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Search Results: 1 - 10 of 22763 matches for " Pui-ying Lam "
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Heat Shock Modulates Neutrophil Motility in Zebrafish
Pui-ying Lam, Elizabeth A. Harvie, Anna Huttenlocher
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0084436
Abstract: Heat shock is a routine method used for inducible gene expression in animal models including zebrafish. Environmental temperature plays an important role in the immune system and infection progression of ectotherms. In this study, we analyzed the impact of short-term heat shock on neutrophil function using zebrafish (Danio rerio) as an animal model. Short-term heat shock decreased neutrophil recruitment to localized Streptococcus iniae infection and tail fin wounding. Heat shock also increased random neutrophil motility transiently and increased the number of circulating neutrophils. With the use of the translating ribosome affinity purification (TRAP) method for RNA isolation from specific cell types such as neutrophils, macrophages and epithelial cells, we found that heat shock induced the immediate expression of heat shock protein 70 (hsp70) and a prolonged expression of heat shock protein 27 (hsp27). Heat shock also induced cell stress as detected by the splicing of X-box binding protein 1 (xbp1) mRNA, a marker for endoplasmic reticulum (ER) stress. Exogenous expression of Hsp70, Hsp27 and spliced Xbp1 in neutrophils or epithelial cells did not reproduce the heat shock induced effects on neutrophil recruitment. The effect of heat shock on neutrophils is likely due to a combination of complex changes, including, but not limited to changes in gene expression. Our results indicate that routine heat shock can alter neutrophil function in zebrafish. The findings suggest that caution should be taken when employing a heat shock-dependent inducible system to study the innate immune response.
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.
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.
Comment on "Theory of high-force DNA stretching and overstretching"
Pui-Man Lam
Physics , 2004, DOI: 10.1103/PhysRevE.70.013901
Abstract: Recently Storm and Nelson [1] (Phys.Rev. E67, 51906 (2003)) introduced the discrete persistent chain model which contains both features of the freely jointed chain (FJC) and the wormlike chain (WLC) models. Equation (20) of their paper is correct only in a special case of large l, the ratio of the persistence length to the monomer length. This special case is unnecessary because the general case can be studied just as easily. Working out the general case, we obtain the force extension relation correct for all values of the parameter l. This force extension relation reduces to the FJC result at small l and to the WLC at large l. At small force, it reduces to the result of Rosa et al (cond-mat/0307015).
Excluded Volume Effects in Gene Stretching
Pui-Man Lam
Quantitative Biology , 2002,
Abstract: We investigate the effects excluded volume on the stretching of a single DNA in solution. We find that for small force F, the extension h is not linear in F but proportion to F^{\chi}, with \chi=(1-\nu)/\nu, where \nu is the well-known universal correlation length exponent. A freely joint chain model with the segment length chosen to reproduce the small extension behavior gives excellent fit to the experimental data of \lambda-Phage DNA over the whole experimental range. We show that excluded volume effects are stronger in two dimensions and also derive results in two dimensions which are different from the three dimensional results. This suggests experiments to be performed in these lower dimensions.
Work stress and problem gambling among Chinese casino employees in Macau
Irene Lai Wong and Pui Sze Lam
Asian Journal of Gambling Issues and Public Health , 2013, DOI: 10.1186/2195-3007-3-7
Abstract: The prior literature has suggested that gaming venue employees might be an at-risk group for developing gambling problems. A variety of occupational stressors and workplace factors were uncovered for causing the elevated risk. However, little theory-driven research has been conducted to investigate Asian gaming venue employees' experience of work stress and gambling behavior. Adopting the transactional theories of stress and coping, this exploratory study examined perceived job satisfaction, work stressors, stress strains, coping responses and gambling behavior among Chinese casino employees in Macau. Semi-structured interviews with fifteen casino employees (9 men and 6 women) were conducted. Many interviewees described working at casino as very stressful. Seven types of workplace stressors were identified. Most were aware of the harmful effects of work stress on their health. They experienced physical and psychological strains despite various coping strategies were employed to alleviate job stress. Many gambled after work to 'unwind'. Using the DSM-IV criteria, one male employee could be categorized as a pathological gambler, and five men exhibited symptoms of problem gambling. In addition to job stress and male gender, other risk factors for problem gambling were also found. The study results have implication for workplace stress prevention and responsible gambling practices.
