Página 25 dos resultados de 60878 itens digitais encontrados em 0.069 segundos

Diverse set of Turing nanopatterns coat corneae across insect lineages

Blagodatski, Artem; Sergeev, Anton; Kryuchkov, Mikhail; Lopatina, Yuliya; Katanaev, Vladimir L.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Corneal surfaces of some insects are coated with nipple-like nanostructures reducing the light reflection. Here we provide an extensive analysis of corneae across insect groups. Using atomic force microscopy, we discover a striking diversity of corneal nanocoatings, omnipresent in arthropods. These fascinating bionanostructures replicate the complete set of the Turing patterns—shapes resulting from the reaction−diffusion modeling underlying many examples of patterning in biological and physicochemical systems. Our work, verging on the interface of nanotechnology and zoology, evolution and biophysics, and ecology and genetics, sheds light on the molecular origin and evolutionary diversification of a beautiful diversity of insect corneal nanostructures. It also describes, to our knowledge, the first-ever biological example of Turing nanopatterns.

Computational and biological studies of mechanical prophylaxis against deep venous thrombosis

Dai, Guohao, 1970-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 151 p.; 8072342 bytes; 8092977 bytes; application/pdf; application/pdf
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Deep vein thrombosis (DVT) of the lower extremity and induced pulmonary embolism are common complications resulting from prolonged periods of bed-rest or immobilization of the limbs. One of the most effective methods of prophylaxis against DVT is external pneumatic compression (EPC). In spite of its wide acceptance as an effective means of prophylaxis, its mechanism remains poorly understood and optimal compression conditions have not been defined. Understanding the biological consequences of EPC is an important goal for optimizing the performance of compression device and providing guidance for clinical use. In the first part of this thesis, a computational model of the leg was developed to simulate hemodynamic conditions under EPC and the influence of different modes of compression were analyzed and compared. Then, a new in vitro cell culture system was developed that can be used to examine the effect of hemodynamic conditions during EPC on endothelial cell (EC) function. The biologic response was assessed through changes in cell morphology and the expression of various pro-thrombotic and anti-thrombotic factors related to EC.; (cont.) The results show that intermittent flow associated with EPC up-regulates EC fibrinolytic potential and vasomotor function. Using DNA microarray technology...

Adenovirus-based exogenous gene expression in mammalian cells

El-Mogy, Mohamed A.
Fonte: St. Catharines, Ont. : Brock University, Dept. of Biological Sciences, 2010. Publicador: St. Catharines, Ont. : Brock University, Dept. of Biological Sciences, 2010.
Tipo: Artigo de Revista Científica
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Thesis (Ph.D.)--Brock University, 2010.; Brock University. Dept. of Biological Sciences. Thesis; Adenoviruses have been used as a model system for understanding gene expression, DNA replication, gene delivery and other molecular biological phenomenon. In this project, adenovirus was used as a model to study exogenous gene expression in mammalian cells. More specifically, several adenoviral components were identified to enhance gene expression together with components needed for viral DNA replication. The adenoviral elements that enhance gene expression were assembled in an expression vector (pEl). These include the viral inverted terminal repeats (ITRs), the El region, the major late promoter (MLP) and the tripartite leader sequence (TPL). The green florescence protein (GFP) was used as a reporter gene. Various aspects of gene expression were examined including DNA delivery and stability inside the cells as well as mRNA transcription and protein expression. First, the effect of DNA quality on its delivery, stability and expreSSIOn III mammalian cells was studied. Five different conditions of the major DNA contaminants were used in this investigation including ethidium bromide (EtBr) , cesium chloride (CsCl), EtBr/CsCl...

