Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 48
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
PLoS Biol ; 18(3): e3000634, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-32134917

RESUMO

Many decisions rely on how we evaluate potential outcomes and estimate their corresponding probabilities of occurrence. Outcome evaluation is subjective because it requires consulting internal preferences and is sensitive to context. In contrast, probability estimation requires extracting statistics from the environment and therefore imposes unique challenges to the decision maker. Here, we show that probability estimation, like outcome evaluation, is subject to context effects that bias probability estimates away from other events present in the same context. However, unlike valuation, these context effects appeared to be scaled by estimated uncertainty, which is largest at intermediate probabilities. Blood-oxygen-level-dependent (BOLD) imaging showed that patterns of multivoxel activity in the dorsal anterior cingulate cortex (dACC), ventromedial prefrontal cortex (VMPFC), and intraparietal sulcus (IPS) predicted individual differences in context effects on probability estimates. These results establish VMPFC as the neurocomputational substrate shared between valuation and probability estimation and highlight the additional involvement of dACC and IPS that can be uniquely attributed to probability estimation. Because probability estimation is a required component of computational accounts from sensory inference to higher cognition, the context effects found here may affect a wide array of cognitive computations.

2.
ACS Nano ; 14(2): 1350-1359, 2020 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-31442375

RESUMO

Monolayer transition-metal dichalcogenides (TMDCs) in the 2H-phase are promising semiconductors for opto-valleytronic and opto-spintronic applications because of their strong spin-valley coupling. Here, we report detailed studies of opto-valleytronic properties of heterogeneous domains in CVD-grown monolayer WS2 single crystals. By illuminating WS2 with off-resonance circularly polarized light and measuring the resulting spatially resolved circularly polarized emission (Pcirc), we find significantly large circular polarization (Pcirc up to 60% and 45% for α- and ß-domains, respectively) already at 300 K, which increases to nearly 90% in the α-domains at 80 K. Studies of spatially resolved photoluminescence (PL) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, Kelvin-probe force microscopy, and conductive atomic force microscopy reveal direct correlation among the PL intensity, defect densities, and chemical potential, with the α-domains showing lower defect densities and a smaller work function by 0.13 eV than the ß-domains. This work function difference indicates the occurrence of type-two band alignments between the α- and ß-domains. We adapt a classical model to explain how electronically active defects may serve as nonradiative recombination centers and find good agreement between experiments and the model. Scanning tunneling microscopic/spectroscopic (STM/STS) studies provide further evidence for tungsten vacancies (WVs) being the primary defects responsible for the suppressed PL and circular polarization in WS2. These results therefore suggest a pathway to control the opto-valleytronic properties of TMDCs by means of defect engineering.

3.
Nano Lett ; 19(10): 6765-6771, 2019 10 09.
Artigo em Inglês | MEDLINE | ID: mdl-31545901

RESUMO

Interfacial quantum states are drawing tremendous attention recently because of their importance in design of low-dimensional quantum heterostructures with desired charge, spin, or topological properties. Although most studies of the interfacial exchange interactions were mainly performed across the interface vertically, the lateral transport nowadays is still a major experimental method to probe these interactions indirectly. In this Letter, we fabricated a graphene and hydrogen passivated silicon interface to study the interfacial exchange processes. For the first time we found and confirmed a novel interfacial quantum state, which is specific to the 2D-3D interface. The vertically propagating electrons from silicon to graphene result in electron oscillation states at the 2D-3D interface. A harmonic oscillator model is used to explain this interfacial state. In addition, the interaction between this interfacial state (discrete energy spectrum) and the lateral band structure of graphene (continuous energy spectrum) results in Fano-Feshbach resonance. Our results show that the conventional description of the interfacial interaction in low-dimensional systems is valid only in considering the lateral band structure and its density-of-states and is incomplete for the ease of vertical transport. Our experimental observation and theoretical explanation provide more insightful understanding of various interfacial effects in low-dimensional materials, such as proximity effect, quantum tunneling, etc. More important, the Fano-Feshbach resonance may be used to realize all solid-state and scalable quantum interferometers.

