scholarly journals The roles of microtubules and membrane tension in axonal beading, retraction, and atrophy

2019 ◽  
Author(s):  
Anagha Datar ◽  
Jaishabanu Ameeramja ◽  
Alka Bhat ◽  
Roli Srivastava ◽  
Roberto Bernal ◽  
...  
Keyword(s):  
Driving Force ◽  
Membrane Tension ◽  
Controlled Experiments ◽  
Microtubule Depolymerization ◽  
Shape Transformation ◽  
Axonal Atrophy ◽  
Microtubule Stability ◽  
Shape Transformations ◽  
Morphological Transformations ◽  
Theoretical Considerations

AbstractAxonal beading—formation of a series of swellings along the axon—and retraction are commonly observed shape transformations that precede axonal atrophy in Alzheimer’s, Parkinson, and other neurodegenerative conditions. The mechanisms driving these morphological transformations are poorly understood. Here we report controlled experiments which can induce either beading or retraction and follow the time evolution of these responses. By making quantitative analysis of the shape modes under different conditions, measurement of membrane tension, and using theoretical considerations, we argue that membrane tension is the main driving force that pushes cytosol out of the axon when microtubules are degraded, causing axonal thinning. Under pharmacological perturbation, atrophy is always retrograde and this is set by a gradient in the microtubule stability. The nature of microtubule depolymerization dictates the type of shape transformation vis à vis beading or retraction. Elucidating the mechanisms of these shape transformations will facilitate development of strategies to prevent or arrest axonal atrophy due to neurodegenerative conditions.

Shape transformations of Pt nanocrystals enclosed with high-index facets and low-index facets

CrystEngComm ◽  
2021 ◽  
Vol 23 (38) ◽  
pp. 6655-6660
Author(s):  
Chi Xiao ◽  
Na Tian ◽  
Wei-Ze Li ◽  
Xi-Ming Qu ◽  
Jia-Huan Du ◽  
...  
Keyword(s):  
Potential Method ◽  
High Index ◽  
Shape Transformation ◽  
Square Wave ◽  
Wave Potential ◽  
Shape Transformations ◽  
Pt Nanocrystals

Shape transformation between high-index faceted Pt nanocrystals and low-index faceted ones have been achieved by an electrochemical square-wave potential method.

Spatiotemporal control of functional specification and distribution of spindle microtubules with 13, 14 and 15 protofilaments during mitosis in the ciliate Nyctotherus

1985 ◽  
Vol 76 (1) ◽  
pp. 337-355
Author(s):  
U. Eichenlaub-Ritter
Keyword(s):  
Differential Sensitivity ◽  
Microtubule Depolymerization ◽  
Functional Specification ◽  
Microtubule Stability ◽  
Early Anaphase ◽  
Late Telophase ◽  
Spindle Microtubules ◽  
Elongation Phase ◽  
Spatiotemporal Control ◽  
Macronuclear Division

The formation of microtubules with more than 13 protofilaments in the ciliate Nyctotherus ovalis Leidy seems to be a highly ordered process. Such microtubules are restricted to the nucleoplasm and, moreover, to certain stages of nuclear division. They assemble during anaphase of micronuclear mitosis and during the elongation phase of macronuclear division. The number of microtubules with more than 13 protofilaments in the micronuclear nucleoplasm increases as anaphase progresses. Furthermore, assembly of microtubules with 14 and 15 protofilaments seems to proceed concomitantly with net disassembly of 13-protofilament microtubules, because the total amount of polymerized tubulin in the interpolar spindle region remains approximately constant between mid anaphase and late telophase. In addition, evidence for spatial control of the distribution of microtubules with different protofilament numbers in the micronuclear stembody has been found. The percentage of microtubules with 13 protofilaments per stembody cross-section is highest at the ends of the stembody, while the percentage of microtubules with either 14 or 15 protofilaments increases as the middle of the stembody is approached. Temporal control of polymerization of microtubules with high protofilament numbers seems to be exerted independently in the two types of nuclei. For example, when the macronucleus starts to elongate it contains microtubules with more than 13 protofilaments but the metaphase micronucleus still possesses only microtubules with 13 protofilaments at this stage. Control of fidelity of protofilament numbers is not lost in the early stages of micronuclear or macronuclear division when cells are exposed to 2H2O or media containing taxol. Even microtubules that reassemble during recovery of metaphase micronuclei from nocodazole-induced microtubule depolymerization, in either the absence or presence of 2H2O and taxol, possess 13 protofilaments. Similarly, if the introduction of microtubules with 14 and 15 protofilaments is inhibited during early micronuclear anaphase and delayed for 60 min by exposure to nocodazole, such microtubules still assemble during telophase when recovery is permitted. Microtubules that have been assembled under normal conditions show differential sensitivity to nocodazole. During metaphase, nocodazole induces disassembly of most microtubules. There is an increase in microtubule stability that coincides with the appearance of microtubules with high protofilament numbers during early anaphase. However, considerable numbers of 13-protofilament microtubules, as well as microtubules with 14 and 15 protofilaments, exhibit such stability during anaphase.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Microtubule aging probed by microfluidics-assisted tubulin washout

