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21 Janelia Publications

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    02/28/16 | Single neuron morphology in vivo with confined primed conversion.
    Mohr MA, Pantazis P
    Methods in Cell Biology. 2016;133:125-38. doi: 10.1016/bs.mcb.2015.12.005

    Unraveling the structural organization of neurons can provide fundamental insights into brain function. However, visualizing neurite morphology in vivo remains difficult due to the high density and complexity of neural packing in the nervous system. Detailed analysis of neural morphology requires distinction of closely neighboring, highly intricate cellular structures such as neurites with high contrast. Green-to-red photoconvertible fluorescent proteins have become powerful tools to optically highlight molecular and cellular structures for developmental and cell biological studies. Yet, selective labeling of single cells of interest in vivo has been precluded due to inefficient photoconversion when using high intensity, pulsed, near-infrared laser sources that are commonly applied for achieving axially confined two-photon (2P) fluorescence excitation. Here we describe a novel optical mechanism, "confined primed conversion," which employs continuous dual-wave illumination to achieve confined green-to-red photoconversion of single cells in live zebrafish embryos. Confined primed conversion exhibits wide applicability and this chapter specifically elaborates on employing this imaging modality to analyze neural morphology of optically targeted single neurons in the developing zebrafish brain.

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    02/19/16 | Sequential ionic and conformational signaling by calcium channels drives neuronal gene expression.
    Li B, Tadross MR, Tsien RW
    Science (New York, N.Y.). 2016 Feb 19;351(6275):863-7. doi: 10.1126/science.aad3647

    Voltage-gated CaV1.2 channels (L-type calcium channel α1C subunits) are critical mediators of transcription-dependent neural plasticity. Whether these channels signal via the influx of calcium ion (Ca2+), voltage-dependent conformational change (VΔC), or a combination of the two has thus far been equivocal. We fused CaV1.2 to a ligand-gated Ca2+-permeable channel, enabling independent control of localized Ca2+ and VΔC signals. This revealed an unexpected dual requirement: Ca2+ must first mobilize actin-bound Ca2+/calmodulin-dependent protein kinase II, freeing it for subsequent VΔC-mediated accumulation. Neither signal alone sufficed to activate transcription. Signal order was crucial: Efficiency peaked when Ca2+ preceded VΔC by 10 to 20 seconds. CaV1.2 VΔC synergistically augmented signaling by N-methyl-D-aspartate receptors. Furthermore, VΔC mistuning correlated with autistic symptoms in Timothy syndrome. Thus, nonionic VΔC signaling is vital to the function of CaV1.2 in synaptic and neuropsychiatric processes.

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    Fetter LabCardona Lab
    02/18/16 | A circuit mechanism for the propagation of waves of muscle contraction in Drosophila.
    Fushiki A, Zwart MF, Kohsaka H, Fetter RD, Cardona A, Nose A
    eLife. 2016 Feb 18;5:. doi: 10.7554/eLife.13253

    Animals move by adaptively coordinating the sequential activation of muscles. The circuit mechanisms underlying coordinated locomotion are poorly understood. Here, we report on a novel circuit for propagation of waves of muscle contraction, using the peristaltic locomotion of Drosophila larvae as a model system. We found an intersegmental chain of synaptically connected neurons, alternating excitatory and inhibitory, necessary for wave propagation and active in phase with the wave. The excitatory neurons (A27h) are premotor and necessary only for forward locomotion, and are modulated by stretch receptors and descending inputs. The inhibitory neurons (GDL) are necessary for both forward and backward locomotion, suggestive of different yet coupled central pattern generators, and its inhibition is necessary for wave propagation. The circuit structure and functional imaging indicated that the commands to contract one segment promote the relaxation of the next segment, revealing a mechanism for wave propagation in peristaltic locomotion.

