The suprachiasmatic nucleus (SCN) of the hypothalamus is known as the circadian center, which signals synchronizes the numerous cell clocks in the peripheral organs. We made a transgenic mice bearing Per1-promoter fused to firefly luciferase gene, and made a long-term monitoring system of the clock gene expression across hundreds of neurons within the mammalian SCN in organotypic slice culture. Differentially phased neuronal clocks are topographically arranged across the SCN. Synchronous oscillations of thousands of cellular clocks in the SCN are coordinated by precisely timed cell-cell communication, the principle of which is largely unknown. By the real time monitoring system, we demonstrated that the amount of RGS16 (regulator of G protein signalling), a protein known to inactivate Gαi, increases in the morning, allowing time-dependent activation of intracellular cyclic AMP signalling in the SCN. Gene ablation of Rgs16 lengthens circadian period of behavioural rhythm. RGS16-dependent temporal regulation of intracellular G protein signalling coordinates the intercellular synchrony of SCN pacemaker neurons and defines the 24 h rhythm in behaviour. The real time imaging system will clarify a variety of mechanisms in the brain at molecular level.
The suprachiasmatic nucleus is the center of the mammalian circadian clock which is located in adjacent to the third ventricle and directly above the optic chiasm. The circadian rhythm has been modeled as a limit cycle which accounts for the behavior of the multiple circadian oscillators in the SCN. The light exposure shifts the circadian rhythm of the SCN via the induction of Per1/Per2. The anatomical fact that a light responsive region coexists with the light unresponsive region in the SCN leads to the jet lag syndrome after an abrupt shift of light-dark (LD) cycle; The slow shift of the light unresponsive region makes the desynchrony between the environmental LD cycle and the circadian rhythm in the central clock. Further, observations suggest that the SCN measures and stores the information of the day length by modulating the regional phase differences in the SCN.
The circadian clock regulates many aspects of physiology and behavior such as sleep-wake cycles, body temperature, liver metabolism, renal activity, various hormonal secretion and cell proliferation. For the long time, it has been believed that the circadian clock oscillator exists only in the neurons of hypothalamic suprachiasmatic nucleus (SCN) where the circadian center of mammals resides. However, recently we have elucidated that even cultured cell lines involve the intrinsic self-sustained oscillating system. In addition, we also discovered that mammalian cellular circadian clock residing in our body developed cell-autonomously during the cellular differentiation process. Using bioluminescence imaging system to monitor clock gene expression, we show that the circadian bioluminescence activity rhythm is not detected in the mouse embryonic stem (ES) cells. In addition, when those differentiated cells are reprogrammed by expressing Sox2, Klf4, Oct-3/4 and c-Myc genes, those are used to generate induced pluripotent stem (iPS) cells, the circadian oscillation re-disappeared. The in vitro cellular differentiation and reprogramming system using ES cells and stem cell technology may provide a new strategy to understand the cross-talk mechanisms between circadian system and cellular differentiation system.
Animals including humans possess a circadian rhythm system which can control various physiological functions and also symptom expression rhythm of diseases. Chrono-pharmacological approaches have applied to reduce side-effect of drugs and to increase main-effect of drugs. Similar idea was applied to chrono-nutrition field for understanding between circadian rhythm and nutrition/feeding. Restricted feeding during daytime can entrain the circadian rhythm especially peripheral clocks, however importance of meal timing is still unknown. We found meal time after longer starvation is critical for entrainment under 2 meals per day schedule. In addition, food which can release insulin is better for entrainment; for example rapid digestible starch and fish oil containing food. Circadian clock controls absorption and metabolism process of nutrients and foods through the circadian function of transporters and fatty acids synthesis. Therefore the timing of meals affect the body weight gain and obesity. In mice experiments, ratio of high-fat food volume of breakfast: dinner was seat as 0:4, 1:3, 3:1, 4:0. Among 4 groups, breakfast: dinner (3:1) was most ideal feeding pattern for protection of obesity. These findings strongly suggest that the timing of food intake becomes another important factor for health promotion.