4.
Int J Obes (Lond) ; 43(12): 2469-2479, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31455870

RESUMO

BACKGROUND: Obesity-induced hepatocellular carcinoma (HCC) is more prevalent in males than in females, but the underlying mechanism remains unclear. The influence of hepatic androgen receptor (AR) pathway on the gender difference of HCC has been well documented. Here we investigated the role of hepatic lipogenesis, which is elevated in the livers of obese and nonalcoholic fatty liver disease (NAFLD) patients, in stimulating the AR pathway for the male preference of obesity induced HCC. METHODS: Male C57BL/6J mice were fed a fructose-rich high carbohydrate diet (HCD) to induce hepatic lipogenesis. The effect of hepatic lipogenesis on AR was examined by the expression of hydrodynamically injected AR reporter and the endogenous AR target gene; the mechanism was delineated in hepatoma cell lines and validated in male mice. RESULTS: The hepatic lipogenesis induced by a fructose-rich HCD enhanced the transcriptional activity of hepatic AR in male mice, which did not happen when fed a high fat diet. This AR activation was blocked by sh-RNAs or inhibitors targeting key enzymes in lipogenesis, either acetyl-CoA carboxylase subunit alpha (ACCα), or fatty acid synthase (FASN), in vivo and in vitro. Further mechanistic study identified that specific unsaturated fatty acid, the oleic acid (C18:1 n-9), incorporated DAGs produced by hepatic lipogenesis are the key molecules to enhance the AR activity, through activation of Akt kinase, and this novel mechanism is targeted by metformin. CONCLUSIONS: Our study elucidates a novel mechanism underlying the higher risk of HCC in obese/NAFLD males, through specific DAGs enriched by hepatic lipogenesis to increase the transcriptional activity of hepatic AR, a confirmed risk factor for male HCC.

5.
Eur J Neurosci ; 50(1): 1727-1740, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30687963

RESUMO

Pumilio (Pum), an RNA-binding protein, is a key component of neuron firing-rate homeostasis that likely maintains stability of neural circuit activity in all animals, from flies to mammals. While Pum is ubiquitously expressed, we understand little about how synaptic excitation regulates its expression in the CNS. Here, we characterized the Drosophila dpum promoter and identified multiple myocyte enhancer factor-2 (Mef2)-binding elements. We cloned 12 dmef2 splice variants and used a luciferase-based assay to monitor dpum promoter activity. While all 12 dMef2 splice variants enhance dpum promoter activity, exon 10-containing variants induce greater transactivation. Previous work shows dPum expression increases with synaptic excitation. However, we observe no change in dmef2 transcript in larval CNS, of both sexes, exposed to the proconvulsant picrotoxin. The lack of activity dependence is indicative of additional regulation. We identified p300 as a potential candidate. We show that by binding to dMef2, p300 represses dpum transactivation. Significantly, p300 transcript is downregulated by enhanced synaptic excitation (picrotoxin) which, in turn, increases transcription of dpum through derepression of dMef2. These results advance our understanding of dpum by showing the activity-dependent expression is regulated by an interaction between p300 and dMef2.

6.
Indian Heart J ; 70(5): 604-607, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30392495

RESUMO

PURPOSE: To investigate the association of preexisting hypertension at admission with the mortality in patients with systolic heart failure (HF). METHOD: We prospectively investigated the association of preexisting hypertension with the mortality among 1351 patients with HF in Taiwan during an average 12 months (range: 8 months-18 months) follow-up period. A multivariate cox regression analysis for the overall cohort and a subgroup analysis by age were performed. RESULTS: After adjustment for all potential risk factors, the associations of preexisting hypertension with cardiovascular mortality were significantly reduced in the overall cohort and those aged less than 65 years (hazard ratios (HR): 0.53, 95% confidence intervals (CI): 0.33-0.84, and 0.28, 95% CI: 0.11-0.67, respectively). However, the associations with all-cause mortality were not significantly different in these two groups (HR: 0.77, 95% CI: 0.54-1.09, and 0.59, 95% CI: 0.32-1.07, respectively). Furthermore, the associations were all nonsignificant in the patients aged older than 65 years. CONCLUSION: Preexisting hypertension have an inverse association with cardiovascular mortality in the Asian patients with systolic HF, particularly for those with younger ages.


