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192 Publications

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    07/01/20 | Dielectric confinement and excitonic effects in two-dimensional nanoplatelets.
    Ji B, Rabani E, Efros AL, Vaxenburg R, Ashkenazi O, Azulay D, Banin U, Millo O
    ACS Nano. 2020 Jul 01:. doi: 10.1021/acsnano.0c01950

    Quasi-two-dimensional (2D) semiconductor nanoplatelets manifest strong quantum confinement with exceptional optical characteristics of narrow photoluminescence peaks with energies tunable by thickness with monolayer precision. We employed scanning tunneling spectroscopy (STS) in conjunction with optical measurements to probe the thickness-dependent band gap and density of excited states in a series of CdSe nanoplatelets. The tunneling spectra, measured in the double-barrier tunnel junction configuration, reveal the effect of quantum confinement on the band gap taking place mainly through a blue-shift of the conduction band edge, along with a signature of 2D electronic structure intermixed with finite lateral-size and/or defects effects. The STS fundamental band gaps are larger than the optical gaps as expected from the contributions of exciton binding in the absorption, as confirmed by theoretical calculations. The calculations also point to strong valence band mixing between the light- and split-off hole levels. Strikingly, the energy difference between the heavy-hole and light-hole levels in the tunneling spectra are significantly larger than the corresponding values extracted from the absorption spectra. Possible explanations for this, including an interplay of nanoplatelet charging, dielectric confinement, and difference in exciton binding energy for light and heavy holes, are analyzed and discussed.

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    07/01/20 | Membrane potential dynamics underlying context-dependent sensory responses in the hippocampus.
    Zhao X, Wang Y, Spruston N, Magee JC
    Nature Neuroscience. 2020 Jul 1;23(7):881-91. doi: 10.1038/s41593-020-0646-2

    As animals navigate, they must identify features within context. In the mammalian brain, the hippocampus has the ability to separately encode different environmental contexts, even when they share some prominent features. To do so, neurons respond to sensory features in a context-dependent manner; however, it is not known how this encoding emerges. To examine this, we performed electrical recordings in the hippocampus as mice navigated in two distinct virtual environments. In CA1, both synaptic input to single neurons and population activity strongly tracked visual cues in one environment, whereas responses were almost completely absent when the same cue was presented in a second environment. A very similar, highly context-dependent pattern of cue-driven spiking was also observed in CA3. These results indicate that CA1 inherits a complex spatial code from upstream regions, including CA3, that have already computed a context-dependent representation of environmental features.

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    07/01/20 | Preventing cytokine storm syndrome in COVID-19 using α-1 adrenergic receptor antagonists.
    Konig MF, Powell M, Staedtke V, Bai R, Thomas DL, Fischer N, Huq S, Khalafallah AM, Koenecke A, Xiong R, Mensh B, Papadopoulos N, Kinzler KW, Vogelstein B, Vogelstein JT, Athey S, Zhou S, Bettegowda C
    The Journal of Clinical Investigatio. 2020 Jul 01;130(7):3345-47. doi: 10.1172/JCI139642
    07/01/20 | The anatomy and physiology of claustrum-cortex interactions.
    Jackson J, Smith JB, Lee AK
    Annual Review of Neuroscience. 2020 Jul 1;43:231-47. doi: 10.1146/annurev-neuro-092519-101637

    The claustrum is one of the most widely connected regions of the forebrain, yet its function has remained obscure, largely due to the experimentally challenging nature of targeting this small, thin, and elongated brain area. However, recent advances in molecular techniques have enabled the anatomy and physiology of the claustrum to be studied with the spatiotemporal and cell type-specific precision required to eventually converge on what this area does. Here we review early anatomical and electrophysiological results from cats and primates, as well as recent work in the rodent, identifying the connectivity, cell types, and physiological circuit mechanisms underlying the communication between the claustrum and the cortex. The emerging picture is one in which the rodent claustrum is closely tied to frontal/limbic regions and plays a role in processes, such as attention, that are associated with these areas. Expected final online publication date for the , Volume 43 is July 8, 2020. Please see for revised estimates.

