Attachment of growth cones on substrate observed by multi-mode light microscopy

VIEW-MOD: a versatile illumination engine with a modular optical design for fluorescence microscopy

We developed VIEW-MOD (Versatile Illumination Engine with a Modular Optical Design): a compact, multi-modality microscope, which accommodates multiple illumination schemes including variable angle total internal reflection, point scanning and vertical/horizontal light sheet. This system allows combining and flexibly switching between different illuminations and imaging modes by employing three electrically tunable lenses and two fast-steering mirrors. This versatile optics design provides control of 6 degrees of freedom of the illumination source (3 translation, 2 tilt, and beam shape) plus the axial position of the imaging plane. We also developed standalone software with an easy-to-use GUI to calibrate and control the microscope. We demonstrate the applications of this system and software in biosensor imaging, optogenetics and fast 3D volume imaging. This system is ready to fit into complex imaging circumstances requiring precise control of illumination and detection paths, and has a broad scope of usability for a myriad of biological applications.

Rigorous electromagnetic theory for waveguide evanescent field fluorescence microscopy

Recently, waveguide evanescent field fluorescence (WEFF) microscopy was introduced and used to image and analyze cell-substrate contacts. Here, we establish a comprehensive electromagnetic theory in a seven-layer structure as a model for a typical waveguide-cell structure appropriate for WEFF microscopy and apply it to quantify cell-waveguide separation distances. First, electromagnetic fields at the various layers of a model waveguide-cell system are derived. Then, we obtain the dispersion relation or characteristic equation for TE modes with a stratified media as a cover. Waveguides supporting a defined number of modes are theoretically designed for conventional, reverse, and symmetric waveguide structures and then various waveguide parameters and the penetration depths of the evanescent fields are obtained. We show that the penetration depth of the evanescent field in a three-layer waveguide-cell structure is always lower than that of a seven-layer structure. Using the derived electromagnetic fields, the background and the excited fluorescence in the waveguide-cell gap, filled with water-soluble fluorophores, are analytically formulated. The effect of the waveguide structures on the fluorescence and the background are investigated for various modes. Numerical results are presented for the background and the stimulated fluorescence as functions of the water gap width for various waveguide structures, which can be used to find the water gap width. The results indicate that the background and excited fluorescence increase by increasing the penetration depth of the evanescent field. In addition, we show that for various guided modes of a conventional waveguide, the electric fields in the cell membrane and the cytoplasm are evanescent and they do not depend on the waveguide structure and the mode number. However, for the reverse symmetry and symmetric waveguide structures, the waves are sinusoidal in the cell membrane and the cytoplasm for the highest-order modes.

Force- and Ca2+-dependent internalization of integrins in cultured endothelial cells

The effects of mechanical force applied to the integrin clusters at focal contacts were examined in cultured human umbilical vein endothelial cells. When a fibronectin-coated glass bead was attached to the apical cell surface, focal contacts formed beneath the bead that became linked to focal contacts at the basal cell membrane by actin stress fibers in 5 minutes. Integrin dynamics at the basal focal contacts were monitored in live cells in response to a localized mechanical stimulus generated by displacing the glass bead. Traction force transmitted to the basal focal contacts through the stress fibers was monitored by measuring the deformation of the polyacrylamide gel substratum. The force declined in a few seconds, probably owing to decreases in the elastic modulus of the stress fibers. This transient mechanical stimulus caused the dephosphorylation of paxillin and disassembly of integrin clusters at the basal cell membrane in 20 minutes. The disassembly was mediated mainly by clathrin-dependent endocytosis of integrins. The integrin internalization was inhibited in Ca2+- and K+-free solution, and by phenylarsine oxide, a phosphatase inhibitor. These results suggest that a transient mechanical stimulus applied to focal contacts induces Ca2+-dependent dephosphorylation of some proteins, including paxillin, and facilitates clathrin-dependent endocytosis of integrins.

Chapter 7: Total internal reflection fluorescence microscopy

Total internal reflection fluorescence microscopy (TIRFM), also known as evanescent wave microscopy, is used in a wide range of applications, particularly to view single molecules attached to planar surfaces and to study the position and dynamics of molecules and organelles in living culture cells near the contact regions with the glass coverslip. TIRFM selectively illuminates fluorophores only in a very thin (less than 100 nm deep) layer near the substrate, thereby avoiding excitation of fluorophores outside this subresolution optical section. This chapter reviews the history, current applications in cell biology and biochemistry, basic optical theory, combinations with numerous other optical and spectroscopic approaches, and a range of setup methods, both commercial and custom.

Dynamics of integrin clustering at focal contacts of endothelial cells studied by multimode imaging microscopy

Human umbilical vein endothelial cells were stained with FITC-labeled anti-β1 integrin antibody and plated on a glass cover slip to elucidate the mechanism of integrin clustering during focal contact formation. The process of integrin clustering was observed by time-lapse total-internal-reflection fluorescence microscopy, which can selectively visualize the labeled integrins at the basal surface of living cells. The clustering of integrins at focal contacts started at 1 hour after plating and individual clusters kept growing for ∼6 hours. Most integrin clusters (∼80%) elongated towards the cell center or along the cell margin at a rate of 0.29±0.24 μm minute−1. Photobleaching and recovery experiments with evanescent illumination revealed that the integrins at the extending tip of the clusters were supplied from the intracellular space. Simultaneous time-lapse imaging of exocytosis of integrin-containing vesicles and elongating focal contacts showed that most exocytosis occurred at or near the focal contacts followed by their elongation. Double staining of F-actins and integrins demonstrated that stress fibers were located near the integrin clusters and that intracellular punctate integrins were associated with these stress fibers. These results suggest that the clustering of integrins is mediated by actin-fiber-dependent translocation of integrins to the extending tip of focal contacts.

Real-time molecular and cellular analysis: the new frontier of drug discovery

The pharmaceutical industry is currently facing the challenge of maintaining increased efficiency and productivity while contending with a deluge of genomic and high-throughput screening data. To ease the bottlenecks at target validation and lead optimization, the industry must look to the living cell, the ultimate target of all drugs, as a source of new biological knowledge. This new 'cell-centric' perspective must integrate reagents that report on the state of molecular processes within the cell, automated detection and analysis of these processes, and cellular knowledge, building into a single platform.