A unique regulator controls the activation threshold of quorum-regulated genes in Pseudomonas aeruginosa

Siehnel, Richard; Traxler, Beth; An, Ding Ding; Parsek, Matthew R.; Schaefer, Amy L.; Singh, Pradeep K.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Quorum-sensing (QS) systems allow organisms, such as the pathogen Pseudomonas aeruginosa, to link gene expression with their population density and the diffusion and flow characteristics of their environment. The leading hypotheses about QS systems' biological functions necessitate that QS-controlled gene expression be suppressed until a threshold culture density (the quorum) is reached. Despite a detailed understanding of QS in P. aeruginosa, known regulatory elements do not fully explain how the quorum threshold for gene activation is produced. Here we investigated the mechanism with a screening approach that used random gene activation. These experiments uncovered a regulator without close homologs in other species that produces the quorum expression threshold. Expression of this regulator (named QteE) reduces LasR protein stability without affecting LasR transcription or translation. QteE also independently reduces RhlR levels. Because QteE can block QS when signal levels are high, it could provide a mechanism for individual cells to exert autonomous control over their QS regulons. This unique regulator governs two central QS control points in P. aeruginosa and shapes the expression pattern thought fundamental to the biological functions of QS.

Artificial miRNAs mitigate shRNA-mediated toxicity in the brain: Implications for the therapeutic development of RNAi

McBride, Jodi L.; Boudreau, Ryan L.; Harper, Scott Q.; Staber, Patrick D.; Monteys, Alex Mas; Martins, Inâs; Gilmore, Brian L.; Burstein, Haim; Peluso, Richard W.; Polisky, Barry; Carter, Barrie J.; Davidson, Beverly L.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Huntington's disease (HD) is a fatal, dominant neurodegenerative disease caused by a polyglutamine repeat expansion in exon 1 of the HD gene, which encodes the huntingtin protein. We and others have shown that RNAi is a candidate therapy for HD because expression of inhibitory RNAs targeting mutant human HD transgenes improved neuropathology and behavioral deficits in HD mouse models. Here, we developed shRNAs targeting conserved sequences in human HD and mouse HD homolog (HDh) mRNAs to initiate preclinical testing in a knockin mouse model of HD. We screened 35 shRNAs in vitro and subsequently narrowed our focus to three candidates for in vivo testing. Unexpectedly, two active shRNAs induced significant neurotoxicity in mouse striatum, although HDh mRNA expression was reduced to similar levels by all three. Additionally, a control shRNA containing mismatches also induced toxicity, although it did not reduce HDh mRNA expression. Interestingly, the toxic shRNAs generated higher antisense RNA levels, compared with the nontoxic shRNA. These results demonstrate that the robust levels of antisense RNAs emerging from shRNA expression systems can be problematic in the mouse brain. Importantly, when sequences that were toxic in the context of shRNAs were placed into artificial microRNA (miRNA) expression systems...

Time-critical integration of formants for perception of communication calls in mice

Geissler, Diana B.; Ehret, Günter
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Brain mechanisms in humans group together acoustical frequency components both in the spectral and temporal domain, which leads to the perception of auditory objects and of streams of sound events that are of biological and communicative significance. At the perceptual level, behavioral data on mammals that clearly support the presence of common concepts for processing species-specific communication sounds are unavailable. Here, we synthesize 17 models of mouse pup wriggling calls, present them in sequences of four calls to the pups' mothers in a natural communication situation, and record the maternal response behavior. We show that the biological significance of a call sequence depends on grouping together three predominant frequency components (formants) to an acoustic object within a critical time window of about 30-ms lead or lag time of the first formant. Longer lead or lag times significantly reduce the maternal responsiveness. Central inhibition seems to be responsible for setting this time window, which is also found in numerous perceptual studies in humans. Further, a minimum of 100-ms simultaneous presence of the three formants is necessary for occurrence of response behavior. As in humans, onset-time asynchronies of formants and formant durations interact nonlinearly to influence the adequate perception of a stream of sounds. Together...

Critical waves and the length problem of biology

Laughlin, Robert B.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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This paper invokes physical principles to answer the question of why pure reaction–diffusion ideas do not produce a satisfactory explanation of biological growth and form. Two ideas have been missing. One is that oscillation is necessary to achieve the necessary design stability and plasticity. The other is that the system must be tuned to criticality to stabilize the propagation velocity, thus enabling clocks to function as meter sticks. The larger significance is twofold: First, a fundamental piece of the machinery of life is probably invisible to present-day biochemical methods because they are too slow. Second, the simplicity of growth and form identified a century ago by D'Arcy Thompson is probably a symptom of biological engineering strategies, not primitive law.

