scholarly journals Structure of the fission yeast actomyosin ring during constriction

2018 ◽  
Vol 115 (7) ◽  
pp. E1455-E1464 ◽  
Author(s):  
Matthew T. Swulius ◽  
Lam T. Nguyen ◽  
Mark S. Ladinsky ◽  
Davi R. Ortega ◽  
Samya Aich ◽  
...  
Keyword(s):  
Angular Distribution ◽  
Actin Filaments ◽  
Direct Contact ◽  
3D Imaging ◽  
Nearest Neighbor ◽  
Ion Beam ◽  
Leading Edge ◽  
Electron Cryotomography ◽  
Nearest Neighbor Distances ◽  
Gain Access

Cell division in many eukaryotes is driven by a ring containing actin and myosin. While much is known about the main proteins involved, the precise arrangement of actin filaments within the contractile machinery, and how force is transmitted to the membrane, remains unclear. Here we use cryosectioning and cryofocused ion beam milling to gain access to cryopreserved actomyosin rings in Schizosaccharomyces pombe for direct 3D imaging by electron cryotomography. Our results show that straight, overlapping actin filaments, running nearly parallel to each other and to the membrane, form a loose bundle of ∼150 nm in diameter that “saddles” the inward-bending membrane at the leading edge of the division septum. The filaments do not make direct contact with the membrane. Our analysis of the actin filaments reveals the variability in filament number, nearest-neighbor distances between filaments within the bundle, their distance from the membrane, and angular distribution with respect to the membrane.

scholarly journals Structure of the fission yeast actomyosin ring during constriction

2017 ◽  
Author(s):  
Matthew T. Swulius ◽  
Lam T. Nguyen ◽  
Mark S. Ladinsky ◽  
Davi R. Ortega ◽  
Samya Aich ◽  
...  
Keyword(s):  
Schizosaccharomyces Pombe ◽  
Actin Filaments ◽  
Focused Ion Beam ◽  
Nearest Neighbor ◽  
Ion Beam ◽  
Three Dimensional ◽  
Model Organism ◽  
Leading Edge ◽  
Specimen Preparation ◽  
Electron Cryotomography

AbstractCell division in many eukaryotes is driven by a ring containing actin and myosin. While much is known about the main proteins involved, the precise arrangement of actin filaments within the contractile machinery, and how force is transmitted to the membrane remains unclear. Here we use cryosectioning and cryo-focused ion beam milling to gain access to cryo-preserved actomyosin rings in Schizosaccharomyces pombe for direct three-dimensional imaging by electron cryotomography. Our results show that straight, overlapping actin filaments, running nearly parallel to each other and to the membrane, form a loose bundle of approximately 150 nm in diameter that “saddles” the inward-bending membrane at the leading edge of the division septum. The filaments do not make direct contact with the membrane. Our analysis of the actin filaments reveals the variability in filament number, nearest-neighbor distances between filaments within the bundle, their distance from the membrane and angular distribution with respect to the membrane.Significance StatementMost eukaryotic cells divide using a contractile actomyosin ring, but its structure is unknown. Here we use new specimen preparation methods and electron cryotomography to image constricting rings directly in 3D, in a near-native state in the model organism Schizosaccharomyces pombe. Our images reveal the arrangement of individual actin filaments within the contracting actomyosin ring.

Application of Lattice Imaging Techniques to Amorphous Films

1975 ◽  
Vol 33 ◽  
pp. 8-9
Author(s):  
S. R. Herd ◽  
P. Chaudhari
Keyword(s):  
Nearest Neighbor ◽  
Random Network ◽  
Imaging Techniques ◽  
Network Models ◽  
Accurate Method ◽  
Direct Transmission ◽  
Lattice Imaging ◽  
Transmission Electron ◽  
Lattice Planes ◽  
Nearest Neighbor Distances

Electron diffraction and direct transmission have been used extensively to study the local atomic arrangement in amorphous solids and in particular Ge. Nearest neighbor distances had been calculated from E.D. profiles and the results have been interpreted in terms of the microcrystalline or the random network models. Direct transmission electron microscopy appears the most direct and accurate method to resolve this issue since the spacial resolution of the better instruments are of the order of 3Å. In particular the tilted beam interference method is used regularly to show fringes corresponding to 1.5 to 3Å lattice planes in crystals as resolution tests.

scholarly journals Contact formation during fibroblast locomotion: involvement of membrane ruffles and microtubules.