2016 ◽  
Vol 27 (22) ◽  
pp. 3563-3573 ◽  
Author(s):  
Christian Duellberg ◽  
Nicholas Ian Cade ◽  
Thomas Surrey
Keyword(s):  
Molecular Mechanism ◽  
Growth Phase ◽  
Morphological Changes ◽  
Threshold Model ◽  
Theoretical Models ◽  
Age Dependence ◽  
Microtubule Depolymerization ◽  
Microtubule Stability ◽  
Age Dependent

Microtubules switch stochastically between phases of growth and shrinkage. The molecular mechanism responsible for the end of a growth phase, an event called catastrophe, is still not understood. The probability for a catastrophe to occur increases with microtubule age, putting constraints on the possible molecular mechanism of catastrophe induction. Here we used microfluidics-assisted fast tubulin washout experiments to induce microtubule depolymerization in a controlled manner at different times after the start of growth. We found that aging can also be observed in this assay, providing valuable new constraints against which theoretical models of catastrophe induction can be tested. We found that the data can be quantitatively well explained by a simple kinetic threshold model that assumes an age-dependent broadening of the protective cap at the microtubule end as a result of an evolving tapered end structure; this leads to a decrease of the cap density and its stability. This analysis suggests an intuitive picture of the role of morphological changes of the protective cap for the age dependence of microtubule stability.

SHAPE TRANSFORMATION MODELS AND THEIR APPLICATIONS IN PATTERN RECOGNITION

1990 ◽  
Vol 04 (01) ◽  
pp. 65-94 ◽  
Author(s):  
Z.C. LI ◽  
Y.Y. TANG ◽  
T.D. BUI ◽  
C.Y. SUEN
Keyword(s):  
Pattern Recognition ◽  
Chinese Characters ◽  
Computer Algorithms ◽  
Transformation Models ◽  
Shape Transformation ◽  
Geometric Properties ◽  
Shape Transformations ◽  
Computer Recognition ◽  
Theoretical Analyses

This paper presents linear and bilinear shape transformations including basic transformations, analyzes their geometric properties, and provides computer algorithms. The shape transformations can be used to simplify the recognition of Roman letters, Chinese characters and other pictorial patterns by normalizing their shapes to the standard forms. Important theoretical analyses have been performed to illustrate that the linear and bilinear transformations are applicable to computer recognition of digitized patterns. A number of pictorial examples have been computed to confirm the analyses and conclusions made.

Innovative Building Forms Determined by Orthotropic Properties of Folded Sheets Transformed Into Roof Shells

2020 ◽  
Vol 61 (2) ◽  
pp. 111-124
Author(s):  
Aleksandra Prokopska ◽  
Jacek Abramczyk
Keyword(s):  
Computational Models ◽  
High Sensitivity ◽  
Free Form ◽  
Shape Transformation ◽  
Steel Sheets ◽  
Shape Transformations ◽  
Thin Walled ◽  
Orthotropic Properties ◽  
Roof Shells ◽  
Qualitative And Quantitative Characteristics

Qualitative and quantitative characteristics of geometrical and mechanical changes of nominally plane steel sheets folded in one direction, caused by big elastic shape transformations were invented on the basis of the authors' tests, analyzes and computational models of thin-walled folded sheets transformed into shell shapes. Both geometrical and mechanical changes produce significant restrictions in using sheets for shell forms. The deliberate transformations and sheets' characteristics are required to obtain attractive and innovative forms of roof shells and their consistent structures as well as entire buildings. The search for effective solutions related to free forms of buildings and shape transformations of sheets especially in the fields of: shape transformation, effort and stabilization of their walls is necessary due to the high sensitivity of thin-walled open profiles to boundary conditions and loads. A method for shaping such free form buildings that effectively exploit specific orthotropic properties of the transformed sheeting is presented.