HDAC6 is a target for protection and regeneration following injury in the nervous system

Rivieccio, Mark A.; Brochier, Camille; Willis, Dianna E.; Walker, Breset A.; D'Annibale, Melissa A.; McLaughlin, Kathryn; Siddiq, Ambreena; Kozikowski, Alan P.; Jaffrey, Samie R.; Twiss, Jeffery L.; Ratan, Rajiv R.; Langley, Brett
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Central nervous system (CNS) trauma can result in tissue disruption, neuronal and axonal degeneration, and neurological dysfunction. The limited spontaneous CNS repair in adulthood and aging is often insufficient to overcome disability. Several investigations have demonstrated that targeting HDAC activity can protect neurons and glia and improve outcomes in CNS injury and disease models. However, the enthusiasm for pan-HDAC inhibition in treating neurological conditions is tempered by their toxicity toward a host of CNS cell types –a biological extension of their anticancer properties. Identification of the HDAC isoform, or isoforms, that specifically mediate the beneficial effects of pan-HDAC inhibition could overcome this concern. Here, we show that pan-HDAC inhibition not only promotes neuronal protection against oxidative stress, a common mediator of injury in many neurological conditions, but also promotes neurite growth on myelin-associated glycoprotein and chondroitin sulfate proteoglycan substrates. Real-time PCR revealed a robust and selective increase in HDAC6 expression due to injury in neurons. Accordingly, we have used pharmacological and genetic approaches to demonstrate that inhibition of HDAC6 can promote survival and regeneration of neurons. Consistent with a cytoplasmic localization...

Interplay of α-synuclein binding and conformational switching probed by single-molecule fluorescence

Ferreon, Allan Chris M.; Gambin, Yann; Lemke, Edward A.; Deniz, Ashok A.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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We studied the coupled binding and folding of α-synuclein, an intrinsically disordered protein linked with Parkinson's disease. Using single-molecule fluorescence resonance energy transfer and correlation methods, we directly probed protein membrane association, structural distributions, and dynamics. Results revealed an intricate energy landscape on which binding of α-synuclein to amphiphilic small molecules or membrane-like partners modulates conformational transitions between a natively unfolded state and multiple α-helical structures. α-Synuclein conformation is not continuously tunable, but instead partitions into 2 main classes of folding landscape structural minima. The switch between a broken and an extended helical structure can be triggered by changing the concentration of binding partners or by varying the curvature of the binding surfaces presented by micelles or bilayers composed of the lipid-mimetic SDS. Single-molecule experiments with lipid vesicles of various composition showed that a low fraction of negatively charged lipids, similar to that found in biological membranes, was sufficient to drive α-synuclein binding and folding, resulting here in the induction of an extended helical structure. Overall, our results imply that the 2 folded structures are preencoded by the α-synuclein amino acid sequence...

Extracellular reduction of uranium via Geobacter conductive pili as a protective cellular mechanism

Cologgi, Dena L.; Lampa-Pastirk, Sanela; Speers, Allison M.; Kelly, Shelly D.; Reguera, Gemma
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The in situ stimulation of Fe(III) oxide reduction by Geobacter bacteria leads to the concomitant precipitation of hexavalent uranium [U(VI)] from groundwater. Despite its promise for the bioremediation of uranium contaminants, the biological mechanism behind this reaction remains elusive. Because Fe(III) oxide reduction requires the expression of Geobacter's conductive pili, we evaluated their contribution to uranium reduction in Geobacter sulfurreducens grown under pili-inducing or noninducing conditions. A pilin-deficient mutant and a genetically complemented strain with reduced outer membrane c-cytochrome content were used as controls. Pili expression significantly enhanced the rate and extent of uranium immobilization per cell and prevented periplasmic mineralization. As a result, pili expression also preserved the vital respiratory activities of the cell envelope and the cell's viability. Uranium preferentially precipitated along the pili and, to a lesser extent, on outer membrane redox-active foci. In contrast, the pilus-defective strains had different degrees of periplasmic mineralization matching well with their outer membrane c-cytochrome content. X-ray absorption spectroscopy analyses demonstrated the extracellular reduction of U(VI) by the pili to mononuclear tetravalent uranium U(IV) complexed by carbon-containing ligands...