Assuntos
Pressão Sanguínea/fisiologia , Insuficiência Cardíaca Sistólica/epidemiologia , Ventrículos do Coração/fisiopatologia , Hipertensão/epidemiologia , Sistema de Registros , Medição de Risco , Idoso , Causas de Morte/tendências , Feminino , Seguimentos , Insuficiência Cardíaca Sistólica/complicações , Insuficiência Cardíaca Sistólica/fisiopatologia , Humanos , Hipertensão/complicações , Hipertensão/fisiopatologia , Masculino , Pessoa de Meia-Idade , Morbidade/tendências , Prognóstico , Estudos Prospectivos , Volume Sistólico/fisiologia , Taxa de Sobrevida/tendências , Taiwan/epidemiologia
7.
J Neurogenet ; 32(2): 106-117, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29718742

RESUMO

Despite availability of a diverse range of anti-epileptic drugs (AEDs), only about two-thirds of epilepsy patients respond well to drug treatment. Thus, novel targets are required to catalyse the design of next-generation AEDs. Manipulation of neuron firing-rate homoeostasis, through enhancing Pumilio (Pum) activity, has been shown to be potently anticonvulsant in Drosophila. In this study, we performed a genome-wide RNAi screen in S2R + cells, using a luciferase-based dPum activity reporter and identified 1166 genes involved in dPum regulation. Of these genes, we focused on 699 genes that, on knock-down, potentiate dPum activity/expression. Of this subgroup, 101 genes are activity-dependent based on comparison with genes previously identified as activity-dependent by RNA-sequencing. Functional cluster analysis shows these genes are enriched in pathways involved in DNA damage, regulation of cell cycle and proteasomal protein catabolism. To test for anticonvulsant activity, we utilised an RNA-interference approach in vivo. RNAi-mediated knockdown showed that 57/101 genes (61%) are sufficient to significantly reduce seizure duration in the characterized seizure mutant, parabss. We further show that chemical inhibitors of protein products of some of the genes targeted are similarly anticonvulsant. Finally, to establish whether the anticonvulsant activity of identified compounds results from increased dpum transcription, we performed a luciferase-based assay to monitor dpum promoter activity. Third instar larvae exposed to sodium fluoride, gemcitabine, metformin, bestatin, WP1066 or valproic acid all showed increased dpum promoter activity. Thus, this study validates Pum as a favourable target for AED design and, moreover, identifies a number of lead compounds capable of increasing the expression of this homeostatic regulator.


Assuntos
Anticonvulsivantes/farmacologia , Proteínas de Drosophila/metabolismo , Epilepsia/metabolismo , Regulação da Expressão Gênica/efeitos dos fármacos , Proteínas de Ligação a RNA/metabolismo , Convulsões/metabolismo , Animais , Drosophila , Regulação da Expressão Gênica/fisiologia , Interferência de RNA
8.
Dis Model Mech ; 10(2): 141-150, 2017 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-28067623

RESUMO

Epilepsy is a significant disorder for which approximately one-third of patients do not respond to drug treatments. Next-generation drugs, which interact with novel targets, are required to provide a better clinical outcome for these individuals. To identify potential novel targets for antiepileptic drug (AED) design, we used RNA sequencing to identify changes in gene transcription in two seizure models of the fruit fly Drosophila melanogaster The first model compared gene transcription between wild type (WT) and bangsenseless1 (parabss), a gain-of-function mutant in the sole fly voltage-gated sodium channel (paralytic). The second model compared WT with WT fed the proconvulsant picrotoxin (PTX). We identified 743 genes (FDR≤1%) with significant altered expression levels that are common to both seizure models. Of these, 339 are consistently upregulated and 397 downregulated. We identify pumilio (pum) to be downregulated in both seizure models. Pum is a known homeostatic regulator of action potential firing in both flies and mammals, achieving control of neuronal firing through binding to, and regulating translation of, the mRNA transcripts of voltage-gated sodium channels (Nav). We show that maintaining expression of pum in the CNS of parabss flies is potently anticonvulsive, whereas its reduction through RNAi-mediated knockdown is proconvulsive. Using a cell-based luciferase reporter screen, we screened a repurposed chemical library and identified 12 compounds sufficient to increase activity of pum Of these compounds, we focus on avobenzone, which significantly rescues seizure behaviour in parabss flies. The mode of action of avobenzone includes potentiation of pum expression and mirrors the ability of this homeostatic regulator to reduce the persistent voltage-gated Na+ current (INaP) in an identified neuron. This study reports a novel approach to suppress seizure and highlights the mechanisms of neuronal homeostasis as potential targets for next-generation AEDs.


