scholarly journals GTP-dependent formation of straight tubulin oligomers leads to microtubule nucleation

2021 ◽  
Vol 220 (4) ◽  
Author(s):  
Rie Ayukawa ◽  
Seigo Iwata ◽  
Hiroshi Imai ◽  
Shinji Kamimura ◽  
Masahito Hayashi ◽  
...  
Keyword(s):  
Critical Size ◽  
Early Stage ◽  
Negative Stain ◽  
Gtp Binding ◽  
Cellular Factors ◽  
Minor Population ◽  
Negative Stain Electron Microscopy ◽  
Stochastic Events ◽  
Curvature Distribution ◽  
A Minor

Nucleation of microtubules (MTs) is essential for cellular activities, but its mechanism is unknown because of the difficulty involved in capturing rare stochastic events in the early stage of polymerization. Here, combining rapid flush negative stain electron microscopy (EM) and kinetic analysis, we demonstrate that the formation of straight oligomers of critical size is essential for nucleation. Both GDP and GTP tubulin form single-stranded oligomers with a broad range of curvatures, but upon nucleation, the curvature distribution of GTP oligomers is shifted to produce a minor population of straight oligomers. With tubulin having the Y222F mutation in the β subunit, the proportion of straight oligomers increases and nucleation accelerates. Our results support a model in which GTP binding generates a minor population of straight oligomers compatible with lateral association and further growth to MTs. This study suggests that cellular factors involved in nucleation promote it via stabilization of straight oligomers.

scholarly journals GTP-dependent formation of straight oligomers leads to nucleation of microtubules

2020 ◽  
Author(s):  
Rie Ayukawa ◽  
Seigo Iwata ◽  
Hiroshi Imai ◽  
Shinji Kamimura ◽  
Masahito Hayashi ◽  
...  
Keyword(s):  
High Efficiency ◽  
Early Stage ◽  
Synergistic Effects ◽  
Underlying Mechanism ◽  
Small Shift ◽  
Spontaneous Nucleation ◽  
Cellular Factors ◽  
Stochastic Events ◽  
A Minor

AbstractMicrotubule (MT) nucleation is essential for cellular activities, but its mechanism is not known because of the difficulty involved in capturing rare stochastic events in the early stage of polymerization. In cells, MTs are nucleated at tubulin concentrations significantly lower than those required for spontaneous nucleation in vitro. The high efficiency of nucleation is due to the synergistic effects of various cellular factors, but the underlying mechanism has not been clarified yet. Here, combining negative stain electron microscopy and kinetic analysis, we demonstrate that the formation of single-stranded straight oligomers with critical size is essential for nucleation in vitro. While the single-stranded oligomers of GTP-tubulin that form prior to MT nucleation show variable curvatures including a few straight oligomers, only curved oligomers are observed among the GDP-bound counterparts. The Y222F mutation in β-tubulin increases the proportion of straight oligomers and drastically accelerates MT nucleation. Our results support a model in which GTP binding causes a small shift in the distribution of oligomer curvature, generating a minor population of straight oligomers compatible with lateral association and further growth to MTs. Our study suggests that cellular factors involved in nucleation promote it via stabilization of straight oligomers.

scholarly journals Individual BFU-E in polycythemia vera produce both erythropoietin dependent and independent progeny

Blood ◽  
1983 ◽  
Vol 61 (5) ◽  
pp. 876-884 ◽  
Author(s):  
J Cashman ◽  
D Henkelman ◽  
K Humphries ◽  
C Eaves ◽  
A Eaves
Keyword(s):  
Polycythemia Vera ◽  
Peripheral Blood ◽  
Small Volume ◽  
Early Stage ◽  
Final Concentration ◽  
The Other ◽  
Normal Individuals ◽  
Additional Control ◽  
Minor Population ◽  
A Minor