Carbon nanotubes as multifunctional biological transporters and near-infrared agents for selective cancer cell destruction

Kam, Nadine Wong Shi; O'Connell, Michael; Wisdom, Jeffrey A.; Dai, Hongjie
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Biological systems are known to be highly transparent to 700- to 1,100-nm near-infrared (NIR) light. It is shown here that the strong optical absorbance of single-walled carbon nanotubes (SWNTs) in this special spectral window, an intrinsic property of SWNTs, can be used for optical stimulation of nanotubes inside living cells to afford multifunctional nanotube biological transporters. For oligonucleotides transported inside living cells by nanotubes, the oligos can translocate into cell nucleus upon endosomal rupture triggered by NIR laser pulses. Continuous NIR radiation can cause cell death because of excessive local heating of SWNT in vitro. Selective cancer cell destruction can be achieved by functionalization of SWNT with a folate moiety, selective internalization of SWNTs inside cells labeled with folate receptor tumor markers, and NIR-triggered cell death, without harming receptor-free normal cells. Thus, the transporting capabilities of carbon nanotubes combined with suitable functionalization chemistry and their intrinsic optical properties can lead to new classes of novel nanomaterials for drug delivery and cancer therapy.

Influence of ocean winds on the pelagic ecosystem in upwelling regions

Rykaczewski, Ryan R.; Checkley, David M.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Upwelling of nutrient-rich, subsurface water sustains high productivity in the ocean's eastern boundary currents. These ecosystems support a rate of fish harvest nearly 100 times the global mean and account for >20% of the world's marine fish catch. Environmental variability is thought to be the major cause of the decadal-scale biomass fluctuations characteristic of fish populations in these regions, but the mechanisms relating atmospheric physics to fish production remain unexplained. Two atmospheric conditions induce different types of upwelling in these ecosystems: coastal, alongshore wind stress, resulting in rapid upwelling (with high vertical velocity, w); and wind-stress curl, resulting in slower upwelling (low w). We show that the level of wind-stress curl has increased and that production of Pacific sardine (Sardinops sagax) varies with wind-stress curl over the past six decades. The extent of isopycnal shoaling, nutricline depth, and chlorophyll concentration in the upper ocean also correlate positively with wind-stress curl. The size structure of plankton assemblages is related to the rate of wind-forced upwelling, and sardine feed efficiently on small plankters generated by slow upwelling. Upwelling rate is a fundamental determinant of the biological structure and production in coastal pelagic ecosystems...

Amplified temperature dependence in ecosystems developing on the lava flows of Mauna Loa, Hawai'i

Anderson-Teixeira, Kristina J.; Vitousek, Peter M.; Brown, James H.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Through its effect on individual metabolism, temperature drives biologically controlled fluxes and transformations of energy and materials in ecological systems. Because primary succession involves feedbacks among multiple biological and abiotic processes, we expected it to exhibit complex dynamics and unusual temperature dependence. We present a model based on first principles of chemical kinetics to explain how biologically mediated temperature dependence of “reactant” concentrations can inflate the effective temperature dependence of such processes. We then apply this model to test the hypothesis that the temperature dependence of early primary succession is amplified due to more rapid accumulation of reactants at higher temperatures. Using previously published data from the lava flows of Mauna Loa, HI, we show that rates of vegetation and soil accumulation as well as rates of community compositional change all display amplified temperature dependence (Q10 values of ≈7–50, compared with typical Q10 values of 1.5–3 for the constituent biological processes). Additionally, in young ecosystems, resource concentrations increase with temperature, resulting in inflated temperature responses of biogeochemical fluxes. Mauna Loa's developing ecosystems exemplify how temperature-driven...