Assuntos
Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Homeostase , Neurônios Motores/patologia , Propiofenonas/uso terapêutico , Proteínas de Ligação a RNA/genética , Convulsões/tratamento farmacológico , Convulsões/genética , Animais , Anticonvulsivantes , Modelos Animais de Doenças , Regulação para Baixo/efeitos dos fármacos , Regulação para Baixo/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/efeitos dos fármacos , Epilepsia/tratamento farmacológico , Epilepsia/genética , Epilepsia/patologia , Predisposição Genética para Doença , Homeostase/efeitos dos fármacos , Neurônios Motores/efeitos dos fármacos , Neurônios Motores/metabolismo , Propiofenonas/farmacologia , Proteínas de Ligação a RNA/metabolismo , Convulsões/patologia , Análise de Sequência de RNA , Transcrição Genética/efeitos dos fármacos , Transgenes , Regulação para Cima/efeitos dos fármacos , Regulação para Cima/genética
9.
Nano Lett ; 17(1): 78-84, 2017 01 11.
Artigo em Inglês | MEDLINE | ID: mdl-28005390

RESUMO

We report measurements of the infrared optical response of thin black phosphorus under field-effect modulation. We interpret the observed spectral changes as a combination of an ambipolar Burstein-Moss (BM) shift of the absorption edge due to band-filling under gate control, and a quantum confined Franz-Keldysh (QCFK) effect, phenomena that have been proposed theoretically to occur for black phosphorus under an applied electric field. Distinct optical responses are observed depending on the flake thickness and starting carrier concentration. Transmission extinction modulation amplitudes of more than two percent are observed, suggesting the potential for use of black phosphorus as an active material in mid-infrared optoelectronic modulator applications.

10.
Proc Natl Acad Sci U S A ; 113(42): 11937-11942, 2016 10 18.
Artigo em Inglês | MEDLINE | ID: mdl-27702890

RESUMO

Transarterial chemoembolization (TACE) is the main treatment for intermediate stage hepatocellular carcinoma (HCC) with Barcelona Clinic Liver Cancer classification because of its exclusive arterial blood supply. Although TACE achieves substantial necrosis of the tumor, complete tumor necrosis is uncommon, and the residual tumor generally rapidly recurs. We combined tirapazamine (TPZ), a hypoxia-activated cytotoxic agent, with hepatic artery ligation (HAL), which recapitulates transarterial embolization in mouse models, to enhance the efficacy of TACE. The effectiveness of this combination treatment was examined in HCC that spontaneously developed in hepatitis B virus X protein (HBx) transgenic mice. We proved that the tumor blood flow in this model was exclusively supplied by the hepatic artery, in contrast to conventional orthotopic HCC xenografts that receive both arterial and venous blood supplies. At levels below the threshold oxygen levels created by HAL, TPZ was activated and killed the hypoxic cells, but spared the normoxic cells. This combination treatment clearly limited the toxicity of TPZ to HCC, which caused the rapid and near-complete necrosis of HCC. In conclusion, the combination of TPZ and HAL showed a synergistic tumor killing activity that was specific for HCC in HBx transgenic mice. This preclinical study forms the basis for the ongoing clinical program for the TPZ-TACE regimen in HCC treatment.


Assuntos
Antineoplásicos/farmacologia , Carcinoma Hepatocelular/etiologia , Carcinoma Hepatocelular/patologia , Neoplasias Hepáticas/etiologia , Neoplasias Hepáticas/patologia , Transativadores/genética , Triazinas/farmacologia , Animais , Biomarcadores , Carcinoma Hepatocelular/mortalidade , Carcinoma Hepatocelular/terapia , Linhagem Celular Tumoral , Terapia Combinada , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Artéria Hepática/cirurgia , Humanos , Imuno-Histoquímica , Ligadura , Neoplasias Hepáticas/terapia , Imagem por Ressonância Magnética , Camundongos , Camundongos Endogâmicos NOD , Camundongos SCID , Camundongos Transgênicos , Necrose , Recidiva , Tirapazamina , Carga Tumoral/efeitos dos fármacos , Ensaios Antitumorais Modelo de Xenoenxerto
11.
Curr Biol ; 26(11): 1486-93, 2016 06 06.
Artigo em Inglês | MEDLINE | ID: mdl-27212408