Abstract Erythropoietic progenitors from peripheral blood of normal individuals or patients with polycythemia vera (PV) were cultured in methylcellulose medium containing 2.5 U/ml of erythropoietin (Ep). After 7–9 days, colonies considered to be early stage large bursts were individually removed, resuspended in a small volume of fresh methylcellulose medium, and then divided between 2 dishes. To one of these secondary cultures, sufficient Ep was added to bring the concentration of Ep up to approximately 3 U/ml. To the other was added an equal volume of medium but no Ep. The final concentration of Ep in these cultures was determined to be less than 0.01 U/ml. Nine days later, both types of secondary cultures were scored for the presence of colonies containing 8 or more hemoglobinized erythroblasts. Of 90 primary colonies from 3 normal individuals assessed in this way, 59 gave secondary erythroid colonies in the high Ep cultures, while none gave secondary erythroid colonies in the low Ep cultures. Additional control experiments in which primary colonies from normal individuals were divided into duplicate high Ep cultures showed that on average, the procedure used divided primary colonies equally. Of 109 primary colonies from 5 PV patients that yielded secondary erythroid colonies in the high Ep cultures, 21 yielded no secondary erythroid colonies in the low Ep cultures. The other 88 yielded erythroid colonies in both, but the secondary colonies in the low Ep cultures were consistently smaller in size and significantly fewer in number. Similar results were obtained when primary colonies were generated in cultures to which no Ep was added. These findings indicate that primitive BFU-E in patients with PV can be subdivided into 2 populations: a minor population restricted to the production of erythroid colony-forming cells (Ep- dependent progenitors) that require Ep for their detection, and a major population that is not restricted in this way. In addition, these experiments show that most of the primitive BFU-E that generate Ep- independent progenitors also produce significant numbers of cells that are Ep-dependent.

scholarly journals Individual BFU-E in polycythemia vera produce both erythropoietin dependent and independent progeny

Blood ◽  
1983 ◽  
Vol 61 (5) ◽  
pp. 876-884 ◽  
Author(s):  
J Cashman ◽  
D Henkelman ◽  
K Humphries ◽  
C Eaves ◽  
A Eaves
Keyword(s):  
Polycythemia Vera ◽  
Peripheral Blood ◽  
Small Volume ◽  
Early Stage ◽  
Final Concentration ◽  
The Other ◽  
Normal Individuals ◽  
Additional Control ◽  
Minor Population ◽  
A Minor

Erythropoietic progenitors from peripheral blood of normal individuals or patients with polycythemia vera (PV) were cultured in methylcellulose medium containing 2.5 U/ml of erythropoietin (Ep). After 7–9 days, colonies considered to be early stage large bursts were individually removed, resuspended in a small volume of fresh methylcellulose medium, and then divided between 2 dishes. To one of these secondary cultures, sufficient Ep was added to bring the concentration of Ep up to approximately 3 U/ml. To the other was added an equal volume of medium but no Ep. The final concentration of Ep in these cultures was determined to be less than 0.01 U/ml. Nine days later, both types of secondary cultures were scored for the presence of colonies containing 8 or more hemoglobinized erythroblasts. Of 90 primary colonies from 3 normal individuals assessed in this way, 59 gave secondary erythroid colonies in the high Ep cultures, while none gave secondary erythroid colonies in the low Ep cultures. Additional control experiments in which primary colonies from normal individuals were divided into duplicate high Ep cultures showed that on average, the procedure used divided primary colonies equally. Of 109 primary colonies from 5 PV patients that yielded secondary erythroid colonies in the high Ep cultures, 21 yielded no secondary erythroid colonies in the low Ep cultures. The other 88 yielded erythroid colonies in both, but the secondary colonies in the low Ep cultures were consistently smaller in size and significantly fewer in number. Similar results were obtained when primary colonies were generated in cultures to which no Ep was added. These findings indicate that primitive BFU-E in patients with PV can be subdivided into 2 populations: a minor population restricted to the production of erythroid colony-forming cells (Ep- dependent progenitors) that require Ep for their detection, and a major population that is not restricted in this way. In addition, these experiments show that most of the primitive BFU-E that generate Ep- independent progenitors also produce significant numbers of cells that are Ep-dependent.

Polysaccharide Structures in the Outer Mucilage of Arabidopsis Seeds Visualized by AFM

2020 ◽  
Author(s):  
MAK Williams ◽  
V Cornuault ◽  
AH Irani ◽  
VV Symonds ◽  
J Malmström ◽  
...  
Keyword(s):  
Average Length ◽  
American Chemical Society ◽  
Md Simulations ◽  
Chemical Society ◽  
Side Chains ◽  
Rhamnogalacturonan I ◽  
Afm Imaging ◽  
Minor Population ◽  
The Stability ◽  
A Minor

© 2020 American Chemical Society. Evidence is presented that the polysaccharide rhamnogalacturonan I (RGI) can be biosynthesized in remarkably organized branched configurations and surprisingly long versions and can self-assemble into a plethora of structures. AFM imaging has been applied to study the outer mucilage obtained from wild-type (WT) and mutant (bxl1-3 and cesa5-1) Arabidopsis thaliana seeds. For WT mucilage, ordered, multichain structures of the polysaccharide RGI were observed, with a helical twist visible in favorable circumstances. Molecular dynamics (MD) simulations demonstrated the stability of several possible multichain complexes and the possibility of twisted fibril formation. For bxl1-3 seeds, the imaged polymers clearly showed the presence of side chains. These were surprisingly regular and well organized with an average length of ∼100 nm and a spacing of ∼50 nm. The heights of the side chains imaged were suggestive of single polysaccharide chains, while the backbone was on average 4 times this height and showed regular height variations along its length consistent with models of multichain fibrils examined in MD. Finally, in mucilage extracts from cesa5-1 seeds, a minor population of chains in excess of 30 μm long was observed.

