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103 Publications

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    09/01/22 | A serotonergic axon-cilium synapse drives nuclear signaling to maintain chromatin accessibility
    Shu-Hsien Sheu , Srigokul Upadhyayula , Vincent Dupuy , Song Pang , Andrew L. Lemire , Deepika Walpita , H. Amalia Pasolli , Fei Deng , Jinxia Wan , Lihua Wang , Justin Houser , Silvia Sanchez-Martinez , Sebastian E. Brauchi , Sambashiva Banala , Melanie Freeman , C. Shan Xu , Tom Kirchhausen , Harald F. Hess , Luke Lavis , Yu-Long Li , Séverine Chaumont-Dubel , David E. Clapham
    Cell. 2022 Sep 01;185(18):3390-3407. doi: 10.1016/j.cell.2022.07.026

    Chemical synapses between axons and dendrites mediate much of the brain’s intercellular communication. Here we describe a new kind of synapse – the axo-ciliary synapse - between axons and primary cilia. By employing enhanced focused ion beam – scanning electron microscopy on samples with optimally preserved ultrastructure, we discovered synapses between the serotonergic axons arising from the brainstem, and the primary cilia of hippocampal CA1 pyramidal neurons. Functionally, these cilia are enriched in a ciliary-restricted serotonin receptor, 5-hydroxytryptamine receptor 6 (HTR6), whose mutation is associated with learning and memory defects. Using a newly developed cilia-targeted serotonin sensor, we show that optogenetic stimulation of serotonergic axons results in serotonin release onto cilia. Ciliary HTR6 stimulation activates a non-canonical Gαq/11-RhoA pathway. Ablation of this pathway results in nuclear actin and chromatin accessibility changes in CA1 pyramidal neurons. Axo-ciliary synapses serve as a distinct mechanism for neuromodulators to program neuron transcription through privileged access to the nuclear compartment.

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    07/08/22 | Melding Synthetic Molecules and Genetically Encoded Proteins to Forge New Tools for Neuroscience.
    Kumar P, Lavis LD
    Annual Review Neuroscience. 2022 Jul 08;45:131-150. doi: 10.1146/annurev-neuro-110520-030031

    Unraveling the complexity of the brain requires sophisticated methods to probe and perturb neurobiological processes with high spatiotemporal control. The field of chemical biology has produced general strategies to combine the molecular specificity of small-molecule tools with the cellular specificity of genetically encoded reagents. Here, we survey the application, refinement, and extension of these hybrid small-molecule:protein methods to problems in neuroscience, which yields powerful reagents to precisely measure and manipulate neural systems.

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    07/03/22 | Multifunctional fluorophores for live-cell imaging and affinity capture of proteins
    Kumar P, Jason D. Vevea , Edwin R. Chapman , Luke D. Lavis
    bioRxiv. 2022 Jul 03:. doi: 10.1101/2022.07.02.498544

    The development of enzyme-based self-labeling tags allow the labeling of proteins in living cells with synthetic small-molecules. Use of a fluorophore-containing ligand enables the visualization of protein location inside cells using fluorescence microscopy. Alternatively, deployment of a biotin-containing ligand allows purification of tagged protein using affinity resins. Despite these various applications of self-labeling tags, most ligands serve a single purpose. Here, we describe self-labeling tag ligands that allow both visualization and subsequent capture of a protein. A key design principle is exploiting the chemical properties and size of a rhodamine fluorophore to optimize cell-permeability of the ligand and the capture efficiency of the biotin conjugate. This work generates useful “multifunctional” fluorophores with generalizable design principles that will allow the construction of new tools for biology.

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    07/01/22 | Kinetic principles underlying pioneer function of GAGA transcription factor in live cells.
    Tang X, Li T, Liu S, Wisniewski J, Zheng Q, Rong Y, Lavis LD, Wu C
    Nature Structural and Molecular Biology. 2022 Jul 01;29(7):665-676. doi: 10.1038/s41594-022-00800-z

    How pioneer factors interface with chromatin to promote accessibility for transcription control is poorly understood in vivo. Here, we directly visualize chromatin association by the prototypical GAGA pioneer factor (GAF) in live Drosophila hemocytes. Single-particle tracking reveals that most GAF is chromatin bound, with a stable-binding fraction showing nucleosome-like confinement residing on chromatin for more than 2 min, far longer than the dynamic range of most transcription factors. These kinetic properties require the full complement of GAF's DNA-binding, multimerization and intrinsically disordered domains, and are autonomous from recruited chromatin remodelers NURF and PBAP, whose activities primarily benefit GAF's neighbors such as Heat Shock Factor. Evaluation of GAF kinetics together with its endogenous abundance indicates that, despite on-off dynamics, GAF constitutively and fully occupies major chromatin targets, thereby providing a temporal mechanism that sustains open chromatin for transcriptional responses to homeostatic, environmental and developmental signals.