RESUMO

Emergence of antibiotic resistance, an evolutionary process of major importance for human health [1], often occurs under changing levels of antibiotics. Selective sweeps, in which resistant cells become dominant in the population, are a critical step in this process [2]. While resistance emergence has been studied in laboratory experiments [3-8], the full progression of selective sweeps under fluctuating stress, from stochastic events in single cells to fixation in populations, has not been characterized. Here, we study fluctuating selection using Escherichia coli populations engineered with a stochastic switch controlling tetracycline resistance. Using microfluidics and live-cell imaging, we treat multiple E. coli populations with the same total amount of tetracycline but administered in different temporal patterns. We find that populations exposed to either short or long antibiotic pulses are likely to develop resistance through selective sweeps, whereas intermediate pulses allow higher growth rates but suppress selective sweeps. On the basis of single-cell measurements and a dynamic growth model, we identify the major determinants of population growth and show that both physiological memory and environmental durations can strongly modulate the emergence of resistance. Our detailed quantification in a model synthetic system provides key lessons on the interaction between single-cell physiology and selection that should inform the design of treatment regimens [9-12] and the analysis of phenotypically diverse populations adapting under fluctuating selection [13-17].


Assuntos
Escherichia coli/efeitos dos fármacos , Escherichia coli/genética , Seleção Genética , Resistência a Tetraciclina , Tetraciclina/farmacologia , Microrganismos Geneticamente Modificados/efeitos dos fármacos , Microrganismos Geneticamente Modificados/genética
12.
Acta Cardiol Sin ; 32(2): 223-30, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-27122953

RESUMO

BACKGROUND: Acute myocarditis is an inflammatory disease of the myocardium. Although a fulminant course of the disease is difficult to predict, it may lead to acute heart failure and death. Previous studies have demonstrated that reduced left ventricular systolic function and prolonged QRS duration can predict the fulminant course of acute myocarditis. This study aimed to identify whether prolonged QTc interval could also be predictive of fulminant disease in this population. METHODS: We retrospectively included 40 patients diagnosed with acute myocarditis who were admitted to our hospital between 2002 and 2013. They were divided into the fulminant group (n = 9) and the non-fulminant group (n = 31). Clinical symptoms, laboratory findings, electrocardiographic, and echocardiographic parameters were analyzed. Multivariate logistic regression analysis was used to identify the independent factors predictive of fulminant disease. RESULTS: Patients with fulminant myocarditis had a higher mortality rate than those with non-fulminant disease (55.6% vs. 0%, p < 0.001). Multivariate analysis revealed that wider QRS durations (133.22 ± 45.85 ms vs. 92.81 ± 15.56 ms, p = 0.030) and longer QTc intervals (482.78 ± 69.76 ms vs. 412.00 ± 33.31 ms, p = 0.016) were significant predictors associated with a fulminant course of myocarditis. CONCLUSIONS: Prolonged QRS duration and QTc interval, upon patient admission, may be associated with an increased risk of fulminant disease and increased in-hospital mortality. Therefore, early recognition of fulminant myocarditis and early mechanical support could provide improved patient outcomes. KEY WORDS: Fulminant myocarditis • Predictors • QRS complex • QTc interval.

13.
ACS Appl Mater Interfaces ; 7(31): 17155-61, 2015 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-26183173

RESUMO

To expand the applications of graphene in optoelectronics and microelectronics, simple and effective doping processes need to be developed. In this paper, we demonstrate an aqueous process that can simultaneously transfer chemical vapor deposition grown graphene from Cu to other substrates and produce stacked graphene/dopant intercalation films with tunable work functions, which differs significantly from conventional doping methods using vacuum evaporation or spin-coating processes. The work function of graphene layers can be tuned from 3.25 to 5.10 eV, which practically covers the wide range of the anode and cathode applications. Doped graphene films in intercalation structures also exhibit excellent transparency and low resistance. The polymer-based solar cells with either low work function graphene as cathodes or high work function graphene as anodes are demonstrated.