SHAPE TRANSFORMATIONS OF VESICLES BUILT OF AMPHIPHILIC MOLECULES

2008 ◽  
Vol 03 (03) ◽  
pp. 397-420 ◽  
Author(s):  
W. T. GÓŹDŹ
Keyword(s):  
Recent Work ◽  
Colloidal Particles ◽  
Spontaneous Curvature ◽  
Shape Transformation ◽  
Rigid Object ◽  
Amphiphilic Molecules ◽  
Shape Transformations ◽  
External Stimuli

We review our recent work on the shape transformations of vesicles subject to external stimuli. Possible shape transformations resulting from the change of the spontaneous curvature, volume, or composition of the components on the surface of a vesicle are examined within the framework of the spontaneus curvature model. The influence of encapsulated or adhered rigid object such as microtubules or colloidal particles on the shape transformation is also investigated. A few cases of shape transformations encountered in experiments are described.

Shape and Shape Transformation of Heated Human Red Cells

1949 ◽  
Vol 26 (1) ◽  
pp. 35-45
Author(s):  
ERIC PONDER
Keyword(s):  
Serum Albumin ◽  
Red Cells ◽  
Red Cell ◽  
Shape Transformation ◽  
Shape Transformations ◽  
Higher Temperature ◽  
Shape Changes ◽  
Human Red Cells

This paper describes the shape changes and shape transformations observed in human red cells heated for 2 min. to 48, 50 and 52° C. The first change observed is an irregularity of the cell; this is followed by sphering, but the spherical forms can be turned into irregularly shaped disks again by the addition of serum albumin. The sphering is accordingly part of a reversible disk-sphere transformation due to the loss of a (recoverable) anti-sphering substance from the cells. At a slightly higher temperature 50°C.) fragmentation of the cells occurs with the production of fragments which are also capable of undergoing something equivalent to a disk-sphere transformation. The properties upon which the shape transformations depend are therefore not necessarily dependent on the integrity of the red cell as a unit. The fragments derived from the cell may be unequally haemoglobinized, and the Hb is usually lost in a step-wise, as opposed to an all-or-none, manner. Taken together with the loss of anti-sphering substance and an accompanying loss of potassium from the cells, the shape changes preceding fragmentation and the step-wise loss of Hb suggest that the phenomena observed in the heated red cell are part of a process of disintegration of a plastic Hb-bearing ‘solid’.

scholarly journals Microtubules regulate pancreatic β cell heterogeneity via spatiotemporal control of insulin secretion hot spots

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Kathryn P Trogden ◽  
Justin S Lee ◽  
Kai M Bracey ◽  
Kung-Hsien Ho ◽  
Hudson McKinney ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Hot Spots ◽  
Cell Heterogeneity ◽  
Microtubule Depolymerization ◽  
Β Cell ◽  
Microtubule Stability ◽  
Mouse Islets ◽  
Regulation Of Secretion ◽  
Glucose Stimulated Insulin Secretion ◽  
Spatiotemporal Control

Heterogeneity of glucose-stimulated insulin secretion (GSIS) in pancreatic islets is physiologically important but poorly understood. Here, we utilize mouse islets to determine how microtubules affect secretion toward the vascular extracellular matrix at single cell and subcellular levels. Our data indicate that microtubule stability in the β-cell population is heterogenous, and that GSIS is suppressed in cells with highly stable microtubules. Consistently, microtubule hyper-stabilization prevents, and microtubule depolymerization promotes capacity of single β-cell for GSIS. Analysis of spatiotemporal patterns of secretion events shows that microtubule depolymerization activates otherwise dormant β-cells via initiation of secretion clusters (hot spots). Microtubule depolymerization also enhances secretion from individual cells, introducing both additional clusters and scattered events. Interestingly, without microtubules, the timing of clustered secretion is dysregulated, extending the first phase of GSIS and causing oversecretion. In contrast, glucose-induced Ca2+ influx was not affected by microtubule depolymerization yet required for secretion under these conditions, indicating that microtubule-dependent regulation of secretion hot spots acts in parallel with Ca2+ signaling. Our findings uncover a novel microtubule function in tuning insulin secretion hot spots, which leads to accurately measured and timed response to glucose stimuli and promotes functional β-cell heterogeneity.

