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84 Publications

Showing 1-10 of 84 results
09/25/19 | Rational design of fluorogenic and spontaneously blinking labels for super-resolution imaging.
Zheng Q, Ayala AX, Chung I, Weigel AV, Ranjan A, Falco N, Grimm JB, Tkachuk AN, Wu C, Lippincott-Schwartz J, Singer RH, Lavis LD
ACS Central Science. 2019 Sep 25;5(9):1602-1613. doi: 10.1021/acscentsci.9b00676

Rhodamine dyes exist in equilibrium between a fluorescent zwitterion and a nonfluorescent lactone. Tuning this equilibrium toward the nonfluorescent lactone form can improve cell-permeability and allow creation of "fluorogenic" compounds-ligands that shift to the fluorescent zwitterion upon binding a biomolecular target. An archetype fluorogenic dye is the far-red tetramethyl-Si-rhodamine (SiR), which has been used to create exceptionally useful labels for advanced microscopy. Here, we develop a quantitative framework for the development of new fluorogenic dyes, determining that the lactone-zwitterion equilibrium constant () is sufficient to predict fluorogenicity. This rubric emerged from our analysis of known fluorophores and yielded new fluorescent and fluorogenic labels with improved performance in cellular imaging experiments. We then designed a novel fluorophore-Janelia Fluor 526 (JF)-with SiR-like properties but shorter fluorescence excitation and emission wavelengths. JF is a versatile scaffold for fluorogenic probes including ligands for self-labeling tags, stains for endogenous structures, and spontaneously blinking labels for super-resolution immunofluorescence. JF constitutes a new label for advanced microscopy experiments, and our quantitative framework will enable the rational design of other fluorogenic probes for bioimaging.

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09/04/19 | Isomeric tuning yields bright and targetable red Ca indicators.
Deo C, Sheu S, Seo J, Clapham DE, Lavis LD
Journal of the American Chemical Society. 2019 Sep 04;141(35):13734-13738. doi: 10.1021/jacs.9b06092

Targeting small-molecule fluorescent indicators using genetically encoded protein tags yields new hybrid sensors for biological imaging. Optimization of such systems requires redesign of the synthetic indicator to allow cell-specific targeting without compromising the photophysical properties or cellular performance of the small-molecule probe. We developed a bright and sensitive Ca indicator by systematically exploring the relative configuration of dye and chelator, which can be targeted using the HaloTag self-labeling tag system. Our "isomeric tuning" approach is generalizable, yielding a far-red targetable indicator to visualize Ca fluxes in the primary cilium.

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08/13/19 | Bright and photostable chemigenetic indicators for extended in vivo voltage imaging.
Abdelfattah AS, Kawashima T, Singh A, Novak O, Liu H, Shuai Y, Huang Y, Campagnola L, Seeman SC, Yu J, Zheng J, Grimm JB, Patel R, Friedrich J, Mensh BD, Paninski L, Macklin JJ, Murphy GJ, Podgorski K, Lin B, Chen T, Turner GC, Liu Z, Koyama M, Svoboda K, Ahrens MB, Lavis LD, Schreiter ER
Science. 2019 Aug 13;365(6454):699-704. doi: 10.1126/science.aav6416

Imaging changes in membrane potential using genetically encoded fluorescent voltage indicators (GEVIs) has great potential for monitoring neuronal activity with high spatial and temporal resolution. Brightness and photostability of fluorescent proteins and rhodopsins have limited the utility of existing GEVIs. We engineered a novel GEVI, "Voltron", that utilizes bright and photostable synthetic dyes instead of protein-based fluorophores, extending the combined duration of imaging and number of neurons imaged simultaneously by more than tenfold relative to existing GEVIs. We used Voltron for in vivo voltage imaging in mice, zebrafish, and fruit flies. In mouse cortex, Voltron allowed single-trial recording of spikes and subthreshold voltage signals from dozens of neurons simultaneously, over 15 min of continuous imaging. In larval zebrafish, Voltron enabled the precise correlation of spike timing with behavior.

