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Search Results: 1 - 10 of 224688 matches for " R. Meldrum Robertson "
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Possible Involvement of Cone Opsins in Distinct Photoresponses of Intrinsically Photosensitive Dermal Chromatophores in Tilapia Oreochromis niloticus
Shyh-Chi Chen, R. Meldrum Robertson, Craig W. Hawryshyn
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0070342
Abstract: Dermal specialized pigment cells (chromatophores) are thought to be one type of extraretinal photoreceptors responsible for a wide variety of sensory tasks, including adjusting body coloration. Unlike the well-studied image-forming function in retinal photoreceptors, direct evidence characterizing the mechanism of chromatophore photoresponses is less understood, particularly at the molecular and cellular levels. In the present study, cone opsin expression was detected in tilapia caudal fin where photosensitive chromatophores exist. Single-cell RT-PCR revealed co-existence of different cone opsins within melanophores and erythrophores. By stimulating cells with six wavelengths ranging from 380 to 580 nm, we found melanophores and erythrophores showed distinct photoresponses. After exposed to light, regardless of wavelength presentation, melanophores dispersed and maintained cell shape in an expansion stage by shuttling pigment granules. Conversely, erythrophores aggregated or dispersed pigment granules when exposed to short- or middle/long-wavelength light, respectively. These results suggest that diverse molecular mechanisms and light-detecting strategies may be employed by different types of tilapia chromatophores, which are instrumental in pigment pattern formation.
Natural Variation in the Thermotolerance of Neural Function and Behavior due to a cGMP-Dependent Protein Kinase
Ken Dawson-Scully, Gary A. B. Armstrong, Clement Kent, R. Meldrum Robertson, Marla B. Sokolowski
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0000773
Abstract: Although it is acknowledged that genetic variation contributes to individual differences in thermotolerance, the specific genes and pathways involved and how they are modulated by the environment remain poorly understood. We link natural variation in the thermotolerance of neural function and behavior in Drosophila melanogaster to the foraging gene (for, which encodes a cGMP-dependent protein kinase (PKG)) as well as to its downstream target, protein phosphatase 2A (PP2A). Genetic and pharmacological manipulations revealed that reduced PKG (or PP2A) activity caused increased thermotolerance of synaptic transmission at the larval neuromuscular junction. Like synaptic transmission, feeding movements were preserved at higher temperatures in larvae with lower PKG levels. In a comparative assay, pharmacological manipulations altering thermotolerance in a central circuit of Locusta migratoria demonstrated conservation of this neuroprotective pathway. In this circuit, either the inhibition of PKG or PP2A induced robust thermotolerance of neural function. We suggest that PKG and therefore the polymorphism associated with the allelic variation in for may provide populations with natural variation in heat stress tolerance. for's function in behavior is conserved across most organisms, including ants, bees, nematodes, and mammals. PKG's role in thermotolerance may also apply to these and other species. Natural variation in thermotolerance arising from genes involved in the PKG pathway could impact the evolution of thermotolerance in natural populations.
Reduction in Neural Performance following Recovery from Anoxic Stress Is Mimicked by AMPK Pathway Activation
Tomas G. A. Money, Michael K. J. Sproule, Amr F. Hamour, R. Meldrum Robertson
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0088570
Abstract: Nervous systems are energetically expensive to operate and maintain. Both synaptic and action potential signalling require a significant investment to maintain ion homeostasis. We have investigated the tuning of neural performance following a brief period of anoxia in a well-characterized visual pathway in the locust, the LGMD/DCMD looming motion-sensitive circuit. We hypothesised that the energetic cost of signalling can be dynamically modified by cellular mechanisms in response to metabolic stress. We examined whether recovery from anoxia resulted in a decrease in excitability of the electrophysiological properties in the DCMD neuron. We further examined the effect of these modifications on behavioural output. We show that recovery from anoxia affects metabolic rate, flight steering behaviour, and action potential properties. The effects of anoxia on action potentials can be mimicked by activation of the AMPK metabolic pathway. We suggest this is evidence of a coordinated cellular mechanism to reduce neural energetic demand following an anoxic stress. Together, this represents a dynamically-regulated means to link the energetic demands of neural signaling with the environmental constraints faced by the whole animal.
