The gene expression differs in the nuclei of normal and malignant mammalian cells, and transcription is a critical initial step, which defines the difference. The mechanical properties of ...transcriptionally active chromatin are still poorly understood. Recently we have probed transcriptionally active chromatin of the nuclei subjected to mechanical stress, by Atomic Force Microscopy (AFM) 1. Nonetheless, a systematic study of the phenomenon is needed.
Nuclei were deformed and studied by AFM. Non-deformed nuclei were studied by fluorescence confocal microscopy. Their transcriptional activity was studied by RNA electrophoresis.
The malignant nuclei under the study were stable to deformation and assembled of 100–300 nm beads-like units, while normal cell nuclei were prone to deformation. The difference in stability to deformation of the nuclei correlated with DNA supercoiling, and transcription-depended units were responsive to supercoils breakage. The inhibitors of the topoisomerases I and II disrupted supercoiling and made the malignant nucleus prone to deformation. Cell nuclei treatment with histone deacetylase inhibitors (HDACIs) preserved the mechanical stability of deformed malignant nuclei and, at the same time, made it possible to observe chromatin decondensation up to 20–60 nm units. The AFM results were supplemented with confocal microscopy and RNA electrophoresis data.
Self-assembly of transcriptionally active chromatin and its decondensation, driven by DNA supercoiling-dependent rigidity, was visualized by AFM in the mechanically deformed nuclei.
We demonstrated that supercoiled DNA defines the transcription mechanics, and hypothesized the nuclear mechanics in vivo should depend on the chromatin architecture.
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•Mechanically deformed normal and malignant cells nuclei were assessed by AFM.•The nuclei of the malignant cells revealed a landscape assembled from 100 to 300 nm beads-like rigid units.•Topoisomerases I and II inhibitors broke supercoils, making nuclear chromatin prone to deformation.•Chromatin decondensation, induced by HDACIs treatment, revealed ∼20 nm rigid units.•The landscape represented transcription events, dependent on the DNA supercoiling.
Nuclear rigidity is traditionally associated with lamina and densely packed heterochromatin. Actively transcribed DNA is thought to be less densely packed. Currently, approaches for direct ...measurements of the transcriptionally active chromatin rigidity are quite limited.
Isolated nuclei were subjected to mechanical stress at 60 g and analyzed by Atomic Force Microscopy (AFM).
Nuclei of the normal fibroblast cells were completely flattened under mechanical stress, whereas nuclei of the cancerous HeLa were extremely resistant. In the deformed HeLa nuclei, AFM revealed a highly-branched landscape assembled of ~400 nm closed-packed globules and their structure was changing in response to external influence. Normal and cancerous cells' isolated nuclei were strikingly different by DNA resistance to applied mechanical stress. Paradoxically, more transcriptionally active and less optically dense chromatin of the nuclei of the cancerous cells demonstrated higher physical rigidity. A high concentration of the transcription inhibitor actinomycin D led to complete flattening of HeLa nuclei, that might be related to the relaxation of supercoiled DNA tending to deformation. At a low concentration of actinomycin D, we observed the intermediary formation of stochastically distributed nanoloops and nanofilaments with different shapes but constant width ~ 180 nm. We related this phenomenon with partial DNA relaxation, while non-relaxed DNA still remained rigid.
The resistance to deformation of nuclear chromatin correlates with fundamental biological processes in the cell nucleus, such as transcription, as assessed by AFM.
A new outlook to studying internal nuclei structure is proposed.
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•The method of the imaging of transcriptionally active chromatin by AFM via nuclei mechanical stress was proposed.•Nuclear DNA of normal or transcriptionally inactive cells nuclei was completely flattened under mechanical stress.•HeLa cells' nuclei were sustainable to deformation, revealing the globular higher-packed architecture of the supercoiled DNA.•Transcription inhibitor actinomycin D relaxed tensions of supercoiled DNA reducing its resistance to mechanical stress.•Our results demonstrate a relationship between nuclear mechanics and transcription.
The scintillation crystal bismuth germanate (BGO) is widely used in many applications. The unique technique developed in the Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia, allows ...routine production of top quality large-sized BGO crystals. One of the important properties of a scintillation crystal is its radiation hardness. The intensive study of the radiation hardness of BGO crystals has been carried out by the collaboration of the Institutes of Siberian Branch of the Russian Academy of Science, Novosibirsk. The influence of the raw material purity and growth procedure on radiation hardness has been studied. The final tests of the crystal radiation hardness were performed by irradiating it with gamma rays from the radioactive source. The degradation of a light output of the best crystals is less than 10% after irradiation with doses of 10-100 krad expected in astrophysics experiments at a satellite. Based on the results of this study, the radiation hard BGO crystals for the "INTEGRAL" and "ASTRO-H" satellite missions have been made. A selfrecovery of the crystal light output is clearly seen. The time scale of the self recovery strongly depends on a dose of irradiation. It is days for 1 krad irradiation, weeks - for a 10 krad dose and a much longer period is required for 100 krad irradiation. All the crystals irradiated with a dose of 100 krad completely recover after annealing. The study reveals that there will be no essential degradation if this dose will be integrated over years of operation.
Small-angle neutron and X-ray scattering data for HeLa nuclei with the normal and suppressed transcription activities are reported. Small-angle neutron scattering data demonstrate the presence of a ...bifractal structure inside a nucleus. The logarithmic fractal structure is observed in the range from the size of the nucleus to several hundreds of nanometer, whereas the volume fractal structure exists at smaller scales down to a nucleosome structure. Small-angle X-ray scattering data show that the presence of the volume fractal structure correlates with the transcription activity of a cell. In view of the successful description of chromatin by the fractal globule model (Hi–C method data), a scenario for the formation of the bifractal structure inside the nucleus has been proposed. A system of transport channels (logarithmic fractal) is located inside close-packed chromatin, whereas active chromatin is localized near transport channels or inside them and forms volume fractal structures due to the transcription activity. Thus, the logarithmic fractal structure ensures the uniform distribution of voids at various scales, which is potentially necessary for the transcription and transport of substances inside the nucleus, whereas the volume fractal structure is due to the transcription activity of the cell.
The decomposition of methane on molybdenum nanoparticles was studied experimentally at room temperature. The molybdenum nanoparticles were synthesized in the gas phase using UV laser photolysis of ...Mo(CO)
6
vapor in a flow reactor. The working part of the flow reactor was equipped with quartz windows for introducing the radiation from a pulsed Nd:YaG laser operating at the fourth harmonic (266 nm) at a frequency of 10 Hz. Methane was used as a carrier gas. As a result of irradiation of a mixture of methane with Mo(CO)
6
vapors in the gas phase at room temperature, nanoparticles with sizes of 2–50 nm were synthesized. The phase composition of the nanoparticles included pure molybdenum, molybdenum carbide Mo
2
C, and molybdenum oxide MoO
3
. During the reaction, the hydrogen yield was measured with a VG-7 highly sensitive hydrogen analyzer based on a semiconductor metal–dielectric sensor. The measured H
2
concentration varied from 5 to 25 ppm depending on the concentration of Mo(CO)
6
. The possibility of methane decomposition on molybdenum nanoparticles at room temperature was discussed based on the obtained data.
To control the parameters of PIN photodiodes during their mass production, a high-performance automated multifunctional stand has been developed. The stand provides measurement of dark current, ...capacitance at operating voltage, and response to a light signal with simultaneous connection of up to 16 photodiodes and successive verification of their characteristics.
The design of the MEG II experiment Baldini, A. M.; Baracchini, E.; Bemporad, C. ...
The European physical journal. C, Particles and fields,
05/2018, Letnik:
78, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The MEG experiment, designed to search for the
μ
+
→
e
+
γ
decay, completed data-taking in 2013 reaching a sensitivity level of
5.3
×
10
-
13
for the branching ratio. In order to increase the ...sensitivity reach of the experiment by an order of magnitude to the level of
6
×
10
-
14
, a total upgrade, involving substantial changes to the experiment, has been undertaken, known as MEG II. We present both the motivation for the upgrade and a detailed overview of the design of the experiment and of the expected detector performance.
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