Seunghoon Han

Microtubule- and dynein-mediated movement of Orientia tsutsugamushi to the microtubule organizing center

ABSTRACT The host cell microfilaments and microtubules (MTs) are known to play a critical role in the life cycles of several pathogenic intracellular microbes by providing for successful invasion and promoting movement of the pathogen once inside the host cell cytoplasm.Orientia tsutsugamushi, an obligate intracellular bacterium, enters host cells by induced phagocytosis, escapes to the cytosol, and then replicates in the cytosol. ECV304 cells infected withO. tsutsugamushi revealed the colocalization of the MT organizing center (MTOC) and cytosolic orientiae by indirect immunofluorescence assay. Using immunofluorescence microscopy in the presence and absence of MT-depolymerizing agents (colchicine and nocodazole), it was shown that the cytosolic oriential movement was mediated by MTs. By transfection study (overexpression of dynamitin [also called p50], which is known to associate with dynein-dependent movement), the movement of O. tsutsugamushi to the MTOC was also mediated by dynein, the minus-end-directed MT-related motor. Although the significance of this movement in the life cycle ofO. tsutsugamushi was not proven, we propose that the cytosolic O. tsutsugamushi bacteria use MTs and dyneins to propel themselves from the cell periphery to the MTOC.

Exploitation of the Endocytic Pathway by Orientia tsutsugamushi in Nonprofessional Phagocytes.

ABSTRACT Orientia tsutsugamushi, a causative agent of scrub typhus, is an obligate intracellular bacterium that requires the exploitation of the endocytic pathway in the host cell. We observed the localization of O. tsutsugamushi with clathrin or adaptor protein 2 within 30 min after the infection of nonprofessional phagocytes. We have further confirmed that the infectivity of O. tsutsugamushi is significantly reduced by drugs that block clathrin-mediated endocytosis but not by filipin III, an inhibitor that blocks caveola-mediated endocytosis. In the present study, with a confocal microscope, O. tsutsugamushi was sequentially colocalized with the early and late endosomal markers EEA1 and LAMP2, respectively, within 1 h after infection. The colocalization of O. tsutsugamushi organisms with EEA1 and LAMP2 gradually disappeared until 2 h postinfection, and then free O. tsutsugamushi organisms were found in the cytoplasm. When the acidification of endocytic vesicles was blocked by treating the cells with NH4Cl or bafilomycin A, the escape of O. tsutsugamushi organisms from the endocytic pathway was severely impaired, and the infectivity of O. tsutsugamushi was drastically reduced. To our knowledge, this is the first report that the invasion of O. tsutsugamushi is dependent on the clathrin-dependent endocytic pathway and the acidification process of the endocytic vesicles in nonprofessional phagocytes.

Filter characteristics of a chirped volume holographic grating.

We compare and analyze the filter properties of transmission-type volume holographic gratings, especially the dispersion characteristics for uniform and chirped gratings. It is theoretically and experimentally shown that the dispersion characteristics can be controlled by introducing one-dimensional chirping to the volume grating in a photorefractive crystal. The filter response including output power and dispersion comes from a combined effect of the spatial spectra of the grating structure, input beam, and output-coupling fiber mode. Filter responses can be designed by controlling these parameters for optical communication applications.

Wavelength-Band Selection Filter Based on Surface Plasmon Resonance and Phase Conjugation Holography

A wavelength-band selection filter using a metal-coated polymer holographic grating and utilizing surface plasmon resonance for use in optical wireless communication is proposed. The proposed device is mainly composed of a total internal reflection prism, the hypotenuse surface of which is covered with a metal-coated volumetric polymer holographic grating. The feasibility of the proposed device for use as a wavelength-band selection filter was tested experimentally

Remote multiplexing of holograms with random patterns from multimode fiber bundles

We propose the remote multiplexing of holograms with random patterns from a multimode fiber bundle used as the reference beams. The random pattern reference beam is characterized by the superposition and concatenation of propagation modes of multimode fiber and free space. For angle, shift, and wavelength remote multiplexing we compare two methods of laser coupling to the fiber bundle, i.e., direct coupling and lens coupling. A theoretical discussion that uses mode orthogonality is provided to describe multiplexing characteristics, and the theory is verified by experimental results. These remote-multiplexing methods can be applied to general multimode waveguide arrays for construction of compact and integrated optical systems in which multiplexing can be controlled remotely.

Dispersion characteristics of holographic multiple-channel demultiplexers

Chromatic dispersion characteristics over multiple channels in holographic grating (HG) demultiplexers are modeled and analyzed, theoretically and experimentally. The dispersion arises from a combination of out-coupling lens aberration and the HG phase structure. A theoretical model of the channel spectrum of a demultiplexer was assembled, based on the first-order Born approximation of the volume diffraction and verified by experimental and numerical data. These results show that the HG phase structure becomes an effective design parameter that could be used to control the dispersion in a high-performance multiple-channel dense wavelength-division-multiplexing demultiplexer.

Photopolymer-based demultiplexers with Superposed holographic gratings

A photopolymer-based demultiplexer structure with two superposed holographic gratings is proposed and demonstrated for the first time. The demultiplexer is constructed from a holographic recording with two coherent beam sets. In the proposed scheme, two different channels of optical signals are coupled into a common single-mode fiber (SMF) by means of diffractions from the two superposed gratings. The coupled spectral channels are selected by tuning the spatial location of the SMF. The wavelength separation between two spectral channels that couple into the same optical fiber can be controlled by varying the angle between the two beams used for the formation of the holographic gratings.

Characteristics of remote hologram multiplexing with random pattern references from a multimode fiber bundle

We propose and characterize the remote multiplexing of holograms with random pattern references from a multimode fiber bundle. The random pattern reference is modeled by using the superposition and concatenation of propagation modes of multimode fibers and free space. We compare two laser-coupling methods to the fiber bundle, i.e., direct coupling and lens coupling, for angle, shift, and wavelength remote multiplexings. The optimum laser-coupling method for each multiplexing is analyzed based on the theoretical model and experimental results. Retrieved hologram images show that 1-D intensity variation of the image might occur for the 90-deg geometry holograms in relation to the random pattern properties. Environmental variation effects such as vibration and temperature variation are also discussed and examined. These remote multiplexing methods can be applied to general multimode waveguide arrays to construct compact and integrated optical systems, where multiplexing can be performed at remote places.

Molecular characterization of a group of proteins containing ankyrin repeats in Orientia tsutsugamushi.

Abstract: Orientia tsutsugamushi, an obligate intracellular bacterium, is the causative agent of scrub typhus. The sequencing and analysis of full genomic DNA of O. tsutsugamushi has revealed at least 19 genes thus far encoding proteins with different numbers of ankyrin repeat domains. We have cloned several genes containing ankyrin repeats from the genome and produced fusion proteins to characterize their functions in host cells. It is likely that the proteins with ankyrin repeat domains expressed in O. tsutsugamushi‐infected cells may control the synthesis or stability of host proteins to modulate the various cellular functions after infection. The exploitation of host factors by ankyrin repeat proteins of O. tsutsugamushi may also play a critical role in its pathogenesis.

Optical Cyclic Wavelength Shifter Using a Dual-Band Polymer Holographic Grating

We propose a cyclic wavelength shifter, that can be applied to optical networks or code-division multiple access (CDMA) systems. The shifter is based on a dual-band polymer holographic grating and operated by applying strain or rotation. Using this device, constant-weight cyclically permutable codes in various CDMA systems might be implemented easily compared with using other optical methods.