Glial Hsp70 Protects K+ Homeostasis in the Drosophila Brain during Repetitive Anoxic Depolarization
Gary A. B. Armstrong, Chengfeng Xiao, Jennifer L. Krill, Laurent Seroude, Ken Dawson-Scully, R. Meldrum Robertson
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0028994
Abstract: Neural tissue is particularly vulnerable to metabolic stress and loss of ion homeostasis. Repetitive stress generally leads to more permanent dysfunction but the mechanisms underlying this progression are poorly understood. We investigated the effects of energetic compromise in Drosophila by targeting the Na+/K+-ATPase. Acute ouabain treatment of intact flies resulted in subsequent repetitive comas that led to death and were associated with transient loss of K+ homeostasis in the brain. Heat shock pre-conditioned flies were resistant to ouabain treatment. To control the timing of repeated loss of ion homeostasis we subjected flies to repetitive anoxia while recording extracellular [K+] in the brain. We show that targeted expression of the chaperone protein Hsp70 in glial cells delays a permanent loss of ion homeostasis associated with repetitive anoxic stress and suggest that this is a useful model for investigating molecular mechanisms of neuroprotection.
Stress Preconditioning of Spreading Depression in the Locust CNS
Corinne I. Rodgers, Gary A. B. Armstrong, Kelly L. Shoemaker, John D. LaBrie, Christopher D. Moyes, R. Meldrum Robertson
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0001366
Abstract: Cortical spreading depression (CSD) is closely associated with important pathologies including stroke, seizures and migraine. The mechanisms underlying SD in its various forms are still incompletely understood. Here we describe SD-like events in an invertebrate model, the ventilatory central pattern generator (CPG) of locusts. Using K+ -sensitive microelectrodes, we measured extracellular K+ concentration ([K+]o) in the metathoracic neuropile of the CPG while monitoring CPG output electromyographically from muscle 161 in the second abdominal segment to investigate the role K+ in failure of neural circuit operation induced by various stressors. Failure of ventilation in response to different stressors (hyperthermia, anoxia, ATP depletion, Na+/K+ ATPase impairment, K+ injection) was associated with a disturbance of CNS ion homeostasis that shares the characteristics of CSD and SD-like events in vertebrates. Hyperthermic failure was preconditioned by prior heat shock (3 h, 45°C) and induced-thermotolerance was associated with an increase in the rate of clearance of extracellular K+ that was not linked to changes in ATP levels or total Na+/K+ ATPase activity. Our findings suggest that SD-like events in locusts are adaptive to terminate neural network operation and conserve energy during stress and that they can be preconditioned by experience. We propose that they share mechanisms with CSD in mammals suggesting a common evolutionary origin.
Silicon Nanocrystals: Fundamental Theory and Implications for Stimulated Emission
V. A. Belyakov,V. A. Burdov,R. Lockwood,A. Meldrum
Advances in Optical Technologies , 2008, DOI: 10.1155/2008/279502
Abstract: Silicon nanocrystals (NCs) represent one of the most promising material systems for light emission applications in microphotonics. In recent years, several groups have reported on the observation of optical gain or stimulated emission in silicon NCs or in porous silicon (PSi). These results suggest that silicon-NC-based waveguide amplifiers or silicon lasers are achievable. However, in order to obtain clear and reproducible evidence of stimulated emission, it is necessary to understand the physical mechanisms at work in the light emission process. In this paper, we report on the detailed theoretical aspects of the energy levels and recombination rates in doped and undoped Si NCs, and we discuss the effects of energy transfer mechanisms. The theoretical calculations are extended toward computational simulations of ensembles of interacting nanocrystals. We will show that inhomogeneous broadening and energy transfer remain significant problems that must be overcome in order to improve the gain profile and to minimize nonradiative effects. Finally, we suggest means by which these objectives may be achieved.
Thin PDMS Films Using Long Spin Times or Tert-Butyl Alcohol as a Solvent
John H. Koschwanez, Robert H. Carlson, Deirdre R. Meldrum
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0004572
Abstract: Thin polydimethylsiloxane (PDMS) films are frequently used in “lab on a chip” devices as flexible membranes. The common solvent used to dilute the PDMS for thin films is hexane, but hexane can swell the underlying PDMS substrate. A better solvent would be one that dissolves uncured PDMS but doesn't swell the underlying substrate. Here, we present protocols and spin curves for two alternatives to hexane dilution: longer spin times and dilution in tert-butyl alcohol. The thickness of the PDMS membranes under different spin speeds, spin times, and PDMS concentrations was measured using an optical profilometer. The use of tert-butyl alcohol to spin thin PDMS films does not swell the underlying PDMS substrate, and we have used these films to construct multilayer PDMS devices.