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    05/06/20 | Whole-brain profiling of cells and circuits in mammals by tissue clearing and light-sheet microscopy.
    Ueda HR, Dodt H, Osten P, Economo MN, Chandrashekar J, Keller PJ
    Neuron. 2020 May 06;106(3):369-387. doi: 10.1016/j.neuron.2020.03.004

    Tissue clearing and light-sheet microscopy have a 100-year-plus history, yet these fields have been combined only recently to facilitate novel experiments and measurements in neuroscience. Since tissue-clearing methods were first combined with modernized light-sheet microscopy a decade ago, the performance of both technologies has rapidly improved, broadening their applications. Here, we review the state of the art of tissue-clearing methods and light-sheet microscopy and discuss applications of these techniques in profiling cells and circuits in mice. We examine outstanding challenges and future opportunities for expanding these techniques to achieve brain-wide profiling of cells and circuits in primates and humans. Such integration will help provide a systems-level understanding of the physiology and pathology of our central nervous system.

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    06/25/20 | Controlling motor neurons of every muscle for fly proboscis reaching.
    McKellar CE, Siwanowicz I, Dickson BJ, Simpson JH
    eLife. 2020 Jun 25;9:. doi: 10.7554/eLife.54978

    We describe the anatomy of all the primary motor neurons in the fly proboscis and characterize their contributions to its diverse reaching movements. Pairing this behavior with the wealth of genetic tools offers the possibility to study motor control at single-neuron resolution, and soon throughout entire circuits. As an entry to these circuits, we provide detailed anatomy of proboscis motor neurons, muscles, and joints. We create a collection of fly strains to individually manipulate every proboscis muscle through control of its motor neurons, the first such collection for an appendage. We generate a model of the action of each proboscis joint, and find that only a small number of motor neurons are needed to produce proboscis reaching. Comprehensive control of each motor element in this numerically simple system paves the way for future study of both reflexive and flexible movements of this appendage.

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    06/23/20 | Employing NaChBac for cryo-EM analysis of toxin action on voltage-gated Na+ channels in nanodisc
    Gao S, Valinsky WC, On NC, Houlihan PR, Qu Q, Liu L, Pan X, Clapham DE, Yan N
    Proceedings of the National Academy of Sciences of the U.S.A.. 2020 Jun 23;117(25):14187-93. doi: 10.1073/pnas.1922903117

    NaChBac, the first bacterial voltage-gated Na+ (Nav) channel to be characterized, has been the prokaryotic prototype for studying the structure–function relationship of Nav channels. Discovered nearly two decades ago, the structure of NaChBac has not been determined. Here we present the single particle electron cryomicroscopy (cryo-EM) analysis of NaChBac in both detergent micelles and nanodiscs. Under both conditions, the conformation of NaChBac is nearly identical to that of the potentially inactivated NavAb. Determining the structure of NaChBac in nanodiscs enabled us to examine gating modifier toxins (GMTs) of Nav channels in lipid bilayers. To study GMTs in mammalian Nav channels, we generated a chimera in which the extracellular fragment of the S3 and S4 segments in the second voltage-sensing domain from Nav1.7 replaced the corresponding sequence in NaChBac. Cryo-EM structures of the nanodisc-embedded chimera alone and in complex with HuwenToxin IV (HWTX-IV) were determined to 3.5 and 3.2 Å resolutions, respectively. Compared to the structure of HWTX-IV–bound human Nav1.7, which was obtained at an overall resolution of 3.2 Å, the local resolution of the toxin has been improved from ∼6 to ∼4 Å. This resolution enabled visualization of toxin docking. NaChBac can thus serve as a convenient surrogate for structural studies of the interactions between GMTs and Nav channels in a membrane environment.