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    06/15/22 | 2,7-Diaminobenzopyrylium Dyes Are Live-Cell Mitochondrial Stains2,7-Diaminobenzopyrylium Dyes Are Live-Cell Mitochondrial Stains
    Banala S, Tkachuk AN, Patel R, Kumar P, Brown TA, Lavis LD
    ACS Bio & Med Chem Au. 2022 Jun 15;2(3):307-12. doi: 10.1021/acsbiomedchemau.1c00068

    Small-molecule fluorescent stains enable the imaging of cellular structures without the need for genetic manipulation. Here, we introduce 2,7-diaminobenzopyrylium (DAB) dyes as live-cell mitochondrial stains excited with violet light. This amalgam of the coumarin and rhodamine fluorophore structures yields dyes with high photostability and tunable spectral properties.

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    05/03/22 | Bromodomains regulate dynamic targeting of the PBAF chromatin remodeling complex to chromatin hubs.
    Kenworthy CA, Haque N, Liou S, Chandris P, Wong V, Dziuba P, Lavis LD, Liu W, Singer RH, Coleman RA
    Biophysical Journal. 2022 May 3;121(9):1738-1752. doi: 10.1016/j.bpj.2022.03.027

    Chromatin remodelers actively target arrays of acetylated nucleosomes at select enhancers and promoters to facilitate or shut down the repeated recruitment of RNA Pol II during transcriptional bursting. It is poorly understood how chromatin remodelers such as PBAF dynamically target different chromatin states inside a live cell. Our live-cell single molecule fluorescence microscopy study reveals chromatin hubs throughout the nucleus where PBAF rapidly cycles on and off the genome. Deletion of PBAF's bromodomains impairs targeting and stable engagement of chromatin in hubs. Dual color imaging reveals that PBAF targets both euchromatic and heterochromatic hubs with distinct genome binding kinetic profiles that mimic chromatin stability. Removal of PBAF's bromodomains stabilizes H3.3 binding within chromatin indicating that bromodomains may play a direct role in remodeling of the nucleosome. Our data suggests that PBAF's dynamic bromodomain mediated engagement of a nucleosome may reflect the chromatin remodeling potential of differentially bound chromatin states.

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    02/28/22 | Melding Synthetic Molecules and Genetically Encoded Proteins to Forge New Tools for Neuroscience.
    Kumar P, Lavis LD
    Annual Review of Neuroscience. 2022 Feb 28:. doi: 10.1146/annurev-neuro-110520-030031

    Unraveling the complexity of the brain requires sophisticated methods to probe and perturb neurobiological processes with high spatiotemporal control. The field of chemical biology has produced general strategies to combine the molecular specificity of small-molecule tools with the cellular specificity of genetically encoded reagents. Here, we survey the application, refinement, and extension of these hybrid small-molecule:protein methods to problems in neuroscience, which yields powerful reagents to precisely measure and manipulate neural systems. Expected final online publication date for the , Volume 45 is July 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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    02/28/22 | Melding Synthetic Molecules and Genetically Encoded Proteins to Forge New Tools for Neuroscience.
    Kumar P, Lavis LD
    Annual Review Neuroscience. 2022 Feb 28:. doi: 10.1146/annurev-neuro-110520-030031

    Unraveling the complexity of the brain requires sophisticated methods to probe and perturb neurobiological processes with high spatiotemporal control. The field of chemical biology has produced general strategies to combine the molecular specificity of small-molecule tools with the cellular specificity of genetically encoded reagents. Here, we survey the application, refinement, and extension of these hybrid small-molecule:protein methods to problems in neuroscience, which yields powerful reagents to precisely measure and manipulate neural systems. Expected final online publication date for the , Volume 45 is July 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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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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    02/07/22 | The complexin C-terminal amphipathic helix stabilizes the fusion pore open state by sculpting membranes.
    Courtney KC, Wu L, Mandal T, Swift M, Zhang Z, Alaghemandi M, Wu Z, Bradberry MM, Deo C, Lavis LD, Volkmann N, Hanein D, Cui Q, Bao H, Chapman ER
    Nature Structural & Molecular Biology. 2022 Feb 07;29(2):97-107. doi: 10.1038/s41594-021-00716-0

    Neurotransmitter release is mediated by proteins that drive synaptic vesicle fusion with the presynaptic plasma membrane. While soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs) form the core of the fusion apparatus, additional proteins play key roles in the fusion pathway. Here, we report that the C-terminal amphipathic helix of the mammalian accessory protein, complexin (Cpx), exerts profound effects on membranes, including the formation of pores and the efficient budding and fission of vesicles. Using nanodisc-black lipid membrane electrophysiology, we demonstrate that the membrane remodeling activity of Cpx modulates the structure and stability of recombinant exocytic fusion pores. Cpx had particularly strong effects on pores formed by small numbers of SNAREs. Under these conditions, Cpx increased the current through individual pores 3.5-fold, and increased the open time fraction from roughly 0.1 to 1.0. We propose that the membrane sculpting activity of Cpx contributes to the phospholipid rearrangements that underlie fusion by stabilizing highly curved membrane fusion intermediates.

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