1988 ◽  
Vol 106 (3) ◽  
pp. 747-760 ◽  
Author(s):  
G Rinnerthaler ◽  
B Geiger ◽  
J V Small
Keyword(s):  
Actin Filaments ◽  
Leading Edge ◽  
Fiber Assembly ◽  
Contact Formation ◽  
Contact Patterns ◽  
Fluorescence And Electron Microscopy ◽  
Cell Substrate ◽  
History Of ◽  
Cytoskeletal Elements ◽  
Primordial Cell

We have correlated the motility of the leading edge of fibroblasts, monitored by phase-contrast cinematography, with the relative distributions of several cytoskeletal elements (vinculin, tubulin, and actin) as well as with the contact patterns determined by interference reflection microscopy. This analysis has revealed the involvement of both ruffles and microspikes, as well as microtubules in the initiation of focal contact formation. Nascent vinculin sites within the leading edge or at its base, taken as primordial cell-substrate contacts, were invariably colocalized with sites that showed a history of transient, prolonged, or cyclic ruffling activity. Extended microspike structures, often preceded the formation of ruffles. Immunofluorescent labeling indicated that some of these primordial contacts were in close apposition to the ends of microtubules that penetrated into the leading edge. By fluorescence and electron microscopy short bundles of actin filaments found at the base of the leading edge were identified as presumptive, primordial contacts. It is concluded that ruffles and microspikes, either independently or in combination, initiate and mark the sites for future contact. Plaque proteins then accumulate (within 10-30 s) at the contract site and, beneath ruffles, induce localized bundling of actin filaments. We propose that all primordial contacts support traction for leading edge protrusion but that only some persist long enough to nucleate stress fiber assembly. Microtubules are postulated as the elements that select, stabilize, and potentiate the formation of these latter, long-lived contacts.

STUDY OF THERMODYNAMIC PROPERTIES OF ZINC-BLENDE-TYPE SEMICONDUCTORS: TEMPERATURE AND PRESSURE DEPENDENCES

2011 ◽  
Vol 25 (12n13) ◽  
pp. 1041-1051 ◽  
Author(s):  
HO KHAC HIEU ◽  
VU VAN HUNG
Keyword(s):  
Nearest Neighbor ◽  
Thermodynamic Quantities ◽  
Atomic Displacements ◽  
Zinc Blende ◽  
The Mean ◽  
Temperature And Pressure ◽  
Analytical Expressions ◽  
Theoretical Results ◽  
Nearest Neighbor Distances ◽  
Statistical Moment Method

Using the statistical moment method (SMM), the temperature and pressure dependences of thermodynamic quantities of zinc-blende-type semiconductors have been investigated. The analytical expressions of the nearest-neighbor distances, the change of volumes and the mean-square atomic displacements (MSDs) have been derived. Numerical calculations have been performed for a series of zinc-blende-type semiconductors: GaAs , GaP , GaSb , InAs , InP and InSb . The agreement between our calculations and both earlier other theoretical results and experimental data is a support for our new theory in investigating the temperature and pressure dependences of thermodynamic quantities of semiconductors.

The angular distribution of scattered and sputtered 40-keV particles on polycrystalline targets

1968 ◽  
Vol 46 (6) ◽  
pp. 753-758 ◽  
Author(s):  
E. Formann ◽  
F. P. Viehböck ◽  
H. Wotke
Keyword(s):  
Angular Distribution ◽  
Activation Analysis ◽  
Hard Sphere ◽  
Ion Beam ◽  
Radioactive Tracer ◽  
Angular Distributions ◽  
Tracer Technique ◽  
Potential Approximation ◽  
Radioactive Tracer Technique ◽  
Graphite Rods

Based on the hard-sphere potential approximation, angular distributions of scattered particles at different mass ratios M1:M2 were calculated. The results were compared with experiments carried out with the following atoms:[Formula: see text]The sputtered particles from the target as well as from the incident-ion beam were collected on graphite rods and measured by either activation analysis or a radioactive tracer technique.

Tobacco harm reduction – time for grassroots action

2018 ◽  
Vol 21 (3) ◽  
Author(s):  
Mirosław Dworniczak
Keyword(s):  
Direct Contact ◽  
Electronic Cigarettes ◽  
Reliable Data ◽  
Medical Community ◽  
Healthcare Personnel ◽  
Health Prevention ◽  
Tobacco Harm Reduction ◽  
Access To Knowledge ◽  
Gain Access ◽  
New Devices

The fight against tobacco smoking is one of the priorities of contemporary health prevention. Previous, globally used methods were effective only to some point. The introduction of new devices, such as electronic cigarettes and heat-not-burn products, provides an opportunity to extend the list of tools supporting the fight against smoking. Considering the limited knowledge of professional advisors in this regard, the paper presents basic data on electronic cigarettes, e-liquids, and the possible adverse effects. In Poland, these new devices met with distrust and even reluctance of decision-making authorities, resulting in the lack of reliable data on these products addressed to the medical community. Therefore, it was proposed that healthcare personnel being in direct contact with patients should gain access to knowledge on electronic cigarettes, which is essential for advising those who wish to quit the addiction. With minimum information about these products, they will be able to convey this knowledge to their patients. At the same time, attention was drawn to the risks associated with the use of these products by children and adolescents.