14.
J Natl Cancer Inst ; 107(10)2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26206949

RESUMO

BACKGROUND: Hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) shows a higher incidence in men, mainly because of hepatitis B X (HBx)-mediated enhancement of androgen receptor (AR) activity. We aimed to examine this pathway in hepatocarcinogenesis and to identify drug(s) specifically blocking this carcinogenic event in the liver. METHODS: HBx transgenic mice that spontaneously develop HCC (n = 28-34 per group) were used, either by knockout of hepatic AR or by castration. Efficacy of several HCC-targeted drugs in suppressing HBx-induced AR activity was evaluated, and cellular factors mediating suppression were investigated in cultured cells. Tissue specificity of the candidate drug was validated using mouse tissues. Data were analyzed with Chi-square and Student's t tests. All statistical tests were two-sided. RESULTS: The androgen pathway was shown to be important in early stage hepatocarcinogenesis of HBx transgenic mice. The tumor incidence was decreased from 80% to 32% by AR knockout (P < .001) and from 90% to 25% by early castration (P < .001). Sorafenib markedly inhibited the HBx-enhanced AR activity through activating the SHP-1 phosphatase, which antagonized the activation of Akt/GSK3ß and c-Src by HBx. Moreover, SHP-1 protein level was much higher in the liver than in testis, which enabled sorafenib to inhibit aberrant AR activity in the HBx-expressing liver, while not affecting the physiological AR function in normal liver or testis. CONCLUSIONS: The androgen pathway may be a druggable target for the chemoprevention of HBV-related HCC, and sorafenib might be used as a tissue- and disease-specific regimen for the chemoprevention of HBV-related HCC.


Assuntos
Antineoplásicos/farmacologia , Carcinoma Hepatocelular/prevenção & controle , Vírus da Hepatite B/metabolismo , Hepatite B/complicações , Neoplasias Hepáticas/prevenção & controle , Niacinamida/análogos & derivados , Compostos de Fenilureia/farmacologia , Inibidores de Proteínas Quinases/farmacologia , Proteína Tirosina Fosfatase não Receptora Tipo 6/metabolismo , Receptores Androgênicos/efeitos dos fármacos , Transativadores/metabolismo , Fatores Etários , Animais , Carcinoma Hepatocelular/virologia , Ativação Enzimática/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Quinase 3 da Glicogênio Sintase/antagonistas & inibidores , Glicogênio Sintase Quinase 3 beta , Vírus da Hepatite B/patogenicidade , Incidência , Neoplasias Hepáticas/virologia , Masculino , Camundongos , Camundongos Transgênicos , Niacinamida/farmacologia , Orquiectomia , Proteína Tirosina Fosfatase não Receptora Tipo 6/efeitos dos fármacos , Proteínas Proto-Oncogênicas c-akt/antagonistas & inibidores , Receptores Androgênicos/metabolismo , Transdução de Sinais/efeitos dos fármacos , Sorafenibe , Transativadores/genética
15.
PLoS Comput Biol ; 11(5): e1004189, 2015 May.
Artigo em Inglês | MEDLINE | ID: mdl-25978332

RESUMO

Studying ion channel currents generated distally from the recording site is difficult because of artifacts caused by poor space clamp and membrane filtering. A computational model can quantify artifact parameters for correction by simulating the currents only if their exact anatomical location is known. We propose that the same artifacts that confound current recordings can help pinpoint the source of those currents by providing a signature of the neuron's morphology. This method can improve the recording quality of currents initiated at the spike initiation zone (SIZ) that are often distal to the soma in invertebrate neurons. Drosophila being a valuable tool for characterizing ion currents, we estimated the SIZ location and quantified artifacts in an identified motoneuron, aCC/MN1-Ib, by constructing a novel multicompartmental model. Initial simulation of the measured biophysical channel properties in an isopotential Hodgkin-Huxley type neuron model partially replicated firing characteristics. Adding a second distal compartment, which contained spike-generating Na+ and K+ currents, was sufficient to simulate aCC's in vivo activity signature. Matching this signature using a reconstructed morphology predicted that the SIZ is on aCC's primary axon, 70 µm after the most distal dendritic branching point. From SIZ to soma, we observed and quantified selective morphological filtering of fast activating currents. Non-inactivating K+ currents are filtered ∼3 times less and despite their large magnitude at the soma they could be as distal as Na+ currents. The peak of transient component (NaT) of the voltage-activated Na+ current is also filtered more than the magnitude of slower persistent component (NaP), which can contribute to seizures. The corrected NaP/NaT ratio explains the previously observed discrepancy when the same channel is expressed in different cells. In summary, we used an in vivo signature to estimate ion channel location and recording artifacts, which can be applied to other neurons.