Insulin-like growth factor-1 in myocardial tissue: interaction with tumor necrosis factor
Meijing Wang, Ben Tsai, John W Brown, Daniel R Meldrum
Critical Care , 2003, DOI: 10.1186/cc2387
Abstract: Insulin-like growth factor (IGF)-1 is a well characterized growth factor for a variety of cells and plays a role in the regulation of myocardial structure and function. There is evidence that IGF-1 improves cardiac performance and muscle survival in heart subjected to ischemia/reperfusion [1,2]. Therefore, elucidating the IGF-1 signaling pathways, especially in relation to cell survival, may help to promote the potential use of IGF-1 in the treatment of heart disease.Using an ex vivo murine model, Davani and coworkers [1], in this issue of Critical Care, demonstrate that IGF-1 confers cardiac protection from reperfusion injury via mitochondria-dependent mechanisms. Because of its vital role in myocardial energy production, the quantity of functional mitochondria is essential to myocardial activity and health. Davani and coworkers propose that the ratio of mitochondrial DNA (mtDNA) to nuclear DNA (nDNA), which is increased during ischemia and reduced with reperfusion, is a very sensitive marker of cardiac injury. They then use the mtDNA : nDNA ratio to demonstrate that IGF-1, which prevents the reduction in mtDNA : nDNA ratio that occurs during reperfusion, confers myocardial cytoprotection. The mtDNA : nDNA ratio emphasizes the importance of mitochondria-related mechanisms in reperfusion injury, and it also provides a novel reference for evaluating cardiac injury.Two distinct forms of cell death, namely necrosis and apoptosis, are involved in the survival effect of IGF-1 in the cardiovascular system. IGF-1 not only inhibits necrosis via preservation of mitochondrial function, specifically by inhibiting membrane permeability and cytochrome C release in mitochondria, but also it reduces apoptosis through the inhibition of death signals generated by mitochondria [3].IGF-1 survival signals are mediated by binding to its receptor, the type 1 IGF receptor. This receptor is a heterotetramer containing cytosolic substrates (insulin receptor substrate [IRS], Shc, and Gab-1),
Dually Fluorescent Core-Shell Microgels for Ratiometric Imaging in Live Antigen-Presenting Cells
Xianfeng Zhou, Fengyu Su, Yanqing Tian, Deirdre R. Meldrum
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0088185
Abstract: Core-shell microgels containing sensors/dyes in a matrix were fabricated by two-stage free radical precipitation polymerization method for ratiometric sensing/imaging. The microgels composing of poly(N-isopropylacrylamide) (PNIPAm) shell exhibits a low critical solution temperature (LCST), underwent an entropically driven transition from a swollen state to a deswollen state, which exhibit a hydrodynamic radius of ~450 nm at 25°C (in vitro) and ~190 nm at 37°C (in vivo). The microgel’s ability of escaping from lysosome into cytosol makes the microgel be a potential candidate for cytosolic delivery of sensors/probes. Non-invasive imaging/sensing in Antigen-presenting cells (APCs) was feasible by monitoring the changes of fluorescence intensity ratios. Thus, these biocompatible microgels-based imaging/sensing agents may be expected to expand current molecular imaging/sensing techniques into methods applicable to studies in vivo, which could further drive APC-based treatments.
Application of synthetic biology in cyanobacteria and algae
Bo Wang,Jiangxin Wang,Weiwen Zhang,Deirdre R. Meldrum
Frontiers in Microbiology , 2012, DOI: 10.3389/fmicb.2012.00344
Abstract: Cyanobacteria and algae are becoming increasingly attractive cell factories for producing renewable biofuels and chemicals due to their ability to capture solar energy and CO2 and their relatively simple genetic background for genetic manipulation. Increasing research efforts from the synthetic biology approach have been made in recent years to modify cyanobacteria and algae for various biotechnological applications. In this article, we critically review recent progresses in developing genetic tools for characterizing or manipulating cyanobacteria and algae, the applications of genetically modified strains for synthesizing renewable products such as biofuels and chemicals. In addition, the emergent challenges in the development and application of synthetic biology for cyanobacteria and algae are also discussed.
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