Occlusive thrombus formation on disrupted atherosclerotic plaque is the major cause of cardiovascular events. Accumulating evidence indicates that inflammation plays a key role in plaque instability and thrombus formation. The thrombotic response to plaque disruption (rupture or erosion) is regulated by the thrombogenicity of exposed plaque constituents, local hemorheology, systemic thrombogenicity and fibrinolytic activity. Platelet adhesion and aggregation are recognized as initial steps in arterial thrombus formation under rapid flow conditions. However, tissue factor is expressed in atherosclerotic plaques, coagulation pathways are also rapidly activated at plaque disruption sites. Autopsy studies of acute myocardial infarction have revealed that thrombi on disrupted plaques are principally composed of aggregated platelets and a large amount of fibrin with many inflammatory cells. Thrombi from ruptured plaques are significantly richer in fibrin than those on eroded plaques, and more tissue factor is expressed in ruptured than eroded plaques.On the other hand, plaque disruption does not always result in total thrombotic occlusion. Although the detail mechanisms of arterial thrombus propagation in vivo remain unclear, recent studies have demonstrated that increased vascular wall thrombogenicity together with a substantial blood flow alteration is crucial for occlusive thrombus formation leading to the onset of cardiovascular events.
Laboratory analysis of space materials is an important method to study origin of solar system. Among the laboratory analysis, microscopy is very useful because space materials have complex and fine structures. Large differences of isotopic composition are common among the space materials. Isotopes can be used as tracers to study origin and evolution of space materials. Conventional mass spectrometry is limited to apply for microanalysis, but recently, isotope microscopy is developed and the situation is gradually changed. The isotope microscopy can obtain precise isotopic image of fine structures of space materials and analyze formation processes of the structure in detail. Here we report studies of oldest materials of the solar system, presolar grains formed in circum stellar, and ice fossils formed in molecular cloud.
Annular dark-field (ADF) imaging in scanning transmission electron microscopy (STEM) is an effective tool for the characterization of local crystal structure, because ADF imaging has high compositional sensitivity and intuitive interpretability. Here we review our results of high sensitivity and high precision analyses of crystal structures using STEM imaging. We show the validity and the limitation of incoherent imaging approximation of ADF imaging. We also show a recent result of spatially-resolved diffractometry, in which the diffraction patterns are fully acquired as a function of probe coordination.
Complex electronic oxides such as manganites with charge, spin and orbital (lattice) degrees of freedom have been studied extensively so far because of their unusual physical properties such as colossal magnetoresistance (CMR) effect and metal-insulator transition accompanying with the charge/orbital ordered (CO/OO) structures. Here overall structural features about CO/OO and magnetic microstructures associated with electronic phase separations, which are regarded as one of the important factors to grasp their unusual physical properties, are reviewed. In particular, transmission electron microscopy (TEM) studies are focused on in this article, including electron diffraction, high-resolution TEM, Lorentz TEM and electron small-angle scattering experiments.
Organisms are composed of cells as a unit, which are made of macromolecules, such as proteins, nucleotides and lipids. Their assembly/disassembly such as cytoskeleton or bindings with small ligands are related to physical and/or chemical reactions in the cells, which are essential for life activities. Since the size of them is around nm to micrometer, light microscopy has little ability to observe their structure in the cells directly. Transmission electron microscopy gives us their two-dimensional images at nanometer resolutions but they are projected one. Thus, it is difficult to identify their three-dimensional structure due to their overprint. Even though a very thin section is observed, its thickness is far larger than that of proteins and so their three-dimensional information is hidden. We, therefore, need to restore their 3D structures by three-dimensional electron microscopy to identify them clearly. We here describe the principles of the three-dimensional reconstruction techniques from TEM images and their attentions.
Electron Energy Loss Spectroscopy (EELS) equipped with Transmission Electron Microscope (TEM) at lower-kV has been carried out for precise characterization of low-k interconnect dielectrics. Structural changes after plasma processes such as dry etch and ashing were characterized by using valence EELS (V-EELS) at lower accelerating voltage such as 80kV. Because the electron irradiation damage and the unexpected effects of Cerencov radiation can be significantly ignored at low-kV VEELS, so that we could derive more precise dielectric constant profile by Kramers-Kronig Analysis (KKA) than characterization at conventional 200 kV. Of course dielectric constant by high energy electron measurement such as TEM only gives electron polarization intensity inherently, however it is useful to characterize the electrical damage structures at high spatial resolution. At the adjacent of the side wall, the peak at 2eV is significantly increased in ε2, it assumed that defects such as silicon dangling bonds were generated during the Cu/Low-k processing. It has been demonstrated that the combination of conventional composition analysis and VEELS at low-kV (80keV) is very useful for characterization of the damages in the patterned Cu / low-k interconnect structure for advanced ULSI processing.