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11 Janelia Publications

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    06/29/22 | A geometric framework to predict structure from function in neural networks
    Biswas T, Fitzgerald JE
    Physical Review Research. 2022 Jun 29;4(2):023255. doi: 10.1103/PhysRevResearch.4.023255

    Neural computation in biological and artificial networks relies on nonlinear synaptic integration. The structural connectivity matrix of synaptic weights between neurons is a critical determinant of overall network function. However, quantitative links between neural network structure and function are complex and subtle. For example, many networks can give rise to similar functional responses, and the same network can function differently depending on context. Whether certain patterns of synaptic connectivity are required to generate specific network-level computations is largely unknown. Here we introduce a geometric framework for identifying synaptic connections required by steady-state responses in recurrent networks of rectified-linear neurons. Assuming that the number of specified response patterns does not exceed the number of input synapses, we analytically calculate all feedforward and recurrent connectivity matrices that can generate the specified responses from the network inputs. We then use this analytical characterization to rigorously analyze the solution space geometry and derive certainty conditions guaranteeing a non-zero synapse between neurons. Numerical simulations of feedforward and recurrent networks verify our analytical results. Our theoretical framework could be applied to neural activity data to make anatomical predictions that follow generally from the model architecture. It thus provides novel opportunities for discerning what model features are required to accurately relate neural network structure and function.

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    Svoboda LabDarshan Lab
    06/18/22 | Distributing task-related neural activity across a cortical network through task-independent connections
    Christopher M. Kim , Arseny Finkelstein , Carson C. Chow , Karel Svoboda , Ran Darshan
    bioRxiv. 2022 Jun 18:. doi: 10.1101/2022.06.17.496618

    Task-related neural activity is widespread across populations of neurons during goal-directed behaviors. However, little is known about the synaptic reorganization and circuit mechanisms that lead to broad activity changes. Here we trained a limited subset of neurons in a spiking network with strong synaptic interactions to reproduce the activity of neurons in the motor cortex during a decision-making task. We found that task-related activity, resembling the neural data, emerged across the network, even in the untrained neurons. Analysis of trained networks showed that strong untrained synapses, which were independent of the task and determined the dynamical state of the network, mediated the spread of task-related activity. Optogenetic perturbations suggest that the motor cortex is strongly-coupled, supporting the applicability of the mechanism to cortical networks. Our results reveal a cortical mechanism that facilitates distributed representations of task-variables by spreading the activity from a subset of plastic neurons to the entire network through task-independent strong synapses.

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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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    06/12/22 | Metamorphosis of memory circuits in Drosophila reveal a strategy for evolving a larval brain.
    James W. Truman , Jacquelyn Price , Rosa L. Miyares , Tzumin Lee
    bioRxiv. 2022 Jun 12:. doi: 10.1101/2022.06.09.495452

    Insects like Drosophila produce a second brain adapted to the form and behavior of a larva. Neurons for both larval and adult brains are produced by the same stem cells (neuroblasts) but the larva possesses only the earliest born neurons produced from each. To understand how a functional larval brain is made from this reduced set of neurons, we examined the origins and metamorphic fates of the neurons of the larval and adult mushroom body circuits. The adult mushroom body core is built sequentially of γ Kenyon cells, that form a medial lobe, followed by α’β’, and αβ Kenyon cells that form additional medial lobes and two vertical lobes. Extrinsic input (MBINs) and output (MBONs) neurons divide this core into computational compartments. The larval mushroom body contains only γ neurons. Its medial lobe compartments are roughly homologous to those of the adult and same MBONs are used for both. The larval vertical lobe, however, is an analogous “facsimile” that uses a larval-specific branch on the γ neurons to make up for the missing α’β’, and αβ neurons. The extrinsic cells for the facsimile are early-born neurons that trans-differentiate to serve a mushroom body function in the larva and then shift to other brain circuits in the adult. These findings are discussed in the context of the evolution of a larval brain in insects with complete metamorphosis.

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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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    06/07/22 | Neural circuit pathology driven by Shank3 mutation disrupts social behaviors.
    Kim S, Kim Y, Song I, Ujihara Y, Kim N, Jiang Y, Yin HH, Lee T, Kim IH
    Cell Reports. 2022 Jun 07;39(10):110906. doi: 10.1016/j.celrep.2022.110906

    Dysfunctional sociability is a core symptom in autism spectrum disorder (ASD) that may arise from neural-network dysconnectivity between multiple brain regions. However, pathogenic neural-network mechanisms underlying social dysfunction are largely unknown. Here, we demonstrate that circuit-selective mutation (ctMUT) of ASD-risk Shank3 gene within a unidirectional projection from the prefrontal cortex to the basolateral amygdala alters spine morphology and excitatory-inhibitory balance of the circuit. Shank3 ctMUT mice show reduced sociability as well as elevated neural activity and its amplitude variability, which is consistent with the neuroimaging results from human ASD patients. Moreover, the circuit hyper-activity disrupts the temporal correlation of socially tuned neurons to the events of social interactions. Finally, optogenetic circuit activation in wild-type mice partially recapitulates the reduced sociability of Shank3 ctMUT mice, while circuit inhibition in Shank3 ctMUT mice partially rescues social behavior. Collectively, these results highlight a circuit-level pathogenic mechanism of Shank3 mutation that drives social dysfunction.

