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187 Publications

Showing 121-130 of 187 results
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    Looger LabLavis Lab
    04/01/12 | A genetically encoded fluorescent protein in echinoderms marks the history of neuronal activity.
    Verdecia MA, Looger LL, Lavis L, Graumann J, Mandel G, Brehm P
    Luminescence. 2012 Apr;27:170

    Since the original identification of GFP from jellyfish and corals, the genetically encoded fluorescent proteins have become mainstream indicators for imaging. Functionally homologous candidates exist in more highly evolved bioluminescent invertebrates, including echinoderms. For example, in brittlestars, stimulus-evoked bioluminescence is transient, lasting seconds, and emanates from specialized cells (photocytes). Prior to light emission, we observe little or no green fluorescence. However, concurrent with light emission, an intense green, calcium-dependent fluorescence develops that persists indefinitely.

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    04/01/12 | Calcium signaling in dendritic spines.
    Higley MJ, Sabatini BL
    Cold Spring Harb Perspect Biol. 2012 Apr 01;4(4):a005686. doi: 10.1101/cshperspect.a005686

    Calcium (Ca(2+)) is a ubiquitous signaling molecule that accumulates in the cytoplasm in response to diverse classes of stimuli and, in turn, regulates many aspects of cell function. In neurons, Ca(2+) influx in response to action potentials or synaptic stimulation triggers neurotransmitter release, modulates ion channels, induces synaptic plasticity, and activates transcription. In this article, we discuss the factors that regulate Ca(2+) signaling in mammalian neurons with a particular focus on Ca(2+) signaling within dendritic spines. This includes consideration of the routes of entry and exit of Ca(2+), the cellular mechanisms that establish the temporal and spatial profile of Ca(2+) signaling, and the biophysical criteria that determine which downstream signals are activated when Ca(2+) accumulates in a spine. Furthermore, we also briefly discuss the technical advances that made possible the quantitative study of Ca(2+) signaling in dendritic spines.

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    04/01/12 | Escape behaviors in insects.
    Card GM
    Current Opinion in Neurobiology. 2012 Apr;22:180-6. doi: 10.1016/j.conb.2011.12.009

    Escape behaviors are, by necessity, fast and robust, making them excellent systems with which to study the neural basis of behavior. This is especially true in insects, which have comparatively tractable nervous systems and members who are amenable to manipulation with genetic tools. Recent technical developments in high-speed video reveal that, despite their short duration, insect escape behaviors are more complex than previously appreciated. For example, before initiating an escape jump, a fly performs sophisticated posture and stimulus-dependent preparatory leg movements that enable it to jump away from a looming threat. This newfound flexibility raises the question of how the nervous system generates a behavior that is both rapid and flexible. Recordings from the cricket nervous system suggest that synchrony between the activity of specific interneuron pairs may provide a rapid cue for the cricket to detect the direction of an approaching predator and thus which direction it should run. Technical advances make possible wireless recording from neurons while locusts escape from a looming threat, enabling, for the first time, a direct correlation between the activity of multiple neurons and the time-course of an insect escape behavior.

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    04/01/12 | Target-specific output patterns are predicted by the distribution of regular-spiking and bursting pyramidal neurons in the subiculum.
    Kim Y, Spruston N
    Hippocampus. 2012 Apr;22(4):693-706. doi: 10.1002/hipo.20931

    Pyramidal neurons in the subiculum project to a variety of cortical and subcortical areas in the brain to convey information processed in the hippocampus. Previous studies have shown that two groups of subicular pyramidal neurons–regular-spiking and bursting neurons–are distributed in an organized fashion along the proximal-distal axis, with more regular-spiking neurons close to CA1 (proximal) and more bursting neurons close to presubiculum (distal). Anatomically, neurons projecting to some targets are located more proximally along this axis, while others are located more distally. However, the relationship between the firing properties and the targets of subicular pyramidal neurons is not known. To study this relationship, we used in vivo injections of retrogradely transported fluorescent beads into each of nine different regions and conducted whole-cell current-clamp recordings from the bead-containing subicular neurons in acute brain slices. We found that subicular projections to each area were composed of a mixture of regular-spiking and bursting neurons. Neurons projecting to amygdala, lateral entorhinal cortex, nucleus accumbens, and medial/ventral orbitofrontal cortex were located primarily in the proximal subiculum and consisted mostly of regular-spiking neurons (\~{}80%). By contrast, neurons projecting to medial EC, presubiculum, retrosplenial cortex, and ventromedial hypothalamus were located primarily in the distal subiculum and consisted mostly of bursting neurons (\~{}80%). Neurons projecting to a thalamic nucleus were located in the middle portion of subiculum, and their probability of bursting was close to 50%. Thus, the fraction of bursting neurons projecting to each target region was consistent with the known distribution of regular-spiking and bursting neurons along the proximal-distal axis of the subiculum. Variation in the distribution of regular-spiking and bursting neurons suggests that different types of information are conveyed from the subiculum to its various targets.

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    Sternson LabLooger LabLavis Lab
    03/27/12 | Selective esterase-ester pair for targeting small molecules with cellular specificity.
    Tian L, Yang Y, Wysocki LM, Arnold AC, Hu A, Ravichandran B, Sternson SM, Looger LL, Lavis LD
    Proceedings of the National Academy of Sciences of the United States of America. 2012 Mar 27;109:4756-61. doi: 10.1073/pnas.1111943109

    Small molecules are important tools to measure and modulate intracellular signaling pathways. A longstanding limitation for using chemical compounds in complex tissues has been the inability to target bioactive small molecules to a specific cell class. Here, we describe a generalizable esterase-ester pair capable of targeted delivery of small molecules to living cells and tissue with cellular specificity. We used fluorogenic molecules to rapidly identify a small ester masking motif that is stable to endogenous esterases, but is efficiently removed by an exogenous esterase. This strategy allows facile targeting of dyes and drugs in complex biological environments to label specific cell types, illuminate gap junction connectivity, and pharmacologically perturb distinct subsets of cells. We expect this approach to have general utility for the specific delivery of many small molecules to defined cellular populations.

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    03/23/12 | Quantitative analysis of photoactivated localization microscopy (PALM) datasets using pair-correlation analysis.
    Sengupta P, Lippincott-Schwartz J
    BioEssays : news and reviews in molecular, cellular and developmental biology. 2012 May;34(5):396-405. doi: 10.1002/bies.201200022

    Pointillistic based super-resolution techniques, such as photoactivated localization microscopy (PALM), involve multiple cycles of sequential activation, imaging, and precise localization of single fluorescent molecules. A super-resolution image, having nanoscopic structural information, is then constructed by compiling all the image sequences. Because the final image resolution is determined by the localization precision of detected single molecules and their density, accurate image reconstruction requires imaging of biological structures labeled with fluorescent molecules at high density. In such image datasets, stochastic variations in photon emission and intervening dark states lead to uncertainties in identification of single molecules. This, in turn, prevents the proper utilization of the wealth of information on molecular distribution and quantity. A recent strategy for overcoming this problem is pair-correlation analysis applied to PALM. Using rigorous statistical algorithms to estimate the number of detected proteins, this approach allows the spatial organization of molecules to be quantitatively described.

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    03/16/12 | Sexual deprivation increases ethanol intake in Drosophila.
    Shohat-Ophir G, Kaun K, Azanchi R, Mohammed H, Heberlein U
    Science. 2012 Mar 16;335(6074):1351-5. doi: 10.1126/science.1215932

    The brain’s reward systems reinforce behaviors required for species survival, including sex, food consumption, and social interaction. Drugs of abuse co-opt these neural pathways, which can lead to addiction. Here, we used Drosophila melanogaster to investigate the relationship between natural and drug rewards. In males, mating increased, whereas sexual deprivation reduced, neuropeptide F (NPF) levels. Activation or inhibition of the NPF system in turn reduced or enhanced ethanol preference. These results thus link sexual experience, NPF system activity, and ethanol consumption. Artificial activation of NPF neurons was in itself rewarding and precluded the ability of ethanol to act as a reward. We propose that activity of the NPF-NPF receptor axis represents the state of the fly reward system and modifies behavior accordingly.

