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Search Results: 1 - 10 of 3256 matches for " Harukazu Nakamura "
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Learning of Soccer Player Agents Using a Policy Gradient Method : Coordination Between Kicker and Receiver During Free Kicks
Harukazu Igarashi, Koji Nakamura & Seiji Ishihara
International Journal of Artificial Intelligence and Expert Systems , 2011,
Abstract: As an example of multi-agent learning in soccer games of the RoboCup 2D Soccer SimulationLeague, we dealt with a learning problem between a kicker and a receiver when a direct free kickis awarded just outside the opponent’s penalty area. We propose how to use a heuristic functionto evaluate an advantageous target point for safely sending/receiving a pass and scoring. Theheuristics include an interaction term between a kicker and a receiver to intensify theircoordination. To calculate the interaction term, we let a kicker/receiver agent have areceiver’s/kicker’s action decision model to predict a receiver’s/kicker’s action. Parameters in theheuristic function can be learned by a kind of reinforcement learning called the policy gradientmethod. Our experiments show that if the two agents do not have the same type of heuristics, theinteraction term based on prediction of a teammate’s decision model leads to learning a masterservantrelation between a kicker and a receiver, where a receiver is a master and a kicker is aservant.
Nkx2.2+ Progenitors Generate Somatic Motoneurons in the Chick Spinal Cord
Hitoshi Gotoh, Katsuhiko Ono, Tadashi Nomura, Hirohide Takebayashi, Hidekiyo Harada, Harukazu Nakamura, Kazuhiro Ikenaka
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0051581
Abstract: Heterogeneous classes of neurons are present in the spinal cord and are essential for its function. Expression patterns of transcription factors in neural progenitor cells determine neuron subtypes during development. Nkx2.2 is expressed in the progenitor cell pool located just ventrally to the Olig2-positive pool and is indispensable for V3 interneuron generation in the spinal cord and also for visceral motoneuron generation in the hindbrain. However, whether Nkx2.2-positive progenitor cells generate diverse classes of neuron is not fully understood. Using a chick lineage tracing method in a genetically-defined manner, we found that Nkx2.2-expressing progenitor cells differentiate into general visceral motoneurons as well as sim1-positive V3 interneurons. Surprisingly, we further observed that Nkx2.2-expressing progenitors differentiate into somatic motoneuron. Our findings suggest that the different classes of motoneurons are derived from more complex sources than were previously expected in the chick spinal cord.
Optogenetic Probing and Manipulation of the Calyx-Type Presynaptic Terminal in the Embryonic Chick Ciliary Ganglion
Ryo Egawa, Shoko Hososhima, Xubin Hou, Hidetaka Katow, Toru Ishizuka, Harukazu Nakamura, Hiromu Yawo
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0059179
Abstract: The calyx-type synapse of chick ciliary ganglion (CG) has been intensively studied for decades as a model system for the synaptic development, morphology and physiology. Despite recent advances in optogenetics probing and/or manipulation of the elementary steps of the transmitter release such as membrane depolarization and Ca2+ elevation, the current gene-manipulating methods are not suitable for targeting specifically the calyx-type presynaptic terminals. Here, we evaluated a method for manipulating the molecular and functional organization of the presynaptic terminals of this model synapse. We transfected progenitors of the Edinger-Westphal (EW) nucleus neurons with an EGFP expression vector by in ovo electroporation at embryonic day 2 (E2) and examined the CG at E8–14. We found that dozens of the calyx-type presynaptic terminals and axons were selectively labeled with EGFP fluorescence. When a Brainbow construct containing the membrane-tethered fluorescent proteins m-CFP, m-YFP and m-RFP, was introduced together with a Cre expression construct, the color coding of each presynaptic axon facilitated discrimination among inter-tangled projections, particularly during the developmental re-organization period of synaptic connections. With the simultaneous expression of one of the chimeric variants of channelrhodopsins, channelrhodopsin-fast receiver (ChRFR), and R-GECO1, a red-shifted fluorescent Ca2+-sensor, the Ca2+ elevation was optically measured under direct photostimulation of the presynaptic terminal. Although this optically evoked Ca2+ elevation was mostly dependent on the action potential, a significant component remained even in the absence of extracellular Ca2+. It is suggested that the photo-activation of ChRFR facilitated the release of Ca2+ from intracellular Ca2+ stores directly or indirectly. The above system, by facilitating the molecular study of the calyx-type presynaptic terminal, would provide an experimental platform for unveiling the molecular mechanisms underlying the morphology, physiology and development of synapses.