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07/11/19 | Multi-color single molecule imaging uncovers extensive heterogeneity in mRNA decoding.
Boersma S, Khuperkar D, Verhagen BM, Sonneveld S, Grimm JB, Lavis LD, Tanenbaum ME
Cell. 2019 Jul 11;178(2):458-72. doi: 10.1016/j.cell.2019.05.001

mRNA translation is a key step in decoding genetic information. Genetic decoding is surprisingly heterogeneous, as multiple distinct polypeptides can be synthesized from a single mRNA sequence. To study translational heterogeneity, we developed the MoonTag, a new fluorescence labeling system to visualize translation of single mRNAs. When combined with the orthogonal SunTag system, the MoonTag enables dual readouts of translation, greatly expanding the possibilities to interrogate complex translational heterogeneity. By placing MoonTag and SunTag sequences in different translation reading frames, each driven by distinct translation start sites, start site selection of individual ribosomes can be visualized in real-time. We find that start site selection is largely stochastic, but that the probability of using a particular start site differs among mRNA molecules, and can be dynamically regulated over time. Together, this study provides key insights into translation start site selection heterogeneity, and provides a powerful toolbox to visualize complex translation dynamics.

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06/21/19 | Chemistry of photosensitive fluorophores for single-molecule localization microscopy.
Jradi FM, Lavis LD
ACS Chemical Biology. 2019 Jun 21;14(6):1077-90. doi: 10.1021/acschembio.9b00197

The development of single-molecule localization microscopy (SMLM) has sparked a revolution in biological imaging, allowing 'super-resolution' fluorescence microscopy below the diffraction limit of light. The last decade has seen an explosion in not only optical hardware for SMLM but also the development or repurposing of fluorescent proteins and small-molecule fluorescent probes for this technique. In this review, written by chemists for chemists, we detail the history of single-molecule localization microscopy and collate the collection of probes with demonstrated utility in SMLM. We hope it will serve as a primer for probe choice in localization microscopy as well as an inspiration for the development of new fluorophores that enable imaging of biological samples with exquisite detail.

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01/25/19 | Probing nicotinic acetylcholine receptor function in mouse brain slices via laser flash photolysis of photoactivatable nicotine.
Arvin MC, Wokosin DL, Banala S, Lavis LD, Drenan RM
Journal of Visualized Experiments : JoVE. 2019 Jan 25(143):. doi: 10.3791/58873

Acetylcholine (ACh) acts through receptors to modulate a variety of neuronal processes, but it has been challenging to link ACh receptor function with subcellular location within cells where this function is carried out. To study the subcellular location of nicotinic ACh receptors (nAChRs) in native brain tissue, an optical method was developed for precise release of nicotine at discrete locations near neuronal membranes during electrophysiological recordings. Patch-clamped neurons in brain slices are filled with dye to visualize their morphology during 2-photon laser scanning microscopy, and nicotine uncaging is executed with a light flash by focusing a 405 nm laser beam near one or more cellular membranes. Cellular current deflections are measured, and a high-resolution three-dimensional (3D) image of the recorded neuron is made to allow reconciliation of nAChR responses with cellular morphology. This method allows for detailed analysis of nAChR functional distribution in complex tissue preparations, promising to enhance the understanding of cholinergic neurotransmission.

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12/10/18 | Whole-cell, 3D and multi-color STED imaging with exchangeable fluorophores.
Spahn C, Grimm JB, Lavis LD, Lampe M, Heilemann M
Nano Letters. 2018 Dec 10;19(1):500-5. doi: 10.1021/acs.nanolett.8b04385

We demonstrate STED microscopy of whole bacterial and eukaryotic cells using fluorogenic labels that reversibly bind to their target structure. A constant exchange of labels guarantees the removal of photobleached fluorophores and their replacement by intact fluorophores, thereby circumventing bleaching-related limitations of STED super-resolution imaging. We achieve a constant labeling density and demonstrate a fluorescence signal for long and theoretically unlimited acquisition times. Using this concept, we demonstrate whole-cell, 3D, multi-color and live cell STED microscopy.