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    03/16/12 | Sexual experience affects ethanol intake in Drosophila through Neuropeptide F.
    Shohat-Ophir G, Kaun K, Azanchi R, Heberlein U
    Science. 03/2012;335(6074):1351-5. doi: 10.1126/science.1215932

    The brain’s reward systems reinforce behaviors required for species survival, including sex, food consumption, and social interaction. Drugs of abuse co-opt these neural pathways, which can lead to addiction. Here, we used Drosophila melanogaster to investigate the relationship between natural and drug rewards. In males, mating increased, whereas sexual deprivation reduced, neuropeptide F (NPF) levels. Activation or inhibition of the NPF system in turn reduced or enhanced ethanol preference. These results thus link sexual experience, NPF system activity, and ethanol consumption. Artificial activation of NPF neurons was in itself rewarding and precluded the ability of ethanol to act as a reward. We propose that activity of the NPF–NPF receptor axis represents the state of the fly reward system and modifies behavior accordingly.

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    03/15/12 | Cutting edge: the role of IFN-α receptor and MyD88 signaling in induction of IL-15 expression in vivo.
    Colpitts SL, Stoklasek TA, Plumlee CR, Obar JJ, Guo C, Lefran\c cois L
    Journal of Immunology. 2012 Mar 15;188(6):2483-7. doi: 10.4049/jimmunol.1103609

    IL-15 plays a multifaceted role in immune homeostasis, but the unreliability of IL-15 detection has stymied exploration of IL-15 regulation in vivo. To visualize IL-15 expression, we created a transgenic mouse expressing emerald-GFP (EmGFP) under IL-15 promoter control. EmGFP/IL-15 was prevalent in innate cells including dendritic cells (DCs), macrophages, and monocytes. However, DC subsets expressed varying levels of EmGFP/IL-15 with CD8(+) DCs constitutively expressing EmGFP/IL-15 and CD8(-) DCs expressing low EmGFP/IL-15 levels. Virus infection resulted in IL-15 upregulation in both subsets. By crossing the transgenic mice to mice deficient in specific elements of innate signaling, we found a cell-intrinsic dependency of DCs and Ly6C(+) monocytes on IFN-α receptor expression for EmGFP/IL-15 upregulation after vesicular stomatitis virus infection. In contrast, myeloid cells did not require the expression of MyD88 to upregulate EmGFP/IL-15 expression. These findings provide evidence of previously unappreciated regulation of IL-15 expression in myeloid lineages during homeostasis and following infection.

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    03/09/12 | Triggering a cell shape change by exploiting preexisting actomyosin contractions.
    Roh-Johnson M, Shemer G, Higgins CD, McClellan JH, Werts AD, Tulu US, Gao L, Betzig E, Kiehart DP, Goldstein B
    Science. 2012 Mar 9;335(6073):1232-5. doi: 10.1126/science.1217869

    Apical constriction changes cell shapes, driving critical morphogenetic events, including gastrulation in diverse organisms and neural tube closure in vertebrates. Apical constriction is thought to be triggered by contraction of apical actomyosin networks. We found that apical actomyosin contractions began before cell shape changes in both Caenorhabitis elegans and Drosophila. In C. elegans, actomyosin networks were initially dynamic, contracting and generating cortical tension without substantial shrinking of apical surfaces. Apical cell-cell contact zones and actomyosin only later moved increasingly in concert, with no detectable change in actomyosin dynamics or cortical tension. Thus, apical constriction appears to be triggered not by a change in cortical tension, but by dynamic linking of apical cell-cell contact zones to an already contractile apical cortex.

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