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    Baker Lab
    02/16/16 | Sex-specific regulation of Lgr3 in Drosophila neurons.
    Meissner GW, Luo SD, Dias BG, Texada MJ, Baker BS
    Proceedings of the National Academy of Sciences of the United States of America. 2016 Feb 18:. doi: 10.1073/pnas.1600241113

    The development of sexually dimorphic morphology and the potential for sexually dimorphic behavior in Drosophila are regulated by the Fruitless (Fru) and Doublesex (Dsx) transcription factors. Several direct targets of Dsx have been identified, but direct Fru targets have not been definitively identified. We show that Drosophila leucine-rich repeat G protein-coupled receptor 3 (Lgr3) is regulated by Fru and Dsx in separate populations of neurons. Lgr3 is a member of the relaxin-receptor family and a receptor for Dilp8, necessary for control of organ growth. Lgr3 expression in the anterior central brain of males is inhibited by the B isoform of Fru, whose DNA binding domain interacts with a short region of an Lgr3 intron. Fru A and C isoform mutants had no observed effect on Lgr3 expression. The female form of Dsx (Dsx(F)) separately up- and down-regulates Lgr3 expression in distinct neurons in the abdominal ganglion through female- and male-specific Lgr3 enhancers. Excitation of neural activity in the Dsx(F)-up-regulated abdominal ganglion neurons inhibits female receptivity, indicating the importance of these neurons for sexual behavior. Coordinated regulation of Lgr3 by Fru and Dsx marks a point of convergence of the two branches of the sex-determination hierarchy.

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    02/18/16 | Structured dendritic inhibition supports branch-selective integration in CA1 pyramidal cells.
    Bloss EB, Cembrowski MS, Karsh B, Colonell J, Fetter RD, Spruston N
    Neuron. 2016 Feb 18:. doi: 10.1016/j.neuron.2016.01.029

    Neuronal circuit function is governed by precise patterns of connectivity between specialized groups of neurons. The diversity of GABAergic interneurons is a hallmark of cortical circuits, yet little is known about their targeting to individual postsynaptic dendrites. We examined synaptic connectivity between molecularly defined inhibitory interneurons and CA1 pyramidal cell dendrites using correlative light-electron microscopy and large-volume array tomography. We show that interneurons can be highly selective in their connectivity to specific dendritic branch types and, furthermore, exhibit precisely targeted connectivity to the origin or end of individual branches. Computational simulations indicate that the observed subcellular targeting enables control over the nonlinear integration of synaptic input or the initiation and backpropagation of action potentials in a branch-selective manner. Our results demonstrate that connectivity between interneurons and pyramidal cell dendrites is more precise and spatially segregated than previously appreciated, which may be a critical determinant of how inhibition shapes dendritic computation.

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    Magee Lab
    02/17/16 | Axonal filtering allows reliable output during dendritic plateau-driven complex spiking in CA1 neurons.
    Apostolides PF, Milstein AD, Grienberger C, Bittner KC, Magee JC
    Neuron. 2016 Feb 17;89(4):770-783. doi: 10.1016/j.neuron.2015.12.040

    In CA1 pyramidal neurons, correlated inputs trigger dendritic plateau potentials that drive neuronal plasticity and firing rate modulation. Given the strong electrotonic coupling between soma and axon, the >25 mV depolarization associated with the plateau could propagate through the axon to influence action potential initiation, propagation, and neurotransmitter release. We examined this issue in brain slices, awake mice, and a computational model. Despite profoundly inactivating somatic and proximal axon Na(+) channels, plateaus evoked action potentials that recovered to full amplitude in the distal axon (>150 μm) and triggered neurotransmitter release similar to regular spiking. This effect was due to strong attenuation of plateau depolarizations by axonal K(+) channels, allowing full axon repolarization and Na(+) channel deinactivation. High-pass filtering of dendritic plateaus by axonal K(+) channels should thus enable accurate transmission of gain-modulated firing rates, allowing neuronal firing to be efficiently read out by downstream regions as a simple rate code.

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    02/17/16 | Calcium imaging of neural circuits with extended depth-of-field light-sheet microscopy.
    Quirin S, Vladimirov N, Yang C, Peterka DS, Yuste R, Ahrens MB
    Optics Letters. 2016 Feb 17;41(5):855-8. doi: 10.1364/OL.41.000855

    Increasing the volumetric imaging speed of light-sheet microscopy will improve its ability to detect fast changes in neural activity. Here, a system is introduced for brain-wide imaging of neural activity in the larval zebrafish by coupling structured illumination with cubic phase extended depth-of-field (EDoF) pupil encoding. This microscope enables faster light-sheet imaging and facilitates arbitrary plane scanning—removing constraints on acquisition speed, alignment tolerances, and physical motion near the sample. The usefulness of this method is demonstrated by performing multi-plane calcium imaging in the fish brain with a 416×832×160  μm field of view at 33 Hz. The optomotor response behavior of the zebrafish is monitored at high speeds, and time-locked correlations of neuronal activity are resolved across its brain.

