Real-Time Polarization-Resolved Imaging of Living Tissues Based on Two-Photon Excitation Spinning-Disk Confocal Microscopy

Laser scanning microscopy using high-peak-power ultrashort near infrared light pulses can visualize biological microstructures by utilizing non-linear optical processes, such as multi-photon excitation and sum frequency generation. Here we introduced a polarization-resolving detection methodology for a laser scanning microscopy system equipped with a spinning-disk confocal scanner. The developed system achieved high-speed intravital imaging of living tissues with resolving their signals to orthogonally polarized components. First, we applied the system to a liposomal vesicle labeled with the fluorescent lipophilic dye and confirmed the orientation map of the lipid bilayer. Next, by detecting polarization-resolved second harmonic generation signals, the structural orientations of the collagen fibers in fixed mouse tissues were visualized without exogenous or genetic fluorophore labeling. Finally, we demonstrated in vivo polarization-resolved second harmonic generation imaging of the collagen fibers in the mouse skeletal muscles at a 56 Hz temporal resolution. We expect that our developed methodology can achieve real-time visualization, thus, revealing the conformational changes of supramolecular structures in living animals

Solid state diffusion bonding of doped tungsten alloys with different thermo-mechanical properties

To develop joints using W materials with different thermo-mechanical properties, solid state diffusion bonding involving two different W materials (pure W, K-doped W, or K-doped W-3%Re) and using a pure V interlayer (1.5 mm, 0.5 mm, or 0.05 mm thick) were carried out at 1250 °C for 1 h. The use of a thin interlayer was found to be effective from the point of optimizing the strength and thermal diffusivity. Diffusion bonding at lower temperatures or utilizing W materials with higher recrystallization temperatures were also determined to be effective because pure W can recrystallize at 1250 °C. Further evaluation of a wide range of interlayer thicknesses and thermo-mechanical test conditions is necessary based on the present work to obtain optimum W/V/W joints

Real-Time Polarization-Resolved Imaging of Living Tissues Based on Two-Photon Excitation Spinning-Disk Confocal Microscopy

Laser scanning microscopy using high-peak-power ultrashort near infrared light pulses can visualize biological microstructures by utilizing non-linear optical processes, such as multi-photon excitation and sum frequency generation. Here we introduced a polarization-resolving detection methodology for a laser scanning microscopy system equipped with a spinning-disk confocal scanner. The developed system achieved high-speed intravital imaging of living tissues with resolving their signals to orthogonally polarized components. First, we applied the system to a liposomal vesicle labeled with the fluorescent lipophilic dye and con firmed the orientation map of the lipid bilayer. Next, by detecting polarization-resolved second harmonic generation signals, the structural orientations of the collagen fibers in fixed mouse tissues were visualized without exogenous or genetic fluorophore labeling. Finally, we demonstrated in vivo polarization-resolved second harmonic generation imaging of the collagen fibers in the mouse skeletal muscles at a 56 Hz temporal resolution. We expect that our developed methodology can achieve real-time visualization, thus, revealing the conformational changes of supramolecular structures in living animals

Dynamics and function of ERM proteins during cytokinesis in human cells

The molecular mechanism that governs cytoskeleton-membrane interaction during animal cytokinesis remains elusive. Here, we investigated the dynamics and functions of ERM (Ezrin/Radixin/Moesin) proteins during cytokinesis in human cultured cells. We found that ezrin is recruited to the cleavage furrow through its membrane-associated domain in a cholesterol-dependent but largely Rho-independent manner. While ERMs are dispensable for furrow ingression, they play a pivotal role in contractile activity of the polar cortex. Notably, when anillin and supervillin are codepleted, ERMs increasingly accumulate at the cleavage furrow and substantially contribute to the furrow ingression. These results reveal a supportive role of ERMs in cortical activities during cytokinesis, and also provide insight into the selective mechanism that preferentially associates cytokinesis-relevant proteins with the division site

Multi-point Scanning Two-photon Excitation Microscopy by Utilizing a High-peak-power 1042-nm Laser

The temporal resolution of a two-photon excitation laser scanning microscopy (TPLSM) system is limited by the excitation laser beam's scanning speed. To improve the temporal resolution, the TPLSM system is equipped with a spinning-disk confocal scanning unit. However, the insufficient energy of a conventional Ti:sapphire laser source restricts the field of view (FOV) for TPLSM images to a narrow region. Therefore, we introduced a high-peak-power Yb-based laser in order to enlarge the FOV. This system provided three-dimensional imaging of a sufficiently deep and wide region of fixed mouse brain slices, clear four-dimensional imaging of actin dynamics in live mammalian cells and microtubule dynamics during mitosis and cytokinesis in live plant cells

