The University of Tokyo , abbreviated as Todai , is a research university located in Bunkyo, Tokyo, Japan. The University has 10 faculties with a total of around 30,000 students, 2,100 of whom are foreign. Its five campuses are in Hongō, Komaba, Kashiwa, Shirokane and Nakano. It is the first of Japan's National Seven Universities, and is considered the most prestigious university in Japan. It ranks as the highest in Asia and 21st in the world according to the Academic Ranking of World Universities 2014. Wikipedia.
Hatakeyama M.,University of Tokyo
Cell Host and Microbe | Year: 2014
Helicobacter pylori is a gastric bacterial pathogen that is etiologically linked to human gastric cancer. The cytotoxin-associated gene A (CagA) protein of H. pylori, which is delivered into gastric epithelial cells via bacterial type IV secretion, is an oncoprotein that can induce malignant neoplasms in mammals. Upon delivery, CagA perturbs multiple host signaling pathways by acting as an extrinsic scaffold or hub protein. On one hand, signals aberrantly raised by CagA are integrated into a direct oncogenic insult, whereas on the other hand, they engender genetic instability. Despite its decisive role in the development of gastric cancer, CagA is not required for the maintenance of a neoplastic phenotype in established cancer cells. Therefore, CagA-conducted gastric carcinogenesis progresses through a hit-and-run mechanism in which pro-oncogenic actions of CagA are successively taken over by a series of genetic and/or epigenetic alterations compiled in cancer-predisposing cells during long-standing infection with cagA-positive H. pylori. ©2014 Elsevier Inc.
Ueda M.,University of Tokyo
Annual Review of Condensed Matter Physics | Year: 2012
Gaseous Bose-Einstein condensates with nonzero spin feature multicomponent order parameters that reflect the internal degrees of freedom. They exhibit a rich variety of superfluid and magnetic phenomena similar or complementary to those of superfluid helium-3. The unprecedented degree of manipulability of atomic gases makes spinor condensates a unique playground for exploring symmetry breaking, topological excitations, and the interplay between superfluidity and magnetism. An overview of these subjects is provided. Copyright © 2012 by Annual Reviews. All rights reserved.
Ezawa M.,University of Tokyo
Physical Review Letters | Year: 2013
Silicene (a monolayer of silicon atoms) is a two-dimensional topological insulator (TI) that undergoes a topological phase transition to a band insulator under external electric field Ez. We investigate a photoinduced topological phase transition from a TI to another TI by changing its topological class by irradiating circular polarized light at fixed Ez. The band structure is modified by photon dressing with a new dispersion, where the topological property is altered. By increasing the intensity of light at E z=0, a photoinduced quantum Hall insulator is realized. Its edge modes are anisotropic chiral, in which the velocities of up and down spins are different. At Ez>Ecr with a certain critical field Ecr, a photoinduced spin-polarized quantum Hall insulator emerges. This is a new state of matter, possessing one Chern number and one-half spin-Chern numbers. We newly discover a single Dirac-cone state along a phase boundary. A distinctive hallmark of the state is that one of the two Dirac valleys is closed and the other open. © 2013 American Physical Society.
Ezawa M.,University of Tokyo
Physical Review Letters | Year: 2012
Silicene is a monolayer of silicon atoms forming a two-dimensional honeycomb lattice, which shares almost every remarkable property with graphene. The low-energy structure of silicene is described by Dirac electrons with relatively large spin-orbit interactions due to its buckled structure. The key observation is that the band structure is controllable by applying electric field to silicene. We explore the phase diagram of silicene together with exchange field M and by applying electric field E z. A quantum anomalous Hall (QAH) insulator, valley polarized metal (VPM), marginal valley polarized metal (M-VPM), quantum spin Hall insulator, and band insulator appear. They are characterized by the Chern numbers and/or by the edge modes of a nanoribbon. It is intriguing that electrons have been moved from a conduction band at the K point to a valence band at the K ′ point for E z>0 in the VPM. We find in the QAH phase that almost flat gapless edge modes emerge and that spins form a momentum-space Skyrmion to yield the Chern number. It is remarkable that a topological quantum phase transition can be induced simply by changing electric field in a single silicene sheet. © 2012 American Physical Society.
Hayashi T.,University of Tokyo
Cell host & microbe | Year: 2012
The Helicobacter pylori type IV secretion effector CagA is a major bacterial virulence determinant and critical for gastric carcinogenesis. Upon delivery into gastric epithelial cells, CagA localizes to the inner face of the plasma membrane, where it acts as a pathogenic scaffold/hub that promiscuously recruits host proteins to potentiate oncogenic signaling. We find that CagA comprises a structured N-terminal region and an intrinsically disordered C-terminal region that directs versatile protein interactions. X-ray crystallographic analysis of the N-terminal CagA fragment (residues 1-876) revealed that the region has a structure comprised of three discrete domains. Domain I constitutes a mobile CagA N terminus, while Domain II tethers CagA to the plasma membrane by interacting with membrane phosphatidylserine. Domain III interacts intramolecularly with the intrinsically disordered C-terminal region, and this interaction potentiates the pathogenic scaffold/hub function of CagA. The present work provides a tertiary-structural basis for the pathophysiological/oncogenic action of H. pylori CagA. Copyright © 2012 Elsevier Inc. All rights reserved.