Assuntos
Drosophila melanogaster/fisiologia , Canais Iônicos/metabolismo , Modelos Neurológicos , Neurônios Motores/fisiologia , Potenciais de Ação , Animais , Fenômenos Biofísicos , Biologia Computacional , Simulação por Computador , Drosophila melanogaster/citologia , Fenômenos Eletrofisiológicos , Neurônios Motores/ultraestrutura , Técnicas de Patch-Clamp
16.
Evolution ; 69(6): 1448-1460, 2015 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-25908222

RESUMO

Populations can adapt to changing environments by using allelic diversity, yet whether diversity is recently derived or ancestral is often debated. Although evolution could productively use both types of diversity in a changing environment, their relative frequency has not been quantified. We address this question experimentally using budding yeast strains that harbor a tandem repeat containing URA3 gene, which we expose to cyclical selection and counterselection. We characterize and quantify the dynamics of frameshift events in the URA3 gene in eight populations over 12 cycles of selection and find that ancestral alleles account for 10-20% of all adaptive events. Using a general model of fluctuating selection, we determine how these results depend on mutation rates, population sizes, and fluctuation timescales. We quantify the contribution of derived alleles to the adaptation process using the de novo mutation rate along the population's ancestral lineage, a novel measure that is applicable in a wide range of settings. We find that the adaptive dynamics undergoes a sharp transition from selection on ancestral alleles to selection on derived alleles as fluctuation timescales increase. Our results demonstrate that fluctuations can select between different modes of adaptation over evolutionary timescales.


Assuntos
Saccharomycetales/genética , Adaptação Fisiológica/genética , Alelos , Evolução Biológica , Meio Ambiente , Taxa de Mutação , Saccharomycetales/fisiologia , Seleção Genética , Fatores de Tempo
17.
Sci Rep ; 5: 9693, 2015 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-25892370

RESUMO

Graphene thin films have great potential to function as transparent electrodes in organic electronic devices, due to their excellent conductivity and high transparency. Recently, organic light-emitting diodes (OLEDs)have been successfully demonstrated to possess high luminous efficiencies with p-doped graphene anodes. However, reliable methods to fabricate n-doped graphene cathodes have been lacking, which would limit the application of graphene in flexible electronics. In this paper, we demonstrate fully solution-processed OLEDs with n-type doped multilayer graphene as the top electrode. The work function and sheet resistance of graphene are modified by an aqueous process which can also transfer graphene on organic devices as the top electrodes. With n-doped graphene layers used as the top cathode, all-solution processed transparent OLEDs can be fabricated without any vacuum process.

18.
Brain ; 138(Pt 4): 891-901, 2015 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-25681415

RESUMO

Seizure can result from increased voltage-gated persistent sodium current expression. Although many clinically-approved antiepileptic drugs target voltage-gated persistent sodium current, none exclusively repress this current without also adversely affecting the transient voltage-gated sodium current. Achieving a more selective block has significant potential for the treatment of epilepsy. Recent studies show that voltage-gated persistent sodium current amplitude is regulated by alternative splicing offering the possibility of a novel route for seizure control. In this study we identify 291 splicing regulators that, on knockdown, alter splicing of the Drosophila voltage-gated sodium channel to favour inclusion of exon K, rather than the mutually exclusive exon L. This change is associated with both a significant reduction in voltage-gated persistent sodium current, without change to transient voltage-gated sodium current, and to rescue of seizure in this model insect. RNA interference mediated knock-down, in two different seizure mutants, shows that 95 of these regulators are sufficient to significantly reduce seizure duration. Moreover, most suppress seizure activity in both mutants, indicative that they are part of well conserved pathways and likely, therefore, to be optimal candidates to take forward to mammalian studies. We provide proof-of-principle for such studies by showing that inhibition of a selection of regulators, using small molecule inhibitors, is similarly effective to reduce seizure. Splicing of the Drosophila sodium channel shows many similarities to its mammalian counterparts, including altering the amplitude of voltage-gated persistent sodium current. Our study provides the impetus to investigate whether manipulation of splicing of mammalian voltage-gated sodium channels may be exploitable to provide effective seizure control.


