7,373 research outputs found

    Limits of feedback control in bacterial chemotaxis

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    Inputs to signaling pathways can have complex statistics that depend on the environment and on the behavioral response to previous stimuli. Such behavioral feedback is particularly important in navigation. Successful navigation relies on proper coupling between sensors, which gather information during motion, and actuators, which control behavior. Because reorientation conditions future inputs, behavioral feedback can place sensors and actuators in an operational regime different from the resting state. How then can organisms maintain proper information transfer through the pathway while navigating diverse environments? In bacterial chemotaxis, robust performance is often attributed to the zero integral feedback control of the sensor, which guarantees that activity returns to resting state when the input remains constant. While this property provides sensitivity over a wide range of signal intensities, it remains unclear how other parameters affect chemotactic performance, especially when considering that the swimming behavior of the cell determines the input signal. Using analytical models and simulations that incorporate recent experimental evidences about behavioral feedback and flagellar motor adaptation we identify an operational regime of the pathway that maximizes drift velocity for various environments and sensor adaptation rates. This optimal regime is outside the dynamic range of the motor response, but maximizes the contrast between run duration up and down gradients. In steep gradients, the feedback from chemotactic drift can push the system through a bifurcation. This creates a non-chemotactic state that traps cells unless the motor is allowed to adapt. Although motor adaptation helps, we find that as the strength of the feedback increases individual phenotypes cannot maintain the optimal operational regime in all environments, suggesting that diversity could be beneficial.Comment: Corrected one typo. First two authors contributed equally. Notably, there were various typos in the values of the parameters in the model of motor adaptation. The results remain unchange

    Sexual pheromone modulates the frequency of cytosolic Ca2+ bursts in Saccharomyces cerevisiae

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    Transient and highly regulated elevations of cytosolic Ca2+ control a variety of cellular processes. Bulk measurements using radioactive Ca2+ and the luminescent sensor aequorin have shown that in response to pheromone, budding yeast cells experience a rise of cytosolic Ca2+ that is mediated by two import systems composed by the Mid1-Cch1-Ecm7 protein complex, and the Fig 1 protein. Although this response has been largely studied, there is no report on Ca2+ dynamics at the single cell level. Here, using protein calcium indicators we show that both vegetative and pheromone-treated yeast cells exhibit discrete and asynchronous Ca2+ bursts. Most bursts reach maximal amplitude in 1-10 secs, span between 7 and 30 secs and decay fitting a single exponential model. In vegetative cells bursts are scarce but preferentially occur when cells are transitioning G1 and S phase. Upon pheromone presence Ca2+ burst occurrence increases dramatically, persisting during cell growth polarization. Pheromone concentration modulates burst frequency in a mechanism that depends on Mid1, Fig 1 and a third, still unidentified, import system. We also show that the calcineurin-responsive transcription factor Crz1 experiences nuclear localization bursts during the pheromone response.Fil: Carbo, Natalia. Instituto Pasteur de Montevideo; UruguayFil: Tarkowski, Nahuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas; ArgentinaFil: Perez Ipiña, Emiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Ponce Dawson, Silvina Martha. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Aguilar, Pablo Sebastián. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

    Confocal laser scanning microscope, raman microscopy and western blotting to evaluate inflammatory response after myocardial infarction

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    Cardiac muscle necrosis is associated with inflammatory cascade that clears the infarct from dead cells and matrix debris, and then replaces the damaged tissue with scar, through three overlapping phases: the inflammatory phase, the proliferative phase and the maturation phase. Western blotting, laser confocal microscopy, Raman microscopy are valuable tools for studying the inflammatory response following myocardial infarction both humoral and cellular phase, allowing the identification and semiquantitative analysis of proteins produced during the inflammatory cascade activation and the topographical distribution and expression of proteins and cells involved in myocardial inflammation. Confocal laser scanning microscopy (CLSM) is a relatively new technique for microscopic imaging, that allows greater resolution, optical sectioning of the sample and three-dimensional reconstruction of the same sample. Western blotting used to detect the presence of a specific protein with antibody-antigen interaction in the midst of a complex protein mixture extracted from cells, produced semi-quantitative data quite easy to interpret. Confocal Raman microscopy combines the three-dimensional optical resolution of confocal microscopy and the sensitivity to molecular vibrations, which characterizes Raman spectroscopy. The combined use of western blotting and confocal microscope allows detecting the presence of proteins in the sample and trying to observe the exact location within the tissue, or the topographical distribution of the same. Once demonstrated the presence of proteins (cytokines, chemokines, etc.) is important to know the topographical distribution, obtaining in this way additional information regarding the extension of the inflammatory process in function of the time stayed from the time of myocardial infarction. These methods may be useful to study and define the expression of a wide range of inflammatory mediators at several different timepoints providing a more detailed analysis of the time course of the infarct

    MMW FM-CW ground-based SAR

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    This paper presents the design of two ground based synthetic aperture radar (GB-SAR) systems working at 94 and 300 GHz respectively. Frequency-modulated continuous-wave (FM-CW) technique is used for both systems, being described in the first section. Afterwards the first design at 94GHz is presented, explaining its geometry of exploration and describing the architecture of the W-band radar setup. Regarding the integrated receiver system, two models of low noise (LNA) and medium power amplifiers are disclosed, presenting noise figure and S parameters curves comprising frequencies between 75 and 110 GHz (W-band). Finally the second radar setup working at 300GHz is presented, depicting the hardware block diagram and explaining the main performance parameters of the system

    A γ-secretase inhibitor, but not a γ-secretase modulator, induced defects in BDNF axonal trafficking and signaling: evidence for a role for APP.

