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142 Publications

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    10/06/22 | Rationalized deep learning super-resolution microscopy for sustained live imaging of rapid subcellular processes.
    Qiao C, Li D, Liu Y, Zhang S, Liu K, Liu C, Guo Y, Jiang T, Fang C, Li N, Zeng Y, He K, Zhu X, Lippincott-Schwartz J, Dai Q, Li D
    Nature Biotechnology. 2022 Oct 06:. doi: 10.1038/s41587-022-01471-3

    The goal when imaging bioprocesses with optical microscopy is to acquire the most spatiotemporal information with the least invasiveness. Deep neural networks have substantially improved optical microscopy, including image super-resolution and restoration, but still have substantial potential for artifacts. In this study, we developed rationalized deep learning (rDL) for structured illumination microscopy and lattice light sheet microscopy (LLSM) by incorporating prior knowledge of illumination patterns and, thereby, rationally guiding the network to denoise raw images. Here we demonstrate that rDL structured illumination microscopy eliminates spectral bias-induced resolution degradation and reduces model uncertainty by five-fold, improving the super-resolution information by more than ten-fold over other computational approaches. Moreover, rDL applied to LLSM enables self-supervised training by using the spatial or temporal continuity of noisy data itself, yielding results similar to those of supervised methods. We demonstrate the utility of rDL by imaging the rapid kinetics of motile cilia, nucleolar protein condensation during light-sensitive mitosis and long-term interactions between membranous and membrane-less organelles.

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    09/19/22 | Structural Diversity within the Endoplasmic Reticulum-From the Microscale to the Nanoscale.
    Obara CJ, Moore AS, Lippincott-Schwartz J
    Cold Spring Harbor Perspectives in Biology. 2022 Sep 19:. doi: 10.1101/cshperspect.a041259

    The endoplasmic reticulum (ER) is a continuous, highly dynamic membrane compartment that is crucial for numerous basic cellular functions. The ER stretches from the nuclear envelope to the outer periphery of all living eukaryotic cells. This ubiquitous organelle shows remarkable structural complexity, adopting a range of shapes, curvatures, and length scales. Canonically, the ER is thought to be composed of two simple membrane elements: sheets and tubules. However, recent advances in superresolution light microscopy and three-dimensional electron microscopy have revealed an astounding diversity of nanoscale ER structures, greatly expanding our view of ER organization. In this review, we describe these diverse ER structures, focusing on what is known of their regulation and associated functions in mammalian cells.

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    09/03/22 | Motion of single molecular tethers reveals dynamic subdomains at ER-mitochondria contact sites
    Christopher J. Obara , Jonathon Nixon-Abell , Andrew S. Moore , Federica Riccio , David P. Hoffman , Gleb Shtengel , C. Shan Xu , Kathy Schaefer , H. Amalia Pasolli , Jean-Baptiste Masson , Harald F. Hess , Christopher P. Calderon , Craig Blackstone , Jennifer Lippincott-Schwartz
    bioRxiv. 2022 Sep 03:. doi: 10.1101/2022.09.03.505525

    To coordinate cellular physiology, eukaryotic cells rely on the inter-organelle transfer of molecules at specialized organelle-organelle contact sites1,2. Endoplasmic reticulum-mitochondria contact sites (ERMCSs) are particularly vital communication hubs, playing key roles in the exchange of signaling molecules, lipids, and metabolites3. ERMCSs are maintained by interactions between complementary tethering molecules on the surface of each organelle4,5. However, due to the extreme sensitivity of these membrane interfaces to experimental perturbation6,7, a clear understanding of their nanoscale structure and regulation is still lacking. Here, we combine 3D electron microscopy with high-speed molecular tracking of a model organelle tether, VAPB, to map the structure and diffusion landscape of ERMCSs. From EM reconstructions, we identified subdomains within the contact site where ER membranes dramatically deform to match local mitochondrial curvature. In parallel live cell experiments, we observed that the VAPB tethers that mediate this interface were not immobile, but rather highly dynamic, entering and leaving the site in seconds. These subdomains enlarged during nutrient stress, indicating ERMCSs can readily remodel under different physiological conditions. An ALS-associated mutation in VAPB altered the normal fluidity of contact sites, likely perturbing effective communication across the contact site and preventing remodeling. These results establish high speed single molecule imaging as a new tool for mapping the structure of contact site interfaces and suggest that the diffusion landscape of VAPB is a crucial component of ERMCS homeostasis.