The Role of Chain Entropy in an Analytic Model of Protein Binding in Single-DNA Stretching Experiments
Pui-Man Lam,Richard M. Neumann
Physics , 2011, DOI: 10.1103/PhysRevE.84.032901
Abstract: We show that the simple analytical model proposed by Zhang and Marko (Phys. Rev. E 77, 031916 (2008)) to illustrate Maxwell relations for single-DNA experiments can be improved by including the zero-force entropy of a Gaussian chain. The resulting model is in excellent agreement with the discrete persistent-chain model and is in a form convenient for analyzing experimental data.
Force Induced Unzipping of DNA with Long Range Correlated Noise
Pui-Man Lam,Yi Zhen
Physics , 2011, DOI: 10.1088/1742-5468/2011/06/P06023
Abstract: We derive and solve a Fokker-Planck equation for the stationary distribution of the free energy, in a model of unzipping of double-stranded DNA under external force. The autocorrelation function of the random DNA sequence can be a general form, including long range correlations. In the case of Orstein-Uhlenbeck noise, characterized by a finite correlation length, our result reduces to the exact result of Allahverdyan et al, with the average number of unzipped base pairs going as ~1/f^2 in the white noise limit, where f is the deviation from the critical force. In the case of long range correlated noise, where the integrated autocorrelation is divergent, we find that is finite at f=0, with its value decreasing as the correlations become longer range. This shows that long range correlations actually stabilize the DNA sequence against unzipping. Our result is also in agreement with the findings of Allahverdyan et al, obtained using numerical generation of the long range correlated noise.
Stretching self-interacting, partially directed, flexible and semi-flexible polymers by an external force
Pui-Man Lam,Yi Zhen
Physics , 2010, DOI: 10.1088/1742-5468/2010/05/P05011
Abstract: We study the model of a partially directed flexible or semi-flexible homopolymer on a square lattice, subject to an externally applied force, in a direction either parallel to, or perpendicular to the preferred direction. The polymer is self-interacting and can therefore undergo a collapse transition. We show that this model can be solved and we obtain the force-temperature phase diagrams which, for the case of flexible polymers, agree with that of Brak et al obtained using a different method. At sufficiently low temperatures, the polymer conformation changes from compact to coil state as the force is increased beyond a critical value. This transition is second or first order for the completely flexible or semi-flexible polymer, respectively.
Unzipping DNA from the condensed globule state--Effects of unraveling
Pui-Man Lam,J. C. Levy
Physics , 2006,
Abstract: We study theoretically the unzipping of a double stranded DNA from a condensed globule state by an external force. At constant force, we find that the double stranded DNA unzips an at critical force Fc and the number of unzipped monomers M goes as M~(Fc-F)^{-3}, for both the homogeneous and heterogeneous double stranded DNA sequence. This is different from the case of unzipping from an extended coil state in which the number of unzipped monomers M goes as M~(Fc-F)^{-chi}, where the exponent chi is either 1 or 2 depending on whether the double stranded DNA sequence is homogeneous or heterogeneous respectively. In the case of unzipping at constant extension, we find that for a double stranded DNA with a very large number N of base pairs, the force remains almost constant as a function of the extension, before the unraveling transition, at which the force drops abruptly to zero. Right at the unraveling transition, the number of base pairs remaining in the condensed globule state is still very large and goes as N^{3/4}, in agreement with theoretical predictions of the unraveling transition of polymers stretched by an external force.
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