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    06/06/22 | Direct Observation of Compartment-Specific Localization and Dynamics of Voltage-Gated Sodium Channels.
    Liu H, Wang H, Pitt GS, Liu ZJ
    Journal of Neuroscience. 2022 Jun 06:. doi: 10.1523/JNEUROSCI.0086-22.2022

    Brain enriched voltage-gated sodium channel (VGSC) Na1.2 and Na1.6 are critical for electrical signaling in the central nervous system. Previous studies have extensively characterized cell-type specific expression and electrophysiological properties of these two VGSCs and how their differences contribute to fine-tuning of neuronal excitability. However, due to lack of reliable labeling and imaging methods, the sub-cellular localization and dynamics of these homologous Na1.2 and Na1.6 channels remain understudied. To overcome this challenge, we combined genome editing, super-resolution and live-cell single molecule imaging to probe subcellular composition, relative abundances and trafficking dynamics of Na1.2 and Na1.6 in cultured mouse and rat neurons and in male and female mouse brain. We discovered a previously uncharacterized trafficking pathway that targets Na1.2 to the distal axon of unmyelinated neurons. This pathway utilizes distinct signals residing in the intracellular loop 1 (ICL1) between transmembrane domain I and II to suppress the retention of Na1.2 in the axon initial segment (AIS) and facilitate its membrane loading at the distal axon. As mouse pyramidal neurons undergo myelination, Na1.2 is gradually excluded from the distal axon as Na1.6 becomes the dominant VGSC in the axon initial segment and nodes of Ranvier. In addition, we revealed exquisite developmental regulation of Na1.2 and Na1.6 localizations in the axon initial segment and dendrites, clarifying the molecular identity of sodium channels in these subcellular compartments. Together, these results unveiled compartment-specific localizations and trafficking mechanisms for VGSCs, which could be regulated separately to modulate membrane excitability in the brain.Direct observation of endogenous voltage-gated sodium channels reveals a previously uncharacterized distal axon targeting mechanism and the molecular identity of sodium channels in distinct subcellular compartments.

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    06/02/22 | Allosteric interactions prime androgen receptor dimerization and activation.
    Wasmuth EV, Broeck AV, LaClair JR, Hoover EA, Lawrence KE, Paknejad N, Pappas K, Matthies D, Wang B, Feng W, Watson PA, Zinder JC, Karthaus WR, de la Cruz MJ, Hite RK, Manova-Todorova K, Yu Z, Weintraub ST, Klinge S, Sawyers CL
    Molecular Cell. 2022 Jun 02;82(11):2021-31. doi: 10.1016/j.molcel.2022.03.035

    The androgen receptor (AR) is a nuclear receptor that governs gene expression programs required for prostate development and male phenotype maintenance. Advanced prostate cancers display AR hyperactivation and transcriptome expansion, in part, through AR amplification and interaction with oncoprotein cofactors. Despite its biological importance, how AR domains and cofactors cooperate to bind DNA has remained elusive. Using single-particle cryo-electron microscopy, we isolated three conformations of AR bound to DNA, showing that AR forms a non-obligate dimer, with the buried dimer interface utilized by ancestral steroid receptors repurposed to facilitate cooperative DNA binding. We identify novel allosteric surfaces which are compromised in androgen insensitivity syndrome and reinforced by AR's oncoprotein cofactor, ERG, and by DNA-binding motifs. Finally, we present evidence that this plastic dimer interface may have been adopted for transactivation at the expense of DNA binding. Our work highlights how fine-tuning AR's cooperative interactions translate to consequences in development and disease.

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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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    Sternson Lab
    06/01/22 | Development of an adrenocortical cell model of calcium signaling modulation to decipher the molecular mechanisms responsible for primary aldosteronism
    BakhtaFedlaoui , Teresa Cosentino , Zeina R. Al Sayed , Isabelle Giscos-Douriez , Fabio L. Fernandes-Rosa , Jean-SébastienHulot , Chris Magnus , Scott M. Sternson , Maria Christina Zennaro , Sheerazed Boulkroun
    Archives of Cardiovascular Diseases Supplements. 2022 Jun 01;14(2):160. doi: 10.1016/j.acvdsp.2022.04.153

    Primary aldosteronism (PA) is the most frequent form of secondary hypertension. The identification of germline or somatic mutations in different genes coding for ion channels and defines PA as a channelopathy. These mutations promote activation of calcium signaling, the main trigger for aldosterone biosynthesis.

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