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    06/12/22 | Super-Resolution Imaging of Fas/CD95 Reorganization Induced by Membrane-Bound Fas Ligand Reveals Nanoscale Clustering Upstream of FADD Recruitment.
    Frazzette N, Cruz AC, Wu X, Hammer JA, Lippincott-Schwartz J, Siegel RM, Sengupta P
    Cells. 2022 Jun 12;11(12):. doi: 10.3390/cells11121908

    Signaling through the TNF-family receptor Fas/CD95 can trigger apoptosis or non-apoptotic cellular responses and is essential for protection from autoimmunity. Receptor clustering has been observed following interaction with Fas ligand (FasL), but the stoichiometry of Fas, particularly when triggered by membrane-bound FasL, the only form of FasL competent at inducing programmed cell death, is not known. Here we used super-resolution microscopy to study the behavior of single molecules of Fas/CD95 on the plasma membrane after interaction of Fas with FasL on planar lipid bilayers. We observed rapid formation of Fas protein superclusters containing more than 20 receptors after interactions with membrane-bound FasL. Fluorescence correlation imaging demonstrated recruitment of FADD dependent on an intact Fas death domain, with lipid raft association playing a secondary role. Flow-cytometric FRET analysis confirmed these results, and also showed that some Fas clustering can occur in the absence of FADD and caspase-8. Point mutations in the Fas death domain associated with autoimmune lymphoproliferative syndrome (ALPS) completely disrupted Fas reorganization and FADD recruitment, confirming structure-based predictions of the critical role that these residues play in Fas-Fas and Fas-FADD interactions. Finally, we showed that induction of apoptosis correlated with the ability to form superclusters and recruit FADD.

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    06/02/22 | Targeting LIPA independent of its lipase activity is a therapeutic strategy in solid tumors via induction of endoplasmic reticulum stress.
    Liu X, Viswanadhapalli S, Kumar S, Lee T, Moore A, Ma S, Chen L, Hsieh M, Li M, Sareddy GR, Parra K, Blatt EB, Reese TC, Zhao Y, Chang A, Yan H, Xu Z, Pratap UP, Liu Z, Roggero CM, Tan Z, Weintraub ST, Peng Y, Tekmal RR, Arteaga CL, Lippincott-Schwartz J, Vadlamudi RK, Ahn J, Raj GV
    Nature Cancer. 2022 Jun 02;3(7):866-884. doi: 10.1038/s43018-022-00389-8

    Triple-negative breast cancer (TNBC) has a poor clinical outcome, due to a lack of actionable therapeutic targets. Herein we define lysosomal acid lipase A (LIPA) as a viable molecular target in TNBC and identify a stereospecific small molecule (ERX-41) that binds LIPA. ERX-41 induces endoplasmic reticulum (ER) stress resulting in cell death, and this effect is on target as evidenced by specific LIPA mutations providing resistance. Importantly, we demonstrate that ERX-41 activity is independent of LIPA lipase function but dependent on its ER localization. Mechanistically, ERX-41 binding of LIPA decreases expression of multiple ER-resident proteins involved in protein folding. This targeted vulnerability has a large therapeutic window, with no adverse effects either on normal mammary epithelial cells or in mice. Our study implicates a targeted strategy for solid tumors, including breast, brain, pancreatic and ovarian, whereby small, orally bioavailable molecules targeting LIPA block protein folding, induce ER stress and result in tumor cell death.

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    02/01/22 | Organization of translating secretome mRNAS on endoplasmic reticulum
    Choi H, Liao Y, Yoon YJ, Grimm J, Lavis LD, Singer RH, Lippincott-Schwartz J
    Biophysical Journal. 2022 Feb 01;121(3):33a. doi: 10.1016/j.bpj.2021.11.2550

    The endoplasmic reticulum (ER) has a complex morphology comprised of stacked sheets, tubules, and three-way junctions, which together function as a platform for protein synthesis of membrane and secretory proteins. Specific ER subdomains are thought to be spatially organized to enable protein synthesis activity, but precisely where these domains are localized is unclear, especially relative to the plethora of organelle interactions taking place on the ER. Here, we use single-molecule tracking of ribosomes and mRNA in combination with simultaneous imaging of ER to assess the sites of membrane protein synthesis on the ER. We found that ribosomes were widely distributed throughout different ER morphologies, but the synthesis of membrane proteins (including Type I, II, and multi-spanning) and an ER luminal protein (Calreticulin) occurred primarily at three-way junctions. Lunapark played a key role in stabilizing transmembrane protein mRNA at three-way junctions. We additionally found that translating mRNAs coding for transmembrane proteins are in the vicinity of lysosomes and translate through a cap-independent but eIF2-dependent mechanism. These results support the idea that discrete ER subdomains co-exist with lysosomes to support specific types of protein synthesis activities, with ER-lysosome interactions playing an important role in the translation of secretome mRNAs.