Otx2 Is Involved in the Regional Specification of the Developing Retinal Pigment Epithelium by Preventing the Expression of Sox2 and Fgf8, Factors That Induce Neural Retina Differentiation
Daisuke Nishihara,Ichiro Yajima,Hiromasa Tabata,Masato Nakai,Nagaharu Tsukiji,Tatsuya Katahira,Kazuhisa Takeda,Shigeki Shibahara,Harukazu Nakamura,Hiroaki Yamamoto
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0048879
Abstract: The retinal pigment epithelium (RPE) shares its developmental origin with the neural retina (NR). When RPE development is disrupted, cells in the presumptive RPE region abnormally differentiate into NR-like cells. Therefore, the prevention of NR differentiation in the presumptive RPE area seems to be essential for regionalizing the RPE during eye development. However, its molecular mechanisms are not fully understood. In this study, we conducted a functional inhibition of a transcription factor Otx2, which is required for RPE development, using early chick embryos. The functional inhibition of Otx2 in chick eyes, using a recombinant gene encoding a dominant negative form of Otx2, caused the outer layer of the optic cup (the region forming the RPE, when embryos normally develop) to abnormally form an ectopic NR. In that ectopic NR, the characteristics of the RPE did not appear and NR markers were ectopically expressed. Intriguingly, the repression of Otx2 function also caused the ectopic expression of Fgf8 and Sox2 in the outer layer of the optic cup (the presumptive RPE region of normally developing eyes). These two factors are known to be capable of inducing NR cell differentiation in the presumptive RPE region, and are not expressed in the normally developing RPE region. Here, we suggest that Otx2 prevents the presumptive RPE region from forming the NR by repressing the expression of both Fgf8 and Sox2 which induce the NR cell fate.
Schwann-Spheres Derived from Injured Peripheral Nerves in Adult Mice - Their In Vitro Characterization and Therapeutic Potential
Takehiko Takagi, Ken Ishii, Shinsuke Shibata, Akimasa Yasuda, Momoka Sato, Narihito Nagoshi, Harukazu Saito, Hirotaka J. Okano, Yoshiaki Toyama, Hideyuki Okano, Masaya Nakamura
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0021497
Abstract: Multipotent somatic stem cells have been identified in various adult tissues. However, the stem/progenitor cells of the peripheral nerves have been isolated only from fetal tissues. Here, we isolated Schwann-cell precursors/immature Schwann cells from the injured peripheral nerves of adult mice using a floating culture technique that we call “Schwann-spheres." The Schwann-spheres were derived from de-differentiated mature Schwann cells harvested 24 hours to 6 weeks after peripheral nerve injury. They had extensive self-renewal and differentiation capabilities. They strongly expressed the immature-Schwann-cell marker p75, and differentiated only into the Schwann-cell lineage. The spheres showed enhanced myelin formation and neurite growth compared to mature Schwann cells in vitro. Mature Schwann cells have been considered a promising candidate for cell-transplantation therapies to repair the damaged nervous system, whereas these “Schwann-spheres" would provide a more potential autologous cell source for such transplantation.
Human genome research enters a new phase
Harukazu Suzuki, Yoshihide Hayashizaki
Genome Biology , 2005, DOI: 10.1186/gb-2005-6-8-337
Abstract: The Human Genome Meeting (HGM) is an annual event organized by the Human Genome Organization (HUGO) for scientists working on the human genome. This year's HGM was the tenth anniversary meeting, with approximately 500 presentations covering a wide variety of work on the human genome. In his opening remarks, the president of HUGO, Yoshiyuki Sakaki (RIKEN Genomic Sciences Center, Yokohama, Japan), commented that participants would have plenty of opportunities to find out "what is going on in the post (human) genome sequencing era". This report discusses a few of the latest research findings that were presented at the meeting.It is clear that large-scale sequencing facilities are still important, and indeed essential, for genome science. Richard Gibbs (Baylor College of Medicine, Houston, USA) reported that the genome sequencing projects of many animal species, including the Rhesus macaque, orangutan, Tammar wallaby, cow, and the honeybee, are ongoing and will soon provide us with valuable resources for the analysis of these organisms and for comparative genomics. He also reported that the phase I plan of the human HapMap project, in which common single-nucleotide polymorphisms (SNPs) are covered at a resolution of 5 kilobases (kb), has now been completed.The completion of the human genome sequence and the progress of the HapMap project have facilitated genetic approaches to disease-associated genes and regions. Kari Stefansson (deCODE Genetics, Reykjavik, Iceland) described the genetics of complex traits in the Icelandic population: among more than 50 ongoing projects, 30 are focused on the mapping of disease-associated loci, 15 on gene isolation and eight on drug development. He reported that LTA4 hydrolase, an enzyme involved in leukotriene B4 biosynthesis, is associated with myocardial infarction (MI), and that LTB4 upregulation by ionomycin stimulation of neutrophils is higher in MI patients than in healthy people. The deCODE team has recently developed a drug, DG
Polychotomization of continuous variables in regression models based on the overall C index
Harukazu Tsuruta, Leon Bax
BMC Medical Informatics and Decision Making , 2006, DOI: 10.1186/1472-6947-6-41
