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110 Janelia Publications

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    06/01/20 | Nanoscopic visualization of restricted nonvolume cholinergic and monoaminergic transmission with genetically encoded sensors.
    Zhu PK, Zheng WS, Zhang P, Jing M, Borden PM, Ali F, Guo K, Feng J, Marvin JS, Wang Y, Wan J, Gan L, Kwan AC, Lin L, Looger LL, Li Y, Zhang Y
    Nano Letters. 2020 Jun;20(6):4073-83. doi: 10.1021/acs.nanolett.9b04877

    How neuromodulatory transmitters diffuse into the extracellular space remains an unsolved fundamental biological question, despite wide acceptance of the volume transmission model. Here, we report development of a method combining genetically encoded fluorescent sensors with high-resolution imaging and analysis algorithms which permits the first direct visualization of neuromodulatory transmitter diffusion at various neuronal and non-neuronal cells. Our analysis reveals that acetylcholine and monoamines diffuse at individual release sites with a spread length constant of ∼0.75 μm. These transmitters employ varied numbers of release sites, and when spatially close-packed release sites coactivate they can spillover into larger subcellular areas. Our data indicate spatially restricted (i.e., nonvolume) neuromodulatory transmission to be a prominent intercellular communication mode, reshaping current thinking of control and precision of neuromodulation crucial for understanding behaviors and diseases.

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    05/25/20 | jYCaMP: an optimized calcium indicator for two-photon imaging at fiber laser wavelengths.
    Mohr MA, Bushey D, Aggarwal A, Marvin JS, Kim JJ, Marquez EJ, Liang Y, Patel R, Macklin JJ, Lee C, Tsang A, Tsegaye G, Ahrens AM, Chen JL, Kim DS, Wong AM, Looger LL, Schreiter ER, Podgorski K
    Nature Methods. 2020 May 25;17(1):694-97. doi: 10.1038/s41592-020-0835-7

    Femtosecond lasers at fixed wavelengths above 1,000 nm are powerful, stable and inexpensive, making them promising sources for two-photon microscopy. Biosensors optimized for these wavelengths are needed for both next-generation microscopes and affordable turn-key systems. Here we report jYCaMP1, a yellow variant of the calcium indicator jGCaMP7 that outperforms its parent in mice and flies at excitation wavelengths above 1,000 nm and enables improved two-color calcium imaging with red fluorescent protein-based indicators.

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    04/17/20 | Temperature-dependent sex determination is mediated by pSTAT3 repression of Kdm6b..
    Weber C, Zhou Y, Lee JG, Looger LL, Qian G, Ge C, Capel B
    Science. 2020 Apr 17;368(6488):303-306. doi: 10.1126/science.aaz4165

    In many reptiles, including the red-eared slider turtle (), sex is determined by ambient temperature during embryogenesis. We previously showed that the epigenetic regulator is elevated at the male-producing temperature and essential to activate the male pathway. In this work, we established a causal link between temperature and transcriptional regulation of We show that signal transducer and activator of transcription 3 (STAT3) is phosphorylated at the warmer, female-producing temperature, binds the locus, and represses transcription, blocking the male pathway. Influx of Ca, a mediator of STAT3 phosphorylation, is elevated at the female temperature and acts as a temperature-sensitive regulator of STAT3 activation.

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    02/08/20 | A fast genetically encoded fluorescent sensor for faithful in vivo acetylcholine detection in mice, fish, worms and flies.
    Borden P, Zhang P, Shivange AV, Marvin JS, Cichon J, Dan C, Podgorski K, Figueiredo A, Novak O, Tanimoto M, Shigetomi E, Lobas MA, Kim H, Zhu P, Zhang Y, Zheng WS, Fan C, Wang G, Xiang B, Gan L, Zhang G, Guo K, Lin L, Cai Y, Yee AG, Aggarwal A, Ford CP, Rees DC, Dietrich D, Khakh BS, Dittman JS, Gan W, Koyama M, Jayaraman V, Cheer JF, Lester HA, Zhu JJ, Looger LL
    bioRxiv. 2020 Feb 8:. doi: https://doi.org/10.1101/2020.02.07.939504

    Here we design and optimize a genetically encoded fluorescent indicator, iAChSnFR, for the ubiquitous neurotransmitter acetylcholine, based on a bacterial periplasmic binding protein. iAChSnFR shows large fluorescence changes, rapid rise and decay kinetics, and insensitivity to most cholinergic drugs. iAChSnFR revealed large transients in a variety of slice and in vivo preparations in mouse, fish, fly and worm. iAChSnFR will be useful for the study of acetylcholine in all animals.