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    01/01/22 | ER proteins decipher the tubulin code to regulate organelle distribution.
    Zheng P, Obara CJ, Szczesna E, Nixon-Abell J, Mahalingan KK, Roll-Mecak A, Lippincott-Schwartz J, Blackstone C
    Nature. 2022 Jan 01;601(7891):132-138. doi: 10.1038/s41586-021-04204-9

    Organelles move along differentially modified microtubules to establish and maintain their proper distributions and functions. However, how cells interpret these post-translational microtubule modification codes to selectively regulate organelle positioning remains largely unknown. The endoplasmic reticulum (ER) is an interconnected network of diverse morphologies that extends promiscuously throughout the cytoplasm, forming abundant contacts with other organelles. Dysregulation of endoplasmic reticulum morphology is tightly linked to neurologic disorders and cancer. Here we demonstrate that three membrane-bound endoplasmic reticulum proteins preferentially interact with different microtubule populations, with CLIMP63 binding centrosome microtubules, kinectin (KTN1) binding perinuclear polyglutamylated microtubules, and p180 binding glutamylated microtubules. Knockout of these proteins or manipulation of microtubule populations and glutamylation status results in marked changes in endoplasmic reticulum positioning, leading to similar redistributions of other organelles. During nutrient starvation, cells modulate CLIMP63 protein levels and p180-microtubule binding to bidirectionally move endoplasmic reticulum and lysosomes for proper autophagic responses.

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    12/11/21 | Unraveling Single-Particle Trajectories Confined in Tubular Networks
    Yunhao Sun , Zexi Yu , Christopher Obara , Keshav Mittal , Jennifer Lippincott-Schwarz , Elena F Koslover
    arXiv. 2021 Dec 11:

    The analysis of single particle trajectories plays an important role in elucidating dynamics within complex environments such as those found in living cells. However, the characterization of intracellular particle motion is often confounded by confinement of the particles within non-trivial subcellular geometries. Here, we focus specifically on the case of particles undergoing Brownian motion within a tubular network, as found in some cellular organelles. An unraveling algorithm is developed to uncouple particle motion from the confining network structure, allowing for an accurate extraction of the diffusion coefficient, as well as differentiating between Brownian and fractional Brownian dynamics. We validate the algorithm with simulated trajectories and then highlight its application to an example system: analyzing the motion of membrane proteins confined in the tubules of the peripheral endoplasmic reticulum in mammalian cells. We show that these proteins undergo diffusive motion with a well-characterized diffusivity. Our algorithm provides a generally applicable approach for disentangling geometric morphology and particle dynamics in networked architectures.

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    11/01/21 | An open-access volume electron microscopy atlas of whole cells and tissues.
    Xu CS, Pang S, Shtengel G, Müller A, Ritter AT, Hoffman HK, Takemura S, Lu Z, Pasolli HA, Iyer N, Chung J, Bennett D, Weigel AV, Freeman M, Van Engelenburg SB, Walther TC, Farese RV, Lippincott-Schwartz J, Mellman I, Solimena M, Hess HF
    Nature. 2021 Nov 1;599(7883):147-51. doi: 10.1038/s41586-021-03992-4

    Understanding cellular architecture is essential for understanding biology. Electron microscopy (EM) uniquely visualizes cellular structures with nanometre resolution. However, traditional methods, such as thin-section EM or EM tomography, have limitations in that they visualize only a single slice or a relatively small volume of the cell, respectively. Focused ion beam-scanning electron microscopy (FIB-SEM) has demonstrated the ability to image small volumes of cellular samples with 4-nm isotropic voxels. Owing to advances in the precision and stability of FIB milling, together with enhanced signal detection and faster SEM scanning, we have increased the volume that can be imaged with 4-nm voxels by two orders of magnitude. Here we present a volume EM atlas at such resolution comprising ten three-dimensional datasets for whole cells and tissues, including cancer cells, immune cells, mouse pancreatic islets and Drosophila neural tissues. These open access data (via OpenOrganelle) represent the foundation of a field of high-resolution whole-cell volume EM and subsequent analyses, and we invite researchers to explore this atlas and pose questions.

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    11/01/21 | Whole-cell organelle segmentation in volume electron microscopy.
    Heinrich L, Bennett D, Ackerman D, Park W, Bogovic J, Eckstein N, Petruncio A, Clements J, Pang S, Xu CS, Funke J, Korff W, Hess HF, Lippincott-Schwartz J, Saalfeld S, Weigel AV, COSEM Project Team
    Nature. 2021 Nov 01;599(7883):141-46. doi: 10.1038/s41586-021-03977-3

    Cells contain hundreds of organelles and macromolecular assemblies. Obtaining a complete understanding of their intricate organization requires the nanometre-level, three-dimensional reconstruction of whole cells, which is only feasible with robust and scalable automatic methods. Here, to support the development of such methods, we annotated up to 35 different cellular organelle classes-ranging from endoplasmic reticulum to microtubules to ribosomes-in diverse sample volumes from multiple cell types imaged at a near-isotropic resolution of 4 nm per voxel with focused ion beam scanning electron microscopy (FIB-SEM). We trained deep learning architectures to segment these structures in 4 nm and 8 nm per voxel FIB-SEM volumes, validated their performance and showed that automatic reconstructions can be used to directly quantify previously inaccessible metrics including spatial interactions between cellular components. We also show that such reconstructions can be used to automatically register light and electron microscopy images for correlative studies. We have created an open data and open-source web repository, 'OpenOrganelle', to share the data, computer code and trained models, which will enable scientists everywhere to query and further improve automatic reconstruction of these datasets.

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