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    02/17/16 | Virginia Orange: A versatile, red-shifted fluorescein scaffold for single- and dual-input fluorogenic probes.
    Grimm JB, Gruber TD, Ortiz G, Brown TA, Lavis LD
    Bioconjugate Chemistry. 2016 Feb 17;27(2):474-80. doi: 10.1021/acs.bioconjchem.5b00566

    Fluorogenic molecules are important tools for biological and biochemical research. The majority of fluorogenic compounds have a simple input-output relationship, where a single chemical input yields a fluorescent output. Development of new systems where multiple inputs converge to yield an optical signal could refine and extend fluorogenic compounds by allowing greater spatiotemporal control over the fluorescent signal. Here, we introduce a new red-shifted fluorescein derivative, Virginia Orange, as an exceptional scaffold for single- and dual-input fluorogenic molecules. Unlike fluorescein, installation of a single masking group on Virginia Orange is sufficient to fully suppress fluorescence, allowing preparation of fluorogenic enzyme substrates with rapid, single-hit kinetics. Virginia Orange can also be masked with two independent moieties; both of these masking groups must be removed to induce fluorescence. This allows facile construction of multi-input fluorogenic probes for sophisticated sensing regimes and genetic targeting of latent fluorophores to specific cellular populations.

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    02/16/16 | Multifocus microscopy with precise color multi-phase diffractive optics applied in functional neuronal imaging.
    Abrahamsson S, Ilic R, Wisniewski J, Mehl B, Yu L, Chen L, Davanco M, Oujedi L, Fiche J, Hajj B
    Biomedical Optics Express. 2016 Feb 16;7(3):855-69. doi: 10.1364/BOE.7.000855

    Multifocus microscopy (MFM) allows high-resolution instantaneous three-dimensional (3D) imaging and has been applied to study biological specimens ranging from single molecules inside cells nuclei to entire embryos. We here describe pattern designs and nanofabrication methods for diffractive optics that optimize the light-efficiency of the central optical component of MFM: the diffractive multifocus grating (MFG). We also implement a “precise color” MFM layout with MFGs tailored to individual fluorophores in separate optical arms. The reported advancements enable faster and brighter volumetric time-lapse imaging of biological samples. In live microscopy applications, photon budget is a critical parameter and light-efficiency must be optimized to obtain the fastest possible frame rate while minimizing photodamage. We provide comprehensive descriptions and code for designing diffractive optical devices, and a detailed methods description for nanofabrication of devices. Theoretical efficiencies of reported designs is ≈90% and we have obtained efficiencies of > 80% in MFGs of our own manufacture. We demonstrate the performance of a multi-phase MFG in 3D functional neuronal imaging in living C. elegans.

     

    Additional authors include:

    Xin Jin, Joan Pulupa, Christine Cho, Mustafa Mir, Mohamed El Beheiry, Xavier Darzacq, Marcelo Nollmann, Maxime Dahan, Carl Wu, Timothée Lionnet, J. Alexander Liddle, and Cornelia I. Bargmann

     

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    02/16/16 | PSF engineering in multifocus microscopy for increased depth volumetric imaging.
    Hajj B, El Beheiry M, Dahan M
    Biomedical Optics Express. 2016 Feb 16;7(3):726-31. doi: 10.1364/BOE.7.000726

    Imaging and localizing single molecules with high accuracy in a 3D volume is a challenging task. Here we combine multifocal microscopy, a recently developed volumetric imaging technique, with point spread function engineering to achieve an increased depth for single molecule imaging. Applications in 3D single molecule localization-based super-resolution imaging is shown over an axial depth of 4 µm as well as for the tracking of diffusing beads in a fluid environment over 8 µm.

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