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Search Results: 1 - 10 of 6210 matches for " Kar-Lai Poon "
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Collective Cell Migration Drives Morphogenesis of the Kidney Nephron
Aleksandr Vasilyev,Yan Liu,Sudha Mudumana,Steve Mangos,Pui-Ying Lam,Arindam Majumdar,Jinhua Zhao,Kar-Lai Poon,Igor Kondrychyn,Vladimir Korzh,Iain A. Drummond
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1000009
Abstract: Tissue organization in epithelial organs is achieved during development by the combined processes of cell differentiation and morphogenetic cell movements. In the kidney, the nephron is the functional organ unit. Each nephron is an epithelial tubule that is subdivided into discrete segments with specific transport functions. Little is known about how nephron segments are defined or how segments acquire their distinctive morphology and cell shape. Using live, in vivo cell imaging of the forming zebrafish pronephric nephron, we found that the migration of fully differentiated epithelial cells accounts for both the final position of nephron segment boundaries and the characteristic convolution of the proximal tubule. Pronephric cells maintain adherens junctions and polarized apical brush border membranes while they migrate collectively. Individual tubule cells exhibit basal membrane protrusions in the direction of movement and appear to establish transient, phosphorylated Focal Adhesion Kinase–positive adhesions to the basement membrane. Cell migration continued in the presence of camptothecin, indicating that cell division does not drive migration. Lengthening of the nephron was, however, accompanied by an increase in tubule cell number, specifically in the most distal, ret1-positive nephron segment. The initiation of cell migration coincided with the onset of fluid flow in the pronephros. Complete blockade of pronephric fluid flow prevented cell migration and proximal nephron convolution. Selective blockade of proximal, filtration-driven fluid flow shifted the position of tubule convolution distally and revealed a role for cilia-driven fluid flow in persistent migration of distal nephron cells. We conclude that nephron morphogenesis is driven by fluid flow–dependent, collective epithelial cell migration within the confines of the tubule basement membrane. Our results establish intimate links between nephron function, fluid flow, and morphogenesis.
Optogenetic in vivo cell manipulation in KillerRed-expressing zebrafish transgenics
Cathleen Teh, Dmitry M Chudakov, Kar-Lai Poon, Ilgar Z Mamedov, Jun-Yan Sek, Konstantin Shidlovsky, Sergey Lukyanov, Vladimir Korzh
BMC Developmental Biology , 2010, DOI: 10.1186/1471-213x-10-110
Abstract: We report an in vivo modification of this technique using a fluorescent microscope and membrane-tagged KR (mem-KR)-expressing transgenic zebrafish. We generated several stable zebrafish Tol2 transposon-mediated enhancer-trap (ET) transgenic lines expressing mem-KR (SqKR series), and mapped the transposon insertion sites. As mem-KR accumulates on the cell membrane and/or Golgi, it highlights cell bodies and extensions, and reveals details of cellular morphology. The photodynamic property of KR made it possible to damage cells expressing this protein in a dose-dependent manner. As a proof-of-principle, two zebrafish transgenic lines were used to affect cell viability and function: SqKR2 expresses mem-KR in the hindbrain rhombomeres 3 and 5, and elsewhere; SqKR15 expresses mem-KR in the heart and elsewhere. Photobleaching of KR by intense light in the heart of SqKR15 embryos at lower levels caused a reduction in pumping efficiency of the heart and pericardial edema and at higher levels - in cell death in the hindbrain of SqKR2 and in the heart of SqKR15 embryos.An intense illumination of tissues expressing mem-KR affects cell viability and function in living zebrafish embryos. Hence, the zebrafish transgenics expressing mem-KR in a tissue-specific manner are useful tools for studying the biological effects of ROS.The introduction of efficient transgenesis into the field of developmental biology opened the possibility to eradicate cells through the incorporation of tissue-specific and inducible toxic proteins [1-4], with cell death as an experimental endpoint. In addition, the ability to dose-dependently modulate the level of induced damage may be even more useful when investigating the long-term effects of experimental insult and/or recovery of affected cells. Fluorescent proteins not only faithfully report the presence of tagged proteins but, upon illumination, they also generate reactive oxygen species (ROS). The level of ROS generated can be modulated by a dose of i
Collective Cell Migration Drives Morphogenesis of the Kidney Nephron
Aleksandr Vasilyev,Yan Liu,Sudha Mudumana,Steve Mangos,Pui-Ying Lam,Arindam Majumdar,Jinhua Zhao,Kar-Lai Poon,Igor Kondrychyn,Vladimir Korzh,Iain A Drummond
