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7 Janelia Publications

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    09/02/19 | Software for lattice light-sheet imaging of FRET biosensors, illustrated with a new Rap1 biosensor.
    O’Shaughnessy EC, Stone OJ, LaFosse PK, Azoitei ML, Tsygankov D, Heddleston JM, Legant WR, Wittchen ES, Burridge K, Elston TC, Betzig E, Chew T, Adalsteinsson D, Hahn KM
    The Journal of Cell Biology. 2019 Sep 2;218(9):3153-3160. doi: 10.1083/jcb.201903019

    Lattice light-sheet microscopy (LLSM) is valuable for its combination of reduced photobleaching and outstanding spatiotemporal resolution in 3D. Using LLSM to image biosensors in living cells could provide unprecedented visualization of rapid, localized changes in protein conformation or posttranslational modification. However, computational manipulations required for biosensor imaging with LLSM are challenging for many software packages. The calculations require processing large amounts of data even for simple changes such as reorientation of cell renderings or testing the effects of user-selectable settings, and lattice imaging poses unique challenges in thresholding and ratio imaging. We describe here a new software package, named ImageTank, that is specifically designed for practical imaging of biosensors using LLSM. To demonstrate its capabilities, we use a new biosensor to study the rapid 3D dynamics of the small GTPase Rap1 in vesicles and cell protrusions.

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    07/01/19 | Augmin accumulation on long-lived microtubules drives amplification and kinetochore-directed growth.
    David AF, Roudot P, Legant WR, Betzig E, Danuser G, Gerlich DW
    Journal of Cell Biology. 2019 Jul 01;218(7):2150-68. doi: 10.1083/jcb.201805044

    Dividing cells reorganize their microtubule cytoskeleton into a bipolar spindle, which moves one set of sister chromatids to each nascent daughter cell. Early spindle assembly models postulated that spindle pole-derived microtubules search the cytoplasmic space until they randomly encounter a kinetochore to form a stable attachment. More recent work uncovered several additional, centrosome-independent microtubule generation pathways, but the contributions of each pathway to spindle assembly have remained unclear. Here, we combined live microscopy and mathematical modeling to show that most microtubules nucleate at noncentrosomal regions in dividing human cells. Using a live-cell probe that selectively labels aged microtubule lattices, we demonstrate that the distribution of growing microtubule plus ends can be almost entirely explained by Augmin-dependent amplification of long-lived microtubule lattices. By ultrafast 3D lattice light-sheet microscopy, we observed that this mechanism results in a strong directional bias of microtubule growth toward individual kinetochores. Our systematic quantification of spindle dynamics reveals highly coordinated microtubule growth during kinetochore fiber assembly.

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    06/27/19 | High-resolution imaging reveals how the spindle midzone impacts chromosome movement.
    Pamula MC, Carlini L, Forth S, Verma P, Suresh S, Legant WR, Khodjakov A, Betzig E, Kapoor TM
    The Journal of Cell Biology. 27 Jun 2019;218(8):2529-44. doi: 10.1083/jcb.201904169

    In the spindle midzone, microtubules from opposite half-spindles form bundles between segregating chromosomes. Microtubule bundles can either push or restrict chromosome movement during anaphase in different cellular contexts, but how these activities are achieved remains poorly understood. Here, we use high-resolution live-cell imaging to analyze individual microtubule bundles, growing filaments, and chromosome movement in dividing human cells. Within bundles, filament overlap length marked by the cross-linking protein PRC1 decreases during anaphase as chromosome segregation slows. Filament ends within microtubule bundles appear capped despite dynamic PRC1 turnover and submicrometer proximity to growing microtubules. Chromosome segregation distance and rate are increased in two human cell lines when microtubule bundle assembly is prevented via PRC1 knockdown. Upon expressing a mutant PRC1 with reduced microtubule affinity, bundles assemble but chromosome hypersegregation is still observed. We propose that microtubule overlap length reduction, typically linked to pushing forces generated within filament bundles, is needed to properly restrict spindle elongation and position chromosomes within daughter cells.