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    06/22/20 | A far‐red fluorescent chemogenetic reporter for in vivo molecular imaging
    Li C, Tebo AG, Thauvin M, Plamont M, Volovitch M, Morin X, Vriz S, Gautier A
    Angewandte Chemie International Edition. 06/2020:. doi: 10.1002/anie.202006576

    Far‐red emitting fluorescent labels are highly desirable for spectral multiplexing and deep tissue imaging. Here, we describe the generation of frFAST (far‐red Fluorescence Activating and absorption Shifting Tag), a 14‐kDa monomeric protein that forms a bright far‐red fluorescent assembly with (4‐hydroxy‐3‐methoxy‐phenyl)allylidene rhodanine (HPAR‐3OM). As HPAR‐3OM is essentially non‐ fluorescent in solution and in cells, frFAST can be imaged with high contrast in presence of free HPAR‐3OM, which allowed the rapid and efficient imaging of frFAST fusions in live cells, zebrafish embryo/larvae and chicken embryo. Beyond enabling genetic encoding of far‐red fluorescence, frFAST allowed the design of a far‐ red chemogenetic reporter of protein‐protein interactions, demonstrating its great potential for the design of innovative far‐red emitting biosensors.

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    06/22/20 | A neural representation of naturalistic motion-guided behavior in the zebrafish brain.
    Yildizoglu T, Riegler C, Fitzgerald JE, Portugues R
    Current Biology. 2020 Jun 22;30(12):2321-33. doi: 10.1016/j.cub.2020.04.043

    All animals must transform ambiguous sensory data into successful behavior. This requires sensory representations that accurately reflect the statistics of natural stimuli and behavior. Multiple studies show that visual motion processing is tuned for accuracy under naturalistic conditions, but the sensorimotor circuits extracting these cues and implementing motion-guided behavior remain unclear. Here we show that the larval zebrafish retina extracts a diversity of naturalistic motion cues, and the retinorecipient pretectum organizes these cues around the elements of behavior. We find that higher-order motion stimuli, gliders, induce optomotor behavior matching expectations from natural scene analyses. We then image activity of retinal ganglion cell terminals and pretectal neurons. The retina exhibits direction-selective responses across glider stimuli, and anatomically clustered pretectal neurons respond with magnitudes matching behavior. Peripheral computations thus reflect natural input statistics, whereas central brain activity precisely codes information needed for behavior. This general principle could organize sensorimotor transformations across animal species.

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    06/17/20 | Genome-wide kinetic properties of transcriptional bursting in mouse embryonic stem cells.
    Ochiai H, Hayashi T, Umeda M, Yoshimura M, Harada A, Shimizu Y, Nakano K, Saitoh N, Liu Z, Yamamoto T, Okamura T, Ohkawa Y, Kimura H, Nikaido I
    Science Advances. 2020 Jun 17;6(25):eaaz6699. doi: 10.1126/sciadv.aaz6699

    Transcriptional bursting is the stochastic activation and inactivation of promoters, contributing to cell-to-cell heterogeneity in gene expression. However, the mechanism underlying the regulation of transcriptional bursting kinetics (burst size and frequency) in mammalian cells remains elusive. In this study, we performed single-cell RNA sequencing to analyze the intrinsic noise and mRNA levels for elucidating the transcriptional bursting kinetics in mouse embryonic stem cells. Informatics analyses and functional assays revealed that transcriptional bursting kinetics was regulated by a combination of promoter- and gene body-binding proteins, including the polycomb repressive complex 2 and transcription elongation factors. Furthermore, large-scale CRISPR-Cas9-based screening identified that the Akt/MAPK signaling pathway regulated bursting kinetics by modulating transcription elongation efficiency. These results uncovered the key molecular mechanisms underlying transcriptional bursting and cell-to-cell gene expression noise in mammalian cells.

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