Differential recruitment of nuclear receptor coactivators may determine alternative RNA splice site choice in target genes

Auboeuf, Didier; Dowhan, Dennis H.; Kang, Yun Kyoung; Larkin, Kimberly; Lee, Jae Woon; Berget, Susan M.; O'Malley, Bert W.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The biological consequences of steroid hormone-mediated transcriptional activation of target genes might be difficult to predict because alternative splicing of a single neosynthesized precursor RNA can result in production of different protein isoforms with opposite biological activities. Therefore, an important question to address is the manner in which steroid hormones affect the splicing of their target gene transcripts. In this report, we demonstrate that individual steroid hormones had different and opposite effects on alternative splicing decisions, stimulating the production of different spliced variants produced from genes driven by steroid hormone-dependent promoters. Steroid hormone transcriptional effects are mediated by steroid hormone receptor coregulators that also modify alternative splicing decisions. Our data suggest that activated steroid hormone receptors recruit coregulators to the target promoter that participate in both the production and the splicing of the target gene transcripts. Because different coregulators activating transcription can have opposite effects on alternative splicing decisions, we conclude that the precise nature of the transcriptional coregulators recruited by activated steroid receptors...

Repeated learning makes cultural evolution unique

Strimling, Pontus; Enquist, Magnus; Eriksson, Kimmo
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Although genetic information is acquired only once, cultural information can be both abandoned and reacquired during an individual's lifetime. Therefore, cultural evolution will be determined not only by cultural traits' ability to spread but also by how good they are at sticking with an individual; however, the evolutionary consequences of this aspect of culture have not previously been explored. Here we show that repeated learning and multiple characteristics of cultural traits make cultural evolution unique, allowing dynamical phenomena we can recognize as specifically cultural, such as traits that both spread quickly and disappear quickly. Importantly, the analysis of our model also yields a theoretical objection to the popular suggestion that biological and cultural evolution can be understood in similar terms. We find that the possibility to predict long-term cultural evolution by some success index, analogous to biological fitness, depends on whether individuals have few or many opportunities to learn. If learning opportunities are few, we find that the existence of a success index may be logically impossible, rendering notions of “cultural fitness” meaningless. On the other hand, if individuals can learn many times, we find a success index that works...

Positron emission tomography provides molecular imaging of biological processes

Phelps, Michael E.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 01/08/2000 Português
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Diseases are biological processes, and molecular imaging with positron emission tomography (PET) is sensitive to and informative of these processes. This is illustrated by detection of biological abnormalities in neurological disorders with no computed tomography or MRI anatomic changes, as well as even before symptoms are expressed. PET whole body imaging in cancer provides the means to (i) identify early disease, (ii) differentiate benign from malignant lesions, (iii) examine all organs for metastases, and (iv) determine therapeutic effectiveness. Diagnostic accuracy of PET is 8–43% higher than conventional procedures and changes treatment in 20–40% of the patients, depending on the clinical question, in lung and colorectal cancers, melanoma, and lymphoma, with similar findings in breast, ovarian, head and neck, and renal cancers. A microPET scanner for mice, in concert with human PET systems, provides a novel technology for molecular imaging assays of metabolism and signal transduction to gene expression, from mice to patients: e.g., PET reporter gene assays are used to trace the location and temporal level of expression of therapeutic and endogenous genes. PET probes and drugs are being developed together—in low mass amounts...

Generation of keratinocytes from normal and recessive dystrophic epidermolysis bullosa-induced pluripotent stem cells

Itoh, Munenari; Kiuru, Maija; Cairo, Mitchell S.; Christiano, Angela M.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Embryonic stem cells (ESCs) have an unlimited proliferative capacity and extensive differentiation capability. They are an alternative source for regenerative therapies with a potential role in the treatment of several human diseases. The clinical use of ESCs, however, has significant ethical and biological obstacles related to their derivation from embryos and potential for immunological rejection, respectively. These disadvantages can be circumvented by the alternative use of induced pluripotent stem cells (iPSCs), which are generated from an individual's (autologous) somatic cells by exogenous expression of defined transcription factors and have biological characteristics similar to ESCs. In recent years, patient-specific iPSCs have been generated to study disease mechanisms and develop iPSC-based therapies. The development of iPSC-based therapies for skin diseases requires successful differentiation of iPSCs into cellular components of the skin, including epidermal keratinocytes. Here, we succeeded in generating iPSCs not only from normal human fibroblasts but also from fibroblasts isolated from the skin of two patients with recessive dystrophic epidermolysis bullosa. Moreover, we differentiated both of these iPSCs into keratinocytes with high efficiency...

Cell membrane GM1 ganglioside is a functional coreceptor for fibroblast growth factor 2

Rusnati, Marco; Urbinati, Chiara; Tanghetti, Elena; Dell'Era, Patrizia; Lortat-Jacob, Hugues; Presta, Marco
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
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Free gangliosides bind fibroblast growth factor 2 (FGF2), thus preventing cell interaction and biological activity of the growth factor in endothelial cells. Here we investigated the role of cell-associated gangliosides in mediating the biological activity of FGF2. Treatment of endothelial cells of different origin with the ganglioside biosynthesis inhibitors fumonisin B1, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol or D-1-threo-1-phenyl-2-hexa-decanoylamino-3-pyrrolidino-1-propanol-HCl, impairs their capacity to proliferate when exposed to FGF2. Also, the mitogenic activity of FGF2 is inhibited by the GM1-binding cholera toxin B subunit (CTB). Conversely, overloading of endothelial GM 7373 cell membranes with exogenous GM1 causes a 10-fold increase of the mitogenic potency of FGF2. 125I-FGF2 binds to cell membrane GM1 (Kd = 3 nM) in complex ganglioside/heparan sulfate-deficient Chinese hamster ovary (CHO)-K1-pgsA745 cell mutants that were overloaded with exogenous GM1. Moreover, FGF2 competes with FITC-CTB for the binding to cell membrane GM1 in different CHO cell lines independently of their capacity to express heparan sulfate proteoglycans. Conversely, CTB inhibits cell proliferation triggered by FGF2 in CHO cells overexpressing the tyrosine kinase FGF receptor 1. Finally...

Go2 G protein mediates galanin inhibitory effects on insulin release from pancreatic β cells

Tang, Guanghua; Wang, Ying; Park, Sangeun; Bajpayee, Neil S.; Vi, Diana; Nagaoka, Yoshiko; Birnbaumer, Lutz; Jiang, Meisheng
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The neuropeptide galanin regulates numerous physiological activities in the body, including feeding and metabolism, learning and memory, nociception and spinal reflexes, and anxiety and related behaviors. Modulation of blood glucose levels by suppressing insulin release was the first reported activity for galanin. This inhibition was mediated by one or more pertussis toxin-sensitive G proteins of the Gi/o subfamily. However, the molecular identities of the specific G protein(s) and intracellular effectors have not been fully revealed. Recently, we demonstrated that mice lacking Go2, but not other members of the Gi/o protein family, secrete more insulin than controls upon glucose challenge, indicating that Go2 is a major transducer for the inhibitory regulation of insulin secretion. In this study, we investigated galanin signaling mechanisms in β cells using cell biological and electrophysiological approaches. We found that islets lacking Go2, but not other Gi/o proteins, lose the inhibitory effect of galanin on insulin release. Potentiation of ATP-sensitive potassium (KATP) and inhibition of calcium currents by galanin were disrupted by anti-Go2α antibodies. Galanin actions on KATP and calcium currents were completely lost in Go2−/− β cells. Furthermore...

Blinking and nonradiant dark fraction of water-soluble quantum dots in aqueous solution

Yao, Jie; Larson, Daniel R.; Vishwasrao, Harshad D.; Zipfel, Warren R.; Webb, Watt W.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Water-soluble quantum dots (qdots) are now being used in life sciences research to take advantage of their bright, easily excited fluorescence and high photostability. Although the frequent erratic blinking and substantial dark (never radiant) fractions that occur in all available qdots may interfere with many applications, these properties of individual particles in biological environments had not been fully evaluated. By labeling Qdot-streptavidin with organic dyes, we were able to distinguish individual dark and bright qdots and to observe blinking events as qdots freely diffused in aqueous solution. Bright fractions were measured by confocal fluorescence coincidence analysis (CFCA) and two-photon cross-correlation fluorescence correlation spectroscopy (FCS). The observed bright fractions of various preparations were proportional to the ensemble quantum yields (QYs), but the intrinsic brightness of individual qdots was found to be constant across samples with different QYs but the same emission wavelengths. Increasing qdots' illuminated dwell time by 10-fold during FCS did not change the fraction of apparently dark qdots but did increase the detected fraction of blinking qdots, suggesting that the dark population does not arise from millisecond blinking. Combining CFCA with wide-field imaging of arrays of qdots localized in dilute agarose gel...