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    04/26/19 | Dynamic super-resolution structured illumination imaging in the living brain.
    Turcotte R, Liang Y, Tanimoto M, Zhang Q, Li Z, Koyama M, Betzig E, Ji N
    Proceedings of the National Academy of Sciences of the United States of America. 2019 Apr 26;116(19):9586-91. doi: 10.1073/pnas.1819965116

    Cells in the brain act as components of extended networks. Therefore, to understand neurobiological processes in a physiological context, it is essential to study them in vivo. Super-resolution microscopy has spatial resolution beyond the diffraction limit, thus promising to provide structural and functional insights that are not accessible with conventional microscopy. However, to apply it to in vivo brain imaging, we must address the challenges of 3D imaging in an optically heterogeneous tissue that is constantly in motion. We optimized image acquisition and reconstruction to combat sample motion and applied adaptive optics to correcting sample-induced optical aberrations in super-resolution structured illumination microscopy (SIM) in vivo. We imaged the brains of live zebrafish larvae and mice and observed the dynamics of dendrites and dendritic spines at nanoscale resolution.

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    03/19/19 | Cytoskeletal control of antigen-dependent T cell activation.
    Colin-York H, Javanmardi Y, Skamrahl M, Kumari S, Chang VT, Khuon S, Taylor A, Chew T, Betzig E, Moeendarbary E, Cerundolo V, Eggeling C, Fritzsche M
    Cell Reports. 2019 Mar 19;26(12):3369-3379.e5. doi: 10.1016/j.celrep.2019.02.074

    Cytoskeletal actin dynamics is essential for T cell activation. Here, we show evidence that the binding kinetics of the antigen engaging the T cell receptor influences the nanoscale actin organization and mechanics of the immune synapse. Using an engineered T cell system expressing a specific T cell receptor and stimulated by a range of antigens, we found that the peak force experienced by the T cell receptor during activation was independent of the unbinding kinetics of the stimulating antigen. Conversely, quantification of the actin retrograde flow velocity at the synapse revealed a striking dependence on the antigen unbinding kinetics. These findings suggest that the dynamics of the actin cytoskeleton actively adjusted to normalize the force experienced by the T cell receptor in an antigen-specific manner. Consequently, tuning actin dynamics in response to antigen kinetics may thus be a mechanism that allows T cells to adjust the lengthscale and timescale of T cell receptor signaling.

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    03/07/19 | Cytoskeletal actin patterns shape mast cell activation.
    Colin-York H, Li D, Korobchevskaya K, Chang VT, Betzig E, Eggeling C, Fritzsche M
    Communications Biology. 2019;2:93. doi: 10.1038/s42003-019-0322-9

    Activation of immune cells relies on a dynamic actin cytoskeleton. Despite detailed knowledge of molecular actin assembly, the exact processes governing actin organization during activation remain elusive. Using advanced microscopy, we here show that Rat Basophilic Leukemia (RBL) cells, a model mast cell line, employ an orchestrated series of reorganization events within the cortical actin network during activation. In response to IgE antigen-stimulation of FCε receptors (FCεR) at the RBL cell surface, we observed symmetry breaking of the F-actin network and subsequent rapid disassembly of the actin cortex. This was followed by a reassembly process that may be driven by the coordinated transformation of distinct nanoscale F-actin architectures, reminiscent of self-organizing actin patterns. Actin patterns co-localized with zones of Arp2/3 nucleation, while network reassembly was accompanied by myosin-II activity. Strikingly, cortical actin disassembly coincided with zones of granule secretion, suggesting that cytoskeletal actin patterns contribute to orchestrate RBL cell activation.

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    01/18/19 | Cortical column and whole-brain imaging with molecular contrast and nanoscale resolution.
    Gao R, Asano SM, Upadhyayula S, Pisarev I, Milkie DE, Liu T, Singh V, Graves AR, Huynh GH, Zhao Y, Bogovic JA, Colonell J, Ott CM, Zugates CT, Tappan S, Rodriguez A, Mosaliganti KR, Sheu S, Pasolli HA, et al
    Science (New York, N.Y.). 2019 Jan 18;363(6424):eaau8302. doi: 10.1126/science.aau8302

    Optical and electron microscopy have made tremendous inroads toward understanding the complexity of the brain. However, optical microscopy offers insufficient resolution to reveal subcellular details, and electron microscopy lacks the throughput and molecular contrast to visualize specific molecular constituents over millimeter-scale or larger dimensions. We combined expansion microscopy and lattice light-sheet microscopy to image the nanoscale spatial relationships between proteins across the thickness of the mouse cortex or the entire Drosophila brain. These included synaptic proteins at dendritic spines, myelination along axons, and presynaptic densities at dopaminergic neurons in every fly brain region. The technology should enable statistically rich, large-scale studies of neural development, sexual dimorphism, degree of stereotypy, and structural correlations to behavior or neural activity, all with molecular contrast.

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