Differential contributions of nonmuscle myosin IIA and IIB to cytokinesis in human immortalized fibroblasts

Nonmuscle myosin II (NMII) plays an important role in cytokinesis by constricting a contractile ring. However, it is poorly understood how NMII isoforms contribute to cytokinesis in mammalian cells. Here, we investigated the roles of the two major NMII isoforms, NMIIA and NMIIB, in cytokinesis using a WI-38 VA13 cell line (human immortalized fibroblast). In this cell line, NMIIB tended to localize to the contractile ring more than NMIIA. The expression level of NMIIA affected the localization of NMIIB. Most NMIIB accumulated at the cleavage furrow in NMIIA-knockout (KO) cells, and most NMIIA was displaced from this location in exogenous NMIIB-expressing cells, indicating that NMIIB preferentially localizes to the contractile ring. Specific KO of each isoform elicited opposite effects. The rate of furrow ingression was decreased and increased in NMIIA-KO and NMIIB-KO cells, respectively. Meanwhile, the length of NMII-filament stacks in the contractile ring was increased and decreased in NMIIA-KO and NMIIB-KO cells, respectively. Moreover, NMIIA helped to maintain cortical stiffness during cytokinesis. These findings suggest that appropriate ratio of NMIIA and NMIIB in the contractile ring is important for proper cytokinesis in specific cell types. In addition, two-photon excitation spinning-disk confocal microscopy enabled us to image constriction of the contractile ring in live cells in a three-dimensional manner

In vivo two-photon microscopic observation and ablation in deeper brain regions realized by modifications of excitation beam diameter and immersion liquid.

In vivo two-photon microscopy utilizing a nonlinear optical process enables, in living mouse brains, not only the visualization of morphologies and functions of neural networks in deep regions but also their optical manipulation at targeted sites with high spatial precision. Because the two-photon excitation efficiency is proportional to the square of the photon density of the excitation laser light at the focal position, optical aberrations induced by specimens mainly limit the maximum depth of observations or that of manipulations in the microscopy. To increase the two-photon excitation efficiency, we developed a method for evaluating the focal volume in living mouse brains. With this method, we modified the beam diameter of the excitation laser light and the value of the refractive index in the immersion liquid to maximize the excitation photon density at the focal position. These two modifications allowed the successful visualization of the finer structures of hippocampal CA1 neurons, as well as the intracellular calcium dynamics in cortical layer V astrocytes, even with our conventional two-photon microscopy system. Furthermore, it enabled focal laser ablation dissection of both single apical and single basal dendrites of cortical layer V pyramidal neurons. These simple modifications would enable us to investigate the contributions of single cells or single dendrites to the functions of local cortical networks

Protocol for constructing an extensive cranial window utilizing a PEO-CYTOP nanosheet for in vivo wide-field imaging of the mouse brain

Summary: Large-scale optical measurements have revealed the anatomical and functional connectivity among brain regions underlying brain functions. Here, we describe how to construct a cranial window utilizing a polyethylene-oxide-coated CYTOP (PEO-CYTOP) nanosheet that suppresses bleeding on the brain surface of mice. We demonstrate in vivo two-photon imaging through the PEO-CYTOP nanosheet at the subcellular resolution in the parietal region of the mouse brain. This protocol improves the surgical procedure and expands the optically observable regions, thereby promoting understanding of brain function.For complete details on the use and execution of this protocol, please refer to Takahashi et al. (2020)

Advanced easySTED microscopy based on two-photon excitation by electrical modulations of light pulse wavefronts

We developed a compact stimulated emission depletion (STED) two-photon excitation microscopy that utilized electrically controllable components. Transmissive liquid crystal devices inserted directly in front of the objective lens converted the STED light into an optical vortex while leaving the excitation light unaffected. Light pulses of two different colors, 1.06 and 0.64 mu m, were generated by laser diode-based light sources, and the delay between the two pulses was flexibly controlled so as to maximize the fluorescence suppression ratio. In our experiments, the spatial resolution of this system was up to three times higher than that obtained without STED light irradiation, and we successfully visualize the fine microtubule network structures in fixed mammalian cells without causing significant photo-damage. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen