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192 Publications

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    07/17/13 | NGL-2 Regulates Pathway-Specific Neurite Growth and Lamination, Synapse Formation, and Signal Transmission in the Retina
    Soto F, Watkins KL, Johnson RE, Schottler F, Kerschensteiner D
    Journal of Neuroscience. May-07-2014;33(29):11949 - 11959. doi: 10.1523/JNEUROSCI.1521-13.2013

    Parallel processing is an organizing principle of many neural circuits. In the retina, parallel neuronal pathways process signals from rod and cone photoreceptors and support vision over a wide range of light levels. Toward this end, rods and cones form triad synapses with dendrites of distinct bipolar cell types, and the axons or dendrites, respectively, of horizontal cells (HCs). The molecular cues that promote the formation of specific neuronal pathways remain largely unknown. Here, we discover that developing and mature HCs express the leucine-rich repeat (LRR)-containing protein netrin-G ligand 2 (NGL-2). NGL-2 localizes selectively to the tips of HC axons, which form reciprocal connections with rods. In mice with null mutations in Ngl-2 (Ngl-2⁻/⁻), many branches of HC axons fail to stratify in the outer plexiform layer (OPL) and invade the outer nuclear layer. In addition, HC axons expand lateral territories and increase coverage of the OPL, but establish fewer synapses with rods. NGL-2 can form transsynaptic adhesion complexes with netrin-G2, which we show to be expressed by photoreceptors. In Ngl-2⁻/⁻ mice, we find specific defects in the assembly of presynaptic ribbons in rods, indicating that reverse signaling of complexes involving NGL-2 regulates presynaptic maturation. The development of HC dendrites and triad synapses of cone photoreceptors proceeds normally in the absence of NGL-2 and in vivo electrophysiology reveals selective defects in rod-mediated signal transmission in Ngl-2⁻/⁻ mice. Thus, our results identify NGL-2 as a central component of pathway-specific development in the outer retina.

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    07/14/13 | Functional labeling of neurons and their projections using the synthetic activity-dependent promoter E-SARE.
    Kawashima T, Kitamura K, Suzuki K, Nonaka M, Kamijo S, Takemoto-Kimura S, Kano M, Okuno H, Ohki K, Bito H
    Nature Methods. 2013 Jul 14;10(9):889-95. doi: 10.1038/nmeth.2559

    Identifying the neuronal ensembles that respond to specific stimuli and mapping their projection patterns in living animals are fundamental challenges in neuroscience. To this end, we engineered a synthetic promoter, the enhanced synaptic activity-responsive element (E-SARE), that drives neuronal activity-dependent gene expression more potently than other existing immediate-early gene promoters. Expression of a drug-inducible Cre recombinase downstream of E-SARE enabled imaging of neuronal populations that respond to monocular visual stimulation and tracking of their long-distance thalamocortical projections in living mice. Targeted cell-attached recordings and calcium imaging of neurons in sensory cortices revealed that E-SARE reporter expression correlates with sensory-evoked neuronal activity at the single-cell level and is highly specific to the type of stimuli presented to the animals. This activity-dependent promoter can expand the repertoire of genetic approaches for high-resolution anatomical and functional analysis of neural circuits.

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    Singer Lab
    07/12/13 | mRNA on the move: the road to its biological destiny.
    Eliscovich C, Buxbaum AR, Katz ZB, Singer RH
    The Journal of Biological Chemistry. 2013 Jul 12;288(28):20361-8. doi: 10.1074/jbc.R113.452094

    Cells have evolved to regulate the asymmetric distribution of specific mRNA targets to institute spatial and temporal control over gene expression. Over the last few decades, evidence has mounted as to the importance of localization elements in the mRNA sequence and their respective RNA-binding proteins. Live imaging methodologies have shown mechanistic details of this phenomenon. In this minireview, we focus on the advanced biochemical and cell imaging techniques used to tweeze out the finer aspects of mechanisms of mRNA movement.

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    07/10/13 | Contributions of the 12 neuron classes in the fly lamina to motion vision.
    Tuthill JC, Nern A, Stephen L. Holtz , Rubin GM, Reiser MB
    Neuron. 07/2013;79:128-140. doi: http://dx.doi.org/10.1016/j.neuron.2013.05.024

    Motion detection is a fundamental neural computation performed by many sensory systems. In the fly, local motion computation is thought to occur within the first two layers of the visual system, the lamina and medulla. We constructed specific genetic driver lines for each of the 12 neuron classes in the lamina. We then depolarized and hyperpolarized each neuron type and quantified fly behavioral responses to a diverse set of motion stimuli. We found that only a small number of lamina output neurons are essential for motion detection, while most neurons serve to sculpt and enhance these feedforward pathways. Two classes of feedback neurons (C2 and C3), and lamina output neurons (L2 and L4), are required for normal detection of directional motion stimuli. Our results reveal a prominent role for feedback and lateral interactions in motion processing and demonstrate that motion-dependent behaviors rely on contributions from nearly all lamina neuron classes.

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    07/08/13 | Live imaging of whole mouse embryos during gastrulation: migration analyses of epiblast and mesodermal cells.
    Ichikawa T, Nakazato K, Keller PJ, Kajiura-Kobayashi H, Stelzer EH, Mochizuki A, Nonaka S
    PLoS One. 2013 Jul 8;8(7):e64506. doi: 10.1371/journal.pone.0064506

    During gastrulation in the mouse embryo, dynamic cell movements including epiblast invagination and mesodermal layer expansion lead to the establishment of the three-layered body plan. The precise details of these movements, however, are sometimes elusive, because of the limitations in live imaging. To overcome this problem, we developed techniques to enable observation of living mouse embryos with digital scanned light sheet microscope (DSLM). The achieved deep and high time-resolution images of GFP-expressing nuclei and following 3D tracking analysis revealed the following findings: (i) Interkinetic nuclear migration (INM) occurs in the epiblast at embryonic day (E)6 and 6.5. (ii) INM-like migration occurs in the E5.5 embryo, when the epiblast is a monolayer and not yet pseudostratified. (iii) Primary driving force for INM at E6.5 is not pressure from neighboring nuclei. (iv) Mesodermal cells migrate not as a sheet but as individual cells without coordination.

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    07/08/13 | The evolution of Drosophila melanogaster as a model for alcohol research.
    Devineni AV, Heberlein U
    Annual Reviews of Neuroscience. 2013 Jul 8;36:121-38. doi: 10.1146/annurev-neuro-062012-170256

    Animal models have been widely used to gain insight into the mechanisms underlying the acute and long-term effects of alcohol exposure. The fruit fly Drosophila melanogaster encounters ethanol in its natural habitat and possesses many adaptations that allow it to survive and thrive in ethanol-rich environments. Several assays to study ethanol-related behaviors in flies, ranging from acute intoxication to self-administration and reward, have been developed in the past 20 years. These assays have provided the basis for studying the physiological and behavioral effects of ethanol and for identifying genes mediating these effects. In this review we describe the ecological relationship between flies and ethanol, the effects of ethanol on fly development and behavior, the use of flies as a model for alcohol addiction, and the interaction between ethanol and social behavior. We discuss these advances in the context of their utility to help decipher the mechanisms underlying the diverse effects of ethanol, including those that mediate ethanol dependence and addiction in humans.

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    Singer Lab
    07/05/13 | Single cell analysis of RNA-mediated histone H3.3 recruitment to a cytomegalovirus promoter-regulated transcription site.
    Newhart A, Rafalska-Metcalf IU, Yang T, Joo LM, Powers SL, Kossenkov AV, Lopez-Jones M, Singer RH, Showe LC, Skordalakes E, Janicki SM
    The Journal of Biological Chemistry. 2013 Jul 5;288(27):19882-99. doi: 10.1074/jbc.M113.473181

    Unlike the core histones, which are incorporated into nucleosomes concomitant with DNA replication, histone H3.3 is synthesized throughout the cell cycle and utilized for replication-independent (RI) chromatin assembly. The RI incorporation of H3.3 into nucleosomes is highly conserved and occurs at both euchromatin and heterochromatin. However, neither the mechanism of H3.3 recruitment nor its essential function is well understood. Several different chaperones regulate H3.3 assembly at distinct sites. The H3.3 chaperone, Daxx, and the chromatin-remodeling factor, ATRX, are required for H3.3 incorporation and heterochromatic silencing at telomeres, pericentromeres, and the cytomegalovirus (CMV) promoter. By evaluating H3.3 dynamics at a CMV promoter-regulated transcription site in a genetic background in which RI chromatin assembly is blocked, we have been able to decipher the regulatory events upstream of RI nucleosomal deposition. We find that at the activated transcription site, H3.3 accumulates with sense and antisense RNA, suggesting that it is recruited through an RNA-mediated mechanism. Sense and antisense transcription also increases after H3.3 knockdown, suggesting that the RNA signal is amplified when chromatin assembly is blocked and attenuated by nucleosomal deposition. Additionally, we find that H3.3 is still recruited after Daxx knockdown, supporting a chaperone-independent recruitment mechanism. Sequences in the H3.3 N-terminal tail and αN helix mediate both its recruitment to RNA at the activated transcription site and its interaction with double-stranded RNA in vitro. Interestingly, the H3.3 gain-of-function pediatric glioblastoma mutations, G34R and K27M, differentially affect H3.3 affinity in these assays, suggesting that disruption of an RNA-mediated regulatory event could drive malignant transformation.

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    Baker Lab
    07/03/13 | Genetic and neural mechanisms that inhibit Drosophila from mating with other species.
    Fan P, Manoli DS, Ahmed OM, Chen Y, Agarwal N, Kwong S, Cai AG, Neitz J, Renslo A, Baker BS, Shah NM
    Cell. 2013 Jul 3;154(1):89-102. doi: 10.1016/j.cell.2013.06.008

    Genetically hard-wired neural mechanisms must enforce behavioral reproductive isolation because interspecies courtship is rare even in sexually na{\"ıve animals of most species. We find that the chemoreceptor Gr32a inhibits male D. melanogaster from courting diverse fruit fly species. Gr32a recognizes nonvolatile aversive cues present on these reproductively dead-end targets, and activity of Gr32a neurons is necessary and sufficient to inhibit interspecies courtship. Male-specific Fruitless (Fru(M)), a master regulator of courtship, also inhibits interspecies courtship. Gr32a and Fru(M) are not coexpressed, but Fru(M) neurons contact Gr32a neurons, suggesting that these genes influence a shared neural circuit that inhibits interspecies courtship. Gr32a and Fru(M) also suppress within-species intermale courtship, but we show that distinct mechanisms preclude sexual displays toward conspecific males and other species. Although this chemosensory pathway does not inhibit interspecies mating in D. melanogaster females, similar mechanisms appear to inhibit this behavior in many other male drosophilids.

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    Looger LabLeonardo Lab
    07/03/13 | Two-photon imaging of nonlinear glutamate release dynamics at bipolar cell synapses in the mouse retina.
    Borghuis BG, Marvin JS, Looger LL, Demb JB
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience. 2013 Jul 3;33(27):10972-85. doi: 10.1523/JNEUROSCI.1241-13.2013

    Alpha/Y-type retinal ganglion cells encode visual information with a receptive field composed of nonlinear subunits. This nonlinear subunit structure enhances sensitivity to patterns composed of high spatial frequencies. The Y-cell’s subunits are the presynaptic bipolar cells, but the mechanism for the nonlinearity remains incompletely understood. We investigated the synaptic basis of the subunit nonlinearity by combining whole-cell recording of mouse Y-type ganglion cells with two-photon fluorescence imaging of a glutamate sensor (iGluSnFR) expressed on their dendrites and throughout the inner plexiform layer. A control experiment designed to assess iGluSnFR’s dynamic range showed that fluorescence responses from Y-cell dendrites increased proportionally with simultaneously recorded excitatory current. Spatial resolution was sufficient to readily resolve independent release at intermingled ON and OFF bipolar terminals. iGluSnFR responses at Y-cell dendrites showed strong surround inhibition, reflecting receptive field properties of presynaptic release sites. Responses to spatial patterns located the origin of the Y-cell nonlinearity to the bipolar cell output, after the stage of spatial integration. The underlying mechanism differed between OFF and ON pathways: OFF synapses showed transient release and strong rectification, whereas ON synapses showed relatively sustained release and weak rectification. At ON synapses, the combination of fast release onset with slower release offset explained the nonlinear response of the postsynaptic ganglion cell. Imaging throughout the inner plexiform layer, we found transient, rectified release at the central-most levels, with increasingly sustained release near the borders. By visualizing glutamate release in real time, iGluSnFR provides a powerful tool for characterizing glutamate synapses in intact neural circuits.

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    Svoboda Lab
    07/02/13 | Aβ induces astrocytic glutamate release, extrasynaptic NMDA receptor activation, and synaptic loss.
    Talantova M, Sanz-Blasco S, Zhang X, Xia P, Akhtar MW, Okamoto S, Dziewczapolski G, Nakamura T, Cao G, Pratt AE, Kang Y, Tu S, Molokanova E, McKercher SR, Hires SA, Sason H, Stouffer DG, Buczynski MW, Solomon JP, Michael S, Powers ET, Kelly JW, Roberts A, Tong G, Fang-Newmeyer T, Parker J, Holland EA, Zhang D, Nakanishi N, Chen HV, Wolosker H, Wang Y, Parsons LH, Ambasudhan R, Masliah E, Heinemann SF, Piña-Crespo JC, Lipton SA
    Proceedings of the National Academy of Sciences of the United States of America. 2013 Jul 2;110(27):E2518-27. doi: 10.1073/pnas.1306832110

    Synaptic loss is the cardinal feature linking neuropathology to cognitive decline in Alzheimer’s disease (AD). However, the mechanism of synaptic damage remains incompletely understood. Here, using FRET-based glutamate sensor imaging, we show that amyloid-β peptide (Aβ) engages α7 nicotinic acetylcholine receptors to induce release of astrocytic glutamate, which in turn activates extrasynaptic NMDA receptors (eNMDARs) on neurons. In hippocampal autapses, this eNMDAR activity is followed by reduction in evoked and miniature excitatory postsynaptic currents (mEPSCs). Decreased mEPSC frequency may reflect early synaptic injury because of concurrent eNMDAR-mediated NO production, tau phosphorylation, and caspase-3 activation, each of which is implicated in spine loss. In hippocampal slices, oligomeric Aβ induces eNMDAR-mediated synaptic depression. In AD-transgenic mice compared with wild type, whole-cell recordings revealed excessive tonic eNMDAR activity accompanied by eNMDAR-sensitive loss of mEPSCs. Importantly, the improved NMDAR antagonist NitroMemantine, which selectively inhibits extrasynaptic over physiological synaptic NMDAR activity, protects synapses from Aβ-induced damage both in vitro and in vivo.

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