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    01/03/20 | The neuropeptide Drosulfakinin regulates social isolation-induced aggression in Drosophila.
    Agrawal P, Kao D, Chung P, Looger LL
    Journal of Experimental Biology. 2020 Jan 03;223(2):. doi: 10.1242/jeb.207407

    Social isolation strongly modulates behavior across the animal kingdom. We utilized the fruit fly to study social isolation-driven changes in animal behavior and gene expression in the brain. RNA-seq identified several head-expressed genes strongly responding to social isolation or enrichment. Of particular interest, social isolation downregulated expression of the gene encoding the neuropeptide (), the homologue of vertebrate cholecystokinin (CCK), which is critical for many mammalian social behaviors. knockdown significantly increased social isolation-induced aggression. Genetic activation or silencing of neurons each similarly increased isolation-driven aggression. Our results suggest a U-shaped dependence of social isolation-induced aggressive behavior on signaling, similar to the actions of many neuromodulators in other contexts.

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    11/12/19 | Biosensors show the pharmacokinetics of S-Ketamine in the endoplasmic reticulum.
    Bera K, Kamajaya A, Shivange AV, Muthusamy AK, Nichols AL, Borden PM, Grant S, Jeon J, Lin E, Bishara I, Chin TM, Cohen BN, Kim CH, Unger EK, Tian L, Marvin JS, Looger LL, Lester HA
    Frontiers in Cellular Neuroscience. 2019 Nov 12;13:499. doi: 10.3389/fncel.2019.00499

    The target for the "rapid" (<24 h) antidepressant effects of S-ketamine is unknown, vitiating programs to rationally develop more effective rapid antidepressants. To describe a drug's target, one must first understand the compartments entered by the drug, at all levels-the organ, the cell, and the organelle. We have, therefore, developed molecular tools to measure the subcellular, organellar pharmacokinetics of S-ketamine. The tools are genetically encoded intensity-based S-ketamine-sensing fluorescent reporters, iSKetSnFR1 and iSKetSnFR2. In solution, these biosensors respond to S-ketamine with a sensitivity, S-slope = delta(F/F)/(delta[S-ketamine]) of 0.23 and 1.9/μM, respectively. The iSKetSnFR2 construct allows measurements at <0.3 μM S-ketamine. The iSKetSnFR1 and iSKetSnFR2 biosensors display >100-fold selectivity over other ligands tested, including R-ketamine. We targeted each of the sensors to either the plasma membrane (PM) or the endoplasmic reticulum (ER). Measurements on these biosensors expressed in Neuro2a cells and in human dopaminergic neurons differentiated from induced pluripotent stem cells (iPSCs) show that S-ketamine enters the ER within a few seconds after appearing in the external solution near the PM, then leaves as rapidly after S-ketamine is removed from the extracellular solution. In cells, S-slopes for the ER and PM-targeted sensors differ by <2-fold, indicating that the ER [S-ketamine] is less than 2-fold different from the extracellular [S-ketamine]. Organelles represent potential compartments for the engagement of S-ketamine with its antidepressant target, and potential S-ketamine targets include organellar ion channels, receptors, and transporters.

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    09/23/19 | Single-cell reconstruction of emerging population activity in an entire developing circuit.
    Wan Y, Wei Z, Looger LL, Koyama M, Druckmann S, Keller PJ
    Cell. 2019 Sep 23;179(2):. doi: 10.1016/j.cell.2019.08.039

    Animal survival requires a functioning nervous system to develop during embryogenesis. Newborn neurons must assemble into circuits producing activity patterns capable of instructing behaviors. Elucidating how this process is coordinated requires new methods that follow maturation and activity of all cells across a developing circuit. We present an imaging method for comprehensively tracking neuron lineages, movements, molecular identities, and activity in the entire developing zebrafish spinal cord, from neurogenesis until the emergence of patterned activity instructing the earliest spontaneous motor behavior. We found that motoneurons are active first and form local patterned ensembles with neighboring neurons. These ensembles merge, synchronize globally after reaching a threshold size, and finally recruit commissural interneurons to orchestrate the left-right alternating patterns important for locomotion in vertebrates. Individual neurons undergo functional maturation stereotypically based on their birth time and anatomical origin. Our study provides a general strategy for reconstructing how functioning circuits emerge during embryogenesis.

