Tadao Sugiura

Movement of micrometer-sized particles in the evanescent field of a laser beam

We report that small particles with diameters of 1-27 microm have moved in the evanescent fields produced by a laser beam. The evanescent field in the experiment was produced in the near field of the surface of a highrefractive-index sapphire prism illuminated by a 1.06-microm YAG laser beam with an incident angle larger than the critical angle. Both polystyrene latex spheres and glass spheres bounced and ran along the surface of the prism when the laser beam was on. The maximum running speed obtained was approximately 20 microm/s. A micrograph of the running particles is shown with plots of the measured velocity versus the incident angle of the laser beam. Applications of this phenomenon are also discussed.

Shootin1 interacts with actin retrograde flow and L1-CAM to promote axon outgrowth

Actin polymerizes near the leading edge of nerve growth cones, and actin filaments show retrograde movement in filopodia and lamellipodia. Linkage between actin filament retrograde flow and cell adhesion molecules (CAMs) in growth cones is thought to be one of the mechanisms for axon outgrowth and guidance. However, the molecular basis for this linkage remains elusive. Here, we show that shootin1 interacts with both actin filament retrograde flow and L1-CAM in axonal growth cones of cultured rat hippocampal neurons, thereby mediating the linkage between them. Impairing this linkage, either by shootin1 RNA interference or disturbing the interaction between shootin1 and actin filament flow, inhibited L1-dependent axon outgrowth, whereas enhancing the linkage by shootin1 overexpression promoted neurite outgrowth. These results strengthen the actin flow–CAM linkage model (“clutch” model) for axon outgrowth and suggest that shootin1 is a key molecule involved in this mechanism.

Near-field scanning optical microscope with a laser trapped probe

We made an experiment of near-field microscopic imaging using a laser-beam trapped probe. Differently from a conventional near-field (and/or photon-tunneling) scanning optical microscope, the probe is physically isolated from the scanning microscope system; it is trapped and scanned on the sample surface by the radiation force of near-infrared laser beam. The distance between the probe and the sample surface is maintained to be constant (zero) during scanning. Another laser beam for microscopic imaging is incident on the sample surface in the condition of total internal reflection; the probe on the sample couples with the photons localized near the sample surface as the evanescent filed and scatters out. The scattered photons are collected through an microscope objective lens, which is the same lens as the one used for focusing the infrared laser beam on the probe. A near-field image of the sample surface is formed, as the probe is laterally scanned on the sample. The experimental setup of the proposed microscope is described and the image data obtained with the developed microscope are shown for refractive samples and fluorescent samples with sub micrometer structure.

KNApSAcK Metabolite Activity Database for Retrieving the Relationships Between Metabolites and Biological Activities

Databases (DBs) are required by various omics fields because the volume of molecular biology data is increasing rapidly. In this study, we provide instructions for users and describe the current status of our metabolite activity DB. To facilitate a comprehensive understanding of the interactions between the metabolites of organisms and the chemical-level contribution of metabolites to human health, we constructed a metabolite activity DB known as the KNApSAcK Metabolite Activity DB. It comprises 9,584 triplet relationships (metabolite-biological activity-target species), including 2,356 metabolites, 140 activity categories, 2,963 specific descriptions of biological activities and 778 target species. Approximately 46% of the activities described in the DB are related to chemical ecology, most of which are attributed to antimicrobial agents and plant growth regulators. The majority of the metabolites with antimicrobial activities are flavonoids and phenylpropanoids. The metabolites with plant growth regulatory effects include plant hormones. Over half of the DB contents are related to human health care and medicine. The five largest groups are toxins, anticancer agents, nervous system agents, cardiovascular agents and non-therapeutic agents, such as flavors and fragrances. The KNApSAcK Metabolite Activity DB is integrated within the KNApSAcK Family DBs to facilitate further systematized research in various omics fields, especially metabolomics, nutrigenomics and foodomics. The KNApSAcK Metabolite Activity DB could also be utilized for developing novel drugs and materials, as well as for identifying viable drug resources and other useful compounds.

Rab33a Mediates Anterograde Vesicular Transport for Membrane Exocytosis and Axon Outgrowth

Axon outgrowth requires plasma membrane expansion, which results from post-Golgi vesicular transport and fusion. However, the molecular mechanisms regulating post-Golgi vesicular trafficking for membrane expansion and axon outgrowth remain unclear. Here, we show that Rab33a expression became upregulated during axon outgrowth of cultured rat hippocampal neurons. Rab33a was preferentially localized to the Golgi apparatus and to synaptophysin-positive vesicles that are transported along the growing axon. Previous studies showed that synaptophysin is localized to post-Golgi vesicles transported by fast axonal transport in developing neurons. Reduction of Rab33a expression by RNAi (RNA interference) inhibited the anterograde transport of synaptophysin-positive vesicles, leading to their decrease in axonal tips. Furthermore, this treatment reduced membrane fusion of synaptophysin-positive vesicles at the growth cones and inhibited axon outgrowth. Overexpression of Rab33a, on the other hand, induced excessive accumulation of synaptophysin-positive vesicles and concurrent formation of surplus axons. These data suggest that Rab33a participates in axon outgrowth by mediating anterograde axonal transport of synaptophysin-positive vesicles and their concomitant fusion at the growth cones.

Dynamic axial-position control of a laser-trapped particle by wave-front modification

The axial position of a laser-trapped particle has been controlled by modification of the wave front by means of a membrane deformable mirror. The mirror gives wave-front modulation in terms of Zernike polynomials. By modulation of the Zernike defocus term we can modulate the particle position under conditions of laser trapping. A polystyrene particle of 1-microm diameter was moved along the optical axis direction for a distance of 2370 nm in minimum steps of 55.4 nm. We also demonstrated particle oscillation along the optical axis by changing the focal position in a sinusoidal manner. From the frequency dependency of the amplitude of particle oscillation we determined the spring constant as 91.7 nN/m.

Shootin1–cortactin interaction mediates signal–force transduction for axon outgrowth

The shootin1–cortactin interaction participates in netrin-1–induced F-actin–adhesion coupling and in the promotion of traction forces for axon outgrowth.

Rupture force measurement of biotin-streptavidin bonds using optical trapping

Optical trapping has been applied to investigate the bond rupture force between biotin attached to a microparticle and streptavidin attached to a substrate. The force for rupturing the bonds was loaded vertically by pulling the particle from the substrate and detected by measuring the displacement of the particle from the equilibrium position in the optical trap. The displacement was measured by detecting light the light scattered from the particle in an evanescent field, and the field was generated by total internal reflection of a beam output from a high-NA objective lens. From the histogram yielded from the rupture force measurements, the most frequent rupture force was determined to be between 3.6 and 5.4 pN with a loading rate of 7.7pN∕s.

Enhancement of laser trapping force by spherical aberration correction using a deformable mirror

We have developed a method to enhance axial trapping force in optical tweezers by aberration correction of a laser beam with a membrane deformable mirror. The axial trapping force is strongly dependent on the quality of the laser beam spot, which is deteriorated by aberration due to the refractive index mismatch between a cover glass and water. The aberration correction, therefore, is crucial for stable trapping of a particle and for weak-force measurement with laser trapping. We have evaluated spring constants of the trapping force in the axial direction with and without aberration correction. The enhancement factor of the spring constants by the aberration correction has been achieved as 1.35 for the case of 5-mm sample thickness and as 1.83 for the case of 10-mm sample thickness. The numerical simulation is coincident with the experimental results. [DOI: 10.1143/JJAP.42.L701]

Holography with surface-plasmon-coupled waveguide modes.

We report on an attempt to use the enhancement effect of surface-plasmon resonance to improve the image quality of a waveguide hologram. With a structure consisting of a waveguide medium sandwiched between a metal film and a hologram, we obtained holographic images reconstructed by surface-plasmon-coupled waveguide modes. Comparison of the holographic images reconstructed by TM and TE modes indicates that the surface-plasmon effect is responsible for better image quality in diffraction efficiency and image contrast.