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    Clues to Alzheimer disease (AD) pathogenesis come from a variety of different sources including studies of clinical and neuropathological features, biomarkers, genomics and animal and cellular models. An important role for amyloid precursor protein (APP) and its processing has emerged and considerable interest has been directed at the hypothesis that Aβ peptides induce changes central to pathogenesis. Accordingly, molecules that reduce the levels of Aβ peptides have been discovered such as γ-secretase inhibitors (GSIs) and modulators (GSMs). GSIs and GSMs reduce Aβ levels through very different mechanisms. However, GSIs, but not GSMs, markedly increase the levels of APP CTFs that are increasingly viewed as disrupting neuronal function. Here, we evaluated the effects of GSIs and GSMs on a number of neuronal phenotypes possibly relevant to their use in treatment of AD. We report that GSI disrupted retrograde axonal trafficking of brain-derived neurotrophic factor (BDNF), suppressed BDNF-induced downstream signaling pathways and induced changes in the distribution within neuronal processes of mitochondria and synaptic vesicles. In contrast, treatment with a novel class of GSMs had no significant effect on these measures. Since knockdown of APP by specific siRNA prevented GSI-induced changes in BDNF axonal trafficking and signaling, we concluded that GSI effects on APP processing were responsible, at least in part, for BDNF trafficking and signaling deficits. Our findings argue that with respect to anti-amyloid treatments, even an APP-specific GSI may have deleterious effects and GSMs may serve as a better alternative

    Cognitive outcome and gamma noise power unrelated to neuregulin 1 and 3 variation in schizophrenia

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    Background Neuregulins are a family of signalling proteins that orchestrate a broad range of cellular responses. Four genes encoding Neuregulins 1–4 have been identified so far in vertebrates. Among them, Neuregulin 1 and Neuregulin 3 have been reported to contribute to an increased risk for developing schizophrenia. We hypothesized that three specific variants of these genes (rs6994992 and rs3924999 for Neuregulin 1 and rs10748842 for Neuregulin 3) that have been related to this illness may modify information processing capacity in the cortex, which would be reflected in electrophysiological parameters (P3b amplitude or gamma noise power) and/or cognitive performance. Methods We obtained DNA from 31 patients with schizophrenia and 23 healthy controls and analyzed NRG1 rs6994992, NRG1 rs3924999 and NRG3 rs10748842 promoter polymorphisms by allelic discrimination with real-time polymerase chain reaction (PCR). We compared cognitive outcome, P300 amplitude parameters and an electroencephalographic measure of noise power in the gamma band between the groups dichotomized according to genotype. Results Contrary to our hypothesis, we could not detect any significant influence of variation in Neuregulin 1/Neuregulin 3 polymorphisms on cognitive performance or electrophysiological parameters of patients with schizophrenia. Conclusions Despite our findings, we cannot discard that other genetic variants and, more likely, interactions between those variants and with genetic variation related to different pathways may still influence cerebral processing in schizophrenia

    The Motility and Chemotactic Response of Escherichia coli

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    We have studied several aspects of the chemotactic network of Escherichia coli, as well as the motility of these cells near solid surfaces. In the first chapter, we develop a novel assay for our research that takes advantage of a "self-trapping" phenomenon in which fully motile bacteria rotate in place at a solid boundary. We then use this assay to study the chemotactic and thermotactic response to impulse stimuli, quantifying the response of the bacteria to heat and serine. In addition, our data illustrates the amplification in the chemotactic network and the motor. We provide evidence that CheZ is actively regulated in its role as the network phosphatase. In chapter 4, we further study the impulse response at the lower limit of attractant concentrations and find that bacteria are capable of sensing and responding to single molecules of amino acids. Our data is compared to existing models with the aid of a calculation of diffusion inside the cell. The fit of the model is further improved under a modification inspired by our finding that CheZ is actively regulated. Finally we use our self-trapping assay to understand transitions between the run and tumble states in wild-type bacteria, and show that a single filament organizes the flagella bundle and drives the transitions between the run and tumble states of bacterial swimming

    Sost and its paralog Sostdc1 coordinate digit number in a Gli3-dependent manner.

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    WNT signaling is critical in most aspects of skeletal development and homeostasis, and antagonists of WNT signaling are emerging as key regulatory proteins with great promise as therapeutic agents for bone disorders. Here we show that Sost and its paralog Sostdc1 emerged through ancestral genome duplication and their expression patterns have diverged to delineate non-overlapping domains in most organ systems including musculoskeletal, cardiovascular, nervous, digestive, reproductive and respiratory. In the developing limb, Sost and Sostdc1 display dynamic expression patterns with Sost being restricted to the distal ectoderm and Sostdc1 to the proximal ectoderm and the mesenchyme. While Sostdc1(-/-) mice lack any obvious limb or skeletal defects, Sost(-/-) mice recapitulate the hand defects described for Sclerosteosis patients. However, elevated WNT signaling in Sost(-/-); Sostdc1(-/-) mice causes misregulation of SHH signaling, ectopic activation of Sox9 in the digit 1 field and preaxial polydactyly in a Gli1- and Gli3-dependent manner. In addition, we show that the syndactyly documented in Sclerosteosis is present in both Sost(-/-) and Sost(-/-); Sostdc1(-/-) mice, and is driven by misregulation of Fgf8 in the AER, a region lacking Sost and Sostdc1 expression. This study highlights the complexity of WNT signaling in skeletal biology and disease and emphasizes how redundant mechanism and non-cell autonomous effects can synergize to unveil new intricate phenotypes caused by elevated WNT signaling

    Self-organization of swimmers drives long-range fluid transport in bacterial colonies.

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    Motile subpopulations in microbial communities are believed to be important for dispersal, quest for food, and material transport. Here, we show that motile cells in sessile colonies of peritrichously flagellated bacteria can self-organize into two adjacent, centimeter-scale motile rings surrounding the entire colony. The motile rings arise from spontaneous segregation of a homogeneous swimmer suspension that mimics a phase separation; the process is mediated by intercellular interactions and shear-induced depletion. As a result of this self-organization, cells drive fluid flows that circulate around the colony at a constant peak speed of ~30 µm s-1, providing a stable and high-speed avenue for directed material transport at the macroscopic scale. Our findings present a unique form of bacterial self-organization that influences population structure and material distribution in colonies

    The roles of vasoactive intestinal polypeptide in circadian entrainment of suprachiasmatic nucleus

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    In mammalian hypothalamus, the suprachiasmatic nucleus: SCN) generates daily behavioral and physiological rhythms as a circadian pacemaker. The 20,000 SCN neurons synchronize to each other and to the ambient cues to generate coherent daily rhythms. Vasoactive intestinal polypeptide: VIP), a neuropeptide produced by SCN neurons, plays a major role in synchronizing SCN neurons to each other. Whether VIP mediates synchrony to environmental cues and how synchrony within the SCN is achieved has not been examined extensively. We recorded PERIOD::LUCIFERASE: PER2::LUC) expression from SCN explant cultures over multiple days following VIP application at different circadian time points to generate a phase response curve which reliably predicted the phase relationship between the SCN and daily increases in VIP. VIP shifted PER2::LUC rhythms in time- and dose-dependent manner. VIP rapidly increased intracellular cAMP in most SCN neurons and simultaneous antagonism of adenylate cyclase: AC) and phospholipase C: PLC) was required to block the VIP-induced phase shifts of SCN PER2 rhythms. We conclude that VIP entrains circadian timing among SCN neurons through rapid and parallel changes in AC and PLC activities. While performing the experiments mentioned above, we found that a single VIP pulse reliably reduced the PER2::LUC rhythm amplitude in the SCN explants. The amplitude reduction was dose-dependent, but not circadian. We found that the amplitude reduction was primarily explained by reduced synchrony among SCN neurons, with little effect on the amplitude of individual neurons. To test if VIP modulates the amplitude of circadian rhythm in vivo, we compared the effects of light on locomotor rhythms in wild-type and VIP-deficient mice. We found that constant light reduced the amplitude of behavioral rhythms in wild type, but not in Vip-/-, mice. Because, theoretically, reduced synchrony among oscillators can facilitate their entrainment to periodic signals, we tested if VIP accelerates entrainment of animals to an 8-h advanced light-cycle or SCN explants to a 10-h advanced temperature cycle. We found that VIP doubled the speed of circadian entrainment both in vivo and in vitro. We conclude that reduced synchrony by VIP accelerates entrainment. Finally, we characterized the spatiotemporal expression of one of the three major VIP receptors, VPAC2R, in various brain areas and SCN. We characterized the specificity of a new antibody and found moderate to weak levels of VPAC2R in cortex, hippocampus, olfactory bulb, cerebellum, arcuate nucleus in hypothalamus, amygdala and ventrolateral thalamus and high levels in the SCN. VPAC2R expression was observed from rostral to caudal SCN with stronger expression in dorsomedial area. SCN neurons expressing VIP or vasopressin all expressed VPAC2R. We found intracellular VPAC2 expression mainly along cell bodies and dendrites, but not along their axons. We found that VPAC2R levels in the SCN do not oscillate in light-dark cycles or in constant conditions. We conclude that VPAC2R presents broadly in the SCN throughout the day to mediate circadian synchrony in the SCN. Taken together, these experiments suggest that VIP signaling mediate entrainment to the daily light cycle and an altered schedule by jet lag or day night shift work through wide expression of VPAC2R in the SCN
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