scholarly journals Irreversible and Repeatable Shape Transformation of Additively Manufactured Annular Composite Structures

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1383
Author(s):  
Bona Goo ◽  
Jong-Bong Kim ◽  
Dong-Gyu Ahn ◽  
Keun Park
Keyword(s):  
Composite Structures ◽  
Memory Function ◽  
Dimensional Accuracy ◽  
Transformation Method ◽  
Manufacturing Cost ◽  
Thermal Stimulus ◽  
4D Printing ◽  
Shape Transformation ◽  
Shape Transformations ◽  
Accuracy And Repeatability

Four-dimensional (4D) printing is a unique application of additive manufacturing (AM) which enables additional shape transformations over time. Although 4D printing is an interesting and attractive phenomenon, it still faces several challenges before it can be used for practical applications: (i) the manufacturing cost should be competitive, and (ii) the shape transformations must have high dimensional accuracy and repeatability. In this study, an irreversible and repeatable thermoresponsive shape transformation method was developed using a material extrusion type AM process and a plain thermoplastic polymer (ABS) without a shape-memory function. Various types of annular discs were additively manufactured using printing paths programmed along a circular direction, and additional heat treatment was conducted as a thermal stimulus. The programmed circumferential anisotropy led to a unique 2D-to-3D shape transformation in response to the thermal stimulus. To obtain more predictable and repeatable shape transformation, the thermal stimulus was applied while using a geometric constraint. The relevant dimensional accuracy and repeatability of the constrained and unconstrained thermal deformations were compared. The proposed shape transformation method was further applied to AM and to the in situ assembly of a composite frame–membrane structure, where a functional membrane was integrated into a curved 3D frame without any additional assembly procedure.

scholarly journals Shape remodeling and blebbing of active cytoskeletal vesicles

2016 ◽  
Vol 2 (4) ◽  
pp. e1500465 ◽  
Author(s):  
Etienne Loiseau ◽  
Jochen A. M. Schneider ◽  
Felix C. Keber ◽  
Carina Pelzl ◽  
Gladys Massiera ◽  
...  
Keyword(s):  
Molecular Motors ◽  
Contractile Activity ◽  
Lipid Vesicles ◽  
Building Blocks ◽  
Living Cells ◽  
Force Balance ◽  
Actin Network ◽  
Shape Transformation ◽  
Cytoskeletal Network ◽  
Morphological Transformations

Morphological transformations of living cells, such as shape adaptation to external stimuli, blebbing, invagination, or tethering, result from an intricate interplay between the plasma membrane and its underlying cytoskeleton, where molecular motors generate forces. Cellular complexity defies a clear identification of the competing processes that lead to such a rich phenomenology. In a synthetic biology approach, designing a cell-like model assembled from a minimal set of purified building blocks would allow the control of all relevant parameters. We reconstruct actomyosin vesicles in which the coupling of the cytoskeleton to the membrane, the topology of the cytoskeletal network, and the contractile activity can all be precisely controlled and tuned. We demonstrate that tension generation of an encapsulated active actomyosin network suffices for global shape transformation of cell-sized lipid vesicles, which are reminiscent of morphological adaptations in living cells. The observed polymorphism of our cell-like model, such as blebbing, tether extrusion, or faceted shapes, can be qualitatively explained by the protein concentration dependencies and a force balance, taking into account the membrane tension, the density of anchoring points between the membrane and the actin network, and the forces exerted by molecular motors in the actin network. The identification of the physical mechanisms for shape transformations of active cytoskeletal vesicles sets a conceptual and quantitative benchmark for the further exploration of the adaptation mechanisms of cells.

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