Super-sectioning with multi-sheet reversible saturable optical fluorescence transitions (RESOLFT) microscopy.

Light-sheet fluorescence microscopy is an invaluable tool for four-dimensional biological imaging of multicellular systems due to the rapid volumetric imaging and minimal illumination dosage. However, it is challenging to retrieve fine subcellular information, especially in living cells, due to the width of the sheet of light (>1 µm). Here, using reversibly switchable fluorescent proteins (RSFPs) and a periodic light pattern for photoswitching, we demonstrate a super-resolution imaging method for rapid volumetric imaging of subcellular structures called multi-sheet RESOLFT. Multiple emission-sheets with a width that is far below the diffraction limit are created in parallel increasing recording speed (1-2 Hz) to provide super-sectioning ability (<100 nm). Our technology is compatible with various RSFPs due to its minimal requirement in the number of switching cycles and can be used to study a plethora of cellular structures. We track cellular processes such as cell division, actin motion and the dynamics of virus-like particles in three dimensions.

DaXi-high-resolution, large imaging volume and multi-view single-objective light-sheet microscopy.

The promise of single-objective light-sheet microscopy is to combine the convenience of standard single-objective microscopes with the speed, coverage, resolution and gentleness of light-sheet microscopes. We present DaXi, a single-objective light-sheet microscope design based on oblique plane illumination that achieves: (1) a wider field of view and high-resolution imaging via a custom remote focusing objective; (2) fast volumetric imaging over larger volumes without compromising image quality or necessitating tiled acquisition; (3) fuller image coverage for large samples via multi-view imaging and (4) higher throughput multi-well imaging via remote coverslip placement. Our instrument achieves a resolution of 450 nm laterally and 2 µm axially over an imaging volume of 3,000 × 800 × 300 µm. We demonstrate the speed, field of view, resolution and versatility of our instrument by imaging various systems, including Drosophila egg chamber development, zebrafish whole-brain activity and zebrafish embryonic development - up to nine embryos at a time.

S-polarized light-sheets improve resolution and light-efficiency in oblique plane microscopy.

Oblique plane microscopy (OPM) offers 3D optically sectioned imaging with high spatial- and temporal-resolution while enabling conventional sample mounting. The technique uses a concatenation of three microscopes, two for remote focusing and a tilted tertiary microscope, often including an immersion objective, to image an oblique sample plane. This design induces Fresnel reflections and a reduced effective aperture, thus impacting the resolution and light efficiency of the system. Using vectorial diffraction simulations, the system performance was characterized based on illumination angle and polarization, signal to noise ratio, and refractive index of the tertiary objective immersion. We show that for samples with high fluorescent anisotropy, s-polarized light-sheets yield higher average resolution for all system configurations, as well as higher light-efficiency. We also provide a tool for performance characterization of arbitrary light-sheet imaging systems.

Cell cycle-linked vacuolar pH dynamics regulate amino acid homeostasis and cell growth.

Amino acid homeostasis is critical for many cellular processes. It is well established that amino acids are compartmentalized using pH gradients generated between organelles and the cytoplasm; however, the dynamics of this partitioning has not been explored. Here we develop a highly sensitive pH reporter and find that the major amino acid storage compartment in Saccharomyces cerevisiae, the lysosome-like vacuole, alkalinizes before cell division and re-acidifies as cells divide. The vacuolar pH dynamics require the uptake of extracellular amino acids and activity of TORC1, the v-ATPase and the cycling of the vacuolar specific lipid phosphatidylinositol 3,5-bisphosphate, which is regulated by the cyclin-dependent kinase Pho85 (CDK5 in mammals). Vacuolar pH regulation enables amino acid sequestration and mobilization from the organelle, which is important for mitochondrial function, ribosome homeostasis and cell size control. Collectively, our data provide a new paradigm for the use of dynamic pH-dependent amino acid compartmentalization during cell growth/division.

Increasing the field-of-view in oblique plane microscopy via optical tiling.

Fast volumetric imaging of large fluorescent samples with high-resolution is required for many biological applications. Oblique plane microscopy (OPM) provides high spatiotemporal resolution, but the field of view is typically limited by its optical train and the pixel number of the camera. Mechanically scanning the sample or decreasing the overall magnification of the imaging system can partially address this challenge, albeit by reducing the volumetric imaging speed or spatial resolution, respectively. Here, we introduce a novel dual-axis scan unit for OPM that facilitates rapid and high-resolution volumetric imaging throughout a volume of 800 × 500 × 200 microns. This enables us to perform volumetric imaging of cell monolayers, spheroids and zebrafish embryos with subcellular resolution. Furthermore, we combined this microscope with a multi-perspective projection imaging technique that increases the volumetric interrogation rate to more than 10 Hz. This allows us to rapidly probe a large field of view in a dimensionality reduced format, identify features of interest, and volumetrically image these regions with high spatiotemporal resolution.

A versatile oblique plane microscope for large-scale and high-resolution imaging of subcellular dynamics.

We present an oblique plane microscope (OPM) that uses a bespoke glass-tipped tertiary objective to improve the resolution, field of view, and usability over previous variants. Owing to its high numerical aperture optics, this microscope achieves lateral and axial resolutions that are comparable to the square illumination mode of lattice light-sheet microscopy, but in a user friendly and versatile format. Given this performance, we demonstrate high-resolution imaging of clathrin-mediated endocytosis, vimentin, the endoplasmic reticulum, membrane dynamics, and Natural Killer-mediated cytotoxicity. Furthermore, we image biological phenomena that would be otherwise challenging or impossible to perform in a traditional light-sheet microscope geometry, including cell migration through confined spaces within a microfluidic device, subcellular photoactivation of Rac1, diffusion of cytoplasmic rheological tracers at a volumetric rate of 14 Hz, and large field of view imaging of neurons, developing embryos, and centimeter-scale tissue sections.