Abstract: We used the overall discrimination index C, introduced by Harrel, as a measure of the predictive ability of an independent regressor variable and derived a method for polychotomization mathematically. Since the na?ve application of our method, like some existing methods, gives rise to positive bias, we developed a parametric method that minimizes this bias and assessed its performance by the use of Monte Carlo simulation.The overall C is closely related to the area under the ROC curve and the produced di(poly)chotomized variable's predictive performance is comparable to the original continuous variable. The simulation shows that the parametric method is essentially unbiased for both the estimates of performance and the cutoff points. Application of our method to the predictor variables of a previous study on rhabdomyolysis shows that it can be used to make probability profile tables that are applicable to the diagnosis or prognosis of individual patient status.We propose a polychotomization (including dichotomization) method for independent continuous variables in regression models based on the overall discrimination index C and clarified its meaning mathematically. To avoid positive bias in application, we have proposed and evaluated a parametric method. The proposed method for polychotomizing continuous regressor variables performed well and can be used to create probability profile tables.In modern diagnostic and descriptive prognostic research, regression models are often used to model an illness-related outcome based on a number of independent regressor variables, also referred to as diagnostic indicators or prognostic predictors [1]. Such regressor variables can be categorical or numerical. From the vantage point of applicability in a clinical setting, categorization (often dichotomization) of continuous independent variables can be useful. Obtaining a prediction at the bedside without computer is easier with a prediction table based on categorized variables t
LRRN4 and UPK3B Are Markers of Primary Mesothelial Cells
Mutsumi Kanamori-Katayama,Ai Kaiho,Yuri Ishizu,Yuko Okamura-Oho,Okio Hino,Masaaki Abe,Takumi Kishimoto,Hisahiko Sekihara,Yukio Nakamura,Harukazu Suzuki,Alistair R. R. Forrest,Yoshihide Hayashizaki
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0025391
Abstract: Mesothelioma is a highly malignant tumor that is primarily caused by occupational or environmental exposure to asbestos fibers. Despite worldwide restrictions on asbestos usage, further cases are expected as diagnosis is typically 20–40 years after exposure. Once diagnosed there is a very poor prognosis with a median survival rate of 9 months. Considering this the development of early pre clinical diagnostic markers may help improve clinical outcomes.
Expression of ATF3 and axonal outgrowth are impaired after delayed nerve repair
Harukazu Saito, Lars B Dahlin
BMC Neuroscience , 2008, DOI: 10.1186/1471-2202-9-88
Abstract: The number of neurons and Schwann cells expressing ATF3 declined and the length of axonal outgrowth was impaired if the repair was delayed. The decline was more rapid in motor neurons than in sensory neurons and Schwann cells. Regeneration distances over time correlated to number of ATF3 stained neurons and Schwann cells. Many neurofilament stained axons grew along ATF3 stained Schwann cells. If nerve repair was delayed the majority of Schwann cells in the distal nerve segment stained for NCAM.Delayed nerve repair impairs nerve regeneration and length of axonal outgrowth correlates to ATF3 expression in both neurons and Schwann cells. Mainly non-myelinating Schwann cells (NCAM stained) are present in distal nerve segments after delayed nerve repair. These data provide a neurobiological basis for the poor outcomes associated with delayed nerve repair. Nerve trunks should, if possible, be promptly repaired.Impaired nerve regeneration and weakened target reinnervation are significant clinical problems after nerve injury when the repair of a nerve trunk is delayed [1-3]. Clinically, recovery of motor function is also less than sensory recovery after delayed repair [4], possibly due to the outgrowth of sensory axons interfering with the outgrowth of motor axons [5,6]. In delayed nerve repair the previously injured neurons are reactivated upon the additional injury leading to axonal outgrowth [7]. After a nerve injury Schwann cells are rapidly activated at site of the lesion [8] and in the distal nerve segment with proliferation and remodelling of the extracellular matrix [9]. The insufficient nerve regeneration after delayed nerve repair has been attributed to an inability of Schwann cells to support axonal outgrowth [10,11]. However, detailed signal transduction mechanisms underlying the impaired nerve regeneration are not well understood.Activating transcription factor 3 (ATF3) is rapidly expressed in neurons and Schwann cells after injury and is preceeded by phosphory
Irrelevance of Conjectural Variation in a Private Duopoly with Consistent Conjectures: The Relative Performance Approach and Network Effects  [PDF]
Yasuhiko Nakamura
Modern Economy (ME) , 2013, DOI: 10.4236/me.2013.49A002
Abstract:

This paper explores the equilibrium market outcomes in the contexts of both quantity-setting and price-setting private duopolies with the consistent conjectures of two private firms, wherein they maximize the weighted sum of their own profits and their respective opponent firm’s profit. Similar to the private duopoly without network effects wherein the two private firms maximize their genuine relative profits, in the private duopoly with network effects such that both firms maximize the weighted sum of their own profits and their respective opponent firm’s profit, we show that the equilibrium outcomes in the quantity-setting competition with the consistent conjectures of both firms are equivalent to those in the price-setting competition with the consistent conjectures of both firms.

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