PLOS Biology , 2009, DOI: 10.1371/journal.pbio.1000009
Abstract: Tissue organization in epithelial organs is achieved during development by the combined processes of cell differentiation and morphogenetic cell movements. In the kidney, the nephron is the functional organ unit. Each nephron is an epithelial tubule that is subdivided into discrete segments with specific transport functions. Little is known about how nephron segments are defined or how segments acquire their distinctive morphology and cell shape. Using live, in vivo cell imaging of the forming zebrafish pronephric nephron, we found that the migration of fully differentiated epithelial cells accounts for both the final position of nephron segment boundaries and the characteristic convolution of the proximal tubule. Pronephric cells maintain adherens junctions and polarized apical brush border membranes while they migrate collectively. Individual tubule cells exhibit basal membrane protrusions in the direction of movement and appear to establish transient, phosphorylated Focal Adhesion Kinase–positive adhesions to the basement membrane. Cell migration continued in the presence of camptothecin, indicating that cell division does not drive migration. Lengthening of the nephron was, however, accompanied by an increase in tubule cell number, specifically in the most distal, ret1-positive nephron segment. The initiation of cell migration coincided with the onset of fluid flow in the pronephros. Complete blockade of pronephric fluid flow prevented cell migration and proximal nephron convolution. Selective blockade of proximal, filtration-driven fluid flow shifted the position of tubule convolution distally and revealed a role for cilia-driven fluid flow in persistent migration of distal nephron cells. We conclude that nephron morphogenesis is driven by fluid flow–dependent, collective epithelial cell migration within the confines of the tubule basement membrane. Our results establish intimate links between nephron function, fluid flow, and morphogenesis.
The zebrafish model system in cardiovascular research: A tiny fish with mighty prospects
Kar Lai Poon,Thomas Brand
Global Cardiology Science & Practice , 2012, DOI: 10.5339/gcsp.2013.4
Abstract: The zebrafish Danio rerio, a tropical freshwater fish, belongs to the family of cyprinidae, which in the last 30 years has developed into a very popular model organism for studies of embryonic development and human diseases. Initially the zebrafish species has been selected on the basis of its small size of approximately 3-5 cm, its transparency during development and its high fertility, qualities first identified by George Stresinger, the founding father of zebrafish research [1]. The ability to house thousands of small fishes and the ease of screening mutations in the translucent embryos made it feasible to perform large-scale forward genetic screens in a vertebrate model organism. The abundance of eggs obtained, approximately 200 eggs per female per week, is ideal for genetic and statistical analysis. The mutagenesis screens performed in the early 1990s have led to the identification of genes important in vertebrate organogenesis in an unbiased fashion [2-3]. Many of the isolated mutants have now been fully characterized and the mutated genes mapped, as the zebrafish genome sequencing completes. The knowledge derived has led to a better understanding of the underlying genetic networks governing vertebrate development. More sophisticated phenotype-based screens have since been developed to screen for mutations in defined biological processes [4].
Peritoneal Adipocytes and Their Role in Inflammation during Peritoneal Dialysis
Kar Neng Lai,Joseph C. K. Leung
Mediators of Inflammation , 2010, DOI: 10.1155/2010/495416
Abstract: Adipose tissue is a major site of chronic inflammation associated with peritoneal dialysis (PD) frequently complicating peritonitis. Adiposity-associated inflammation plays a significant contributory role in the development of chronic inflammation in patients undergoing maintenance PD. However, the molecular and cellular mechanisms of this link remain uncertain. Adipose tissue synthesizes different adipokines and cytokines that orchestrate and regulate inflammation, insulin action, and glucose metabolism locally and systemically. In return, inflammation retards adipocyte differentiation and further exacerbates adipose dysfunction and inflammation. An understanding of the inflammatory roles played by adipose tissue during PD and the healing mechanism of injured mesothelium will help to devise new therapeutic approach to slow the progression of peritoneal damage during peritoneal dialysis. This article reviews the roles of peritoneal adipose tissue in chronic peritoneal inflammation under PD and in serosal repair during PD.
Cytokines and Their Roles in the Pathogenesis of Systemic Lupus Erythematosus: From Basics to Recent Advances
Desmond Yat Hin Yap,Kar Neng Lai
Journal of Biomedicine and Biotechnology , 2010, DOI: 10.1155/2010/365083
Abstract: Systemic lupus erythematosus (SLE) is a complex auto-immune disorder which involves various facets of the immune system. In addition to autoantibody production and immune complex deposition, emerging evidences suggest that cytokines may act as key players in the immunopathogenesis of SLE. These cytokines assume a critical role in the differentiation, maturation and activation of cells and also participate in the local inflammatory processes that mediate tissue insults in SLE. Certain cytokines such as the IL-6, IL-10, IL-17, BLys, type I interferons (IFN) and tumor necrosis factor- (TNF-) are closely linked to pathogenesis of SLE. The delineation of the role played by these cytokines not only fosters our understanding of this disease but also provides a sound rationale for various therapeutic approaches. In this context, this review focuses on selected cytokines which exert significant effect in the pathogenesis of SLE and their possible clinical applications.
Influence of the aspect ratio on the endovascular treatment of intracranial aneurysms: A computational investigation  [PDF]
Abraham Yik-Sau Tang, Siu-Kai Lai, Kar-Ming Leung, Gilberto Ka-Kit Leung, Kwok-Wing Chow
Journal of Biomedical Science and Engineering (JBiSE) , 2012, DOI: 10.4236/jbise.2012.58054
Abstract: Intracranial aneurysm, a localized dilation of arterial blood vessels in the Circle of Willis and its branches, is potentially life threatening, due to massive bleeding in the subarachnoid space upon rupture. In clinical practice, one minimally invasive surgical procedure is the implantation of a metallic stent to cover the aneurysm neck. This flow diverting device can reduce the flow into the aneurysm and enhance the prospect of thrombosis, a condition expected to reduce the risk of growth and rupture. The biomechanical and haemo-dynamic factors in stented and nonstented situations are studied by computational fluid dynamics. Unlike earlier models with straight or curved parent blood vessels, the aneurysm is now located near an arterial bifurcation. The influence of the aspect (depth to neck) ratio of the aneurysm on the flow dynamics will be emphasized, especially in the post-operation stages. More precisely, the maximum flow velocity, the variations of wall shear stress, the risk of stent migration and volumetric flow rate after endovascular treatment will be studied. Aneurysms with larger aspect ratios (i.e. smaller neck sizes for constant depth) generally pose a greater risk in terms of these flow parameters. These results will assist the applications and design of stents in future neurosurgical therapy. The approach is limited to a nonelastic model, without taking into account of questions like stent expansion and interaction with tissue.
Empirical Analysis of Factors Affecting the E-Book Adoption—Research Agenda  [PDF]
J. K. L. Poon
Open Journal of Social Sciences (JSS) , 2014, DOI: 10.4236/jss.2014.25011
Abstract: Advances in information technology encourage the development of e-books. The 2010 Horizon Report predicts that e-book will be one of the six technologies most likely to affect higher education in coming years. Despite the huge investment in developing the e-book market, customer take-up over the past decades is still far below expectations. The success of e-book adoption depends on the implementation of an educational model that addresses learner needs as well as content relevance. To understand customer behavior intention in adopting e-books and to address the lack of holistic approach in adoption research, this project is proposed to investigate the intention of college students in using e-books. This cross-sectional research utilizes the Technology Acceptance Model (TAM) and four additional variables, namely, personal innovativeness of information technology, social influences, perceived costs, and environmental consciousness. The study is expected to contribute to the literature by providing an empirically validated extended TAM regarding e-books. Moreover, the results will provide important and useful information for academicians and publishers.