scholarly journals Second messenger Ap4A polymerizes target protein HINT1 to transduce signals in FcεRI-activated mast cells

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Jing Yu ◽  
Zaizhou Liu ◽  
Yuanyuan Liang ◽  
Feng Luo ◽  
Jie Zhang ◽  
...  
Keyword(s):  
Mast Cells ◽  
Transcriptional Activation ◽  
Second Messenger ◽  
Signaling Mechanism ◽  
Cellular Processes ◽  
Negative Stain ◽  
Competitive Mechanism ◽  
Rat Basophilic Leukemia Cells ◽  
Negative Stain Electron Microscopy ◽  
Basophilic Leukemia

Abstract Signal transduction systems enable organisms to monitor their external environments and accordingly adjust the cellular processes. In mast cells, the second messenger Ap4A binds to the histidine triad nucleotide-binding protein 1 (HINT1), disrupts its interaction with the microphthalmia-associated transcription factor (MITF), and eventually activates the transcription of genes downstream of MITF in response to immunostimulation. How the HINT1 protein recognizes and is regulated by Ap4A remain unclear. Here, using eight crystal structures, biochemical experiments, negative stain electron microscopy, and cellular experiments, we report that Ap4A specifically polymerizes HINT1 in solution and in activated rat basophilic leukemia cells. The polymerization interface overlaps with the area on HINT1 for MITF interaction, suggesting a possible competitive mechanism to release MITF for transcriptional activation. The mechanism depends precisely on the length of the phosphodiester linkage of Ap4A. These results highlight a direct polymerization signaling mechanism by the second messenger.

scholarly journals Ultrastructural and Biophysical Characterization of Hepatitis C Virus Particles Produced in Cell Culture

2010 ◽  
Vol 84 (21) ◽  
pp. 10999-11009 ◽  
Author(s):  
Pablo Gastaminza ◽  
Kelly A. Dryden ◽  
Bryan Boyd ◽  
Malcolm R. Wood ◽  
Mansun Law ◽  
...  
Keyword(s):  
Cell Culture ◽  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Structural Characteristics ◽  
Buoyant Density ◽  
Hcv Rna ◽  
Membrane Bilayer ◽  
Biophysical Characterization ◽  
Negative Stain ◽  
A Minor

ABSTRACT We analyzed the biochemical and ultrastructural properties of hepatitis C virus (HCV) particles produced in cell culture. Negative-stain electron microscopy revealed that the particles were spherical (∼40- to 75-nm diameter) and pleomorphic and that some of them contain HCV E2 protein and apolipoprotein E on their surfaces. Electron cryomicroscopy revealed two major particle populations of ∼60 and ∼45 nm in diameter. The ∼60-nm particles were characterized by a membrane bilayer (presumably an envelope) that is spatially separated from an internal structure (presumably a capsid), and they were enriched in fractions that displayed a high infectivity-to-HCV RNA ratio. The ∼45-nm particles lacked a membrane bilayer and displayed a higher buoyant density and a lower infectivity-to-HCV RNA ratio. We also observed a minor population of very-low-density, >100-nm-diameter vesicular particles that resemble exosomes. This study provides low-resolution ultrastructural information of particle populations displaying differential biophysical properties and specific infectivity. Correlative analysis of the abundance of the different particle populations with infectivity, HCV RNA, and viral antigens suggests that infectious particles are likely to be present in the large ∼60-nm HCV particle populations displaying a visible bilayer. Our study constitutes an initial approach toward understanding the structural characteristics of infectious HCV particles.

scholarly journals Structure–function mapping of a heptameric module in the nuclear pore complex

2012 ◽  
Vol 196 (4) ◽  
pp. 419-434 ◽  
Author(s):  
Javier Fernandez-Martinez ◽  
Jeremy Phillips ◽  
Matthew D. Sekedat ◽  
Ruben Diaz-Avalos ◽  
Javier Velazquez-Muriel ◽  
...  
Keyword(s):  
Nuclear Pore Complex ◽  
Protein Domain ◽  
Integrative Approach ◽  
Nuclear Pore ◽  
Mapping Data ◽  
Phenotypic Data ◽  
Negative Stain ◽  
Domain Mapping ◽  
Gene Duplication And Loss ◽  
Negative Stain Electron Microscopy