scholarly journals High Rac1 activity is functionally translated into cytosolic structures with unique nanoscale cytoskeletal architecture

2019 ◽  
Vol 116 (4) ◽  
pp. 1267-1272 ◽  
Author(s):  
Daniel J. Marston ◽  
Karen L. Anderson ◽  
Mark F. Swift ◽  
Marie Rougie ◽  
Christopher Page ◽  
...  
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Network Architecture ◽  
Structural Changes ◽  
Epithelial Mesenchymal Transition ◽  
Spatial Cues ◽  
Mesenchymal Transition ◽  
Rac1 Activity ◽  
Structural Regime ◽  
Electron Cryotomography

Rac1 activation is at the core of signaling pathways regulating polarized cell migration. So far, it has not been possible to directly explore the structural changes triggered by Rac1 activation at the molecular level. Here, through a multiscale imaging workflow that combines biosensor imaging of Rac1 dynamics with electron cryotomography, we identified, within the crowded environment of eukaryotic cells, a unique nanoscale architecture of a flexible, signal-dependent actin structure. In cell regions with high Rac1 activity, we found a structural regime that spans from the ventral membrane up to a height of ∼60 nm above that membrane, composed of directionally unaligned, densely packed actin filaments, most shorter than 150 nm. This unique Rac1-induced morphology is markedly different from the dendritic network architecture in which relatively short filaments emanate from existing, longer actin filaments. These Rac1-mediated scaffold assemblies are devoid of large macromolecules such as ribosomes or other filament types, which are abundant at the periphery and within the remainder of the imaged volumes. Cessation of Rac1 activity induces a complete and rapid structural transition, leading to the absence of detectable remnants of such structures within 150 s, providing direct structural evidence for rapid actin filament network turnover induced by GTPase signaling events. It is tempting to speculate that this highly dynamical nanoscaffold system is sensitive to local spatial cues, thus serving to support the formation of more complex actin filament architectures—such as those mandated by epithelial−mesenchymal transition, for example—or resetting the region by completely dissipating.

Determining the Ratio of the Precipitated versus Substituted Arsenic by XAFS and SIMS in Heavy Dose Arsenic Implants in Silicon

2001 ◽  
Vol 669 ◽  
Author(s):  
M. A. Sahiner ◽  
S. W. Novak ◽  
J. C. Woicik ◽  
J. Liu ◽  
V. Krishnamoorty
Keyword(s):  
Solid Solubility ◽  
Amorphous Materials ◽  
Nearest Neighbor ◽  
Secondary Ion Mass Spectrometry ◽  
Local Environment ◽  
Coordination Numbers ◽  
Annealing Conditions ◽  
X Ray Absorption ◽  
Secondary Ion ◽  
Nearest Neighbor Distances

ABSTRACTDoping silicon with arsenic by ion implantation above the solid solubility level leads to As clusters and/or precipitates in the form of monoclinic SiAs causing electrical deactivation of the dopant. Information on the local structure around the As atom, and the As concentration depth profiles is important for the implantation and annealing process in order to reduce the precipitated As and maximize the electrically activated As. In this study, we determined the local As structure and the precipitated versus substituted As for As implants in CZ (001) Si wafers, with implant energies between 20 keV and 100 keV, and implant doses ranging from 1 × 1015/cm2 to 1 × 1018/cm2. The samples were subjected to different thermal annealing conditions. We used secondary ion mass spectrometry (SIMS) and UT- MARLOWE simulations to determine the region where the As-concentration is above the solid solubility level. By x-ray absorption fine structure spectroscopy (XAFS), we probed the structure of the local environment around As. XAFS being capable of probing the short-range order in crystalline and amorphous materials provides information on the number, distance and chemical identity of the neighbors of the main absorbing atom. Using Fourier analysis, the coordination numbers (N) and the nearest-neighbor distances (R) to As atoms in the first shell were extracted from the XAFS data. When As precipitates as monoclinic SiAs, the nearest-neighbor distances and coordination numbers are ∼2.37 Å and ∼3, as opposed to ∼2.40 Å and ∼4 when As is substitutional. Based on this information, the critical implant dose where the precipitation/clustering of As starts, and the ratio of the substitutional versus cluster/precipitate form As in the samples were determined.

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