Innovation and Social Impact in Higher Education: Some Lessons from Tohoku University and the Open University of Hong Kong  [PDF]
Carol Poon Man Wai
Open Journal of Social Sciences (JSS) , 2017, DOI: 10.4236/jss.2017.59011
Abstract: In recent years, Hong Kong Education Authority has been zealously encouraging schools to reform the current teaching profession, so as to raise students’ critical thinking and creativity, as well as to enhance their innovation and motivation of learning. Along with this, American scholars (Clements 2013 [1]; Levi 2013 [2]; McCarthy 2009 [3]; McWilliam 2009 [4]) have encouraged the educational circles vigorously that they should apply innovation teaching in the teaching profession. Actually this strategy has been widely examined in United State and Japan for a period of time and the outcome is quite fruitful. Based on the lessons from Massachusetts Institute of Technology, this paper aims to shed light on a heavily under-researched multidisciplinary area: innovation and education. With a focus in the Tohoku University in Japan and The Open University of Hong Kong, this paper will examine the issue via cultural history, education policy and related social systems together with “the traditional custom”. Furthermore, this paper aims to redefine the concept of innovation in nowadays higher education teaching, to serve as a reference for potential change agents as they consider ways and means to created improved learning environments at universities and institutions, to enhance the educational circles’ interest and understanding in utilizing such new medium as well as the social power. And finally it examines and compares the social impact on the introduction of innovation teaching in higher education profession. Apart from literature studies, this paper will carry out a field study and interview in both Hong Kong and Japan, and also field observation in Tohoku University.
Plasmonic-Resonant Bowtie Antenna for Carbon Nanotube Photodetectors
Hongzhi Chen,Ning Xi,King Wai Chiu Lai,Liangliang Chen,Carmen Kar Man Fung,Jianyong Lou
International Journal of Optics , 2012, DOI: 10.1155/2012/318104
Abstract: The design of bowtie antennas for carbon nanotube (CNT) photodetectors has been investigated. CNT photodetectors have shown outstanding performance by using CNT as sensing element. However, detection wavelength is much larger than the diameter of the CNT, resulting in small fill factor. Bowtie antenna can confine light into a subwavelength volume based on plasmonic resonance, thus integrating a bowtie antenna to CNT photodetectors can highly improve photoresponse of the detectors. The electric field enhancement of bowtie antennas was calculated using the device geometry by considering fabrication difficulties and photodetector structure. It is shown that the electric field intensity enhancement increased exponentially with distance reduction between the CNT photodetector to the antenna. A redshift of the peak resonance wavelength is predicted due to the increase of tip angles of the bowtie antennas. Experimental results showed that photocurrent enhancement agreed well with theoretical calculations. Bowtie antennas may find wide applications in nanoscale photonic sensors. 1. Introduction With the development of nanotechnologies, one-dimensional (1D) materials, including nanowires and nanotubes, emerged as important components in photonics and optoelectronics [1]. Compared to bulk materials, 1D materials possess a number of unique properties arose from their geometries, making them potential candidates to outperform traditional optical devices. In particular, carbon nanotubes (CNTs) are of great interest for exploring as functional elements for 1D photodetectors due to their perfect nanohollow cylinder structure [2, 3]. However, a critical challenge for obtaining high-performance 1D photodetectors is the dimension incompatibility between photodetectors and optical wavelengths. The radial sizes of CNTs are much smaller than detection wavelengths, resulting in low fill factor and responsivity. Motivated by this challenge, optical antennas were designed to integrate with CNT photodetectors so as to bridge the gap between nanosize sensing elements and microsize wavelengths. Due to plasmonic resonance, optical antennas can confine strong optical near fields in a volume far below a cubic wavelength of excitation light. This can greatly enhance photon absorption owing to the increase of coupling between CNT and vibrating electrical fields of photons. By integrating CNT photodetectors with optical antennas, the nanoscale photodetectors can be made with outstanding performance and photon absorption efficiency. There are two main categories of photodetectors:
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