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    08/01/19 | Inaccurate secondary structure predictions often indicate protein fold switching.
    Mishra S, Looger LL, Porter LL
    Protein Science. 2019 Aug;28(9):1487-93. doi: 10.1002/pro.3664

    Although most proteins conform to the classical one-structure/one-function paradigm, an increasing number of proteins with dual structures and functions have been discovered. In response to cellular stimuli, such proteins undergo structural changes sufficiently dramatic to remodel even their secondary structures and domain organization. This "fold-switching" capability fosters protein multi-functionality, enabling cells to establish tight control over various biochemical processes. Accurate predictions of fold-switching proteins could both suggest underlying mechanisms for uncharacterized biological processes and reveal potential drug targets. Recently, we developed a prediction method for fold-switching proteins using structure-based thermodynamic calculations and discrepancies between predicted and experimentally determined protein secondary structure. Here we seek to leverage the negative information found in these secondary structure prediction discrepancies. To do this, we quantified secondary structure prediction accuracies of 192 known fold-switching regions (FSRs) within solved protein structures found in the Protein Data Bank (PDB). We find that the secondary structure prediction accuracies for these FSRs vary widely. Inaccurate secondary structure predictions are strongly associated with fold-switching proteins compared to equally long segments of non-fold-switching proteins selected at random. These inaccurate predictions are enriched in helix-to-strand and strand-to-coil discrepancies. Finally, we find that most proteins with inaccurate secondary structure predictions are underrepresented in the PDB compared with their alternatively folded cognates, suggesting that unequal representation of fold-switching conformers within the PDB could be an important cause of inaccurate secondary structure predictions. These results demonstrate that inconsistent secondary structure predictions can serve as a useful preliminary marker of fold switching. This article is protected by copyright. All rights reserved.

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    08/01/19 | Quantitative in vivo imaging of neuronal glucose concentrations with a genetically encoded fluorescence lifetime sensor.
    Díaz-García CM, Lahmann C, Martínez-François JR, Li B, Koveal D, Nathwani N, Rahman M, Keller JP, Marvin JS, Looger LL, Yellen G
    Journal of Neuroscience Research. 2019 Aug 01;97(8):946-60. doi: 10.1002/jnr.24433

    Glucose is an essential source of energy for the brain. Recently, the development of genetically encoded fluorescent biosensors has allowed real time visualization of glucose dynamics from individual neurons and astrocytes. A major difficulty for this approach, even for ratiometric sensors, is the lack of a practical method to convert such measurements into actual concentrations in ex vivo brain tissue or in vivo. Fluorescence lifetime imaging provides a strategy to overcome this. In a previous study, we reported the lifetime glucose sensor iGlucoSnFR-TS (then called SweetieTS) for monitoring changes in neuronal glucose levels in response to stimulation. This genetically encoded sensor was generated by combining the Thermus thermophilus glucose-binding protein with a circularly permuted variant of the monomeric fluorescent protein T-Sapphire. Here, we provide more details on iGlucoSnFR-TS design and characterization, as well as pH and temperature sensitivities. For accurate estimation of glucose concentrations, the sensor must be calibrated at the same temperature as the experiments. We find that when the extracellular glucose concentration is in the range 2-10 mM, the intracellular glucose concentration in hippocampal neurons from acute brain slices is ~20% of the nominal external glucose concentration (~0.4-2 mM). We also measured the cytosolic neuronal glucose concentration in vivo, finding a range of ~0.7-2.5 mM in cortical neurons from awake mice.

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    07/29/19 | Kilohertz frame-rate two-photon tomography.
    Kazemipour A, Novak O, Flickinger D, Marvin JS, Abdelfattah AS, King J, Borden P, Kim J, Al-Abdullatif S, Deal P, Miller E, Schreiter E, Druckmann S, Svoboda K, Looger L, Podgorski K
    Nature Methods. 2019 Jul 29;16(8):778-86. doi: 10.1101/357269

    Point-scanning two-photon microscopy enables high-resolution imaging within scattering specimens such as the mammalian brain, but sequential acquisition of voxels fundamentally limits imaging speed. We developed a two-photon imaging technique that scans lines of excitation across a focal plane at multiple angles and uses prior information to recover high-resolution images at over 1.4 billion voxels per second. Using a structural image as a prior for recording neural activity, we imaged visually-evoked and spontaneous glutamate release across hundreds of dendritic spines in mice at depths over 250 microns and frame-rates over 1 kHz. Dendritic glutamate transients in anaesthetized mice are synchronized within spatially-contiguous domains spanning tens of microns at frequencies ranging from 1-100 Hz. We demonstrate high-speed recording of acetylcholine and calcium sensors, 3D single-particle tracking, and imaging in densely-labeled cortex. Our method surpasses limits on the speed of raster-scanned imaging imposed by fluorescence lifetime.

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