The nuclear pore complex (NPC) is a multiprotein assembly that serves as the sole mediator of nucleocytoplasmic exchange in eukaryotic cells. In this paper, we use an integrative approach to determine the structure of an essential component of the yeast NPC, the ∼600-kD heptameric Nup84 complex, to a precision of ∼1.5 nm. The configuration of the subunit structures was determined by satisfaction of spatial restraints derived from a diverse set of negative-stain electron microscopy and protein domain–mapping data. Phenotypic data were mapped onto the complex, allowing us to identify regions that stabilize the NPC’s interaction with the nuclear envelope membrane and connect the complex to the rest of the NPC. Our data allow us to suggest how the Nup84 complex is assembled into the NPC and propose a scenario for the evolution of the Nup84 complex through a series of gene duplication and loss events. This work demonstrates that integrative approaches based on low-resolution data of sufficient quality can generate functionally informative structures at intermediate resolution.

Prevalence of Subclinical Depression among College Students: A Review

2021 ◽  
Vol 27 (1) ◽  
pp. 16-33
Author(s):  
Anamika Modi Jain ◽  
M. Jha
Keyword(s):  
College Students ◽  
Health Care Providers ◽  
Mental Health Problems ◽  
Early Stage ◽  
Severe Depression ◽  
Data Repository ◽  
Care Providers ◽  
Teachers And Parents ◽  
A Minor ◽  
Subclinical Depression

INTRODUCTION - Early adult stage is the transition from adolescence to young adulthood, presents significant challenges like the chance to manage one’s life and affect more independent roles. A number of them adjust with these challenges and a few couldn’t manage these stressors which can cause the mental health problems. Among these problems depression is very common, and it is very difficult to detect in early stage, which often identified as a minor or subclinical depression. SD patients were in a mean position between non-depressive and depressive patients with regard to social isolation and physical destruction; women were overrepresented in the depressive and sub-depressive groups” (Schnieder et al. 2000). Study suggests the prevalence rate of subclinical depression was very high, which need urgent attention for identification and treatment. If it is ignored or left untreated long term effect may be appear in the form of major or severe depression. METHOD - A comprehensive systematic search of published literature and journal articles from Google Scholar, Pub Med, MEDLINE and EBSCO was taken. Search strategy specific to each data repository was used. During initial search 642 titles were retrieved and finally 38 empirical researches were selected based on the inclusion criteria. RESULT - Total 38 articles were selected, out of 38 approx 36 studies shows the rate of prevalence of Subclinical depression among college students and some studies based on impact and factors associated with subclinical depression. CONCLUSION - It is very important that health care providers, counselors, teachers and parents should pay special attention for early detection and treatment of subclinical depressive symptoms in early adults.

Neurofilament proteins are co-expressed with desmin in heart conduction system myocytes

1990 ◽  
Vol 97 (1) ◽  
pp. 11-21
Author(s):  
M. Vitadello ◽  
M. Matteoli ◽  
L. Gorza
Keyword(s):  
Subcellular Distribution ◽  
Ultrastructural Level ◽  
Rabbit Heart ◽  
Cardiac Cells ◽  
Structural Components ◽  
Minor Population ◽  
Neuronal Proteins ◽  
Tissue Homogenates ◽  
A Minor

We have recently shown that specialized myocytes of the rabbit heart express a cytoskeletal protein similar to the M subunit of neurofilaments (NF). Since this result was obtained using a single anti-NF-M monoclonal antibody, we tested on conduction myocytes a panel of five anti-NF antibodies, specific for each of the three NF subunits and for phosphorylated and non-phosphorylated epitopes. Two antibodies, one specific for the L subunit and one for phosphorylated M subunit of NF, reacted with specialized myocytes in immunohistochemistry. In immunoblots on conduction tissue homogenates the two antibodies recognized two polypeptides with electrophoretic mobility and solubility properties identical to those of NF-L and NF-M in the sciatic nerve. The subcellular distribution of NF immunoreactivity in specialized myocytes was very similar to desmin localization; namely, it was distributed on large filamentous bundles and on fine filaments localized transversely at the level of the Z line. At the ultrastructural level, immunoreactive filaments were localized in the intermyofibrillar space and connected myofibrils with mitochondria. Co-expression of NF proteins and desmin was also observed in vitro in a minor population of cardiac myocytes cultured from embryonic rabbit heart. In most cases NF immunoreactivity co-localized with desmin, especially where filaments were well organized, but in some cells anti-NF and anti-desmin antibodies labelled different filamentous structures. These results indicate that NF proteins are structural components of the cytoskeleton of specialized myocytes and show a subcellular distribution very similar to desmin. Such a composition of intermediate filaments indicates that in these cardiac cells muscle differentiation is compatible with the expression of neuronal proteins.

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