Assuntos
Processamento Alternativo/genética , Proteínas de Drosophila/genética , Convulsões/genética , Convulsões/prevenção & controle , Canais de Sódio Disparados por Voltagem/genética , Animais , Animais Geneticamente Modificados , Drosophila , Vaga-Lumes , Luciferases de Renilla/genética , Masculino
19.
Seizure ; 24: 44-51, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25457452

RESUMO

This narrative review is intended to introduce clinicians treating epilepsy and researchers familiar with mammalian models of epilepsy to experimentally tractable, non-mammalian research models used in epilepsy research, ranging from unicellular eukaryotes to more complex multicellular organisms. The review focuses on four model organisms: the social amoeba Dictyostelium discoideum, the roundworm Caenorhabditis elegans, the fruit fly Drosophila melanogaster and the zebrafish Danio rerio. We consider recent discoveries made with each model organism and discuss the importance of these advances for the understanding and treatment of epilepsy in humans. The relative ease with which mutations in genes of interest can be produced and studied quickly and cheaply in these organisms, together with their anatomical and physiological simplicity in comparison to mammalian species, are major advantages when researchers are trying to unravel complex disease mechanisms. The short generation times of most of these model organisms also mean that they lend themselves particularly conveniently to the investigation of drug effects or epileptogenic processes across the lifecourse.


Assuntos
Pesquisa Biomédica/métodos , Pesquisa Biomédica/tendências , Modelos Animais de Doenças , Epilepsia/etiologia , Epilepsia/terapia , Animais , Humanos
20.
Mol Neurobiol ; 51(1): 57-67, 2015 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-24677068

RESUMO

The voltage-gated sodium channel (Nav) plays a key role in regulation of neuronal excitability. Aberrant regulation of Nav expression and/or function can result in an imbalance in neuronal activity which can progress to epilepsy. Regulation of Nav activity is achieved by coordination of a multitude of mechanisms including RNA alternative splicing and translational repression. Understanding of these regulatory mechanisms is complicated by extensive genetic redundancy: the mammalian genome encodes ten Navs. By contrast, the genome of the fruitfly, Drosophila melanogaster, contains just one Nav homologue, encoded by paralytic (DmNa v ). Analysis of splicing in DmNa v shows variants exhibit distinct gating properties including varying magnitudes of persistent sodium current (INaP). Splicing by Pasilla, an identified RNA splicing factor, alters INaP magnitude as part of an activity-dependent mechanism. Enhanced INaP promotes membrane hyperexcitability that is associated with seizure-like behaviour in Drosophila. Nova-2, a mammalian Pasilla homologue, has also been linked to splicing of Navs and, moreover, mouse gene knockouts display seizure-like behaviour.Expression level of Navs is also regulated through a mechanism of translational repression in both flies and mammals. The translational repressor Pumilio (Pum) can bind to Na v transcripts and repress the normal process of translation, thus regulating sodium current (INa) density in neurons. Pum2-deficient mice exhibit spontaneous EEG abnormalities. Taken together, aberrant regulation of Nav function and/or expression is often epileptogenic. As such, a better understanding of regulation of membrane excitability through RNA alternative splicing and translational repression of Navs should provide new leads to treat epilepsy.


Assuntos
Membrana Celular/fisiologia , Ativação do Canal Iônico , Canais de Sódio Disparados por Voltagem/metabolismo , Processamento Alternativo/genética , Sequência de Aminoácidos , Animais , Homeostase , Modelos Biológicos , Dados de Sequência Molecular , Canais de Sódio Disparados por Voltagem/química , Canais de Sódio Disparados por Voltagem/genética
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA