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Abstract. In 1948. Shinya Inoue arrived in the United Suites tor graduate studies at Princeton. A year later he came to Woods Hole, starting a long tradition of summer research [...]

From determining the optical properties of simple molecular crystals to establishing the preferred handedness in highly complex vertebrates, molecular chirality profoundly influences the structural, mechanical and optical properties of both synthetic and biological matter on macroscopic length scales (1, 2). In soft materials such as amphiphilic lipids and liquid crystals, the competition between local chiral interactions and global constraints imposed by the geometry of the self-assembled structures leads to frustration and the assembly of unique materials (3-6). An example of particular interest is smectic liquid crystals, where the two-dimensional layered geometry cannot support twist and chirality is consequently expelled to the edges in a manner analogous to the expulsion of a magnetic field from superconductors (7-10). Here we demonstrate a consequence of this geometric frustration that leads to a new design principle for the assembly of chiral molecules. Using a model system of colloidal membranes (11), we show that molecular chirality can control the interfacial tension, an important property of multi-component mixtures. This suggests an analogy between chiral twist, which is expelled to the edges of two-dimensional membranes, and amphiphilic surfactants, which are expelled to oil-water interfaces (12). As with surfactants, chiral control of interfacial tension drives the formation of many polymorphic assemblages such as twisted ribbons with linear and circular topologies, starfish membranes, and double and triple helices. Tuning molecular chirality insitu allows dynamical control of line tension, which powers polymorphic transitions between various chiral structures. These findings outline a general strategy for the assembly of reconfigurable chiral materials that can easily be moved, stretched, attached to one another and transformed between multiple conformational states, thus allowing precise assembly and nanosculpting of highly dynamical and designable materials with complex topologies., In experiments on chiral self-assembly, we used a two-component mixture consisting of 880-nm-long rod-like fd viruses and the non-adsorbing polymer Dextran. In aqueous suspension, fd viruses alone have purely repulsive [...]

We propose image processing algorithms for measuring two-dimensional distributions of linear birefringence using a pair of variable retarders. Several algorithms that use between two and five recorded frames allow us to optimize measurements for speed, sensitivity, and accuracy. We show images of asters, which consist of radial arrays of microtubule polymers recorded with a polarized light microscope equipped with a universal compensator. Our experimental results confirm our theoretical expectations. The lowest noise level of 0.036 nm was obtained when we used the five-frame technique and four-frame algorithm without extinction setting. The two-frame technique allows us to increase the speed of measurement with acceptable image quality. OCIS codes: 180.0180, 260.1440, 260.2130, 260.5430, 170.1530, 120.5410.

Filopodia that protrude forward from the lamellipodium, located at the leading edge of a neuronal growth cone, are needed to guide the extension of a nerve cell. At the core of each filopodium an actin bundle forms and grows into the lamellipodium. By using kymographs of time-lapse polarized light images we examined the relationship between the behavior of the filopodia, the actin bundles immediately proximal to the filopodia, and the shapes and composition of actin bundles in the whole lamellipodium. We find that the shapes of actin bundles, such as tilt, fork, and fused zones, originate at the leading edge and are surprisingly well preserved during retrograde transport of the actin cytoskeleton in the whole lamellipodium. The number of filaments that make up the radial actin bundles, as displayed by their birefringence retardation, also is preserved during retrograde flow over a distance of 4-8 [[micro]meter] from the leading edge into the lamellipodium. Thus, the disposition of the actin bundles in the lamellipodium frozen at any time point preserves and portrays a history of the past behavior of actin bundles proximal to the filopodia and the behavior of the filopodia themselves. These findings suggest that the arrangement of actin bundles in static image records, such as electron or fluorescence micrographs of fixed and stained specimens, can in fact reveal the sequence of the past history of filopodial behavior and the generation, density, fusion, etc. of the filaments in the actin bundles.

In an effort to establish the imaging properties of a new type of polarized-light microscope, we recorded images of small, uniaxial, birefringent crystals. We show that the sequence of in-focus and out-of-focus images, the so-called point-spread function, of a submicroscopic crystal can be used to measure the orientation of its optic axis in three-dimensional space. By analogy to conoscopic images out-of-focus images reveal the changes in relative phase shift between the extraordinary and the ordinary rays that propagate at different directions through the crystal. We also present simulated images of a pointlike anisotropic scattering particle and compare these with our experimental findings. The theoretical model is based on a complete vectorial theory for partial coherent imaging by use of polarized light and high-numerical-aperture lenses. [C] 2000 Optical Society of America OCIS codes: 180.6900, 120.2130, 260.1440, 180.3170, 050.1940.

Ten years ago we reported the first measurement of the distribution of birefringence in asters dispersed in lysates of Spisula oocytes; the observations were made with a new type of [...]

The neuronal growth cone appears at the tip of dendrites and axons where it plays an important role in the navigation of dendritic and axonal growth. Growth cones are rich [...]

Actin bundles play an important role in many kinds of cell activities, such as muscle contraction, cytoplasmic streaming, cell migration, and acrosomal reaction. Using our modified polarized light microscope (1), [...]

Recent advances and improvements on the polarizing light microscope have allowed for noninvasive imaging of cellular fine structures with high sensitivity and resolution irrespective of specimen orientation (1, 2). We [...]

The advanced polarization microscope, Pol-Scope, enables direct and precise analysis of the molecular structure of living cells through a novel combination of novel electro-optical devices, polarization algorithms and digital image processing. Pol-Scope uses a precision universal compensator comprising of two variable retarder plates to compensate for any specimen birefringence. The specimen under observation is illuminated with nearly circular polarized light. The instrument is extremely useful for measuring optical anisotropies.

The polarized light microscope has traditionally been an important tool for studying fine structure in living cells (1, 2). However, conventional design allows for retardance imaging only in a narrow [...]

We observed mitosis and cytokinesis of Drosophila Kc cells without functional mitotic centrosomes and compared our results to control cells to elucidate the roles of centrosomes in cell division dynamics. […]