell adhesion that depend on remodeling the actin cytoskeleton, but the underlying mechanisms are unknown. We show that the αE-catenin actin-binding domain (ABD) binds cooperatively to individual actin filaments and that binding is accompanied by a conformational change in the actin protomer that affects filament structure. αE-catenin ABD binding limits barbed-end growth, especially in actin filament bundles. αE-catenin ABD inhibits actin filament branching by the Arp2/3 complex and severing by cofilin, both of which contact regions of the actin protomer that are structurally altered by αE-catenin ABD binding. In epithelial cells, there is little correlation between the distribution of αE-catenin and the Arp2/3 complex at developing cell–cell contacts. Our results indicate that αE-catenin binding to filamentous actin favors assembly of unbranched filament bundles that are protected from severing over more dynamic, branched filament arrays.

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