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11/01/18 | Stability, affinity and chromatic variants of the glutamate sensor iGluSnFR.
Marvin JS, Scholl B, Wilson DE, Podgorski K, Kazemipour A, Mueller JA, Schoch-McGovern S, Wang SS, Quiroz FJ, Rebola N, Bao H, Little JP, Tkachuk AN, Hantman AW, Chapman ER, Dietrich D, DiGregorio DA, Fitzpatrick D, Looger LL
Nature Methods. 2018 Nov;15(11):9386-9. doi: 10.1038/s41592-018-0171-3

Single-wavelength fluorescent reporters allow visualization of specific neurotransmitters with high spatial and temporal resolution. We report variants of intensity-based glutamate-sensing fluorescent reporter (iGluSnFR) that are functionally brighter; detect submicromolar to millimolar amounts of glutamate; and have blue, cyan, green, or yellow emission profiles. These variants could be imaged in vivo in cases where original iGluSnFR was too dim, resolved glutamate transients in dendritic spines and axonal boutons, and allowed imaging at kilohertz rates.

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10/03/18 | A toolbox for multiplexed super-resolution imaging of the E. coli nucleoid and membrane using novel PAINT labels.
Spahn CK, Glaesmann M, Grimm JB, Ayala AX, Lavis LD, Heilemann M
Scientific Reports. 2018 Oct 03;8(1):14768. doi: 10.1038/s41598-018-33052-3

Maintenance of the bacterial homeostasis initially emanates from interactions between proteins and the bacterial nucleoid. Investigating their spatial correlation requires high spatial resolution, especially in tiny, highly confined and crowded bacterial cells. Here, we present super-resolution microscopy using a palette of fluorescent labels that bind transiently to either the membrane or the nucleoid of fixed E. coli cells. The presented labels are easily applicable, versatile and allow long-term single-molecule super-resolution imaging independent of photobleaching. The different spectral properties allow for multiplexed imaging in combination with other localisation-based super-resolution imaging techniques. As examples for applications, we demonstrate correlated super-resolution imaging of the bacterial nucleoid with the position of genetic loci, of nascent DNA in correlation to the entire nucleoid, and of the nucleoid of metabolically arrested cells. We furthermore show that DNA- and membrane-targeting labels can be combined with photoactivatable fluorescent proteins and visualise the nano-scale distribution of RNA polymerase relative to the nucleoid in drug-treated E. coli cells.

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08/29/18 | Cell-specific chemical delivery using a selective Nitroreductase-Nitroaryl pair.
Gruber TD, Krishnamurthy C, Grimm JB, Tadross MR, Wysocki LM, Gartner ZJ, Lavis LD
ACS Chemical Biology. 2018 Aug 29;13(10):1888-96. doi: 10.1021/acschembio.8b00524

The utility of small molecules to probe or perturb biological systems is limited by the lack of cell-specificity. "Masking" the activity of small molecules using a general chemical modification and "unmasking" it only within target cells overcomes this limitation. To this end, we have developed a selective enzyme-substrate pair consisting of engineered variants of E. coli nitroreductase (NTR) and a 2-nitro- N-methylimidazolyl (NM) masking group. To discover and optimize this NTR-NM system, we synthesized a series of fluorogenic substrates containing different nitroaromatic masking groups, confirmed their stability in cells, and identified the best substrate for NTR. We then engineered the enzyme for improved activity in mammalian cells, ultimately yielding an enzyme variant (enhanced NTR, or eNTR) that possesses up to 100-fold increased activity over wild-type NTR. These improved NTR enzymes combined with the optimal NM masking group enable rapid, selective unmasking of dyes, indicators, and drugs to genetically defined populations of cells.

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